Tektronix 175 Instruction Manual

Instruction Manual

Model 175

Autoranging Multimeter

01983, Keithley Instruments, Inc.

Cleveland, Ohio, U.S.A.

Document Number 175-901-01

SPECIFICATIONS

TABLE OF CONTENTS

Paragraph

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

2.1

2.2

2.3

2.3.1

2.3.2

2.3.3

2.4

2.4.1

2.4.2

2.4.3

2.4.4

2.5

2.6

2.6.1

2.6.2

2.7

2.7.1

2.7.2

2.7.3

2.7.4

2.7.5

2.7.6

2.7.7

2.7.8

2.7.9

2.7.10

2.7.11

2.8

2.8.1

2.8.2

2.8.3

2.8.4

3.1

3.2

3.3

3.4

3.5

3.5.1

3.5.2

3.5.3

3.5.4

3.5.5

‘SECTION l-GENERAL INFORMATION

Introduction .............................

Getting Started ..........................

Unpacking and Inspection .................

Specifications ...........................

Warranty Information .....................

Manual Addenda .........................

Safety Symbols and Terms.

Optional Accessories. .....................

SECTION 2-BENCH OPERATION

Introduction ....................................

High Energy Circuit Precautions. ...................

Preparation for Use ..............................

LinePower.. .................................

Battery Pack Power. ...........................

Batten, Charging ..............................

Front Panel Familiarization ........................

Display ......................................

Front Panel Controls ...........................

Input Terminals ...............................

Current Fuse Replacement ......................

Error Messages .................................

Operating Conditions ............................

Environmental Conditions. ......................

Maximum Allowable Input ......................

Basic Bench Measurements .......................

Power-Up

Relative Mode ................................

DC Voltage Measurements. .....................

TRMS AC Voltage Measurements.

Resistance Measurements ......................

Current Measurements (DC or TRMS AC) .........

AC Plus DC Measurements .....................

dl3 Measurements .............................

dl3 Measurement Considerations and Applications

MINtMAX and 100 Point Logger Operation .......

DiodeTest ...................................

TRMS Consideration .............................

AC Voltage Offset .............................

TRMS Measurements Comparison ...............

Crest Factor ..................................

Extended Frequency Response ..................

SECTION 3-PERFORMANCE VERIFICATION

Introduction ....................................

Environmental Conditions .........................

Recommended Test Equipment. ...................

Initial Conditions ................................

Verification Procedure ............................

DC Voltage Accuracy Check ....................

AC Voltage Accuracy Check ....................

Resistance Accuracy Check

DC Current Accuracy Check ....................

AC Current Accuracy Check ....................

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

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

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

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

Title

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

......

..........

......

... ..

......

Peg.3

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

2-1 2-1 2~1 2-l 2-l 2-1 2~2 2-2 2-2 2-3 2-3 2-3 2-3 2-3 2-4 2-4 2-4 2-4 2-4

2-9 2-9 2-9

3-2 3-2 3-2 3-3

TABLE OF CONTENTS

Paragraph

4.1

4.2

4.3

4.3.1

4.3.2

4.3.3

4.3.4

4.3.5

4.3.6

4.4

4.4.1

4.4.2

4.4.3

4.4.4

4.5

4.6

4.7

5.1

5.2

5.3

5.4

5.4.1

5.4.2

5.4.3

54.4

5.4.5

5.5

5.6

5.7

5.7.1

5.7.2

5.7.3

5.7.4

5.7.5

5.7.6

5.7.7

5.7.8

Title Page

SECTION 4-THEORY OF OPERATION

Introduction ..................................................................................

Overall Functional Description ...................................................................

AnalogCircuitry ...............................................................................

Multiplexer .................................................................................

InputBufferAmplifier ........................................................................

~2VRefetenceSource ........................................................................

AiDConverter ..............................................................................

Input Signal Conditioning .....................................................................

ACConverter ...............................................................................

DigitalCircuitry ...............................................................................

Microcomputer .............................................................................

AddressDecoding ...........................................................................

PIA .......................................................................................

Display Board

DigitalCalibration .............................................................................

PowerSupply ................................................................................

Model17588atten/Option ......................................................................

SECTION 5-MAINTENANCE

Introduction ..................................................................................

Top Cover Removal/Installation .................................................................

Batten/ Pack (Model 1768) Installation .............................................................

Troubleshooting ..............................................................................

RecommendedTestEquipment ................................................................

SelfDiagnosticProgram ......................................................................

PowerSupplyChecks ........................................................................

AfDConverterandDisplay ...................................................................

Signalconditioning ..........................................................................

LineFuseReplacement .........................................................................

Special Handling of Static Sensitive Devices .......................................................

Front Panel Calibration .........................................................................

Recommended Calibration Equipment ..........................................................

CalibrationJumper.. ........................................................................

Environmentalconditions .....................................................................

DC Voltage Calibration

ACVoltageCalibration .........................................................................

Resistance Calibration. .......................................................................

Frequencycompensation .....................................................................

CalibrationStorage ............................................................................

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

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

4-l 4-1 4-l 4-2 4-2 4-2 4-2 4-3 4-4 45 4-5 4-5 4-5 4-5 4-5 4-5 4-5

5-1 5-l 5-l 5-l 5-l 5-2 5-4 5-4 5-4 5-6 5-6 5-7 5-7

5-7

5-7 5-8

5-8 59

6.1

6.2

6.3

6.4

6.5

SECTION 6-REPLACEABLE PARTS Introduction

ReplaceableParts .............................................................................

Orderinginformation

FactoryService.. .............................................................................

Component Location Drawings and Schematic Diagrams ...........................................

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

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

6-l 6-l 6-l 6-l 6-l

LIST OF ILLUSTRATIONS

Figure 2-1 2-2 2-3 2-4 2-5 2-6

2-7

4-1

4-2

4-3

4-4

4-5

4-6

5-l

5-2

6-l

6-2

6-3

6-4

6-5

6-6

6-7

6-8

Title

Model175FrontPanel ..................................................

DC Voltage Measurements.

TAMS AC Voltage Measurements.

