SSR relay problem solution

[mdkmdk]

Hello everyone,

I have a goldsmith oven to which I had to change an SSR relay because when it reached 475 degrees centigrade the temperature increase stopped. Since the oven must reach 800 degrees in about two hours, I have to solve the problem.

I changed all the main components to the oven: thermoregulator, thermocouple, resistance. The problem of increasing the temperature was present even before changing all these components.

I ordered an SSR relay of the same brand and model as the one mounted on the oven: Crydom D2425.

Since it was panel mounted I proceeded to modify the panel to put a heatsink in it.

Between the heatsink and the relay I put some Thermalright TFX thermal paste which has a high thermal conductivity power and is also used in computers and can withstand up to 300 degrees.

After having reassembled everything I turned on the oven, this time it reached 100 degrees centigrade after 10-15 minutes the increase in temperature stopped.

I wonder where he went wrong about the SSR relay changing as I think I've done everything possible. Could anyone help me? Thank you in advance for your reply.

I attach some photos to the message.

 

[marconi]

Thank you. Tuning the controller is I regret to say largely 'trial and error'.

Next let us reduce the I value from 210 to 180. Reducing this time increases the integral action I and helps to reduce the error quicker as the temperature PV gets closer to the set value SV, but it can also increase oscillations so some more trial and error with this value. The integral action makes up for the reducing drive from the P proportional action since P depends on the error and the error is decreasing.

Please use 800C as the set value from the moment you turn on the oven. We are attempting to tune the system to achieve 800C 'quickly' not 1000C. If you set SV at 1000C the controller does not use proportionate control until close to 1000C and the temperature enters the proportional control band centered around 1000C. We want proportionate control to kick in as the oven nears 800C. The SV value determines the midpoint of the proportional band.

Please understand the oven and controller has two 'behaviours' working at the same time. From cold to set value temperature the oven is operating in its transient mode since there is the biggest change in temperature. As the oven temperature reaches the set value the transient behaviour should reduce and the oven enters its steady state behaviour only making small changes to keep the temperature near to 800C.

Transient response - Wikipedia - https://en.wikipedia.org/wiki/Transient_response#:~:text=In%20electrical%20engineering%20and%20mechanical,the%20equilibrium%20of%20the%20system.

 

[mdkmdk]

Thank you. Tuning the controller is I regret to say largely 'trial and error'.

Next let us reduce the I value from 210 to 180. Reducing this time increases the integral action I and helps to reduce the error quicker as the temperature PV gets closer to the set value SV, but it can also increase oscillations so some more trial and error with this value. The integral action makes up for the reducing drive from the P proportional action since P depends on the error and the error is decreasing.

Please use 800C as the set value from the moment you turn on the oven. We are attempting to tune the system to achieve 800C 'quickly' not 1000C. If you set SV at 1000C the controller does not use proportionate control until close to 1000C and the temperature enters the proportional control band centered around 1000C. We want proportionate control to kick in as the oven nears 800C. The SV value determines the midpoint of the proportional band.

View attachment 99614

Please understand the oven and controller has two 'behaviours' working at the same time. From cold to set value temperature the oven is operating in its transient mode since there is the biggest change in temperature. As the oven temperature reaches the set value the transient behaviour should reduce and the oven enters its steady state behaviour only making small changes to keep the temperature near to 800C.

Transient response - Wikipedia - https://en.wikipedia.org/wiki/Transient_response#:~:text=In%20electrical%20engineering%20and%20mechanical,the%20equilibrium%20of%20the%20system.

Should I leave the other variables "d = 0", "t = 2" and "AT = yes" unchanged and change only the variable "I" from 210 to 180?

Could I do the test by entering a lower temperature like 500 degrees or does it always need to set 800 degrees? Putting 500 degrees in an hour I would have the response and I could do the test faster, otherwise like the previous test I will proceed by setting SV to 800.

 

[marconi]

Should I leave the other variables "d = 0", "t = 2" and "AT = yes" unchanged and change only the variable "I" from 210 to 180?

Could I do the test by entering a lower temperature like 500 degrees or does it always need to set 800 degrees? Putting 500 degrees in an hour I would have the response and I could do the test faster, otherwise like the previous test I will proceed by setting SV to 800.

Yes leave those variables unchanged. Only change I. You can use 500C for the test.

