Omega TX787, TX788 User Manual

PC-Only Programmable Transmitter

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Models TX787 and TX788 are microprocessor-based 2-wire transmitters that feature high accuracy and
high long-term stability. Setting the new standard in ease of setup, these transmitters feature PC-Only™
configuration technology. The unique Communications Adapter provides a fully isolated serial interface
and power source, allowing the transmitter to be configured with a “PC-Only” - no external power
supply, calibrator or meter is required!

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Before beginning the process of setting up the transmitter , it is important to understand the difference between
calibration and configuration. The transmitter’s precision references (4 and 20 milliamps out; resistance,
voltage and current as appropriate; and a thermal reference) are calibrated at the factory and may be adjusted
later if necessary . Configuration is the process of defining the sensor type and range in engineering units.
Configuration is performed by connecting the transmitter to a PC and running the configuration software.
Because the Communications Adapter provides power to the transmitter’s microprocessor, it is not necessary to
provide any external power to the transmitter in order to configure it.

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CalibrCalibr

To calibrate the transmitter, connect a 24VDC power supply , a 250Ω load
and multi-meter (in milliamp mode) in series to the transmitter's output.

1.Upload

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Configuration may be performed with a transmitter on-line or off-line.
When a transmitter is on-line, the upload and download icons will be
distinctly black. If no transmitter is on-line, those icons will be grey .

1.Upload Current configuration from the transmitter

2.Configure

•If the current “Sensor Type” does not match the application, click

on the “Sensor Selection” box then select the appropriate “tab” at the
top of the “Input Sensor Selection” screen.

•Make one selection from the “Input Connection” and “Type” boxes

(if offered) for the selected sensor type. Leave the “Mode” as “Stan­dard” or the “Transfer Function” as “Linear” for now. Click the “OK”
button to return to the Configuration Screen.

•Select the Engineering Units (from the pull down menu), enter the

“Zero Scale” and “Full Scale” values and the “Burnout” mode
(transmitter to go above full scale or below zero scale upon input
failure).

•Click the "Set to Optimal" button to optimize the

transmitter's filtering.

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1. Install the Configuration and Calibration software

Run “setup.exe” on the distribution diskette and follow the on-screen instructions.

Note: the software contained on the distribution diskette runs under Windows 95 and Windows NT .
If you are running Windows v3.1, contact Omega Engineering.

2. Connect the Communications Adapter to the computer and transmitter.

3. Identify the serial port to which the Adapter is connected.

Select “Options” from the menu bar , then click “Communications” and select the correct COMM port from the pull­down menu. Note that if you change the serial port you must exit the software and restart it with the correct setting.

4. Configure the transmitter.

What you will need:

Calibration

•PC

• Communications Adapter

• Transmitter

• Multimeter

• 24VDC power supply

Configuration

•PC

• Communications Adapter

• Transmitter

2.Click on the Calibration Icon

3.Output Calibration: Select "Output 4mA", enter the mA reading from

the meter into the dialog box and click "Send to Device." Repeat for 20mA
calibration.

4A. Input Calibration Models XXXXX-X000 (e.g. TX787-0000):
Provide a precision 100.00mV source to the transmitter , select "Input mV"
on the Device Calibration screen, wait for the on-screen display to settle,
then click "Send to Device." Repeat the procedure, substituting a 300.00Ω
input (4-wire connection) and selecting "Input Ohms."

4B. Input Calibration Models XXXXX-X001 (e.g. TX787-0001):
Provide a precision 300.00mV source to the transmitter , select "Input
mV" on the Device Calibration screen, wait for the on-screen display to
settle, then click "Send to Device." Repeat procedure, substituting a 15.00
Volt input and selecting "Input V olts", and substituting a 50mA input,
selecting "Input mA." Note that the input terminals are different for each of
the signal levels.

5. To calibrate the cold junction compensation reference, select “T em-
perature,” enter the nominal ambient temperature in the dialog box, set

the input simulation type to match the input simulator (i.e., type J thermo­couple), verify that the simulator is set to the proper value, then click “Send
to Device.”

3.Download New configuration to the transmitter.

6. Click “Close.” A message in the lower left corner of the screen will

indicate the progress of the download and finally that the download has
been successfully completed.

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The TX787 and T788 is capable of performing many functions in addition to the simple example outlined in the Quick Start exercise.