Resistance Measurements ...............................................

Current Measurements Between 2000mA and 20A.

Current Measurements up to 2000mA

Model 175 Typical AC Frequency Response

Simplified Block Diagram ................................................

Simplified Schematic of the Multiplexer

Simplified Schematic of the Input Buffer Amplifier ...........................

AIDConverter .........................................................

Resistance Measurements Ratiometric Technique. ...........................

Simplified Schematics of Ohms Circuitry

Segment Identification ..................................................

CalibrationJumper.. ...................................................

Modell75ExplodedView ................................................

Model 175 Display Assembly .............................................

Display Board, Component Location Drawing, Dwg. No. 175-110. ..............

Model 1758 Battery Pack, Component Location Drawing, Dwg. No. 1755.100 ....

Mother Board, Component Location Drawing, Dwg. No. 175-100 ..............

Mother Board, Schematic Diagram, Dwg. No. 175.106 .......................

Display Board, Schematic Diagram, Dwg. No. 175.116

Model 1758 Battery Pack, schematic Diagram, Dwg. No. 1758-106 .............

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

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

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

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

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

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

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

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

Page

2-2 2-5 2-5

2-6 2-6 2-6

2.11 4-l 4-2

4-2 4-3 4-4 4-4 5-2 5-9 6-2 6-3 6-9

811 6-13

6-17 6-21 6-23

iii

LIST OF TABLES

Table 2-l 2-2 2-3 2-4 2-5 2-6 3-l 3-2 3-3 3-4 3-5 5-l

5-2

5-3

5-4 5-5 5-6 5-7 5-8 5-9

5-10 6-l 6-2 6-3 6-4

ErrorMessages .....................................

Model 175 Maximum Allowable Inputs ..................

dB Specifications for DC Volts (6OOL1 Refl d8 Specifications for AC Volts (6OOfl Refl

Levels for Other Reference Impedances .................

Comparison of Average and TRMS Meter Readings Equipment Specifications.

Limits for DC Voltage Verification ......................

Limits for AC Voltage Verification ......................

Limits for Resistance Verification .......................

Limits for DC Current Verification ......................

Recommended Troubleshooting Equipment.

Troubleshooting Modes ..............................

Power Supply Checks. ...............................

A/D Converter Checks ...............................

Display Board Checks.. ..............................

Static Sensitive Devices ..............................

Recommended Calibration Equipment ..................

DC Voltage Calibration ...............................

AC Voltage Calibration ...............................

Resistance Calibration.

MotherBoard,PartsList ..............................

Display Board, Parts List. .............................

Model 1758 Battery Pack, Parts List ....................

Model 1758 Spare Pats List. ..........................

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

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

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

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

Title

.......

......

Page

......

SAFETY PRECAUTIONS

The following safety precautions should be observed before operating the Model 175.

This instrument is intended for use by qualified personnel who

recognize shock hazards and are familiar with the safety precautions required to avoid possible injury. Read over the manual carefully before operating this instrument.

Exercise extreme caution when a shock hazard is present at the instru-

ment’s input. The American National Standards Institute (ANSI) states that a shock hazard exists when voltage levels greater than 30V rms or

42.4V peak are present. A good safety practice is to expect that a

hazardous voltage is present in any unknown circuit before measuring.

Inspect the test leads for possible wear, cracks or breaks before each

use. If any defects are found, replace with test leads that have the same

measure of safety as those supplied with the instrument.

For optimum safety do not touch the test leads or the instrument while

power is applied to the circuit under test. Turn the power off and discharge all capacitors, before connecting or disconnecting the instru-

ment.

Do not touch any object which 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.

Exercise extreme safety when testing high energy power circuits (AC

line or mains, etc.). Refer to the operation section.

Do not exceed the instrument’s maximum allowable input as defined in

the specifications and operation section.

MODEL 175 AUTORANGING DMM

Features:

04% Digit LCD Display *Fast Autoranging *Bench or Portable *Digital Calibration

lOO Point Data Logger

10~V/10mW10nA Sensitivity

~0.03% Basic DCV Accuracy

TRMS AC

dBm/Relative Functions

Min/Max Reading Hold *Safety Input Jacks *lOA Capability

lOOkHz Specified AC Bandwidth

Options:

*Model 1758 Rechargeable Battery Pack *Model 1753 IEEE-488 Interface

SECTION 1

GENERAL INFORMATION

1.1 INTRODUCTION

This instruction manual contains the necessary information for operating and maintaining the Model 175 Autoranging

Multimeter and the Model 1758 Rechargeable Battery Pack.

The information is divided into the following sections:

Section 1 contains general information and provides guidelines for using this manual. Important safety information is also presented here.

Section 2 contains detailed bench operation information for the Model 175.

Section 3 contains the information needed to verify the accuracy of the Model 175. Performance verification can be done upon receipt of the unit or whenever the basic accuracy is in question.

For the more technically oriented, information on theory of operation, and maintenance and servicing is contained in Section 4 through 6.

NOTE The Model 1753 IEEE-488 interface comes supplied with its own instruction manual.

1.2 GE-iTING STARTED Perform the following steps in sequence to acquaint yourself

auicklv and safelv with the basic operation of the Model 175.

Verify that the Model 175 was not damaged in transit, es explained in paragraph 1.3.

Carefully read the safety precautions and warnings found preceding this section and the first two sections (General Information and Bench Operation) of this manual.

Referring to paragraph 2.3.1 (Line Power) set the line voltage switch and plug the power cord into a properly grounded outlet. If the optional battery pack is installed the charge circuitry will be activated.

Acquaint yourself with the controls and display of the

Model 175 as follows:

A. Turn on the Model 175 by pressing in the ON/OFF

pushbutton. All of the zeroee will be displayed briefly.

B. Connect the supplied test leads to the

VOLTS/OHMS/mA and COM input jacks, and short them together.

C. Select AC volts and autoranging by pressing in the

AC/DC, V and AUTO pushbuttons. The AC, mV and AUTO annunciators will be displayed. Pressing any of

the other range pushbuttons will put the Model 175 in

manual ranging es indicated by the absence of the AUTO annunciator.