 

[Darkwood]

Tried skipping through quickly so sorry if already mentioned, the colour coding on your thermocouple wires could be from a different global zone thus identified incorrectly, assuming the controller has been configured for the therm' type it is monitoring, not doing so will give the wrong feedback voltages and the wrong temperatures. Type K And J are commonly used but must be correctly input into the PID controller fir it to Interpret what the thermocouple resistance feeds back is.

 

[marconi]

Thermocouple Cable Colour Codes and Tolerances - TC Ltd - https://www.tc.co.uk/thermocouple-information/thermocouple-colour-code.html

The k type thermocouple has red and green wires which would indicate it is using the German colour code red for plus and green for minus. This is how it is connected to the controller. See #49.

mdkmdk - could you send me details of the thermocouple please? Is it made in Germany. Do the red and green wires go all the way to the thermocouple or have you joined the thermocouple wires to the red and green wires which go to the controller?

If you have a small permanent magnet and hold it near the red wire and then the green wire the wire which is most magnetic is the negative lead.

 

[mdkmdk]

Yes leave those variables unchanged. Only change I. You can use 500C for the test.

I did the test you suggested by changing the variable 'I' and setting it to '180':
The oven reached the temperature of 475 degrees and the heating turned off.
It dropped to 486 degrees while the heating was off.
The temperature dropped, and at 474 degrees it started again.
The temperature dropped to 466 degrees, and the heating turned on again.
The heating turned off at 477 degrees.
Then I finished the test as it never seemed to reach 500 degrees.

Thermocouple Cable Colour Codes and Tolerances - TC Ltd - https://www.tc.co.uk/thermocouple-information/thermocouple-colour-code.html

The k type thermocouple has red and green wires which would indicate it is using the German colour code red for plus and green for minus. This is how it is connected to the controller. See #49.

mdkmdk - could you send me details of the thermocouple please? Is it made in Germany. Do the red and green wires go all the way to the thermocouple or have you joined the thermocouple wires to the red and green wires which go to the controller?

If you have a small permanent magnet and hold it near the red wire and then the green wire the wire which is most magnetic is the negative lead.

Tried skipping through quickly so sorry if already mentioned, the colour coding on your thermocouple wires could be from a different global zone thus identified incorrectly, assuming the controller has been configured for the therm' type it is monitoring, not doing so will give the wrong feedback voltages and the wrong temperatures. Type K And J are commonly used but must be correctly input into the PID controller fir it to Interpret what the thermocouple resistance feeds back.

A few months ago I also changed the thermocouple. Before replacing it I did the test with the magnet and it showed that it was a type K thermocouple. Later I replaced it with a new one of the same type, obviously K. I remember that before changing it I inquired about the colors of the wires and it emerged that they probably refer to the German colour code.

 

[marconi]

Please could you clarify ‘salt from off… ‘?

 

[mdkmdk]

Please could you clarify ‘salt from off… ‘?

It dropped to 486 degrees while the heating was off. Sorry for the accidental mistake, I made the change to the reply and it will be visible shortly after being checked by the forum moderators.

 

[marconi]

First it seems to me the controller is working and that 25C or so away from 500C seems to me quite good after the initial period of heat up. Would you please leave for longer and find out how close the oven temperature settles to 500C?

Jogged by Westward10's post I am thinking about the error in measuring the oven temperature PV introduced by the connection of the thermocouple's red and green leads to the metal terminals on the back of the controller. These two connections are the other half of the thermocouple circuit. A thermoelectric circuit has a hot sensing end thermocouple and a cold reference end thermocouple. The combined circuit produces a voltage/current proportional to the difference between the temperatures of each end. See:

Thermocouple Cold (Reference) Junction Compensation - https://blog.beamex.com/thermocouple-cold-junction-compensation

The reference thermocouple made by the terminal connections will reduce the voltage produced by the hot end. Thus temperature measurements by the hot end thermocouple will be seen by the controller as lower than they actually are. The controller has a an SC value for correcting sensor measurement errors so I will come back to you later about entering a value other than 0.

The problem is that the reference temperature 'cold junction' is actually getting warmer and warmer as the oven does because the terminals are enclosed in a space near the oven and ssr.

How accurate does the temperature need to be for your purpose?

 

[mdkmdk]

First it seems to me the controller is working and that 25C or so away from 500C seems to me quite good after the initial period of heat up. Would you please leave for longer and find out how close the oven temperature settles to 500C?

