Keithley 238 Service Manual

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Model 238 High Current

Source Measure Unit

Service Manual

Contains Servicing Information

WARRANTY

Keithley Instruments, Inc. warrants this product to be free from defects in material and workmanship for a period of 1 year from date of shipment.

Keithley Instruments, Inc. warrants the following items for 90 days from the date of shipment: probes, cables, rechargeable batteries, diskettes, and documentation.

During the warranty period, we will, at our option, either repair or replace any product that proves to be defective.

To exercise this warranty, write or call your local Keithley representative, or contact Keithley headquarters in Cleveland, Ohio. You will be given prompt assistance and return instructions. Send the product, transportation prepaid, to the indicated service facility. Repairs will be made and the product returned, transportation prepaid. Repaired or replaced products are warranted for the balance of the original warranty period, or at least 90 days.

LIMITATION OF WARRANTY

This warranty does not apply to defects resulting from product modification without Keithley’s express written consent, or misuse of any product or part. This warranty also does not apply to fuses, software, non-rechargeable batteries, damage from battery leakage, or problems arising from normal wear or failure to follow instructions.

THIS WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED OR IMPLIED, INCLUDING ANY IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. THE REMEDIES PROVIDED HEREIN ARE BUYER’S SOLE AND EXCLUSIVE REMEDIES.

NEITHER KEITHLEY INSTRUMENTS, INC. NOR ANY OF ITS EMPLOYEES SHALL BE LIABLE FOR ANY DIRECT, INDIRECT, SPECIAL, INCIDENT’ OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OF ITS INSTRUMENTS AND SOFTWARE EVEN IF KEITHLEY INSTRUMENTS, INC., HAS BEEN ADVISED IN ADVANCE

OF THE POSSIBILITY OF SUCH DAMAGES. SUCH EXCLUDED DAMAGES SHALL INCLUDE, BUT ARE NOT LIMITED TO: COSTS OF REMOVAL AND INSTALLATION, LOSSES SUSTAINED AS THE RESULT OF INJURY TO ANY PERSON. OR DAMAGE To PROPERTY.

KeithIey Instruments, Inc. l 28775 Aurora Road l Cleveland, OH 44139 l 440-248-0400 l Fax: 44@248-6168 l http:Nwww.keithley.com

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10199

Model 238 High Current Source Measure Unit

Service Manual

01990, Keithley instruments, Inc.

Test Instrument Group

Cleveland, Ohio, U.S.A.

Third Printing, May 2000

Document Number: 238-902-01 Rev. C

Manual Print History

The print history shown below lists the printing dates of all Revisions and Addenda created for this manual. The

Revision Level letter increases alphabetically as the manual undergoes subsequent updates. Addenda, which are released between Revisions, contain important change information that the user should incorporate immediately into the manual. Addenda are numbered sequentially. When a new Revision is created, all Addenda associated with the previous Revision of the manual are incorporated into the new Revision of the manual. Each new Revision includes a revised copy of this print history page.

Revision B (Document Number 238-902-01) Revision C (Document Number 238-902-01)

..................................................

......................................................

August 1992

May 2000

All Keithley product names are trademarks or registered trademarks of Keithley Instruments, Inc. Other brand and product names are trademarks or registered trade.marks of their respective holders.

Safety Precautions

The following safety precautions should be observed before using this product and any associated instrumentation. Although some instruments and accessories would normally be used with non-hazardous voltages, there are situations where hazardous conditions may be present.

This product is intended for use by qualified personnel who recognize shock hazards and are familiar with the safety precautions required to avoid possible injury. Read the operating information carefully before using the product.

The types of product users are: Responsible body is the individual or group responsible for the use

and maintenance of equipment, for ensuring that the equipment is operated within its specifications and operating limits, and for ensuring that operators are adequately trained.

Operators use the product for its intended function. They must be trained in electrical safety procedures and proper use of the instrument. They must be protect&J from electric shock and contact with hazardous live circuits.

Maintenance personnel perform routine procedures on the product to keep it operating, for example, setting the line voltage or replacing consumable materials. Maintenance procedures are described in the manual. The procedures explicitly state if the operator may perform them. Otherwise, they should be performed only by service personnel.

Service personnel are trained to work on live circuits, and perform safe installations and repairs of products. Only properly trained service personnel may perform installation and service procedures.

Users of this product must be protected from electric shock at all times. The responsible body must ensure that users are prevented access and/or insulated from every connection point. In some cases, connections must be exposed to potential human contact. Product users in these circumstances must be trained to protect themselves from the risk of electric shock. If the circuit is capable of operating

at or above 1000 volts, no conductive part of the circuit may be exposed.

As described in the International Electrotechnical Commission @EC) Standard IEC 664, digital multimeter measuring circuits (e.g., Keithley Models 175A. 199,2000,2001,2002. and 2010) are Installation Category II. All other instruments’ signal terminals are Installation Category I and must not be connected to mains.

Do not connect switching cards directly to unlimited power circuits. They are intended to be used with impedance limited sources. NEVER connect switching cards directly to AC mains. When connecting sources to switching cards, install protective devices to limit fault current and voltage to the card.

Before operating an instrument, make sure the line cord is connected to a properly grounded power receptacle. Inspect the connecting cables, test leads, and jumpers for possible wear, cracks, or breaks before each use.

For maximum safety, do not touch the product, test cables, or any other instruments while power is applied to the circuit under test. ALWAYS remove power from the entire test system and discharge any capacitors before: connecting or disconnecting cables orjump- ers, installing or removing switching cards, or making internal changes, such as installing or removing jumpers.

Exercise extreme caution when a shock hazard is present. Lethal voltage may be present on cable connectorjacks or test fixtures. The American National Standards Institute (ANSI) states that a shock

hazard exists when voltage levels greater than 30V RMS, 42.4V peak, or 60VDC are present. A good safety practice is to expect

that hazardous voltage is present in any unknown circuit before measuring.

Do not touch any object that could provide a current path to the common side of the circuit under test or power line (earth) ground. Always make measurements with dry hands while standing on a

dry, insulated surface capable of withstanding the voltage being

measured.

The instrument and accessories must be used in accordance with its specifications and operating instructions or the safety of the equip ment may be impaired.

The WARNING heading in a manual explains dangers that might result in personal injury or death. Always read the associated information very carefully before performing the indicated procedure.

Do not exceed the maximum signal levels of the instruments and accessories, as defined in the specifications and operating information, and as shown on the instrument or test fixture panels, or switching card.

When fuses are used in a product, replace with same type and rating for continued protection against fire hazard.

Chassis connections must only be used as shield connections for measuring circuits, NOT as safety earth ground connections.

If you are using a test fixture, keep the lid closed while power is applied to the device under test. Safe operation requires the use of a lid interlock.

Ifa@ screw is present, connect it to safety earth ground using the wire recommended in the user documentation.

The ! A symbol on an instrument indicates that the user should refer to the operating instructions located in the manual.

The

symbol on an instrument shows that it can source or mea-

m sure 1000 volts or more, including the combined effect of normal and common mode voltages. Use standard safety precautions to avoid personal contact with these voltages.

The CAUTION heading in a manual explains hazards that could damage the instrument. Such damage may invalidate the warranty.

Instrumentation and accessories shall not be connected to humans.

Before performing any maintenance, disconnect the line cord and all test cables.

To maintain protection from electric shock and lire. replacement components in mains circuits, including the power transformer, test leads, and input jacks, must be purchased from Keithley Instruments. Standard fuses, with applicable national safety approvals, may be used if the rating and type are the same. Other components that are not safety related may be purchased from other suppliers as

long as they are equivalent to the original component. (Note that selected parts should be purchased only through Keithley Instruments to maintain accuracy and functionality of the product.) If you are unsure about the applicability of a replacement component, call a

Keithley Instruments office for information.

To clean an instrument, use a damp cloth or mild, water based cleaner. Clean the exterior of the instrument only. Do not apply cleaner directly to the instrument or allow liquids to enter or spill on the instrument. Products that consist of a circuit board with no case or chassis (e.g., data acquisition board for installation into a computer) should never require cleaning if handled according to in-

structions. If the board becomes contaminated and operation is af-

fected, the board should be returned to the factory for proper cleaning/servicing.

Rev. 10199

Model 238 Source Measure Unit Specifications

SOURCE-MEASURE UNIT: Sources voltage while measuring current, or

sources current while measuring voltage.

FUNCTION: Can be used as DC source or meter, sweep source, or full

source-measure unit.

SOURCE-DELAY-MEASURE CYCLE:

Source

- Source-Delay-Measure Cycle - -

Default

I I

Delay

Default Delay: Fixed delay for instrument settling. User Delay: Additional delay for device under test or system capaci-

tance.

MEASURE:

Integration Time:

Fast 416 psec. Medium Line Cycle

Elapsed Time: Measures and stores time from sweep trigger to mea-

surement complete for each step of sweep.

RANGING:

Source: Auto-ranging through keypad entry; fixed range selectionusing

rotary dial and SELECT keys (DC function). Fully programmable in SWEEP function.

Measure: Auto or fixed range. Fixed range selection made by choice of

COMPLIANCE value.

FILTER: Takes n measurements, calculates and outputs average (n = 2,4,

8,16, or 32, selectable). SUPPRESS: Subtracts displayed measurement from subsequent readings. MENU: DC Measurement Delay, Default Delay On/Off, Local/Remote

Sense, 50/6OHz, IEEE Address, Self Tests. DATA ENTRY: Numeric keypad or detented rotary dial. TRIGGER:

Input and Output: Set for any phrise of SOURCE-DELAY-MEASURE

sequence or trigger output at end of sweep.

Origin: Internal, External (including front panel MANUAL TRIGGER

button), IEEE-488 bus (TALK, GET, “X9.

MEMORY: Stores one full sweep (up to 1000 points) of source, delay, and

measure values, elapsed times, and sweep parameters. Lithium battery

backup. INTERLOCK: Use with test fixture or external switch. Normally closed;

open puts instrument in standby.

267 ts::: (60 Hz)

20.00 msec. (50 Hz)

Delay

Measure

Integration Tie

4-digit resolution Sdigit resolution Sdigit resolution

VOLTAGE

SOURCE V

RANGE ACCURACY

(Max.

Value) SIZE 18=-WC)

f1.5000V 100 FV *(0X133% + 8OOpV 100 PV 10 PV f(O.OZS% + 4501’.

f15.000V 1mV *(0.033%+ 2.7mV) f110.00V 1OmV f(0.033%+ 24mV)

I, = Oulput current I, = Full scale on selected current range

I Spe&cations apply for 5digit resolution. For 4-d@ resolution add 1OOppm of

range. Assumes remote sense for I > lOOpA.

2 On the 1A range use [1,&l x 25OpV. COMPLIANCE: Bipolar current limit set with single value.

Maximum: flA WOOmA on the 1lOV range).

STEP (1 Year,

+ [1,/I,] x 600~V)z

Minimum: fl% of selected voltage range.

Accuracy, Step Size: Same as current source.

NOISE (p-p typical):

Range

110 v < 3ppm of range

15 v

1.5v WIDEBAND NOISE: 0.1 to 2OMHz,8mV p-p typical. OVERSHOOT: ~0.01% (IlOV step, 1OmA range). SETTLING TIME: <5OOpsec. to 0.01% (1lOV step, 1OmA range). NMRR: >60dB at 50 or 6OHz (LINE CYCLE integration time selected). CMRRz>120dBatDC,50or60Hz (LINECYCLE integration timeselected). INPUT IMPEDANCE (as a voltmeter): >lOW paralleled by <20pF.

< 3ppm of range <lOppm of range

MEASURE V

ACCURACY’

RESOLUTION 4-Diait S-Diait

1mV 100 PV f(0.025%+ 13mV)

1OmV

O.l-1oHz

1mV f(0.025%+ 1OmV)

(1 Year,

w-28°C)

+ ~I,/I,l x 6cQw

CURRENT

SOURCE I

RANGE ACCURACY ACCURACW

(Max.

Value) SIZE

f1.0000 nA 100 fA k(O.3 %+ 450 fA) 100 f.4 10 IA f(0.3 %+ 100 fAy *10.000 nA 1 pA f(03 %+ 2 pAI 1 pA 100 fA &CO3 %+ 1 pA) fllM.00 nA 10 pA f(O.Zl%+ 20 pA) 1OpA f1.0000 fl 100 pA f(0.05%+ 200 PA) 100 pA 10 pA f(0.04 %+ 60 pAI *10.000 /lA 1 nA xk(0.05%+ 2 nA) 1 nA 100 pA f(0.035%+700 pA) floO.OO pA 10 IL4 +(0.05%+ 2OnA) 1onA fl.OOOOmA 100 XL4 +(o.a5%+ 200 nA) 100 nA 10 nA f(0.035%+ 60 nA) +1o.OOomA 1 @ *(0.05%+ 2 @, 1 fl loOnA f(0.038%+600 nA) *1oO.oomA 10 fl *co.1 %+ 20 @A) lOti 1 @ HO.1 %+ 6 +A) f1.0900 A 100 pA f(0.12%+ 700 @A) lOO@ 1OM f(0.12 %+3CKJ @A)

‘Speciilcations apply for 5-d@ resolution. For 4-digit resolution, alI offset terms

are 2OOppm of range.

20ffset spedfication applies for 23°C i 1°C with suppression. Temperature

coefficient SOfA/“C.

STEP

(1 Year,

W-2800

4-D&$ S-Digit

MEASURE I

RESOLUTION

1 pA f(0.21 %+ 6pA)

1 nA f(0.035%+ 6nAf

(1 Year,

18”-28°C)

Specifications subject to change without notice.

COMPLIANCE: Bipolar voltage limit set with single value.

Maximum: fllOV (*15V on the 1A range). Minimum: fl% of selected current range. Accuracy, Step Size: Same as voltage source.

NOISE (p-p of range): O.l-1OHz <3pim (<20ppm on InA, 10~4 and IA

ranges). OVERSHOOT: ~0.01% typical (lOmA step, R, = 1OkQ). SETTLING TIME: <500psec. to 0.01% (lOmA step, R, = 1OkQ). OUTPUT R, C: >lOW paralleled by <20pF (on 1nA range).

IEEE-488 BUS IMPLEMENTATION

MUCTILINE COMMANDS: DCL, LLO, SDC, GET, GTL, UNT, UNL, SI’E,

SPD. UNILINE COMMANDS: IFC, REN, EOI, SRQ, ATN. INTERFACE FUNCTIONS: SHI, AI-II, T6, TEO, L4, LEO, SRI, RLI, PPO,

DCI, DTI, CO, El. All front panel functions and setups are available over the IEEE-488 bus, in

addition to Status, Service Request, Output Format, EOI, Trigger, and

Terminator.

IEEE-488 address is set from front panel menu.

EXECUTION SPEED

MINIMUM SOURCE-DELAY-MEASURE CYCLE TIME: lmsec. RESPONSE TO IEEE-488 COMMAND (as a source): 25msec. MEASUREMENT RATE: lmsec. per point into internal buffer. CONTINUOUS MEASUREMENT SPEED (source DC value over IEEE-

488 bus): 110 readings per second. TRIGGER LATENCY TIME: c2msec.

GENERAL

LOAD CAPACITANCE: Stable into 20,OOOpF typical. REMOTE SENSE: Corrects for up to 2V drop in each output lead. Maxi-

mum lw2 per sense lead for rated accuracy. Residual output resistance

(as a voltage source) is 0.5R. GUARD: Output Resistance: 512kQ.

Maximum Output Current: f2mA. Open Circuit Offset Relative to Output HI: XZ.mV max.

ISOLATION (Output LO to chassis): Typically >lOk’R in parallel with

650pF. MAXIMUM COMMON MODE VOLTAGE: 200V peak. CONNECTORS: Outputs: 3-lug triax.

Trigger Input/Output: BNC. Interloclo 3-pin miniature DIN.

TEMPERATURE COEFFICIENT to’-lS’=C & 28=5O“Cl:

f(O.l x applicable accuracy specification)/“C.

ENVIRONMENT:

Operating: O”-5O”C, 70% relative humidity up to 35°C. Linearly derate

3% RH/T, 35=50°c.

Storage: -25’ to 65°C. WARM-W: One hour to rated accuracy. COOLING: Internal fan forced air cooling. POWER: 105-125 or 210-250V AC (external switch selectable), 90- 1lOV

and 180-220V version available. 120VA max. DIMENSIONS, WEIGHT: 89mm high x435mm wide x 448mm deep (3!4

in. x 17% in. x 1% in.). Net weight 9kg (19.75 lbs.). ACCESSORIES SUPPLIED:

Model 7078-m-10: Triax to Triax Cable, 3m (10 ft.1 (2 supplied)

Model 236ILC-3: Interlock Cable ACCESSORIES AVAILABLE:

Model 8000-10: Equipment Rack for 3 SMUs (10 in.1

Model 8000-14: Equipment Rack for 4 SMUs (14 in.1

Table of Contents

SECTION 1

1.1

1.2

1.3

1.4

1.5

1.5.1

1.5.2

1.5.3

1.5.4

1.5.5

1.5.6

1.5.7

1.5.8

1.5.9

- Performance Verification

INTRODUCTION ENVIRONMENTAL CONDITIONS

INITIALCONDITIONS .........................................................

REQUIREDTESTEQUIPMENT ...................................................

VERIFICATION PROCEDURES

Equipment Characterization CommonModeVerification Voltage Source Verification VoltageMeasureVerification

RemoteSenseVerification ......................................................

Low Current (1nA to lOmA) Measure Ranges Verification Low Current (1nA to lOmA) Source Ranges Verification lOOmA and 1A Measure Ranges Verification lOOmA and 1A Source Ranges Verification

..............................................................

SECTION 2 - Calibration

2.1

2.2

2.3

2.4

2.5

2.6

2.6.1

2.6.2

2.6.3

2.6.4

2.7

2.8

LNTRODUCTION RECOMMENDED CALIBRATION EQUIPMENT ENVIRONMENTAL CONDITIONS WARM-UPPERIOD CALLOCK CALIBRATION PROCEDURES

Equipment Characterization Voltagecalibration lOOmA and 1A Ranges Calibration

Low Current Ranges Calibration (1nA - lOmA) CALIBRATION ERRORS CALIBRATION PROGRAM

..............................................................

....................................................................

................................................

...................................................

....................................................

..................................................... l-6

.....................................................

.................................................... l-8

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........................................................... 2-5

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l-l 1-l l-l l-l l-l l-3

l-7

l-10 l-11 1-13 1-16 1-16

2-l 2-l 2-1 2-l 2-2 2-2 2-2

2-8 2-11 2-13 2-14

SECTION 3 - Maintenance

3.1

3.2

3.3

3.4

3.5

3.6

3.7

3.8

3.8.1

INTRODUCTION..

LINEFUSEREPLACEMENT .....................................................

FANFlLTERCLEANING BAl-I’ERY REPLACEMENT HANDLING AND CLEANING PRECAUTIONS DISASSEMBLY INSTRUCTIONS SPECIAL HANDLING OF STATIC SENSITIVE DEVICES TROUBLESHOOTING

Recommended Test Equipment

............................................................ 3-l

3-l

........................................................

......................................................

......................................

..................................................

................................

.......................................................... 3-8

..................................................

3-l 3-2 3-2

3-4 3-8

3-8

3.8.2

3.8.3 Power Supply Checks

3.8.4 Analog Control Lines

3.8.5 AnalogSwitching

3.8.6 Digital and Display Checks

Diagnostics

.................................................................

.........................................................

..........................................................

............................................................

.....................................................

3-8 3-10 3-10 3-11 3-12

SECTION 4

4.1

4.2

4.2.1

4.2.2

4.2.3

4.3

4.4

4.4.1

4.4.2

4.4.3

4.4.4

4.5

- Principles of Operation

INTRODUCTION ANALOGCIRCUrrRY

V/IControlandReadback OutputModule

V/IFeedback A/DCONVERTER DIGITALCIRCUITRY

I/OController

Souce/MeasureController

Communications

DisplayCircuitry

POWERSUI?PLY ..............................................................

..............................................................

..........................................................

......................................................

..............................................................

...............................................................

............................................................. 4-8

..........................................................

...............................................................

.............................................................

SECTION 5 - Replaceable Parts

5.1 INTRODUCTION

5.2

5.3 ORDERING INFORMATION

5.4 FACTORYSERVICE

5.5

PARTSLISTS .................................................................

SCHEMATIC DIAGRAMS AND COMPONENT LOCATION DRAWINGS ...................

..............................................................

............................................................

.....................................................

4-l

4-2 4-2 44 4-5

4-8 4-8 49 49 4-9 4-10

5-l 5-l 5-l 5-l 5-l

List of Illustrations

SECTION 1

Figure l-l Setup for Equipment Characterization Figure l-2 Setup for Common Mode Verification Figure l-3 Setup for Voltage Source Ranges Verification Figure l-4 Setup for Voltage Measure Ranges Verification Figure l-5 Figure l-6 Figure l-7 Figure l-8 Setup for lOOmA and 1A Measure Ranges Verification Figure l-9 Setup for lOOmA and 1A Source Ranges Verification

- Performance Verification

....................................

..............................

.............................

Setup for Remote Sense Verification Setup for Low Current Measure Ranges Verification (1nA to lOmA) Setup for Low Current Source Ranges Verification (1nA to lOmA)

.....................................

SECTION 2 - Calibration

Figure 2-1 Calibration Switch (Cal Lock) Figure 2-2 Figure 2-3 Figure 2-4 Figure 2-5 Figure 2-6 Figure 2-7

Setup for Equipment Characterization Setup for VoltsCalibration Setup for lOOmA and 1A Ranges Calibration Current Ranges Calibration (1nA to lOmA) Ul Error Status Word U7 Calibration Status Word

...................................................... 2-14

................................................ 2-2

.......................................... 2-3

.................................................. 2-6

..................................... 2-9

..................................... 2-11

................................................. 2-14

.......................

.........................

.............

...............

. . . l-5 . . .

l-6 . . . l-7 . . . l-9 . . . l-10 . . .

1-12 . . . 1-15 . . . 1-17 . . .

1-18

SECTION 3 - Maintenance

Figure 3-l Figure 3-2. Figure 3-3. Figure 3-4. Figure 3-5

Line Voltage Switch and Line Fuse DigitalBoard OutputBoard.. Analog Board (Shields Removed) Model 238 Exploded View

............................................................

..........................................................

..................................................

SECTION 4 - Principles of Operation

Figure 4-l. Figure 4-2. Figure 4-3. Figure 4-4. Figure 4-5. Damping Relay Contact Bounce

OveraIIBlockDiagram Simplified Schematic of V/I Control and Readback Output Module (Simplified Schematic Diagram) V/I Feedback (Simplified Schematic)

...............................................

............................................ 3-l

.............................................

. . . 4-l

..........................

............................

....................................

........................................

. . . 4-2 . . . 4-5 . . . 4-6 . . . 4-7

3-3 3-5 3-6 3-7

List of Tables

SECTION 1

Table l-l Table l-2 Table l-3 Table l-4 Table l-5

Table l-6 Table l-7 Table 1-8 Table l-9

- Performance Verification

Required Test Equipment Specifications for Alternate Equipment

Model 263 I-Source Characterization ................................................

VoltageSourceVerification VoltageMeasureVerification Allowable Reading Calculations for Low Current Measure Verification (1vA to lOmA).

Low Current Measure Verification (1nA to lOmA) .....................................

Allowable Reading Calculations for Low Current Source Verification (lnA to lOmA)

Low Current Source Verification (1nA to lOmA) .......................................

SECTION 2 - Calibration

Table 2-l Table 2-2 Table 2-3 Table 2-4

RequiredTestEquipment

Specifications for Alternate Equipment ..............................................

Model 263 I-Source Characterization ................................................

Calibration Error Messages ........................................................

SECTION 3 - Maintenance

Table 3-l Table 3-2 Table 3-3 Table 3-4

Table 3-5 Table 3-6 Table 3-7 Table 3-8 Table 3-9 Table 3-10

LineFuseSelection Recommended Troubleshooting Equipment

FowerSupplyChecks Analog Switching; Current Ranging Analog Switching; Current Ranging Analog Switching; Feedback Analog Switching; Sensing Analog Switching; A/D Multiplexing DigitalCircuitryChecks DisplayCircuitryChecks

..........................................................

..............................................

.........................................................

.......................................................

.....

.......

..........................................................

...............................................................

..........................................

............................................................. 3-10

................................................

.......................................................

.........................................................

...............................................

...........................................................