Select DC volts by releasing (outi the AC DC

pushbutton (V still selected]. The AC annunciator will turn off.

Select autoranging ohms by pressing in the !!

pushbutton (DC still selected) and AUTO pushbutton. The n annunciator will turn on. Press the AC:DC pushbutton in (AC selected) and note the “Err” message indicating that this is an invalid mode.

Select AC or DC current by setting the AC DC

pushbutton accordingly and pressing I,? ihe A pushbutton. The annunciator that reflects the selected range will turn on. Note that current will not autorange and that the 10 AMPS and COM input jacks must be used on the 10A range.

Select

5. When you are comfortable with the controls of the Model 175, go on and make the desired meaeurements using Section 2, Bench Operation es a guide.

1.3 UNPACKING AND INSPECTION The Model 175 Bench DMM was carefully inspected, both

mechanically and electrically, before shipment. Upon recelv

ing the Model 175, carefully unpack all items from the ship-

ping carton and check for any obvious signs of physical damage that might have occurred during shipment. Report the damage to the shipping agent immediately. Retain the

dB by placing the Model 175 in AC or DC volts and pressing the dB pushbutton. The dB annunc~etor will turn on. Press the dB button again fo take the

Model 175 out of the dB measurement mode.

REL (relative) can be used with any measurement furw tion: volts, ohms, amps or dB. For example, place the

Model 175 in ohms and autorange. The display wll read approximately 00.141!, which is the test lead resistance. Press the REL pushbutton. The REL any nunciator will turn on and the display will now reed

OO.OOI2. The relative level of 0.1411 will be subtracted

from all subsequent ohm measurements. Press the REL pushbutton a second time to cancel the REL level.

To activate the 100 point DATA LOGGER with MIN/MAX, press and hold in the STOiCLR pushbut-

ton. When the reading rate A = 0 is displayed let go of the button, The ST0 annunciator will turn on Press the RCL pushbutton and the last data point will be

displayed briefly followed by the reading (data]. Other data points can be displayed by holding in the RCL button. Turn off the DATA LOGGER by pressing the

STOlCLR pushbutton again.

1-l

original packing materials in case reshipment becomes necessan/. The following items are included with every Model

175 order:

*Model 175 Autoranging Multimete! *Model 175 instruction Manual

‘Model 1751 Safety Test Lead *Additional accessories as ordered.

1.4 SPECIFICATIONS Detailed Model 175 specifications may be found immediately

preceding the table of contents of this manual.

1.5 WARRANTY INFORMATION

Warranty information may be found on the inside back cover

of this manual. Should it be necessary to exercise thewarranty, contact your Keithley representative or the factory to determine the correct course of action. Keithley Instruments maintains service facilities in the United States, West Germany, Great Britain, France, the Netherlands. Switzerland and Austria. Information concerning the application, operation or service of your instrument may be directed to the applications engineer at any of theses locations. Check the inside front cover of this manual for addresses.

1.6 MANUAL ADDENDA Information concerning improvements or changes to the in-

strument which occur after the printing of this manual will be found on an addendum sheet included with this manual. Be sure to review these changes before attempting to operate or service the instrument.

1.7 SAFETY SYMBOLS AND TERMS

The following safety symbols and terms are used in this manual or found on the Model 175.

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

The symbol ,$ of 1OOOV or more may be present on the terminal(s). Standard safety practices should be observed when such dangerous voltages are encountered.

The WARNING heading in this manual explains dangers that could result in personal injury or death.

The CAUTION heading in this manual explains hazards that could damage the instrument.

1.8 OPTIONAL ACCESSORIES

The following accessories can be used with the Model 175.

Model 1010 Single Rack Mounting Kit-Use to mount

one Model 175 in a standard 5 x X 19” rack.

on the w,trument indicates that a potential

Model 1017 Dual Rack Mounting Kit-Use to mount two Model 175’s in a standard 5 x X 19” rack.

Model 1301 Temperature Probe-A rugged low cost temperature probe designed to allow precision temperature measurements from -55OC to 150°C.

Range: -55’C to 150°C

Output: lmV/OC; compatible with any DMM with at least

IOM12 input impedance. Accuracy: f2OC from O” to 100°C; *YC from -5Y to 0°C and 100’ to 150°C

Power: 9V alkaline or C-Zn (NEDA 1604) battery.

Model 1600A High Voltage Probe-Extends the DMM to

40kV.

Maximum Input: 40kV DC or peak AC to 300Hr

Input Resistance:lOOOM12

Division Ratio: 1OOO:l

Ratio Accuracy: f2.5% from 1kV to 40kV DC, *3.5% if 200mV or 2V ranges of Model 175 are used; -3dB at 300Hz

AC Operating Temperature: 0’ to 50°C

Model 1651 50.Ampere Current Shunt-The external O.OOlI2 f I%, measurements from O-50A DC or AC.

Model 1681 Clip-On Test Lead Set-contains two leads,

1.2m (48 inches) long terminated with banana plugs and

spring action clip on probes.

Model 16ElZA RF Probe-Permits voltage measurements

from 1OOkHz to 250MHr.

AC to DC transfer accuracy: *ldB from 1OOkHz to 250MHr at IV, peak responding, calibrated in rms of a sine wave.

Maximum Allowable Input: 42V AC peak, 200V IDC + AC peak)

Model 1684 Hard Shell Carrying Case-Hard vinyl case, 1OOmm x 300mm x 350mm 14 x I3 x I4 inches1 has a fit-

ted foam insert with room for the Model 175, instruction

manual and small accessories. Model 1685 Clamp-On AC Probe-Measures AC current

by clamping onto a single conductor. Interruption of the cir-

cuit under test is unnecessary. The Model 1685 detects cur-

rent by sensing the changing magnetic field produced by the

current flow.

