Keithley 7158 Service manual

Model 7158 low Current

Scanner Card

Instruction Manual

Contains Operating and Servicing Information

Model 7158 Low Current Scanner Card

Instruction Manual

0 1987, Keithley Instruments, Inc.

Test Instrumentation Group

All rights reserved.

Cleveland, Ohio, U.S.A.

June 1990, Second Printing

Document Number: 7158-901-01 Rev. B

SAFETY PRECAUTIONS

The following safety precautions should be observed before using this
product and any associated instrumentation. Although 6ome 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.

Exercise extreme caution when a shock hazard is present. Lethal voltage
may be present on cable connector jacks 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.
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 we.

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 be-

fore: connecting or disconnecting cables or jumpers, installing or

removing switching cards, or making internal changes, such as installing

or removing jumpers.

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.

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

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 main. When connecting sources to switch­ing cards, install protective devices to limit fault current and voltage to
the 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.

If a @ screw is present on the test fixture, connect it to safety earth
ground using #18 AWG or larger wire.

The
more may be present on the terminals. Refer to the product manual for de­tailed operating information.

Instrumentation and accessories should not be connected to humans
Maintenance should be performed by qualified service personnel. Before

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

symbol on an instrument or accessory indicates that 1OOOV or

f

SPECIFICATIONS

MODEL 7158 LOW CURRENT SCANNER CARD

CHANNBLS PER CARD: 10
CONTACT CONFIGURATION: Single pole. When a channel is open, sign81 HI is con-

nected to signal LO. Signal LO is common for ail 10 channels and aulput.

CONNIXTOR TYPE; BNC
RELAY DRIVE CURRENT: lOOmA per card typical.

MAXIMUM SIGNAL LEVEL; lOOmA, 3OV, peak (resistive load)
368 BANDWImHz lM& typical.
CONTACT LIFE: 10’ closures (cold switching); 10’ closures (at maximum signal level)
CONTACT RESISTANCE: <Xl to rated life
CONTACT POTBNTIALr <20,&V
ACTUATION TIME: <Ims, exclusive of mainframe
OPPSET CURReNT: <10’“A (<3 x 10-laA typical)
COMMON MODR VOLTAGE: 3OV peak

GENRRAL
ENVIRONMENT,

Operating: 8’ to 50°C, up to 35’C at 70% RH
storage: -2.5” to 65°C

DIMENSIONS, WEIGHI! 32mm high x 114mm wide x 272mm long (1%” x 4%” x

10%“). Net weight 0.5gkg (20.5 oz.)
ACCBSSORY SUPPLIED; Model 4801 Low Noise Cable
ACCBSSORY AVAILABLG; Model 4804 t&x female to BNC male adapter

Specifications subject to change without notice.

TABLE OF CONTENTS

SECTION 1 - GENERAL INFORMATION

1.1

1.2

1.3

1.4
I.5
I.6

Introduction.

warrant\~ Information

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

Safety Symbols and Terms ...........................

Unpackmg and lnspectlon ............................

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

........................................ 1

................................ 1

SECTION 2 - OPERATION

2.1 Introduction .........................................

2.2 Safety Precautions ...................................

2.2.1 High Impedance Considerations

2.2.2 Static Precautions ..................................

2.3 Connections and Cabling .............................

2.4 Installation and Removal .............................

2.5 Operation ..........................................

2.5.1

2.52 Operation Notes ..................................

2.6

Scanner Control of the Channels

Applications. .......................................

.................... 5

................... 11

SECTION 3 - SERVICING INFORMATION

3. I

3.2

3.3

3.4

3.5

3.6

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

Handling and Cleaning .............................

Relay Replacement ..................................

Recommended Test Equipment

Offset Current Test .................................

Contact Resistance Test ..............................

....................... W

2
2
2
3

5
5

6
6
8

10

18
18

25
25
26

W
29

SECTION 4 - REPLACEABLE PARTS

4.1

4.2

4.3

4.4

4.5

introduction ........................................

Parts Lists .........................................

Ordering Information ...............................

Factory Service .....................................

