User’s Guide
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TABLE OF
CONTENTS
TX91
Miniature Two-Wire Thermocouple Transmitter
Page
1
Section 1 Introduction
1.1 General Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
1.2 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8
1.3 Models Available . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Section 2 Unpacking Instructions
Section 3 Installation
8
9
11
3.1 Mounting the TX91 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2 Wiring the TX91 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
i
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TABLE OF
CONTENTS
TX91
Miniature Two-Wire Thermocouple Transmitter
Page
18
Section 4 Calibration Instructions
4.1 Equipment Required . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.2 Set-up of Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
4.3 Calibration Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Section 5 Troubleshooting Guide
Section 6 Accessories
Section 7 Specifications
Appendix A
25
26
27
Intrinsically Safe Interconnection Diagram . . . . . . . . . . . . . . . . . . . . . 30
ii
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Introduction
1
1.1 General Description
®
The OMEGA TX90 Series Temperature Transmitters consist of the
TX91 Miniature Two-Wire Thermocouple Transmitter and the
TX92 Miniature Two-Wire RTD Transmitter. This manual is written
for the OMEGA TX91 Thermocouple Transmitter.
The TX91 Transmitter accepts thermocouple sensor types J, K, T,
or E and will produce a standard 4-20 mA output signal propor-
tional to that produced by its attached input temperature sensor.
Transmission of the proportional current output may be
accomplished by using copper wires.
1
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Introduction
1
(For Mounting)
Figure 1-1. Photo of TX90 Series Transmitter
12
Figure 1-2. General Dimensions (in inches)
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1
Introduction
The TX91 transmitter is normally powered by an unregulated DC
power supply as shown in Figure 1-3. The proportionally-transmit-
ted signal begins at 4 mA, at the low end of its temperature range,
and increases to 20 mA, at the high end of its temperature range.
(There are various temperature ranges and thermocouple types
available for the TX91. To order, refer to Section 1.3 for correct
Model Numbers and Range Codes.)
COPPER
THERMOCOUPLE
WIRES
DC SUPPLY
11-44 VDC
TX91
THERMOCOUPLE
TRANSMITTER
Input
3
Figure 1-3. TX91 Thermocouple Transmitter
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Introduction
1
The TX91 two-wire transmitter receives and measures signals from
thermocouples and sends an output current of 4-20 mA which is directly
proportional to the thermocouple millivolt input. It is designed to
connect with only two copper wire leads that will supply the voltage to
operate the transmitter from a DC power supply, and also carry the
output current. The output current is then used for recording, computing
or controlling.
If the TX91 is mounted inside a protection head, such as the OMEGA
NB1 Protection Head (see Figure 3-1), the thermocouple extension wires
are replaced by two copper wires that carry the 4-20 mA signal and DC
voltage to operate the transmitter. (Refer to the OMEGA Temperature
Handbook for information on NB1 Thermocouple Assembly.)
04
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Introduction
1
The TX91 has reverse supply polarity protection and will operate with a
wide range of supply voltages (11 to 44VDC). It has an input sensor
break-protection circuit that forces the output current to go upscale when
the thermocouple wire opens. It also is provided with a screw terminal,
where the output current can be measured without interrupting the
power loop. The TX91 does NOT provide isolation between its input and
the 4-20 mA output; therefore, an undergrounded thermocouple junction
is suggested to prevent possible ground loops.
Note that most thermocouple transmitters with 4-20 mA outputs,
including the TX91, are proportional with respect to the thermocouple
input voltage. However, the relationship between temperature and
millivolt for all the thermocouple types is somewhat non-linear. This
leads to maximum error at approximately the midpoint of the range as
shown in Figure 1-4.
05
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1
Introduction
06
Figure 1-4. Straight line Approximation of Curve
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1
Introduction
1.2 Features
• 4-20 mA output
•
0.1% full-scale accuracy (with respect to the mV input signal)
• Upscale break protection
• Low cost
1.3 Models Available
Table 1-1. Range Code
Input Types
J
Range
K
T
E
0 to 1200°F
J2
J3
J4
J5
J6
K2
T2
T3
T4
E2
-40 to 1300°F
-40 to 1500°F
-40 to 1750°F
-40 to 1000°F
K3
K4
K5
K6
E3
E4
E5
E6
07
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1
Introduction
TX91 Models Available
Description
Model Number
TX91-(*)
NB1TX-(*)
Thermocouple transmitter (J, K, T, or E)
NB1 thermocouple probe, 12" L, /4" O.D.,
ungrounded junction, 304SS sheath, TX91Transmitter
1
*Insert range code from Table 1-1
For complete information on NB1 Thermocouple Probes, see the OMEGA
Temperature Handbook.
