Omega 871A, 872A User Manual

®

User’s Guide

http://www.omega.com

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Only model 871A has
CE certification

Digital Thermometers

871A and 872A

omega.com

TM

OMEGA

®

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It is the policy of OMEGA to comply with all worldwide safety and EMC/EMI regulations that apply. OMEGA is
constantly pursuing certification of its products to the European New Approach Directives. OMEGA will add the
CE mark to every appropriate device upon certification.

The information contained in this document is believed to be correct but OMEGA Engineering, Inc. accepts no liability for any
errors it contains, and reserves the right to alter specifications without notice.

WARNING: These products are not designed for use in, and should not be used for, patient connected applications.

TABLE OF CONTENTS

MODEL 871A AND MODEL 872A

DIGITAL THERMOMETERS

SECTION PAGE

SECTION 1 INTRODUCTION .................................................................. 1

1.1 General Description ................................................................... 1

1.2 Features ..................................................................................... 1

2.1 Accessory Items......................................................................... 1

SECTION 2 INSTALLATION .................................................................... 2

2.1 Unpacking.................................................................................. 2

2.2 Battery Installation ..................................................................... 2

SECTION 3 OPERATION ......................................................................... 3

3.1 Controls and Indicators.............................................................. 3

3.2 Operating Procedure.................................................................. 5

SECTION 4 SERVICE INFORMATION .................................................... 5

4.1 Verification Check...................................................................... 5

4.1.1 Functionality Check ................................................................... 5

4.1.2 Accuracy Check......................................................................... 6

4.2 Calibration for Model 871A ........................................................ 6

4.2.1 Equipment Needed .................................................................... 6

4.2.2 Environmental Conditions.......................................................... 6

4.2.3 Setup.......................................................................................... 7

4.2.4 Calibration Procedure ................................................................ 7

4.3 Calibration for Model 872A ........................................................ 8

4.3.1 Equipment Needed .................................................................... 8

4.3.2 Environmental Conditions.......................................................... 8

4.3.3 Setup.......................................................................................... 8

4.3.4 Calibration Procedure ................................................................ 9

4.4 Disassembly for Model 871A and Model 872A.........................10

4.5 Troubleshooting Guide .............................................................11

4.5.1 DC Voltage checks Model 871A ...............................................12

4.5.2 DC Voltage Checks Model 872A ..............................................12

4.5.3 Waveform Checks Model 871A ................................................13

4.5.4 Waveform Checks Model 872A ................................................13

SECTION 5 SPECIFICATIONS FOR MODEL 871A

AND MODEL 872A .............................................................13

5.1 Parts List ...................................................................................16

i

SECTION 1 INTRODUCTION

1.1 GENERAL DESCRIPTION

The OMEGA

®

Model 871A and Model 872A Digital Thermometers are
ultrasensitive hand held instruments. Low power LSI devices combined
with a large 0.6" (15 mm) LCD, deliver reliability, extended battery life, and
an extremely readable readout. One nine volt battery will deliver 100 hours
of continuous operation.

The 871A and 872A are operationally identical except for minor differences
related to each model’s thermocouple input: Model 871A is designed for
use with type K (Chromel-Alumel) thermocouples; Model 872A is designed
for use with type J (Iron-Constantan) thermocouples.

Cold junction electronic circuitry in the Model 871A and Model 872A
automatically compensates for ambient temperature changes. A special
integrating A/D converter corrects for thermocouple non-linearity during
each digitization cycle. The resulting conformity to the standard
thermocouple voltage table is within 1ºC over the entire measurement span of
the instrument.

Although the 871A and 872A are ideal for temperature measurement in the
field, they also function well as bench instruments when equipped with the
optional tilt stand. The Model 871A and Model 872A provide dual inputs,
selectable scales (ºF/ºC), 1.0º and 0.1º resolution, and an analog output.
The versatile dual input configuration permits two point temperature
measurement such as those required in process monitoring. The analog
output allows interfacing with chart recorders or data acquisition system’s
functioning as an electronic ice-point reference.

1.2 FEATURES

• Wide temperature range • Dual thermocouple inputs

• Selectable scales (ºF/ºC) • Analog output

• 0.1º and 1.0º resolution • Heavy duty construction

• 0.25% accuracy

1.2.1 ACCESSORY ITEMS
SC-GG-[*]-30-36-SMP-M Thermocouple sensor (supplied with

KS-871 Tilt stand
SC-800 Soft carrying case
880-A2 Deluxe carrying case
U9VL 9 V lithium battery
SMP-[*]-M Subminiature thermocouple connector, male
SMP-[*]-F Subminiature thermocouple connector,

OS-201-1 2 oz. jar of high thermal conductivity paste

*Insert thermocouple type: J for Model 872, K for Model 871

unit) if purchased separately.

female

for fast surface measurements

1

SECTION 2 INSTALLATION

2.1 UNPACKING

Remove the Packing List and verify that all equipment has been received. If there
are any questions about the shipment, please call OMEGA Customer Service
Department at 800-622-2378 or [phone].

