Strange Input Values on Eurotherm 3216 Controller

Eurotherm might. How did the phone call go?

One of the possibilities is that someone is cycling the power to the instrument. If that individual can stop doing that, then the problem will go away.

They are looking in to it I was just wondering if anyone else has come across a similar problem.

And turning on and off a controller should not change the value being read from an input.

<...turning on and off a controller should not change the value being read from an input...>

WALOOB! HowTF is it going to read and display anything if there's no power attached to it <rhetorical question - NNTR>?

Assuming that it works in some fashion, at some point, then I'm guessing that the input wiring is picking up electrical noise from the output wiring, which is probably switched power to the heaters.

As the controller asserts control on power-up it switches the output, the noise makes for crazy readings.

It's a single loop controller, so it only has one analog input; I suppose that all those 16 PT100's have to be spread out in some fashion, maybe they're too close and parallel to a heater element?

Does the displayed temperature (PV) variable stabilize after a short period of time or remain at an offset value in error state?

If the display does not stabilize after a short period of time after cycling the power and return an accurate value, you need to check the programming thoroughly and verify which state the display recovery is set to: (Last know good value, peak value, average value, etc.)

You also need to make sure the "flash" memory and/or on-board memory backup option is present and active so that the programming remains stable through power interruptions.

If there is a memory backup on board that requires a battery or capacitor for power it may be bad.

One possibility that comes to mind is that the controller is configured with a lot of damping (input filtering). Upon power-up, the controller begins by indicating some random value, then will eventually settle in on the correct temperature after enough time constants have passed.

If I were the one troubleshooting this, I'd disconnect the RTD, then connect a known resistor to the input to simulate a stable temperature without all the cabling to possibly pick up any electrical noise. Power down, power up, repeat several times to look for patterns (e.g. Does it always power up with the same value, or does it power up with random values? Does the problem go away entirely?).

Thanks for the suggestions I will try to diagnose it over the next few weeks with your them in mind. Its hard when it is an intermittent fault. I have just replaced the controller with a known working one and it seems to be running fine atm.

I am just wondering if because I have an array of 16 pt100's it might be trying to pull to much current for this controller.

Thanks for the help I will post my findings (if any) might just be a faulty controller).