Component Layout and Schematic Diagram

33
33
33
35

........... 35

LIST OF TABLES

SECTION 2 - OPERATION

2-l
2-2
2-3

2-4
2-5

2-6
2-7

Example Channel Assignments in 2-P& Mode. 12
Example Channel Assignments in l-Pole Mode 13
Example Channel Assignments in Matrix (O-Pole)
Mode 14
Scanner Control of Model 7158 4-Pole Mode 15
Scanner Control of Model 7l58 2-Pole Mode 15

Scanner Control of Model 7l58 l-Pole Mode. 16
Scanner Control of Model 7158 Matrix (O-Pole) Mode. 17

SECTION 3 - SERVICING INFORMATION

3-l

Recommended Test Equipment, 27

SECTION 4 - REPLACEABLE PARTS

4-l
4-2

Model 7l58 Electrical Parts. 34
Model 7158 Mechanical Parts 35

iii/iv

LIST OF ILLUSTRATIONS

SECTION 2 - OPERATION

2-l Multi-Card Connection. 7
2-2 Installing Card in Model 705, 9
2-3 Installing Card in Model 706.. 10
2-4 Model 7l58 Simplified Schematic, 11
2-5 Capacitor Leakage Schematic 20
2-6
2-7 Measuring Leakages with One

Capacitor Leakage Instrument Setu

Car 23

x ““”

SECTION 3 - SERVICING INFORMATION

., 21

3-l
3-2
3-3 Contact Resistance 31

Offset Current 28
Coax Pigtail Preparation. 30

SECTION 4 - REPLACEABLE PARTS

4-l Model 7l58 Component Layout 36

4-2

Model 7l58 Schematic Diagram 37

v/vi

SECTION 1

GENERAL INFORMATION

1.1 INTRODUCTION

The Model 7l58 Low Current Scanner Card has ten channels of paired

single-pole single-throw (SET), normally open (NO) relays. The card
will switch any one of ten signals to one output, or switch one signal
to any one of ten outputs.

Signal HI is connected to signal LO (analog ground) when the scanner
mainframe channel is open, and to output HI when the channel is clos­ed. Signal LO is common to all ten channels and the output. An addi­tional relay isolates all circuitry on the card from the output when no

channel is closed.

Features of the scanner card include:

l Low offset current error (<IpA specified, <30fA typical)
l Switching of AC or DC signals up to lOOmA.
l BNC input and output connectors.
l Two outputs for daisy-chaining of Model 7158 cards.
l Configurable for low current or low voltage switching.

The Model 7l58 is field-installable in the Models 705 and 706 scanner
mainframes.

1.2 WARRANTY INFORMATION

Warranty information is stated on the inside front cover of this manual.
If there is a need for service, contact the Keithley representative or
authorized repair facility in your area. Check the back cover for ad­dresses. The service form supplied at the end of the manual should
be used to provide the service facility with information concerning any
difficulty.

1

1.3 MANUAL ADDENDA

Product improvements or changes to this manual will be explained on
an addendum included with the manual. It is recommended that this
information be incorporated immediately into the appropriate ptaces
in the manual.

If an additional instruction manual is required, order the manual
package (Keithley Part Number 7158-901-00). The manual package in­cludes an instruction manual and all pertinent addenda.

1.4 SAFETY SYMBOLS AND TERMS

The symbol A on the card denotes that the user should refer to the
operating instructions.

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

The CAUTION used in this manual explains hazards that could damage
the card.

1.5 UNPACKING AND INSPECTION

The Model 7158 was inspected both electrically and mechanically before
shipment. Upon receiving the Model 7l58, unpack all items from the

shippin carton and check for any obvious damage that may have oc-

curred 6: urmg transit. Report any damage to the shipping agent. Re-

tain and use the original packaging materials in case reshipment is
necessary. The following items are shipped with every Model 7158:

Model 7158 Low Current Scanner Card
Model 7l58 Instruction Manual
Model 4801 Low Noise Coax Cable (48 in., supplied accessory)

2

The following item is an optional accessory:

Model 4804 Triax (F) to BNC (M) Adapter

1.6 SPECIFICATIONS

Detailed specifications of the Model 7158 precede the Table of Contents

of this manual.

314

SECTION 2

OPERATION

2.1 INTRODUCTION

This section contains an operation overview, safety information, con­nections and cabling information, an installation procedure, operating
instructions, and an application for the card.

2.2 SAFETY PRECAUTIONS

WARNING

Maintain inputs and outputs withln 30V peak of earth
ground. lMn off all power and discharge stored energy in
external cimultry before making or breaklng connections.

1. The maximum signal level is lOOmA peak (30V compliance).

2. Make sure the scanner mainframes are grounded through an earth
grounded receptacle before operation.

3. Inspect all connections for wear and defects such as cracks and ex­posed wires.

2.2.1 High Impedance Considerations

Because of the high impedance circuits on the card, be careful when
handling it to avoid contamination from such foreign materials as body
oils. Such contamination can substantially lower leakage resistance,
degrading performance.

