Tektronix 7057A Instruction Manual

Model 7057A Thermocouple Scanner Card Instruction Manual

Contains Operating and Servicing Information

Publication Date: January 1992
Document Number: 7057A-901-01 Rev. D

WARRANTY

LIMITATION OF WARRANTY

Safety Precautions

The following safety precautioos should be obsewed before using this product and any asno­ciated instrumcntatioo. Although some inrtromeots and accessories woold nonnally bo used
with nowhazardous voltages, there arc situations wberc hazardous conditions may be present.

This product is intended for use by qualified personnel who rccogoiu: shock hazards and are
familiar with tbc safety pnxaotions rcqoircd to avoid possible injuly. Read lbe operating it]­formation carefully before using the product.

‘The types of product users arc:
Kesponsiblc body is tbe iodividunl or group responsible for the USC sod owinleoaoce of

equipment, for ensuring tlnt the equipment ia operated within its spccilications and operat­ing limits, and for ensuring that operators are adequately trained.

Operators use the product for its intended function. Tbey most be trained in electrical safety
procedures and proper use of the iostrument. ‘lhey most be protected from electric shock and
~onmt with hazardous live circuits.

Maintenance personnel perform mutioe procedures oo the product to keep it operadog, for
example, setting the hoc voltage or replacing consumable materials. Maintenance proccdurcs
am dcacribed in the manual. The procedures explicitly state if the operator ~nay perform them.
Othcrwisc, they should be performed only by senice pcnonoel.

Service personnel are trained to work on live circuits, sod perfoonn safe installations sod re­pairs of products. Ooly properly trained setvice personocl may perform installation and scr­vice procedures.

Exercise extreme caution whco a shock hazard is present. Lethal voltage may be present on
cable coonector jacks or test fixtures. 111~ American National Standards lostitute (ANSI)
stam that a shock hazard exists wheo 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.

Users of this product must be protected fmm electric shock at all timer. The responsible body
must eosum thtat wets aw pwented a.cce~s aod/orinsulatcd from every connection point. lo some
cases, conoectiuns most be exposed to potential buman cootact. Product usa io these circuo­stances must be trained to protect themselves from the risk of electric shock. If the circuit is ca­pable of operating at or abovc 1wO volts, no conductive part of the circuit may be exposed.

AY described in the Ioteroational Electratechnical Commission (IEC) Standard IEC 664, dig­ital multimcter measuring circuits (e.g., Keifhley Models 175A, 199, 2OOQ,2COl, 2002, and

2010) are Installation Category II. All other instruments signal tennioals are Installation Cat­egory I and must oat be conoected to mains.

Do not conoect switching cards directly to unlimited power circuits. They are inlendcd to bc
used with impedance limited sources. NEVER connect switching cards directly to AC mains.
Wheo conoccting sources to switching cards. iostall protective devices to limit fault current
sod voltage to tbc card.

Before operating ao 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 bcforc each oso.

For maximum safety, do not touch the product, test cables, or any other instrumcots while pow­er is applied to the circuit under test. ALWAYS remove power from the entire test system sod
dischuge soy capxitors before: coooccting or disconnecting cables or jumpers, installing 01

removing switching cards. or making iotemtil chaogcs, socb as installing or nzmoviog jumpers.
Vu not touch soy object that could provide a con-cot path to tbc common side of the circuit

under test or power line (eatth) ground. Always make measurements witb dry hands while
standing oo a dly, insulated surface capable of withstanding tbc voltage bciog measured.

The instrument and accessories most be used in accordance with its specifications and op­eratiog iostructioos or tbe safety of the equipment may be impaired.

Do not exceed the maximum signal levels of the instruments and accessories. as defined in
tbe speciticationr sod operatiog information, and es show on the instrument or test fixture
panels, or switcbiog cant.

When fores are used in a product, replace with same type sod rntiog forcootioued pmtectioo
against fire hazard.

Cbassir connections must only be used as shield coooectioos for me~suriog circoits, NOT as
safety eaflh ground connections.

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

1ra@

screw is present, connect it to safety earth ground uaiog the wire recommended in

the user documentation.

The ! symbol on an iostroment indicates that the user should refer to the operating ill-

n

stmctions located io tbc manual.

The h

symbol on al iostmment shows that it CNI source or IIICRIIUII: loo0 volts or more, ill­eluding the combined etTect of normal ad common mode voltages. Use stiuldarrl safety precau­lions to avoid pcrsooal cootect with these voltages.

TIE WARNING beading in A manual enplaios dangers that might result in personal injury or
death. Always read the associated information wy carefully hcfore ptxformiog the indicated

pC"CCdU~C.

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

lostrumcntatioo and accessories shall not be connected to humans.

