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PID Thermocouple Issue

Discussion in 'ELECTRICAL ISSUES - POWER YOUR MACHINES & SHOP' started by jbolt, Aug 19, 2017.

  1. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    I just powered up a PID for the first time on my heat treat furnace build. The thermocouple temp display on the PID changes erratically, large swings from tens to hundreds.

    The PID is an Auberins SYL-2352P. Manual Here.

    The thermocouple is a TC-K-KLN type K high temp thermocouple for kiln.

    I have it wired it per the manual and double checked the settings, the polarity and connections. I also tried grounding the negative side to the enclosure per the manuals suggestions but it still jumps around erratically.

    Anyone have an idea as to what is causing this?
     
  2. den-den

    den-den United States Active Member Active Member

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    My first thought is poor connections on the thermocouple wire, second is power supply problems.
     
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  3. Doodle

    Doodle United States Active Member Active Member

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    I assume you are using Wiring diagram shown in 5.5 Figure 6 which has the k type thermocouple (TC) wired to terminal 4 of the controller which should be the (+) lead of the TC, and terminal 5 of the controller has the (-) lead of the TC. I have to assume it is running on the main power you selected as 120VAC or 220VAC and the controller appears to be operational at the selected voltage. You have only used thermocouple type wire (for k type TC) to connect between the TC and terminals 4, 5 of the controller and that you know you can't just use any old wire to do that. At 4.15 you have tried to set the digital filter by setting the range from 1 to 20 (have to start small and work up to 20 for filter). If the filter is set to 0 it is OFF and not used this is why you need to try using it by selecting 1. Since you are experiencing fluctuations in readings try 1 for a setting and work your way up to 20 to see where the filter begins to work. I would expect the higher the filter number the slower the response to temperature displayed rise or fall. Type K TC's react very quickly and in the application you have the controller should do a good job without worrying over filer response time, but it must be considered. At 4.7 you have set the controller to code zero so it knows it is a type K TC.

    Now another place to look is at the TC and its wiring route, the voltage developed by the TC is very small and it remains very small even at temperature extremes in the range of the TC. Therefore you must route the TC and its wiring away from any electrical wiring carrying current. If you have the TC wiring run with A/C power lines, separate the TC wiring. When routing the TC wires, cross A/C wires at 90 degrees to minimize coupling.

    Now how is it responding?
     
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  4. whitmore

    whitmore United States Active Member Active Member

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    That model has an 'autotune' feature, and will explore for a while when you invoke it. It could be that you're
    watching fluctuations because the little brain is experimenting with settings and hasn't learned the
    furnace yet.
     
  5. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    Thanks Doodle! Filter was the ticket. Set to 1 the TC value settled to 30. I measured the temp of the inside of the oven with a infared thermometer at 80 so I added 50 to the offset. It is now holding between 79-80.

    Next is figuring out a test program to verify the heating elements work. The manual is not very intuitive.

    I eventually plan on doing a break in period to make sure the excess moisture is out but that will have to wait until I have more time.

    Sent from my SM-G955U using Tapatalk
     
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  6. Linghunt

    Linghunt United States Active Member Active Member

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    I don't see a ground terminal on that controller. Not heard of that manufacturer but that makes me suspect of them. You got the fix, but if you had troubling wiring issue, you could remove the entire controller, and TC and power up n the bench to verify. Use of Ice bath as well.
     
  7. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    The fix didn't last. I came back to it later and when I turned on the PID the TC reading was +90 deg and fluctuating plus/minus 20. I removed the offset and have been trying different filter levels. Every time I go up a filter level the base TC reading would increase and still with fluctuations. When I got to filter level 7 the TC dropped to 90 and now is slowly falling, now at 71 +- 3 and slowly still falling. I don't really know what to make of it. I'll keep trying the filter levels. How long should it take the TC to stabilize?
     
  8. Linghunt

    Linghunt United States Active Member Active Member

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    When you get really tired on it. Remove the controller and wire it to a suicide plug for 120AC. You got some K type T/C wire.

    T/C wires on side to controller and take the other side and just twist the wires together. crude, but it does work. No other wire types or terminal blocks etc. Red and Yellow wires right? Red ( -) Yellow (+)

    Try a stable temperature to measure. Make one. Many options... get two big blocks of metal, sandwich the thermocouple in the middle and place them on the stove or hot plate at low setting. let it stabilize to equilibrium and thermal mass of metal will hold it there. Now you can mess with controller software. Perhaps it's software or unit is junk.

    Look for a Default setting to clear out what you have done. Get unit back to how it was shipped from factory.

    I'm thinking the warmer heat sink so you are up in the range of the K thermocouple. You could go with Ice water bath too.

    What is upper limit for your heat treating processes? I have a K on one oven and a J on the other one.

    If all that works out, let's talk about the rest of the wires and such in your oven control design.
     
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  9. Linghunt

    Linghunt United States Active Member Active Member

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    ohh, T/C stabilize pretty fast. if you have isolated type a longer lag. that info can be found on specification sheet for those.
     