The following items are included:

Quantity Description

1 871 or 872 Digital Thermometer
2 Beaded Wire Thermocouples
1 TAS Transition Adapter
1 9 Volt Alkaline Battery
1 Operator’s Manual

Upon receipt of shipment, inspect the container and equipment for any sign of
damage. Take particular note of any evidence of rough handling in transit.
Immediately report any damage to the shipping agent.

NOTE

The carrier will not honor any claims unless all shipping material is
saved for their examination. After examining and removing contents,
save packing material and carton in the event reshipment is necessary.

2.2 BATTERY INSTALLATION

Turn the model 871/872A 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.

A 9 V battery is supplied with the instrument but not installed. To install the
battery, remove the cover from the battery compartment by sliding it off in the
direction of the arrow located on the battery cover. The battery connector snaps
on and off the 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 a manner (see Figure 2-1) 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 a long
period of time or in a high temperature environment, remove the battery to
prevent damage due to leakage.

WARNING

2

Figure 2-1. Battery Installation

SECTION 3 OPERATION

The Model 871A is designed to work with any type K thermocouple probe or sen­sor, fitted with an OMEGA miniature thermocouple connector SMP-K-M or industry
equivalent.

The Model 872A is designed to work with any type J thermocouple probe
or sensor, fitted with an OMEGA miniature connector SMP-J-M or
industry equivalent.

3.1 CONTROL AND INDICATORS

Figure 3-1 and Table 3-1 illustrate and describe the controls and indicators on the
871A and 872A.

Figure 3-1. Model 871A Controls and Indicators

*Model 872A has same controls and indicators, only range selections differ.

3

TABLE 3-1

MODEL 871A AND MODEL 872A

CONTROLS AND INDICATORS

ITEM CONTROL/INDICATOR FUNCTION

1. ON/OFF switch Turns unit on or off.

2. Scale and range selector Allows user to select: ºF or ºC scale,
any of four possible thermocouple
ranges, and 1.0º or 0.1º resolution.

3. Thermocouple selector Allows user to read either of two
thermocouples by simply turning
the dial.

4. Thermocouple input jacks Allows direct connection of two
thermocouples to the unit via an
OMEGA miniature male connector.

5. Analog output jack, The analog output is a nonlinearized,

+mV OUT and -mV OUT cold junction compensated, amplified

thermocouple output. (Not isolated
from selected TC input.) Use a
recorder to monitor temperature or
a sensitive DMM to make higher
resolution reading. Refer to mV
output specifications for mV output
to temperature ratios.

6. Low battery indicator When the battery level is low, BAT
will appear in upper left corner of
the display. Battery should then be
replaced to avoid error erroneous
readings due to battery failure.

7. Overrange/open When an overrange indication or

thermocouple indication open thermocouple condition exits,

a 1 followed by blanked digits will
appear in the display.

4

3.2 OPERATING PROCEDURE

1. Turn power on.

2. Select scale and range (see Tables 3-2 and 3-3).

3. Select thermocouple TC1 or TC2.

4. Connect one or two thermocouples to the input jacks.

5. Connect a recorder to the analog output to monitor temperatures,
or connect DMM to make high resolution readings, if desired.

MODEL 871A TEMPERATURE RANGE

Range Span Resolution

200°F -40.0° to 199.9°F 0.1°F

2000°F -40° to 1999°F 1°F

200°C -40.0° to 199.9°C 0.1°C

1370°C -40° to 1370°C 1°C

TABLE 3-2

TABLE 3-3

MODEL 872A TEMPERATURE RANGE

Range Span Resolution

200°F -40.0° to 199.9°F 0.1°F

1400°F -40° to 1400°F 1°F

200°C -40.0° to 199.9°C 0.1°C
760°C -40° to 760°C 1°C

SECTION 4 SERVICE INFORMATION

4.1 VERIFICATION CHECK

4.1.1 Functionality Check

Attach the GG-TC-K-24-36-SMP beaded wire thermocouple probe
(supplied) to the Model 871A and the GG-TC-J-24-36-SMP beaded wire
thermocouple probe (supplied) to the Model 872A. Hold the sensor end
between two fingers. The reading should change from ambient to between
77º to 104º F (25º to 40ºC).