..........................................................

l-2 l-3 14 l-8 l-9 l-11 1-12 1-13

1-14

2-l 2-2 2-5 2-13

3-1 3-8

3-11 3-11 3-12 3-12 3-12 3-13 3-14

SECTION 4 - Principles of Operation

Table 4-l

VoltsRangeRelays

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4-8

SECTION 1

Performance Verification

1.1 INTRODUCTION

The procedures outlined in this section may be used to

verify that the instrument is operating within the limits stated in the specifications at the front of this manual. Performance verification may be performed when the instrument is first received to ensure that no damage or n&adjustment has occurred during shipment. Verification may also be performed whenever there is question of instrument accuracy, or following calibration, if desired.

NOTE

If the instrument is still under warranty (less than 1 year from the date of shipment), and its performance falls outside the specified range, contact your Keithley representative or the factory to determine the correct course of action.

Before attempting any of the following procedures, make sure you are familiar with the controls and operation of the Model 238. Refer to the Model 238 Operator’s Manual for complete information.

1.3 INITIAL CONDITIONS

WARNING The Source Measure Unit is equipped with a 3-wire power cord that contains a separate ground wire and is designed to be used with grounded outlets. When proper connections are made, instrument chassis is connected to power line ground. Failure to use a grounded outlet may result in injury or death due to electric shock.

The Model 238 must be turned on and allowed to warm up for at least one hour before beginning the verification procedures. If the instrument has been subject to extremes of temperature (outside the range specified in paragraph 1.2), additional time should be allowed for internal temperatures to reach normal operating temperature. Typically, it takes one additional hour to stabilize a unit that is 10°C (18°F) outside the specified temperature range.

1.4 REQUIRED TEST EQUIPMENT

Table l-l lists all the test equipment required for verification. The procedures for performance verification are based on using this exact equipment.

WARNING The procedures in this section are for use only by qualified service personnel. Do not perform these procedures unless qualified to do so. Many of these steps in this section may expose you to potentially lethal voltages that could result in personal injury or death if normal safety precautions are not observed.

1.2 ENVIRONMENTAL CONDITIONS

All measurements should be made at 18-2B°C (65432°F) and at less than 70% humidity.

Alternate equipment may be used as long as the substitute equipment has specifications at least as good as those listed in Table 1-2. Note that equipment characterization (paragraph 1.5.1) is not required if using equipment that meets the specifications in Table 1-2.

1.5 VERIFICATION PROCEDURES

The following paragraphs contain the detailed procedures for verifying the one year accuracy specifications of the Model 238 using the equipment listed in Table l-l.

NOTE The allowable reading limits in these procedures only reflect the specifications of the Model 238. They do not include error contributed by test equipment.

l-l

SECTION 1 Performance Verification

These procedures are intended for use only by qualified personnel using accurate and reliable test equipment. If the instrument is out of specifications and not under warranty, refer to the calibration section of this manual.

WARNING Lethal voltages (up to 1OOV) will be connetted to the Model 8006 test fixture. To avoid a possible shock hazard, the safety in- nals of the Model 238.

terlock circuit must be connected to the Model 238.

Connect the test fixture screw to safety earth ground using #18 AWG wire minimum before use. Turn off all power before connecting or disconnecting wires or cables.

Also, keep in mind that GUARD is always enabled. Thus, a lethal voltage on OUTPUT HI is also present on the two GUARD termi-

Table l-l Required Test Equipment

Manufacturer

Keithley

Keithley 193A 5-l /2 digit DMM

Keithley

Model

263

617

Description

5-l/2 digit Calibrator/ Source

41/2 digit Electrometer

Specifications

2nA,2OnA ranges; +(0.0625% + 10 counts) 2OOnA range; &(0.035% + 10 counts)

2OOmV, 2V ranges; +(0.005% + 2 counts) 2OV-1OOOV ranges; +(0.007% + 1 count) 2OOR-200WZ ranges; +(0.007% + 2 counts) 200@-2mA ranges; &(0.09% + 10 counts)

2pA range; +(1.6% + 66 counts) 20 A range; ~-0.6% + 7 counts) 2 obl pA range; k&6% + 1 count) 2nA range; +(0.25% + 5 counts) 2OnA range; +(0.25% + 1 count) 2001~4 range; &(0.25% + 1 count) 2fi range; +(0.15% + 4 counts)

2OpA range; &(0.15% + 1 count) Keithley Keithley Fluke Valhalla Keithley

Keithley

Pomona

1-2

8006 236-TLC-3 343A 2500E R-249-100

R-263-l k R-263-100K

7078-TRX

6172 2-slot male to 3-lug

B-24

Test Fixture Interlock Cable DC Voltage Calibrator Current Calibrator 1OOQ Resistor

1161 Resistor 1OOkQ Resistor

3-slot triax cable

(3 required)

female triax adapter

(2 required)

Banana plug cable

(6 required)

lOV-1OOV ranges; +0.002% lOOmA-1A ranges; +0.025%

+O.l%, &20ppm/“C +O.l%, +lOppm/“C +O.l%, +lOppm/“C

Performance Verification

SECTION 1

Table 1-2 Specifications for Alternate

Equipment

Instrument Type DMM

Source DC Current

Measure DC Current 250ppm rdg +5OOnA

1 s.1

In order to verify the I@, lo@, lOOl.tA, 1mA and 1Om.A source and measure ranges of the Model 238, the 0.9p.A, 9p.A, 9Ol.& 0.9mA and 9mA outputs of the Model 263 are characterized.

1. Connect the Model 263 source, Model 193A DMM

2. Configure the source and DMM as follows:

3. Zero the Model 193A as follows: A. At the SENSE 1 (HI) terminal of the test socket,

C. On the Model 193A, enable ZERO to cancel test

D. Relocate the jumper back to the SENSE 1 termi-

4. In the space provided below, use a pencil to record the actual value of the 100&J resistor from the display of the Model 193A.

Equipment Characterization

and Model 8006 test fixture as shown in Figure l-l. Install the 1OOwZ resistor (in Table l-1) in the AXIAL KELVIN CLIPS test socket of the test fixture.

Model 263 - Amps function, +0.9OOOOfl on 2lrA range, GUARD enabled and output in standby. Model 193A - Ohms function on the 2OOkQ range,

disconnect the jumper whose other end is connected to BINDING POST 2 on the Signal Panel.

B. Connect that jumper to the SENSE 2 (LO) termi-

nal of the test socket. This shorts the Ohms Sense input of the Model 193A at the test socket.

lead resistance.

nal of the test socket. Make sure the connections at the Component Test Module are correct as shown in Figure l-l.

look0 =

Required Specifications Same as Keithley 193A

(see Table l-l)

0.9nA, 9nA, 9OnA, Same as Keithley 263 (see Table l-l)

0.9@; +lBOppm 9pA, 90/.&A, 9oopA, 9mA;

fl70ppm

9OmA; k230ppm

0.9A; f625ppm

lcQ

5. Set the Model 193A to the DCV function and the 200mV range, and disable zero.

6. To cancel any offset, zero the Model 193A by shorting its input (VOLTS HI to LO) and enabling zero.

7. Remove the short from the input of the Model 193A and place the Model 263 in operate to source +0.9OOOOl.tA to the 1OOkQ resistor

8. In the space below, use a pencil to record the voltage drop across the resistor from the display of the Model 193A.

V100m =

9. Calculate (to 5-l/2 digits) the current through the 100162 resistor as follows:

Io.sfl = - = @

Io.9~ is the characterized current for the 2@ range of

the Model 263. It is used to check the $A measurement range of the Model 238. Using a pencil, record the calculated value of Io.s,,A in Entry 1 of Table l-3.

10. Place the Model 263 in standby.

11. Set the Model 193A to the 2V range.

12. Set the Model 263 to source 9.OOOOfl on the 2OpA range and enable operate.

13. As performed in steps 8 and 9, measure the voltage across the 1OOm resistor and calculate the current.

lWk0 =

Iqi~=-= PA

I9@ is the characterized current for the 2Olt.A range of the Model 263. It is used to check the IO@ measurement range of the Model 238. Using a pencil, record the calculated value of IgM in Entry 2 of Table l-3.

14. Place the Model 263 in standby.

15. In the test fixture, remove the 1OOkQ resistor and in-

stall the lkrcz resistor (R-263-lk).

16. On the Model 193A, select the Ohms function, 2kQ

range and disable zero.

17. Repeat step 3 to zero the Model 193A.

18. Measure and record the value of the 1wZ resistor.

RW =

19. Set the Model 193A to DCV and the 200mV range,

and disable zero.

20. To cancel any offset, zero the Model 193A by shorting its input (VOLTS HI to LO) and enabling zero.

21. Remove the short from the input of the Model 193A and set the Model 263 to source 90.000pA on the 2OOlrA range and enable operate.

v100kn

RlC0kn

V100m

RlOOkn

1-3

SECTION 2 Performance Verification

22. Record the voltage measurement from the Model 193A and calculate the current.

vMl=

go@=-=

Vlkn

cw-\

Rlkn

190,~ is the characterized current for the 2OO@ range

of the Model 263. It is used to check the lOOpA measurement range of the Model 238. Using a pencil, record the calculated value of 190~ in Entry 3 of Table l-3.

23. Place the Model 263 in standby.

24. Set the Model 193A to the 2V range.

25. Set the Model 263 to source 0.9OOOOmA on the 2mA range, and enable operate.

26. Record the voltage measurement from the Model 193A and calculate the current.

v1ko=

VlCWl

IO.WA = - =

RIO09

10.~ is the characterized current for the 2rruA range

of the Model 263. It is used to check the 1mA measurement range of the Model 238. Using a pencil, record the calculated value of Io.hn~ in Entry 4 of Table l-3.

27. Place the Model 263 in standby.

28. In the test fixture, remove the 1kQ resistor and install the 1OOQ resistor (R-249-100).

29. On the Model 193A, select the Ohms function, 200R range and disable zero.

30. Repeat step 3 to zero the Model 193A.

31. Measure and record the value of the 1OOR resistor.

Rloon =

32. Set the Model 193A to DCV and the 2V range, and disable zero.

33. To cancel any offset, zero the Model 193A by shorting its input (VOLTS HI to LO) and enabling zero.

34. Remove the short from the input of the Model 193A and set the Model 263 to source 9.OOOOmA on the 20mA range and enable operate.

35. Record the voltage measurement from the Model 193A and calculate the current.

loon =

VW09

1-c-z

R1KX-J

IB,,A is the characterized current for the 2OmA range of the Model 263. It is used to check the 1OmA measurement range of the Model 238. Using a pencil, record the calculated value of IsmA in Entry 5 of Table l-3.

36. Place the Model 263 in standby.

Table 1-3 Model 263 I-Source Characterization

263 I-Source

Programmed

Entry 1

2 3

Range

2P4

2oP4

2ooJ.A 4 5

Ihe~aracterizedI-sourcevvaluesshouldbewithinthelistedlimik.Theselimikarebssedon90-&yspedficationsof theMcdelsZ63 and 193kAcharacterizedvaluethatdoesnot fallwithintheselimikindicatesacalculationerror,orthat theModel263and/orModel 193A is out of specification.

2omA

Value

0.9OOOOltA

9.oooopA

9o.ooopA

0.90000mA

9.oooomA

Characterized

I-Source Value Value Limits*

10.9pA =

Isp~ =

19qlA =

10.9mA = Igm.4 = 9rfd +5.4pA

I-Source

0.9p.A +450pA

9pA k4.3n.A

9OpA +45nA

0.9mA *43onA

l-4

SECTION 2

Performance Verification

Banana Plug Cables (5)

Warning: Connect to Safety Earth Ground

A. Connections

Signal PalMI

Component Test Module

Source

(Source I)

_-- -.. -m--a.

-. -* -.

Model 8006 Test Fixture

263

COMMON

707&TRX--

Cable

_.“.

-I

Model 193A DMM

i-l volts

193A DMM

(Measure Q and V)

8. Schematic Equivalent

Figure l-1 Setup for Equipment Characterization

1-5

SECTION 1

Performance Verification

1.5.2 Common Mode Verification

Set up the equipment as shown in Figure l-2 and perform the following steps for common mode verification.

1. While in standby, program the Model 238 as follows; j TIME at LINECYCLE PERIOD, source at

+l.OOOOuA, and compliance at 1V on the 1.5V range.

Interlock Cable (236~ILC-3)

2. Place the Model 238 in OPERATE and, using a pencil, record the voltage measurement in the space provided below.

+1pA =

3. From the keypad, change the source value to

-1.OOOOl.tA and record that measurement. V-l&A =

4. Subtract the two voltage measurements from each other Verify that the absolute value of the result is

_ --* __

<l.ZUmV

I v+1fl- V-IU I <1.20mV

Warning: Connect to Safety Earth Ground

Figure 1-2

8006 Test Fixture

A. Connections

238

(Source I, Measure V)

B. Schematic Equivalent

Setup for Common Mode Verification

Shorted Output

1-6

SECTION 1

Performance Verification

1.5.3

Voltage Source Verification

Set up the equipment as shown in Figure l-3 and perform the following steps to verify the voltage source.

WARNING The following procedure uses hazardous voltages (1OOV) that could cause injury or death. Exercise extreme caution when encountering these lethal voltage levels.

1. Set the Model 193A to measure DCV on the 200mV

range.

2. While in standby, set the Model 238 to source OV on the 1.5V range and set compliance to lOmA.

3. Temporarily disconnect the banana cable from BINDING POST 2 at the rear panel of the test fixture and connect it to VOLTS LO of the Model 193A. This will short the input of the Model 193A DMM.

Interlock Cable (236~ILC-3)

]

4. On the Model 193A, press ZERO to cancel any measurement offsets.

5. Reconnect the banana cable to BINDING POST 2 of

the test fixture.

6. Place the Model 238 in operate and verify that the reading on the DMM is within the limits shown in the first entry of Table 1-4. Use the filter if the reading is noisy.

7. Press the SELECT 4 button to select the 15V range and verify that the DMM reading is within the allowable limits in Table l-4.

8. Using Table l-4 as a guide, repeat step 7 to check the OV output on the 11OV range.

9. From the keypad, program the Model 238 to source +lV on the 1.5V range and verify that reading on the 193A DMM is within the allowable limits.

10. Repeat step 9 for a source value of -lV.

11. Using Table 1-4 as a guide, check source values of +lOV and +lOOV.

12. Program the Model 238 to OV and place it in standby.

238

Figure 1-3

8006 Test Fixture

A. Connections

OUTPUTHI @

238

(Source v) OUTPUT LO

B. Schematic Equivalent

Setup for Voltage Source Ranges Verification

193A DMM

Banana Plug Cables (2)

l HI

a Lo (Measure V)

193A DMM

1-7

343A Range

Table l-5 Voltage Measure Verification

238

Compliance Limit

343A Output & Measuring Range*

SECTION 1

Performance Verification

Allowable Reading

mYT to 2PC)

1ov

ov 1.5v -0.00045v to +0.00045v ov ov

+lV

1ov -lv

1ov +lOV 1ov

-lov 15v -9.9962V to -10.0038V

1oov +lOOV 1oov -loov

15v

1lOV

-00.0013v to +00.0013v

-000.010v to +ooo.o1ov

1.5v +0.99927V to +l.O0073V

1.5v -0.99927V to -1.00073V

15v +9.9962V to +lO.O038V

1lOV +99.965V to +lOO.O35V 11ov -99.965V to -100.035v

Interlock Cable (236~ILC-3)

238

Figure Z-4

800

16 Test Fixture

A. Connections

343A

DC Calibrator

oUTPUT _ l

(Source V)

B. Schematic Equivalent

Setup for Voltage Measure Ranges Verification

I I

- .-..

DC Calibrator

@ OUTPUTHI

OUTPUT Lo

J VJ

238

(Measure V)

l-9

SECTION 1

Performance Verification

1.5.5 Remote Sense Verification

Set up the equipment as shown in Figure 1-5. The 1kQ resistor (R-263-l k) is installed in the Kelvin test socket. Per-

form the following steps to verify remote sense accuracy:

WARNING

When a Model 238 is programmed for re-

mote sensing, hazardous voltage may be pre-

sent on the SENSE and OUTPUT terminals when the unit is in operate regardless of the programmed voltage or current. To avoid a possible shock hazard, always turn off all power before connecting or disconnecting cables to the Source Measure Unit or the associated test fixture.

interlock Cable (236-ILC-3)

1. While in standby, place the Model 238 in remote sense and set it to source 1OV with a compliance limit of 1OmA on the 1OmA measurement range. Place the

Model 238 in standby.

2. Set the Model 193A DMM to DCV and select the 20V range.

3. TeGporarily disconnect the banana cable from VOLTS HI of the DMM at the rear panel of the test fixture (BINDING POST 11, and connect it to VOLTS LO of the DMM. This shorts the input of the Model 193A DMM.

4. On the Model 193A DMM, enable zero to cancel any offsets.

5. Re-connect the banana cable to BINDING POST 1 of the test fixture.

6. Place the Model 238 in operate and verify that the reading on the DMM is within the following allowable l⁢ 9.994OV to 10.006OV.

7. Place the Model 238 in standby and local sense.

Figure 1-5

l-10

.a 81 IQ

ci?“?

Q, ,8

gs 8

8006 Test Fixture

A. Connections

8. Schematic Equivalent Setup for Remote Sense Verification

7076-TRX Cables (3)

Performance Verification

SECTION 1

1.5.6

Low Current (1 nA to 1 OmA)

Measure Ranges Verification

Set up the equipment as shown in Figure l-6 and perform the following steps to verify the 1nA to 1OmA measure ranges:

1. Use Table 1-6 to calculate the allowable readings for the 1rnA through 1OmA ranges. The values for Io.~,

IPM, Igofi, Io.gmA and IhA were previously calculated

and recorded in Table l-3. After calculating these readings, transfer them to Table l-7.

2. While in standby, configure the Model 238 to measure current by setting it to source OV on the 1.5V source range.

3. While in standby, set the Model 263 to the 2nA range and enable guard.

4. Set the compliance limit of the Model 238 to 1nA on the InA measurement range and enable operate.

Verify that the current measurement on the Model 238 is within the allowable limits listed in the first entry of Table l-7.

5. On the Model 238, change the compliance limit to 1OnA on the 101~4 measurement range. Verify that the reading on this measurement range is within the limits specified in the table.

6. Using Table l-7, check the rest of the Model 238 current ranges with the output of the Model 263 in standby.

7. Set the Model 263 to output +0.9OOOOnA on the 2nA

range, and set the Model 238 compliance limit to 1nA on the 11~4 measurement range.

8. Verify that the reading is within the limits specified in the table.

9. On the Model 263, change the output to negative polarity and verify that the reading is within the limits specified in the table.

10. Using Table l-7 as a guide, check the 1OnA through 1OmA measurement ranges of the Model 238.

11. Place the Model 263 in standby.

Table 1-6 Allowable Reading Calculations for Low Current Measure Verification (1pA to 10mA)

238

Measure

Range Reading Calculations*

101.t.A

100/.~A

In-IA +Io.g,,,~ + [ (0.00035) Io.g,,,~ + 60nA ] =

lOIlL +Igti + [ (0.00038) &A + 6001~4 I=

T.- T- T*. T.. --AK

l”.Ypl, rw, ‘rym, Lwlr,,4, QI,U lgmA cue ““lii”llxl Ir”In I aole I-J

Allowable reading limits are to be transferred to Table 1-7.

***

The calculated allowable readings should be within listed typical limits. These limits are based on the 90day specifications of the Model 263 and 193A. A calculated allowable reading that does not fall within these limits indicates a calculation error, or that the Model 263 and/or Model 193A is out of specification.

+Io.glrA~[(0.0004)Io.g1rA+60pAl=

-Io.g,ue+~O.00O4)Io.gru\+6OpAl= -m.------ M --.----- PA

+1~~+[(0.00035)1~~+700pA1= + _._____ I.IA

-I~CIA+[(0.00035)Ig~+700pAl=

+Igo@ f. [ (0.00035s> Igo@ + 6nA 1 =

-IgoltA + I: (0.00035> IN,,A + 6nA I=

-Io.sm~+ [ (0.00035) IO.- + 6OnA ] =

-1gmA + [ (0.00038) LA + 6OOnA I=

^-^ -I-r-:--2 L--- ‘F-L-- - -

+ _._____ PA

- _._____ PA

+::I_:: @

+- . _ _ _ _ _ mA

--. _ _____ mA

+- . _ _ _ - mA

-- . ___I mA

Allowable Reading**

Lower Limit

ti +

Typical

Upper Limit Limits***

+ _._____ PA

+-.-s-m- CIA

- _.____ PA

--:::::: /.LA

+- . _ _ _ _ _ mA

--. _ ____ mA

:::::I: 2

+0.9OOOOpA +870pA

-0.90000~ +870pA

+9.OOOOp.A +8nA

-9.OOOOpA &8nA

+9O.OOOpA ~831.~4

-9O.OOOp4 +83nA

+0.9OOOOmA +8OOnA

-0.90000mA~800nA

+9.0000d +9.4pA

-9.OOOOmA &9.4pA

l-11

SECTION 1

Performance Verijcation

Figure l-6.

Grdund Link

Note : 263 GUARD enabled

Banana Plug C&la

263 Source

(Source I)

6172 2-Slot to 3-Lug Female Tr&x adapter

7076-TRX

Cable

238 (Measure I)

Setup for Low Current Measure Ranges Vkrijication (InA to ZOmA)

Table 1-7 Low Current Measure Verification (InA to 10mA)

238

263

Range

263 Output & Measure Range*

2nA Standby

Compliance Limit

1lIA

Allowable Readings**

(18OC to 28OC)

-0.00010nA to +0.00010nA

Standby lOIL4 -00.0010nA to +00.0010nA 2nA Standby 1OOllA -000.006nA to +OOO.O06nA 2nA Standby

2nA

Standby 10pA

Standby 2nA

Standby ImA 2nA Standby

lOOpA

1OmA

-0.00006pA to +O.O0006pA

-00.0007pA to +OO.O007pA

-000.006pA to +ooo.O06~A

-0.00006mA to +O.O0006mA

-00.0006mA to +OO.O006mA

2nA +0.9000onA II-IA -0.8972OnA to -0.9028OnA

2nA -0.90000nA

2onA

+9.oooonA

h-IA

l&IA

+0.8972OnA to +0.9028OnA

-8.972OnA to -9.028OnA

2onA -9.oooonA lOIL4 +8.972OnA to +9.028OnA

2oOnA +9o.ooonA 2oOnA

&A &A

-9o.ooonA lOonA

+0.90000pA

-0.90000pA

20vA +9.OOOOpA 20pA -9.OOOOpA

200pA 200pA

+90.000pA

-9O.OOOpA lOOpA

2mA +0.90000mA 2mA

20mA

-0.90000mA 1mA

+9.0000mA 1OmA

20mA -9.oooomA lOmA

*238 set to source OV on the 1.5V source range.

**Allowable readings for the 1pA through 1OmA ranges are calculated in Table l-6.

lOonA

UA &A

10pA 10pA

lOOpA

1mA

-89.805nA to -90.195nA +89.805nA to +90.195nA

to -

to +

to -

to +

to -

to +

to -

to +

to -

to +

1-12

Performance Verification

SECTION 2

1.5.7

Low Current (1 nA to IOmA)

Source Ranges Verification

Set up the equipment as shown in Figure 1-7 and perform the following steps to verify the 1nA to 1OmA source ranges:

1. Use Table l-8 to calculate the allowable readings for the 1mA through 1OmA ranges. The values for Io.gM, 19@, Igo@, IO.CQ,A and 19n~ were previously calculated and recorded in Table l-3. After calculating the allowable readings, transfer them to Table l-9.

2. While in standby, configure the Model 238 to source OnA on the InA source range with a compliance limit of 1.5V on the 1.5V measurement range.

3. While in standby, configure the Model 263 to source On4 on the 2nA range.

4. With Zero Check enabled, zero correct the Mode1617 on the 2pA range.

5. On the Model 617, disable Zero Check and place the Model 238 in operate. Verify that the reading on the

Model 617 is within the limits specified in the first

entry of Table l-9.

6. Set the Model 617 to the 20pA range, and set the

Model 238 to source OnA on the 1OnA range. Verify

that the reading on the Model 617 is within the limits specified in the second entry of Table l-9.

7. Using Table l-9 as a guide, set the Model 238 to source zero on the lOOnA through 1OmA ranges and check that the subsequent readings are within the listed limits.

8. Place the Model 617 in zero check and select the

20pA range.

