PID/SSR setup help

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KoreyI

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Hello,

I am having some issues with my setup. I'm not sure if the issue is in my wiring, or if I might have a defective PID or defective SSR. I have attached my wiring diagram and below are some more details:

I am using the MYPIN TA4 PID Controller.

I will set my target temperature. As the actual temperature approaches the target temperature, the output light on the PID and the light on the SSR itself will begin to blink. Once the temperature exceeds the target temperature, the output light and the SSR light turn off completely. However, the heating element stays on.

Eventually, I unplug the entire unit from the wall and the heating element immediately goes off obviously.

I will plug the unit back into the wall (at which point the temperature is still above the target temperature) and the heating element does not come back on. It only comes back on once it has dropped again below the target temperature. It then climbs again and overshoots the target to repeat the process.

To troubleshoot, I disconnected the wires connecting the PID to the SSR and tested to see if the elements turned on, and they didn't, so I don't think the SSR is stuck.

I also figured this might be an autotuning issue with my PID controller: Everytime I go to autotune, the autotune light comes on (solid) and then stays on. I have let it go for up to forty minutes at times and it never goes off (which to me seems like its not completing the autotune process). Further, when I go into the settings on the PID, the P, I, and D values are all at their default, so the autotuning never changed them. So as of now, I'm leaning towards a defective PID? Unless you all have some other ideas.

Attached is my wiring diagram. It is using a 220v plug.

Thanks in advance to anyone who can help.
 

processhead

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I am not so sure that the SSR is ok.

The LED on the SSR basically is telling you whether the SSR is being requested to turn on.

From your description, It sounds like the PID is working normally. What doesn't make sense is why the SSR is keeping the element energized, even when the temperature SP is met, the LED on the SSR is off.

The way to test this is to securely connect a voltmeter across the element terminals and repeat the scenario you described above.

If you have 220 volts across the element when the SSR is supposed to be off, then you can safely assume that it is being gated on, and then staying stuck in the on state when the control signal to it is calling for it to be off.

You can also test the control signal that the PID sends to the SSR. When the PID output is off, you should see 0 volts DC at the control input terminals of the SSR. When the PID output is on, you should see a DC voltage (typically 12 volts DC) at the control input terminals of the SSR.
 
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KoreyI

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I am not so sure that the SSR is not the problem here.

The LED on the SSR basically is telling you whether the SSR is being requested to turn on.

From your description, It sounds like the PID is working normally. What doesn't make sense is why the SSR is keeping the element energized, even when the temperature SP is met, the LED on the SSR is off.

The way to test this is to securely connect a voltmeter across the element terminals and repeat the scenario you described above.

If you have 220 volts across the element when the SSR is supposed to be off, then you can safely assume that it is being gated on, and then staying stuck in the on state when the control signal to it is calling for it to be off.

You can also test the control signal that the PID sends to the SSR. When the PID output is off, you should see 0 volts DC at the control input terminals of the SSR. When the PID output is on, you should see a DC voltage (typically 12 volts DC) at the control input terminals of the SSR.
Thanks, I will test this once I get a chance a report back.
 

jimyson

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Looks like your switch isn't doing anything. I personally have the PID on the SSR control inputs and a switch on a 2 pole contactor. I am also 110 though.
 
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KoreyI

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Purchased a new SSR the other day and replaced the old one. Ran another test and here is what happened:

Autotune completed when I ran it at a low temperature and the oven was regulating flawlessly at 150 degrees. When I checked the input side of the SSR, it was shifting between about 20V and 0.2V respectively when it was regulating.

Problem was when I upped the set temperature to 350, the elements start glowing as they should; also, now that autotune was completed, the PID was showing a PV (im assuming it is some indexed number on a scale of 100 about how much power the PID is outputting) that was decreasing accordingly as the actual temp neared the target temp. Even when the PV reached zero (and the input side of SSR was reading no voltage) the elements were still blazing and all regulation went back out the window.

IM so confused by this.... Why is the SSR able to open and close at low temperatures, but as soon as the elements go full power, it seems to get stuck and won't turn the elements off? The only thing I can possibly think of at this point is that the SSR is getting too hot by the time it gets up to the higher temperatures and the heat is destroying the SSR by the time it gets up there, whereas at the low temperatures it was still working. Odd though, considering I have a fan and a huge heatsink on the SSR.
 

processhead

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Problem was when I upped the set temperature to 350, the elements start glowing as they should; also, now that autotune was completed, the PID was showing a PV (im assuming it is some indexed number on a scale of 100 about how much power the PID is outputting) that was decreasing accordingly as the actual temp neared the target temp. Even when the PV reached zero (and the input side of SSR was reading no voltage) the elements were still blazing and all regulation went back out the window.
The PV you mentioned is the process temperature measured by an RTD or thermocouple. Normally, it will display in degrees C or F.
I'm not sure why yours would be displayed as 0-100?
Are you confident that your process temperature is being accurately displayed on the PID?

Is it possible you were describing the CV instead of the PV?

BTW, what are you controlling with glowing elements?
 

augiedoggy

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Purchased a new SSR the other day and replaced the old one. Ran another test and here is what happened:

Autotune completed when I ran it at a low temperature and the oven was regulating flawlessly at 150 degrees. When I checked the input side of the SSR, it was shifting between about 20V and 0.2V respectively when it was regulating.

Problem was when I upped the set temperature to 350, the elements start glowing as they should; also, now that autotune was completed, the PID was showing a PV (im assuming it is some indexed number on a scale of 100 about how much power the PID is outputting) that was decreasing accordingly as the actual temp neared the target temp. Even when the PV reached zero (and the input side of SSR was reading no voltage) the elements were still blazing and all regulation went back out the window.

IM so confused by this.... Why is the SSR able to open and close at low temperatures, but as soon as the elements go full power, it seems to get stuck and won't turn the elements off? The only thing I can possibly think of at this point is that the SSR is getting too hot by the time it gets up to the higher temperatures and the heat is destroying the SSR by the time it gets up there, whereas at the low temperatures it was still working. Odd though, considering I have a fan and a huge heatsink on the SSR.
do you have any pictures of your wiring? what size wires are you using to the elements and to and from the ssr inside the panel?
what is the specs on the ssr your using? also did you use thermal paste between the heatsink and ssr? without it the heatsink wont work very effectively.
 

MichaelBD

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Just wondering if you already found out what was causing the problem? Im having EXACTLY the same problem and in the process of figuring a solution.

Michael
 
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