Temperature measurement using thermocouple connected to analog input module

Hello faizudin;

The following manual will give you information on your analog module and on the scaling of TC inputs.

SIMATIC S7-300 S7-300 Automation System Module Data

Chapter 6.7 shows the 6ES7331-7KF02-0AB0 analog input module connections ansd parameters. For TC connections the range modules should be placed in the A position, as you mention. Parameters for the TC channels should also be selected properly in the HWConfig editor. You do not mention that you have done so, but let’s presume all configurations and wiring have been done properly.

Chapter 5 discusses the analog values representation In Step 7; table 5,32 shows how the TC type T values are represented (see the attached table).

Notice that if you read (decimal) 4000 in your analog input address (say PIW 512, look at the HWConfig configuration for that analog input) the temperature you are reading corresponds to 400.0 °C. If you read -2700 in the same address the corresponding temperature is -270.0. Notice the pattern?
So you do not need FC 105 to scale the TC input value; all you need is to divide by 10 (as a REAL value)

To convert the integer value to the correct temperature you start by converting the decimal value in the PIWxxx address that corresponds to you channel to a REAL value (use the convert instructions I-DI and then DI-R); once the value is REAL, then simply DIV_R by 10.0.

Hope this helps,

Daniel Chartier

Edit: it would be interesting to see what the CPU is complaining about when you load the scaling blocks. Please open the diagnostic buffer of the PU and look for messages related to these. We can help you decypher the contents of the diagnostic buffer if you have trouble understanding the messages. Save the contents (As Text) and post them here if you want more help.
D.C.

https://www.automation.siemens.com/mcms/sce/en/advanced_training/training_material/download_training_material/Pages/Default.aspx

Module B2 examines analog signal processing, so itwould cover your present needs.
If you are thinking of using the TC as part of a PID control loop, study Module B3 .
Hope this helps,
Daniel Chartier