9. Place the Model 238 in standby and program it source -0.9nA on the 1nA source range.

10. While sti.U in standby, set the Model 263 to source +0.9nA on the 2nA range.

11. Place both the Models 238 and 263 in operate, and disable Zero Check on the Model 617. Verify that the reading on the Model 617 is within the limits speci-

fied in the table.

12. Place the Model 617 in zero check, and the Models

263 and 238 in standby.

13. On both the Models 263 and 238, reverse the polarity of the sources. That is, set the Model 238 to +0.9nA and the Model 263 to 4.9nA.

14. Place the Models 238 and 263 in operate, and disable zero check on the Model 617. Verify that the reading on the Model 617 is stiU within the limits specified in the table.

15. Using Table l-9 as a guide, repeat the basic procedure in steps 8 through 14 to check the 1OnA through 1OmA source ranges. Note that for the $A through 1OmA ranges, the source values for the Model 238 are taken from Table l-3.

16. Place the Model 617 in zero check, and the Models

263 and 238 in standby.

Table l-8 Allowable,Reading Calculations for Low Current Source Verification (1n.A to lOmA)

238

Source

Range Reading Calculations* Lower Limit Upper Limit

lOj.tA ~[(0.00050)19pA+2.00nA]= --.--- nA

lOOpA +[(0.00050)190~+20*00nA1=

1mA +[(0.00050)1o.sm~+200.0nA1=

1omA

+[(0.0005)Io.9,++2OOpAl=

~[(0.0005>19mA+2*00pA1=

- _.____ nA + _.____ nA

- __.__ nA

- _.____ /LA + _.____ /LA

- _.___ fl

Allowable Reading**

-----

__.__ nA

_*___ fl

Typical Limits***

+ 0.6500nA

+6.5001-A

+65.OOnA

+ 0.6500pA

+6.5OOpA

* v IV v IT ~1 * * , .- ~~~~ m-t.,. . *

l-13

SECTION 2

Performance Verification

Table 1-9 Low Current Source Verification (InA to lOmA)

263 I-Source

617

Output Source Source 617 Allowable Ratings**

Range Range Setting

2PA 2PA

20pA

22 Standby

200pA

2onA 2nA

Standby 1nA OnA -0.45OOpA to +0.45OOpA Standby 1OnA OnA

Standby ~JJ.A Standby Standby

2oonA 2nA Standby 1mA

w4 2nA

20pA 2nA

Standby 1OmA -2.oooj.lA to +2.000)&4

+o.gllA

-0.9nA

200pA 2onA

+9nA 1onA -9nA -29.00pA to +29.OOpA

-9IL4

238 I-Source*

Range Value*** (18T to 28°C)

-2.OOOpA to +2.OOOpA

lOmA OnA -2O.OOpA to +20.OOpA

-2OO.OpA to +200.0pA

1OclA

low-4 OCLA

-2.ooonA to +2.ooOnA

-2o.oonA to +2o.OOnA

-2oo.onA to +2OO.onA

InA

49n4 -3.150pA to +3.15OpA +0.9nA

+9nA

200pA 2oonA +9onA lOOIL -90nA -209.0pA to +209.0pA

-90nA i-9onA

2onA

2cLA

+0.9pA

-0.9p.A

2oP4 +%A lo@

-9clA

-109pA

+Io.a)lA

-19pA fI9pl

IL4 to +

nA to +

IL4

2oonA +9opA

-9opA

+o.gmA 1mA

2P4

2ooJ.L4

2mA

1OWA

-0.9m4

2lJ-A

2omA

+9mA lomA

-9mA

* 238 compliance limit set to 1.W on the 1.1V measurement range. ** Allowable readings for the 1M thru 1OmA source ranges are calculated in Table 1-8. ‘** For the 1p-l thru 1OmA ranges, program the Model 238 to source the characterized I-source values from Table 1-3.

-19@LA S&OlrA

-1osmA fI0.9mA

-I%4

fISmA

II‘4 to + IL4

I-IA to + IL4

I-IA to + nA

l-14

Interlock Cable (236~ILC-3)

Performance Verification

SECTION 1

warning: (

to Safety Ei

Ground

A. Connections

8006 Test Fixture

1 /ol+-gy”

238

Note : 617 GUARD dualled

263 source

617 Electrometer

Figure 1-7

238

(Source 1)

OUTPUTHI @

OUTPUT LO

INPUT

617

Electrometer

(Measure I)

B. Schematic Equivalent

Setup for Low Current Sou,rce Ranges Verification (InA to ZOmA)

@ OUTPUT

. COMMON Source

263

(Source I)

l-15

SECTION 1

Performance Verification

1.5.8 1OOmA and 1A Measure Ranges Verification

Set up the equipment as shown in Figure l-8. A copper short is installed in the test socket.

lOOmA Measure Range Verification

Perform the following steps to verify the 100mA measurement range:

While in standby, set the Model 238 to source OV on the 1.5V source range, and set compliance to 1OOmA.

Remove the short from the test fixture and place the Model 238 in standby.

Verify that the current reading (Iz.& on the Model 238 is within the following limits:

Ius = &6fl

Place the short in the test fixture socket and set the calibration source to output +9OmA.

Verify that the current reading (IUS) on the Model 238

is within the following limits:

IUS = 89.904mA to 90.096mA

Set the calibration source to output -9OmA.

Verify that the current reading (IUS) on the Model 238 is within the following limits:

Ius = -89.904mA to -90.096mA

Place the Models 343A and 238 in standby.

IA Measure Range Verification

Perform the following steps to verify the 1A measurement range:

While in standby, set the Model 238 to source OV on the 1.5V source range and set compliance to 1A.

Remove the short from the test fixture and place the Model 238 in operate. Verify that the current reading (IUS) on the Model 238 is within the following limits:

Ius = +300yA

Place the short in the test fixture and set the calibration source to output +9OOmA on the 1A range.

Verify that the current reading &a) on the Model 238 is within the following limits:

IUS = 898.62mA to 901.38mA

Set the calibration source to output -9OOmA.

Verify that the current reading (IUS) on the Model 238 is within the following limits:

IUS = -898.62mA to -901.38mA

Place the Models 343A and 238 in standby.

1.5.9

1OOmA and 1A Source Ranges Verification

The equipment setup for both lOOmA and 1A source verification is shown in Figure 1-9.

1-16

Interlock Cable (236~ILC-3)

Performance Verification

Banana Plug

SECTION 1

Warning to Saietv

: Conne

Earth

A. Connections

DC Calibrator + l

343A

8006 Test Fixture

Source

707%TRX -

Cable

2500 E

Current Calibrator (Source I)

l +O-

OUT

a-a-

-1

Short

238

2500E Current Calibrator

-I

238 (Measure I)

--@ OUTPUTHI

OUTPUT LO

Figure l-8

8. Schematic Equivalent

Setup for lOOmA and 1A Measure Ranges Verification

1-17

SECTION 1

Performance Verification

Warning: CON

to Safety

Earth

Banana Plug Cables , (6 Required)

Interlock Cable (236.ILC-3)

2500E Current

Figure l-9

8006 Test Fixture

7078-TRX -

Cable

A. Connections

2500 E

Current

Calibrator

343A

DC Calibrator + l

Source

(Source I)

a+.

IN OUT

B. Schematic Equivalent

Setup for IOOmA ami IA Source Ranges Verification

238

I I I

238 (Source I)

@ OUTPUTHI

OUTPUT LO

1-18

SECTION 2

Performance Verification

lOOmA Source Range Verification

Perform the following steps to verify the lOOmA source range:

While in standby, set the Model 238 to source OmA on the 1OOmA source range and set compliance to

1.5v.

Set the Model 193A to the 2OOM range.

Set the Model 343A to OV and place the Model 2500E on the lOOpA range.

Place the Model 238 in operate and verify that the current measurement on the Model 193A (1193~) is within the following limits:

Set the Model 238 to output +9OmA, and set the calibration source to output -9OmA on the lOOmA range.

Verify that the current measurement from the Model 193A (&A) is within the fdOWing h-&S:

11%~ = @.11ooId

Set the Model 238 to output -9OmA, and set the cali-

bration source to output +90&I on the lOOmA

range.

Verify that the current measurement from the Model 193A (1193~) is within the following limits:

1193~ = ~0.110thll+l

9. Place the Model 238 and the calibration source in standby.

1A Source Range Verification

Perform the following steps to verify the 1A source

range:

While in standby, set the Model 238 to source OA on the 1A range and set compliance to 1.5V.

While in standby, set the Model 343A to OV and place the Model 2500E on the 1mA range.

Place the Models 238 and 343A in operate, and verify that the current reading on the Model 193A (1193~) is within the following limits:

1193~ = k700pA

Set the Model 238 to output +0.900A and the calibration source to output-O.900A.

Verify that the current reading on the Model 193A

(1193~) is within the fohowing limits:

1193~ = +1.78d

Set the Model 238 to output-O.900A and the calibration source to output +0.900A.

Verify that the current reading on the Model 193A

(1193~) is within the following limits:

1193~ = +1.78&

1-19

SECTION 2

Calibration

2.1 INTRODUCTION

Calibration should be performed every 12 months, or if

the performance verification procedure (Section 1) shows that the Model 238 is out of specifications. If any of the calibration steps cannot be performed without error,

refer to the troubleshooting information in this manual. If

the problem persists, call your Keithley representative or the factory for further information.

Calibration of the Model 238 is performed over the IEEE-488 bus. This section contains the step-by-step calibration procedures, and a program written in Microsoft QuickBASIC that can be used.

Before attempting any of the following procedures, make sure you are familiar with the controls and operation of the Model 238. Refer to the Model 238 Operator’s Manual for complete information.

WARNING The procedures in this section are for use only be qualified service personnel. Do not perform these procedures unless qualified to do so. Many of the steps in this section may expose you to potentially lethal voltages that could result in personal injury or death if normal safety precautions are not observed.

2.2 RECOMMENDED CALIBRATION EQUIPMENT

Table 2-l lists recommended calibration equipment. Note that the Models 263 and 193A must be within their go-day specifications as listed in the table. Alternate equipment may be used as long as their accuracy is at least as good as the specifications listed in Table 2-2.

2.3 ENVIRONMENTAL CONDITIONS

Calibration should be performed under laboratory conditions having an ambient temperature of 23°C + l°C and a relative humidity of less than 70%.

2.4 WARM-UP PERIOD

WARNING The Source Measure Unit is equipped with a 3-wire power cord that contains a separate ground wire and is designed to be used with grounded outlets. When proper connections

are made, instrument chassis is connected to power line ground. Failure to use a grounded outlet may result in injury or death due to electric shock.

Manufacturer

Keithley Keithley

Fluke Valhalla

Table 2-l

Model

263

193A

8006 R-249-100 R-263-l k R-2631OOK 343A 2500E Current Calibrator

Description

5-l /2 digit Calibrator/ Source 5-l /2 digit DMM

Test Fixture lOOn Resistor 1m Resistor 1OOwZ Resistor DC Voltage Calibrator

Required Test Equipment

Specifications

2nA,2OnA ranges; +(0.0625% + 10 counts) 200nA range; +(0.035% + 10 counts) 2OOmV, 2V ranges; +(0.005% + 2 counts) 2OV-1OOOV ranges; +(0.007% + 1 count) 200!&2OOm ranges; +(0.007% + 2 counts) 2OOfl,2mA ranges; +(0.09% + 10 counts)

LO.1 %, *20ppm/“C

&O.l%, +lOppm/“C &O.l%, +lOppm/“C

IO-1OOV ranges; &0.002% lOOmA-1A ranges; +0.025%

2-1

SECTION 2

Calibration

Table 2-2 Specifications for Alternate

Equipment

Instrument Type

DMM

Source DC Current

Turn on the Model 238 and allow it to warm up for at least one hour before performing the calibration procedures. If the instrument has been subjected to extremes of temperature or humidity, allow at least one additional hour for the internal temperature to stabilize. Typically, it takes one additional hour to stabilize a unit that is 10°C (18OF) outside the specified temperature range.

Required Specifications

Same as Keithley 193A (see Table l-1)

0.9nA, 9nA, 9On4, Same as Keithley 263 (see Table 2-l)

0.9pA; +180ppm 9pA, 90pA, 9001.(A, 9mA; +170ppm 9OmA; +230ppm

0.9mA; k625ppm

2.5 CAL LOCK

A switch (CAL LOCK), accessible through the rear panel with a thin shaft screwdriver (see Figure 2-0, is used to prevent inadvertent calibration of the Model 238. CAL LOCK is a two position (in and out) pushbutton switch. With the CAL LOCK switch in the locked “out” position, storage of calibration constants in nonvolatile memory cannot take place. Temporary calibration values can be entered and used with CAL LOCK in the “out” position. However, when power is turned off, the newly entered calibration constants will be lost.

When calibration is performed with CAL LOCK in the unlocked “in” position, calibration constants will be stored in nonvolatile memory when the C59 command is sent over the bus.

2.6 CALIBRATION PROCEDURES

The step-by-step procedures for calibrating the Model 238 are provided here. Calibration is divided into three

separate procedures that are independent of one another. That is, any or all (in any order) of the three procedures can be performed. The three procedures include; voltage

calibration (paragraph 2.6.2), 1OOmA and 1A calibration

(paragraph 2.6.31, and low current ranges calibration

(paragraph 2.6.4).

Calibration is performed using the “C” command over

the IEEE-488 bus. Details concerning the use of the “C” command and other commands are contained in Section 3 of the Model 238 Operator’s Manual.

WARNING Lethal voltage (up to 1OOV) will be connected to the Model8006 test fixture. To avoid a possible shock hazard, the safety interlock cir-

cuit must be connected to the Model 238.

Connect the test fixture screw to safety earth ground us-

ing #18 AWG wire minimum before use. Turn off all power before connecting or disconnecting wires or cables.

Model 238 + Rear Panel

Figure 2-1 Calibration Switch (Cal Lock)

2-2

L Calibration

Switch

Also, keep in mind that GUARD is always enabled. Thus, a lethal voltage on OUTPUT HI is also present on the two GUARD terminals of the Model 238.

2.6.1 Equipment Characterization

In order to calibrate the lpA, lOpA, lOOpA, 1mA and 1OmA source and measure ranges of the Model 238, the

0.9pA, 9pA, 9Oj.tA, 0.9mA and 9mA outputs of the Model 263 are characterized.

1. Connect the Model 263 source, Model 193A DMM and Model 8006 test fixture as shown in Figure 2-2.

Install the 1OOwZ resistor (in Table 2-l) in the AXIAL KELVIN CLIPS test socket of the test fixture.

SECTION 2

Calibration

Banana Plug Cables (5)

Warning: Connect to Safety Earth Ground

A. Connections

B. Schematic Equivalent

Signal Panel

Component Test

Module

Source

(Source I)

Model 8006 Test Fixture

OUTPUT

263

COMMON

7078-TRX-

Cable

Source HI

Source LO \

I I

Model 193A DMM

Model 263 Source

n VONS

sense R

I -a “‘7

Installed

193A DMM

(Measure &2 and

Figure 2-2

Setup for Equipment Characterization

2. Configure the source and DMM as follows: Model 263 - Amps function, +0.90000~A on 2pA

range, Guard enabled and output in standby. Model 193A - Ohms function on the 2OOkn range.

3. Zero the Model 193A as follows:

A. At the SENSE 1 (HI) terminal of the test socket,

disconnect the jumper whose other end is connected to BINDING POST 2 on the Signal Panel.

B. Connect that jumper to the SENSE 2 (LO) termi-

nal of the test socket. This shorts the Ohms Sense input of the Model 193A at the test socket.

C. On the Model 193A, enable zero to cancel test

lead resistance.

D. Relocate the jumper back to the SENSE 1 termi-

nal of the test socket. Make sure the connections at the Component Test Module are correct as shown in Figure 2-2.

4. In the space provided below, use a pencil to record the actual value of the 1OOkQ resistor from the display of the Model 193A:

lOOki2 =

5. Set the Model 193A to the DCV function and the 200mV range, and disable zero.

6. To cancel any offset, zero the Model 193A by shorting its input (VOLTS HI to LO) and enabling zero.

2-3

SECTION 2 Cdibrution

Remove the short from the input of the Model 193A and place the Model 263 in operate to source +0.9OOOOp.A to the 1OOkQ resistor In the space below, use a pencil to record the voltage

8. drop across the resistor from the display of the Model 193A:

v100kn =

Calculate (to 5-l/2 digits) the current through the

1OOwZ resistor as follows:

VlOOkn

10.9pA = - =

CLA

Rl@%Q

Io.gw is the characterized current for the 2@ range of the Model 263. It is used to calibrate the Q.A range of the Model 238. Using a pencil, record the calculated value of Io.gw in Entry 1 of Table 2-3.

10.

Place the Model 263 in standby.

11.

Set the Model 193A to the 2V range.

12.

Set the Model 263 to source 9.0000~ on the 20+4 range and enable operate. As performed in steps 8 and 9, measure the voltage

13. across the lOOwL resistor and calculate the current:

lmlkn =

VlOOkn

Igfl=-=

r-LA

Rlookn

IgM is the characterized current for the 20@ range of the Model 263. It is used to calibrate the lo&4 range of the Model 238. Using a pencil, record the calculated value of Ig,,A in Entry 2 of Table 2-3.

14.

Place the Model 263 in standby.

15.

In the test fixture, remove the 1OOkQ resistor and install the 1kQ resistor (R-263-lk). On the Model 193A, select the Ohms function, 2kS2

16. range and disable zero.

17.

Repeat step 3 to zero the Model 193A.

18.

Measure and record the value of the ll& resistor:

IliD=

19.

Set the Model 193A to DCV and the 200mV range,

ki2

and disable zero.

To cancel any offset, zero the Model 193A by short-

20.

ing its input (VOLTS HI to LO) and enabling zero.

21.

Remove the short from the input of the Model 193A and set the Model 263 to source 90.000+4 on the 200@ range and enable operate.

22.

Record the voltage measurement from the Model

193A and calculate the current:

Vlki-2 =

Ix,,A is the characterized current for the 200@ range of the Model 263. It is used to calibrate the 1OOM range of the Model 238. Using a pencil, record the calculated value of 190~ in Entry 3 of Table 2-3. Place the Model 263 in standby.

23. Set the Model 193A to the 2V range.

24. Set the Model 263 to source 0.9OOOOmA on the 2mA

25.

range, and enable operate. Record the voltage measurement from the Model

26. 193A and calculate the current:

U-l=

‘Vlkn

Io.%nA = - =

.-d

Rlkn

IO.- is the characterized current for the 2mA range of the Model 263. It is used to calibrate the 1m.A range of the Model 238. Using a pencil, record the calculated value of IOLWA in Entry 4 of Table 2-3. Place the Model 263 in standby.

27. In the test fixture, remove the 1wZ resistor and install

28. the IOOR resistor (R-249-100). On the Model 193A, select the Ohms function, 200R

29. range and disable zero.

30.

Repeat step 3 to zero the Model 193A. Measure and record the value of the lOOn resistor:

31.

loon =

32.

Set the Model 193A to DCV and the 2V range, and

disable zero.

33.

To cancel any offset, zero the Model 193A by shorting its input (VOLTS HI to LO) and enabling zero. Remove the short from the input of the Model 193A

34. and set the Model 263 to source 9.OOOOmA on the 20mA range and enable operate.

35.

Record the voltage measurement from the Model

193A and calculate the current:

I-=-=

Km-l =

V100n

Rloon

IA~A is the characterized current for the 2OmA range of the Model 263. It is used to calibrate the 1OmA range of the Model 238. Using a pencil, record the calculated value of 1~ in Entry 5 of Table 2-3.

36.

Place the Model 263 in standby.

NOTE

To store calibration constants in nonvolatile

memory, place the CAL LOCK switch to the unlocked “in” position (see paragraph 2.5).

With the switch in the locked “out” position,

calibration will be temporary. That is, the new calibration constants will be lost when the instrument is turned off.

2-4

Table 2-3 Model

Entry Range

263 I-Source

Programmed

Value

I-Source Characterization

263

Characterized

I-Source Value Value Limits*

SECTION 2

Culibrution

I-Source

3 2ool.lA

4 2mA

5 2omA

2.6.2

For voltage calibration, connect the Model 193A DMM to the Model 238 via the Model 8006 test fixture as shown in Figure 2-3. Jumper A is initially installed to short the output of the Model 238 and the input of the Model 193A.

Perform the following steps to calibrate the voltage source and measure ranges:

1. Set the Model 193A DMM to DC volts and

2. With the short (Jumper A) installed, zero the Model

3. Place the Model 238 in operate. The calibration mode

4. Over the IEEE-488 bus, send the following command

Voltage Calibration

WARNING

The following procedure uses hazardous

voltages (1OOV) that could cause injury or

death. Exercise extreme caution when encountering these lethal voltage levels. Make sure to connect the Model 8006 interlock circuit to the Model 238

autorange.

193A by enabling zero.

cannot be entered with the Model 238 in standby.

to enter the calibration mode:

cox

Note: All other calibration commands (Cl through C59) will be ignored unless the CO command is first sent over the bus.

wf4

2@44

0.9000pA

9.ooop.A

9o.ooopA

0.9000mA

9.ooomA 1!3mA =

10.9@ =

19~ =

19opA =

10.9mA =

5. With the short still installed, send the following com-

mand over the bus to perform common mode calibration:

ClX

Note: Common mode calibration takes approximately 30 seconds to complete.

6. Remove the short (Jumper A) and send the following

command to source +OV on the 1.5V range:

7. From the display of the Model 193A, record the volt-

age reading (VMSR):

8. Send the measured voltage reading (VMSR) over the

bus with the C3 command as follows to calibrate off-

set for the +1.5V source and measurement range:

c3,vhisRX

For example, if the reading on the Model 193A is

+O.O0036V, send C3,.00036X or C3,36E-5X over the

bus.

9. Send the following command to source +1.4V on the

1.5V range: c4x

10. From the display of the Model 193A, record the voltage reading (VMSR):

VMSR =

11. Send the measured voltage reading (VMSR) over the bus with the C5 command as follows to calibrate

gain for the +1.5V source and measurement range:

c5,vMsRX

0.9p.A +450pA

9@ &4.3nA

9oJ.L.A &-45nA

0.9mA 243onA

9mA &5.4j.lA

MSR=

2-5

SECTION 2 Calibration

Interlock Cable (236~ILC-3)

Warning: Connect to Safety Earth Ground

A. Connections

B. Schematic Equivalent

Jumper A

8006 Test Fixture

238

(Source v) OUTPUT LO

OUTPUTHI @

Jumper A’

Model 238 t

193A DMM

I I

Banana wug Cables (3)

I Volts

. HI

0 LO (Measure V)

193A

DMM

Figure 2-3 Setup for Volts Calibration

12. Send the following command to source -0V on the

1.5V range:

C6X

13. From the display of the Model 193A, record the voltage reading (VMSR):

MSR =

14. Send the measured voltage reading (VMSR) over the bus with the C7 command as follows to calibrate off-

set for the -1.5V source and measurement range:

c7,vMSRx

15. Send the following command to source -lV on the

1.5V range:

C8X

2-6

16. From the display of the Model 193A, record the voltage reading (VMSR):

VM5R =

17. Send the measured voltage reading (VMSR) over the

bus with the C9 command as follows to calibrate

gain for the -1.5V source and measurement range:

c9,hSRx

18. Send the following command to source +OV on the 15V range:

ClOX

19. From the display of the Model 193A, record the voltage reading (VMSR):

MSR =

Send the measured voltage reading (VMSR) over the

20. bus with the Cl1 command as follows to calibrate

offset for the +15V source and measurement range:

Cl 1,VMSFx

21.

Send the following command to source +14V on the 15V range:

C12X

22.

From the display of the Model 193A, record the volt-

age reading (VMSR):

MSR=

23.

Send the measured voltage reading (VMSR) over the bus with the Cl3 command as follows to calibrate gain for the +15V source and measurement range:

c13,vh4sRX

24.

Send the following command to source -0V on the

15V range:

c14x

25.

From the display of the Model 193A, record the voltage reading (VMSR):

MSR=

26.

Send the measured voltage reading (VMSR) over the bus with the Cl5 command as follows to calibrate offset for the -15V source and measurement range:

c15,vhGRX

27.

Send the following command to source -14V on the 15V range:

C16X

28.

From the display of the Model 193A, record the voltage reading (VMSR):

hSR =

29.

