Omega TX91 User Manual

MADE IN

F M

APPROVED

TX91

Thermocouple Two-Wire

Temperature Transmitter

User’sGuide

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

FOR NON-WARRANTY REPAIRS, consult OMEGA for current repair charges. Have the following information available BEFORE contacting OMEGA:

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© Copyright 2005 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 the prior written consent of OMEGA ENGINEERING, INC.

TABLE OF	TX91
CONTENTS
	Miniature Two-Wire Thermocouple Transmitter
		Page
Section 1 Introduction		1
1.1	General Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. . . 1
1.2	Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. . 8
1.3	Models Available . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. . 8
Section 2 Unpacking Instructions		9
Section 3 Installation		11

3.1 Mounting the TX91 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.2 Wiring the TX91 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

i

TABLE OF	TX91
CONTENTS	Miniature Two-Wire Thermocouple Transmitter
		Page
Section 4 Calibration Instructions		18
4.1	Equipment Required . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. . . 18
4.2	Set-up of Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. . 19
4.3	Calibration Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. . 20
Section 5 Troubleshooting Guide		25
Section 6 Accessories		26
Section 7 Specifications		27
Appendix A

Intrinsically Safe Interconnection Diagram . . . . . . . . . . . . . . . . . . . . . 30

ii

1Introduction

1.1General 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 proportional to that produced by its attached input temperature sensor. Transmission of the proportional current output may be accomplished by using copper wires.

1

Introduction 1

(For Mounting)

	Figure 1-1.	Photo of TX90 Series Transmitter	12
	Figure 1-2.	General Dimensions (in inches)

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.)

THERMOCOUPLE	COPPER
	WIRES
	DC SUPPLY
TX91	11-44 VDC
THERMOCOUPLE
TRANSMITTER
Input

3

Figure 1-3. TX91 Thermocouple Transmitter

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

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

05	shown in Figure 1-4.

1 Introduction

06

Figure 1-4. Straight line Approximation of Curve