Handle the card only by the edges. If you remove the relay covers, be

careful not to touch board surfaces or exposed parts.

To avoid dirt build-up over a period of time, operate the scanner and
scanner card only in a clean environment. If contamination is suspected,

the card should be carefully cleaned using the procedure given in
paragraph 3.2.

2.2.2 Static Precautions

The card’s IC chips are static-sensitive and can be damaged by static
discharge, rendering the card partially or completely inoperative. For
that reason, be careful not to touch exposed areas of the circuit board
if static is thought to be a problem,

CAUTION
Static discharge to exposed circuits can damage the card
and might invalidate the warranty.

2.3 CONNECTIONS AND CABLING

Signal input and output connections are made with BNC connectors
on the card. The locations for each channel input and the outputs are
indicated on the relay covers. The two output connectors permit multi­ple Model 7158 cards to be connected together. For example, a 20.channel
scanner system can be connected as shown in Figure 2-l.

In addition to card-to-card connections, the Model 4801 low noise cable
can be used for scanner-to-scanner connections when daisy-chaining
up to five scanner mainframes.

CAUTION CAUTION
Keithley’s Model 7058 low current scanner card has trlax Kelthley’s Model 7058 low current scanner card has trlax
connectors, Be careful not to interchange trlax and BNC connectors, Be careful not to interchange trlax and BNC
connectors to avold damaging them. connectors to avold damaging them.

Caps are provided for all connectors. Unused connectors should be cap­ped to prevent contamination of the insulators, which could degrade
performance.

The supplied low noise coax cable has a conductive lubricant (graphite)

to minimize the error current caused by friction between cable insulators
and conductors. This becomes a consideration when measuring cur­rent levels in the picoamp range. Since cable flexing due to vibration
and cable expansion and contraction due to temperature fluctuation
cause friction, the signal cables should be fastened to a rigid surface
and not subject to temperature changes. (The temperature changes nor-

mally experienced in laboratory environments are not a problem).

Figure 2-1. Multi-Card Connection

2.4 INSTALLATION AND REMOVAL

The procedures to install the Model 7l58 in the Model 705 or 706 Scan­ners are similar except for the card orientation. See Figure 2-2 for a
Model 705 and Figure 2-3 for a Model 706.

WARNING

Turn off the scanner mainframe and disconnect the power

cord before installing or removing scanner cards.

CAUTION

Leave the Model 7158 In Its anti-static bag until ready for

cabling snd installing to avoid possible static damage.

Once the card is cabled, insert it card edge first into the scanner main­frame by aligning it with the grooves in the appropriate slot. Make sure
it is proper1 seated into the mainframe connector. Push the locking
tabs forwar 1( to the center of the card to lock it in.

To remove a card, first turn off the mainframe and all other equipment
connected to the card. Unfasten the locking tabs on the card by pull­ing the tabs outward. Grasp the end of the card and carefully pull it
out of the mainframe.

I

J

Figure 2-2. Installing Card in Model 705

9

Figure 2-3. lnstalllng Card In Model 706

2.5 OPERATION

As shown in Figure 24 for current switching, each channel on the
Model 7158 has a pair of single-pole single-thmw (SKI), normally open
(NO) relays. ‘Ihe relay pair switches signal HI between signal IQ (analog
ground) and output HI. Signal LO (outside shell of the BNC) is com­mon to all channels and outputs in the system.

An additional relay isolates all circuitry on the card from the outputs
when no channel is closed. That is, the isolation relay is open when
all channels are open, and it is closed when any channel is closed,

10

The card is designed for scanning current sources: when a channel is
not selected, a current path is maintained through its signal HI to LO
relay. This protects sensitive devices under test from spikes when
switching an ammeter in and out of each circuit.

The Model 7158 can also be configured for voltage switching (schematic
shown in Figure 2-48). This configuration is made possible by remov-

ing the socketed driver chips (Ul and U2) for the channel HI to LO

relay coils. (These chips are static sensitive. See paragraph 3.2 for handl-

ing precautions)

A. Current Swltchlng

6

8. Voltage Switching

Flgure 2-4. Model 7166 Slmpllfled Schematic

- -

11

2.5.1 Scanner Control of the Channels

Since the Model 7158 is a lo-channel card, set the scanner to the 2-pole
mode when using theMode 7158 by itself or when intermixing with
other lo-channel cards (such as Models 7056,705& 7OC”, 7066, and 7067).
In the 2-pole mode, each scanner channel controls one channel on one
lo-channel card.

As an example, consider the combination of a Model 7158 and Model

7059. ‘table 2-l shows the scanner and card channel assignments for
a master scanner.

