tegwin
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| posted on 22/9/12 at 05:33 PM |
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OT: PID process controller
Anyone know anything about PID process controllers?
I am converting a 1Kw toaster oven into a basic re-flow oven for assembling surface mount PCBs.
I have a Sestos D1S PID controller hooked up via a solid state relay driving the heating elements which all works fine.
The only issue is actually setting the controller up.
It switches off the load before the setpoint as you would expect but because of the latent heat in the elements the temperature continues to rise
quite a bit. Obviously not ideal...
I am unsure which of the parameters I should change to stop this happening. Any ideas?
Options include:
Absolute value upper limit
Absolute value lower limit
Upper limit
Lower limit
Hysteresis
integral (0.1c)
differential (0.1s/degreeC)
hysteresis time(S)
control period (S)
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Would the last person who leaves the country please switch off the lights and close the door!
www.verticalhorizonsmedia.tv
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HowardB
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| posted on 22/9/12 at 08:00 PM |
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I had a cal9000 controller to do a similar thing, but it had a handy auto-learn function. Made the job a dodle,..
not sure that helps, but I would be inclined to start in the hysteresis area
Howard
Fisher Fury was 2000 Zetec - now a 1600 (it Lives again  and goes zoom)
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I predict a Riot
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| posted on 22/9/12 at 08:08 PM |
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A PID controller is a three way controller.
Proportional
Integer
Derivative
If you like the derivative controller will learn, you might just need to give it a few cycles.
Check that the three functions are all turned on, sometimes a PID will work better with one function turned off - usually the derivative.
Is there no PDF on line?
"Honesty is a very expensive gift. Do not expect it from cheap people ". Warren Buffet on Expectation
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tegwin
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| posted on 22/9/12 at 09:14 PM |
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Not that I can find....
I am not sure it is that inteligent..... I can manually adjust all the parameters...... Should I just have left them at default and done a few
cycles to see if it figured its own stuff out!?
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Would the last person who leaves the country please switch off the lights and close the door!
www.verticalhorizonsmedia.tv
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Xtreme Kermit
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| posted on 22/9/12 at 09:39 PM |
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Hmmm. Hysteresis adjustment won't help with overshoot. It controls how far the temp falls from the control point before the heat kicks in again.
It is a loooooong time since I did any control theory but it feels like you want to switch up the integrator so that it starts turning the power down
earlier. This will limit the overshoot.
Caveats. Had a couple of pints of cider and not done this for 30 years...
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I predict a Riot
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| posted on 22/9/12 at 09:45 PM |
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The hysteresis is the tolerance.
Set it all back to default settings.
Put in the basic settings e.g. Temp required and just cycle it.
You can then fine tune one parameter at a time until it stabilises.
Three glasses of wine, one bottle of beer and about to break out the whiskey.
You probably won't get any more sense out of me tonight.
"Honesty is a very expensive gift. Do not expect it from cheap people ". Warren Buffet on Expectation
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SteveWalker
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| posted on 22/9/12 at 09:59 PM |
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If you can't find an autotune function, then you can calculate the figures quite easily.
I have a pdf of the manual for a West 6100 controller, which includes the method of calculating the figures. U2U me if you want me to email a copy -
although you should be able to download a copy easily enough for yourself.
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tegwin
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| posted on 23/9/12 at 11:02 AM |
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Thanks for your thoughts guys.
Managed to find a translation of the sestos instructions and I believe it is now running through an autotune routine.... it will either work or burn
my workshop down... fingers crossed!
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Would the last person who leaves the country please switch off the lights and close the door!
www.verticalhorizonsmedia.tv
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