Send the measured voltage reading (VMSR) over the bus with the Cl7 command as follows to calibrate gain for the -15V source and measurement range:

c17,vMsRX

30.

Send the following command to source +OV on the 11OV range:

C18X

31.

From the display of the Model 193A, record the volt-

age reading (VIUISR):

VMSR =

32.

Send the measured voltage reading (VMSR) over the bus with the Cl9 command as follows to calibrate

offset for the +llOV source and measurement range:

c19x,vmx

SECTION 2

Calibration

33.

Send the following command to source +lOOV on the

11OV range:

c2ox

34.

From the display of the Model 193A, record the voltage reading (VMSR):

b5R =

35.

Send the measured voltage reading (VMSR) over the bus with the C21 command as follows to calibrate gain for the +llOV source and measurement range:

c21,vhW.X

36.

Send the following command to source -0V on the 11OV range:

C22X

37.

From the display of the Model 193A, record the voltage reading (VMSR):

MSR=

38.

Send the measured voltage reading (VMSR) over the bus with the C23 command as follows to calibrate

offset for the -1lOV source and measurement range:

C23,v~s~X

39.

Send the following command to source -lOOV on the

11OV range:

c24X

40.

From the display of the Model 193A, record the voltage reading (VMSR):

VMSR =

41.

Send the measured voltage reading (VMSR) over the bus with the C25 command as follows to calibrate gain for the -1lOV source and measurement range:

C25,V~stzX

42.

Send the following command over the bus to exit calibration: Note: Check that the CAL LOCK switch is in the desired position;

“out” for temporary calibration.

c59x

If the switch is in the “out” position, the message “TEMPORARY CAL” will be briefly displayed to in-

dicate that newly entered cal constants will be lost when the Model 238 is turned off. Permanent calibration can still be done by setting the calibration

switch to the “in” position, and sending COX and

C59X over the bus in that order.

After sending the C59X command, the Model 238

will go into standby.

“in” for permanent calibration, or

2-7

SEC7’ION 2 Calibrah’on

2.6.3

IOOmA and 1A Ranges Calibration

To calibrate the lOOmA and 1A ranges, connect the circuit

shown in Figure 2-4.

100mA Range Calibration

Perform the following steps to calibrate the 1OOmA source and measure range:

1. Set the Model 193A to the 200@ (DC) range.

2. Place theMode 238 in operate. The calibration mode cannot be entered with the Model 238 in standby.

3. Over the IEEE-488 bus, send the following command to enter the calibration mode:

cox

Note: All other calibration commands (Cl through C59) will be ignored unless the CO command is first sent over the bus.

4. Send the following command to source +OmA on the lOOmA range:

gain for the +lOOmA source and measurement range:

c37,1+9onAX

12. Send the following command to source -On-& on the lOOmA range:

C38X

Set the Model 343A to OV and place the Model 2500E

13.

on the lOO@ range. From the display of the Model 193A, record the off-

14.

set current (IO&:

I+llA=

Send the current reading (I-om~) over the bus with the

15.

C39 command as follows to calibrate gain for the

-1OOmA source and measurement range: C39,1.o,,,~X

Send the following command to source -90mA:

16. c4ox

17.

Set the calibration source to +9OmA on the lOOmA range.

18.

From the display of the Model 193A, record the current reading (I-193A):

c34X

5. Set the Model 343A to output OV and place the Model 2500E on the lOO@ range.

6. From the display of the Model 193A, record the offset current (I+o&:

+OmA =

7. Send the current reading &,,A) over the bus with the C35 command as follows to calibrate offset for the lOOmA range:

C35,1+&

8. Send the following command to source +9OmA: C36X

9. Set the calibration source to output -90mA on the lOOmA range and, from the display of the Model 193A, record the current reading &A):

193A =

10. Calculate the actual current (1+9OmA) using the following calculation:

+9OmA = 90mA + 1193A =

11. Send the calculated current reading (I+gomA) over the bus with the C37 command as follows to calibrate

I-193A =

19.

Calculate the actual current using the following cal-

culation:

= r%h-tki + I-193A =

I-!?OmA

Send the calculated current reading (1-9om~) over the

20. bus with the C41 command as follows to calibrate

gain for the -1OOmA source and measure range:

C41,lwmAx

Send the following command over the bus to exit

21.

calibration:

Note: Check that the CAL LOCK switch is in the de-

sired position;

“in” for permanent calibration, or

“out” for temporary calibration.

c59x

If the switch is in the “out” position, the message

“TEMPORARY CAL” will be briefly displayed to indicate that newly entered cal constants will be lost when the Model 238 is turned off. Permanent calibration can still be done by setting the calibration switch to the “in” position, and sending COX and C59X over the bus in that order.

After sending the C59X command, the Model 238 will go into standby.

2-8

VEPE

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aJnw!zl t-1 9008

- Xtll-8LOL

WKI

JoleJq!le3

(I -Jnos)

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l +@

8EZ

(I =JnoS) 8EZ

1~1ndlno @

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6-Z

SECTION 2 Calibration

1A Range Calibration

Perform the following steps to calibrate the 1A source and measure range:

1. Set the Model 193A to the 2mA (DC) range.

2. Place the Model 238 in operate. The calibration mode cannot be entered with the Model 238 in standby.

3. Over the IEEE-488 bus, send the following command to enter the calibration mode:

cox

Note: All other calibration commands (Cl through

C59) will be ignored unless the CO command is first sent over the bus.

4. Send the following command to source +OmA on the 1A range:

C26X

5. Set the Model 343A to OV and place the Model 2500E on the lOO/.tA range.

6. From the display of the Model 193A, record the off-

Set current (I+OA):

I+OA =

7. Send the current reading (I+OA) over the bus with the C27 command as follows to calibrate offset for the +lA source and measure range:

C27,1+o~X

8. Send the following command to source +0.9A:

C28X

9. Set the calibration source to -0.9A on the 1A range

10. From the display of the Model 193A, record the cur-

rent (1193A):

193A =

11. Calculate the actual current (1+0.9A) using the follow- ing calculation:

h9A = 0.9A + 1193A =

12. Send the calculated current reading h.9A) over the bus with the C29 command as follows to calibrate gain for the +lA source and measure range:

c%,I+O.SAx

13. Send the following command to source -0A on the 1A range:

c3ox

14.

Set the Model 343A to OV and place the Model 2500E on the lOO@ range. From the display of the Model 193A, record the off-

15.

Set current (I-OA):

I-OA =

Send the current reading (I-OA) over the bus with the

16. C31 command as follows to calibrate offset for the

-lA source and measure range:

C31,IaAX

17. Send the following command to source -0.9A:

c32X

Set the calibration source to +0.9A on the 1A range.

18. From the display of the Model 193A, record the cur-

19. rent (1493A):

I-193A =

20.

CahdatetheaCtUalCLUTent (1.0.9A) using the follow-

ing calculation:

I-0.9A = -0.9A + I-193A =

Send the calculated reading (h9A) over the bus with

21. the C33 command as follows to calibrate gain for the

-lA source and measure range:

c33,1-o.d

Send the following command over the bus to exit

22. calibration:

Note: Check that the CAL LOCK switch is in the desired position;

“in” for permanent calibration, or

“out” for temporary calibration.

c59x

If the switch is in the “out” position, the message

After sending the C59X command, the Model 238 will go into standby.

2-10

SECTION 2

Calibration

2.6.4

Low Current Ranges Calibration

(lnA-10mA)

Connect the characterized Model 263 calibrator to the Model 238 as shown in Figure 2-5. The characterized Isource values (Io.~, IgM, 190~~ IO.SmA and &A) of the Model 263 that are used to calibrate the ll.tA through 1OmA ranges were determined in the equipment characterization procedure (paragraph 2.6.1) and recorded in Table

2-3.

Perform the following steps to calibrate the InA through

1OmA measurement ranges:

NOTE If controlling the Model 263 from the front panel, always select the lowest possible current range. Over the bus, AUTO range can be used.

4. Send the following command over the IEEE488 bus to calibrate offset for the InA measurement range:

c42X

Note: Calibration takes approximately 20 seconds to complete.

5. Place the Model 263 in operate to source 0.9nA to the Model 238.

6. Send the following command over the bus to calibrate gain for the 1nA measurement range:

C43,0.9E-9X

Note: Calibration takes approximately 20 seconds to

complete.

7. Place the Model 263 in standby and set it to 91~4.

8. Send the following command over the bus to calibrate offset for the 101-A measurement range:

C44X

Note: Calibration takes approximately 10 seconds to complete.

9. Place the Model 263 in operate to source 9nA to the Model 238.

10. Send the following command over the bus to calibrate gain for the 1OnA measurement range:

1. In standby, set the Model 263 to 0.9nA and enable Guard.

2. Place the Model 238 in Operate. The calibration mode cannot be entered with the Model 238 in standby.

3. Over the IEEE-488 bus, send the following command to enter the calibration mode:

cox

Note: All other calibration commands (Cl through

C59) will be ignored unless the CO command is first sent over the bus.

6172 2-Slot to 3-Lug

Female Triax adapter

Banana Plug Cable

Ground Link

263 Source

(Source I)

Note : 263 GUARD enabled

Figure 2-5

Current Ranges Calibration (InA to lOmA)

707%TRX

Cable

C45,9E-9X

Note: Calibration takes approximately 10 seconds to

complete.

11. Place the Model 263 in standby and set it to 9OnA.

12. Send the following command over the bus to calibrate offset of the lOOnA measurement range:

C46X

Note: Calibration takes approximately four seconds

to complete.

13. Place the Model 263 in operate to source 9OnA to the Model 238.

238 (Measure I)

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knnnnnnnnf

2-11

SECTION 2 Calibration

14.

Send the following command over the bus to cali-

brate gain for the lOOnA measurement range:

C47,90E-9X

Note: Calibration takes approximately four seconds to complete.

15.

Place the Model 263 in standby and set it to 0.9l.lA. Send the following command over the bus to cali-

16. brate offset for the ~JJA measurement range:

C48X

17.

Place the Model 263 in operate.

18.

Send the value for Io.gM (from Table 2-3) over the bus with the C49 command as follows to calibrate gain for the 1pA measurement range:

c49,10.9BAX

For example, if Io.gM = 0.90036@, send C49,0.90036E-6X. Place the Model 263 in standby and set it to 9M.

19.

20.

Send the following command over the bus to cah-

brate offset for the 10j~A measurement range:

c5ox

Place the Model 263 in operate.

21. Send the value for 19M (from Table 2-3) over the bus

22. with the C51 command as follows to calibrate gain for the lOpA measurement range:

c51,19&lAx

23.

Place the Model 263 in standby and set it to 90@. Send the following command over the bus to cali-

24. brate offset for the 1OOll.A measurement range:

c52X

Place the Model 263 in operate.

25.

26.

Send the value for Igo@ (from Table 2-3 ) over the bus with the C53 command as follows to calibrate gain

for the lOOkA measurement range:

c53,190llAx

27.

Place the Model 263 in standby and set it to 0.9mA. Send the following command over the bus to cali-

28. brate offset for the 1mA measurement range:

c54X

29.

Place the Model 263 in operate.

30.

Send the value for Io.gmA (from Table 2-3) over the bus with the C55 command as follows to calibrate gain of

the 1mA measurement range:

c55,10.9mAX

31.

Place the Model 263 in standby and set it to 9mA. Send the following command over the bus to cali-

32. brate offset for the 1OmA measurement range:

C56X

33.

Place the Model 263 in operate. Send the value for 1~ (from Table 2-3) over the bus

34. with the C57 command as follows to calibrate gain for the 1OmA measurement range:

C57,ItiX

35.

Place the Model 263 in standby and set it to OmV.

36.

Place the Model 263 in operate.

37.

Send the following command over the bus to cali-

brate the 1nA through 1OmA source ranges:

C58X

Note: Calibration of the low current source ranges takes approximately four minutes to complete.

Note: Check that the CAL LOCK switch is in the desired position;

“out” for temporary calibration.

38.

Send the following command over the bus to exit calibration and store the cal constants:

c59x

If the switch is in the “out” position, the message

‘TEMPORARY CAL” will be briefly displayed to in-

dicate that newly entered cal constants will be lost when the Model 238 is turned off. Permanent calibration can still be done by setting the calibration

switch to the “in” position, and sending COX and

C59X over the bus in that order.

After sending the C59X command, the Model 238

will go into standby.

39.

Place the 263 into standby.

“in” for permanent calibration, or

2-12

SECTION 2

Culibrufion

2.7 CALIBRATION ERRORS

Calibration errors and subsequent error messages that

could occur during calibration are explained in Table 2-4. It is important to realize that if any of these errors (except IN CAL) occur, calibration is compromised. Even though some errors will cause default cal constants to be used,

they do not guarantee specified accuracy. When a calibration error occurs, find and fix the problem and repeat

calibration.

Since calibration error messages are briefly displayed by the Model 238, they can be easily overlooked. For this reason it is strongly recommended that calibration errors be detected and displayed by the calibration program. The

following steps provide the general procedure required to detect calibration errors over the IEEE-488 bus:

1. Program the Model 238 to generate an SRQ on an error by sending the M32 command over the bus.

2. When an SRQ occurs (error), send the Ul command and then address the Model 238 to talk.

3. Display the character string (Ul Error Status Word) from the Model 238 on the computer CRT and refer to Figure 2-6 to determine the error type.

4. After displaying the Ul error status word, send the U7 command and address the Model 238 to talk.

5. Display the character string (U7 Calibration Status Word) on the computer CRT and refer to Figure 2-7 to determine which calibration step failed. This status word also provides the status of the CAL LOCK switch.

Table 2-4 Calibration Error Messages

Message

IN CAL

IN STBY

CAL COMI’LI

CAL MODE ERR

CAL VALUE ERR

CAL ADC ZERO

CAL ADC GAIN

CAL SRC ZERO

CAL SRC GAIN

Note: Durin opened.

In this event, the OPERATE and STANDBY transition is detected and the measurement conversion used to compute the calibration constant is ignored. The front panel message “IN STBY” is displayed when this occurs.

the execution of a calibration step in which the Model 238 takes a measurement conversion, it is possible the instrument can transi-

f tion from 0

ERATE to STANDBY. This can occur beacuse it was specifically programmed to do so, or because the test fixture safety interlock was

Explanation

Tried to set the instrument to a state that is illegal while in the calibration mode. Legal com-

mands include; C (calibration), N (operate/standby), 0 (output sense) and U (status). From the front panel, only o operations are ignore 1

The Model 238 is in standby. The calibration command sent over the bus will not be executed.

(See Note). Compliance has occurred during calibration. Check test setup connections and instrument

settings.

Common mode calibration error. Output of Model 238 is not shorted or unit is defective. The

cal constant from the previous calibration will be used.

Invalid calibration value sent to the Model 238. This calibration step is ignored (not attempted). Calibration constant from previous calibration will be used.

Measure offset calibration error. Calibration is attem ceptable limits. The transmitted value is ignored an stead. Possible problems include; incorrect cal constant value, defective calibration equipment (or connections), or defective Model 238.

Measure gain calibration error. Calibration is attem ceptable limits. The transmitted value is ignored an x stead. Possible problems include; incorrect cal constant value, defective calibration equipment (or connections), or defective Model 238.

Source offset calibration error. Calibration is attempted using a value that is not within acceptable limits. The transmitted value is ignored and a default cal constant value is used instead. Possible problems include; incorrect cal constant value, defective calibration equipment (or connections), or defective Model 238.

Source gain calibration error. Calibration is attempted using a value that is not within acceptable limits. The transmitted value is ignored and a default cal constant value is used instead. Possible problems include; incorrect cal constant value, defective calibration equipment (or connections), or defective Model 238.

crate/standby and output sense can be set. All illegal commands and

ted using a value that is not within ac-

a default cal constant value is used in-

ted using a value that is not within ac-

a default cal constant value is used in-

2-13

SECTION 2 Calibration

-I-

r-5

ERSbbb...

Most Significant Bit 4 & Least Significant Bit

26-Bit ASCII String 0 = No Error

1 = Error

b b b <TERM + EOlr

Figure 2-6

Identifier

Most Significant Bit

Least Significant Blt

Ul Error Status Word

Trigger Overrun IDDC IDDCO Interlock Present Illegal Measure Range Illegal Source Range Invalid Sweep Mix Log Cannot Cross Zero

Autoranging Source with Pulse Sweep

In Calibration In Standby Unit is a 236 IOU DPRAM Failed IOU EEROM Failed IOU Cal Checksum Error

DPRAM Lockup DPRAM Link Error Cal ADC Zero Error Cal ADC Gain Error Cal SRC Zero Error Cal SRC Gain Error Cal Common Mode Error Cal Compliance Error Cal Value Error Cal Constants Error

Cal Invalid Error

2.8 CALIBRATION PROGRAM

r-4

CSPnn,

Figure 2-7

2-14

b <TERM + EOI>

0 = Unit is Uncalibrated t = Unit is Calibrated

0 = Cal Lock Switch is Unlocked 1 = Cal Lock Switch is Locked

(Present Cal Constants Will Not be Saved)

Calibration Step in Progress

U7 Calibration Status Word

The following program can be used to calibrate the Model 238. Configure the recommended equipment and software per manufacturers instructions and type in the program.

NOTE

The program does not calibrate the 1A range

since the equipment used to calibrate that range is not programmable and thus, cannot be controlled over the IEEE-488 bus.

'Rev. B 10/11/90 *****************************************************************************

Model 238 Calibration Program '* NOTE: Program calibrates voltage and InA-1OmA current ranges only. '* Equipment Required: Model 193A DMM, Model 263 Calibrator

‘* 193A address =

10; 238 address - 16; 263 address = 8 '* Computer: IBM PC, AT or compatible '* IEEE-488 interface card: IOtech, CEC, or National PC-II or IIA '* Operating system: PC-DOS or MS-DOS, version 3.0 or later '* Programming language: Microsoft QuickBASIC version 4.0 or later '* IEEE-488 bus driver: IOtech Driver488, version 2.3 or later

(kkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkk

’

* * * x x * * x *

CLS OPTION BASE 1 DIM char(5), char$(5>, Ical(8), msgS(3) '

Dimension arrays. DIM ErrS(9) FOR I = FOR I =

1 TO 5: READ char$(I >: NEXT I

1 TO 8: READ Ical( NEXT I FOR I - 1 TO 3: READ msg$(I): NEXT I FOR I

= 1 TO 9: READ Err$(I): NEXT I

Dly = 3

tkkkkkkkkkkkkkkkkkkk INITIALIZE IEEE-488 ’

OPEN "\DEV\IEEEOUT" FOR OUTPUT AS I1 OPEN "\DEV\IEEEIN" FOR INPUT AS 412 Start: IOCTL #l, "BREAK" PRINT #l, "RESET" PRINT Sl, "REMOTE" PRINT ~71, "CLEAR" PRINT r'il,

"TIME OUT 30" PRINT #l, "LOL" CLS

Read prompt strings.

Read cal currents.

Read procedure messages.

Read error messages.

' '

Measurement delay (seconds).

INTERFACE kkkkkkkkkkkkkkkkkkkkkkkkk

Open IEEE-488 output path.

Open IEEE-488 input path.

Reset interface.

Warm start interface.

Assert remote enable.

Send device clear.

30 second bus time out.

Enable Local Lockout

Clear screen.

LOCATE 12, 23

PRINT " Model 238 Calibration Program"

LOCATE 21, 12

PRINT "NOTE: This program does NOT calibrate lOOmA and 1A ranges."

LOCATE 22, 12 PRINT 'Refer to Service Manual for complete information.” LOCATE 14, 10 GOSUB KeyCheck

’ Check for operator signal.

‘kkkhXXkkkkkRX~Xkk SELECT FUNCTION(S) TO CALIBRATE k*kkXkXX*XRR*XXkkk*X***k*

SelCal:

CLS GOSUB TypeCheck

E = 0: Cl = 0

' Clear error counter.

PRINT "Select function to calibrate:"

PRINT FOR I =I 1 TO 3

PRINT ”

‘I .

, I;

"- "; msg$(I ); " calibration"

’ Loop for all 3 selections.

NEXT I PRINT

InCal: INPUT "Select calibration function (l-3)"; cal

IF cal < 1 OR cal > 3 THEN BEEP: GOT0 InCal

~XkXXkXkkkXkRXXXkXXXkXkk INITIALIZE 238

PRINT II, PRINT lil, PRINT II, PRINT 111,

"OUTPUT 16;M32,X” "OUTPUT 16;BO,,X" "OUTPUT 16;OOX" "OUTPUT 16;KOYOX"

'***************** CHECK CAL LOCK SWITCH STATUS

PRINT i/l,

PRINT #l,

"OUTPUT 16;U7X" "ENTER 16"

LINE INPUT #2, STS

IF MID$(ST$, 7, 1) = "1" THEN

XkXkkXkkkXkXRXXkhXXkXkkXkkkkXXkkk

* 238 SRQ on error.

' Zero bias output level for safety. ' Local sensing. * Enable EOI, hold-off,terminator.

RkXkXkRkXXkkRRXXkkkkXXkkkkXX

' Request calibration status word. * Address 238 to talk. * Input cal status word. ’ Check cal lock switch status.

BEEP

PRINT "Model 238 Cal Lock switch is in locked position."

PRINT *'Calibration will be only temporary.*' PRINT Cl = 1 GOSUB KeyCheck

END IF

’

‘****************** ENABLE BUS SRQ ERROR TRAPPING

XXkkXXXXkXkhkkRXXkXXXXkXXkk

ON PEN GOSUB ErrCheck

PEN ON PRINT i/l, "ARM SRQ"

' Point to error routine. * Enable error detection. ’ Enable SRQ.

’

‘XkkkkXXXXXXkXkXkXXXkXk MAIN PROGRAM LOOP

’

ON cal GOSUB CalVolt, CalLow

IF cal

= 3 THEN

XkkkkkkXXkkkkXkRkkkkkkXXkXkXkXkXkkX

GOSUB CalVolt GOSUB CalLow

END IF

PRINT : BEEP PRINT Hl, "CLEAR" PRINT msg$(cal); PRINT E;

**error(s) detected during calibration."

" calibration procedure completed.**

* Send DCL.

PRINT IF Cl =

1 THEN PRINT 'NOTE: Calibration is temporary.'

INPUT "Rerun calibration program (y/n)'*; INS

= LEFT$( INS, 1)

INS

IF INS =

“y” OR INS = PRINT II, "LOCAL" CLOSE 1: CLOSE 2 END

IkkkXkkkXXRkkkkkkkkkkXUXkkXXkkkXXkkkkkkXkXXXkkXkkkXXkXkkXXkXkkkkXkkkkkkkkkkkk

‘X ~kkkXkkXXkkkkkkkkkkXkkkkkkkkXXkkkkkkkkXkkXXkkXkXXkkkXXkkkkkXkkkkXkkkkXkkkkXkk

'*Y'* THEN GOT0 SelCal

' Restore local operation. ' Close I/O files. ' End of program.

VOLTAGE FUNCTION CALIBRATION ROUTINES

CalVolt: CLS

PRINT **Voltage Calibration Procedure.'*

PRINT "See Service Manual for details on test connections." PRINT PRINT *'Short 238 output and 193A input." GOSUB KeyCheck PRINT tl,

PRINT #l, PRINT #l,

"OUTPUT lO;FOROS3GlX" "OUTPUT 16;NlX" "OUTPUT 16;COX"

' 193A DCV, 6-112 digits,auto range. * Put 238 in operate.

' Put 238 in cal mode. PRINT *'Performing common mode adjustment." PRINT "Please wait approximately 30 seconds for completion." PRINT PRINT #l, PRINT 81,

"OUTPUT 16;ClX" "OUTPUT 1O;ZlX"

* Calibrate 238 common mode.

' Zero 193A. BEEP PRINT #l, PRINT Ul,

"OUTPUT 16;C59X" "OUTPUT 16;NOX"

* Remove 238 from cal mode.

' Put 238 in standby. PRINT "Remove short from 238 output and 193A input." PRINT "Make sure 238 output is properly connected to 193A input." PRINT BEEP PRINT **WARNING: Hazardous voltage may be present on terminals." PRINT GOSUB KeyCheck PRINT r'll, PRINT #l,

"OUTPUT 16;NlX" "OUTPUT 16;COX"

' Put 238 in operate.