Table 2-l. Example Channel Assignments In 2.Pole Mode

.~.

Card 1 - Model 7158

10 channels

Scanner
Ch. No. Ch. No.

7158 Scanner

Card 2

- Model 7059

10 channels

7059

Ch. No. Ch. No.

001

002
003
004
005
006

007

008

009 9

010 10

The Model 7l58 can be mtxed with cards other than lo-channel cards,
but there are complications when changing the pole mode to support
a mix of card types. When using a Model 7l58 in combination with a

20.channel card, such as the Model 7064, set the scanner to l-pole mode.
In this mode, each scanner channel controls one channel on one
20-channel card. The effect on the Model 7l58 channel assignmen% is
shown in Table 2-2.

1 011
2 012
3 073
ii 014

015
6 016
7 017

8

018

019

020 lo”

1
2
3
4
5

,6

7

8

NOTE

In the l-pole scanner mode, close one channel at a time when
using the Model 7158. Otherwise, other channels are closed on
the card and show up on the mainframe display. For example,
close channels 2 and 5, channels 1 and 6 also close.

Table 2-2. Example Channel Asslgnments In l-Pole Mode

Card 1 - Model 7158

r

10 ch; WlS

Scanner
Ch. No. Ch. No.

001
002
003
004
005
006

0”:
009
010
011
012
013
014
015
016

017
018
019

020

7158

3

:
5
5
6
6
7
7

i

;
10
10

I

Card 2

20

Scanner
Ch. No.

021
022
023
024
025
026
027
028
029
030
031
032
033
034
035
036
037
038
039
040

de1 7064

lnels

7064

Ch. No.

1
2

3
4

:

i

9
10
11
12
13
14
15
16
17

:i
20

Next, consider a mix of a lo-channel card

card (Model 7064), and a matrix card (Mode 7052) in a Model 706 scan­ner mainframe. Since a matrix card is present, the scanner is set to
matrix (O-pole) mode. The scanner crosspoints and card channel
assignments for a master scanner are shown in Table 2-3.

Model 7l58), a 20-channel

\

Table 2-3. Example Channel Assignments in Matrix

(O-Pole Mode)

lard 1 - Model ‘7l.V

10 cha

l”“l

els

t c

7158

:h. No.

:
3
4
5

;
8
9

10

706

:rosspoi”l

001,l
002,l

003,l
004,l
005,l
001,2

002.2
003,2
004,2

005.2

Card 2 - Model 7064

20 chal

706

Crosspoints

006.1 007.3

006.1 006,3
007,l 0073
007,l 006,3

008.1 ow,3
008,l 0063
009,l 007,3
009,l 006,3

010.1 007,3

010.1 006,3

006.2 007,3
006,2 006,3

007,2 007,3

00x2 006,3
008,2 0073
008,2 006,3
009,2 007.3
009,2 006,3

010,2 007,3

010.2 006,3

R”l

els

:h. No.

i (

7064

:
3

t
6
7
8

9
10
11
12
13
14
15
16
17
18
19

20

kd 3 - h

Colum”!

706

Zrosspoinl

011.1
011,2
011,3
011,4
012,l
012,2
ol2,3
ol2,4

013.1
ol3.2

013.3

013.4
014,l

014.2
014,3
014,4

015.1
015,2
015,3
015,4

Id 7052
, 4 rows

___~

7052

:ohmn,

Row

__~

;*;
113

1.4

2,1

E
214

3.1

3.2

3.3

3.4

4.1

4.2
4,3
4,4

t:

;,3
5,4

When using 20.channel cards in matrix mode, two crosspoints must
be closed for each of the card channels.

in general, the rules for choosing different scanner pole modes are:
matrix (O-pole) - If a matrix card is present.

l-pole - If a 20-channel card is present, but no matrix card.

2-p& - If a lo-channel card is present, but no 20-channel or matrix

cards.

14

4.pole - If 4-pole switching is desired with two 2-pole, IO-channel cards.

Tables 2-4 through 2-7 list the scanner channels that conhol Model 7158
channels for all scanner pole configurations.

Table 2-4. Scanner Control of Model 7158 cl-Pole Mode

Scanner

Card No.

1

s
4

2
i

9

10

Table 2-5. Scanner Control of Model 7158 2-Pole Mode

Card No.

1

:

4
5
6
7
8

lo”

Channel No.

01-10
01-10

11-20

11-20
21-30
21-30
31-40
31-40
41-50
41-50

Scanner

Channel No.