5

4.1.2 Accuracy Check

1. Prepare a pure-water ice bath (see paragraph 4.2.3, step 5).

2. Connect a thermocouple probe to input 1 of the unit.

3. Immerse the probe into the pure-water ice bath and allow ten
minutes for thermal stabilization.

4. Turn on the instrument and use Tables 4-1 and 4-2 to verify
that the readings on each range are within specification.

Range Allowable Reading

2000°F 32° ± 2°

200°F 32.0° ± 1.8°

1370°C 0° ± 1°

200°C 0.0° ± 1.0°

TABLE 4-1

MODEL 871A RANGE CHART

TABLE 4-2

MODEL 872A RANGE CHART

Range Allowable Reading

1400°F 32° ± 2°

200°F 32.0° ± 1.8°
760°C 0° ± 1°
200°C 0.0° ± 1.0°

4.2 CALIBRATION FOR MODEL 871A

4.2.1 Equipment Needed

1. DC Voltage Calibrator with 1 ±0.01% of setting ± 20 µV accuracy.

2. 100: 1 divider: 1.98 kilohm and 20 ohm wirewound resistors with

0.02% ratio accuracy or better.

3. OMEGA TRC III Ice Point Reference Chamber or distilled water ice
bath.

4. OMEGA type K TRP Reference Probe or make a thermocouple transi­tion junction (see paragraph 4.2.3).

4.2.2 Environmental Conditions

To meet all specifications, the conditions for calibration should be an
ambient temperature 23º ± 1ºC; relative humidity less than 80%.

6

4.2.3 Setup

(Refer to Figure 4-1.)

1. To make a thermocouple transition junction, silver solder a piece of
copper wire to each (type K) thermocouple wire and insulate the
junction with a waterproof jacket.

2. Connect the thermocouple wires from the type K transition junction to
an OMEGA miniature thermocouple connector SMP-K-M.

3. Plug in the miniature connector to input TC1 of the Model 871A.

4. Connect the copper wires to the 100:1 divider (see Figure 4-1) with the
copper/wire (positive) junction connected through the 1.98 kilohm
resistor, to the dc calibrator positive terminal.

5. Prepare a distilled water ice bath as follows:

a. Drill a hole in the cap of a Dewar flask or Thermos

the transition junction.

b. Firmly pack the flask with pea-size ice chips made from distilled

water and then fill the flask with distilled water.*
c. Replace the melted ice with more ice while removing excess water.
d. Place cap on the flask and insert the transition junction into the

flask. Allow 20 minutes for temperature stabilization.

*Using tap water may cause inaccuracies due to contaminants.

*The 20Ω resistor must be held at a uniform
temperature during calibration.

Figure 4-1. Calibration Setup for Model 871A

TM

to accommodate

4.2.4 Calibration Procedure

It is not necessary to disassemble the case for calibration. All adjustments
are accessible by removing the covers shown in Figure 4-2.

1. Remove the battery and trimmer compartment covers from the Model 871A.

2. Turn the Model 871A on and perform the calibration adjustments listed
in Table 4-3.

7

Figure 4-2. Access to Calibration Adjustments

TABLE 4-3

CALIBRATION ADJUSTMENTS FOR MODEL 871A

871 Calibrator Trimmer Desired

Step Adjustment Range Setting (V) Adjust Reading

1 Input Offset Null 220ºC 0.0000 R109 00.0ºC
2 + Gain (X1) 1370ºC 5.3039 R104 1320ºC
3 + Gain (X10) 200ºC 0.6939 R105 170.0ºC
4 - Gain 200ºC -0.1527 R103 -40.0ºC
5 ºF Offset 200ºF 0.000 R102 32.0ºF

4.3 CALIBRATION FOR MODEL 872A

4.3.1 Equipment Needed

1. DC voltage calibrator with ±0.01% of setting and ± 20 µV accuracy.

2. 100: 1 divider: 1.98 kilohm and 20 ohm wirewound resistors with 0.02%

ratio accuracy or better.

3. OMEGA TRC III Ice Point Reference Chamber or distilled water ice bath.

4. OMEGA type J TRP Reference Probe or make a thermocouple

transition junction (see paragraph 4.3.3).

4.3.2 Environmental Conditions

To meet all specifications, the conditions for calibration should be: an
ambient temperature of 23º ± 1ºC; relative humidity less than 80%.

4.3.3 Setup

1. To make a thermocouple transition junction, silver solder a piece of

copper wire to each (type J) thermocouple wire and insulate the
junction with a waterproof jacket.

2. Connect the thermocouple wires from the type J transition junction to

an OMEGA miniature connector SMP-J-M.