' Put 238 in cal mode. PRINT *'Performing voltage calibration.'* PRINT "Press ESC to abort procedure and restart program." FOR I = 2 TO 25

INS =

PRINT II,

INKEYS: IF IN$,= CHRS(27) THEN PRINT II, '*CLEAR'*: GOT0 SelCal

"OUTPUT 16;C"; I; "X" GOSUB Delay PRINT II,

"ENTER 10"

INPUT 12, Vmsr

I=I+l

PRINT #i/l,

"OUTPUT 16;C*; I; ","; Vmsr; "X"' Send cal value to 238. NEXT I PRINT Cl,

"OUTPUT 16;C59X" PRINT Cl, "OUTPUT 16;NOX" PRINT #l, RETURN

‘XkhhkkXXXXkXkkXXkXXXXUXUkXkXkXXXXXXXkkXkXXXXkkUkXXkkXXkXXXkXXXkXkkkkUXkUXkkU ‘R

tUXXXkXkkXXXkXYkXkkXXUkkkkkkXXUkkXXXkkUkkXXXkkkXkXXkkUkkXkkkXkkUXXXkUkXkkXXXX

’

"OUTPUT lO;ZOR5X"

1NA -

1OMA CURRENT RANGE CALIBRATION ROUTINES

* Loop for all cal points.

* Send cal command to 238. ' Wait for settling. ' Get reading from 193A. ' Input 193A reading. ' Increment C command value.

' Loop back for next cal point. ' Exit calibration procedure. ' Put 238 in standby. * Disable 193A zero mode, IOOOV range.

CalLow: CLS PRINT "1nA -

1OmA Current Range Calibration." PRINT "Make sure 263 and 238 are properly connected.'* PRINT '*See Service Manual for complete details." PRINT GOSUB KeyCheck

PRINT #l,

"OUTPUT 08;FlROWlX"

* 263 amps,auto range,guard on.

'INPUT 263 CHARACTERIZATION PARAMETERS

CharCheck:

INPUT "Enter 263 characterization parameters (y/n)**; INS

= LEFTStINS, 1)

INS

IF INS =

“N” OR INS =

"n" THEN GOT0 NoChar

IF INS <> "y" AND INS <> "Y" THEN BEEP: GOT0 CharCheck

InChar: PRINT "Enter the following 263 characterization parameters." PRINT "See Service Manual for 263 characterization procedure." PRINT FOR I = 1 TO 5

' Loop for all parameters

PRINT "Enter parameter for 263 "; char$(I); '* **; * Prompt for parameter.

INPUT char(I) NEXT I

* Input parameter. ' Loop back for next parameter.

NoChar: FOR I - 1 TO 5

IF char(I) = 0 THEN

BEEP PRINT **Improper characterization parameters are presently entered."

GOT0 InChar END IF NEXT I PRINT GOSUB KeyCheck PRINT *'Performing 1nA -

1OmA current measurement calibration procedure."

PRINT "Press ESC to abort procedure and restart program.*' PRINT i/l, PRINT #l,

"OUTPUT 16;NlX"

"OUTPUT 16;COX" J=l:K=l FOR I = 42 TO 57

INS =

PRINT II,

INKEYS: IF INS = CHRS(27) THEN PRINT Cl, "CLEAR": GOT0 SelCal

"OUTPUT 08;V"; Ical( "X" GOSUB Delay PRINT i/l,

"OUTPUT 16;C"; I; "X" GOSUB Delay

I =I+1

PRINT II,

"OUTPUT 08;OlX"

GOSUB Delay

IF I > 47 THEN

PRINT #l, K=K+l

"OUTPUT 16;C"; I; ","; char(K); "Xl'

' Put 238 in operate. ' Put 238 in cal mode. ' Initialize array index counters. ' Loop for all cal points.

* Program 263 current value. ' Allow settling time. ' Send cal offset command. ' Settling time. ' Increment C command value. ' Put 263 in operate. ' Settling time. * Use characterized values for >lOOnA

* Increment array counter.

ELSE PRINT #l, "OUTPUT 16;C"; I; ","; IcaltJ); **X**

END IF

GOSUB Delay J =J+l

PRINT II,

"OUTPUT 08;OOX"

NEXT I

' 1NA -

PRINT Cl,

PRINT II,

1OMA SOURCE CALIBRATION

"OUTPUT 08;F2RlX" "OUTPUT 08;VOX"

"OUTPUT 08;OlX"

' Settling time. ' Increment array index. ' Put 263 in standby. ' Loop back for next cal point.

' 263 200mV range. * 263 OmV output. * Put 263 in operate.

GOSUB Delay

PRINT #l,

"TIME OUT 240"

* Select 4 minute bus time out.

PRINT : BEEP PRINT "Performing 1nA PRINT "Please wait approximately 3-4 minutes for completion." PRINT 111, PRINT Cl, PRINT Cl, PRINT II, PRINT /Cl, RETURN

"OUTPUT lb;C58X" "OUTPUT lb;C59X" "OUTPUT 16;NOX" "OUTPUT 08;OOX" "TIME OUT 30"

KeyCheck:

- 1OmA source calibration." '

Cal 238 lnA-1OmA source.

Exit 238 cal mode.

Put 238 in standby.

Put 263 in standby.

Restore 30 sec. bus time out.

Check keyboard input routine. PRINT "Press SPACE or ENTER key to continue (ESC to end program)." PRINT Lpl: INS = INKEYS: IF INS <> "" THEN GOT0 Lpl Lp3: INS - INKEYS: IF INS - "" THEN GOT0 Lp3

IF INS = CHRS(27) THEN

* Check for ESC.

CLS

OutMsg: PRINT "Program terminated"

PRINT Wl, "CLEAR" PRINT 81, "ABORT" PRINT #l, "LOCAL"

' Send DCL. ' Send IFC.

' Restore local operation. CLOSE 1 CLOSE 2 END

END IF

IF INS <> CHR$(32) AND INS <> CHR$(l3) THEN BEEP: GOT0 Lpl

RETURN

Delay:

t = TIMER

Lp2: IF (TIMER -

RETURN

t) < Dly THEN GOT0 Lp2

ErrCheck:

IF IOCTL$(2) <> "0" THEN

PRINT i/l, "SPOLL"

INPUT R2, SB

IF SB = 0 THEN RETURN

PRINT #1,

"SPOLL 16" INPUT #2, SB IF (SB AND 32) <> 0 THEN

E=E+l BEEP PRINT #I, PRINT #l,

"OUTPUT 16;UlX" ' Request error word. "ENTER 16"

INPUT 62, Err$ PRINT GOSUB CalStep PRINT "Model 238 **; GOSUB DispErr PRINT "

Error on calibration step C"; ST; I'." PRINT "See calibration error message list in Service Manual." PRINT GOSUB KeyCheck

RETURN

* Delay subroutine

' Error check subroutine. * Driver ready for command? ' Check for non-SRQ interrupt.

* Serial poll 238. ' Input serial poll byte. ' Check for error. * Increment error counter.

' Input error word.

PRINT "Continuing...*' END IF RETURN

DispErr:

IF MIDStErrS, 7, 1) IF MID$(Err$, 14, 1) IF MIDStErrS, 13, 1) -

FOR L = 1 TO 9

IF MID$(Err$, L + 20, 1) = "1" THEN PRINT Err$(L);

NEXT L RETURN

"1" THEN PRINT *'Interlock Present";

"1" THEN PRINT "In Standby**; "1" THEN PRINT "In Calibration";

' Display error subroutine,

' Check cal error messages.

CalStep: PRINT #l, "OUTPUT 16;U7X" PRINT #l, "ENTER 16" LINE INPUT $42, ST$

ST = VAL(MID$(ST$, 4, 2))

RETURN

TypeCheck:

PRINT #l,

PRINT Il, "ENTER 16"

INPUT 112, ST$ IF LEFT$(ST$, 3) <> "238" THEN

END IF RETURN

' Characterization prompt strings

DATA "2uA range (approx. 0.9uA)"

DATA "20uA range (approx. 9uA)"

DATA "200uA range (approx. 90uA)" DATA "2mA range (approx. 0.9mAY' DATA "20mA range (approx. 9mA)"

' 'Current calibration data

DATA 0.9E-9,9E-9,90E-9,0.9E-6,9E-6,90E-6,0.9E-3,9E-3

t * Procedure message data strings

DATA "Voltage"

DATA "1nA to 1OmA current ranges"

DATA"Voltage and 1nA to 1OmA current ranges"

"OUTPUT 16;UOX"

BEEP PRINT "Unit is not a Model 238." GOT0 OutMsg

* Determine cal step for cal error.

' Request cai status word. ' Address 236 to talk. ' Input cal status word. * Convert step to variable.

' Make sure unit is a 238.

'Error message strings.

DATA *'Cal ADC Zero*',**Cal ADC Gain","Cal SRC Zero","Cal SRC Gain"

DATA "Cal Common Mode","Cal Compliance",*'Cal Value"

DATA "Cal Constants","Cal Invalid*'

SECTION 3

Maintenance

3.1 INTRODUCTION

This section contains information necessary to maintain and troubleshoot the Model 238.

WARNING Other than line fuse replacement and fan filter cleaning, the procedures included in this section are for use only by qualified service personnel. Do not perform these procedures unless qualified to do so. Troubleshooting steps may expose you to potentially lethal

voltages that could result in injury or death if normal safety precautions are not observed.

3.2 LINE FUSE REPLACEMENT

A rear panel fuse located adjacent to the line voltage switch (see Figure 3-l) protects the power line input of the Source Measure Unit. If the fuse needs to be replaced (line voltage switch setting changed or suspected blown fuse), perform the following steps:

LINE VOLTAGE LINE FUSE

SELECTED SLOW BLOW

With the power off, place the end of a flat-blade screwdriver into the slot in the rear panel LINE FUSE holder. Push in gently and rotate the fuse carrier onequarter turn counterclockwise. Release pressure on the holder and its internal spring will push the fuse and carrier out of the holder. Remove the fuse and replace it with the type recommended in Table 3-l.

Table 3-l Line Fuse Selection

Line Voltage

195-250V 0.625A, 25OV, 3AG, Slo Blo FU-27

90-125V 1.25A, 25OV, 3AG, Slo Blo FU-28

Do not use a fuse with a higher current rating than specified, or instrument damage may occur. If the instrument repeatedly blows fuses, locate and correct the cause of the trouble before replacing the fuse. See paragraph 3.8 for troubleshooting information.

Install the new fuse and the fuse carrier into the holder by reversing the above procedure.

Fuse Type Part Number

CAUTION

Keithley

Figure 3-1 Line Voltage Switch and Line Fuse

WARNING

Make sure the Source Measure Unit is dis-

connected from the power line and other equipment before replacing the fuse.

3.3 FAN FILTER CLEANING

The Model 238 has an internal cooling fan to vent heat out of the instrument case. The fan has a filter to keep dirt and dust from entering the instrument case. Contamination on pc boards could result in degraded performance. The fan filter must be cleaned periodically to maintain internal cleanliness and proper ventilation.

3-1

SECTION 3

Maintenance

Perform the following steps to remove and clean the fan filter element:

1. Turn off the Model 238. The fan must be off in order to prevent dirt and dust from being ingested into the instrument case while removing the filter element.

2. Position the instrument such that you are facing the rear panel. The cooling fan is internally mounted to the right-hand end of the rear panel. The filter assembly is mounted to the rear panel in front of the

fan intake vents.

Remove the two screws that secure the vented shroud of the filter assembly to the rear panel. The filter assembly will swing away from the rear panel allowing the filter element to be removed.

To clean the filter element, blow out the dust and dirt with pressurized air or nitrogen.

Reinstall the filter assembly onto the rear panel. The two hinges of the filter assembly shroud fit into the rear panel vents. Make sure the filter element covers all the rear panel intake vents.

3.4 BAll-ERY REPLACEMENT

When line power to the Model 238 is turned off, the lithium battery on the digital board provides backup power to the memory in which user programmed setup conditions and sweep data are stored. The battery has enough capacity to maintain data for one year of continuous power off, or two years if the Model 238 is on for 12 hours every day. The battery by itself has a shelf life of eight years. Although the Model 238 will operate without a battery, it will not retain any setup conditions or sweep data when turned off. The instrument wiIl power up to the factory default conditions.

The battery may be replaced with any 2450 lithium coin cell. It can also be ordered from Keithley (part number BA-44).

Replacement of the lithium battery is normally a safe procedure as long as these safety precautions are followed.

WARNING

The precautions below must be followed to

avoid possible personal injury.

1. Do not short the battery terminals together.

2. Do not incinerate or otherwise expose to excessive heat (>6O’C).

3. Keep lithium batteries away from all liquids.

4. Do not recharge lithium batteries.

5. Observe proper polarity when inserting battery into holder.

Replace the battery as follows:

Turn off the power, disconnect the line cord, and remove all test leads.

After allowing at least three minutes for internal capacitors to discharge, remove the top cover (see paragraph 3.6).

The battery is on the digital board (see Figure 3-2 for location). Pry the battery out of its holder using a non-metallic tool.

WARNING

Do not use a metal tool to pry out the battery as you could short the terminals.

Install the new battery, taking care to observe proper polarity as stamped on the battery holder. The plus

(+) terminal of the battery faces up.

Reinstall the top cover.

3.5 HANDLING AND CLEANING PRECAUTIONS

When troubleshooting or otherwise working inside the instrument, care should be taken not to indiscriminately touch PC board traces and open wires to avoid contaminating them with body oils or other foreign matter. Areas covered by a shield within the Model 238 have high impedance devices or sensitive circuitry where contamination could cause degraded performance.

The same general precautions apply when replacing

parts in these areas. When unsoldering and soldering

parts, be careful not to spread the flwc around the board

to adjacent areas.

1. Using a squeeze bottle, carefully apply clean, uncontaminated methanol to the area to be cleaned. Use sufficient solution to thoroughly wet the circuit board.

2. Using a small, clean brush, wipe the area thoroughly until it is free of flux or contaminants. In some cases, it may be helpful to tilt the board at an angle and brush contaminants away from the affected area, allowing contaminated residue and methanol to run off the board.

3-2

Battery -B

I !

- IEEE Connector

- J20

- J22

4 i--

-J16

SECTION 3

Mainterzance

J24 -

Power _ Switch

4-l

*,-

1 _

- J8

- J23

- J18

Pi9

Figure 3-2. Digital Board

3-3

SECTION 3

3. Wash the area again with fresh, clean methanol, allowing it to drain, flushing contaminants off the board.

4. Once the area is thoroughly cleaned, it should be dried with pressurized dry clean air or nitrogen. Do not use compressed air from an ordinary air compressor, as oil particles in the air could contaminate

the circuit board.

5. After cleaning or parts replacement, check to see that

any components connected to the Teflon@) insulators are not physically touching the board or adjacent parts.

3.6 DISASSEMBLY INSTRUCTIONS

If it is necessary to troubleshoot the instrument or to replace a component, use the following disassembly procedure. Disassembly should be done in the order that it is presented since many steps depend on a previously performed procedure.

NOTE

Connector designations on the illustrations use either a “P” or “J” prefix. A ‘T” indicates

that the connector is a plug type, while “J” in-

dicates that it is a receptacle. For example, I?10 is a plug connector that mates to receptacle JlO.

WARNING Disconnect the line cord and any test leads from the instrument, and wait at least three minutes to allow high voltage capacitors to discharge before beginning disassembly.

1. Remove the top cover as follows: A. The top cover is secured to the chassis by six

screws. Four are located at the top of the instrument and two are located at the rear. Remove those six screws.

B. Slide the top cover towards the rear of the instru-

ment until it separates completely from the chassis.

2. Remove the bottom cover as follows: A. If installed, remove the four plastic feet located

on the bottom cover. Each foot is secured with a single screw.

B. The bottom cover is secured to the chassis by two

screws located at the rear of the instrument. Remove those two screws.

C. Slide the bottom cover towards the rear until it

completely separates from the chassis.

CAUTION When reinstalling the bottom cover, use the proper screws to install the four feet. Screws that are too long will cause damage to the internal circuit boards. The front feet are secured by #6-32x5/8” screws, the rear feet are secured by #632x1/2” saews.

If leaving the feet off in order to install the instrument in a rack, do not use the original screws to secure the bottom cover. Instead, use the four short screws (#6-32xX/4”) supplied with the rack mount kit.

3. If the cooling fan needs to be removed, proceed as follows. Otherwise, proceed to step 4.

A. Disconnect P22 (fan) from J22 on the digital

board (see Figure 3-2).

B. Disconnect the ground wire from the rear panel.

C. Remove the four fasteners that secure the fan to

the rear panel.

D. Pull the fan out of the instrument case.

4. Remove the output board (see Figure 3-3) as follows:

Note: The output board is mounted on the analog board adjacent to the rear panel.

WARNING To avoid burns from excessive heat, make sure that the heat sink on the output board is cool enough to handle. If the heat sink is hot, wait until it is cool before attempting to remove the output board.

A. Disconnect P16 from J16 on the digital board (see

Figure 3-2).

B. Remove the four screws that secure the output

board assembly to the analog board.

C. Grasp the heat sink and lift up the output board

assembly a few inches. Disconnect P15 from J15 which is located on the analog board directly under the output board.

D. Lift the output board out of the instrument case.

5. Remove the analog board (see Figure 3-4) as follows: A. Remove the analog board shield. It is secured to

the analog board with four screws.

B. Remove the inner shield. It is secured to the ana-

log board with three screws.

C. Disconnect P19 (ribbon cable from digital board)

from J19.

D. Disconnect P8 and P18 from J8 and J18 on the

digital board.

E. Disconnect the connector for the OUTPUT LO

banana jack from J27.

F. Disconnect the SMB triax connectors from Jll,

J12 and J13.

SECTION 3

Maintenance

Sink

Figure 3-3.

G. Place the instrument on its right side and, from WARNING

the case bottom, remove the seven screws that To provide protection from possible electric secure the analog board to the mounting rails.

H. Place the instrument in the normal upright posi-

tion and carefully manipulate the analog board assembly out of the instrument case.

I. Remove the bottom shield of the analog board. It

is secured to the analog board by the five remaining screws accessible from the component side of the board.

6. Remove the rear panel assembly as follows: A. Disconnect P20 (AC line filter) and P22 (fan)

from J20 and J22 on the digital board.

B. At the back of the instrument, remove the two

nuts that secure the IEEE-488 interface connector to the rear panel.

C. Remove the four screws that attach the rear

panel to the side panels of the instrument. Two of these screws also secure the fan filter assembly to the rear panel.

D. To provide clearance, pull the rear panel out-

ward a little and then disconnect P21 (Trigger and Interlock) from J21 on the digital board.

E. Separate the rear panel from the instrument case.

Output Board

shock, when re-assembling make sure the ground wires from the AC power outlet and cooling fan are connected to the rear panel.

Remove the digital board (see Figure 3-2) as follows:

A. Disconnect the display board ribbon cable from

J24.

B. Place the instrument on its left side. From the

bottom of the instrument case, notice that there are eight screws (seven slotted and one Phillips) securing the digital board to the three mounting rails. The Phillips head screw installs into a kep nut on the other side of the board. Remove this screw first and make sure not to lose the kep nut.

C. Remove the other seven screws that secure the

digital board to the mounting rails. Be sure not to let the digital board fall when the last screw is removed.

D. Place the instrument in the normal upright posi-

tion and remove the digital board from the case.

3-5

SECTION 3

Maintenance

E. Remove the top and bottom shield for the digital

board. This shield assembly is secured to the board by four screws.

8. Remove the display board as follows: A. At the front panel, pull off the rotary knob.

B. Remove each of the four decorative strips from

the side panels as follows: a. From inside the case, place a thin blade

screwdriver into one of the holes where the decorative strip is secured.

C. Carefully push outwards until the strip dis- G.

engages from one of the fasteners.

J15 -

Grommet

r-l

I I

Pull the strip away from the side panel.

Note: To reinstall, align the strip in the recessed part of the side panel and press the strip at the locations of the fasteners.

E. Remove the four screws that secure the front

panel assembly to the side panels and disengage the front panel assembly from the chassis.

F. Loosen the four Allen set screws securing the

bezel assemblies to the front panel. Remove the bezel assemblies from the front panel. Lift the display board away from front panel.

Output board located here

- 1 1 1

P18 J19-c

Jll

1 Sense HI

J-l3

output LO

J12

Output HI

-l

Figure 3-4.

3-6

Analog Board (Shields Removed)

SECTION 3

Maintenance

Figwe 3-5

Model 238 Exploded View

3-7

SECTION 3

The instrument can be m-assembled by reversing the above procedure. Make sure that all parts are properly seated and secured, and that all connections are properly made. To ensure proper operation, shields must be replaced and fastened securely.

WARNING To ensure continued protection against safety hazards, ground (green wire attached to AC power receptacle) and fan ground are connected to the rear panel.

3.7

SPECIAL HANDLING OF STATIC

verify that power line

SENSITIVE DEVICES

3.8.1 Recommended Test Equipment

Success in troubleshooting complex equipment like the Model 238 depends not only on the skill of the technician, but relies on the use of accurate, reliable test equipment. Table 3-2 lists the equipment recommended for

troubleshooting the Model 238. Other equipment, such as logic analyzers and capacitance checkers, could also be helpful.

Table 3-2 Recommended Troubleshooting

Equipment

Equipment Use

CMOS devices operate at very high impedance levels for low power consumption. As a result, any static that builds up on your person or clothing may be sufficient to

destroy these devices, if they are not handled properly.

Use the following precautions to avoid damaging them.

ICs should be transported and handled only in containers specially designed to prevent static build-up. Typically, these parts will be received in anti-static containers of plastic or foam, Keep these devices in their original containers until ready for installation.

Remove the devices from their protective containers only at a properly grounded workstation. Also, ground yourself with a suitable wrist strap.

Handle the devices only by the body; do not touch the pins.

Any printed circuit board into which the device is to be inserted must also be grounded to the bench or table.

Use only anti-static type solder sucker.

Use only grounded tip solder irons.

Once the device is installed in the pc board, it is normally adequately protected, and normal handling can resume.

Five function DMM with Power supply and DC

0.1% basic DCV accuracy, volta 1OM input impedance

Dual-trace, triggered Digital and analog sweep oscilloscope, DC to 5oMHz

Digital frequency

counter

e checks; analog

sign tracing continuity, logic levels,

waveform checks.

Checking clock frequencies.

3.8.2 Diagnostics

The Model 238 has some internal diagnostic capabilities

to aid in troubleshooting.

Power-up and MEMORY TEST

On power-up or when the Memory Test is run, the Model 238 performs a series of tests on its memory elements. If a failure occurs, one or more front panel messages are displayed.

3.8 TROUBLESHOOTING

The troubleshooting information contained in this sec-

tion is intended for use by qualified personnel having a

basic understanding of analog and digital circuitry. The

individual should also be experienced at using typical test equipment as well as ordinary troubleshooting procedures. The information presented here has been written to assist in isolating a defective circuit or circuit section. Isolation of a specific component is left to the technician. Note that schematic diagrams and component location drawings, which are an essential aid to troubleshooting, are included in Section 5.

3-8

Perform the following steps to perform the Memory Test:

1. Enable MENU and use the rotary knob to display ‘MEMORY TEST”.

2. Press ENTER. If the test passes, the display will blank for a couple of seconds and display the next menu item. Otherwise, a failure will cause one or more front panel messages to be displayed. Note: The Memory Test can also be run by sending JlX over the bus.

The front panel messages associated with memory ele-

ment failures are explained as follows.

SECTION 3

Maintenance

Message

CAL INVALID ERR

Explanation

On power-up, this message will indicate that one or more calibration errors exist. The Model 238 needs to be m-calibrated.

CAL CONSTANTS ERR One or more calibration constants are not within allowable limits. Default cal constants

will be used. Try re-calibrating the Model 238. Repeated failures may indicate defective E*ROM (U33).

IOU CAL CHECKSUM Checksum test of calibration constants failed. Try recalibrating instrument. Repeated

failures may indicate a defective EzROM (U33).

UNCALIBRATED

There are no calibration constants stored in memory. The E*ROM (U33) may be defective. Note that the Source Measure light blinks.

IOU DPRAM FAILED

The dual-port RAM for the I/O controller has failed making the instrument non-func-

tional. The DPFWM (U12) may be defective. IOU EEROM FAILED DPRAM LOCKUP

The E*ROM (U33) in the I/O controller has failed making the instrument non-functional.

The source/measure controller cannot respond to the I/O controller due to R4M (U13),

EPROM (U17), or microprocessor (U25) failure. The instrument is non-functional. DPRAM LINK ERR

Communications error in the DPRAM (U12) between the I/O controller and the source/

measure controller. The unit is non-functional. IF

NOTE: There are error messages assedated with calibration and are covered in the calibration se&m of this manual.