01-10

11-20
21-30
31-40

41-50
51-60

61-70
71-80

81.90

91.100

I

7158

Channel No.

l-10
l-10
l-10
l-10
l-10
l-10
l-10

l-10

l-10

l-10

7158

Channel No.

l-10
l-10
l-10
l-10
l-10
l-10
l-10
l-10
l-10
l-10

Scanner

705, 706
705, 706

706
706
706
706
706

706
706
706

Scanner

705, 706

705, 706

706
706
706
706
706
706

706
706

15

Table 2-6. Scanner Control of Model 7158 l-Pole Mode

__-

Card 1

Scanner

Ch. No.

Card 2

Scanner
Ch. No.

Card 3

Scanner
Ch. No.

Card 4

Scanner
Ch. No.

Card 5

Scanner
Ch. No.

7258

Ch. No.

01, 02

03, 04
05, 06

07, 08
09, 10

ii32

15: 16

17, 18

19, 20

705, 706

Card 6

Scanner
Ch. No.

101, 102
103, 104
105, 106

107. 108

109, 110

111, 1x2
113, 114

115, 116
117, 118

119, 120

706

21, 22
23, 24

25, 26

27, 28
29, 30
31, 32
33, 34
35, 36

37, 38
39, 40

705, 706

Card 7

Scanner
Ch. No.

121, 122
123, 124

125, 126

127, 128
129,130
131, 132
133,134
135,136

137’ 138

139, 140

706

41, 42
43, 44
45, 46
47, 48
49, 50
51, 52
53, 54
55, 56
57, 58
59, 60

706

Card 8

Scanner
Ch. No.

141, 142
143, 144
145, 146

147. 148
149, 150
151, 152
153, 154

155, 156

157, 158

159, 160

706

61, 62
63, 64
65, 66
6% 68
69, 70
71, 72

73, 74

75, 76

77, 78

79, 80

706

Card 9

Ch. No.

161, 162
163, 164
165, 166
167, 168
169, 170
171, 172

173, 174
175, 176
177, 178
179, 180

706

81, 82
83, 84
85, 86

87, 88
89, 90
91, 92
93, 94
95, 96

97, 98

99, 100

706

Card 10

Scanner
Ch. No.

181, 182
183, 184

185, 186

187, 188
189, 190
191, 192
193, 194
195, 196

197, 198
199, 200

706

1

3’
4
5
6

8’
9

10

Chmio

-L-

:

3
4
5

;
8
9

10

Table 2-7. Scanner Control of Model 7158 Matrlx (O-Pole) Mode

1 Card 1

7158

Ch. No.

06, 1 11, 1

07. 1
08, 1 13, 1
09, 1

10, 1 15, 1

06, 2 11, 2
07, 2 12, 2

08, 2 13, 2

12. 1

14, 1

:

3
4
5

r+
8
9

10

Card 6

icanner

:h.

26, 1

27, 1
28, 1
29, 1
30, 1

26, 2

27, 2
28, 2

29, 2

3a

706

Card 7

Scanner
Ch. No.

31, ‘1
32, 1
33, 1
34, 1

35, 1

31, 2
32, 2

33, 2
34, 2

35, 2

706

Card 8

kanner
Ch. No.

36, 1

37’ 1
38, 1
39, 1
40, 1
36, 2

37, 2
38, 2
39, 2

40,

706

Card 9

Scanner
Ch. No.

41, 1
42, 1

43, 1
44 1

45, 1
41, 2
42, 2
43, 2

44 2
45, 2

706

Card 10

Scanner
Ch. No.

46, 1

47. 1

4% 1

49, 1
50, 1
46, 2

47, 2

‘Ia 2
49, 2

50, 2

706

I

n.58

:h. No.

1

2
3
4

5

6

7
8

9

10

17

2.5.2 Operation Notes

1. Extreme environmental conditions can cause the offset current to
exceed the 1pA specification. If the card has been exposed to high
humidity and/or temperahue (for example during shipping), stabilize
the board within the specified environmental limits for 24 hours.

2. When a channel is opened or closed, there is a charge transfer in

the picocoulomb range. This is because of the mechanical release
or closure of the contacts, the contact to coil capacitance, and the
stray capacitance between signal and relay drive lines. The charge
transfer causes a current pulse. The effect on the signal depends on
the magnitude of the source being measured.

3. Each relay on the Model 7158 draws lOmA. For current switching,
there are either ten or eleven relays energized with any combination
of open and closed channels. The maximum current draw of one
card from the mainframe power supply is 1lOmA. (For voltage swit­ching, there are between zero and eleven relays energized for any
open/closed channel combination.) There are no restrictions on the

maximum number of simultaneous channel closures unless relays
from other card types are energized at the same time.