Range: 2, 20 and 200A rms Accuracy: 54% of range at 60Hz; + 6% of range at 50Hz Temperature Coefficient: +0.05%/°C on 20A and 200A

range; k0.3%/°C on 2A range

Maximum Allowable Current: 300A rms

Maximum Conductor Voltage: 6OOV rms

Conversion Ratio: O.lV/A rms

Model 1751 Safety Test Leads-This is the test lead set

supplied with each Model 175. Finger guards and shrouded

banana plugs help minimize the chance of making contact

with live circuitry.

Model 1753 IEEE-488 Interface-Field installable programmable option provides isolated data output. Switch-

selectable talk onlyoraddressable modes. Mounts within and

a-terminal shunt permits current

l-2

Model 1754 Universal Test Lead Kit-12 piece test lead kit, with interchangeable plug-in accessories. Kit includes: one set of test leads (i-red. l-black), two spade lugs, two standard banana plugs, two phone tips (.060DIA.), two hooks and two miniature alligator clips (with boots).

Model 1758 Rechargeable Battery Pack-Provides six hours

minimum operation from full charge, recharges within 10 hours and is field installable.

Model 7008 IEEE-488 Digltal Cabl+Useful for connecting the Model 1753 to the IEEE-488 bus. The Model 7008-3 is 0.9m (3ft) in length and has a standard IEEE-488 connector at each end. The Model 7008-6 is 1.8m (6ft) in length.

l-311-4

SECTION 2

BENCH OPERATION

2.1 INTRODUCTION This section contains the information needed to prepare and

operate the Model 175 as a bench DMM. Bench operation consists of using the Modal 175 to perform basic voltage, currant, resistance and dB measurements. Also, the operation of the data logger is covered hare. The capabilities of the

Model 175 can be enhanced with the addition of the Model 1753 IEEE-488 interface. IEEE operation is covered in the Modal 1753 Instruction Manual.

2.2 HIGH ENERGY CIRCUIT PRECAUTIONS To optimize safety when measuring voltage in high energy

distribution circuits, read and use the directions in the follow-

ing warning.

WARNING Dangerous arcs of an explosive nature in a high energy circuit can cause sevare personal injury or death. If the mater is connected to a high energy circuit when set to a currant range, low resistance range or any other low impedance range, the circuit is virtually shorted. Dangerous arcing can result awn when the mater is sat to a voltage range if the minimum safety spacing is reduced.

When making measurements in high energy circuits use test

leads that meat the following requirements:

1. Test leads should be fully insulated.

2. Only use test leads that can be connected to the circuit leg. alligator or spade plugs) for hands-off measurement.

3. Do not use test leads that decrease voltage spacing. This diminishes arc protection and creates a hazardous condition.

Use the following sequence when testing power circuits:

1. De-energize the circuit using the regular installed connactdisconnect device such as the circuit breaker, main switch, etc.

2. Attach the test leads to the circuit under test. Use appropriate safety rated leads for this application.

3. Sat the DMM to the proper function and range.

4. Energize the circuit using the installed connect-disconnect device and make measurements without disconnecting the

DMM.

5. De-energize the circuit using the installed connectdisconnect device.

6. Disconnect the test leads from the circuit under test.

2.3 PREPARATION FOR USE

2.3.1 Line Power

The Model 175 is provided with a three-wire line cord which

mates with third-wire grounded receptacles. Connect the ins strumant to AC line power as follows:

1. Sat the LINE VOLTAGE switch on the back of the instrument to correspond to line voltage available. Ranges are

105.12511 or 210.250V 50/60Hz AC.

CAUTION Connect only to the line voltage selected. Application of incorrect voltage can damage the instrument.

2. Plug the power cord into a properly grounded outlet. WARNING

Ground the instrument through a properly grounded receptacle before operation. Failure to ground the instrument can result in savere injury or death in the avent of

short circuit or malfunction.

NOTE Although the Model 175 is specified at 50 and 60Hz the instrument may be operated at 400Hz and 440Hz. Add ona. count to instrument specifications under this condition.

2.3.2 Battev Pack Power The Modal 175 may also be operated from rechargeable

sealed nickel-cadmium batteries contained in the optional

Model 1758 Rechargeable Batwry Pack. The battery pack will operate the Modal 175 for up to six hours The BAT annunciator will turn on when the battery charge is insufficient to maintain accurate readings. Refer to Section 5, paragraph 5.3 for installation procedures.

2.3.3 Battery Charging After the Model 1758 Battery Pack is installed in the Model

175 it can be charged and recharged as follows:

1. Connect the instrument to line power as described in paragraph 2.3.1.

2. With the power switch off, the battery charge circuitry is automatically energized to charge the battery at the maximum rata. When the battery pack is first installed, or if it is completely discharged, allow it to charge for ten hours.

2-1

NOTE For maximum battery efficiency only charge the battery pack after it has become discharged and only charge until it is fully charged (=,lOhours). Continuous charging over long periods of time

will not damage the batteries but, usefu life will gradually decrease. This loss is not permanent and may be restored by cycling the battery pack through several complete charge/discharge

cycles. The battery pack is capable of 500 to 1000 charge/discharge cycles before replacement is needed.

Do not make measurements with the BAT an-

nunciator on as the readings may be erroneous.

3. When the Model 175 is in use on line power, the battery charger maintains a trickle charge on the battery pack.

2.4 FRONT PANEL FAMILIARIZATION

The following paragraphs and Figure 2-l provide a brief description of the display, front panel controls and input ter-

minals.

2.4.1 Display

The Model 175 has a 4 % digit liquid crystal display (LCD). The minus sign is displayed. The plus sign is implied by the

absence of the minus sign. The following annunciators are displayed on the LCD.

BAT-Low battery indicator for the Model 1758.

AC-AC selected (DC implied by absence of AC annun-

ciator).

mV or V-Millivolts or volts selected. n, kR or Mn-Ohms, kilohms or megohms selected. p, mA or A-Microamps, milliamps or amps selected.

RMT (Remote)-Model 175 being controlled over the

IEEE-488 bus (Model 1753 installed). C-Model 175 in calibration mode. AUTO-Autorange selected.

REL--Relative selected.

dB-Decibel selected. STO-Data being stored. RCL-Data being recalled. RCL flashes when buffer is full

during logging cycle.

