Automation Direct 205

[Tom 0]

I have an application that is used to control temperatures of a thermoformer. I am using a 205 PLC with a 260 processor. I am having a problem with the temperature modules with erratic temperature readings. The thermocouples are located on the heating element its self (calrod heater) and the heaters are located in drawers that slide into the machine with mating plugs. I am using twisted shielded pair K-type thermocouple cable and used grounded and ungrounded thermocouples. I have grounded the heaters, and applied the jumpers as in the manual. Using data view monitoring the raw value before any averaging I see jumps as high as 10 - 20 degrees F. We run a number of thermoformers of the same type using AB PLCs or Eurotherm temperature controllers with no problems. Any and all suggestions appreciated.

[Shiner 2]

Boy it sure sounds like a grounding issue. I know you say you have everything grounded but which end of the devices is grounded? What is the grounding scheme of the devices vs the PLC. Is the supply voltage for the devices coming from the same power supply as the PLC?