gaannesh

Temerature controller

5 posts in this topic

Hi

I have a rubber molding machine in that there is digital temperature  controllers  and one unit showing CJE as error and i found at the back there is glass diode like thing got burned.

It looks like zener diode with marking at one end and i connected new zenor diode of 5v and still the problem is there .

I would like to know is it Zenor diode or thermister?

Its one end is connected at thermocouple terminal and other at another terminal.

 

 

 

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Post the manufacturer name and model number of the temperature controller

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The glass thing is very likely the cold junction compensator, probably a thermistor.

It is critical that it be an exact replacement, not just any thermistor, because any error in the CJ measurement is an error in the reported thermocouple measurement.

Older Honeywell's had an external CJ, but it was not glass device, it had a brass heat sink and short lead with a ring terminal. 

Good luck

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I was thinking about this.  I haven't known of a CJ compensator going bad - it's a passive device, a resistor.

What is more likely is

- the CJ was removed and re-connected improperly (heard that any number of times)

- the voltage regulator that creates a constant current source that drives the CJ circuit is bad; a fairly high probability

- the sense circuit that reads the the voltage drop that represents the temperature has failed; possible.

Any of those options has a higher probability than a bad passive resistor. 

I mention this because you could go through all the effort of getting a replacement CJ, only to find out that the error is still there, and CJ is still dysfunctional.

I'd be inclined to substitute a resistor across wherever the CJ thermistor is supposed to go and see if the error disappears.

With no idea of what the thermistor is, I'd probably start with a 1K, then 2.2K, then a 3.3K resistor and see if any makes the error disappear.  If the error disappears and the indicated temperature increases when the resistor is connected (assuming the T/C is hot) then it says that the CJ device is bad and that substituting some resistance makes the circuit happy, even if it's the wrong resistance.

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On Wednesday, January 18, 2017 at 10:04 PM, gaannesh said:

Hi

I have a rubber molding machine in that there is digital temperature  controllers  and one unit showing CJE as error and i found at the back there is glass diode like thing got burned.

It looks like zener diode with marking at one end and i connected new zenor diode of 5v and still the problem is there .

I would like to know is it Zenor diode or thermister?

Its one end is connected at thermocouple terminal and other at another terminal.

 

 

 

 

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