2.4.2 Front Panel Controls ON/OFF-Pressing in this pushbutton turns the Model 175

on. Releasing (out) this pushbutton turns the instrument off.

REL (Relative)-This pushbutton allows readings to be made with respect to any baseline value. Also allows zeroing

of on range readings. See paragraph 2.7.2 for more detailed

information on REL. dB-This pushbutton selects the dB function and is used

along with the ACV or DCV function. Measurements are

made in dBm referenced to 600% REL can be used to make any voltage level the OdB reference point for dB measurements.

DATA LOGGER-Has min/max and 100 point reading storage capacity; records data at one of six selectable rates from every reading to 1 rdglhr. Records maximum and minimum conversion during the period the data logger is active at the rate of 3lsec.

1. STO/CLR-Pressing this button initiates the logging sequence. Pressing the button a second time shuts off the data logger.

2. RCL-Pressing and holding this button in scrolls the data pointer. To read the data at a particular point, simply release the button.

AC/DC-This switch is used along with the volts (V), current (A), and dB functions. Depressing (in) this pushbutton selects AC and releasing (out) this pushbutton selects DC.

V-Depressing this pushbutton selects the volts function. O-Depressing this pushbutton selects the ohms function.

The AC/DC pushbutton must be released (out).

A-Depressing this pushbutton selects the current function.

Range Push Buttons

1. AUTO-Depressing this pushbutton causes volts and ohms to autorange. In current, it selects the 10A range (no autoranging in current).

2-2

%iEiq

175 AUTORANGING MVLTIMETER

Figure 2-l. Model 175 Front Panel

2. Manual ranging is accomplished by depressing the ap propriate range button.

2.4.3 Input Terminals

The input terminals are intended to be used with safety shrouded test leads to help minimize the possibility of contact with live circuits. Safety shrouded test leads are supplied with the Model 175.

VOLTS/OHMS/mA and COM (Red and Black)-Use this pair of terminals for all volt, ohm, milliamp and dB measurements.

10 AMPS and COM (White and Black)-Use this pair exclusively for measuring currant up to 10A (up to 20A for 15

seconds,.

2.4.4 Current Fuse Replacement The current fuse protects the 200pA through 2000mA ranges

from an input currant greater than 2A. To replace the current fuse, perform the following steps:

1. Turn off the power and disconnect the power line and test

leads.

2. Place the end of a flat-blade screwdriver into the slot in the fuse holder on the front panel. Press in slightly and rotate the fuse carrier one-quarter turn counterclockwise.

Release pressure and remove the fuse carrier and the fuse.

Table 2-1. Error Messages

3. Remove the defective fuse and replace it with the following type: ?A, 250V. 3AG. normal-blow Keithley part

number FU-13, or equivalent.

CAUTION

Use only the recommended fuse type. If a fuse with a higher current rating is installed, instrument damage may occur.

2.5 ERROR MESSAGES Table 2-l lists the error messages associated with basic front

panel operation. Note that the instrument has a number of other massages that are discussed in the appropriate sections of this manual.

2.6 OPERATING CONDITIONS

2.6.1 Environmental Conditions All measurements should be made at an ambient temperature

within the range of OOC to 5OOC. and with a relative humidity of 0% to 80% up to 35OC. For instruments above 35OC derate humidity 3% per OC up to 50°C. If the instrument has

been subjected to extremes of temperature, allow sufficient time for internal temperatures to reach environmental conditions. Typically, it takes one hour to stabilize a unit that is

10°C (18OF, out of specified temperature range.

Comments

Model 175 locks up. See Section 5 for troubleshooting information.

Model 175 locks up, but operation can be restored by pressing any one of the four momentary pushbuttons. If restored, calibration is invalid as indicated by the flashing “C” annunciator. See Section 5 for troubleshooting information.

Overrange input applied to the Model 175. Leading minus sign indicates that input signal has a negative value.

“AC” and “R” annunciators flash. Correct problem by releasing (out, AC/DC pushbutton.

Table 2-2. Model 175 Maximum Allowable Inputs

Ranges -

200mV. 2V

20-1ooov

200mV

2.750V

200w-2000mA

10A

All

Maximum Allowable Inputs 1OOOVDC or peak AC for less than 10s~ par minute.

300Vrms continuous.

1OOOVDC or peak AC. 750Vrms 1OOOV peak for lass than 1Osec per minute. 300Vrms continuous. lO’V*Hz maximum. 750Vrms. 1OOOV peak. 107V*Hz maximum. 2A, 250VDC or rms (fuse protected).

10A continuous; 20A for lbec (unfused,. 450VDC or peak AC

2-3

2.6.2 Maximum Allowable Inputs

2.7.2 Relative Mode

Table 2-2 lists the maximum allowable inputs for the Model

175.

2.7 BASIC BENCH MEASUREMENTS Basic measurement techniques for using the Model 175 to

measure AC and DC volts, resistance, AC and DC current and dB are covered in the following paragraphs. Also included is the operation of the MIN/MAX and 100 point data logger.

WARNING

Before operating the Model 175, observe the safety precautions found preceding Section 1. When testing high energy power circuits follow the procedure found in paragraph 2.2 High Energy Circuit Precautions. Failure to observe these and other safety precautions found in this manual could result in severe injury or death.

The COM terminal on the Model 175 is designed to float above earth ground to avoid ground loop problems.

WARNING Hazardous voltages may be applied to the COM terminal. The maximum allowable voltage between the COM terminal and chassis ground is 500V. Destruction of insulation, which could present a shock hazard, may occur if the 500V maximum is exceeded.

CAUTION

Do not exceed the maximum input limits

shown in Table 2-2.

2.7.1 Power-Up NOTE

The software revision level of the Model 175 can be displayed upon power-up by running the diagnostic program. See Section 5, Maintenance, for more information.

Turn on the Model 175 by pressing in the ON/OFF switch. The following will occur:

1. Reset-All zeros will be briefly displayed before going into

the measurement mode.

2. RAM Test-If this test fails the Model 175 will lock up with zeros displayed.

3. NVRAM Test-If this test fails the display will show the error message “cErr”

Refer to Table 2-l for mc~re information pertaining to error messages.