Jogged by Westward10's post I am thinking about the error in measuring the oven temperature PV introduced by the connection of the thermocouple's red and green leads to the metal terminals on the back of the controller. These two connections are the other half of the thermocouple circuit. A thermoelectric circuit has a hot sensing end thermocouple and a cold reference end thermocouple. The combined circuit produces a voltage/current proportional to the difference between the temperatures of each end. See:

Thermocouple Cold (Reference) Junction Compensation - https://blog.beamex.com/thermocouple-cold-junction-compensation

The reference thermocouple made by the terminal connections will reduce the voltage produced by the hot end. Thus temperature measurements by the hot end thermocouple will be seen by the controller as lower than they actually are. The controller has a an SC value for correcting sensor measurement errors so I will come back to you later about entering a value other than 0.

The problem is that the reference temperature 'cold junction' is actually getting warmer and warmer as the oven does because the terminals are enclosed in a space near the oven and ssr.

How accurate does the temperature need to be for your purpose?

From 475 to 500 degrees it would take a long time since the heating stops constantly.

I completely redone the panel when the resistance was changed and I made the preparation for the new thermocouple since it did not have a bolt on which to stand. I soldered it at a slight angle to prevent the thermocouple wires from getting close to the resistor wires and the oven exhaust pipe.

It is important for me that the temperature is accurate and real and that it reaches 800 degrees as soon as possible.

 

[James]

Part of the problem may well be that you Simpley are not giving the auto tune long enough to do its calculations.

it will never complete if you keep stopping it when you think it is not working correctly.
it may well take a number of hours to complete.
some large furnaces, the auto tune can take days to complete.

 

[mdkmdk]

Part of the problem may well be that you Simpley are not giving the auto tune long enough to do its calculations.

it will never complete if you keep stopping it when you think it is not working correctly.
it may well take a number of hours to complete.
some large furnaces, the auto tune can take days to complete.

I keep it on for a few hours, always with autotuning active, then at a certain point I turn it off.

 

[mdkmdk]

First it seems to me the controller is working and that 25C or so away from 500C seems to me quite good after the initial period of heat up. Would you please leave for longer and find out how close the oven temperature settles to 500C?

Jogged by Westward10's post I am thinking about the error in measuring the oven temperature PV introduced by the connection of the thermocouple's red and green leads to the metal terminals on the back of the controller. These two connections are the other half of the thermocouple circuit. A thermoelectric circuit has a hot sensing end thermocouple and a cold reference end thermocouple. The combined circuit produces a voltage/current proportional to the difference between the temperatures of each end. See:

Thermocouple Cold (Reference) Junction Compensation - https://blog.beamex.com/thermocouple-cold-junction-compensation

The reference thermocouple made by the terminal connections will reduce the voltage produced by the hot end. Thus temperature measurements by the hot end thermocouple will be seen by the controller as lower than they actually are. The controller has a an SC value for correcting sensor measurement errors so I will come back to you later about entering a value other than 0.

The problem is that the reference temperature 'cold junction' is actually getting warmer and warmer as the oven does because the terminals are enclosed in a space near the oven and ssr.

How accurate does the temperature need to be for your purpose?

One thing that is coming to my mind now is that when the oven was connected via the internal relay of the temperature controller and not directly with the SSR I did a test and saw that overshooting and undershooting near 800 degrees worked well. Could the problem be related to the fact that it is now connected directly with the SSR?

 

[Avo Mk8]

It is important for me that the temperature is accurate and real and that it reaches 800 degrees as soon as possible.

In your post #100 above, if the photo on the left is the new configuration, and on the right is the old, then can you tell us:
Do both the thermocouple wires transition to the same conductor material (eg copper) at the ceramic choc block on the side of the oven, or are the wires still maintained as K thermocouple lead materials until they get to the controller?
Hopefully the cold junction is not on the side of the oven?

Are you measuring, or able to measure, the actual temperature of the oven with an independent device?

 

[mdkmdk]

In your post #100 above, if the photo on the left is the new configuration, and on the right is the old, then can you tell us:
Do both the thermocouple wires transition to the same conductor material (eg copper) at the ceramic choc block on the side of the oven, or are the wires still maintained as K thermocouple lead materials until they get to the controller?
Hopefully the cold junction is not on the side of the oven?

Are you measuring, or able to measure, the actual temperature of the oven with an independent device?

The rigid conductors of the thermocouple terminate in the ceramic terminal from the top in the photo. In the lower part of the ceramic terminal two wires come out, one red and one green respectively made of the same materials as the thermocouple. Externally they are contained in a fiberglass sheath. I cannot understand what is meant by cold junction.