4. System response is affected by cable capacitance. This should be con­sidered when the sources are connected to the scanner. Use of a feed­back ammeter (or an electrometer in the FAST mode) for currents
below 10~‘A is recommended to increase measurement speed and
decrease the effects of cable capacitance.

5. Power Limits - To prevent overheating or damage to the relay con­tacts, never exceed the signal level specifications of the card. Max­imum switched and carry current and voltage levels are lOOmA, 30V.
The card can switch low power AC (typical bandwidth up to lMHz).
Maximum switched and carry current and voltage levels are lOOmA,
3OV, peak (resistive loads).

6. Switching Speed -Relay actuation time is lmsec maximum plus the
mainframe programming time. Maximum relay switching rate is 100
cycles per second (10msec). This is the maximum rate of the scan­ner mainframe. For extended relay life, use low power or cold swit­ching (turn on sources after the channel is closed).

2.6 APPLICATIONS

The Model 7158 can be used in a variety of applications to switch low

18

current levels. Typical appltcations include those where sourcing voltage
and measuring current are required, such as:

l Leakage currents (e.g. capacitor, FET gate)
l PCB test coupons
l Materials research and characterization
l Semiconductor sub-threshold current

Voltage applications include those where the Model 7158 can be used
to switch a single-pole of low voltage sources. (Refer to the application
example that follows.)

When measuring low currents, the following sources of noise current
should be considered:

l Triboelectric currents are caused by friction behveen a conductor and

insulator when a coax cable flexes due to vibration or temperature
fluctuation. To minimize, use low noise cables and tie down to a rigid
surface.

l Piezoelechic currents are caused by mechanical stress to the insulating

materials of connectors. Remove the stress from the insulators and
use material with low piezoelectric effects to minimize.

l Electrochemical effects generate current between PCB conductors due

to contamination of the card surface. To minimize, handle the card
by the edges only and follow the cleaning instructions in paragraph

3.2.

For a specific application, consider measuring capacitor leakage cur­rent to calculate insulation resistance. The amount of leakage current

depends on the capacitor dielectric material as well as the applied
voltage. The schematic of Figure 2-5 shows a Model 705517056 card on
the source side, but a Model 7158 could be used in its voltage configma­tion when the test voltage does not exceed 3OV.

The configuration shown is the direct method of measuring leakage
currents: a feedback type picoammeter in series with the capacitor

under test. This test is fully explained (including controlling software

19

and test fixture construction) in Application Note #l20, “Capacitor

Leakage Measurements”,

NOTE

The indirect method, with a voltmeter reading the voltage drop
across a resistor in series with the capacitor, is recommended
for capacitor values above l@ to maintain stability and noise
performance.

The instrument setup is shown in Figure 2-6. For clarity, only four chan­nels are shown. Obviously, all ten channels are available for testing
purposes.

r----

--7-----1

Figure 2-5. Capacitor Leakage Schematic

20

Figure 2-6. Capacitor Leakage Instrument Setup

The internal voltage source of a Model 617 electrometer stagger charges

the capacitors when the corresponding channels are closed on a Model
7056 general purpose card. (At this time, the signal HI to Lo relay on

21

the Model 7158 is closed, completing the circuit.) Resistor Rl is needed
to limit current in case the capacitor is shorted and it also helps reduce
noise.

After each capacitor is fully charged (usually 10 times RlC), the Model
7I58 channel is programmed to close. This switches in the Model 617

for reading current or resistance (V/I mode).

Once the Model 617 has settled and the measurement is taken, the
Model 7l58 channel is opened and the signal HI to LO relay closes to

shunt the current to ground. Then the Model 7056 channel is opened
to avoid a current surge through the electrometer and resistors Rl and
R2 bleed off the capacitor charge.

With this two-card configuration, the capacitors have equal soak times.
This is important when comparing low leakage levels (picoamps).

Having equivalent soak times is not as critical at higher leakage levels
(e.g. the nanoamp range of tantalum capacitors). In this case, the one­card configuration shown in Figure 2-7 is sufficient. Since the settling
time of the Model 617 is less when measuring higher currents, the chan­nels can be switched faster.

22

-- --

------- -------

SHlELDED TEST FIXTURE SHlELDED TEST FIXTURE

Figure 2-7. Maasurlng Leakages wlth One Card Figure 2-7. Maasurlng Leakages wlth One Card

23/24

SECTION 3

SERVICING INFORMATION

3.1 INTRODUCTION

‘This section describes tests for verifying the performance of the Model

7158. Perform these tests in an environment of 18’C to 28’C up to 70%
RH.

Because of the low signal levels measured in these tests, the test cables
should be kept as still as possible to help minimize noise.