When the relative mode is selected with an on-scale reading on the display the following occurs:

1. The REL annunciator is displayed.

2. The next reading is stored.

3. The stored reading is then algebraically subtracted from all subsequent readings and displayed.

A REL level can be established for any measurement function

(Volts, Ohms, Amps and dB1 and is effective only on that function. Changing functions will not affect a REL level already established. However, if another REL level is set (on any function) the previous REL level will be cancelled. For example, place the 175 in the R function and select the 2OOn range. Short the test leads and press the REL button. Note that the REL annunciator is on. Select DCV and note that the

REL annunciator is off, indicating that there is not a REL level established for DCV. Switch back to 0 and note that the REL level is still there. Again, go to DCV and set a REL level of

+ IV. The REL annunicator will go on. Switch back to n and note that the REL annunciator is off, indicating that the REL level for 0 is cancelled.

Once a REL level is established for a measurement function, that stored level will be the same regardless of what range the Model 175 is on. For example, if + IV is established as the REL level on the 20VDC range, + IV will also be the REL level on the 1OOOVDC range.

It is important to note that the use of REL reduces the dynamic range of measurements by that level. For instance, assume that the REL level is +lV and the Model 175 is manually set to the 2V range. The maximum positive displayed reading, before overranging, would be +0.9999\1. This is because the A/D converter would be seeing 1.9999V (maximum) from the input. Thus, the dynamic range of measurement is -1.9999V to + 0.9999V (2.999BV) as compared to the normal -1.9999V to + 1.9999V (3.9998V). The dynamic range of measurement has been reduced by IV. The effects on dynamic range can be reduced by selecting a higher range or using autorange.

2.7.3 DC Voltage Measurements The Model 175 can make DC voltage measurements between

1OhV and IOOOV. The basic procedure is as follows: I. Connect the test leads to the VOLTS and COM terminals

of the Model 175.

2. Select the DCV function.

3. Select a range consistent with the expected voltage. For automatic range selection, press in the AUTO pushbutton.

NOTE Manual ranging is recommended for routine measurements above 200V.

2-4

4. Connect the test leads to the source as shown in Figure 2-2. If the positive source terminal is connected to the COM terminal of the instrument, the display will show a negative value. If the negative source terminal is connected to the COM terminal, the display will show a positive value.

5. Observe the display; if the “OL” message is shown, select a higher range until a normal reading is shown. Always use the lowest possible range for the best resolution.

6. Take the reading from the display.

NOTE High input impedance j VlOOOMRl DC volts measurements can be made on the 200mV and

2V ranges by releasing (out) all the function

pushbunons (AC/DC, V, R, A).

VOLTAGE

SOURCE

Figure 2-2. DC Voltage Measurements

2.7.4 TRMS AC Voltage Measurements The Model 175 can make TRMS AC voltage measurements

between IOwV and 75OV. Proceed as follows:

1. Connect the test leads to the VOLTS and COM terminals of the Model 175.

2. Select the ACV function.

3. Select a range consistent with the expected voltage. For automatic range selection, press in the AUTO pushbutton.

NOTE Manual ranging is recommended for routine measurements above 200V.

4. Connect the test leads to the source as shown in Figure

2.3.

5. Observe the display; if the “OL” message is shown, select a higher range until a normal reading is shown. Always use the lowest possible range for the best resolution.

6. Take the reading from the display.

VOLTAGE

Figure 2.3. TRMS AC Voltage Measurements

2.7.5 Resistance Measurements The Model 175 can make resistance measurements between

1OmfI and 200MQ The 2MIf. 20MR and 200M12 ranges will autorange when the MI1 pushbutton is pressed in. Proceed as follows to make resistance measurements:

1. Connect the test leads to the OHMS and COM terminals of the Model 175.

2. Select the II function. NOTE

The message “Err” and flashing II and AC annunciators will be displayed if the AC/DC pushbutton is pressed in. This is an invalid mode. To correct, simply release (out) the AC/DC pushy button.

3. Select a range consistent with the expected resistance. For

automatic range selection. use the autorange mode.

NOTE Zeroing may be necessary to compensate for test lead resistance on the 20011 and 2kR ranqos. Zero the display as follows:

A. Short the to?., leads together.

B, Press the REL pushbutton. The display will zero. C. Proceed to step 4.

4. Connect the test leads to the resistance to be measured as shown in Figure 2-4.

5. Observe the display: if the “OL” message reading is shown, select a higher range until a normal reading is

shown. Always use the lowest possible range for the best resolution.

6. Take the reading from the display

NOTE

See paragraph 2.8 for TRMS considerations.

NOTE It is helpful to shield resistances greater than 106R (1MR) if a stable reading is expected. Place

the resistance in a shielded enclosure and elect trically connect the shield to COM of the Model

175

2-5

Figure 2-4. Resistance Measurements

2.7.6 Current Measurements (DC or TRMS AC) The Model 175 can make DC or TRMS AC current

measurements between lO@A and IOA (20A for 15 seconds).

If the expected current level is in question, make the initial measurement with the 10A range. This will help prevent the inadvertent blowing of the 2A current fuse.

NOTE

For routine measurements above 10A it is recommended that the Model 1651, 50.Ampere current shunt be used.

1. For current measurements between 2000mA and 20A. A. Connect the test loads to the 10 AMPS and COM ter-

minals of the Model 175.

B. Select the ACA or DCA function. C. Select an appropriate range for the expected current.

Current measurements cannot autorange.

D. Connect the test leads to the current source as shown

in Figure 2-6. If an overrange indication is displayed

select a higher range until a normal reading is shown.

Use the lowest possible range for the best accuracy.

E. Make the reading from the display.

CURRENT

TWISTED

SOURCE

Figure 2-5. Current Measurements Between 2000mA

and 20A

CURRENT

SOURCE

NOTE The test leads used must be capable of handling 20A and it is recommended that thev be twisted (see Figure 2-5) to minimize external iields which could affect the Model 175 or other equipment. Also, keep the test leads es short as possible to minimize voltage drop.

