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  • PID Question

    I have a TC-408 PID in my oven, I am not happy with how much the PID lets the temp drop after it had reach temp before turning the elements back on. Is there a way to change this setting so it does not let the temp drop so much? if so what is it and how do I go about doing it?

    Mike

  • #2
    Re: PID Question

    First off, I'm gonna assume this is the PID you have.

    http://aliuy.com/TC-408%20instruction%201.pdf

    From what I gather from your post is that you have too much temp deviation once the temp hits the SP (setpoint) temp? How much temp deviation do you have? Looking over the PID manual, I didn't see any setting that lets you change the deviation. The only setting I found was for the cycle rate after SP is reached, alarm settings, and differentiation time. On the last one (differentiation time), you could possibly lower the time setting to less then 20 seconds, but as the manual states, the temp will start to oscillate to try and maintain a steady temp.

    Have you changed any settings from the initial settings? Or better question. Did you buy this PID new or used? If used, are the settings still have the default values? I would suggest running the auto-tune and let the PID find the best settings for what you want it to maintain the temp at. The auto-tuning setup and instructions are actually very well presented in the manual.

    Hopefully this helps out.

    Comment


    • #3
      Re: PID Question

      thanks.... I have been running the autotune.
      I just thought there might be another setting that could be changed.

      Comment


      • #4
        Re: PID Question

        I'm running the same pid. How much variance are you seeing once the SV (Set value) is achieved? All 5 pid parameters (p, i, d, souf and ot) are used to manage to the set value and can be adjusted to tighten the over/under shoot.

        There are several other things however that I've found to also influence the pid performance. One is the location of the TC and another is the presence or non-presence of a recirculating fan.

        Comment


        • #5
          Re: PID Question

          when I am doing powders that cure at 400F I will see a drop of 15 - 20 degree well the elements are turn off and then come back on. Not that big of a deal as the parts inside do not drop temp as much. But last night I was doing some thin wall parts in wrinkle powder that cure at 375 and the temp would drop down to 330 and the parts would also drop down pretty fast.
          I have a fan in my oven and the TC is located half way up in the middle of one of the walls

          Comment


          • #6
            Re: PID Question

            A drop from 375 to 330 is greater than I would expect. What are the pid parameters set to?

            Are you using an ssr or contactor? If a contactor, have you adjusted the 'ot' setting?

            Comment


            • #7
              Re: PID Question

              SSR

              THe unit was new when I got it and I have not changed anything just ran the autotune.

              Comment


              • #8
                Re: PID Question

                I see a plus +/- 7-10 degrees on my PID and wanted to know as well.

                So far I haven't seen a drop like that though

                Comment


                • #9
                  Re: PID Question

                  How big of an oven are you running and how many elements?

                  Comment


                  • #10
                    Re: PID Question

                    Originally posted by polert
                    1. What type of contactor are you using? If not a cube relay get one of those. SSR are not a great application in oven design. 2.How warm is your shop, and how insulated is your oven ( oven convecting heat faster than generating)? 3.Check the connections on you elements as well.

                    How do you know that the elements or contactor is not closing?

                    I see three variables on the electrical end of things 1. PID not working properly 2. contactor not working properly 3 one of your elements is taking a shit.

                    Myself I have 2 220v $5 indicator light on my enclosure that tells me when current is being applied to elements. Wire them on the output side on contactor.
                    I keep the shop around 55 when I am out there working.
                    the oven has 4" of mineral wool on all the walls and top, it's not seal 100% that' for sure I know it's far from perfect.
                    I know the elements are on because I can see the red light that is on the SRR when the elements are on.

                    Comment


                    • #11
                      Re: PID Question

                      see and everything I read before I built the oven said to use an SSR in an oven because it wont wear out from the turning off and on all the time with the PID

                      Comment


                      • #12
                        Re: PID Question

                        I disagree with a couple of statements here. Many ssr's are rated at multi million cycles. The fact that it does electronic switching rather than electro-mechanical switching extends the life considerably versus a similar priced contactor. Everything I've ever read states that ssr's life spans far exceed electro-mechanical relays.

                        If you are having problems with the oven maintaining temperature with an ssr, using a contactor could make it even worse. SSR's by design are capable of switching multiple times a second. Documentation on most all pid's state that if using a contactor you need to reduce the switching to no more than once every 5-30 seconds. Which therefore makes it more likely to maintain temperature, the ability to switch the elements multiple times per second, or once every 5 to 30 seconds? If you feel the need to slow the switching operation of the pid, that's what the output parameters are designed for(see 'ot' - cycle rate).

                        Maybe I'm missing something, but if you add a time delay to a contactor, then you are effectively defeating the logic of the pid imo. The pid is managing to the set temperature. An SSR or contactor is only in the circuit to switch the elements on/off as the pid circuitry is not capable of supporting the loads of an element(s). SSR's and contactors have no logic capable of managing to a given temperature.

                        The only downside to using an ssr is the need for a decent heatsink.

                        Comment


                        • #13
                          Re: PID Question

                          What's a 'cube relay'?

                          Comment


                          • #14
                            Re: PID Question

                            Originally posted by Doogles
                            What's a 'cube relay'?
                            A small square relay that fits in a base. Often has a clear plastic cover on it, hence the name cube or ice cube relay.

                            Comment


                            • #15
                              Re: PID Question

                              I got my pid from auberins.com it has 30 step ramp/soak 0.2%accuracy, and fuzzy logic enhancement .It drives 6 25amp ssr with no problem.A bit pricey @ $89.00 but to me it was money well spent.Part #SYL-2352P Auber instruments.http://auberins.com/index

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