Struggling With TM221 Thermocouple Somachine Basic Scaling

Afternoon all

I am having a few problems with scaling a thermocouple.

I'm using a TM221CE40R with a TM3TI8 input card and a type K thermocouple -60 to 350 degrees C.

At first i tried setting the config to the default to type K which gives a
"minimum range value" of -2000 (0.1°c)
"maximum range value" of 13000 (0.1°c)

this gave me an analog signal of approx 20 for a temperature of 7 degrees.

setting the scale to the probe values of min -60°c and max +350°c gives a reading of -1°c gives a reading of 0.

I am probably doing something rather stupid as it is the first time I have tried to use this particular input card.

I have had a good google and look on here but can't seem to find the answers.

Thanks in advance

I would check to ensure that the K type thermocouple is “isolated”.
https://www.schneider-electric.com/en/faqs/index?page=content&id=FA334895&actp=search&viewlocale=en_US&searchid=1501554080587#__highlight

http://www.filkab.com/files/category_files/file_3189_bg.pdf

Regards,

You need to enable ”cold junction (CJ)or ice point compensation.

An isothermal thermocouple, one which is the same temperature at both ends, generates 0.0mV (in the absence of a temperature gradient).

So a T/C at room temperature and an AI at room temperature will ”see” 0mV which is the freezing point of water: 0 Deg C.

It is the cold junction compensator that measures the temperature of the AI terminals, room temperature in this case, and adds that value to what the T/C signal provides.

Without cold junction, the AI is reporting a too-low temperature, one which needs CJ added to it for correction.

Sometimes an external CJ sensor is used. Most times it’s built-in and is enabled by configuration setup.

Don't forget that Red is Negative with type "K" thermocouples...
The red lead is also magnetic...I usually use the term "Mag-Negative" to help me remember.

Just realised i have never replied to this,

I gave a few things a try even purchasing a spare PLC and Input card to test the theories but the plc and card worked straight out of the box so i think it may be something to do with the installation. I cannot get to the installation until winter so will update once i have more information.