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

To maintain pmtcctioo from electric shock and ftre, replacement components in mains cir­coils, including the power transfouner, test leads, and ioput jacks, must he purchased from
Keithley Instruments. Standard fuses, with applicable national safety appmvals, may be used

if the ratiog sod type are the same. Other components that are not safety r&ted may hc por-

chased from other suppliers as long as they are equivalent to tbe original component. (Note
that selected parts should be purchased only through Keithley Iostmmcnts to maiotain acco­racy sod fonctiooality of the product.) If you we unsure about the applicability of a replacc­ment component, call a Keithlcy 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 tb the instrument or allow liquids to
enter or spill on the instrument. Products that consist of a circuit hoard with no case or cbas­sis (e.g., data acquisition board for installation into a computer) should neverrequire clean­ing if handled according to instructiuns. If the board becomes contaminated sod operation

is affected. the hoard should he returned to the factory for proper cleaninglserviciog.

tie”. 2rB

SPECIFICATIONS

CHANNELS PER CARD: 9 plus temperature reference.
CONTACT CONFIGURATION: 2 Pole Form A with common guard.

CONNECTOR TYPE: Screw terminals in isothermal block, No. 18 AWG wire

maximum.

RELAY DRIVE CURRENT: 12mA lper relay).

TEMPERATURE OFFSET: i0.05°C maximum from HI to LO of any input or be-

tween any two adjacent channels in one column on the isothermal block. * O.lOC
maximum between an two ferminals on the isothermal block. Maximum addi-

tional dynamic offset J ue fo 10°C step chsngo in environment: *O.l°C after one

hour settling.

TEMPERATURE REFERENCE: Thermistor in a linearized bridge.

REFERENCE OUTPUT: - ,m”,°C, ,Om” at +3O”CI.
REFERENCE ACCURACY: f0.2S°C ,,O’=C to 35OC,, +0.5OC

WARM UP TIME: 1 Hour to rated accuracy.

CONTACT OFFSET VOLTAGE: I,,“.
ACTUATION TIME: < 5ms, exclusive of mainframe.
CONTACT LIFE: > lo* cbs”res.
CONTACT RESISTANCE: < 2n (<O.,O inidall.
C”ANNEL ISOLATION: ‘109O. 1OpF.
INPUT ISOLATION: a 10’R. 15OpF.
COMMON MODE VOLTAGE: 200” peak.
ENVIRONMENT, SPECIFIED: ,O’=C to 35°C. up to 70% R.H.
ENWRONMENTAL, OPERATING: O°C to 50°C, up to 35OC at 70% R.H.

ENVIRONMENTAL. STORAGE: -25OC to +55”C.
DIMENSIONS, WEIGHT: 32mm high x 114mm wide x 272mm long I1 %*’ x

4%“~ 10%“) net weight 0.54kg Illb. 5,502.).

Signaf Level: 42”. 1DDmA. 2VA maximum Inon-inductive load only).

,O”C to 10% and 35°C to 60°Cl.

TABLE OF CONTENTS

SECTION l-GENERAL INFORMATION
Introduction

1.1
Warranty Information

1.2
ManualAddenda

1.3

Safety Symbols and Terms

1.4
SECTION Z-OPERATION

Introduction

Wiring

Operating Considerations,,

2.3

Operating Hints

2.4

Thermocouple Measurement Considerations,

2.5

Measurement Procedure

2.6

SwitchTerminology.. .....................................

2.7

SECTION 3-SERVICING INFORMATION
Calibration Procedure.,

3.1
Calibration Procedures

3.2

Test of Calibration

3.3
Channel Isolation,,

3.4

3.5

Input Isolation, Common Mode
SECTION 4-REPLACEABLE PARTS

introduction,

4.1
ReplaceableParts

4.2
Ordering Information

4.3

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

4.4

4.5

Component Layout and Schematic Diagram

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LIST OF FIGURES

Typical Thermocouple Connections

:

Plug-In Board Assembly.

3

Using GUARD Connection

4

Typical Multiple Channel Analog Connections.
Typical Thermocouple Measurements

Switch Terminology

ii

Chsnnel~lsolation Test Setup
Common Mode Isolation Test Setup

;

Model 7057A. Component Location Drawing

9

Model 7057A. Schematic Diagram

10

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22

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ii
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3
4
5
5
6

7
22
22
26
27

LIST OF TABLES

Summary of Temperature Measurement Procedure

:

NBS Quwtic Coefficients for Types S, R, B, E, J, K and T
Recommended Test Equipment.

3
4

Model 7057A Rep!aceab!e parts .:

5

Model 7057A Replaceable Parts ,Mec”a”~ca,, 24

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SECTION 1

GENERAL INFORMATION

1.1 INTRODUCTION

The Model 7057A is a thermocouple scanner card which is field-installable in an
appropriate scanner mainframe (e.g. Model 7051. Since it combines the func­tions of a thermocouple scanner and uniform temperature reference, it is
especially useful for scanning thermocouples. The input terminals aie HI0 alloy­copper set in an isothermal block to minimize temperature differences. A ther­mistor sensor within the isothermal block is used with a bridge network located
on the Model 7057A to give an indication of the temperature reference or cold
junction. The temperature of the heat sink is used to calculate the corrected
thermocouple output. The output voltages of each thermocouple must be con­verted to temperature PC or OF) using appropriate thermocouple tables or
polynomial equations. In addition any channel may be used for monitoring low­level signals. The Model 7057A uses Z-pole form A contacts for witching of
signals up to 35V peak or IOOmA peak. Input and output connections 818 made
through the rear panel of the scanner mainframe using #4 screw terminals on the

Model 7057A.

