Heat treating oven

G

Grandpa Jon

Joined
Oct 28, 2020
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12
Happy Labor Day-

I'm in a pickle here: I completed my HTO here not to long ago following Mr. JHeaton/Red Beard Ops electrical/electronics format. I've been having issues with the PV (program value) over-shooting the SV (set value) as much as 30F. In order to capture and maintain a temp of 1650 I would put the Auber PID into "hold" as it neared the 1650. In doing so, I blew through 3 20A fuses when I decided to go another route. So I sat down watched everything Auber had regarding the 2352P controller. I did go in and change the setting for auto tuning which helped somewhat. The issue I have now is once the PV reached my SV, the SV began do decrease and the PV followed in lockstep. I'm guessing that my issue is having to do with the control mode (section 5.3.4 of the operator manual) but to me it's all Greek. Any direction or assistance regarding this would be greatly appreciated! Thnx
 
Hey G Grandpa Jon ,

From what I gather, it's pretty common for ovens to over heat initially.

That's why people recommend soaking at the desired temp for a little while. Once at temp it'll be easier for the PID to maintain the temp at that point.

That's when you put the blade in the oven, after it's at temp and maintaining.

I'm not an expert at PIDs really, just kinda talking... C Cushing H. wrote quite the extensive article a while back on the topic.
 
I used the same design, but had to adapt it to run on 110v, which is a good bit less power. I have the same pid.

What changes have you made exactly as far as how you've programmed the pid?

Are you starting in on/off mode (0 under AT), then switching it to 1, or 2, then running autotune? Or are you ramping up in 1 or 2 in AT? For some reason I do seem to notice a small difference when ramping up using 0, than 1 or 2 although the manual says it shouldn't, because its effectively in on/off mode until it initiates the autotune cycle.

I will say, I dont think I would recommend ramping in 3 though. I do a new autotune every time I ramp up.
 
I read the manual of that controller when I built my oven and decided against it because it seemed a bit complicated to program. If I recall correctly, you have to program a ramp up to the temperature you want and then a hold time at the temperature you want. It sounds like you have a ramp up and when it reaches the set point, it goes to the next program step which is probably a ramp down. Previously, you switched it to HOLD before it finished the first program step, so you never entered the ramp down.

I think you should investigate why it was blowing the fuses, I cannot see how pressing the HOLD button on the controller could possibly cause that.
 
I have an Auber PID, but one of the simple ones that doesn't do ramp/soak times. It was great the first few times, then overshot the temps a lot (30-40 degrees) for some reason on one of the next times I used it. I checked the wires and found nothing amiss/loose. The next time, it just overshot by a few degrees and then maintained the temp well when it auto corrected even with opening and closing the kiln lid a few times to add/remove blades. It's weird that the PV and SV are both declining? Is there a ramp down or something programmed?
 
The declining happens when the following temp is lower than the current steps temp. To program an actual soak. You need to put the two steps at the same temperature for the amount of time you want the soak to last. If you want to ramp up or down, you put the starting temp on one step, and the ending temp on the next step, then on the first step you put the amount of time you want it to take to get to the second temperature.

Or if you just want to program just an indefinite soak, you put the temp you want, and enter the time as 0. This will just ramp up. And hold at that temperature.

As far as overshooting. I seriously recommend you check what the autotune settings are. Especially if using the oven at different temperature ranges for different steels, or parts of the heat treatment.
 
One thing people don't think about is this:
It took you many tries to learn to walk. You couldn't get up sometimes. Sometimes you fell down before you got to where you were headed. Sometimes you couldn't stop going and crashed into things. As you did it more times your brain learned the right amount of muscle power to make walking controlled. Eventually you could run and jump accurately.

The Autotune function on the controller is sort of the same. It takes multiple running cycles to learn how to run the heating elements and hit the target. If you keep changing things every time, it will never learn.

Set all the parameters and run it in Autotune 10 times. Turn the power off each time and re-start from a cold oven. This is how it will learn to control the heating elements accurately.
 
I know you have a lot more experience than me with this.

I was thinking that after you've set the parameters, and its decided what the autotune settings should be it doesn't change them once it's gone into 3 mode. Which is why I run an autotune cycle every time I heat it up, and especially everytime I change the ovens target temp. Am I doing it wrong?
 
I don't think there is anything wrong with repeating the autotune. I have to do that on the toaster oven controller every time I change the set temperature by 50°F or I get fluctuations of about 5°F. On the heat treating oven, the same parameters work well over a much larger range and I can go from carbon steel to stainless without autotuning at different set points.

There is no telling what kind of autotuning a particular controller implements. I would be surprised if cheap controllers benefited from repeated autotuning, even if they advertise their advanced fuzzy logic control.
 
I'm not sure. The way I do it though I never get any fluctuations over 1 degree +/- on whatever heat I'm using.
 
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