8

3. Plug in the miniature connector to input TC1 of the Model 872A.

4. Connect the copper wires to the 100:1 divider (see Figure 4-3) with the
iron wire connected through the 1.98 kilohm resistor, to the dc calibra­tor positive terminal.

5. Prepare a distilled water bath as outlined in paragraph 4.2.3, step 5.

*The 20Ω resistor must be held at a uniform

temperature during calibration.

Figure 4-3. Calibration Setup for Model 872A

4.3.4 Calibration Procedure

It is not necessary to disassemble the case for calibration. All adjustments
are accessible by removing the covers shown in Figure 4.2.

1. Remove the battery and trimmer compartment covers from the Model
872A.

2. Turn the Model 872A on and perform the calibration adjustments listed
in Table 4-4.

TABLE 4-4

CALIBRATION ADJUSTMENTS FOR MODEL 872A

9

872A Calibrator Trimmer Desired

Step Adjustment Range Setting (V) Adjust Reading

1 Input Offset Null 200ºC 0.0000 R109 00.0ºC
2 + Gain (X1) 760ºC 4.2922 R104 760ºC
3 + Gain (X10) 200ºC 1.02217 R105 190.0ºC
4 - Gain 200ºC -.19604 R103 -40.0ºC
5 ºF Offset 200ºF 0.000 R102 32.0ºF

4.4 DISASSEMBLY FOR MODEL 871A AND MODEL 872A

The PC board and LCD assembly are not secured once the case retaining
screws are removed. Be careful not to allow the PC board and LCD
assembly to fall out or shift out of position.

1. Place the unit face down on a bench or other similar surface and
remove the battery compartment cover. Remove and disconnect the
battery. Remove the two #4-40 x 7/8 retaining screws.

2. Grasp the bottom cover at the input jack end and with a lifting
and forward pushing motion (see Figure 4-4 and Figure 4-5), carefully
remove the bottom cover. While removing the cover, feed the
battery connector through the access hole in bottom of the
battery compartment.

3. 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,
between the circuit board and the LCD.

4. To remove the PC board from the top cover, grasp the TC switch
assembly and lift until the input jacks become disengaged from the
cover. The PC board can now be removed using a slight clockwise
motion to free the two switch knobs from their normal positions in
the case.

5. 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.

6. The two switch knobs can be removed from the PC board assembly by
simply pulling them off the switch shafts.

7. The LCD assembly, along with the strip connector, lifts out of the case.

8. To reassemble the unit, reverse the above procedure.

NOTE

Proper alignment of the strip connector is necessary when reinstalling the
LCD assembly. Make sure that the conductor side of the strip connector is
positioned against the plastic support of the assembly.

WARNING

Be sure to replace the on-off switch cover. Common-mode
voltage will be present on the switch, creating a possible hazard if
the cover is not replaced

10

Figure 4-4. Removing the Cover

Figure 4-5. Disassembled Model 871A and Model 872A

4.5 TROUBLESHOOTING GUIDE

The troubleshooting information is intended to be used by qualified elec­tronic maintenance personnel who are familiar with the proper use of stan­dard electronic test equipment.

To gain access to the PC board, refer to the first three paragraphs of the
disassembly instructions. Utilize the Parts List, Schematic and Component
Layout for identifying parts and checkpoint locations. The following checks
should be made with the Models 871A and 872A set to the 200ºC Range.

11

4.5.1 DC Voltage Checks For Model 871A

1. Battery: VBAT > 7 V

2. Power Supplies:
V + to È (Analog Ground) = +2.8 ± 0.4 V
V + to È (Digital Ground) = +5 ± 1 V

3. Reference Diode: CR101 to È (Analog Ground) = -1.23 ± 0.03 V

4. Negative Reference Divider: (Reference to È Analog Ground)

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:

U103A PIN 3 to È = 150 ±25mV
U103B, PIN 6 to È = -150 ± 25 mV

6. Cold Junction Voltage:

(Ambient temperature 25º ±3ºC)

-COM to È = 1.0 ±0.6 mV

4.5.2 DC Voltage Checks For Model 872A

1. Battery: VBAT > 7 V

2. Power Supplies:

V + to È (Analog Ground) = +2.8 ± 0.4 V
V + to È (Digital Ground) = +5 + 1 V

3. Reference Diode: CR101 to È (Analog Ground)= -1.23 ±0.03 V

4. Negative Reference Divider: (Reference to È Analog Ground)

R119

Pin mV* Pin mV* Pin mV*

2 -312 5 -274 8 -267
3 -293 6 -272 9 -254
4 -277 7 -271 10 -242

*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 3 to È =190 ±30 mV
U103B, Pin 6 to È = -180 ±30 mV

