PID Thermocouple Issue

Thanks for all the suggestions so far.

I gave up last night at about filter level 15 with the TC readings still drifting. I powered up the PID this morning, still at filter setting 15, here are the TC readings over 45 minutes. The readings are of the ambient temp of the oven with no heating by the elements. I have not yet run a program to turn on the heating elements since I do not yet trust the TC readings at ambient.

Ambient temp in the oven is 73.
7:30 power ON. Initial TC reading 238
7:36 TC reading drops to 85.
7:46 TC reading drifts back and forth between 85 and 80
8:00 TC reading drifts upward to 92
8:10 TC reading is 103 and slowly climbing.
8:15 TC reading is 109 and still climbing.

The unit is in "Hold" mode with no program running. Auto tune is something that has to be initiated in the setup menu so the PID should not be trying to calibrate.

I'm going to take Linghunt's advice and pull the PID out of the enclosure and just run the TC attached to the PID and see what happens.
 
And while you are doing that look for sources of electrical noise like transformers, computer wires, VFD's. When it is out of the enclosure, check to see what level of the digital filter is good and compare to the installed value. You will get it running so don't be discouraged and you will love how it works.
 
I pulled the PID and thermocouple from the oven. I hooked up the PID to the same 220 vac source and with no other changes to the PID the TC reading started at over 1000 and over 10 minutes settled to 230 with plus/minus 10. This is a 100 plus change just by removing from the enclosure.

I reset the filter to 20 and the TC reading went to 115 with plus/minus 5.

At this point I changed the power source to 110vac. TC readings were the same.

Next I reset the filter to 5 based on a recommendation from someone running a similar setup. TC went to 85 with plus/minus 5 fluctuations (ambient is still 73).

Next I swapped out the kiln TC for a general purpose K type TC. The generalpurpose TC at the same #5 filter setting quickly settled to 85 with plus/minus 5 fluctuations.

I then got a glass of ice water and a probe type kitchen thermometer. The kitchen thermometer settled at 32.5. I dropped in the GP TC and it dropped to 21 and has been fluctuating between 1 and 25.

The 110 vac and 220 vac circuits are dedicated circuits with nothing else running on them. I have also tried turning off the LED shop lights with no effect. No other electrical is running in the shop.

All I can conclude is that the PID is faulty.
 
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Sounds like the controller is not the best. I would expect the Actual Reading to be constant maybe +/- 1 F.

I just set mine to achieve Setpoint, I don't use the multi-ramp features. Those are pretty handy depending on the application.

Take a couple pictures of your enclosure ( inside and out ) . As doodle kind-a said, hope you are not running the "program", part of not having the output hooked up so you know it's not a closed loop system. A stable reading 1st, baby steps. Doodle is also correct on the position of T/C to heaters and the entire oven. Gradients in the oven chamber can be an issue as well.

I made an oven out of an old tool box that was inside a salvaged electrical cabinet. It was a junk-yard wars type rig, but I was cash less at the time. I never could get a constant temp across it. I added a convection fan as well. Anyway, I tossed it when I found a super nice 37 inch long x 2 inch furnace from salvage yard in like Arizona. swapped controls over and works great. That one had 3 different T/C inside. Side tracked, but lets see what you got is the point. Might be a physical problem and not electrical. I look , might have picture or two of that old beast.
 
I think the TC is bad. Can you see the junction of the wires at the probe or is in inside a tube? Do you have an substitute TC's?
 
I think the TC is bad. Can you see the junction of the wires at the probe or is in inside a tube? Do you have an substitute TC's?

Hi Doodle, re-read my last post. I did swap out the kiln style K type thermocouple for a general purpose K type thermocouple. The only change was the general purpose TC stabilized (i.e. to the central drift point) a lot quicker. I have since tried another K type thermocouple out of my smoker with the same results.
 
Have you guys seen these Linear Proportional Controllers. Replaces the SSR and controls with a 0-10vdc signal ( 0-5 or 4-20ma options too) .

More spendy, but offers better control vs On/off of an SSR. I use these when I want tighter control window. Not really needed for an oven. Just food for thought.

http://www.crydom.com/en/products/catalog/lpcv-series-control-relays.pdf

These force cooled heat sinks are amazing product, add a fan and you are set. Granted I added this to designs where I was not on a tight budget and able to overkill a design.

http://www.farnell.com/datasheets/3...7.1142274200.1503268041-1976934641.1503268041
 
How much drift in degrees are you seeing. different than what was posted earlier? Is the reading steady over like 15 seconds?
 
Sounds like the controller is not the best. I would expect the Actual Reading to be constant maybe +/- 1 F.

I just set mine to achieve Setpoint, I don't use the multi-ramp features. Those are pretty handy depending on the application.

Take a couple pictures of your enclosure ( inside and out ) . As doodle kind-a said, hope you are not running the "program", part of not having the output hooked up so you know it's not a closed loop system. A stable reading 1st, baby steps. Doodle is also correct on the position of T/C to heaters and the entire oven. Gradients in the oven chamber can be an issue as well.

I made an oven out of an old tool box that was inside a salvaged electrical cabinet. It was a junk-yard wars type rig, but I was cash less at the time. I never could get a constant temp across it. I added a convection fan as well. Anyway, I tossed it when I found a super nice 37 inch long x 2 inch furnace from salvage yard in like Arizona. swapped controls over and works great. That one had 3 different T/C inside. Side tracked, but lets see what you got is the point. Might be a physical problem and not electrical. I look , might have picture or two of that old beast.


Here are some photos of the oven and controls enclosure.

Oven front and control box. The PID has not been re-installed. Green light is main power indicator. Yellow light is the heating element on indicator. The two red indicators are lighted alarm buzzers.

20170820_150921.png


Heat chamber with heating elements and thermocouple. The thermocouple protrudes into the oven 3" and only 1-1/2" are exposed.

20170820_150936.png 20170820_150942.png


Controls enclosure. Two 40A SSR's are mounted to heat sinks at the top of the enclosure.

20170820_150957.png 20170820_151015.png 20170820_151028.png 20170820_151043.png


Back of oven with heating element terminations and thermocouple. The heating elements are not yet hooked up.

20170820_151116.png
 
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