Keithley 871 User manual

Keithley Instruments, Inc.l28775 Aurora Road/Cleveland, Ohio 44139/U.S.A./(216) 24S-04OOlTelex, 96-5469
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©1981, Keithley Instruments, Inc,
I(EITHLEY
Model 871
Digital Thermometer
Instruction Manual
Publication Date: October 1982
Document Number: 871-901-018

871 SPECIFICATIONS
TEMPERATURE SENSOR: Type K
(NiCr-NiAI) thermocouple.
THERMOCOUPLE
INPUTS: Two,
switch selected.
RANGES
GENERAL
DISPLAY:
3~-digit LCD, 0.6" height.
Polarity and decimal point indication.
CONVERSION PERIOD: 400ms (2.5
readings/sec).
OVERRANGE &OPEN-THERMO-
COUPLE
INDICATION: 3least signifi-
cant digits blanked.
MAXIMUM COMMON MODE
VOLTAGE': 500V peak to earth.
TC1 TO TC2
ISOLATION': 500V peak.
mV OUTPUT: Non-linearized, cold-
junction compensated thermocouple
output. (Not isolated from selected
TC
input.)
ACCURACY: ±0.25% of reading
±1°C(0.25% ±1.8°F)
for one year,
18
0to 28°C ambient. Includes N8S
conformity, cold junction compensation
and repeatability errors. Excludes ther-
mocouple errors, however, thermo-
couple errors around
OOC may be comp-
ensated for by
an internal zero adjust-
ment. Extended accuracy from -40°C
to -55°C: +2°/ -Ooc.
REPEATABILITY: ±0.2°C typical for 1
hour at constant ambient temperature.
TEMPERATURE COEFFICIENT: 18° to
28°C; Included
in accuracy specifica-
tion.
From 0° to 18° and 28° to 50°C;
less than ±(0.025% of reading
+O.l°CI/oC.
INPUT CURRENT: 25nA typical; 50nA
maximum.
MAXIMUM ALLOWABLE TC INPUT
OVERLOAD: 150V continuous, 300V
momentary
(10 seconds).
NORMAL MODE REJECTION RATIO:
Greater than 45dB at
50 &60Hz.
COMMON MODE REJECTION
RATIO: Greater than 120dB at
DC, 50
&60Hz.
'WARNING: Ashock hazard exists when
probes or sensors are exposed to voltage
levels greater than 30V rms or 42.4V
peak.
mV OUTPUT ACCURACY (18°-28°C):
±40!'V (OC ranges); ±80!'V (OF
ranges).
OOC = O.OmV. Outputresistance: 17kO.
mV OUTPUT TEMPERATURE COEF-
FICIENT 10°_18°C &28°-500CI:
Less
than (0.1 x-accuracy specification)/oC.
mV OUTPUT PROTECTION: 35V DC
(42V peak) maximum; mV + to mV-
and selected TC input
to mV + or
mV-.
ENVIRONMENTAL LIMITS FOR
OPERATING: 0° to 50°C, less than
80% relative humidity up
to 35°C,
linearly derate
3%R.H./°C 35° to 50°C.
If the instrument has been stored above
18°C
it may typically be operated at
-10°C for 15 minutes.
ENVIRONMENTAL LIMITS FOR
STORAGE: -35°C to 60o C, less than
90% relative humidity up
to 35°C;
linearly derate 3% R.H./oC 35° to
60°C.
COLD-JUNCTION COMPENSATION:
Semiconductor temperature sensor.
THERMOCOUPLE LINEARIZATION:
Multislope A/D with 11 piece-wise-
linear segments between -40°C and
13700
C.
INPUT CONNECTIONS: Two, minia-
ture TC connectors.
mV OUTPUT CONNECTION: Dual
banana jacks.
POWER:
9V alkaline or carbon-zinc
(NEDA 1604) battery.
BATTERY LIFE (CONTINUOUS): 100
hours typical with alkaline battery;
50
hours typical with carbon-zinc battery.
BATTERY INDICATOR: Display indi-
cates
"BAT" when less than 10% of life
remains.