B. Select the ACA or DCA function. C. Select the 10A range. Current does not autorange. D. Connect the test leads to the current source as shown

in Figure 2-5 and make the reading from the display.

NOTE Up to 5A may be applied continuously without degradation of the measurement due to selfhosting effects. Above 5A derate 0.15% rdg per amp for self-heating. For currents between IOA and 20A. specified accuracy can only be obtained when measurements are limited to a maximum of 15 seconds.

2. For current measurements up to 2000mA: A. Connect the test leads to the mA and COM terminals of

the Model 175.

Figure 2-6. Current Measurements up to 2000mA

2.7.7 AC Plus DC Measurements Use the Model 175 to measure TRMS on a signal which has

both AC and DC components as follows:

1. Measure and record the TRMS AC component as described in paragraph 2.7.4.

2. Measure and record the DC component as described in paragraph 2.7.3.

3. Compute the rms value from the following equation:

RMS - DC

-\/E

2 + E,,?

2.7.8 dB Measurements The dB function makes it possible to compress a large range

of readings into a much smaller scope. The relationship between dB and voltage can be expressed by the following equation.

dB = 20 log __

VW,

VFW

2-6

Tables 2-3 and 2-4 list the dB specifications for DC volts and AC volts.

The Model 175 can make dBm measurements referenced to the standard 6OOn impedance or to other impedances. The

relative feature allows measurements in dB independent of impedance.

The basic procedure for placing the instrument in the dB mode is to first select AC or DC volts and then press the dB button. Note that once dB is selected (dB annunciator on), pressing in the 0 or A function pushbuttons will turn dB off.

1. dBm Measurements with 600R Reference Impedance dBm is defined as decibels above or below a 1mW

reference. The standard reference impedance of the Model 175 is 600% What that means is that the Model 175 is designed to read OdBm when the calculated voltage needed to dissipate 1mW through a 600R impedance is applied to the Model 175. That calculated voltage level is

0.7746V as derived from the basic power equation. E=\lP.R E = IlO-3W.6000

E = 0.7746V

Thus with a 600R reference impedance the Model 175 will

read OdBm whenever 0.7746V is applied.

NOTE Do not confuse reference impedance with input impedance. The input impedance of the instrument is still 1OMR (see specifications) in the dB mode.

To make dBm measurements referenced to 60012, pro-

ceed es follows:

A. Connect the test leads to the VOLTS and COM tern

minals of the Model 175.

8. Select the ACV or DCV function. C. Select autorange for optimum resolution. D. Press the dB button. E. Connect the test leads to the voltage source. F. Make the dBm reading from the display.

2. dBm Measurements with Other Reference Impedances dBm measurements can be made with other reference imp

pedances. The most convenient method for using other reference impedances is to algebraically subtract the calculated dB offset for the desired reference impedance

from the reading on the display of the Model 175. Table 2-5 lists common reference impedances and the cork

responding offset values. The following equation can be used to calculate the offset for impedances not listed in Table 2-5:

Offset (foi dBml : 10 log -$,o;j

To make dBm measutements referenced to another em-

pedance, proceed as follows: A. Choose the desired reference impedance.

B. Calculate or look up the offset value in Table 2-5 for the

desired reference impedance.

C. Determine dBm at the desired reference impedance as

follows:

dBm (at ref 2) = 175 reading offset

Examole: Make dBm meawrements references to a

lOOI deference impedance

New ref I

Table 2-3. dB Specifications for DC Volts 16OOI1 Refl.

Table 2-4. dB Specifications for AC Volts l600R Refl

dS Mode lref: 60001

Range / Input

200mV I

1mV to 2mV

I i-58 to -52dBm)

~ (Ei, 2v.750v

*Up to 1 ktiz

OHz- 1

IkHz 2*

0.2

Accuracy (* dSm)

IOkHz- / ZOkHz2OkHz 1 50kHz

! -

0.3 1

0.26

0.56

50kHz1OOkHz

1.2

2-7

i. lOOn is not listed in Table 2-5 so the offset must be

2.7.9 dB Measurement Considerations and Applica-

calculated as follows: tions

offset = 10 log (j$$)

offset = -7.78dB

ii. Subtract -7.78dB from all subsequent displayed

readings on the Model 175.

dBm measurements. referenced to another impedance, can be read directly from the display of the Model 175 by utilizing the REL feature, and an accurate voltage source. The basic procedure is as follows:

A. Calculate or look up the equivalent voltage level (Table

2-5) for OdBm at the desired reference impedance.

8. Input that voltage level to the Model 175. C. With the Model 175 in the dB mode, press the REL

button.

D. dBm measurements referenced to the desired im-

pedance can now be read directly from the display of the Model 175.

3. dBW Measurements dBW is defined as decibels above or below a one watt

reference. The procedure is the same as that found in paragraph 2.7.8 step 2. The only difference is that the reference point is OdBW (1W) rather than OdBm (1mW).

4. dElV Measurements dBV is defined as decibels above or below 1V (OdBV

point). This is a voltage relationship independent of impedance. The basic procedure is to simply subtract 2.22 dl3 ITable 2-5) from all subsequent displayed readings on the Model 175..

5. Relative dB Measurements

Just about any voltage level within the measurement limits of the Model 175 can be established as the OdB point. The basic procedure is to establish that level as the OdB point

by using REL and make the desired dB measurements.

Table 2-5. Levels for Other Reference Impedances

Reference

Impedance

(cl)

8 0.0894 2.828

75 0.2739

150 300 0.5477 600 0.7746

1000 1 .oooo

Equiv. Voltage Level for:

(600!7 Refl

OdBm OdBW OdBm

-18.75 11.25

0.2236

-10.79

9.03

0.3873

6.02

3.01

0.00

1 2.22

Offset

OdBW

V, for OdBm = U10~3W-Z,,, V;z;;:: for OdBW =\6,,,

Offset (for dBm) = 10 log[6:& )

1. Typical Instrument Performance Typically, the Model 175 will perform better than its published dB specification. The following example will illustrate this point:

A. Using the Model 175 in the dB mode 6000 ret)

measure a 1mV RMS. 1kHz source (common application in the communications field). Typically, the Model

175 will read -57.7dBm.

