Omega TX92 User guide

TX92

RTD Temperature Transmitter

FM

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TX92
Miniature Two-Wire RTD Transmitter

Page

Section 1 Introduction 1

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

1.2 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.3 Models Available . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Section 2 Unpacking Instructions 6
Section 3 Installation 8

3.1 Mounting the TX92 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3.2 Wiring the TX92 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

TABLE OF

CONTENTS

i

TX92
Miniature Two-Wire RTD Transmitter

Page

Section 4 Calibration Instructions 15

4.1 Equipment Required . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

4.2 Calibration Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Section 5 Troubleshooting Guide 20
Section 6 Accessories 22
Section 7 Specifications 23
Appendix A

Intrinsically Safe Interconnection Diagram . . . . . . . . . . . . . . . . . . . . . 25

TABLE OF

CONTENTS

ii

1

1

Introduction

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
TX92 RTD Transmitter.

The TX92 Two-Wire RTD Transmitter will produce a standard
4-20 mA output signal proportional to that produced by its RTD
input temperature sensor. Transmission of the proportional current
output may be accomplished by using copper wires. The TX92
RTD Transmitter accepts 100 Ohm, Platinum RTD sensors (PT100,
alpha=0.00385).

Figure 1-1. Photo of TX90 Series Transmitter
Figure 1-2. General Dimensions (in inches)

12

Introduction 1

(For Mounting)

3

1 Introduction

The TX92 transmitter is normally powered by an unregulated DC
power supply as shown in Figure 1-3. The proportionally-transmitted
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 available for the TX92 transmitter. To
order, refer to Section 1.3 Table 1.1 for correct Model Numbers and
Range Codes.)

Figure 1-3. TX92 RTD Transmitter

Input

Output

04

Introduction 1

The TX92 two-wire transmitter will work with 2-wire or 3-wire RTDs
and provides an output current of 4-20 mA proportional to the RTD
sensor. When the transmitter is mounted inside a protection head
(such as the OMEGA NB1 Protection Head) two copper wires now
carry the temperature signal and DC voltage to operate the
transmitter, thereby reducing possible noise pick-up errors. The TX92
does NOT provide isolation between its input and the 4-20 mA
output. Note, however, that the RTD element is electrically insulated.

The TX92 is FM Approved when wired with the proper intrinsic
safety barriers. (See Intrinsically Safe Interconnection Diagram –
Appendix A.)

Model Number Description

TX92-(*) RTD transmitter (100Ω, Pt, alpha = 0.00385)
PRTX-(*) PR-12 RTD probe, 12" L,

1

/4" O.D.,

304SS sheath

TX92 Models Available

1.2 Features

• 4-20 mA output

• ±0.1% full-scale accuracy

(with the respect to the RTD input resistance)

• Upscale break protection

• Low cost

1.3 Models Available

1 Introduction

5

Table 1-1. Range Code

Input Types

Range RTD Range RTD

-40 to 1120˚F 1 -40 to 1500˚F 4

-40 to 1200˚F 2 -40 to 1750˚F 5

-40 to 1300˚F 3 -40 to 1000˚F 6

16

Introduction 1

*Insert range code from Table 1-1

For complete information on PR-12 RTD Probes, see the OMEGA
Temperature Handbook.

7

2

Unpacking

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.

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 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 in event reshipment is necessary.

3.1 Mounting the TX92

The TX92 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
bracket and mounting track.

08

3

Installation

3 Installation

Figure 3-1 Assembly of the TX92 RTD Transmitter Inside

an OMEGA NB1 Protection Head (in inches)

9

DC SUPPLY

12-44VDC

LOAD

MOUNTING

HOLES

Figure 3-2 RT Mounting Track (in inches)

10

Installation 3

CAUTION

HANDTIGHTEN
TRANSMITTER
MOUNTING
SCREWS ONLY.
DO NOT OVER­TIGHTEN.