DIMENSIONS. WEIGHT: 178mm long
x78mm wide x42mm thick (7.0" x
3.1" x1.6"). Net weight 300gm
(10.60z).
ACCESSORIES SUPPLIED: Battery,
manual, Model 8712 Thermocouple
Sensor.
-40.0 to 199.9°C O.l°C
-40 to 1370°C l°C
Temperature
Span Resolution
-40.0 to 199.9°F O.l°F
-40 to 1999°F 1°F
Ranges
WARRANTY
SERVICE POLICY
SAFETY
SYMBOLS AND TERMS
The symbol ~ on the instrument denotes that the user should refer
to the operating instructions.
The symbol
#on the instrument denotes that up to 500V may be
present on the terminal(s).
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.
For service on your Model 871 Digital Thermometer, contact your local
Keithley representative
who will be able to give you immediate
assistance in most
cases. Complete repair and calibration facilities are
maintained 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 the above locations. (Addresses are
located on the back cover.)
We warrant
each of our products to be free from defects in material and
workmanship. Our obligation under this warranty is to repair or replace,
at our option, any instrument or part thereof which, within a
year from
date
of shipment, proves defective upon examination. We will pay local
domestic surface freight costs. (NOTE: This warranty does not cover
battery replacement or damage due to battery leakage.)

TABLE OF CONTENTS
GENERAL INFORMATION. ... .. . . . . . .. . . . . . . . . . .. ..... .. 1
Manual Addenda . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.. 1
Optional Accessories. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.. 1
Probes and Sensors. ..................................
.. 1
Preparation
for Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2
Battery Installation/Replacement. .......................
.. 2
OPERATION. ..... .. . . . . . . . . . . . . . . . . .. ........... .. . . . .. 3
SERVICING INFORMATION. . .. .. .. .. .. .. .. .. .. 5
Verification Procedure " 5
Calibration 5
Probe Matching .......................................
.. 7
Disassembly Instructions
... ............................ .. 8
Troubleshooting
Guide. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 9
Parts
List. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 11
Component Layout 12
Schematic Diagram 13
GENERAL INFORMATION
The Model 871 is supplied ready for use with abattery and athermo-
couple probe (Model
8712). The thermometer is designed to work with
.
any type-K thermocouple probe or sensor that is terminated with a
miniature thermocouple plug. Descriptions
of otheravailable probes and
accessories can
be found below.
MANUAL ADDENDA
Any changes to the instrument which occur after the printing of this
manual will be explained
in an addendum included with the instrument.
OPTIONAL ACCESSORIES
The following optional accessories can be used with the Model 871, and
are obtainable through aKeithley representative.
Model 1304 Soft Carrying Case and Stand for the Model 871.
Model 1306 Heavy Duty Carrying Case is arugged carrying case that
is large enough to accommodate the Model 871 plus various other
articles such
as a spare battery, manual, the Model 8712, etc.
Model 8700 Carrying Case With Belt Clip &Holster for the Model
8714 Probe.
Model 8711A Thermocouple Kit includes Model 8712 Thermocouple
Sensor, 6m (20') of AWG
#24 type Kduplex TC wire, miniature TC
plug/jack, standard TC plug/jack.
Probes
and Sensors
Model 8712 Thermocouple Sensor consists of athree foot TC wire
sensor that
has a beaded thermocouple junction.
Model 8713 Immersion Probe for liquid and general purpose appli-
cations up
to 900°C.
Model 8714A Penetration Probe with coiled cord for measurements
of soft
and semi-frozen solids.
Model 8715 Surface Probe for measurement of flat surfaces of solids.
Model 8716 Air/Gas Probe-Exposed junction within protective shroud
responds to ambient temperature while shielded from incident radiation.

PREPARATION FOR USE
Carefully unpack the Model 871 from its shipping carton and inspect for
any obvious signs of physical damage. Report.any damage to the ship-
ping agent at once. The following items
are included with every Model
871 shipment.
