Omega TX94A User guide

TM

User’s Guide

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TX94A

Ultra-Miniature

Temperature Transmitters

omega.com [email protected]

Servicing North America:

U.S.A. Omega Engineering, Inc.
Headquarters: Toll-Free: 1-800-826-6342 (USA & Canada only)

Customer Service: 1-800-622-2378 (USA & Canada only)
Engineering Service: 1-800-872-9436 (USA & Canada only)
Tel: [phone] Fax: [phone]
e-mail: [email protected]

For Other Locations Visit omega.com/worldwide

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

i

TABLE OF CONTENTS

Section 1 Getting Started

1.1 Unpacking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

1.2 Safety and EMC Considerations . . . . . . . . . . . . . . . . . . .1

1.3 General Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

1.4 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

1.5 Models Available . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

Section 2 Installation

2.1 Mounting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

2.2 Wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

Section 3 Calibration Instructions

3.1 Equipment Required . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

3.2 Set-up of Equipment. . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

3.3 Calibration Procedures. . . . . . . . . . . . . . . . . . . . . . . . . . .7

Section 4 Troubleshooting Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

Section 5 Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

ii

FIGURES & TABLES

Figure 1-1 RTD Transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

Figure 2-1 Assembly inside a Protection Head . . . . . . . . . . . . . . . . . . . .4

Figure 2-2 Wiring Diagram for RTD Transmitter . . . . . . . . . . . . . . . . . . .5

Figure 3-1 Transmitter Calibration Set-Up . . . . . . . . . . . . . . . . . . . . . . . .7

Figure 5-1 Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

Table 1-1 Range Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

Table 1-2 Model Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

Table 3-1 Calibration Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

1.1 Unpacking

Remove the packing list and verify that you have received all equipment. If
you have any questions, contact the nearest Customer Service
Department, as listed on the cover of this manual.

Upon receipt of shipment, inspect the container and equipment for any
signs of damage. Note 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 materials and carton in the event
reshipment is necessary.

1.2 Safety and EMC Considerations

This instrument is a Class III device (8 to 35 Vdc).
Always use a power supply, which complies with EN 60950 safety
standard.

• Do not expose the transmitter to rain or condensing moisture.

• Do not operate the transmitter in flammable or explosive atmosphere.

• As with any electronic instrument, you may encounter high voltage

exposure when installing, calibrating or removing parts of the
transmitter.

EMC Considerations

• Whenever EMC is an issue, always use shielded cables.

• Never run signal and power wires in the same conduit.

• Use signal wire connections with twisted-pair cables.

• Install Ferrite Bead(s) on signal wires close to the instrument if EMC

problems persist.

Failure to follow all instructions and warnings may result in injury!

1.3 General Description

The Two-Wire RTD Transmitter will produce a standard 4-20mA output
signal proportional to that produced by its RTD input temperature sensor.
Transmission of the proportional current output may be accomplished by
using inexpensive copper wire. The RTD transmitter accepts two-wire or
three-wire ohm platinum RTD sensors (PT100,alpha = 0.00385).

1

2

1.3 General Description

The transmitter is normally powered by an unregulated power supply as
shown in Figure 1-1. The proportionally-transmitted signal begins at 4mA,
at the low end of its temperature range, and increases to 20mA, at the
high end of its temperature range. (There are various temperature ranges
available for the transmitter. To order, refer to Section 1.5 for correct
Model Numbers and Range Codes.)

Figure 1-1 RTD Transmitter

The transmitter works with 2 or 3-wire RTDs and provides an output
current of 4-20mA proportional to the RTD Sensor.

When the transmitter is mounted inside a protection head, (see Figure 2-1),
two copper wires now carry the temperature signal and dc voltage to
operate the transmitter, thereby reducing possible noise pick-up errors.

The transmitter does NOT provide isolation between its input and the
4-20 mA output. Note, however, that the RTD element is electrically
insulated.

1.4 Features

• +/-0.1% full-scale accuracy (with respect to the RTD input
resistance)

• 4-20 mA output

• Upscale break protection

• Low Cost

FIELD CONTROL ROOM

3

1.5 Models Available

Table 1-1 Range Code

INPUT TYPES

RANGE RTD

-40 to 120 F (-40 to 49 C) 1

0 to 200 F (-18 to 93 C) 2

0 to 300 F (-18 to 149 C) 3

0 to 500 F (-18 to 260 C) 4

0 to 750 F (-18 to 399 C) 5

0 to 1000 F (-18 to 538 C) 6

Table 1-2 Model Numbers

Model Number Description

TX94A-(*) RTD Transmitter (100 ohm, Pt,

alpha=0.00385)

*Insert range code from Table 1-1

4

2.1 Mounting

The transmitter may be:

1. surface mounted

2. mounted inside a protection head (shown in Figure 2-1)

Figure 2-1 Assembly of the Transmitter

inside an PR-14 Protection Head

SECTION A-A

POWER LINES

RTD WIRES

5

2.2 Wiring

Refer to Figure 2-2

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 (+IN) and (-IN) input terminals.

