PID Toaster - Preliminary Questions

What does the AA and DA stand for on Solid State Relays? Are they interchangeable? The SSR I received is a DA.

Edit: I think I have the answer... One stands for DC in and AC out and the other for AC in AC out?
 
Yes.

Well, sort of. The A stands for AC and the D stands for DC.

In AA vs DA, the first letter is the control input and the second it the load.
 
What do you guys think about this design for a "Knife Tempering Frame?"

Note: I totally robbed most of this design from @Stromberg Knives

I'd be able to insert it into the oven and place it on the rack.

I was thinking that a top and bottom plate would be required so that the knife(s) wouldn't get impacted by direct heat radiating off the elements.

The TC would be inserted into the bottom plate, which the blade edge is resting on.

Not sure if it would matter if I used steel or aluminum on this?



Thanks for the help,
JKeeton
 
Not to overload this thread with questions... but I have another one in addition to the post above!

The new SSR-40DA (made in Taiwan) is working! SO, that's good. I got an 8$ refund for the defective one from eBay.

Now I'm on to figuring out the programming of the PID. I've gotten it set to Fahrenheit and I've confirmed it on "K type" TC mode. I've ran the Auto-Tune function on 400 degrees.

Even with it being "auto-tuned" I'm finding it's over shooting the temp by around 20 degrees... Then it turns the oven off and holds a simi-constant temp, which I think it's "lying to me" about... Another calibrated thermometer I have right on top of the TC is reading a lower temp during this period of time... Then, all of a sudden... when the TC temp (in red) finally shows it's below the set point, the red "actual" TC temp stars wigging out!

I've done some research on the "df" function in the options and how you're supposed to turn it to 000, but mine will only go to 001. Not sure if that's the issue or not. Heard the "df" option is the "trick your boss" function.

Anyway to stop this cheap Chinese controller from overshooting the temperature and flipping out?

Here is a video of what it's doing:

00:00 - 00:26 ; PID is holding a temp above the set-point (But I don't think it's the actual temp of the oven... notice the discrepancy from the red number to the thermometer values)

00:26 - 1:29 ;PID drops below 399 and loses it's mind! ... I think the red number then comes back down to the actual temperature.




Other notes... My Rex-C100 is the knock-off version that only utilizes 3 digit codes instead of 4 digit codes for most of the options.

Edit: I know I was advised to get a better quality PID/SSR package... and I'm suffering now for my mistake!
 
Is that during the auto tune, or after it has been completed and the “correct” PID terms are in use?

It looks like it is auto tuning to me: all auto tuning does specific things so that it can measure the response of the system to those things and Calculate the P, I and D terms.
 
Besides the autotuned functioning being a factor, you have placed a large thermal mass in the oven. It will need to run for at least 30 minutes, maybe longer, to soak the mass and for the PID to autotune to that amount of mass. Every time you use the oven it should run for 30 minutes to get the mass soaked again before placing the blade in.
 
So this is after the oven has been auto-tuned and the auto-tune program is turned off. When it’s auto tuning the little “AT” light on the bottom left of the unit is on. Once it’s done auto-tuning this light will turn off.

Also, at this point, the oven had been running for around 25-30 min.

At the time the video was taken the unit is oscillating. Going up to 420 degrees... shutting the oven off until the temp gets below 399 (while it’s really 375 degrees)... then suddenly dropping to the “right” temperature of around 375 degrees and turning the oven on. Then repeat.

I guess I could try to run the Auto-Tune feature again and see if it gets any better. It’s very wierd to me that the red actuall numbers will hold flat... then suddenly drop 20 degrees in 2 seconds.
 
To elaborate on the issue... I charted this out with a stopwatch! PID was set and auto-tuned to 400F.


Exact testing set-up (Auto-Tuned to this set-up twice in a row) (Right cooking probe is what is charted in Orange Below):



It runs on about a 12 min cycle:


  • Check out the sharp drops on the PID.
  • I wonder if there is a frequency or dead-band setting that I could change? The oven stays shut off for a long time after it hits the 420 mark.
  • I feel like a ~57 degree fluctuation is unacceptable! LOL
 
I guess and inkbird or mypin are in my future! I can't find anything online on how to remedy this issue.
 