1. Model 871 Digital Thermometer
2. Model 871 Instruction Manual
3. Model 8712 Thermocouple Sensor
4. 9V Battery (NEDA 1604)
5. Optional accessories as requested.
BATTERY INSTALLATION/REPLACEMENT
A 9V battery is supplied with the instrument but not installed. Read over
the following installation instructions before attempting
to install or
remove the battery.
WARNING
Turn the Model 871 off and disconnect the input
probes before replacing the battery. Put the cover
back into place on the battery compartment before
resuming use of the instrument.
Remove the cover from the battery compartment by sliding it off in the
direction
of the arrow located on the battery cover. The battery connec-
torsnaps
on and offthe terminals of the battery. Improper installation of
the battery will cause the connecting wires to be severed by excess
strain. proper installation requires that the battery be positioned in such
amanner
(see Figure 1) that the leads protruding from the boot of the
battery connector face toward the outside of the battery compartment.
If the instrument is going to be stored for along period of time or in a
high temperature environment, remove the battery
to prevent leakage
damage.
OPERATION
The Model 871 Digital Thermometer requires the use of K-type TC
probes/sensors, such as the Model 8712 Thermocouple Sensor which is
asupplied accessory.
Low Battery Indicator
Minus sign displayed; plus sign
implied.
IJIOverrange condition or
'\.. .open thermocouple.
1. SET POWER ON.
2. SELECT SCALE AND RANGE.
Fahrenheit: 200°F or 20000F
Celsius: 200°C or 1370
0C
3. SELECT THERMOCOUPLE-TC1
or TC2.
4. INPUT CONNECTORS TC1 and
TC2.
The Model 871 will accommodate
one or
two probes/sensors that are
terminated with standard miniature
type K
TC plugs
5. ANALOG OUTPUT JACKS.
+mV OUT and -mV OUT-Use a
recorder
to monitor temperatures or
asensitive DMM to
make high reso-
lution readings. Use the NBS Ther-
mocouple Calibration Tables for
converting voltage readings into
temperature readings.
Figure
2. Control Layout
WARNING
A shock hazard exists on the Model 871 input ter-
minals when probes or sensors are exposed to volt-
age levels greater than 30V rms or 42.4V peak
(A.N.S.I.).
2Figure
1. Battery Installation
3

4
CAUTION
To avoid instrument damage do not apply more than
150V across the input terminals of the Model 871.
NOTE
Analog output source resistance
is 17kfl. External load
resistance of ~ 10Mfl keeps loading error .s:.O.17% of
reading.
SERVICING INFORMATION
This section contains servicing information for the Model 871.
WARNING
The information presented in this section is intended
onlY for qualified personnel. Turn off the power
before replacing the battery. Replace all covers
before connecting the instrument to potentially
hazardous voltages.
VERIFICATION PROCEDURE
Functionality Check:
While holding the tip
of aclean TC probe between your thumb and
index finger, areading ascending to between 25° and 40°C should be
obtained to confirm the functionality of the Model 871.
Accuracy Check:
1. Prepare apure-water ice bath. (See Calibration Setup Procedure.)
2. Connect a TC probe to input channel 1 (TC1) of the Model 871.
3. Immerse the TC probe into the pure-water ice bath and allow 10
minutes for thermal stabilization.
4. Turn on the Model 871 and use the following table to verify that the
readings on
each range are within specifications.
Table
1. Verification Summary
Range
Allowable Reading
20000F
32°±2°
200°F 32.00±1.8°
1370
0C
oo± 10
200°C 0.0° ±1.0°
Environmental Conditions
The Model 871 should be at an ambient temperature of 23° ±1°C;
relative humidity
less than 80%.
CALIBRATION
Equipment Needed:
1. DC Voltage Calibrator with ± 0.01 % of setting ± 20p.V accuracy5

871
o
CHROMEl
(YELLOW)
ICE
BATH
COPPER
BATTERY COMPARTMENT
Figure 4. Setup Procedure
TRIMMER COMPARTMENT
o
o
Figure 5. Model 871 Rear Panel
Table
2. Calibration Adjustments
lOll" 1.98kO
100:1
VOLT ACE OIVIDER
*The 200 resistor must be held at auniform
temperature during calibration.