IOU RAM (U30) failure. The unit is non-functional.

IOU EPROM (U31) failure. The unit is non-functional.

Display Test

When the display test is run all display segments and front panel lights are tumed,on for a few seconds. Per-

form the following steps to run the display test:

1. Enable MENU and use the rotary knob to display “DISPLAY TEST”.

2. Press ENTER to run the test. Note: The memory test can also be performed by sending J2X over the bus.

A/D Test Mode

The instrument can be placed in the A/D test mode

which allows the A/D multiplexer (Ul) to be stopped in any one of its A/D phases. This allows switching states to

be checked and signal tracing to the A/D input (see A/D

Multiplexing in paragraph 3.8.5).

1. Turn off the Model 238.

2. While holding in the MENU button, turn on the Model 238. Continue to hold in the MENU button until the MENU indicator turns on.

3. Use the rotary knob to display “A/D TEST”. Note that the A/D converter is still running normally at this time.

4. Press ENTER. The following message will be briefly displayed:

ENTER TO EXIT

This is an instructional message indicating that once in the A/D test mode, pressing ENTER will exit the test mode allowing the A/D converter to run normally. The following message will then be displayed:

A/D ZERO TEST

This message indicates that the A/D converter is

locked in the zero phase.

5. The instrument can be placed in any of the other A/D phases (A/D REF, A/D VOLTS and A/D AMPS) with the use of the SELECT buttons.

6. To exit from the A/D test mode, press ENTER.

7. To return the instrument to the normal source/

measure display state, press MENU. Note: The A/D test will remain on the MENU until

power is cycled.

3-9

SECTION 3

Maintenance

Table 3-3.

Step Item

1 Line voltage switch

2 Line fuse 3 Line Power

4 +5v Digital supply 5 +15V Analog supplies

6 &3OV Analog supplies

7 +5V Analog supply 8

+15OV Floating supply

+15V Floating supply

Component Required Condition Remarks

VRl, pin2

VW pm

VR4, pin3

VI=, ps

VR6, pin3

w, ps

J16, pin4 J16, pin1

J8, pin1 is, pa

10 &24V Floating supply

J23, pin1

J% pin4

3.8.3

Table 3-3 shows the various checks that can be made to the power supplies of the Model 238. In addition to the normal voltage checks, it is a good idea to check the various supplies with an oscilloscope for signs of noise or oscillations.

Power Supply Checks

Set to 115V or 230V as required

Check for continuity Remove fuse to check. Plugged into live receptacle; power on +5V &0.25% +15v +lV

-15v +lV +3ov &2V

-30v &2V +5v fO.25% +15ov &!ov

-15ov +2ov +15v *lV +15v &lV i3OV +6V

-30V +6V

3.8.4 Analog Control Lines

Line voltage selection

Reference to digital common. Reference to floating common.

Reference to floating common.

Reference to floating common. Reference to output common.

Reference to output common.

NOTE

To check voltage levels on control lines, reference the measurement to floating common.

CAUTION On the Model 238, remove the ground link from output common when using chassis grounded equipment to make measurements referenced to floating ground. Otherwise, erroneous measurements or possible instrument damage may result.

Control lines, managed by the source/measure controller, are used to drive the various relays, switching FETs and analog switches associated with analog circuitry operation. That is, an appropriate voltage level present on a control line will cause the respective switch to close or open.

These control lines (located on schematic 238-126, page 1)

drive relay coils, gates of switching FETs, and inputs of analog switches. The following summarizes the nominal voltage levels that should be present on the control lines to drive these switching devices.

3-10

Relay Drive

K8, K9, KlO, Kll and K12;

OV = relay switch closed

+5V = relay switch open

Kl, K3, K4, K5, K6 and K15;

OV = relay switch open +5V = relay switch closed

Kl (Output Module)

OV = relay switch open

-15V = relay switch closed

SECTION 3

Maintenance

FET Switch Drive

N-channel FET;

OV = switch closed (on)

-15V = switch open (off)

P-channel FET;

OV = switch closed (on) +15V = switch open (off)

Analog Switch Drive (U45, U48, U49 and U50)

OV = switch closed

+5V = switch open

Other control lines that are not used to drive switching devices are described as follows:

COMPLIANCE-Used for compliance detection. When the Model 238 is in compliance, this control line is at OV. Otherwise, +5V is on this line.

Volts Ranging closed for each of the available voltage ranges. This table applies to both source and measure voltage ranges.

Table 3-5 lists the switches that are

Table 3-4. Analog Switching; Current Ranging

Range

lOomA

1omA

llE$l

1ocLA

1ZC

1onA

InA

Relays

Closed

Kl ‘, K8

K8 K9

l% Kll K12

Range Switches Closed

46429,433, Q37,QW Q51-454, U5OA, U50B

Q5-491437,438 U45A, QlO, Ql 1

U45A, 412,413 U45A, 44,414 U45A, Q4 U45A, 44 U45A, Q4 U45A, Q4 U45A, Q4

Table 3-5. Analog Switching; Current Ranging

POLARITY- Used to provide the appropriate 1OV reference for the clamping circuits. When the instrument is programmed for a positive (+) output, this control line is at nominally +lOV. When programmed for a negative (-1 output, this line is at nominally -lOV.

lOOmA RANGE BIAS - Used to select the appropriate current limit to the output stage. With the instrument on the lOOmA range (source or measure), this control line is at +5V. On the other current ranges this line is at OV.

3.8.5

Tables 3-4 through 3-8 provide the switching states of most of the analog circuit switching devices for the various operating conditions.

Current Ranging - Table 3-4 lists the switches that are closed for each of the nine current ranges. This table applies to both source and measure current ranges. Notice

that on the 1nA range none of the current range relays are closed.

Analog Switching a

Relays

Range

1.5v 15v 1lOV 1lOOV

Feedback - As listed in Table 3-6, analog switches U48 and U49 are used for feedback switching. Each of these two devices has four individual switches and are identified by their circuit schematic pm numbers. The table lists the states of these switches for standby and operate con-

ditions while programmed to source current and voltage.

Sensing - As listed in Table 3-7 three relays are used to

select local or remote sensing. Note that when the instrument is programmed for remote sensing, the relay switches will default to the local sensing states when placed in standby. That is, relay K3 will open, and relays K15 and K5 will close whenever the instrument is placed in standby.

Closed

K4, K6, K7 K4, K6, K7

FET Switches Closed

4241433,435, Q53 424

3-11

SECTION 3

Table 3-6. Analog Switching; Feedback

Analog Switches

Device

U48 u49

Pins Standby

1;;1 10,ll

14,15 Open 14,15

2,3

Source I Measure V

Closed Closed gz Closed

Closed Closed

Open Closed Open

Open

Table 3-7. Analog Switching; Sensing

Relays*

Sense

Local

Remote Closed

T&lay states with 238 in OPERATE. In standby, relays go to local sense states.

Open

Kl5

Closed

Open

Closed

Open

Source V Measure I

Operate Standby

Closed Closed

Open open

Closed Open Open Closed

Closed

Closed Closed Closed

Open Open

Operate

Closed

Closed Open

Open Open

Table 3-8. Analog Switching; A/D Multiplexing

A/D Phase

Reference

V Measure

I Measure

Zero

Ul Switch Closed (pins)

14,15 10,ll

2,3

Output-For safety, there are two relays that are used to disconnect OUTPUT HI and SENSE HI from the rear panel output triax connectors. When the instrument is off, relays Kl and K2 are open. When turned on, these relay switches remain open until the instrument is first placed in operate. These two switches then remain closed while the instrument is powered on.

A/D Multiplexingmultiplexer (Ul) continuously applies a sequence of signals to the input of the A/D converter. These signals include Zero, Reference and Measure (I or V). Only one signal is switched to the A/D input at one time. The switching speed and sequence varies according to how the instrument is programmed to operate.

In the A/D test mode (see paragraph 3.8.2) the A/D converter is locked up in the desired A/D phase. This allows multiplexer switch states to be checked and signal tracing to the A/D input to be performed. Table 3-8 identifies the switch that is closed during each A/D phase. The pin numbers of multiplexer Ul are used to identify each switch.

During normal operation, the A/D

3.8.6 Digital and Display Checks

The digital and display circuitry can be checked out by using the troubleshooting data found in Table 3-9 and 3-10.

Note: The firmware that controls the Model 238 is contained in two EPROMs (U17 and U31). Ifit is necessary to replace one or both of the EPROMs, make sure that both EPROMs installed in the instrument have the same firmware revision level. After installing new firmware, perform factory initialization to write firmware changes to

the E2ROM. Factory initialization is performed by ena-

bling MENU, displaying FACTORY INIT with the rotary

knob, and then pressing ENTER.

CAUTION

The EPROMs are static sensitive devices that

are susceptible to damage by routine handling. Be sure to handle the devices as explained in paragraph 3.7.

3-12

SECTION 3

Maintenance

Table 3-9.

Step

Item/Component

Ul2, U13, U17, U30, U31 and U33

2 U28, pin 18 3 U28, pin 6 (PA4), pin 7 (PA51,

pin 8 (PA6), pm 9 (PA71

4 U28, pin 11 (PBl), pin 12 (PB2)

5 U28, pin 19

6 U25, pins 34 and 35 2MHzm

U25, pin 37 +5v, st5%

U27, pin 9

9 U27, pin 19

Required Condition Remarks

Pass RAM, EPROM, DPRAM and NVRAM tests on power

UP* TTL level pulse every lmsec

Switch data (+5V or OV)

Rotary knob data (+5V to OV) Data input VIA when rotary knob

Variable pulse train (OV to +5V)

+5V signal pulsed OV to +5V INT line every lmsec

+5v (Logic “1”) RESET line

Digital Circuitry Checks

Display will lock if failure occurs.

I/O controller VIA display clock Data in ut to VIA when button

presse CT

turned Data output to display

Bus clock Reset line (goes low momentarily on

power up)

10 U27, pin 18

U27, pin 28

U27, pin 24 (NDAC), 25 (NRFD), 26 (DAV), and data lines conditions

Ul4, pin 19 Variable pulse train

U14, pins 2-9 (PAO-PA7) Variable pulse train Data to VIA from A/D

15 U15, pins 34 and 35 16 u15, pin 37 +5v, +sYo

2MHz squarewave Clock

(OV to +5V)

Goes true (+OV) when ATN line command is sent

See Figure 3-7 for required

(OV to +5V)

2MHzTTL

Handshake sequence

S/M controller VIA data to optos.

Clock Reset line (goes low momentarily on

power up)

3-13

SECTION3

Step

Item/Component

1 P24, pin 15 and 16

U5, U6, U9 and UlO;

OUT1 thru OUT8 u4, pins 4-7,14-17

u7, pins 4-7,14-17 U8,pins4and5

4 P24, pin 10

5 P24, pm 9

P24, pin 8

7 P24, pin 7

Table 3-10

Display Circuitry Checks

Required Condition

+5v, &5% Variable pulses

Variable pulses

Depress any switch located in the first column of switch array on

schematic (236-116). Depress any switch located in the

second column. Depress any switch located in the

third column. Depress any switch located in the

fourth cohm-tn.

Remarks

+5v supply Segment drivers

Digit drivers

Pulse present when button pressed.

3-14

SECTION 4

Principles of Operation

4.1 INTRODUCTION

This section contains a general functional description of the Model 238. Detailed schematics and component location drawings are located at the end of this manual.

I Feedback

* DAC -

+ v - V Clamps

DAC

-----------mm

I Clamps

----

Control <

Source/Me:

Controk

- -

A simplified block diagram of the Model 238 is shown in Figure 4-l. The instrument may be divided into two sections; analog and digital circuitry. The analog and digital sections are electrically isolated from each other by the use of opto-isolators for control and communications. Separate power supplies for the analog and digital sections ensure proper isolation.

--------_--------

Analog

Digital

Figure 4-l. Overall Block Diagram

4-l

SECTION 4 Principles of Operation

4.2 ANALOG CIRCUITRY

The heart of the source is an error amplifier that along with its complex scheme of feedback elements is configured as a bootstrap amplifier. Input stimulus for the amplifier is provided by two user-programmed digital-toanalog converters (DACs). The controlling function (current or voltage) and selected polarity of the source turns on one of four precision clamps allowing an input signal to be applied to the error amplifier. The output voltage from the DAC and the feedback configuration applies a voltage to the input of the error amplifier that will effect a constant level of current or voltage at the output.

Measurement is accomplished by routing properly con-

ditioned feedback levels for voltage and current through

a multiplexer to the analog-to-digital (A/D) converter.

Before proceeding to the details of circuit operation, it may be helpful to clarify what is meant by “controlling

function”. If the instrument is programmed to source a specific current and it does indeed source that current, then it is considered to be current controlled. That is, current is the controlling function. If for some reason the instrument goes into compliance, the programmed current will not be sourced. Instead, the instrument sources a constant voltage (compliance voltage). Thus, voltage becomes the controlling function. Conversely, when pro-

grammed to source voltage, voltage is the controlling function unless the instrument goes into current compliance. In compliance, current becomes the controlling function.

4.2.1

V/I Control and Readback

A simplified schematic diagram of the V/I control and V/I readback circuitry is shown in Figure 4-2. The detailed schematic showing all circuit components is located on page 2 of drawing number 238-126.

Figure 4-2.

n I d+/&

Simplified Schematic of V/I Control and Readback

From Vif Feedback

To Output

stage

4-2

SECTION4

Principles of Operation

mming current and voltage sets the output volt-

Progra age of the two digital-to-analog (DAC) circuits. Programming current controls the output of the I DAC (U23 and U22), and progr the V DAC (II25 and U24). Programming current or voltage for zero output will result with a OV output from the respective DAC. Programming for a full scale output will result with a -lOV output from the respective DAC.

The output voltage from the I DAC is applied to current clamps through resistor networks. Op amp U13 and diode CR11 form the negative current clamp (-1 CLAMI?. The output from the I DAC is inverted by the xl amplifier U51B (x0.1 for the 1A range). The inverted output of U51B is again inverted by U51A. Op amp U17 and diode CR10 form the positive current clamp (+I CLAMP).

The output from the V DAC is inverted by the xl amplifier U12 (x0.1 for the l.lV range) and similarly applied to current clamps through resistor networks. Op amp U15A and diode CR12 form the positive voltage clamp (+V CLAMP). The inverted output of U12 is again inverted by U19. Op amp U15B and diode CR9 form the negative voltage clamp (-V CLAMP).

amming voltage controls the output of

Since the instrument is programmed for a positive out-

put, the +lOV REF will apply a positive voltage to the

common side of the clamps. This positive voltage will reverse-bias diodes CR11 and CR9B and prevent the -1 CLAMP and -V CLAMP from turning on.

With the front end of the bootstrap amplifier set up as de-

scribed, -5V will be fed back (via I FEEDBACK) to U17

and U13. The non-inverting (+> input of U17 will go to OV

(-5V + 5V = OV) forward-biasing CRlO. As a result, the +I CLAMP turns on.

The voltage drop across the load is 20V (5mA x 4kn = 2OV). This voltage is scaled down to 2V and inverted. This -2V is fed back (via V FEEDBACK) to U15A and U15B. The non-inverting (+) input of U15B will go posi-

tive keeping CR12 reverse-biased. As a result, the +V

CLAMP remains off.

Current from +lOV REF will flow into the +I CLAMP,

which is turned on (remember, the other clamps are off). As a result, the feedback configuration and the I DAC

output will apply a voltage to the error amplifier (U14)

that will effect a constant +5mA output current.

During operation, only one of the four precision clamps will be on at one time to control the error amplifier (u14). The controlling function and the programmed polarity (+ or -1 will determine which clamp is on. The following example will explain how this occurs.

Example 1: This example is divided into two parts. Part 1 will explain circuit operation with the instrument sourcing a constant current. Part 2 will explain what happens when the source goes into voltage compliance.

Part 1: Assume that the instrument is sourcing +5mA with a 27V compliance to a 4kn load. Under these conditions the instrument is not in compliance (5m4 x 4kn = 2OV). Thus, current is the controlling function.

The I DAC outputs -5V. Thus, negative voltage appears at the non-inverting (+> input of U13 and positive voltage appears at the non-inverting (+> input of U17. The VDAC outputs approximately -3V. Positive voltage appears at the non-inverting (+> input of U15A and negative voltage appears at the non-inverting (+> input of U15B.

Part 2: Assume the instrument is still programmed to

source +5mA with a compliance of 27V. However, for

one reason or another, the load resistance changes to 6kS2. This load change causes the source to go into compliance

making voltage the controlling function.

With the 4kQ load, the +I CLAMP is on making current

the controlling function (as explained in the Part 1). When the load resistance is increased to 6kQ the voltage

drop across the load would be 30V (5mA x 6ks1= 3OV).

However, voltage is limited at 27V and the source goes

into compliance.

In voltage compliance, the 27V is scaled down to 3V and

inverted. This -3V is fed back (via V FEEDBACK) to U15A. The non-inverting (+) input of U15A will go to OV

(-3V + 3V = OV) forward-biasing CR12. As a result, the +V

CLAMP will turn on.

Current from +lOV REF starts flowing into the +V

CLAMP. With less current flowing into the +I CLAMP,

the voltage at the input of U14 decreases causing the out-

put current of the source to decrease. The resultant feed-

back voltage to U17 will cause its (+) input to increase

4-3

SECTION 4

Principles of Operation

above OV causing CR10 to become reversed-biased. As a result, the +I CLAMF will turn off.

With the +V CLAMP on, the instrument is voltage con-

trolled. The output from the V DAC and the feedback configuration will apply a voltage to the error amplifier (U14) that will effect a constant output voltage of +27V.

Bootstrap amplifier gain is controlled at the output of the error amplifier (U14) by the FET switch 424 and relay K4. On the 1lOV and 1lOOV ranges, the switches are open and xl10 gain is provided. On the lower voltage ranges the switches are closed providing xl1 gain. Device Ul 1 is a xl

buffer between the V/I control circuit and the output

module.

Measurement is accomplished by routing properly conditioned voltage feedback levels (I FEEDBACK and V FEEDBACK) through a multiplexer to the analog-todigital (A/D) converter. Op amp U9A is configured as a non-inverting amplifier for I FEEDBACK. On the 1A range, the FET switch 453 is closed providing x10 gain. On the other current ranges, the FET switch is open configuring U9A as a unity gain amplifier. Op amp U9B is configured as a non-inverting amplifier for V FEEDBACK. On the 1.5V range, the FET switch 433 is closed providing x10 gain. On the higher voltage ranges, the FET switch is open configuring UYB as a unity gain amplifier. The four signals (+lOV reference, V Measure, I Measure and floating common) are multiplexed (Ul) and routed to the A/D converter via buffer U21.

4.2.2

The output stage of the bootstrap amplifier basically consists of a class AB circuit whose bias is controlled by the output of the error amplifier. The simplified schematic diagram of the output module is shown in Figure 4-3. The detailed schematic of the output stage is found on drawings 238-166 and 238-126 (page 2).

Output Module

Low Current Ranges

At the heart of the output stage are power transistors 421 and Q19. The collector of 421 is effectively connected to the +15OV, 120mA power supply, while the collector of Q19 is effectively connected to the -15OV, 120mA power

suPPlY*

When programmed for a zero output, both 421 and Q19 are zero-biased (off). The +15OV supplies are dropped across the high impedance of these two transistors. As a result, zero voltage is present at the output (floating common to output common). When the source is programmed for a positive output, 421 becomes forward-biased (on). The voltage drop across 421 becomes less than +15OV. As a result, the voltage present at the output is the difference between the supply voltage (+15OV) and the voltage drop across 421. For a positive output, Q19 is reverse-biased (off) keeping the negative supply isolated from the output.

Circuitry for a negative output functions in a similar manner. When the source is programmed for a negative output, Q19 becomes forward-biased, resulting with a negative voltage present on the output. Transistor Q21 is reverse-biased isolating the output from the positive

suPPlY*

Bias for the two power transistors are provided by the +3OVF supplies and two 15V zener diodes (VRlO and VR9). This bias circuit is referenced to floating common in order to maintain the bases of the transistors at a voltage that is higher than the output so that they can be forward-biased. Bias control is performed by the output of the error amplifier (MAIN drive). The polarity and magnitude of MAIN determines which transistor is forwardbiased and the amount of bias current that in turn determines the magnitude of the output voltage. For example, as a positive MAIN becomes more positive, more bias current is delivered to the base of 421 resulting in a higher output voltage.

4-4

6.47, C~~3 “7 +3OV, 1A

Principles of Operation

SECTION 4

From V/I

Control

+3OVF

-30VF

v\Rio

x(;;?rrA, F$?@f

W””

Floating Common

019

-15ov

(120 mA)

-6.44VF - 3OV, 1A

Figure 4-3. Output Module (Simplified Schematic Diagram)

036

T?-+

1Amp B

To 1Q Sense

Resistor

1A Current Range

When the 1A range is selected, relay Kl and switches Q41

and 436 are closed. The drive for the 1A stage is provided by the lnA-1OOmA stage. For low output currents (0 to 2OmA), the lnA-lOOmA stage is used. As the current is in-

creased, the transistors in the 1A output stage start to

turn to provide output current up to 1A. To obtain the full

voltage swing on the output, transistors Q43 and 440 are

driven by 6.44 zeners (VRl and VR2).

4.2.3

V/I Feedback

A simplified schematic diagram of the V/I feedback cir-

cuitry is shown in Figure 4-4. The detailed schematic of

this circuitry is provided by page 3 of drawing 238-126.

Amps Ranging - Current range selection is accomplished by activating the appropriate range FET and/or relay. The nominal range resistances, relays and FETs for each of the nine current ranges are shown in the illustration (Figure 4-4). The FET labeled QAB for the 1OOmA range is actually a composite P and N-channel FET. A more detailed look at the lOOmA range is shown in Figure 4-5. In reality, QA is comprised of P-channel FETs QS and QY, and QB is comprised of N-channel FETs Q6, Q7,437 and Q38.

Without special circuitry, current measurement range changes may cause voltage spikes to occur at the output. Voltage spikes are caused by contact bounce of the selected range relay. These spikes occur too fast for the bootstrap amplifier to react to the change in feedback voltage. As a result, the system cannot adjust itself ac-

cordingly to maintain a steady voltage output.

4-5

SECTION 4 Principles of Operation

_ Floating

O I Common 1

FromlnA-lOOmA

Amps Ranging

1OGQ

L..

1nA

1 1 I

Out

Volts “..U-. A

K15y K3

V/I

Control

and

Feedback

Figure 4-4.

V/l Feedback (Simplified Schema tic)

The Model 238 resolves this problem by using circuitry that, in effect, shunts the current ranges with a lOOn resistor whose voltage drop ramps in a linear fashion towards OV. This slow rate of voltage change allows the system to adjust itself keeping the output voltage constant (spike free). The circuitry that accomplishes this consists of FETs QA and QB, and the +15V-to-OV ramps that control them.

The following sequence takes place when a current measurement range change occurs:

with a corresponding voltage ramp across the 100R resistor.

3. The other ramp is activated. Turning on the second FET increases the current carrying capability of the circuit. With both FETs fully on, the current ranges are shunted by the 1OOR resistor.

4. The new range relay and/or FET is activated. Note: If the lOOmA range is the new range, it is already selected. The range change sequence stops at

this point. If a different range is selected, continue on to the next steps.

5. The two voltage ramps are disabled in reverse order.

6. Relay K8 opens completing the range change.

1. Relay K8 closes.

2. The appropriate ramp is activated (RANGE 2 RAMP for + polarity, or RANGE 1 RAMP for - polarity).

The ramp on the gate of the appropriate FET results

4-6

When the lOOmA source range is selected, K8 closes and both ramps are activated to turn on both F’ETS. As long as the 1OOmA range is selected, OV is maintained at the gates of the FETs to keep them on.

Range 1 Ramp

Range 2 Ramp

1 OOmA Range

Principles of Operation

SECTION 4

Figure 4-5.

Op amp U3 is a unity gain amplifier that serves as a buffer between the output and I FEEDBACK. I FEEDBACK is fed back to V/I Control and Readback where it completes the feedback loop and is also routed to the A/D converter for measurement. On the 1A range, the 1AMPB output is switched directly to U8 (via U50), bypassing U3.

Guard -The xl output of U3 is also routed to another xl buffer amplifier (U4) whose output is used as the driven guard for the instrument. Buffer U4 isolates the driven guard from I FEEDBACK.