6. Cold Junction Voltage:

(Ambient temperature 25º ±3ºC)

-COM to È = 1.3 mV ±0.6

12

4.5.3 Waveform Checks For Model 871A

Waveform Checks: Referenced To È (Digital Ground)
Clock U111, Pin 3 360 kHz, 5V pp Square Wave

A/D Clock U112, Pin 5 40 kHz, 5V pp Rectangular Wave
Ref. Clock 1 U102, Pin 9 60 kHz, 5V pp Rectangular Wave
Ref. Clock 2 U102, Pin 14 6 kHz, 5V pp Rectangular Wave
Backplane U101, Pin 20 50 Hz, 5V pp Rectangular Wave

4.5.3 Waveform Checks For Model 872A

Waveform Checks: Referenced To È (Digital Ground)
Clock U111, Pin 3 360 kHz, 5V pp Square Wave

A/D Clock U112, Pin 5 40 kHz, 5V pp Rectangular Wave
Ref. Clock 1 U102, Pin 9 90 kHz, 5V pp Rectangular Wave
Ref. Clock 2 U102, Pin 14 9 kHz, 5V pp Rectangular Wave
Backplane U101, Pin 20 50 Hz, 5V pp Rectangular Wave

SECTION 5 SPECIFICATIONS FOR MODEL 871A AND

MODEL 872A

GENERAL

THERMOCOUPLE INPUTS: Two, switch selected
ACCURACY: ±0.25% of reading +1ºC (0.25% ±1.8ºF) for

one year, 64º to 82ºF (10º to 28ºC) ambient

EXTENDED SPAN ACCURACY: -40º to -55ºC: +2ºC, -0ºC

REPEATABILITY: ±0.2ºC Typical (one hr., constant

ambient temperature)

TEMPERATURE COEFFICIENT: 64º to 82ºF (18º to 28ºC); Less than

±(0.025% of reading +0.1ºC) 1ºC; for
temperatures less than 64ºF (18ºC) or
greater than 82ºF (28ºC)

MAXIMUM ALLOWABLE TC
INPUT OVERLOAD: 35Vdc (42 V peak AC)

NORMAL MODE REJECTION
RATIO: Greater than 45 dB at 50 and 60 Hz

COMMON MODE REJECTION
RATIO (1KΩ UNBALANCE): Greater than 120 dB at dc, 50 and 60 Hz

DISPLAY: 3¹⁄₂ digit LCD, 0.6" height. Polarity and

MAXIMUM COMMON MODE
VOLTAGE: 500 V

decimal point indication

13

SPECIFICATION (con’t)

ENVIRONMENTAL LIMITS
OPERATING: 32º to 122º F (0º to 50ºC), less than 80%

relative humidity up to 95ºF (35ºC), less than
70% relative humidity from 95º to 122ºF (35º
to 50ºC); linearly derate 3% R.H./ºC 35º to
60ºC.

STORAGE: -30º to 140ºF (-35º TO 60ºC), less than 90%

relative humidity up to 95ºF (35ºC); linearly
derate 3% R.H./ºC 35º to 60ºC.

COLD-JUNCTION COMPENSATION: Semiconductor temperature sensor

INPUT CONNECTIONS: OMEGA subminiature thermocouple

connector (2)

mV OUTPUT CONNECTION: Dual banana jacks

POWER: 9 V alkaline or carbon-zinc (NEDA 1604)

battery

BATTERY LIFE CONTINUOUS: 100 hrs. typical with alkaline battery; 50 hrs.

typical with carbon-zinc battery

BATTERY INDICATOR: Display indicates “BAT” when less than

10% of life remains

DIMENSIONS: H: 7.0" (178 mm) x W: 3.1" (78 mm)

x D: 1.6" (42 mm)

WEIGHT: 10.6 oz. (300 grams)

FOR MODEL 871A

TEMPERATURE SENSOR: Type K (NiCr-NiAI) thermocouple

RANGES: 200ºF, 2000ºF, 200ºC, 1370ºC

TEMPERATURE SPAN: -40.0º to 199.9ºF, -40º to 1999ºF

-40.0º to 199.9ºC, -40º to 1370ºC

RESOLUTION: 0.1ºF, 1ºF, 0.1ºC, 1ºC

INPUT CURRENT: 200nA maximum

CONVERSION PERIOD: 400 ms (2.5 readings per sec)

OVERRANGE AND OPEN
THERMOCOUPLE INDICATION: Display blanked except for overrange digit

14

SPECIFICATION (con’t)

mV OUTPUT:

Non-linearized, cold-junction compensated,
amplified thermocouple output (Not isolated
from selected TC input.)
On ºC Scale:
1mV/ºC on 200º range

0.1mV/ºC on 1370º range
0ºC = OmV output
On º F Scale:
5/9 mV/ºF on 200º range
5/90 mV/ºF on 2000º range
0ºF = OmV output

mV OUTPUT ACCURACY
(18º - 28ºC) ±(3% + 1mV) on 200º ranges;

±(3% + 0.1mV) on High ranges
Includes TC non-linearity, excludes TC
errors. Output resistance: 10k ohms

mV OUTPUT TEMPERATURE
COEFFICIENT (0º - 18ºC & 28º -

50ºC): Less than (0.1 x accuracy specification)/ºC

mV OUTPUT PROTECTION: 35 V dc (42 V peak) max; +mV to -mV

and selected TC input to +mV or -mV.

THERMOCOUPLE
LINEARIZATION: Multi-scope A/D with 11 piecewise linear

segments between -40º and 1370ºC

FOR MODEL 872A

TEMPERATURE SENSOR: Type J (Fe-CuNi) thermocouple

RANGES: 200ºF, 1400ºF, 200ºC, 760ºC

TEMPERATURE SPAN: -40.0º TO 199.9ºF, -40º to 1400ºF

-40.0º TO 199.9ºC, -40º to 760ºC

RESOLUTION: 0.1ºF, 1ºF, 0.1ºC, 1ºC

INPUT CURRENT: 25 nA typical; 50 nA max

CONVERSION PERIOD: 400 ms (2.5 readings/sec.)

OVERRANGE AND OPEN
THERMOCOUPLE INDICATION: 3 least significant digits blanked

15

SPECIFICATION (con’t)

mV OUTPUT: Non-linearized, cold-junction compen-

sated, amplified thermocouple output
(Not isolated from selected TC input.)
On ºC Scale:
1mV/ºC on 200º range

0.1mVºC on 760º range
0ºC = OmV output
On ºF Scale:
5/9 mV/ºF on 200º range
5/90 mV/ºF on 1400º range
0ºF = OmV output

mV OUTPUT ACCURACY
(18º - 28º C) ±(5% + 1mV) on 200º ranges;

±(5% + 0.1mV) on High ranges
Includes TC non-linearity, excludes TC
errors. Output resistance: 10k ohms

mV OUTPUT TEMPERATURE
COEFFICIENT (0º - 18ºC
& 28º - 50°C) Less than (0.1 x accuracy specification)/ºC

mV OUTPUT PROTECTION: 35 V dc (42 V peak) max; +mV to -mV and

selected thermocouple input to +mV or -mV.

THERMOCOUPLE LINEARIZATION: Multi-scope A/D with nine piecewise linear

segments between -40º and 760º C

5.1 PARTS LIST

Circuit Description
Desig.

BT101 Battery, 9V NEDA 1604
C101 Cap, 0.22 µF, 100 V, Polyester
C102* Cap, 0.1 µF, 160 V,

Polypropylene

C102** Cap, 0.1 µF, 100 V,

Polypropylene

C103 Cap, 470pF, 1000 V, Ceramic

Disc

C104 Cap, 220pF, 1000 V, Ceramic

Disc

C105, 106 Cap, 10 µF, 16 V, Aluminum

Electrolytic

C107 Cap, 33pF, 1000 V, Ceramic

Disc

C108 Cap, 47pF, 1000 V, Ceramic

Disc

C109* Cap, 0.1 µF, 16 V, Ceramic
C109** Cap, 0.1 µF, 50 V, Ceramic
C110** Cap, 4.7 µF, 16 V, Aluminum

Electrolytic
CR101 Diode, Low Voltage Reference
DS101 Liquid Crystal Display, 3
J101, 102 TC Connector, Female
J103, J104** Jack, Female SMP Connector
J104, 105* Jack, Female
J105** Connector, Battery
J106* Connector, Battery
Q101, 102 Transistor, NPN, Switch, 2N3904
R101 Thick Film Resistor Network

1

⁄2 digit

Circuit Description
Desig.

R102 Pot, 100 kΩ
R103 Pot, 2 kΩ
R104 Pot, 1 kΩ
R105 Pot, 500 Ω
R106* Resistor, 180 kΩ, 5%, 1/4W,

Comp

R106** Resistor, 240 kΩ, 5%, 1/4W,

Comp

R107 Resistor, 47 kΩ, 5%, 1/4W,

Comp

R108 Resistor, 470 kΩ, 5%, 1/4W,

Comp

R109 Pot, 2 kΩ
R110 Thick Film Resistor Network
R111 Resistor, 10 kΩ, 10%, 2W,

Comp

R112 Resistor, 10 MΩ, 10%, 1/4W,

Comp

R113 Resistor, 5.1 kΩ, 5%, 1/4W,

Comp

R114* Resistor, 1 MΩ, 5%, 1/4W,

Comp

R114** Resistor, 1 MΩ, 10%, 1/4W,

Comp

R115, 116* Resistor, Selected, 1%, 1/8W,

Mtf.