DC CALJ8RATOR
871
Calibrator Trimmer Desired
Step Adjustment Range Setting (V)
Adjust Reading
1Input Offset Null 200°C 0.0000
Rl09
OO.ooC
2 +Gain (x 1)
13700C5.3093
Rl04 13200C
3+
Gain (x 10)
200°C 0.6939 Rl05 170.0oC
4
-Gain
200°C -.1527 Rl03 -40.0oC
5
OF Offset 200°F 0.0000
Rl02 32.0oF
1
}
Calibration Procedure
(Fluke 341A or equivalent),
2. 100:1 divider-1.98kfl and 200 resistors, .02% ratio accuracy or bet-
ter, Wirewound.
3. Pure-water ice bath-Dewer Flask or 1quart thermos.
4. K-type TC wire terminated with astandard miniature type K TC plug
(see Figure 3) and acopper wire pair.
:.
~ 0
RED
Figure 3. Type K TC Plug
Calibration Set-Up:
1. Turn on voltage calibrator.
2. Connect the TC plug (Figure 3) to the TCl input of the Model 871.
3. Splice copper wires to the TC wires. Crimp lugs can be used formak-
ing the splice.
4. Connect the other ends of the copper wires to the 100:1 divider as
shown in Figure 4. Connect the copper/iron wire to the positive side.
5. Connect the 100:1 divider to the DC voltage calibrator as shown.
6. Prepare the pure water ice bath as follows:
a. Drill ahole in the cap of aDewar flask or thermos to accomodate
the thermocouples.
b. Firmly pack the flask with pea-size ice cubes made from distilled
water, and then fill the flask with distilled water.
c. Replace the melted
ice with more ice while removing the excess
water.
d.
Place the cap on the flask. Immerse the thermocouples into the
flask and allow 20 minutes for temperature stabilization.
1. Remove the battery cover and trimmer compartment cover from the
Model 871.
(See Figure 5.)
2. Turn the Model 871 on and perform the calibration adjustments listed
in Table 2.
6
PROBE MATCHING
To improve the accuracy of the Model 871 while using aparticular
probe, the calibration
of the Model 871 can be adjusted so that probe
errors in the region of zero (DOC) are compensated. Place the probe in an
ice bath and allow the reading to stabilize. Then reset the zero adjust-
ment
(R109) to a O.ooC reading. 7

TROUBLESHOOTING GUIDE
The following troubleshooting information is intended to be used by
qualified electronic maintenance personnel who are familiar with the
proper
use of standard electronic test equipment.
9
LCD SUPPORT
31462
PAD
30382
LCD
00-27 KNOB
BUSHINGS
871-304
TOP CASE
871-301
FRONT PANEL
OVERLAY
INOT SHOWN)
871-302
Figure 6. Model 871 Exploded View
RETAINING
SCREWS
FEET 14) #4-40 x 7/8
FE-13
BAITERY -I- TJTRIM POT
COVER ~~ _ COVER
30186 _- II ~ -.::::-'l-~~- ~ 30187
~~_." ----~
~ -~ BOITOM CASE
IC SOCKET '--SWITC~og6;VER
SO-84-40 135A-304
TC BRACKET
~<>-\~,\K"" 871-305
HEAT SINK
HS-13
To gain access to the PC board, refer to the first three paragraphs of the
disassembly instructions. Utilize the parts list, schematic and compo-
nent layout
for identifying parts and check point locations. The follow-
ing checks should be made with the Model 871 set to the 200°C Range.
DC Voltage Checks
1. Battery: VBAT)7V
2. Power Supplies:
V+ to~ (Analog Common) = +2.8±OAV
V+ to "'(Digital Common) = +5± 1V
DISASSEMBLY INSTRUCTIONS
To reassemble the Model 871, reverse the above procedure.
To remove the
PC board from the top cover, grasp the TC switch
assembly and lift the board from the cover. The two switch knobs will
remain in the
case.
NOTE
Proper alignment of the strip connector is necessary when
reinstalling the LCD assembly.
