MODIFYING AUTONICS TM4 AS CURRENT LOOP MONITOR ( 1 )

In this article, I made a TM4 controller with thermo cuople input as standart current loop input 4-20mA.

The Autonics TM4 module is an analog thermocouple or RTD input that we usually use as a temperature controller.

I modified it by making a voltage-lowering circuit to make the voltage drop across the resistor a few millivolts to follow the character of the type K thermocouple.

The question is: Can we make this TM4 as an analog current 4-20mA DC controller?

As we all know that TM4 is a controller for monitoring temperature that is connected to temperature sensors such as PT100, Thermo Couple.

The answer is: YES, with a few modifications.

Why K-type thermo couple?

Because by default, TM4 is registered as a controller for the type K temperature sensor.

Why you are not set with another type of thermocouple such as type J or type R with higher reading numbers or other types?

The answer is because we are now not to change the MODBUS register on this controller.

We take advantage of the default of this controller.

MATERIAL PREPARATION AND APPLICATION

To starting the project, we must prepare some materials and applications required.

POWER SUPPLY

We need a Power Supply to make TM4 module can working well. The Voltage we need is 24VDC. It can be your own customize power supply or industrial supply.

In this article, I use an standart made i china power supply. The Maximum output is 3A. But you can use your own PSU as long as it bigger than 1A output.

SENSOR, CONTROLLER

Set up your Autonics TM4 module. Use TM-N2RB for the first module and use TM4-N2RE for the second module and so on.

Also prepare the controller. It would be great if you have a 4-20mA injector signal for scaling.

In this article I am using the AUTONICS TZN4ST-14RC temperature controller which has 4-20mA retransmission.

PLC AND SERIAL COMMUNICATION MODULE

Set up your PLC. In this lesson I use OMRON PLC type CJ2M-CPU12.

The PLC changing the MODBUS register number from AUTONICS TM4 module became to the number we want according to the controller.

The PLC does not instantly connect to a module that uses MODBUS communication. PLC must have a module called Serial Communication Unit.

It can be a Serial Communication Board or it can be a Serial Communication Module/Unit.

MAKING SIMPLE 4-20mA to mV CONVERTER

I made this circuit to convert the current to millivolts myself.

You just need some 0.25 Watts resistors and a 100K trimpot to adjust for display numbers in the MODBUS RTU register address.

The circuit is as follows:

This circuit aims to change the voltage on R1 which ranges from 0.4VDC to 2.0VDC to around 10mV to 50mV.

So that it has almost the same character as the thermocouple input.

The principal of thermo couple is generates a voltage for several milliVolt every changes in temperature on the sensor.

OMRON CPU MODULE AND THE POWER SUPPLY

Im using OMRON CJ2M-CPU12 to make this project. But you can use your another OMRON’s CJ type to make this project work as well.

Then the module also need a Power Supply for it. You can use CJ2W-PA202 or CJ2W-PA205.

ASSEMBLY THE WIRING

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Fig. modified TM4 as MODBUS current loop controller

In the picture I can describe as follows:

The temperature sensor goes to the controller.

The retransmission controller enters the TM4 module via a simple converter that converts the current to milli volts.

PREPARE YOUR SOFTWARE

In this article I use the CX-Programmer software to get online with the OMRON PLC. The version I use is version 9.6

You must install this application in order to be online with this PLC. The download link is available on the OMRON official website HERE. Need LOG Register or SIGN UP to download the files.

Another External download link are HERE. But you need to SIGN UP as register member.

DOWNLOAD MODBUS RTU FILE FOR OMRON PLC

LINK

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Download link here:
https://drive.google.com/file/d/1KV7yLxst5sxGeyOFXI6A-i0WffN307il/

MAKE YOUR PROJECT DIREKTORI IN THE FOLDER OF YOUR PC

Once downloaded, extract the file and place it in a directory.

In this lesson, I put the extracted files in the d:\TM4 AND CJ2 directory.

It must be 6 files inside the ZIP file.

Topic: modified TM4 temperature controller becaming as current loop controller.

TO BE CONTINUED……………..

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