1.2 WARRANTY INFORMATION

Warranty information is stated on the inside front cover of the manual. If there is

a need for service, contact the Keithley representative or authorized repair facility
in your area. Check the back cover of this manual for addresses. The service

form supplied at the end of this manual should be used to provide the repair

facility with adequate information concerning any difficulty.

1.3 MANUAL ADDENDA

Any improvements or changes to this manual will be explained on an addendum
included with this manual.

1.4 SAFETY SYMBOLS AND TERMS

The symbol

i;;i;TbolN

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

instrument.

denotes that the user should refer to the operating instruc-

A

denotes that a high voltage may be present on the ter-

1

SECTION 2

OPERATION

2.1 INTRODUCTION

This section provides information needed to use the Model 7057A with an
*ppropriate scanner mainframe.

2.2 WIRING AND INSTALLATION

1. Wiring Configuration-The Model 7057A has a Z-pole switching configura­tion. It may be used to connect one of nine signals to the output. The tenth
scanner position (Channel 1) is used to monitor the temperature of the input
terminals with a thermistor bridge. Bridge power is derived from a non-

isolated internal supply with jumper provisions for an external isolated supply.
A. lnwt and output connections are made to the screw terminals shown in

Fi& 1.

8. Signal path resistance, including both poles of a channel relay, is typically
less than 1.4?, less than 2Q et end of life.

C. A guard surrounds 811 signal paths and is connected to the heat sink

surrounding the input terminals. Connection to the guard is made at the
isothermal block.

2. Installation-Refer to the scanner mainframe instruction manual for scanner
instructions.

I

I-==

Figure 1. Typical Thermocouple Connections.

3

2.3 OPERATING CONSIDERATIONS

1. Signal Level-IOV peak, 1OmA peak with a resistive load for expected life.
Maximum peak instantaneous rating is 35V.

2. Contact Potential (Laboratory Environment)-Less than I$/ from input to
output when copper wires are used.

3. Isolation-Guarded interchannel resitanceis nominally@!?. Guarded cap*­citance is less than 1OOpF between any two channels.

4. Maximum Levels-A 2OOV peak between channels or from channel to
guard or mainframe (digital) common.

5. Operating Environment-OQC-50°C, up to 35°C at 70% relative humidity.

2.4 OPERATING HINTS

1. The clamp-type screw terminals will accept #I8 to #36 AWG (0.044 to

0.005 inch) wire. Figure 2 shows the mechanical features of the Model
7057A which prevent lead movement after the board is wired.

Figure 2. Plug-h Board Assembly

2. Thermal offset on any given channel is typically repeatable to within a few
hundred nanovolts each time the channel is selected. That is, every time a
channel is selected and allowed to stabilize for a period of time, the channel
will exhibit the same thermal offset to within a few hundred nanovolts. This
offset may be accounted for in the measurement and subtracted from each

reading, to obtain a more precise measurement.

3. To effectively eliminate error voltages produced by leakage current, the
GUARD terminal should be connected to the reference connection on the
channel which is most sensitive to error (that is, the one which has the
lowest source voltage versus the highest resistance). For instance. two
sources are connected to the Model 7057A; one having an equivalent
source voltage of IV with a series resistance of IOOkR and the other having
a source voltage of .lV with a lkn series resistance. The lOOka source
resistance will develop 100 times the error voltage as the lkn Knwze
resistance. Its source voltage however, is only 10 times as great. which
means that the percentage error is 10 times as large on the lV/lOOkn chan-

4

nel. The GUARD would therefore be connected to the reference point of
this channel. ISee Figure 3).

Figure 3. Using GUARD Connection

4. The relay switching time includes a 9&s time interval between releases end
operate conditions. The actuation time is less than 5msec.

5. Reactances in the system cause transients during switching.

6. For scanner systems using two or more plug-in boards output HI and LO on

all Model 7057A plug-in boards should be made using continuous copper
wires. This ensures that the number of copper-to-copper junctions is at a
minimum and therefore unnecessary thermal effects are avoided. Figure 4
shows the method of continuous board-to-board connections.

Figure 4. Typical Multiple-Channel Analog Connections

2.5 THERMOCOUPLE MEASUREMENT CONSIDERATIONS

A thermocouple is B junction formed between two dissimilar metals. If the

junction temperature is T, a voltage E, will be developed between leads A and

B. When connected to B voltmeter two more junctions are formed with meter

terminals, which are usually copper as shown in Figure 5.