If the strip connector has a
conductor side, make sure that side is positioned against
the plastic support of the LCD assembly.
The LCD assembly, along with the strip connector, lifts out
of the case.
WARNING
Be sure to replace the on-off switch cover. Common-
mode voltage will be present on the switch, creating
apossible hazard if the cover is not replaced.
The component side
of the PC board is now exposed and the battery
can be reconnected for troubleshooting. To read the display, some light
downward pressure at the top end
of the circuit board may be required
in order to make contact through the conductive elastomer strip, be-
tween the circuit board and the LCD.
The LCD assembly will remain
in the top cover when the PC board is
removed. Again, be careful not to allow the LCD assembly to fall out
accidentally.
The
PC board and LCD assembly are not secured once the case retain-
ing screws are removed. Be careful not to allow the PC board and LCD
assembly to fall out or shift out of position.
8
Grasp the bottom cover at the input jack end and with alifting and for-
ward pushing motion, carefully remove the bottom cover. While remov-
ing the cover, feed the battery connector through the access opening
in
the bottom of the battery compartment.
Place the unitface down on abench or othersimilar surfaceand remove
the battery compartment cover. Remove and disconnect the battery.
Remove the
two #4-40 x 7/8 retaining screws (see Figure 6).

3. Reference Diode: CR101 to ~ = -1.23 ±0.03V
4. Negative Reference Divider: (Reference to ~)
R119
Pin
mV*
Pin
mV* Pin
mV*
2
-210
5
-204
8
-195
3
-209
6
-199
9
-186
4
-204
7 -198
10
-173
*The setting of R104 and the tolerances of
the resistors within the network (R119)
can affect these levels by ±5%.
5. Deintegrate Comparators:
U103,
Pin 3to ~ =150±25mV
U103B,
Pin6to ~ =-150±25mV
6. Cold Junction Voltage:
(Ambient Temperature 25° ±3°C)
-COM
to.¢. =1.0±0.6mV
Waveform Checks: (Referenced to .. )
Clock
U111, Pin
3360kHz,
5V pp
Square Wave
AID Clock
U112, Pin
540kHz, 5V pp Rectangular Wave
Ref. Clock 1
U102, Pin
960kHz,
5V pp
Rectangular Wave
Ref. Clock 2
U102, Pin 14
6kHz, 5V pp
Rectangular Wave
Backplane
U101, Pin 20
50Hz, 5V pp
Rectangular Wave
Parts List
Circuit
Schematic Keithley
Desig. Description Location
Part No.
BT101 Battery, 9V, NEDA 1604 H4 BA-14
C101 Cap, .22/LF, 100V, Polyester
G3
C-305-.22
C102 Cap, .1/LF, 100V, Polypropylene
G3
C-306-.1
C103 Cap, 470pF, 1000V, Ceramic Disc
E2
C-64-470p
C104 Cap, 220pF, 1000V, Ceramic Disc
02 C-64-220p
C105 Cap, 10/LF, 16V, Aluminum Electrolytic
H4 C-321-10
C106 Cap, 10/LF, 16V, Aluminum Electrolytic
H5
C-321-10
C107 Cap, 33pF, 1000V, Ceramic Disc
C2 C-64-33p
C108 Cap, 47pF, 1000V, Ceramic Disc B2 C-64-47p
C109 Cap,
.1/LF, 16V, Ceramic Disc
C3
C-238-.1
CR101 Diode, Low Voltage Reference
06
DZ-62
DS101 Liquid Crystal Display 3 1/2 digit
F5
00-27
J101 Connector, TC, Female
A1 CS-438
J102 Connector, TC, Female A2 CS-438
J104 Jack, Female
C3
30300-3
J105 Jack, Female
C3
30300-3
J106 Connector, Battery H4 BH-29
0101 Transistor, NPN, Silicon, 2N3904 B2 TG-47
0102 Transistor, NPN, Silicon, 2N3904
B2
TG-47
R101 Thick Film Resistor Network Sev TF-120
R102 Pot, 200k!"! A3 RP-97-200k
R103 Pot, 2k!"!