R115** R115 and U110 are a selected

set

16

Circuit Description
Desig.

R116** R116, R122, and U109 are a

selected set

R117 Thick Film Resistor Network
R118* Resistor, 150 kΩ, 5%, 1/4W,

Comp

R118** Resistor, 5.6 kΩ, 5%, 1/4W,

Comp

R119 Thick Film Resistor Network
R120 Resistor, 10 kΩ, 5%, 1/4W,

Comp

R121** Resistor, 10.0 kΩ, 6.1%, Metal

Film

R122*† Resistor , Selected, 5%, 1/4W,

Comp

R122** R116, R122, and U109 are a

selected set

R123* Resistor, 324 kΩ, 1%, 1/8W, Mtf.
R123** Resistor, 316 kΩ, 1%, 1/8W, Mtf.
R124** Resistor, 10.0 Ω, 0.1%, Metal

film

R126* Resistor, 10 kΩ, 0.1%, MF
R127* Resistor, 9.9 kΩ, 0.1%, MF
R128* Resistor, 4.7 kΩ, 5%, 1/4 W,

Comp
S101 Switch, Rotary
S102 Switch, Rotary
S103 Switch, SPDT, ON-OFF
TC-1, 2 TC Cable

Circuit Description
Desig.

U101 31⁄2 Digit Single Chip A/D

Converter
U102 Dual Synchronous Up Counter
U103, U104* Low Power JFET Input Op Amp
U103, U104** Dual JFET Input Op Amp
U105 COS/MOS Quad Bilateral Switch
U106 CMOS Quad Exclusive OR Gate
U107 Dual “D” Type Flip-Flop
U108 14 Stage Binary Counter
U109* Linear Op Amp
U109** R116, R222, and U109 are a

selected set
U110* Current Source
U110** R115 and U110 are a

selected set
U111 Quad, 2 Input NOR Gate
U112 COS/MOS Divide by “N”

Counter
U113 Quad, 2 Input, AND Gate
U114 Analog Multiplexer
Y101 Resonator, 360 kHz

† Value selected during calibration at factory.
* For Model 871A only
** For Model 872A only
To order parts, specify model and circuit designation.

5.1 PARTS LIST (continued)

17

R120

R127

Jumper

R124

Jumper

R121

R118A

COMPONENT LAYOUT FOR MODEL 871A

COMPONENT LAYOUT FOR MODEL 872A

SCHEMATIC

MODEL 871A DIGITAL THERMOMETER

18

SCHEMATIC

MODEL 872A DIGITAL THERMOMETER

19

WARRANTY/DISCLAIMER

USA

MADE

IN

OMEGA ENGINEERING, INC. warrants this unit to be free of defects in materials and workmanship for a
period of 13 months from date of purchase. OMEGA Warranty adds an additional one (1) month
grace period to the normal one (1) year product warranty to cover handling and shipping time.
This ensures that OMEGA’s customers receive maximum coverage on each product.

If the unit should malfunction, it must be returned to the factory for evaluation. OMEGA’s
Customer Service Department will issue an Authorized Return (AR) number immediately upon
phone or written request. Upon examination by OMEGA, if the unit is found to be defective it will
be repaired or replaced at no charge. OMEGA’s WARRANTY does not apply to defects resulting
from any action of the purchaser, including but not limited to mishandling, improper interfacing,
operation outside of design limits, improper repair, or unauthorized modification. This
WARRANTY is VOID if the unit shows evidence of having been tampered with or shows evidence
of being damaged as a result of excessive corrosion; or current, heat, moisture or vibration;
improper specification; misapplication; misuse or other operating conditions outside of OMEGA’s
control. Components which wear are not warranted, including but not limited to
contact points, fuses, and triacs.

