pid question...asked before , but no real answer.

[mozeppa]

okay ,

i have a 90 lb magma pot and it runs to a pid that is supposed to regulate temperature ....and it does in a baseball park sorta way.
except i don't want the park to be yellowstone!

the pot has its own knob for controlling temp....and everyone says "turn it full on and let the PID control it."

and i did....but the temp yoyo's from 15 degrees too cool to up to 30 degrees too hot.

and the the next wave of help chimes in with ..."after the pot reaches the dialed in temp," (in this case 660 degrees)
"then press the set button and the pid learns the temp setting and will stop after it does."

so i did that...all pressing that set button does is display random numbers every half second into infinity....it never stops
doing that constant flashing of numbers....ever!

so that doesn't work.

too cool to too hot is a 50 degree swing, surely these can be made to be better than that.

would removing the switch on the pot and re-wiring to run on full constant heat with the pid controlling it for temp. be the answer?

edited to say ... bought the pid from a maker on this site that was banned ...and i can't remember his name.

[bosterr]

The answer to your question about disabling the pot thermostat in my case was "Yes". My 20 pound Lyman is about 30 years old and wanted to continue to regulate temp at a point below what my PID was set at. I don't remember what that temp was, but when I wired direct, eliminating the thermostat, it cured all my set temp problems.

[noisewaterphd]

You could try bypassing pot controller, and perhaps swap your PID for a model with a better algorithm.

But, it is also possible that your heating element is just too weak for your pot, and the PID is doing the best it can.

[Mike W1]

FWIW and maybe it's not that much. I would presume that PID is a Mypin and I know lots of folks use them. My 2¢ worth is I had one and was trying to regulate a hot plate. It didn't do very well. I put my Auber SYL-2352 on the hot plate and it keeps it within ± 2 °F, usually closer in fact.

When I ran the Mypin I took the hot plate control out of the circuit and it did help some but never got the control I get with the Auber and I put the hot plate control back in when I hooked the Auber up.

Ended up sending the Mypin back and replaced it with a REX C100 just like I had on my other pot. Running both of them with the REX's and use the Auber for the hot plate and lube heater. Quite happy with both units.

Just reread your post and I don't think you've set it to Autotune correctly. On a Mypin you have to hold the AT button down for a few seconds. It will start to flash when it starts AT'ing and quit flashing when it's done. It takes 2-3 complete cycles above and below your set temperature. If I remember correctly when you change anything on the Mypin units you have to hold the set button down or it doesn't remember the changes.

[JonB_in_Glencoe]

The PID should have a "AT" button for auto-tune, that is what you push for your PID to teach itself to control the temp of your pot, not the "set" button.

What I do is, once the pot is up to temp, I drop in a ingot (not pre-heated), that drops the temp. Then press "AT", the AT indicator will blink while it's learning...as mentioned, it may take 3 cycles to learn.

Now, when you push "AT", if your PID is displaying "random numbers every half second into infinity....it never stops doing that constant flashing of numbers....ever" then I'd suspect you have a defective PID.

[Mike W1]

Sent you a PM

[Tazza]

Mine did that exact same thing, i just didn't know how to use it. I was using mine as a thermostat but didn't know it, i thought i was using it the way it was designed.

After talking with the folks on here, i found out it was very wrong and i used the AT function of my REX-C100 and it will hold spot on if i don't add metal, when i do, it will change but get back to the set temp and stay there.

I'd like to place money on the fact you are using yours the same way as i was before i saw the error of my ways.

When they are tuned in, they are awesome at holding temperature.

[jmorris]

If your PID has "auto tune" it will find the best set of values to control what you have. You will have to look at the manual to see how to turn on auto tune and I suggest you have the pot as full as you normally would in production (mid session) and already close to casting temp, no need in it setting goofy values just to start up.

Bypass all of the original thermostat, you don't need or want it to mess with the PID doing its job.

Once you get it tuned they can be quite accurate. I have an old fridge that I turned into a chicken egg incubator and can maintain internal temp to 0.4 deg F with a PID controlling two light bulbs.

That said the larger you have the hysteresis setting the larger error you allow, where is yours set now? You can think of the hysteresis setting like the lines on a road you have to stay within, the further apart they are the more error you are allowed from where you should be, the closer they are the more constant your inputs to correct error will be.

[runfiverun]

the P sounds like it's working, the I and the D are not tuning things in well enough.

it's like guiding a ship to Australia.
the P points the way, the general south by south west.
the I is more the 260* degree heading.
and the D is the general fight against the waves that push it back and forth.

the auto-tune function has to cycle a couple of times so that you get the direction, the compass reading, and the tiny wave corrections right.

[mozeppa]

will update later as i have much to do.

[mozeppa]

thanks all ...will do!