I saw pretty drastic temperature swings when i did a toaster tempering oven build and ended up pulling out the elements and putting them in a firebrick oven like my austenizing oven and the temp swings disappeared.
 
In your drawing of the frame you made to place the knife in, the steel looks pretty thick. If it has too much thermal mass, the delay time in heating control will make it hard for the PID to figure out how long to fire the heating elements.

1/8" plates are more than thick enough. They mainly are there to block direct radiation from the elements. You need to leave plenty of room for the air to have convection, too. don't completely cover the shelves with metal plates.

BTW, make sure the oven is set to run on HIGH, BAKE., and the temperature dial (if there is one) is at its highest setting. (Or, re-wire the oven to by-pass the controls so elements to run directly off the power cord if that is possible.)
 
Stacy E. Apelt - Bladesmith said:
In your drawing of the frame you made to place the knife in, the steel looks pretty thick. If it has too much thermal mass, the delay time in heating control will make it hard for the PID to figure out how long to fire the heating elements.

1/8" plates are more than thick enough. They mainly are there to block direct radiation from the elements. You need to leave plenty of room for the air to have convection, too. don't completely cover the shelves with metal plates.

BTW, make sure the oven is set to run on HIGH, BAKE., and the temperature dial (if there is one) is at its highest setting. (Or, re-wire the oven to by-pass the controls so elements to run directly off the power cord if that is possible.)
Click to expand...

Hey Stacy E. Apelt - Bladesmith Stacy E. Apelt - Bladesmith thanks for the tips. The drawing of my rack was conceptual. I've been testing it with the picture in post #48 (just one 3/8'' plate). Thanks for the tips on the rack though. 1/8'' sheet would be easier to handle too!

The oven is set on max and bake.

I've been consulting a circuits forum... their advise was as follows (I'll try this today):

MRCHIPS said:
Either the PID controller is busted or it needs tuning.
Disable auto-tuning.
Disable both integral and derivative control by setting the Integral Time and Derivative Time to max (3600 seconds).
Experiment with Proportional control first. P controls the power, i.e. how fast you want to ramp up the temperature. You ought to get some reasonable form of control even if there is deviation from the setpoint.
Start reducing the Integral Time. Integral control is to reduce the error from your setpoint. This ought to correct the error from the setpoint. For temperature control, many times PI control is good enough. Adjust P and I to get best settling time without too much oscillation. Only after the P and I controls are working should you attempt to introduce D control.

The purpose of Derivative control is to take care of short term perturbations. It will also help to reduce oscillations.
Click to expand...
 
I'm having some difficulty understanding the intent behind your setup. The "conceptual" drawing actually looked pretty sound to me. The photo looks nothing like it. At all.

The drawing shows a thick bottom plate, which might reasonably be expected to work as a heatsink, with the thermocouple embedded in it. The plate is shown as being heated by radiated heat from the lower elements. There is a similar top plate which might reasonably be assumed to be heated by radiation from the top elements, and to a degree reasonably similar to the (measured) bottom plate. The blade is shown standing vertically in a rack between the top and bottom plates.

The photo seems to show foil on the shelf so that the bottom plate is not heated directly by radiation from the bottom elements. The control thermocouple is placed above the bottom plate, not within it. It looks like it may even be on top of the second thermocouple. There are no support pillars visible for the top plate. Is there even a top plate? Without one, the primary heating mechanism would seem to be radiated heat from the top elements. The blade is positioned flat on the bottom plate. It is notable that both thermocouples look shiny. This is not generally a good thing when trying to measure/control a process involving radiative heating.

Why have you made such major changes between the concept and testing stages? Did you even realise that you had made changes? Do you realise now that it has been pointed out?

Although I suspect that the controller is not a particularly good one, I am inclined to feel that several aspects of your process setup are contributing to the problem.

I'd suggest you order a new controller and build/test the setup in the drawing while you are waiting for it to arrive.
 
timgunn1962 said:
I'm having some difficulty understanding the intent behind your setup. The "conceptual" drawing actually looked pretty sound to me. The photo looks nothing like it. At all.