Dynamic Input FilteringDynamic Input Filtering

Dynamic Input Filtering

Dynamic Input FilteringDynamic Input Filtering

Filtering is provided to optimize the stability and response time of the transmitter output signal. The filter is set by specifying a Filter Band and a Damping
Time Constant. T o simplify the definition of the filter values, click on the “Set to Optimal” button on the configuration scree n.

Filter BandFilter Band

Filter Band

Filter BandFilter Band

The Filter Band allows the transmitter to be configured to react quickly to significant changes in input while smoothing out small changes. This band

defines the range above and below the current input reading within which the Damping Time Constant will be applied. It is defined as a percent of
the configured span of the transmitter . For example, a 0.5% Filter Band on a transmitter configured for an input range of 200 to 700 deg F would mean
that the Damping Time Constant will be applied to input changes of less than 2.5 deg but that changes of more than 2.5 deg would be immediately
reflected in the output. In general, the larger the full scale range, the smaller the Filter Band should be. Conversely , a larger Filter Band is generally
appropriate for smaller input ranges. Clicking the “Set to Optimal” button triggers the calculation of an appropriate setting based on the currently defined
input range.

DampingDamping

Damping

DampingDamping

Damping defines the length of time, in seconds, that the input will be averaged over to determine the output value when the input change is less than
the Filter Band. Changes in the input that are greater than the Filter Band bypass the Damping filter and are immediately reflected in the output. The

default value of 15 seconds, when used with the optimal Filter Band yields a very stable output while maintaining a fast response to significant changes in
the input.

Input/Output Input/Output

Input/Output

Input/Output Input/Output

Because of slight variations between sensing elements or other loop characteristics, it is sometimes beneficial to “trim” the transmitter so that its output
corrects for these effects. If the measurement error is known, the transmitter may be trimmed “off-line.” “ON-line” trimming allows the characteristics of an
individual sensor to measure and match to the transmitter to which it will be connected in the field. Trimming allows the basic calibration of the transmitter to
be left intact.

Dynamic Sensor SimDynamic Sensor Sim

Dynamic Sensor Sim

Dynamic Sensor SimDynamic Sensor Sim

This option allows a loop to be tested dynamically verifying control logic as well as wiring. The transmitter’s current loop ou tput can be controlled via four
parameters: simulate an input value in raw units (ohm, mV, etc.); simulate an input value in engineering units (e.g. 450 DEG); set an ouput in percent; or set
an ouput in mA. After an initial simulation is selected, the ouput may be incremented or decremented in 1% or 10% steps.

Other Other

Other

Other Other

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The transfer function is the “formula” that the transmitter uses to determine the appropriate output signal for a given input signal. A “Linear” function means
that output is changed in a straight line fashion as the input changes within the configured input zero and full scale range: 0% of range input yields 4 mA
output, 25% of range input yields 8 mA, etc. A “Standard” function means that the transmitter will apply a standard linearization curve for temperature inputs.

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The accuracy of RTD temperature sensing can be increased significantly when the temperature transmitter is “matched” to the individual sensor using a
method called Callender Van Dusen linearization. Doing so requires entering the sensor’ s Alpha, Beta (measured for temperatures above zero and for
temperatures below zero), Sigma, and Ro values into the transmitters' configuration. These values can be requested from the manufacturer when the
sensor is purchased or may be measured by a testing lab.

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USA:

ISO 9001 Certified

Canada:

USA and Canada:

Mexico and
Latin America:

Benelux:

Czech Republic:

France:

Germany/Austria:

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Internet e-mail

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Select this function if the transmitter’s output is to vary with the square root of the input.

Custom PCustom P

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The transmitter can use up to a 10th order polynomial equation (y = A0 + A1x + A2x2 + … + A10x10) as the transfer function by inputting the coefficients
into the transmitter’s configuration.

Custom Custom

Custom

Custom Custom

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The transmitter can use a User Defined table by specifying a .tbl file. The data in the file should be two columns, tab delimited. Up to 140 data pairs may
be listed. The input values in column one must be equally spaced.

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Defining Defining

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Each unit may be assigned an I.D. Tag name of up to eight characters, Job Number up to eight characters, and a “Message” of up to sixteen characters;

stored in the transmitter’s memory. Click on the desired field, enter the text, and click the download icon.

United Kingdom:

IS0 9002 Cerfified

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 product are not designed for use in, and should not be used f or , patient connected applications.

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