Offset correction for RTD module in Micrologix 1500

Hi everyone,

I want to know if there is any possibility of correct a temperature offset directly in the RTD module.

I have a system connected to a PT-100 thermocouple, and this thermocouple linked to the RTD module of the Micrologix 1500.

After some time, I got a +1.5 °C offset in my measurements. I just want to know if there is any possibility to adjust this offset in the PLC programation.

Best regards,

José

http://www.plctalk.net/qanda/showthread.php?t=103561

https://literature.rockwellautomation.com/idc/groups/literature/documents/um/1771-um668_-en-p.pdf

The above links may help you out.
Regards,

Thank you for your response!

I have read the referenced topic. It says that the controller have a Auto-Calibration and it is done when the PLC is powered. I have power on and off several times but the offset seems to be the same allways, any suggestion of the reason? could it be the pt-100?

How do you know you are getting a 1.5 degree offset, what are you comparing it with?

Putting a offset in the program to correct it is no big deal, but you need to know that it is truly 1.5 degrees off.

Thanks bright. Good to know that add the offset in the program is easy, I didn't find a reference that ilustrate that for micrologix1500 or the software rslogix500, only the auto-calibration and I don't know if it works.

I compared the offset with other verified thermocouple

I think you will need to do the offset with PLC logic by adding an offset value to the the calculated temperature. If the program is set up with the module configured for engineering units and the logic is using the input address directly, this might also mean that you need to find and replace those references with your new result including your offset.

On some PLC's the calibration of analogues can be a problem especially those that give a scaled output i.e. PT100 that will give say -50.0 to 150.0 using the PLC card to scale it. I tend to put all Analogues into a scaler with zero and span so that calibration of any small offsets can be done usually via an engineering page on an HMI, This makes commissioning and calibration easy at anytime.

The scaling block I created has raw in, raw low, raw high, scaled low and scaled high resulting in an output that can convert any raw number into a scaled value that can be pressure, temperature, flow etc. Even if the card automatically scales the value I still use it to allow calibration.