PID help

[808blades]

I have a small heat treat kiln I've made and am having trouble with my Inkbird PID set up. The problem is that it undershoots by quite a bit. I ran it in auto tune mode several times and it only overshoots by a degree or two but then falls aprox 20 degrees before climbing back up again. The PID doesn't seem to be able to correct this undershoot what am I missing?

 

[Stacy E. Apelt - Bladesmith]

Sometimes it take a couple hours of running for the PID to "learn" when programming itself.

You may need to change the hysteresis, or one of the other parameters (P or I). Cushing or Tim Gunn hopefully will chime in.

 

[Skiller1nc]

Auto tune should work as Stacy noted, however, you can also try increasing the I value. That will help with response speed and possibly fix undershoot. Too much I will make the controller unstable though.

 

[ER Sheldon]

I too had numerous problems with my Inkbird controller. No matter what adjustments I made, the PID performance remained the same. Autotune also did not have an affect. After many frustrating hours, I did some deeper digging in product reviews online and discovered many people with similar problems. The Inkbird controller just doesn’t function properly as a true PID controller. I scrapped it and bought a Auber Instruments. The new controller works much better and their customer service is top notch.

 

[Stacy E. Apelt - Bladesmith]

I have never used an Inkbird controller, but have read numerous treads where there were problems.

 

[Cushing H.]

Sorry ... should have responded to this earlier ... been busy...

the behavior sounds like your proportional band is too large for the power of your heating elements (or your insulation is really low). People here know I am not a fan of auto tune. Try going manual. Look for the thread “everything you wanted to know about PID controllers ...”, and in there is a discussion of how inkbird treats the proportional band. (Sorry ... I’m ona tablet now, so can’t readily paste in a link to that thread).

also ... I’m with Stacy - several people have had an inkbird controller just not work stably, then switched to a more xpensive one (like an auber) and immediately had much better luck

 

[Cushing H.]

Oh, also your control period might be way too long... set it to as short a period as you can (I think one second on the inkbird...)

 

[808blades]

Thanks so much for your help so far! A few more details. Oven is about .1 cubic feet 120v & 1000w. It took about half hour to get up to 1000 F, once it gets to 1000 output light goes out goes up to about 1002 holds for a few seconds then begins to fall. Once it falls to 1000 output light blinks, at 998 light goes solid but temp falls to 980 before starting to climb again. Thoughts? Thermo couple comes out of top extends about half inch. If I push thermocouple in further it gets in line with the coil and overshoots and undershoots by alot. Thanks again

 

[Stacy E. Apelt - Bladesmith]

I would run the thermocouple in a good inch. Let it overshoot and undershoot for a couple hours while it "learns" in auto-tune. Check the P and I as well as the refresh period, as suggested by others. If that does not get better results, order a good PID from Auber or Omega.