02 RP-97-2k
R104 Pot, 1 k!"!
B4 RP-97-1k
R105 Pot, 500!"!
C2 RP-97-500
R106 Resistor, 180k!"!, 5%, 1/4W, Comp
G3
R-76-180k
R107 Resistor, 47k!"!, 5%, 1/4W, Comp
04
R-76-47k
R108 Resistor, 470k!"!, 5%,
1/4W, Comp
E3 R-76-470k
R109 Pot, 2k!"!
A3 RP-104-2k
R110 Thick Film Resistor Network Sev TF-132
R111 Resistor, 10k!"!, 10%, 2W, Comp
B1
R-3-10k
R112 Resistor, 10M, 10%, 1/4W, Camp
B1 R-76-10M
R113 Resistor, 5.1k!"!, 5%, 1/4W, Camp
E1
R-76-5.1k
R114
Resistor, 1M!"!, 5%, 1/4W, Comp
E1 R-76-1M
R115
Resistor, Selected, 1%, 1/8W, MtF.
B2 R-88-*
R116
Resistor, Selected, 1 %, 1/8W, MtF.
B2 R-88-*
R117
Thick Film Resistor Network Sev TF-122
R118
Resistor, 150k!"!, 5%, 1/4W, Comp
C5
R-76-150k
R119
Thick Film Resistor Network Sev TF-121
R120 Resistor,
10k!"!, 5%, 1/4W, Comp
C2 R-76-10k
R121
Resistor, 10k!"!, 5%, 1/4W, Comp
C2 R-76-10k
R122 Resistor Selected 5%
1/4W Como A3 R-76-*
10 11

PARTS LIST (CONT.)
13
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DESiGNATIONS USED
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COMPONENT LAYOUT
12
Circuit
Schematic Keithley
Desig.
Description
location
Part No.
R122 Resistor, 324k, ±0.5%, 1/4W, Mtf
B3 R-88-324k
R124 Resistor,100f!,
±O.l%, 1/4W, Comp B3 R-88-100
R125 Resistor,6.8k,
±5%, 1/4W, Carbon Film R-76-6.8k
S101
Switch, Rotary Sev SW-428
S102 Switch, Rotary Bl
SW-438
S103 Switch, SPOT, ON-OFF
H4
SW-417
TC-l,2
TC Cable Al,A2 SC-87
Ul01 3% Digit Single Chip
A/D Converter G4 lSI-22
U102 Dual Synchronous Up Counter
F1
IC-282
U103
low Power JFET Input Op Amp 03,04 IC-279
U104
low Power JFET Input Op-Amp E5,H5 IC-279
U105 COS/MOS Quad Bilateral Switch Sev IC-149
U106 CMOS Quad Exclusive
OR Gate Sev IC-226
U107 Dual
"0" Type Flip-Flop B6 IC-l03
U108 14-Stage Binary Counter B5
IC-280
U109
linear Op Amp B2 IC-203
U110 Current Source A2 IC-278
Ul11 Quad 2-lnput
NOR Gate Sev IC-108
Ul12 COS/MOS Divide by NCounter
G2
IC-145
Ul13 Quad, 2-lnput, AND GATE Sev IC-138
Ul14
Analog Multiplexer 04
IC-277
Yl0l
Resonator, 360kHz E2
CR-14

SCHEMATIC
MODEl 871 DIGITAL THERMOMETER
13
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List all control settings and describe problem.
Add'ess _
Model No. 5e'iel No. P.O. No. Dete _
Phona _
KEITHLEY
_____________________ IAttach additional sheets as necessary.)
City Stete .Zip _
Nome _
Company _
SERVICE FORM
Show ablock diagram of your measurement system including all instruments connected (whether power
is turned on or not), Also describe signal source.
Where is the measurement being performed? lfaetary, controlled laboratory, Qut-of-doors, elc,I _
What power line voltage is used? Variation? _
Frequency? Ambient Temperature? of.
Variation? OF. ReI. Humidity? Other?
Any additional information. (If special modifications have'been made by the user, please describe below.)
• Be sure to include your name and phone number on th,s service form.