8
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Unpacking
2
Remove the packing list and verify that all equipment has been
received. If there are any questions about the shipment, please call
the OMEGA Customer Service Department at 1-800-622-2378 or
(203) 359-1660.
Upon receipt of shipment, inspect the container and equipment for
signs of damage. Take particular note of any evidence of rough
handling in transit. Immediately report any damage to the ship-
ping 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 in event reshipment is necessary.
9
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Installation
3
3.1 Mounting the TX91
The TX91 Transmitter may be:
1. surface mounted,
2. mounted inside a protection head (refer to figure 3-1), or
3. installed into the OMEGA mounting track (part number RT) using an
OMEGA mounting bracket (part number TX90-BR).
Figure 3-2 shows the RT mounting track.
Figure 3-3 shows the TX90-BR mounting bracket.
Figure 3-4 shows a typical installation of two transmitters using the
10
mounting bracket and mounting track.
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3
Installation
DC POWER
SUPPLY
LOAD
MOUNTING
HOLES
THERMOCOUPLE
Figure 3-1 Assembly of the TX91 Transmitter Inside
an OMEGA NB1 Protection Head (in inches)
11
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Installation
3
CAUTION
HANDTIGHTEN
TRANSMITTER
MOUNTING
SCREWS ONLY.
DO NOT OVER-
TIGHTEN.
Figure 3-2 RT Mounting Track (in inches)
12
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3
Installation
13
Figure 3-3 TX90-BR Mounting Bracket (in inches)
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Installation
3
MOUNTING TRACK (RT)
MOUNTING
BRACKET
TX90-BR
Figure 3-4 Installation with Bracket and Track (in inches)
14
TX90-BR & RT
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Installation
3
3.2 Wiring the TX91 (Refer to Figure 3-5)
1. Connect a DC power supply in series with the load to the (+PS) and
(-PS) power terminals. Note that the load (usually a monitoring
instrument) may be connected to either the (+) or (-) power lead.
2. Connect the thermocouple to the (+IN) and (-IN) input terminals.
NOTE
A milliamp monitoring instrument can be used in the circuit by
connecting the monitor’s positive lead to (+PS) and the negative lead to
(M). This allows monitoring the current loop without disconnecting the
15
main wiring.
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Installation
3
THERMOCOUPLE
Figure 3-5 Wiring Diagram for the TX91 Potentiometers
16
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Calibration Instructions
4
4.1 Equipment Required
1.
• Precision mV source, with 0.001 mV resolution and 0.002mV
accuracy or
• Precision DVM with 0.002mV accuracy and adjustable mV
source with 0.001mV resolution
• OMEGA TRC III Ice Point Reference (or stable ice bath)
• Temperature Reference Probe (OMEGA P/N: TRP-(*))
*Thermocouple Type: J, K, T, E
2.
• Or a Thermocouple Calibrator/Simulator
17
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Calibration Instructions
4
4.2 Set-up of Equipment
To prepare the ice bath:
a) Fill a glass beaker with crushed ice made from distilled water.
b) Fill the beaker with enough distilled water so that ice just
becomes slush, but not enough to float the ice.
c) Insert the reference thermocouple.
Figure 4-2 shows an alternate set-up. Here, a high precision
thermocouple calibrator, such the OMEGA Model CL511, replaces
the DVM, ice bath, voltage source, etc.
18
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Calibration Instructions
4
4.3 Calibration Procedures (Refer to Figure 4-1)
Connect the calibration equipment according to Figure 4-1 or 4-2.
The thermocouple wire (J, K, T, E) must be of the same
calibration as the transmitter being calibrated. Make sure that the
wiring polarities are correct. (Note that the RED thermocouple
wire is NEGATIVE.)
To check or adjust the calibration:
1. Locate the Z (zero) and S (span) potentiometers.
2. Select, from Table 4-1, the correct mV values for the Z (zero)
and S (span) adjustments that correspond to the Model
Number. For example, for Model TX91-J2, the Z input is -0.885
mV, and the S input is 4.906 mV.
19
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4
Calibration Instructions
If a Thermocouple Calibrator/Simulator is used, such as the OMEGA
Model CL511 Precision Calibrator, select the Temperature Input
Z (zero) and S (span) values.
3. Set the DC mV source to the selected Z (zero) mV value. Adjust the
Z potentiometer to read 4.000 mA on the monitoring instrument.
4. Set the DC mV source to the selected S (span) mV value. Adjust the
S potentiometer to read 20.000 mA on the monitoring instrument.
