Trouble shooting a pid controller

Discussion in 'Power Electronics' started by rotccapt, May 6, 2018.

  1. rotccapt

    Thread Starter New Member

    Jul 30, 2016
    13
    1
    Hello all, I added a pid controller to my kiln so I can use it for heat treating steel. I am using a "Mypin ta4" pid controller powering a solid state relay with heat sink.

    Everything was working well for a while and I have been using it off and on at low temps (350*F) for some other projects. Today I went to normalize a piece of steel which requires 1700*F. The kiln begins to heat up and gets to about 1000*F then the pid shuts off, the whole screen and everything goes dead and begins turning off and on. When the display come back on it has 1900 on the temp line and y on the set line and all the lights are illuminated. I did this 2 times and it got to the same temp and did the same thing. I am assuming that the thermocouple has failed but im not sure. I am using a k type thermocouple. When set to a lower temp the controller works normally and will maintain a temp of about +/- 2*F. Does this sound like a bad thermocouple?

    the manual does not have anything about this error.

    Im sorry if this is the wrong forum for this question.
     
    Last edited: May 6, 2018
  2. crutschow

    Expert

    Mar 14, 2008
    23,081
    6,848
    What is the maximum temperature rating of the thermocouple?
     
  3. rotccapt

    Thread Starter New Member

    Jul 30, 2016
    13
    1
  4. Reloadron

    Distinguished Member

    Jan 15, 2015
    4,441
    2,169
    First I would walk through the controller and check all of the user settings (Parameter Settings) and make sure the controller is setup for a Type K Thermocouple. Something also is a little peculiar about the thermocouple you linked to. The leads look to have red and white insulation which is common to a Type J thermocouple, a Type K is generally Red and Yellow and in both cases the Red lead is the Negative. If you have a small magnet on a Type K thermocouple the magnetic lead is Negative, on a Type J thermocouple the magnetic lead is Positive. While your link clearly says Type K the leads on the pictured thermocouple look like Type J with Red and White insulated leads. Again, this is not always the case but generally is the case. I also would not rule out that the thermocouple could be opening at higher temperatures and many controllers will go upscale when that happens. Also in the parameters check your Upper and Lower limit values. This should be the manual for your controller and the English leaves a little to be desired.

    Something else you may wish to add is an indicator lamp which will clearly show when the elements are ON. While the controller will display an output I would have an indicator lamp across the heating element.

    Ron
     
  5. rotccapt

    Thread Starter New Member

    Jul 30, 2016
    13
    1
    Thank you for the info, I will run through the parameters again and make sure nothing has changed.
     
  6. rotccapt

    Thread Starter New Member

    Jul 30, 2016
    13
    1
    Just ran through my parameters and everything was correct. Also during the parameters I had the kiln set to 200*F and it regulated the temp just fine. Im running another test to 1700 we will see where it get to.
     
  7. Reloadron

    Distinguished Member

    Jan 15, 2015
    4,441
    2,169
    Yeah as something is wrong here somewhere. You are sure this is a K TC as I mentioned earlier. I just can't figure why the controller would behave as you mentioned, blacking out.

    Ron
     
  8. rotccapt

    Thread Starter New Member

    Jul 30, 2016
    13
    1
    Im Just going off the info that came with the TC. The fact that it worked before and not now it's the odd part. If it does not make it to the target temp this time, I'll order a new one and see if that fixes it.
     
  9. Reloadron

    Distinguished Member

    Jan 15, 2015
    4,441
    2,169
    Time will tell I guess. Really would look like a controller failure but it is flat out weird.

    Ron
     
  10. rotccapt

    Thread Starter New Member

    Jul 30, 2016
    13
    1
    Well, it reached the target temp with no problems. So I guess the TC is fine. My hypothesis is either running through the settings fixed something, or the controller got too hot and shut it's self off. It was probably close to 100 in the garage earlier when I was trying to run up the kiln. The controller is mounted to the side of the kiln in the old control box. If I get any more problems I may try mounting it in its own box so that I can add a fan.
     
    Last edited: May 6, 2018
  11. KeepItSimpleStupid

    AAC Fanatic!

    Mar 4, 2014
    3,540
    667
    I found this: http://www.kegkits.com/MYPIN TA4 Programming.htm

    I know what can cause the problem. The cold junction compensation can't handle the ambient temperature. i.e. The temperature of the terminals.

    Some other sensor measures the temperature of the terminals. Usually, the compensation is for a limited range of ambient temperature. many thermocouple measuring designs are stupid.

    This guy https://www.mccdaq.com/usb-data-acquisition/USB-TEMP.aspx for instance, really messes up if a fan blows on it.

    The spade terminals could also contribute if the temperature at the joints are different. Each metal transition is a thermocouple. Solder counts if they used it. If they are all the same temperature, then there is no effect.

    If you had another thermometer or two of them and a Variac, you could probably tell. You could short the TC screws of the controller and control the tempertature manually with a Variac. With the TC shorted at the controller, the controller will read ambient temperature. You would need to monitor that (temperature near the terminals) and the kiln temperature.

    Knowing how it measures the temperature of the TC input terminals would help a lot. Sometimes the device is very far away like it is in the measurement computing device. I think it is in between the space between the terminal blocks and not even close to isothermal with the terminals.

    So, moving the controller likely will work.
     
    Reloadron likes this.
  12. Reloadron

    Distinguished Member

    Jan 15, 2015
    4,441
    2,169
    Yay. :) I also have to agree with KISS as to the ambient temperature the controller is in. It may be getting a little too warm where it is.

    Ron
     
  13. rotccapt

    Thread Starter New Member

    Jul 30, 2016
    13
    1
    I touched the side of the box that the controller is in with the kiln at temp and it is uncomfortably warm. So I think that is a valid possibility. Thinking back I think the last time I had it up that high, it was winter.

    Thank you all for the help.
     
Loading...