Volts Ranging and Sensing-The voltage range resistors are part of a voltage divider network. In general, OUT + is applied to the top of divider. The output of the divider is then routed to a differential amplifier. The other input to the differential amplifier is effectively OUT +. The output of the xl differential output is then fed back to the V/I Control and Readback circuitry.

Op amp U2 is configured as a unity gain amplifier that serves as a buffer between the output and volts ranging circuitry. In local sense (K15 closed, K3 open), the output is accessed internally. In remote sense (K15 open, K3

Damping Relay Contact Bounce

closed), the output is accessed at the load. The xl output of U2 is applied to the negative (-) input of the differential amplifier (U7).

The output of U2 is also applied to the top of the voltage divider for volts ranging. The bottom of the voltage divider network is connected to output common (OUT -) via op amp U47 which is configured as a xl buffer. In local sense (K5 closed), OUT - is accessed internally. In remote sense (K5 open), OUT - is accessed at the load.

Volts range relay K6 determines the resistance of the bottom leg of the voltage divider. Table 4-l identifies the relays for each voltage range. The output of the voltage divider is routed to the + input of the differential amplifier (U7) via op amp U5 which serves as a xl buffer.

Op amp U7 is configured as a xl differential amplifier.

The output voltage (VOUT) of this amplifier will be the

algebraic difference of its two inputs (El - E2 = VOLT). VOUT (V FEEDBACK) is routed back as a bootstrap amplifier feedback loop and also to the A/D multiplexer for measurement.

4-7

SECTION 4 Principles of Operation

Table 41 Volts Range Relays

4.3 A/D CONVERTER

The Source Measure Unit uses a constant frequency, vari-

able pulse width, analog-to-digital converter. The schematic diagram for the A/D converter is located on page 3 of drawing 238-106.

Reading conversions start with a charge balance phase and end with a single slope phase, thus producing two sets of counts from U47 back to the pre-scale counter (U21) and VIA of the source/measure controller.

The A/D input is applied to current offset resistors R63 and R64. The input current is applied to the gate of Q4 via FET switch Q2 converting the bipolar +lOV input to a unipolar current. Operational amplifier US0 and Q4 form an integrator with capacitor C63. This integrator ramps in a positive direction (since the current is negatively offset) until it reaches a threshold, or until a timebase interval occurs and switches on a balance current. This continues for a length of time that is determined by the value in register U44 which is programmed by the source/measure controller.

Device U45 is an 8 bit magnitude comparator which continuously compares the set value to the count value in counter U46. When these two numbers match, the output on pin 19 of U45 stops the A/D converter, thus signaling the end of the charge-balance phase. After determining

that the charge balance has stopped Coy monitoring

counts or timing out), the software sets the final-slope balance line high. This clears U46 making it ready for a new charge-balance phase, and starts the final-slope phase of the A/D converter.

The final-slope phase essentially removes all charge re-

maining on the integrator by ramping the output of U50

to OV. Counts are accumulated during the final-slope and used for calculation of the effective input signal. The

A/D converter is run through a number of phases that

are used to null any error signals present in the A/D or analog front end.

The time base for the A/D converter is provided by an oscillator that consists of inverter U57 and crystal Y2. The

7.68MHz time base, which is a multiple of 60H2, is divided by counters U41 and U40 to provide system timing functions for charge balance control. The 7.68MHz is fed directly to NOR gate U47 where it is gated on and off by the rest of the A/D function. The A/D power supply reference voltages, tional amplifier US6 and associated circuitry. These are reference voltages used in generating currents and thresholds for the A/D converter.

-lOV, and +5V are derived from opera-

4.4 DIGITAL CIRCUITRY

The schematic diagrams for the digital circuitry are located in last section of this manual, drawing number 238-106.

The Source Measure Unit is controlled by two 6809 8-bit 2MHz N-MOS microprocessors. These two microprocessors coordinate aII instrument functions. These include running the display and keyboard, servicing the IEEE-488 interface, and control of alI analog functions.

4.4.1

The schematic diagram for the I/O controller is provided on page 1 of drawing 238-106.

The I/O controller controls the display and front panel controls, the IEEE-488 interface, test fixture lid closure detection, and TRIGGER IN and TRIGGER OUT. It also maintains calibration constants, and contains the major portion of the operating system for the instrument.

At the heart of the I/O controller system is an 8-bit 68B09 microprocessor running at 2MHz. The system master oscillator Yl is an 8MHz canned crystal oscillator. I/O controller peripherals include a 64K X 8 ROM (U31) which contains the program memory, a 32K X 8 static CMOS RAM (U30) which is battery backed up via U29 and the battery (BTl). Calibration constants are stored in nonvolatile memory (U33; E’ROM). A versatile interface

adapter (U28) provides peripheral interface to the 6809

microprocessor. It is primarily used to interface with the

display and keyboard. It is also used to interface TRIG-

GER OUT and TRIGGER IN, as well as monitor the test

I/O Controller

4-8

Principles of Operation

SECTION 4

fixture lid detect interface. A 9914 IEEE488 standard in-

terface (U27) is combined with two transceivers (U34 and

U35) to provide the interface function. All of these pe-

ripheral chips are interfaced to the 6809 via a program-

mable logic device (U26; PAL 16L8).

A NOR gate package (U32) is used to provide protection

for calibration constants stored in non-volatile memory

(U33) during power-up and powerdown.

A power-up reset control circuit (U36) guarantees a de-

layed reset after power-up and a prompt reset on power-

down by sensing power supply threshold.

4.4.2

The schematic diagram for the source/measure controller is provided on page 2 of drawing 238-106.

This controller system also uses a 68B09 microprocessor

(U15). As with the I/O controller (see previous paragraph), it derives its 2MHz operating frequency from the 8MHz crystal (Yl). The peripherals for this 6809 include 3X of ROM (U17), 32K of static RAM (U13), and a versatile interface adapter (U14) which provides interface to the analog circuitry as well as a few other miscellaneous functions.

Source/Measure Controller

Communications are provided by opto-couplers that serve as an interface between the source/measure controller and the analog circuitry. This particular circuit is fairly unique in that control signals are sent through two optos that are driven 1805 out of phase with one another to provide immunity from false glitching.

The outputs of the complimentary opto-couplers are de-

coded by programmable logic device Ul (PAL 2OLlO). From Ul, the signals are sent to various places on the analog board by decoder U39 which determines one of four clock paths as set by the bank select signals 0 and 1 which

are also derived from Ul . This circuit topology provides for a very reliable communications scheme such that the analog circuitry can never receive false data.

Opto-couplers ATI, AT2, AT3, AT7 and AT8 are all involved in the transmission of clock, data, strobe, and the two bank select signals from the VIA of the source/measure controller to the analog board. Opto-coupler AT5 returns a CV/CC constant voltage or constant current level signal to the source/measure controller so that the present state of the analog output can be determined. The A/D converter counts are returned to the microprocessor of the source/measure controller by AT6 which is a high speed opto-coupler.

4.4.4

The schematic diagram for the display circuit is provided on drawing 236-116.

Display Circuitry

Devices U18, U19 and U58 are binary counters that form the core of a software watch-dog timer. This timer moni-

tors software execution of both CPUs via lines that are regularly toggled. If any line fails to toggle within approximately 4msec the entire system will be reset.

As with the I/O controller, all the peripheral chips of the source/measure controller are decoded and controlled by a programmable logic device (U16; PAL 16L8). A/D control as well as A/D counts accumulation are performed by the VIA (U14) with a prescale counter (U21). Inverters (U23) provide a software selectable enable for the high voltage converter in the Model 237 only.

4.4.3

The schematic diagram for the communications circuitry is located on page 4 of drawing 238-106.

Communications

The display, which is controlled by the I/O controller, is basically an 18-d@ alpha-numeric LED display. It consists of nine two-digit display elements (DSl through DS9). Each of these display elements are multiplexed in a matrix fashion. Each display digit has its common cathode connected to sink drivers (U4, U7 and U8). These sink drivers are switched on in a rotating fashion.

The display is divided into two banks of ten columns

such that the DS1 left digit and DS6 left digit are on simultaneously, as can be evidence by the common connections of the inputs of U4 pin 3 and U7 pin 8. This allows the display to be refreshed faster, thus eliminating flicker

associated with line frequency beating with lighting and such. The front panel indicator LEDs (DSIO through DS29) are driven in a similar manner by sink drivers of U8. The anodes of the two separate banks of display elements are driven by source drivers U5 and U6 (left bank),

and U9 and UlO (right bank). These are serial input, par-

4-9

SECTION 4

Principles of Operation

allel output combination shift register/drivers. They interface directly to the I/O controller VIA clock data interface. A strobe is provided by software to load the outputs of the drivers with data. The displays are indexed at a

100Hz (lms) rate.

Circuit components Ul and U2 provide a timer function that allow the selection of either a bright or dim digit and is used for flashing cursor digits. A counter (U2) times out after 256psec and bit 16 of the two serial bank source drivers is fed back into Ul pin 12 and Ul pin 6. Depending on the states of these bits, the LEDs will be on for the entire lmsec duration or l/4 (256pec) duration. The column drivers are selected by a one-of-ten decoder (U3) which is directly driven from the WA of the I/O controller. These columns, as they are selected, also select columns in the front panel key switch matrix through diodes CR1 through CR 10. The column driven low, and the four lines fed back to the VIA of the I/O controller identify which key is pressed.

4.5 POWER SUPPLY

The schematic diagram for the power supply is located on page 4 of drawing 236-106.

The power supply consists of an off line transformer (Tl) which has selectable 115/23OV operation. It is essentially two 115 volts primaries either in series or parallel. In parallel with one of the primary tidings is the cooling fan allowing it to always operate on 115V. The line select switch (S2) allows user selectable line voltages. Switch Sl is the main power switch, Fl is the system fuse, and J2 is a rear panel mounted line filter connector. The secondary of the transformer provides all of the power supply voltages.

The digital power supply (gray transformer secondaries on schematic) is capable of delivering +5V at 1.2A to

power all digital and front panel circuit components. Full

wave rectification is provided by the bridge rectifier CRI.

Capacitors Cl06 and Cl07 provide spike suppression,

while C4 provides filtering. Voltage regulation is pro-

vided by VRl with capacitor C24 on its output for stabil-

ity.

The 15V and 30V analog supplies are derived from the or-

ange colored secondaries. The 15V power supply consists

of a bridge rectifier CR4, filter capacitors C53 and C55,

15V regulators VR3 and VR4, and stability capacitors C91 and C92. A voltage doubler circuit consisting of diodes CR2, CR3, CR6 and CR7, and storage capacitors C52, C54, C56 and C57 combine with adjustable regulators VR5 and VR6, and resistors R6, R7, R8 and R9 to provide the 3ov outputs.

The +5V analog supply (brown secondaries) consists of the bridge rectifier CR5, filter capacitor C7, regulator VR2, and output capacitors C93 and C15. This power supply provides +5V for analog functions.

The 150V supply (yellow secondaries) is provided for the bootstrap amplifier. A bridge rectifier is configured from four diodes; CRB, CR9, CR10 and CR1 1. These diodes rectify and use capacitors C58 and C59 as storage elements. A 15V analog supply is derived from a shunt regulator circuit consisting of resistors R73 and FU4, and regulators VR7 and VRB in parallel with capacitors C95 and C96.

The 30V supply (blue, white/brown and blue/white sec-

ondaries) is used to drive the 1A output stage. Bridge rectifier CR12 provides full-wave rectification while RBO,

R90, Cl10 and Cl19 suppress diode spikes. Triac 47, zener diodes VR9 and VRlO, and resistor R81 provide a clamping circuit that guarantees that the Fl fuse will clear when the instrument is set for 115V operation while connected to the 230V line. Minimum load is guaranteed by resistors R94 and R95. Filtering is provided by capacitors Cl0 and C118.

4-10

SECT

ON5

Replacea

5.1 INTRODUCTION

This section contains replacement parts information,

component location drawings and schematic diagrams for the Model 238.

5.2 PARTS LISTS

Parts are listed alphanumerically in order of their circuit designations. The first parts list contains information for the display board of the Model 238. The next parts list contains information for the digital board of the Model

238. The next parts list contains information for the analog board of the Model 238. The next parts list contains information for the output module. The last parts list contains information on miscellaneous parts that do not pertain to any of the pc boards.

5.3 ORDERING INFORMATION

To place an order, or to obtain information concerning replacement parts, contact your Keithley representative or the factory. See inside front cover for addresses. When ordering, include the following information:

ble Parts

Instrument Model Number Instrument Serial Number Parts Description Circuit Designation (if applicable) Keithley Part Number

If an additional service manual is required, order part number 238-902-00. The manual package will contain the service manual and any applicable addenda.

5.4 FACTORY SERVICE

If the instrument is to be returned to the factory for service, please complete the service form which follows this section and return it with the instrument.

5.5 SCHEMATIC DIAGRAMS AND COMPONENT LOCATION DRAWINGS

Schematic diagrams and component location drawings follow the appropriate replaceable parts list for that particular board.

5-l

TABLE 1. MODEL 238 ANALOG BOARD, PARTS LIST

CIRCUIT DESIG.

Cl2,16 Cl24 Cl27,128 Cl29 c13,17,19,135, 142,150,151, 152,160,161 c130,140,141, 148,149 Cl31 Cl 32 Cl 32 Cl33 Cl38,139,159 c143,144 c153,154 Cl57 Cl58 Cl 70..175,

177..214,

216..223 Cl 76,215,

224..246 Cl8 c20

c21 c22,120 C23 C24,121 C25 C26,122,123 C28,37 c39 c40,41 ,I 34,

156,162

c43 c50,51 C54,76,98,101,

102,115,155

C6 C8 C9,lO

DESCRIPTION

CAP,22PF,2.5%,630V,POLYPROPYLENE CAP,l50PF,l%,500V,MlCA CAP,68PF,2.5%,630V,POLYPROPYLENE CAP,1000PF,10%,1000V,CERAMIC CAP,l5PF,5%,lOOV,CERAMIC

CAP,lOOOPF,l%,50V,CERMANIC

CAP,47000PF,l O%,l OOV,EPOXY CAP,1 OPF,l O%,l OOOV,CERAMIC CAP,1 OPF,l O%,l OOOV,CERAMIC CAP,1 5PF,l0%,200V,CERAMIC CAP,5PF,lO%,lOOOV,CERAMIC CAP,1 OPF,5%,1 OOV,CERMANIC CAP,1 5PF,5%,1 OOV,CERAMIC CAP,680PF,l O%,l OOOV,CERAMIC CAP,470PF,5%,500V,POLYSTYRENE CAP,.lUF,20%,50V,CERAMlC

CAP,.1 UF,20%,50V,CERAMIC

CAP,39PF,2%,50V,CERMANlC CAP,1 5OOPF,l O%,l OOOV,CERMANIC CAP,270PF,2.5%,630V,POLYPROPYLENE CAP,560PF,2.5%,630V,POLYPROPYLENE CAP,1 OOPF,2.5%,630V,POLYPROPYLENE CAP,220PF,2.5%,630V,POLYPROPYLENE CAP,8PF,2.5%,630V,POLYPROPYLENE CAP,33PF,2.5%,630V,POLYPROPYLENE CAP,.OlUF,l0%,l000V,CERAMIC CAP,3300PF,lO%,l OOV,CERMANIC CAP,1 5OPF,l %,l OOV,CERMANIC

CAP,1 UF,20%,5OV, CERAMIC CAP,.OlUF,20%,50V,CERAMIC CAP, 1 OUF,-20+100%,25V,ALUM ELEC

CAP,22PF,lO%,lOOOV,CERAMIC CAP,1 5OPF,l O%,l OOOV,CERAMIC CAP,33PF,l O%,l OOOV,CERAMIC

KEITHLEY PART NO.

C-405-22P c-209-1 5OP C-405-68P C-64-l OOOP C-372-l 5P

c-347-1 OOOP

c-371 -47OOOP C-64-l OP C-64-l OP C-406-15P C-64-5P C-372-l OP C-372-l 5P C-64-680P C-l 38-470P C-365-. 1

C-237-.1

C-348-39P C-64-l 500P C-405-270P C-405-560P c-405-1 OOP C-405-220P C-405-8P c-405-33P C-64-.01 c-430-33OOP C-372-l 50P

C-237-l C-365-.01 c-314-10

C-64-22P C-64-l 50P C-64-33P

CR1 ..4,7,22..26,

28..33 CR34 CR5,6

DIODE,IN3595 (DO-7)

DIODE,BRIDGE,DFlOM DIODE,SILICON,SCHOl-l-KY,SBl20

RF-43

RF-79 RF-78

CR9..16,19,20

DIODE,SILICON,IN4148 (DO-35)

RF-28

Jl1..13 J15 J19 J27

Kl,8 Kl2,15 K2,4..16 20 K3 K9,10,11

P18 PS

Q18 Ql9,31 Q24 Q25..28

Q32,43,44,46,48 TFiANS,CURRENT REGULATOR,CR430 Q36 Q39,40 Q4..7,10..14, 33,35,37,38,

51..54 Q41,42,45,47 Q49,50 Q8,9

SURGE ARRESTOR FOR P18 ASS’Y GROMMET

CONN,SMB,MALE,P.C. MOUNT CONN,MALE,15 PIN CONN,DUAL 7-PIN-BERG CONN,MALE,2PIN

RELAY, (SPST) RELAY (SPST) RELAY,REED, HI VOLTAGE RELAY,REED, HI VOLTAGE RELAY (SPST)

CONNECTOR HOUSING (10 PIN MOLEX) CONNECTOR, HOUSING

TRANS,N CHANNEL JFET,SELECTED J210 TRANS,NPN SILICON,2N3904 (TO-92) TRANS,N CHANNEL JFET,SELECTED J210 TRANS,NPN COMP SILICON AMP,2N5089 TRANS,PNP SILICON 2N3906 (TO-92)

TRANS,CURRENT REGUlATOR,CR120 TRANS,N CHANNEL FET,2N4392 (TO-92) TRANS,SELECTED N CHANNEL JFET,5434

TRANS,NPN CATV SILICON,MPSH17 TRANS,N CHANNEL JFET,5432 (TO-92) TRANS,P CHANNEL JFET,J270 (TO-92)

SA-3 GR-6

cs-545 CS-612-15 CS-389-5 CS-288-2

RL-141 RL-117 RL-119 RL-129 RL-117

CS-287-10 CS-287-3

236-601 TG-47 TG-167-l TG-62 TG-84 TG-219 TG-159 TG-128-l TG-179

TG-221 TG-198 TG-166

RI01 R102 R103,106,109 R104 R107 RllO Rl15 Rll9

R12 R124 R125 Rl26,137,190 R128 Rl29..131 Rl3,29,74,75,

153,155,188,189 R132 Rl34,135 RES,l00K,10%,l/2W,COMPOSITION R138 RES,22K,l0%,l/2W,COMPOSITION Rl39..146 RES,794,.1%,1/lOW,METAL FILM

RES,l2.4K,l%,l/8W,METAL FILM RES,820K,5%,1/4W,COMPOSITION OR FILM RES,l BOK,5%,1/4W,COMPOSITION OR FILM RES,Sl K,5%,1/4W,COMPOSITION OR FILM RES,1.5M,5%,1/4W,COMPOSITlON OR FILM RES,300K,5%,l/4W,COMPOSITION OR FILM RES,200K,5%,1/4W,COMPOSlTlON OR FILM RES,4.99K,l%,l/8W,METAL FILM RES,lOG,2%,1.5W,HY MEG RES,2.4K,5%,1/4W,COMPOSlTlON OR FILM RES,75K,l%,l/8W,METAL FILM RES,l00,1%,1/8W,METAL FILM RES,681,.1%,1/10W,METAL FILM RES,732K,l%,l/4W,PRECISION THIN FILM RES,lOK,.l%,l/lOW, METAL FILM

RES,51 K,5%,1/4W,COMPOSlTlON OR FILM

R-88-l 2.4K R-76-820K R-76-l 80K R-76-91 K R-76-l .5M R-76-300K R-76-200K R-88-4.99K R-289-l OG R-76-2.4K R-88-75K R-88- 100 R-263-681 R-368-732K R-263-l OK

R-76-51 K R-l -1 OOK R-l -22K R-263-794

R14 R147 R15 R150 Rl52,154 R156 Rl6..18 Rl60,161 R163 Rl64,165 RI66 R167 R169 R170 R175 RI 77..184, Rl99..201 R185 Rl91 R2 R20,22 R25,32..35,49,

81,174

R26,192,194 R27,30,171 ..173 R28 R3,21,23,24,133 R31,100,114, 127,159,168,

196..198 R38 R39 R4 R40 R41 R43,54,83,84, 148,149 R44,187 R45,56,57,72, 73,79,80,186 R46 R47,48,116..118,

120..122,136, 176,195

’ R5,6

R50,52,53,66, 71,105,108 R51 R55,82 R58,67 R7 R76 R77 R78

RES, 13.82K, .l%,l/L)W,METAL FILM RES,2734K,.l%,l/aW,METAL FILM RES,300K,.1%,1/8W,METAL FILM

RES,5.lK,5%,1/4W,COMPOSlTlON OR FILM RES,l.8M,5%,1/4W,COMPOSITlON OR FILM RES,l37K,l%,l/aW,METAL FILM RES,lM,O.l%,1/4W,METAL FILM RES,l OK,1 0%,1/2W,COMPOSITION RES,2K,5%,1/4,COMPOSITION OR FILM RES,3.9K,5%,1/4W,COMPOSlTlON OR FILM RES,51 K,5%,1/4W,COMPOSITION OR FILM RES,56.2K,l%,l/aW,METAL FILM RES,5l0,5%,l/4W,COMPOSITION OR FILM RES,250,.l%,l/lOW,WIRE WOUND RES,l M,5%,1/4W, COMPOSITION OR FILM RESISTOR

RES,lOM,5%,l/4W,COMPOSITION OR FILM RES,l82K,l%,l/8W,METAL FILM RES,l OK,1 O%,l W,COMPOSITION RES,l3K,5%,1/4W,COMPOSITION OR FILM RES,560K,5%,1/4W,COMPOSITION OR FILM

RES,lOOK,.l%,l/lOW,METAL FILM

SELECTED RESISTOR SET

RES,49.9,1%,1/8W,COMPOSITION OR RES,lO.lOlK,.1%,75W,WIREWOUND RES,l00K,5%,l/4W,COMPOSITION OR FILM

RES,998K,.l%,l/IW,METAL FILM RES,9.88M,0.5%,1/2W,l200V,METAL OR FILM RES,5.6K,5%,1/4W,COMPOSITION OR FILM RES,lG,2%,1.5W,HY MEG RES,lOOM,1%,1.5W,HY MEG RES,lOK,l%,1/8W,METAL FILM

RES,SOK,.1%,1/8W,METAL FILM RES,lOK,.1%,1/8W,METAL FILM

RES,l5K,5%,1/4W,COMPOSITION OR FILM RES,1OK,5%,l/4W,COMPOSITION OR FILM

RES,lK,5%,1/4W,COMPOSlTlON OR FILM RES,20K,5%,1/4W,COMPOSITION OR FILM

RES,243K,5%,1/4W,COMPOSlTlON OR RES,l50,5%,1/4W, COMPOSITION OR FILM RES,l.l M,5%,1/4W,COMPOSITION OR FILM RES,51,5%,1/4W,COMPOSlTlON OR FILM RES,237,1%,1/8W,METAL FILM RES,4.5K,.l%,l/lOW,METAL FILM RES,7.39K,.l%,l/lOW,METAL FILM

R-377-l 3.82K R-377-27.4K R-377-300K R-76-5.1 K R-76-l .8M R-88-l 37K R-374-l M R-1-1OK R-76-2K R-76-3.9K R-76-51 K R-88-56.2K R-76-51 0 R-291 -250 R-76-l M R-385-l 0.92

R-76-l OM R-88-l 82K R-2-l OK R-76-l 3K R-76-560K

R-263-l OOK 238-600 R-88-49.9 R-384-l 0.101 K R-76-l OOK

R-264-998K R-265-9.88M R-76-5.6K R-289-l G R-289-l OOM R-88-l OK

R-377-90K R-377-l OK

R-76-l 5K R-76-l OK

R-76-l K R-76-20K

R-88-243K R-76-l 50 R-76-l .l M R-76-51 R-88-237 R-263-4.5K R-263-7.39K

R8,157 R85,151 R86,87 R89,193 R9,42,68,123,

162 R92,94 R93,95

R96

R97

R98

RES,49.9K,l%,l/aW,METAL FILM RES,l9.6K,1%,1/8W,METAL FILM RES,lOOK,.1%,1/8W,METAL FILM RES,ll.lK,.l%,l/8W,METAL FILM RES,l K,5%,1/4W,COMPOSITION OR FILM

RES,2.2K,5%,1/4W,COMPOSlTlON OR FILM RES,3.57K,5%,1/4W,COMPOSITION OR RES,l.24K,l%,l/BW,METAL FILM RES,82K,5%,1/4W,COMPOSlTlON OR FILM RES,l8K,5%,1/4W,COMPOSlTlON OR FILM

R-88-49.9K R-88-l 9.6K R-377-l OOK R-377-l 1.1 K R-76-l K

R-76-2.2K R-88-3.57K R-88-l .24K R-76-82K R-76-l 8K

TE2,3,6..8,10, TERMINAL (TEFLON)

12,14,16..19,

22..29 TE20,21 TEFLON TERMINAL

Ul,45,48,50

U10,31,52

Ull

Ul8

u19,47

U2,3

U23,25

U26,28,29,35,

41..43,53

u30

U32

u33 u34 u37 U38 U4,8,13,14,17 u44 U46 u49 U5,7,21,22,24 u51 U6 u9,12,15

IC,SPST CMOS ANALOG SWITCH,DG211 IC,QUAD COMPARATOR,LM339

IC,WIDEBAND CURRENT BUFFER,LH4001 IC,22V OP-AMP,OP-07 IC,2OV OP-AMP,LT1055CN8 IC,OP-AMP,OPAl28 IC-542 IC,l4-BIT CMOS D/A CONVERT,AD7538KN lC,8 STAGE SHIFT/STORE REGISTER,4094

IC,QUAD 2-l LINE DATA SELEC/MULT,74HC158 !C,QUAD LOW POWER JFET,LF444 IC,QUAD 2 INPUT POS AND,74HC08 IC,DUAL D-TYPE FLIP FLOP,74HC74 IC,DARLINGTON ARRAY,2003 IC, 3 TO8 LINE DECODEWDEMULTl,74HCl38 IC,l8V BIFET OP-AMP,AD744 IC,RETRIG MONO MULTIVIB,74HCl23 IC,OCTAL BUFFER,74HC244N IC,SPST CMOS ANALOG SWITCH,DG271 IC,15V OP-AMP, 1007 IC,LOW-PWR BIFET OPAMP,AD648 IC,CMOS SERIAL INPUT 12-BIT DAC,MP7543 IC,DUAL HIGH SPEED OP-AMP,LTl057ACN8

TE-97-l

TE-111

IC-320 IC-219 IC-572 IC-207 IC-672

IC-601 IC-251

IC-587 IC-329 IC-465 IC-337 IC-206 IC-431 IC-586 IC-492

IC-469 IC-508 IC-422 IC-719 IC-419 IC-590

VRl,6 DIODE,ZENER 15V,l N4744A (TO-41)

VRll DIODE,ZENER 6.4V,lN4579 (DO-7)

VRl4,15 DIODE,ZENER 2OOV,l N5388A (CASE 17)

VR2,5 DIODE,ZENER 4.3’.‘,1 N749A (DO-7)

VR3,4

VR9,lO DIODE,ZENER 15V,l N718 (DO-7)

DIODE, ZENER, 12V,IN9638

DZ-75 DZ-73 DZ-74 DZ-63 DZ-54 DZ-18

TABLE 2. MODEL 238 DIGITAL BOARD, PARTS LIST

CIRCUIT DESIG.