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  10. Doodle

    Doodle United States Active Member Active Member

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    Good progress, I question the need for a temperature offset as the TC is giving the correct value for what it is exposed to. You may have to wait hours for the controller to auto tune. From what you describe I believe you now need to find a location in your oven where the temperature stabilizes. Having the TC too close to the heaters can cause wild swings. You can try location as well as shielding (example, a metal shield in front of the TC so it is not directly exposed to the heating source). I would have to go look at the manual again, can do later, but for now... The Solid State Relay (SSR) controls the current to your heater by turning the power ON and OFF, when power is ON to the heating elements either the controller will display a light or the SSR has a light (perhaps both do). What you should expect to see is a long ON time when you start heating. As the Present Value (PV), {PV is the temperature of the TC}, rises and gets closer to the Set Value (SV), the ON time of the SSR will decrease. So look at the SSR ON time light and from a cool or cold start its dwell time will change from a long blink to a rapid series of blinks. That is the indication that the controller is trying to get your Set Value (or Set Point) under stable control. At this time you do not need to run a calibration test of the TC and controller by using water baths or Infrared thermometer readings. The TC and Control are better to rely on right now since everything is new, connections are good, and you are experiencing some control.

    The SSR must be properly heat sinked so it does not run hot in operation. Additionally SSR's always leak a little current so don't expect a complete OFF at the heating elements. The very small amount of current will not effect the heating. They don't wear out and give exceptional control of the load far superior to metal contacts.
     
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  11. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    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.
     
  12. Doodle

    Doodle United States Active Member Active Member

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    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.
     
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  13. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    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.
     
    Last edited: Aug 20, 2017
  14. Linghunt

    Linghunt United States Active Member Active Member

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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.
     
  15. Doodle

    Doodle United States Active Member Active Member

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    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?
     
  16. ddickey

    ddickey United States H-M Supporter - Premium Content H-M Supporter-Premium

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    Do you have a multi meter?
     
  17. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    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.
     
  18. Linghunt

    Linghunt United States Active Member Active Member

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    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
     
  19. Linghunt

    Linghunt United States Active Member Active Member

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    How much drift in degrees are you seeing. different than what was posted earlier? Is the reading steady over like 15 seconds?
     
  20. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    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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  21. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    The drift over 15 seconds can be 2-3 degrees.

    At my last test with the general purpose TC Ieft it in the ice water for several hours with the PID on. At the time I left it the water temp was still 32.5 and the TC was fluctuating between 25 and 1. When I came back several hours later the water temp was 65 and the TC was at -13.
     
  22. Linghunt

    Linghunt United States Active Member Active Member

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    Nice oven. I don't see any electrical noise issues. Did you build that oven? I want one that is like 5 to 6 foot long and internal width and height can be 5" x 5" or so. Just want to treat long rods like 5/16" diameter.

    With output signal disconnected. and T/C in stable temperature environment you should see like +/- 1 degree range. ( rounding on digital signal ) With output disconnected, don't care about PID and what it is doing. you basicly just got a temp meter.

    Do you have a sketch of schematic? I like that you twisted the wire pairs together.

    I'll try and get a picture of my internals so you can see what ugly wiring looks like. Been spoiled over the years with amazing techs.
     
  23. ddickey

    ddickey United States H-M Supporter - Premium Content H-M Supporter-Premium

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    So the water temp went up and TC was reading a colder temp?
    Switch the wires around and see what happens.
     
    Last edited: Aug 20, 2017
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  24. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    Yes I have been building the oven a little at a time over the last several months.

    I don't have a sketch of the wiring.

    Sent from my SM-G955U using Tapatalk
     
  25. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    Hi ddicky the polarity is correct. Already checked that.

    Sent from my SM-G955U using Tapatalk
     
  26. Doodle

    Doodle United States Active Member Active Member

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    Do you still have an offset programmed in to the controller?

    When you substituted the other TC's, did you connect them direct to the control terminals 4,5 ?

    Do you know if your shop humidity is above 40% ? I am considering static discharge damage to controller.
     
  27. rgray

    rgray Active User H-M Supporter-Premium

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  28. jbolt

    jbolt United States Active User H-M Supporter-Premium

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    No offset.

    Yes the substitute TC was wired directly to the PID.

    No the humidity is not that high. I've never had a static issue here especially in the summer months.

    I'm going to contact the vendor tomorrow and see what they have to say.
     
  29. Linghunt

    Linghunt United States Active Member Active Member

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    [​IMG]

    [​IMG]

    [​IMG]

    3 different T/C's on the tube furnace . Pretty ugly wiring job. Swapped out controller for a smaller one and addition got it looking worse that bad.

    Output is off and temperature changes 0.1 F as I watched it for a bit.

    ColdCube and fan in there along with a power contactor and transformer. I built it with what I had to keep price down. Should be a breaker in there out of view. For layout, an example of how not to do it.
     
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  30. Linghunt

    Linghunt United States Active Member Active Member

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    [​IMG]

    [​IMG]

    My little oven. got for next to nothing but controls were trash. The toggle switch turns the output off. This one has an SSR in it along with a really old Watlow PID controller. note the temp off set by around 5 F or so. I think this one required a cold junction reference and I didn't do it. Got a replacement Automation Direct controller to install to match other oven and not got around to it.
     

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