Figure 2-2 Wiring Diagram for RTD Transmitter

3-WIRE

RTD

RED

BLACK

RED

BLACK

JUMPER

WIRE

BLACK

2-WIRE

RTD

6

3.1 Equipment Required

• Precision Decade Resistance Box, with 0.01 ohm resolution and
±0.02 ohm accuracy

or

• Precision RTD Simulator, such as OMEGA CL511 Precision Calibrator

• Precision DMM capable of measuring mA, within 0.001 mA resolution
and ±0.002 mA accuracy

3.2 Calibration Procedures

Connect the calibration equipment according to Figure 3-1. 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 3-1, the correct ohmic values for the Z (zero) and
S (span) adjustments that correspond to the model number.
For example, for Model TX94A-2, the Z value is 92.95 ohms, and the
S value is 135.84 ohms.

If a Thermocouple/RTD Simulator is used, such as the 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.

7

3.2 Calibration Procedures (continued)

Figure 3-1 Transmitter Calibration Set-Up

Table 3-1. Calibration Values

Temperature Resistance Input (Ohms)
Input Range Model Alpha=0.00385
Zero/Span TX94A Zero/Span

-40/120°F -1 84.27 / 119.01

0/200°F -2 92.95 / 135.84

0/300°F -3 92.95 / 156.94

0/500°F -4 92.95 / 197.69

0/750°F -5 92.95 / 246.69

0/1000°F -6 92.95 / 293.46

COPPER WIRE

RTD

CALIBRATOR

(CL511)

DECADE

RESISTANCE BOX

EITHER OR

ZERO

SPAN

*With 250 Ohm Load,

dc Supply must be
at least 12-35 Vdc

DC SUPPLY

8-35 Vdc

DMM

(4-20 mA)

MONITOR

250 Ohms*

(-)

(+)

8

4.1 Troubleshooting Guide

Malfunction or incorrect operation may be caused by:

1. Incorrect Readings:

Check for improper wiring using Figure 2-2 as a guide.

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:

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 maximum allowable loop resistance using the

formula: Loop Resistance (maximum) = Vsupply – 8 V

0.020A

For example, a 24V power supply would give a maximum loop
resistance of: 16 V/0.020A = 800 ohms.

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

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

9

5.1 Specifications

General

Size:

1.40” dia. x 0.93” high

(includes terminal strip)

Weight:

0.53 oz (15g);

0.83 oz (25g) if potted

Ambient Temperature:

-13°F to 185°F

(-25°C to 85°C)

Storage Temperature

-85°F to 257°F

(-65°C to 125°C)

Zero/Span Adj Range: ±25%

Power Supply Voltage

Operating Range: +8 Vdc to +35 Vdc, 28 mA max

required per transmitter

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

hysteresis, and repeatability)

Frequency Response: 3dB@ 3Hz

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

<0.02% / °F of span (4-10 mV span)

Thermal Span Shift: <0.01% / °F of span

0.93 [23.6]
MAX

0.52 [13.2]

0.480 [12.19] 0.480 [12.19]

0.156 [3.96]

for #6-32 SCREW

2 PLCS

0.250 [6.35]

1.40 [35.6]

Figure 5-1 Dimensions

10

5.1 Specifications (continued)

Output

Current Output Span: 4-20 mA dc

Current Output Limits: 3 to 28 mA, typical

Max Loop Resistance: (Vsupply – 8V) / 0.020A = ohms

Load Resistance Effect: 0.01% of span per 300 ohms change

Power Supply Effect: 0.002% of output span per volt

Input

Sensor: 2 or 3-wire RTD

Max. Bridge Current: 0.8 mA

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. OMEGA’s 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; 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.

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 RETURNS, please have the
following information available BEFORE contacting
OMEGA:

1. Purchase Order 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 trademark of OMEGA ENGINEERING, INC.
© Copyright 2017 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.

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

1. Purchase Order number to cover the COST
of the repair,

2. Model and serial number of the 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!

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