The drawing shows a thick bottom plate, which might reasonably be expected to work as a heatsink, with the thermocouple embedded in it. The plate is shown as being heated by radiated heat from the lower elements. There is a similar top plate which might reasonably be assumed to be heated by radiation from the top elements, and to a degree reasonably similar to the (measured) bottom plate. The blade is shown standing vertically in a rack between the top and bottom plates.

The photo seems to show foil on the shelf so that the bottom plate is not heated directly by radiation from the bottom elements. The control thermocouple is placed above the bottom plate, not within it. It looks like it may even be on top of the second thermocouple. There are no support pillars visible for the top plate. Is there even a top plate? Without one, the primary heating mechanism would seem to be radiated heat from the top elements. The blade is positioned flat on the bottom plate. It is notable that both thermocouples look shiny. This is not generally a good thing when trying to measure/control a process involving radiative heating.

Why have you made such major changes between the concept and testing stages? Did you even realise that you had made changes? Do you realise now that it has been pointed out?

Although I suspect that the controller is not a particularly good one, I am inclined to feel that several aspects of your process setup are contributing to the problem.

I'd suggest you order a new controller and build/test the setup in the drawing while you are waiting for it to arrive.
Click to expand...

The current setup (picture) was just me playing around with the PID. I haven't built the rack yet. I posted the conceptual drawing of the rack to see what yall's opinion was on the rack before I built it.

Even with the current "testing setup" I'd expect the temp to be more stable and I'd expect the PID not to make 25-30 degree jumps in 5 seconds.
 
I just though of something the advice from timgunn made me think of. It may not be your issue, but is worth mentioning.

The rate of many lower cost ramp/soak PIDs is the opposite of some others . rate9999 is 9999° degrees per hour ramp rate on some PIDs. StepTime9999 ramp rate is 9999 minutes to the next step on others. Make sure which your program manual calls for. Also, make sure your oven will ramp in the time allotted.

I have to watch for this between my HT oven where rate5000 is a good ramp rate, and a plug in type controller I put on an old smaller oven (like what you are building), where the rate of steptime15 is about right.
 
Stacy E. Apelt - Bladesmith said:
I just though of something the advice from timgunn made me think of. It may not be your issue, but is worth mentioning.

The rate of many lower cost ramp/soak PIDs is the opposite of some others . rate9999 is 9999° degrees per hour ramp rate on some PIDs. StepTime9999 ramp rate is 9999 minutes to the next step on others. Make sure which your program manual calls for. Also, make sure your oven will ramp in the time allotted.

I have to watch for this between my HT oven where rate5000 is a good ramp rate, and a plug in type controller I put on an old smaller oven (like what you are building), where the rate of steptime15 is about right.
Click to expand...

Hey Stacy E. Apelt - Bladesmith Stacy E. Apelt - Bladesmith thanks for the thoughts.

I'm having better success with manually tuning... getting closer! I currently have my P set to 70 and the I&D maxed out to 999. I'm getting around a 35F swing now... which is better than 60F.

I also threw together the frame (Haven't tested with the frame yet):




The Plate is bored 1/2 of the way though so the tip of the TC touches the center of the steel plate.
 
So I think I'm getting somewhere...

With the cage above and a setpoint of 390 I ran a test with these parameters:

P=070; I=999; D=999

Down Cycle > 418-407 1.75 min (11 delta)
Up Cycle > 407-413 in 1.65 min (6 delta)
Down Cycle > 413-404 in 3.5min (9 delta)
Up Cycle > 404-414 in 2.13 min (10 delta)

I'm going to try to fine tune it some more so that I'm not overshooting the setpoint.

T timgunn1962 Stacy E. Apelt - Bladesmith Stacy E. Apelt - Bladesmith - What do yall think is a reasonable expectation of the accuracy (tightness of range of valves) of this toaster PID combo? 10 degrees? Trying to figure out what to shoot for.
 
So I've gotten some pretty good results using this reference! https://web-material3.yokogawa.com/Adjusting PID Manually (short).pdf

These are the results of some of the test I've run recently:



I feel like holding a 2-3 degree window is pretty damn good! I'll continue to use these set-points and slightly adjust them. The cage helped for sure as well.

Thanks for all the help in this thread.

This is a video of it in operation sped up. Look right?

 
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