AT1 ..3,7,8 AT5 AT6

BTl

:iO 118 ClOii,lO7 ClO8,109 c110,119 Cl16 Cl20 Cl21..146 Cl47..176 c15..17,24,33,94

::2 54 c53:55 C56,57 C58,59 C63 C64 C67 C68,70,72

:771 C73,89..93,

95..97

DESCRIPTION

IC,DUAL HIGH CMR/SPEED OPTO,HCPL-2631 IC,OPTPCOUPLER,2601 IC,OPTOCOUPLER,HCPL-2400

BATTERY, LITHIUM BATTERY HOLDER

CAP,33PF,lO%,lOOOV,CERAMIC CAP,1 O,OOOUF,20%,35V,ALUM ELEC CAP,.1 UF,20%,50V,CERAMIC CAP, .02,20%,.5OOV CERAMIC CAP, .l UF,20%,1 OOV EPOXY CAP,71 OPF,2%,50V,CERAMIC CAP,.01 UF,20%,50V,CERAMIC CAP,.01 UF,20%,50V,CERAMIC CAP,.1 UF,20%,50V,CERAMIC CAP, 1 OUF,-20+100%,25V,ALUM ELEC CAP,1 OOOOUF,-20+30%,25V,ALUM ELEC CAP,1 OOUF,20%,63V,ALUM ELEC CAP,1 OOOUF,-10+100%,35V,ELECTROLYTIC CAP,1 OOUF,-10+100%,35V,ALUM ELEC CAP,560UF,20%,200V,ALUM ELEC CAP,.0047UF,l O%,l OOV,POLYPROPYLENE CAP,820PF,lO%,l OOOV,CERAMIC CAP,22PF,l O%,l OOOV,CERAMIC CAP,47PF,l O%,lOOOV,CERAMIC CAP,4700UF,-20+1 OO%,l GV,ALUMINUM CAP,22PF,20%,500V,CERAMlC CAP,1 UF,20%,50’.‘, CERAMIC

KEITHLEY PART NO.

IC-588 IC-239 IC-464

BA-44 BH-34

C-64-33P c-433-1 0000 C-237-. 1 c-22-.02 C-41 6-.l C-348-71 OP C-365-.01 C-365-.01 C-365-. 1 c-314-1 0 C-342-l 0000 c-403-1 00 c-309-1 000 c-295-1 00 C-355-560 C-306-.0047 C-64-820P C-64-22P C-64-47P c-31 3-4700 c-22-22P C-237-l

CR1 CR12 CR13..16,19,20,

23..26 CR2,3,6,7 CR27 CR4,5 CR8..11

JlO J16,23 J18 J20 J22 J8

DIODE, BRIDGE PE05 DIODE,BRIDGE,KBU4B (CASE KBU) DIODE,SILICON,IN4148 (DO-35)

DIODE,SWITCHING,IN4607 (DO-35) DIODE,SILICON,SCHOTTKY,SBl20 DIODE,BRIDGE,VM18 DIODE,SILICON,IN4006 (DO-41)

FUSE, 1.25A,250V FUSE HOLDER FUSE CARRIER

CONN,RIGHT ANGLE,24PIN MODIFIED, CONNECTOR MODIFIED, CONNECTOR MODIFIED CONNECTOR MODIFIED, CONNECTOR CONN, MALE, 3 PIN

CHOKE, 1 -UH

RF-48 RF-64 RF-28

RF-41 -1 RF-78 RF-52 RF-38

FU-28 FH-21 FH-25

cs-507 590-314-4 590-314-10 236-329A 590-314-3 CS-288-3

CH-16

CABLE ASSEMBLY

CA-27-l 2C

TRANS,N-CHANNEL FET,TNOGL TRANS, N CHANNEL JFET,PN5434(TO-92) TRANS,N CHANNEL DUAL FET,MP842 (TO-52) TRANS,NPN SILICON,2N3904 (TO-92) TRANS,N CHANNEL FET,2N4392 (TO-92) TRANS,TRIODE THYRISTOR,MAC223-6

RI R15,17,50,80,87, RES,lK,5%,1/4W,COMPOSITlON OR FILM go,91 R16,23 R2 R20..22,71,81 R25,72,77 R3,4,10,11,28,

83..86,89 R32 R33

‘R34

R35,75,76 R36 R37 R38,39,59..62,65 RES,1OK,5%,1/4W,COMPOSITION OR FILM R41 R42 R43 R44,47 R45,48 R46 R49,52 R51 RES,2.15K,1%,1/8W,METAL FILM R53 R54 R55 R56 R57 R58 R6,8 R63 R64 R7,R9 RES,243,1%,1/8W,METAL FILM R70 R73,74 RES,l5K,10%,2W,COMPOSITION R78,79 R82 R92 R93 R94,95

RES,430,5%,1/4W,COMPOSITION OR FILM

RES NET,3.3K,5%,1.25W RES,330,5%,1/4W,COMPOSlTlON OR FILM RES,lO0,5%,1/4W,COMPOSlTlON OR FILM RES,3.3K,5%,1/4W, COMPOSITION OR FILM RES,470,5%,1/4W,COMPOSlTlON OR FILM

RES,560K,5%,1/4W,COMPOSlTlON OR FILM RES,6.2K,5%,1/4W COMPOSITION OR FILM RES,2K,5%,1/4,COMPOSlTlON OR FILM RES,47K,5%,1/4W,COMPOSITION OR FILM RES,l00,1%,1/8W,METAL FILM RES,4.87K,l%,l/aW,METAL FILM

RES,l42.2K,.02%,1/8W,PRECISION THIN FILM RES,l00K,5%,l/4W,COMPOSITION OR FILM POT,lOK,10%,.5W,NON-WIREWOUND RES,200,5%,1/4W,COMPOSITION OR FILM RES,20K,1%,1/8W,METAL FILM RES,32.4K,l%,l/SW,METAL FILM RES,7.87K,1%,1/8W,METAL FILM

RES,l5,4K,1%,1/8W,METAL FILM RES,lOK,l%,l/8W,METAL FILM RES,7.78K,.02%,1/8W,PREClSlON THIN FILM RES,lM,5%,1/4W, COMPOSITION OR FILM RES,15K,5%,1/4W,COMPOSITION OR FILM RES,5.1K,5%,1/4W,COMPOSITION OR FILM RES,5.62K,l%,l/aW,METAL FILM RES,5l.lK,l%,1/8W,METAL FILM RES,26.7K,l%,l/8W,METAL FILM

RES,996K,.l%,l/4W,METAL FILM

RES,4.3K,5%,1/4W,COMPOSlTlON OR FILM RES NET,1 K,2%,1.7OW RES,510,5%,1/4W,COMPOSITION OR FILM RES,270,5%,1/4W,COMPOSITION OR FILM

RES,5.6K,5%,1/4W,COMPOSlTlON OR FILM

TG-216 TG-174-l TG-175 TG-47 TG-128-l TG-172

R-76-430 R-76-l K

TF-140

R-76-330 R-76-l 00 R-76-3.3K R-76-470

R-76-560K R-76-6.2K R-76-2K R-76-47K R-88-l 00 R-88-4.87K R-76-l OK R-365-l 42.2K R-76-i OOK RP-97-1 OK R-76-200 R-88-20K R-88-32.4K R-88-7.87K R-88-2.15K R-88-i 5.4K R-88-l OK R-365-7.78K R-76-l M R-76-l 5K R-76-5.1 K R-88-5.62K R-88-51 .I K R-88-26.7K R-88-243 R-264-996K R-3-l 5K R-76-4.3K

TF-180-3

R-76-51 0 R-76-270 R-76-5.6K

SWITCH,PUSHBUTTON (6 POLE) SWITCH,SLIDE (DPDT) SWITCH,PUSHBUTTON (2 POLE)

TR-277B (JAPAN) TRANSFORMER, ASSY TR-276

SW-466 SW-476 SW-469

TPI ,2

CONN,TEST POINT

cs-553

i112 u-l 3,30 Ui 4,28 Ui 5,25 U16 u17 U18,19,58 U21,40,46 U23 U26 U27 u29 u31 U32,47 u33 u34 u35 U36 U38 u39 u41 U42,44 U43,52 u45 U48 u49,55 u50 u51,57,59 u54 U56

IC,PAL,20LlO IC,CMOS DUAL PORT RAMJDT7130 IC,32KX8 STATIC CMOS RAM,D43256C-15L IC,VERSATILE INTERFACE ADAPTER,G65SC22

IC,8 BIT MICROPROCESSING UNIT,MC68B09 IC,lO INPUT AND-OR-INVERT ARRAY,PAL16L8 EPROM PROGRAM IC,12 STAGE BINARY COUNTER,74HC4040 IC,DUAL 4 BIT COUNTER,74HCT393 IC,HEX INVERTER,74HC05 IC,i 0 INPUT AND-OR-INVERT ARRAY,PAL16L8 IC,GPIB ADAPTER,9914A IC,NONVOLATILE CONTROLLER DSI 210 EPROM PROGRAM IC,QUAD 2 INPUT NOR,74HC02 IC,PROGRAMMABLE E2ROM 2816B IC,OCTAL INTERFACE BUS,751 60 IC,OCTAL INTERFACE BUS TRANSCEIVER,751 61 IC,SUPPLY VOLTAGE SUPERVISOR,TL7705AC IC,OCTAL BUFFER,74HC244N IC, 3 TO8 LINE DECODER/DEMULTl,74HCl38 IC,DUAL 4 BIT DECADE COUNTER,74HC390 IC,8 STAGE SHIFT/STORE REGISTER,4094 IC,TRIPLE 2 CH MULTI/DEMUX,4053 IC,8 BIT IDENTITY COMP,74HC688 IC,QUAD COMPARATOR,LM339 IC,DUAL D-TYPE FLIP FLOP,74HC74 IC,DUAL LOW NOISE OP-AMP,5534

IC,HEX INVERTER,74HC04 IC,QUAD 2 INPUT NAND,74HCOO IC,DUAL LOW NOISE OP-AMP,NE5532 USE ON TR WIRING CABLE TIE

IC-643 LSI-88 LSI-76 LSI-86 LSI-65 IC-582 238-800-•* IC-407 IC-462 IC-466 IC-682 LSI-49 IC-541 238-801-•* IC-412 LSI-83 IC-298 IC-299 IC-602 IC-469 IC-43 1 IC-500 IC-251 IC-283-l IC-488 IC-219

IC-337 IC-540 16-354 IC-351 IC-501

CC-38-2 VRl

VR2 VR3 VR4 VR5 VR6 VR7,8 VR9, IO

Yl Y2

**ORDER CURRENTLY INSTALLED FIRMWARE LEVEL. FOR EXAMPLE, IF THE FIRMWARE

REVISION LEVEL IS A06, ORDER PART NUMBER 238-800-A06 AND 238-801-A06.

IC,a5V REGULATOR,20MA,LM323 HEAT SINK RIVET, l/8 DIA. X 3/i 6 LG (1) STAKING, HS-25 RIVET, i/8 DIA. X 3116 LG (1) STAKING, HS-25 RIVET, l/8 DIA. X 3116 LG (1) STAKING, HS-25 IC,VOLTAGE REGULATOR,LM317MP IC,VOLTAGE REGULATOR,LM337MP DIODE,ZENER 15V,l N4744A (TO-41) DIODE, ZENER 1 OOV, IN5378B

OSCILLATOR, 8MHZ CRYSTAL, 7.68MHZ

IC-240

HS-22

32469-2 32469-5

32469-6 IC-308 IC-309 DZ-75 DZ-72-2

CR-25-4 CR-29

TABLE 3. MODEL 238 DISPLAY BOARD, PARTS LIST

CIRCUIT DESIG.

Cl ..4 c5

CRl..lO

DSl..9 DSI 0..28

P24

Rl..23,25,27,

29..31.33.34 R24 R26 R28,32

Sl S2..34

;:78 U5:6:9,10

DESCRIPTION

CAP,.OlUF,20%,50V,CERAMlC CAP, 1 OUF,-20+100%,25V,ALUM ELEC

DIODE,SILICON,IN4148 (DO-35)

DIGITAL DISPLAY PILOT LIGHT,RED,LED LED MOUNTS

CABLE ASSEMBLY, 20 CONDUCTOR

RES,82,5%,1/4W,COMPOSITION OR FILM

RES, 15, 5%, i/4 COMPOSITION OR FILM RES, 15, 5%, i/4 COMPOSITION OR FILM RES,3.3K,5%,1/4W, COMPOSITION OR FILM

DIGITAL CONTACTING ENCODER SWITCH, MOMENTARY

IC,QUAD 2 INPUT NOR,74HC02 IC,l2 STAGE BINARY COUNTER,74HC4040 1 OF 10 DECODER, 74HC42 IC,8-CHANNEL SAT SINK DRIVER,UDN-2596A IC,&BIT SERIAL-INPUT,UNC5895A

KEITHLEY PART NO.

C-365-.01 c-314-1 0

RF-28

DD-39 PL-71 MK-22-1

CA-27-9

R-76-82

R-76-l 5 R-76-l 5 R-76-3.3K

SW-472 SW-435

IC-412 IC-407 IC-583 IC-578 IC-537

TABLE 4. MODEL 238 OUTPUT MODULE, PARTS L&T

CIRCUIT

DESIG.

c10,12 c17,19 c20 c21,30 C22,23 C24,25 C26,28 c27,29

CR1 8,26 CR1 9,27 CR20,21 CR7,9 CR8,10..12,17,

22..25

P16,23

Q1,2 Q18,23 Q19,25 Q21,24 Q27 Q34,40 Q35 Q36 Q37 Q38 Q39,44,45,47 Q41 Q42 Q43,46 Q7,8 Q9,20,22,26,28

DESCRIPTION

CAP,3300PF,5%,500V,DlPPED MICA CAP,.O1UF,10%,1000V,CERAMIC CAP,.01 UF,20%,50V,CERAMIC CAP,1 UF,20%,5OV, CERAMIC CAP,1800PF,1%,500V,MICA CAP,3300PF,10%,100V,CERMANIC CAP,2200PF,l%,500V,MICA CAP,6800PF,l %,I OOV,MICA

DIODE,SWITCHING,IN4149 (DO-35) DIODE,1 N5404 DIODE,SCHOTTKY, IN571 1 DIODE,SILICON,lN4148 (DO-35) DIODE,SILICON,l N4937

RELAY,HIGH SENSITIVITY,1 8W-K

HOUSING, CONNECTOR

TRANS,N CHAN MOSPOW FET,2N7000 (TO-92) TRANS,N-CHANNEL FET,IRF630 TRANS,PNP POWER,MJE350 TRANS,NPN SILICON,MJE340 TRANS,PNP SILICON 2N3906 (TO-92) TRANS,P-FIELD EFFECT,MTP20POG TRANS,PNP POWER TRANS, TIPlOG(T0 220) TRANS,P-CHANNEL DMOSFET,VPOl04N3(TO-92) TRANS,PNP POWER TRANS,MJE250(TO-220) TRANS,NPN POWER TRANS, TIP101 (TO 220) TRANS,NPN COMP SILICON AMP,2N5089 TRANS,N-CHANNEL DMOSFET,VNOlOl NS(TO-92) TRANS,NPN POWER TRANS,MJE240(TO-220) TRANS,N-FIELD EFFECT,MTPBONO8 TRANS,P-CHANNEL 200V FET,lRF9630 TRA’NS,NPN SILICON,2N3904 (TO-92)

KEITHLEY PART NO.

C-236-3300P C-64-.01 C-365-.01 C-237-l C-209-1800P c-430-33OOP C-278-2200P C-248-6800P

RF-60 RF-74 RF-69 RF-28 RF-71

RL-140

CS-287-4

TG-195 TG-214 TG-210 TG-209 TG-84 TG-229 TG-231 TG-193 TG-186 TG-230 TG-62-1 TG-192 TG-185 TG-228 TG-215 TG-47

RI,2 R18,19 R20,34,36,39 R21..23,28,37, 38,47,50,55,60, 63,65 R24,26 R25,27 R29,30 R31,32 R45,46 R48,51 R49,52 R53,54 R56,58

RES,158,1%,1/8W,METAL FILM RES,l.lM,5%,1/4W,COMPOSITION OR FILM RES,3.3M,5%,1/4W,COMPOSITION OR FILM RES,51,5%,1/4W,COMPOSlTlON OR FILM

RES,26.1,1%,1/8W,METAL FILM RES,619,1%,1/8W,METAL FILM RES,27.4,1%,1/8W,METAL FILM RES,11.3K,1%,1/8W,METAL FILM RES,l M,5%,1/4W, COMPOSITION OR FILM RES,lOK,5%,1/4W,COMPOSITION OR FILM RES,.51,5%,1 W,COMPOSITION OR FILM RES,2.2M,5%,1/4W,COMPOSITION OR FILM RES,1.8M,5%,1/4W,COMPOSlTlON OR FILM

R-88-l 58 R-76-l .I M R-76-3.3M R-76-51

R-88-26.1 R-88-61 9

R-88-27.4 R-88-l 1.3K R-76-l M R-76-l OK R-357-.51 R-76-2.2M R-76-l .8M

R57,59 R61,64 R62,66 R67,68

RES,100K,5%,1/4W,COMPOSlTlON OR FILM R-76-1 OOK RES,l.5M,5%,1/4W,COMPOSITION OR FILM RES, 680K, 5%,1/4W, COMPOSITION OR FILM RES,470,5%,1/4W,COMPOSITION OR FILM R-76-470

TX-17x1/4x1 l/2 P15 CONNECTOR, HOUSING

R-76-l .5M R-76-680K

CS-638-15

VRl,2 DIODE,ZENER 6.44VJN4577AGED (DO-7)

DZ-58

TABLE 5. MODEL 238 MISCELLANEOUS, PARTS LIST

CIRCUIT DESIG.

KEITHLEY

DESCRIPTION

OVERLAY, FRONT PANEL 238-302

LINE CORD PUSHBUTTON PUSHBUTTON PUSHBUTTON PUSHBUTTON REAR FOOT MOUNTING RAILS 228-3 19 FRONT PANEL 236-304 KNOB 236-305

A/D SHIELD 236-311

OUTPUT SHROUD 236-3 12 WINDOW (RED) BOTTOM SHIELD INNER SHIELD 236-316

TOP SHIELD, ANALOG BOARD 236-3 17

BOTTOM SHIELD INSULATOR 236-323 FILTER SHROUD 236-332 REAR PANEL 236-309 POWER SUPPLY SHIELD 238-306 SUPPORT, PRINTED CIRCUIT BOARD 228-318 CABLE ASSY 3 LUG TRIAX MODIFIED, PRINTED CIRCUIT SUPPORT 228-314-2 BOTTOM SHIELD CAP FILTER FAN FN-25 CAP,1 OOPF,l O%,l OOOV,CERAMIC C-64-i OOP SUPPORT, PRINTED CIRCUIT BOARD TRIAX CONNECTOR CONNECTOR, RIGHT ANGLE SMB TRIAX CONNECTOR CONNECTOR, RIGHT ANGLE SMB cs-759 DECORATIVE STRIP ASSEMBLY DECORATIVE STRIP ASSEMBLY

PART NO.

co-7 228-317-4 228-317-5 228-317-6 228-3 17-7

FE-21

236-314-l 236-315

CA-63- 10

ST- 137-2 CAP-28-1 FL-9

228-318

CS-723 cs-759 CS-723

193-322 193-323

Ji ,2 J25,26

5 J5

J6,7 J9

P20 P22

CABLE ASS’Y (TRIAX, RIGHT ANGLE SMB) CONNECTOR, 3 PIN MALE CABLE ASS’Y (TRIAX, RIGHT ANGLE SMB) BINDING POST BINDING POST (METAL) CONNECTOR,BNC

LINE FILTER

HOUSING, CONNECTOR

CONNECTOR, HOUSING

FRONT FOOT ASSEMBLY

TOP COVER

BOTTOM COVER

CA-72-2 CS-659 CA-72-l BP-1 1-O BP-l 5 cs-249 LF-2

CS-287-5 CS-287-3 706-317 236-324 228-313

Service Form

Model No.

Serial No.

Date

Name and Telephone No. Company

List all control settings, describe problem and check boxes that apply to problem.

Cl Intermittent

m IEEE failure m Front panel operational

Display or output (check one) m Drifts

a Unstable Q Overload

0 Calibration only Q Data required

(attach any additional sheets as necessary) Show a block diagram of your measurement system including all instruments connected (whether power is turned on or not).

Also, describe signal source.

0 Analog output follows display

m Obvious problem on power-up Q All ranges or functions are bad

0 Unable to zero a Will not read applied input

a Certificate of calibration required

0 Particular range or function bad; specify

0 Batteries and fuses are OK m Checked all cables

Where is the measurement being performed? (factory, controlled laboratory, out-of-doors, etc.)

What power line voltage is used?

Relative humidity?

Any additional information. (If special modifications have been made by the user, please describe.)

Be sure to include your name and phone number on this service form.

Other?

Ambient temperature?

“F

Keithley 238 Service Manual

Specifications and Main Features

Frequently Asked Questions

User Manual