OMEGA is pleased to offer suggestions on the use of its various products. However,
OMEGA neither assumes responsibility for any omissions or errors nor assumes liability for any
damages that result from the use of its products in accordance with information provided by
OMEGA, either verbal or written. OMEGA warrants only that the parts
manufactured by it will be as specified and free of defects. OMEGA MAKES NO OTHER
WARRANTIES OR REPRESENTATIONS OF ANY KIND WHATSOEVER, EXPRESSED OR IMPLIED,
EXCEPT THAT OF TITLE, AND ALL IMPLIED WARRANTIES INCLUDING ANY WARRANTY OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE HEREBY DISCLAIMED.
LIMITATION OF LIABILITY: The remedies of purchaser set forth herein are exclusive and the total
liability of OMEGA with respect to this order, whether based on contract, warranty, negligence,
indemnification, strict liability or otherwise, shall not exceed the purchase price of the compo­nent upon which liability is based. In no event shall OMEGA be liable for consequential, inciden­tal or special damages.

CONDITIONS: Equipment sold by OMEGA is not intended to be used, nor shall it be used: (1) as a
“Basic Component” under 10 CFR 21 (NRC), used in or with any nuclear installation or activity; or (2) in
medical applications or used on humans. Should any Product(s) be used in or with any nuclear
installation or activity, medical application, used on humans, or misused in any way, OMEGA assumes
no responsibility as set forth in our basic WARRANTY/ DISCLAIMER language, and additionally,
purchaser will indemnify OMEGA and hold OMEGA harmless from any liability or damage whatsoever
arising out of the use of the Product(s) in such a manner.

RETURN REQUESTS / INQUIRIES

Direct all warranty and repair requests/inquiries to the OMEGA Customer Service Department.
BEFORE RETURNING ANY PRODUCT(S) TO OMEGA, PURCHASER MUST OBTAIN AN AUTHORIZED
RETURN (AR) NUMBER FROM OMEGA’S CUSTOMER SERVICE DEPARTMENT (IN ORDER TO AVOID
PROCESSING DELAYS). The assigned AR number should then be marked on the outside of the return
package and on any correspondence.

The purchaser is responsible for shipping charges, freight, insurance and proper packaging to prevent
breakage in transit.

FOR WARRANTY
following information available BEFORE
contacting OMEGA:

1. P.O. number under which the product was
PURCHASED,

2. Model and serial number of the product under
warranty, and

3. Repair instructions and/or specific
problems relative to the product.

OMEGA’s policy is to make running changes, not model changes, whenever an improvement is possible.
This affords our customers the latest in technology and engineering.

OMEGA is a registered trademark of OMEGA ENGINEERING, INC.
© Copyright 1996 OMEGA ENGINEERING, INC. All rights reserved. This document may not be copied, photocopied, reproduced,

translated, or reduced to any electronic medium or machine-readable form, in whole or in part, without prior written consent of

OMEGA ENGINEERING, INC.

RETURNS, please have the

FOR NON-WARRANTY REPAIRS,

consult
OMEGA for current repair charges. Have the fol­lowing information available BEFORE
contacting OMEGA:

1. P.O. number to cover the COST

of the repair,

2. Model and serial number of product, and

3. Repair instructions and/or specific problems

relative to the product.

Where Do I Find Everything I Need for

Process Measurement and Control?

OMEGA…Of Course!

TEMPERATURE

MU

Thermocouple, RTD & Thermistor Probes, Connectors, Panels & Assemblies

MU

Wire: Thermocouple, RTD & Thermistor

MU

Calibrators & Ice Point References

MU

Recorders, Controllers & Process Monitors

MU

Infrared Pyrometers

PRESSURE, STRAIN AND FORCE

MU

Transducers & Strain Gauges

MU

Load Cells & Pressure Gauges

MU

Displacement Transducers

MU

Instrumentation & Accessories

FLOW/LEVEL

MU

Rotameters, Gas Mass Flowmeters & Flow Computers

MU

Air Velocity Indicators

MU

Turbine/Paddlewheel Systems

MU

Totalizers & Batch Controllers

pH/CONDUCTIVITY

M

U

pH Electrodes, Testers & Accessories

MU

Benchtop/Laboratory Meters

MU

Controllers, Calibrators, Simulators & Pumps

MU

Industrial pH & Conductivity Equipment

DATA ACQUISITION

MU

Data Acquisition & Engineering Software

MU

Communications-Based Acquisition Systems

MU

Plug-in Cards for Apple, IBM & Compatibles

MU

Datalogging Systems

MU

Recorders, Printers & Plotters

HEATERS

MU

Heating Cable

MU

Cartridge & Strip Heaters

MU

Immersion & Band Heaters

MU

Flexible Heaters

MU

Laboratory Heaters

ENVIRONMENTAL
MONITORING AND CONTROL

MU

Metering & Control Instrumentation

MU

Refractometers

MU

Pumps & Tubing

MU

Air, Soil & Water Monitors

MU

Industrial Water & Wastewater Treatment

MU

pH, Conductivity & Dissolved Oxygen Instruments

M618/0896