theprocessguy
Member
I read here a lot but this is my first post. I have an ungrounded type K T/C that is inside a stainless sheath. It is about 1M long and inserted into an electric heating element to monitor internal heater temp. The T/C is literally 1cm from the heating element conductors. The heater is driven by a VFD which as you knows is a very noisy animal. As the voltage is ramped to increase heat, I get a corresponding immediate rise in temperature. Too fast to be a real temp increase. An offset to the tune of 30-50C. As soon as I stop the drive the temperature immediately drops back to normal. The temperature reading itself is also noisy while the drive is running. The T/C is wired directly to an AB Flex I/O module. I have tried grounding the sheath. I have tried grounding one of the T/C pins. I have connected the drain wire, module end only, to an isolated "clean" earth. Someone mentioned removing the grounding spring on the bottom of the Flex terminal base to eliminate the earthing there but I have not done that. I have read about placing a small capacitor across the T/C connection to filter noise but I don't think this would solve my offset issue.
The only thing I have not tried is to use a 4-20 transmitter head. I have these unplugged for now as they seem to also affect my other process T/Cs where I must have a good reading.
Does anyone have an experience with this or any suggestions.
Out of ideas
The only thing I have not tried is to use a 4-20 transmitter head. I have these unplugged for now as they seem to also affect my other process T/Cs where I must have a good reading.
Does anyone have an experience with this or any suggestions.
Out of ideas