PID Help for Dummy

[Old Ugly]

Hope everyone had a Merry Christmas, Happy New Year and stayed away from the BUG.
So I pieced together a PID controller but am not happy with it. When the pot temp. reaches set temp. the
out light shuts off but the temp. keeps rising another 10 or so degrees then falls down to set temp. then the out light comes back on but the temp. keeps dropping another 10 degrees or so then repeats this same cycle. I have also used it on a small kiln and it does the same thing.
I assume I have set one or more of the parameters wrong. I am using an Inkbird controller.
Anyone have an idea what might be wrong? Keep in mind that I (DUMMY) do not understand computers and the technical lingo that comes with them.
I should add that I followed the directions from a brewer on you tube named George to set the controller.
Would the settings for brewing be different than for casting?
Thank you in advance.
Rod (Old Ugly)

[monadnock#5]

I'm about in the same league as you are as far as the technology goes, although I did work in a heat treat dept for a number of years. A PID is a learning computer that will try to hold the temperature you set to a close tolerance.

What you complain about (overshoot) is common to all PID's at whatever the price point. They all have their own quirks and personalities too. There was a type of steel at work that tempered at 1000°F, and Be/Cu that hardened at 620°F. Setting the controller at 1000° would take the heat to the desired temp perfectly, easily within tolerance, every time. Setting the temp to 620° OTOH would produce an overshoot (junk parts) without fail. The fix was to start low 600°, wait until the heat had come all the way up and started falling off, and then dial it in, in 5° increments.

Don't worry about a 10° deviation, you're still in tolerance. What you need to know is what your tolerance is, and how long it takes for your PID to stop rapidly cycling and settle into a holding pattern. Like everything else about casting, there's no standard easy answer. Some of it you have to figure out on your own, as applies to your individual needs. Hope this helps.

[Minerat]

Did you run the auto tune sequence if it has that feature? Mine from Hatch holds about a +\- 5°.

[GasGuzzler]

Did you run the auto tune sequence if it has that feature? Mine from Hatch holds about a +\- 5°.

This ^^

Switching between loads is confusing for the PID as well. Use it on ONE load only and after it has learned THAT load 1-3 times.

[TjB101]

As mentioned above run the Autotune. I’ve run it twice so far and it is still dependent on what’s in the pot. Different mixes of alloys can heat up differently and cause a short spike in the temp.

I set mine for 710. I’ll see it start to pulse the temp at around 690. Sometimes it will go up to 720 and then back down to 700 ... I live with it and am thankful of not cooking a pot to 800+ degrees anymore.

[Mike W1]

First off I'm NOT AN EXPERT but have 4 units that I set up without any problems. They all stay within ± about 2° of the set temperature.

Assuming things are wired properly and set for the proper TC it is my observation that the values that are changed from factory are the P, I & D values. 99.9% of us are not going to be able to set them any better than the Auto Tune (AT) will do it. Other than possibly the OFFSET value we need not be concerned with the other values unless we accidently change one and with those little setting buttons that is more easily done than intended. Not a bad idea to check the parameters against the factory settings if something seems amiss.

Back when I started someone said to set the temperature desired and when you get within 20-30° of that figure engage the autotune function. I cannot dispute that as it's worked for me always but have a gut feeling it's not really relevant. It usually takes several minutes for the AT to do it's thing and settle down and the AT light goes out. It is a good idea to record those P, I and D figures so you can return to using the unit with that particular device and not go thru the AT process again. Reset to them and with the same device and similar conditions you'd be good to go.

When using say your kiln instead of the pot that would either have to be run thru the AT cycle again or use the figures you recorded previously. IF, you put those figures in and then ran AT again the new ones will probably not be exactly the same but the relationship between the P, I & D will work. That's the magic that the PID unit computes even though it's beyond our lay person understanding. Running AT numerous times will not hurt anything, it just takes time that can be avoided.

All my units have been run under similar conditions as regards when AT was run. I don't expect them to operate in my little shop at 40° one time and 85° the next. I have the Lee 10# pots and usually only drain them down maybe 4-6 lbs. before I add more lead to things and that lead comes from an upper feed pot set to temp to match. Don't think it ever drops more than 5° max in the pour pot with that method. And by not using more than that 4-6 lbs before refill apparently the mass doesn't change that much so the effect isn't as drastic as it might be if I emptied or refilled a larger amount. A bigger furnace and draining the mix a larger amount would likely make a difference there I'm sure. Generally I don't see more than about 1° C difference on the PV while casting which I attribute to the method I use and similar operating conditions.

Preheating ingots on a hot plate I only see a couple degrees change on there too which is set at 400° F if I recall correctly. Those prewarmed ingots don't take long to melt in the feeder pot but I don't pay that close of attention to that one truthfully. It'll easily be up to temperature by the time it's time to refill below.

As I've said we don't need PID's but it's nice as in my case to turn on 3 units and know in roughly 20 minutes everything is where I want it with out guessing anymore. Same with my luber machine, turn it on, do something else for a bit and things will be at and maintain the 125° C that my lube likes.

Hope some of this babbling will be of some help.

[Mal Paso]

It is possible that in programming for brewing you turned off the PID function. From what you describe your PID is acting like a thermostat. You should go through setup and check your settings.