3 Installation

11

Figure 3-3 TX90-BR Mounting Bracket (in inches)

Figure 3-4 Installation with Bracket and Track (in inches)

12

Installation 3

MOUNTING TRACK (RT)

MOUNTING
BRACKET
TX90-BR

Figure 3-5 TX90-DIN DIN Rail Mounting Adapter (in inches)

3 Installation

13

3.2 Wiring the TX92 (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 RTD element to the input terminals as shown.

Installation 3

Figure 3-6 Wiring Diagram for the TX92

14

15

4

Calibration Instructions

4.1 Equipment Required

• Precision Decade Resistance Box, with 0.01 ohm resolution and

Ⳳ0.02 ohm accuracy or

• Precision RTD Simulator, such as the OMEGA Model CL511
Precision Calibrator

• Precision DMM capable of measuring mA, with 0.001 mA
resolution and Ⳳ0.002 mA accuracy

• Or a Thermocouple/RTD Calibrator/Simulator

16

Calibration Instructions 4

4.2 Calibration Procedures (Refer to Figure 4-1)

Connect the calibration equipment according to Figure 4-1.
Standard copper test leads are used with RTD instrumentation.

To check or adjust the calibration:

1. Locate the Z (zero) and S (span) potentiometers.

2. Select, from Table 4-1, the correct ohmic values for the Z (zero)
and S (span) adjustments that correspond to the Model
Number. For example, for Model TX92-2, the Z value is 93.04
ohms, and the S value is 135.97 ohms.

17

4 Calibration Instructions

If a Thermocouple/RTD Simulator is used, such as the OMEGA
Model CL511 Precision Calibrator, select the Temperature Input Z
(zero) and S (span) values.

3. Set the decade box to the selected Z (zero) ohmic value. Adjust the
Z potentiometer to read 4.000 mA on the monitoring instrument.

4. Set the decade box to the selected S (span) ohmic 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.

Figure 4-1. TX92 RTD Calibration Set-Up.

18

Calibration Instructions 4

4 Calibration Instructions

19

Table 4-1. Calibration Values for the TX92

Temperature Resistance Input (Ohms)
Input Range Model Alpha = 0.00385
Zero/Span TX92 Zero/Span

-40/120˚F -1 84.27/118.97
0/200˚F -2 93.04/135.97
0/300˚F -3 93.04/156.90
0/500˚F -4 93.04/197.69
0/750˚F -5 93.04/246.65
0/1000˚F -6 93.04/293.39

Malfunction or incorrect operation may be caused by:

1. Incorrect Readings:
Check for improper wiring (Refer to Figure 3-5.)

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:

20

5

Troubleshooting Guide

21

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) = V

supply

-12V

0.020A

For example, a 24V power supply would give a maximum loop
resistance of: 12V/0.020A = 600 ohms.

c) Make sure the power supply is rated for at least 28 mA times the

number of TX92 transmitters being powered. For example, if the
supply is powering 5 transmitters, the supply should be rated for
at least 140 mA.

22

6

Accessories

Model No. Description

TX90-BR Mounting Bracket
PSU-24B Unregulated Power Supply, 24 Volts
TX82B Process Loop-Powered Indicator
RT 48” Mounting Track
TX90-DIN DIN Rail Mounting Adapter
RAIL-35-2 6.5 Section 35mm DIN Rail

23

7

Specifications

General

Size: 1.75" dia. X 1.125" high (includes terminal strip)
Zero/Span Adjustment

Range: ±25%
Power Supply Voltage

Operating Range: +12VDC to +44VDC, 28 mA max required per

transmitter

Accuracy: ±0.1% of full scale (includes effects of hysteresis,

repeatability and linearity proportional to the RTD input)
Ambient Temperature: -13˚F to 185˚F (-25˚C to 85˚C)
Storage Temperature

Range: -85˚F to 193˚F (-65˚C to 89˚C)

Specifications 7

24

Thermal Zero Shift: <0.01%/˚F of span (span >10 mV)

<0.02%/˚F of span (span = 5 to 10 mV)

Thermal Span Shift: <0.01%/˚F of span
Weight: 1.5 oz (50g)

Output

Current Output Span: 4-20 mA DC
Current Output Limits: 3 to 28 mA, typical
Maximum Loop

Resistance: (Vsupply – 12V)/0.020A = ohms

Load Resistance

Effect: 0.05% of span per 300 ohms change

Power Supply Effect: 0.01% of output span per volt
Input Sensor: 2 or 3-wire RTD
Maximum

Bridge Current: 2 mA

Appendix

A

Intrinsically Safe Interconnection Diagram

25

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
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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
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