Recommended maintenance includes inspection of the card and the
card edge connector to ensure good electrical contact.

3.2 HANDLING AND CLEANING

Because of the high impedance of the board, take special care when
handling and using to prevent degradation of performance. Handle the
board by the edges to avoid contaminating it with dirt, body oil, etc.

CMOS and other high-impedance devices are subject to possible static
discharge damage because of the high impedance levels involved. When
handling such devices (indicated by * in the parts list), use the follow-

ing precautions:

1. Such devices should be transported and handled onl in containers
specially designed to prevent or dissipate static bull -up. Typically, ,J
these devices will be received in anti-static containers of plastic or

foam. Keep these parts in their original containers until ready for
installation.

2. Remove the devices from their protective containers only at a
grounded work station. Also, ground yourself with a suita
strap.

roperly

le wrwt

IT

25

3. Handle the devices only by the body; do not touch the pins.

4. Any printed circuit board into which the device is to be inserted must
also be grounded to the bench or table.

5. Use only anti-static de-soldering tools and grounded-tip soldering
irons.

Before cleaning the board, remove the front and rear relay covers. Clean
the board with cotton swabs or a soft brush saturated with an uncon­taminated solvent, .such as Freon@ TMS or TE. After the solvent has
been applied and is still liquid, blow-dry the board with dry-pumped
nitrogen gas.

3.3 RELAY REPLACEMENT

If you have determined that a relay is defective, use the following pro­cedure to replace it:

1. Remove the screws that secure the appropriate relay cover and remove
the cover.

2. Unsolder the defective relay and clean the card holes with a desolder­ing tool or wick. Solder in a replacement relay.

3. Clean the card according to the method given in paragraph 3.2 us-

ing localized cleaning only, then reinstall relay covers.

26

3.4 RECOMMENDED TEST EQUIPMENT

Table 3-1 lists recommended test equipment for performance verifici
tion. Other test equipment may be substituted if specifications equa
or exceed those stated.

Table 3-l. Recommended Test Equipment

Description

--

Scanner Mainframe

Extender Card
Low Noise Coax Cable
Electrometer
‘l’riax to BNC Adapter
Ohmmeter-DMM
Kelvin Test Leads

~___

Specification

-

-

4 feet long

10.“A sensitivity

­<la sensitivity

-

KeithleG 196
Keithley 5806

3.5 OFFSET CURRENT TEST

This test verifies that the offset current for each channel is within
specification.

27

1. Set up the equipment as shown in Figure 3-l with caps on all inputs
and the unused output.

2. Insert the card,into the mainframe.

3. Set the electrometer to the 2pA range and zero check.

4. Turn on the mainframe and close channel 1.

5. Zero correct the Model 677 and release its zero check. Note the off­set current long enough to allow the switching transients to decay
and the current to stabdize. The current indicated by the electrometer
should be less than lpA, exclusive of noise. Open the channel after
taking the reading.

6. Close the remaining channels one at a time and repeat step 5.

28

Figure 3-1. Offset Current

3.6 CONTACT RESISTANCE TEST

This test verifies that the contact resistance of the relays does not ex-

ceed the specification. The procedure is in three parts:

l Setting up equipment.
l Checking contacts of signal HI to LO relays (when channel is open).
l Checking contacts of signal HI to output HI relays in combination

with the isolation relay (when channel is closed).

Setting Up Equipment

1. Turn on the Model 196 DMM and let it warm up (two hours if from
cold-start).

2. Using the following procedure, k repare two BNC male connectors

with coax pigtails as shown in Igore 3-2.

l Use an X-acto” knife to cut and strip 1% inches of outer insula-

tion without cutting the shield.

l With the knife point, unravel the braided shield and twist it off

to the side.

l Strip one inch of insulation off the center conductor.

3. Connect the Model 7158 to the scanner through the Model 7061

Universal Adapter Card, which is used as an extender to allow ac­cess to all connectors.

4. Select the 3OOa range on the Model 196. Temporarily short the test

leads and zero the instrument. Leave zero enabled for the duration
of the test.

Checking Signal HI to LO Relays

5. Connect one of the BNC plugs to an input connector on the card.
Connect the Kelvin leads to the coax pigtail as shown in Figure 3-3A.

6. $th all channels open, verify that the contact resistance is less than

7. Verify the resistance of the remaining signal HI to LO relays by just

moving the BNC plug and Kelvin leads to the remaining input con­nectors and taking readings.

