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Why do I get a delayed response with thermocouple connected to Eurotherm compared with another thermocouple that connects direct to meter?

Our equipment has two heated tungsten platens in a vacuum chamber. The temperature is controlled by Eurotherm controllers. The thermocouples, which connect with the Eurotherms, are stainless steel sheathed (1mm dia) type K, and are fitted into 10mm deep 1.2mm dia holes in the platens. When we start heating there is a 10+ second delay before a temperature increase of 1 degree is measured despite the fact that the measured heat rate is 1.5 oCs-1. We have an additional 1mm deep, 1.2mm dia hole in the platen in which a calibration thermocouple (also 1mm sheathed type k) is located. This thermocouple connects directly into a multimeter with thermocouple input. We have observed that the calibration thermocouple reading starts to increase before the control thermocouple and reaches the 300oC setpoint when the control thermocouple is still at ~ 260oC. This is causing us a large temperature overshoot problem. Can anyone explain why we are getting a delay with the control reading compared with a direct reading?
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this question
  • Bob Anderson (Technical Support Engineer) February 13, 2019 08:45
    Hello Tony,

    I think I would start by checking the mV entering the controller to see if it is giving you the correct display and your input filter time.

    You do not mention what Eurotherm controller you have.

    If you have a 2000 series controller, enter Full Level, Page to iP, then scroll to mV.1 this will give you the mV reading.
    You say you are seeing 260C this equates to 10.56mV for type K.
    If this is correct perhaps you should swap round the thermocouples to see if fault follows the thermocouple.
    If you still get the same reading perhaps you have a 40c difference in the platen.
    Then you could adjust the offset to compensate for this.

    Also check the filter time , Filt, this is normally set to 1.6.
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