B. The calculated dBm level for that source is -57.8dBm.

C. The O.ldBm error is considerably better than the

k2dBm specification. The specifications are intended

to covet worst measurement conditions.

2. Measuring Circuit Gain/Loss

Any point in a circuit can be established as the OdB point. Measurements in that circuit are then referenced to that point expressed in terms of gain I + dB) or loss (-dBl. To set the OdB point:

A. Place the Model 175 in volts, autorange and dB.

B. Connect the Model 175 to the desired location in the

circuit. C. Press the REL button. The display will read OdB. D. Gain/Loss measurements can now be made referenc-

ed to the OdB point.

3. Measuring Bandwidth The Model 175 can be used to determine the bandwidth of an amplifier as follows:

A. Connect a signal generator to the input of the

amplifier. B. Set the Model 175 to ACV and autorange. C. Connect the DMM and a frequency counter to the load

of the amplifier.

D. Adjust the frequency of the signal generator until a

peak AC voltage reading is measured on the Model

175.

E. Press the dB button and then press the REL button.

The OdB point is now established.

F. Increase the frequency input until the Model 175 reads

-3.OOdB. The frequency measured on the frequency

counter is the high end limit of the bandwidth. G. Decrease the frequency input until the dB reading

again falls to -3dB. The frequency measured on the

signal generator is the low end limit of the bandwidth.

4. Determining Q The (1 of a tuned circuit can be determined as follows:

A. Determine the center frequency and bandwidth as ex-

plained in paragraph 2.7.9 step 3.

B. Calculate Q by using the following formula:

Q = Center Frequency/Bandwidth

Offset (for ,,B,,,,) = ,O

log

2.7.10 MINIMAX and 100 Point Data Logger Operation

2.7.11 Diode Test

The data logger can store up to 100 readings and store the

minimum and maximum readings recorded during the period

that the data logger is active. The Data Logger remains active

even after 100 points of data are stored, which means the MINIMAX readings continue to update. The only way to deactivate the Data Logger is to press the STOiCLR button

(ST0 annunciator off1 or cycle power. The 100 points of data are stored at one of six selectable rates from three per second to one reading per hour. Readings for minimum and maxim

mum are sampled at the rate of three per second regardless of the selected rate. The procedure for operating the data

logger is as follows:

Connect the desired measurement configuration to the Model 175. Make sure that the controls of the Model 175 are set appropriately.

Loaainn Data:

Press and hold the STOiCLR pushbutton. The following reading rates will scroll on the display:

r = 0 (every reading) r = 1 (1 rdglsecl

I = 2 (1 rdgll0 set) r = 3 (1 rdglmin) r = 4 (1 rdg/lO min) r = 5 (1 rdgihr)

NOTE There is no need to select a rate if just minimum/maximum readings are desired. Momentarily press the STO/CLR button to start

the logger. Release the STO/CLR pushbutton when the desired reading rata is displayed. The ST0 annunciator will turn on and data will be logged at the selected rate.

NOTE The logging cycle can be terminated at any time bv pressina the STOiCLR button. This shuts off tie’ data logger. However, data is retained and can be recalled at any time as long as the instrument remains on.

Data Retrieval

Data can be retrieved at any time, but a flashing RCL annunciator indicates that the maximum number of readings (100) have been stored.

Press and hold in the RCL pushbutton. The display will

scroll through the data points and MINIMAX (LO/HI). The first data point displayed will be the last stored

reading. The next two data points will be the HI and LO

readings made during that logging cycle. Notice that the longer the RCL pushbutton is held in the faster the data points will scroll on the display.

Release the RCL pushbutton at the desired data point and note the reading (data) on the display. The data pointer can be incremented by steps of one by momantarily holding in the RCL pushbutton.

Shut off the data logger by pressing the STO/CLR pushbutton. All stored data will be retained until a new store cycle has commenced.

The 2kU and 200kfI ranges can be used for testing semiconductor junctions as follows:

1. Select 12 function.

2. Press 2k and 200k pushbuttons [diode symbols1 in simultaneously.

3. Display reads forward V drop of diode at 0.7mA lup to 2VI. Red terminal is positive.

2.8 TRMS CONSIDERATIONS Most DMMs actually measure the average value of an input

waveform but are calibrated to read its RMS equivalent. This poses no problems as long as the waveform being measured is a pure, low-distortion sine wave. For complex. none sinusodial waveforms, however. measurements made with an averagrng type meter can be grossly inaccurate. Because of its TRMS (True Root Mean Square1 measuring capabilities,

the Model 175 provides accurate AC

measurements for a wide variety of AC input waveforms

2.8.1 AC Voltage Offset

Typically the Model 175 will display 25 counts or less of offset on AC volts with the input shorted. This offset is caused by amplifier noise and offset of the TRMS converter. This offset will not affect reading accuracy and should not be zeroed out using the REL feature. The following equation expresses how this offset IV

OFFsETJ is added to the signal input IV,,):

Displayed reading -\,&I2 ~+ iVoiFstri2

As long as V,, is at least 10 times larger than V,,,,,,, negligi~ ble error will occur.

Example: Range = WAC, range

Offset = 25 counts input = 200mV RMS

Displayed Reading :: “!Q@!2 + (.Q025j2~

~$:~~o’,,“,;“oooo”3 = .2OOOV RMS

If REL is used to zero the display. the 25 counts of offset would be subtracted from V,, resulting in an error of 25 counts in the displayed reading.

2.8.2 TRMS Measurement Comparison The RMS value of a pure sine wave is equal to 0.707 times its

peak value. The average value of such a waveform is 0.637 times the peak value. Thus. for an average-responding meter, a correction factor must be designed in. This correction fact tar, K, can be found by dividing the RMS value by the average value as follows:

K = 0.707 = 1.1,

0.637

2-9

+ 46 hidden pages

Tektronix 175 Instruction Manual

Specifications and Main Features

Frequently Asked Questions

User Manual