29

Flgure 3-2. Coax Plgtalt Preparatlon

Checking Signal HI to Output HI Relays and Isolation Relay

8. Connect one of the BNC plugs to an input connector and the other
BNC plug to an output connector. Connect the Kelvin leads to the
coax pigtails as shown in Figure 3-38.

9. Program the scanner to close the channel being tested. This closes
both the signal HI to output HI relay and the isolation relay for

measuring.

IO. Verify that the contact resistance of the relay combination (signal

HI to LO relay and isolation relay) is less than 1% Open the chan­nel after taking the reading.

30

11. Continue with the remaining channels by leaving one BNC plug
on the output connector and moving the other BNC plug and Kelvin

leads to the remaining input connectors. Take readings with the ap-

propriate channel closed.

Flgure 3-3A. Contact Resistance (Slgnal HI to LO Relays)

31

Figure 3-38. Contact Resistance (Signal HI to Output HI

Relays)

32

SECTION 4

REPLACEABLE PARTS

4.1 INTRODUCTION

This section contains replacement parts information, a component
layout, and a schematic diagram for the Model ?l5g.

4.2 PARTS LISTS

Electrical parts are listed in order of circuit designation in Table 4-l. Table

4-2 summarizes mechanical parts.

4.3 ORDERING INFORMATION

To place a parts order or to obtain information about replacement parts,
contact your Keithley representative or the factory. See the back cover

for addresses. When ordering parts, be sure to include the following
information:

l Scanner card model number (7158)
l Card serial number

l Part description
l Circuit description (if applicable)
l Keithley part number

33

Table 4-1. Model 7158 Electrlcal Parts

Circuit
Desig.

Cl

C2-C5

11-112

Kl-K21

RI-RIO

Rll
R12, Rl.3

R14

TE3, TE4,
TE6, TE7,
TEll, TEl

Ul, u2*

u3, u4*
u5*

Sch

Keithley

Description

Capacitor, IOpF, 25V, Aluminum

LOC

-

Al

Part No.

c-314-10

Electrolytic

SW

Capacitor, 0.M 5OV, Ceramic Film
Connector, Coaxial Female

Relay, SI’ST

Resistor, 330kQ, 5%, NW, Carbon

C-237-.1

sev

CS-249

RL70

se” R-76.330k

Composition

Not used

Resistor, 10kfI. 5%. ‘hW, Carbon

82 R-76.1Ok

Composition

Resistor Network, lOkB, 2%, 1.5W,

TF-39

Thick Film

Terminal, Teflon@

sev TE-105-1

IC, Buffer/Line Driver and Receiver, sev IC-520
74HC241
IC, Hex Inverter, 74HC04

sev IC-354

IC, Mnput NAND Gate, 74HCl33 Bl IC-547

Wl

Cable Assembly
Sockets (2) 1

c4 n5a-wo

50-84-20
#18 AWG Bare Buss Wire
X22 AWG Bare Buss Wire
#22 AWG Natural Thinwall Teflon@
Tubing

*These parts are static sensitive. See paragraph 3.2 for handling

precautions.

34

Table 4-2. Model 7155 Mechanlcal Parts

Keithley

.!2!F

1

1
1

1

12

5

6

Description

Bracket, Front Connector Mounting
(CHS-CHlO)

Bracket, Rear Connector Mounting
(CHl-CH4, OUTPUT)

Cable Clamp cc-38-4
Cover, Front Relay (CHS-CHlO) 7158-307
Cover, Rear Relay (CHl-CH4, OUTPUT) 7158-304
Protective Cap (for BNC jacks)
#4-40 x 3116 Phillips pan head sems screw (for

bracket mounting)
#6-32 x l/4 Phillips pan head sems screw (for

cover mounting)

Part No.

7158-303

7158-302

CAP-18

4.4 FACTORY SERVICE

If the scanner card is to be returned to Keithley Instruments for repair,
perform the following:

1. Photocopy and complete the service form at the back of this manual
and include it with the card.

2. Carefully pack the card in the original packing carton.

3. Write ATTENTION REPAIR DEPARTMENT on the shipping label.

Note that it is not necessary to return the scanner mainframe with the
card.

4.5 COMPONENT LAYOUT and SCHEMATIC DIAGRAM

Figure 4-l shows a component layout of the Model 7I58. Figure 4-2
shows a schematic diagram of the Model 7l58.

35

Service Form

Keithley Instruments, Inc.
Test Instrumentation Group
28775 Aurora Road
Cleveland, Ohio 44139

Printed in the U.S.A.