I don't know inkbird but Auber offers an amazing level of programming. You can switch from it PID to a programmable thermostat where you can select the deadband, delay and a bunch more.

[Old Ugly]

Thank you all for your input. At the very least it lessens my fear of going into the settings and experimenting with them a bit. I have the flow chart that came with the controller and a list of brewer Georges suggested settings so I can always go back to them.
I have not played with the self-tuning mode in the output setting section, it was set on Pid, so will start there as suggested by Mike W1. I will also dedicate this PID to casting and use something else for the kiln. If I don't succeed I may also contact Inkbird by email and hope I don't have to learn Chinese.
Thank you all again for your input. Will try to post results but this is going to take awhile.
Bye for now,
Rod (Old Ugly)

[Old Ugly]

It is possible that in programming for brewing you turned off the PID function. From what you describe your PID is acting like a thermostat. You should go through setup and check your settings.

I don't know inkbird but Auber offers an amazing level of programming. You can switch from it PID to a programmable thermostat where you can select the deadband, delay and a bunch more.

Mal Paso,
I believe the Pid is on. Here are my settings in the Pid mode. Control period-1, Proportional band-1, Integral time -540, Derivative time- 200. These are the settings suggested by brewer George.
Thank you for your time and input.
Rod (Old Ugly)

[popper]

out light shuts off but the temp. keeps rising another 10 or so degrees then falls down to set temp. Called overshoot. Do the autotune on a 'full' pot a couple times, then it will be OK. You will get a bit of overshoot later but just let it settle out (5 min or so). If you don't autotune at first, may take an hour to settle down each time. haven't autotuned mine for more then 5 yrs.

[Old Ugly]

OK guys,
I loaded the lead pot and doing as Mike W1 suggested (set in Pid mode) watched temp. until it was 30 degrees below set temp. and reset to self tuning mode. By the time I got it reset the temp. was already above set temp. but it appeared to be working so I let it run for about 1 hr. Checked the high and low temps. and came up with 1.6 degree variance. I think that is pretty darn good. Might even get better with use?
Thank you all for your input, Would have pulled all my hair out (still have a full head) with out your help!!!
Rod (Old Ugly)

[Mike W1]

Glad you got it working for you. Probably should have mentioned it but you now know. Running that AT takes awhile! Seems like one of my units takes 3 up and down cycles before it's completed what it has to do and the other brand requires 4 cycles before it's all done. Probably in my notes somewhere I'd think. And as mentioned long as you enter the appropriate P, I & D figures when you switch your devices it's not a problem switching between them. I just had fun putting more units together for S&G's.

[mattw]

I use MyPin pid's, gave up on InkBird because I could not get them to a stable state even it auto tune. Until my pot gets to less than half full the temperature control is amazing, at a half pot and below it tends to vary by 5 or 6 degrees. I am thinking about running an auto tune at the half full point as it is harder to control. Mine pulses full power to the pot, would like to try one with a linear output so that it controls either the voltage or the current. But, not really needed. BTW, the pair I built are based on SSR's not relays.

[Mal Paso]

Mine pulses full power to the pot, would like to try one with a linear output so that it controls either the voltage or the current. But, not really needed. BTW, the pair I built are based on SSR's not relays.

Modern SSRs switch on and off when the AC cycle is at 0 volts so there is very little electrical noise even when the PID is cycling at a high rate. Something that would burn ordinary relay contacts.

[CarlMc]

Outside the PID settings, if your thermocouple is some distance from the heating element, there's a thermal lag between the heat input to the system and when the sensor reads the change. Meaning the thermocouple and heating element need to be really close to each other.

[Mike W1]

Outside the PID settings, if your thermocouple is some distance from the heating element, there's a thermal lag between the heat input to the system and when the sensor reads the change. Meaning the thermocouple and heating element need to be really close to each other.

I must be missing something about this comment. Odds are the thermocouple has a 5-6' piece of cable on it. The tip of the TC produces a voltage which is fed to the PID. The PID sends a signal to the SSR and either tells it to turn on or off the current to the heating element. The element when turned on doesn't necessarily produce the full heat, thus the lag time for the heat of course. The "brains" of the PID do some magical predictions and feed a signal to the SSR when things need a bit of heat. I don't see where the length of the wires could have anything to do with it unless the PID unit located in one state and the heating element in another state. Course it wouldn't be the first time I was wrong for that matter.

[HATCH]

typically the 6 foot length that more thermocouples have isn't enough to really make a difference.
You can expect a +/- 5 degree @750f variance on a PID.
Quality PID controllers will factor in the overshoot when doing autotune.
Yes, a 1/2 pot of lead will heat differently then a full pot of lead but normally not enough to really matter

[Dragonheart]

There is a lot of information on YouTube on setting an Inkbird. I did several Inkbirds a number of years ago and all are still performing, but they all were set for a single function. To be honest the lengthy PID set up information once in my brain was not memorized or retained and I would have to start back at square one. But the PID should be able to hold within a couple of degrees, even so 10 degrees plus or minus is not a major problem in casting. After more than 50 years, I still don't use anything more than a pot thermometer.