5. Repeat steps 3 and 4, as required, until the readings are exactly
4.000 mA and 20.000 mA. This procedure is necessary since there is
interaction between the two potentiometers.
20
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Calibration Set-up
4
21
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Figure 4-1. Calibration Set-Up
Calibration Instructions
4
SPAN
TX91
ZERO
INPUT
THERMOCOUPLE
WIRE
22
Figure 4-2. Calibration Set-Up. (Alternate)
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4
Calibration Instructions
Table 4-1. Calibration Values for the TX92
Temperature
Input Range
Zero/Span
mV INPUT
REF 32°F
Zero/Span
mV INPUT
REF 32°F
Zero/Span
Model
TX92
Model
TX92
0/1200°F
0/1300°F
0/1500°F
0/1750°F
0/1000°F
0/1200°F
0/1300°F
0/1500°F
0/1750°F
0/1000°F
-J2
-J3
-J4
-J5
-J6
-T2
-T3
-T4
--
-0.855/14.906
-0.885/17.947
-0.885/14.108
-0.885/20.406
-0.885/29.515
-0.674/13.967
-0.674/16.647
-0.674/12.572
--0.674/12.572
--0.674/12.572
-K2
-K3
-K4
-K5
-K6
-E2
-E3
-E4
-E5
-E6
-0.692/13.819
-0.692/16.092
-0.692/10.560
-0.692/15.295
-0.692/22.251
-1.026/15.869
-1.026/19.708
-1.026/17.942
-1.026/26.858
-1.026/40.056
23
--
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Troubleshooting Guide
5
Malfunction or incorrect operation may be caused by:
1. Reversed polarity:
Check the wiring using Figure 3-5 as a guide. If the temperature
of the thermocouple increases while the current magnitude
decreases, the problem could caused by reversed polarity of the:
a) thermocouple wiring
b) power supply leads
c) monitor instrument
2. Loose or broken wires:
Check each terminal connection for tightness. Move each wire
back and forth and note any changes in operation.
3. Too high a load resistance in the output current loop or too low
a current rating on the power supply:
24
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5
Troubleshooting Guide
a) Measure the total resistance of each device (excluding the
transmitter and power supply) in the 20 mA loop, including the
resistance of the lead wires.
b) Calculate the maximum allowable loop resistance using the
formula:
Loop Resistance (maximum) = Vsupply -11V
0.020A
For example, a 24V power supply would give a maximum loop
resistance of: 13V/0.020A = 650 ohms.
c) Make sure the power supply is rated for at least 28 mA times the
number of TX91 transmitters being powered. For example, if the
supply is powering 5 transmitters, the supply should be rated for
at least 140 mA.
25
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Accessories
6
Model No.
Description
TX90-BR
PSU-24B
TX82A
RT
Mounting Bracket
Unregulated Power Supply, 24 Volts
Process Loop-Powered Indicator
48” Mounting Track
26
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Specifications
7
General
SIZE:
1.75" dia. X 1.125" high (includes terminal strip)
25%
ZERO/SPAN ADJUSTMENT
RANGE:
POWER SUPPLY VOLTAGE
OPERATING RANGE:
+11VDC to +44VDC, 28 mA max required per
transmitter
ACCURACY:
0.1% of full scale (includes effects of hysteresis,
repeatability and linearity proportional to the T/C)
AMBIENT TEMPERATURE:
-13°F to 185°F (-25°C to 85°C)
STORAGE TEMPERATURE
RANGE:
27
-85°F to 193°F (-65°C to 89°C)
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Specifications
7
THERMAL ZERO SHIFT:
<0.01%/°F of span (span >5 mV)
<0.02%/°F of span (2-5 mV span)
<0.01%/°F of span
THERMAL SPAN SHIFT:
WEIGHT:
1.5 oz (50g)
Output
CURRENT OUTPUT SPAN:
CURRENT OUTPUT LIMITS:
MAXIMUM LOOP
RESISTANCE:
4-20 mA DC
3 to 28 mA, typical
(Vsupply – 11V)/0.020A = ohms
LOAD RESISTANCE
EFFECT:
POWER SUPPLY EFFECT:
0.05% of span per 300 ohms change
0.01% of output span per volt
Input
SENSOR:
Thermocouple
28
IMPUT BREAK PROTECTION: Upscale
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IMPEDANCE:
200K Ω
Appendix
Intrinsically Safe Interconnection Diagram
A
29
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WARRANTY/DISCLAIMER
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. The 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 malfunctions, 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 having been damaged as a result of
excessive corrosion; or current, heat, moisture or vibration; improper specification; misapplication; or misuse or other operating conditions
outside of OMEGA’s control. Components in which wear is not warranted, include but are 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 the company 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.
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