troubleshooting an oven

I need help troubleshooting an oven controller unit. Once in a while (not always) temp increases steadily 20 degrees above SP causing the unit to shut down.

Here is the two of the main components.
-Honeywell UDC2300 temp controller. SP 170. HL at 190.
-AMF RP11DY0 (110VDC) This is a DC coil contactor.

The temperature reading does not bounce around nor does it react to me wiggling on the thermocouple or its wires. So, I don't think it's the thermocouple that is the problem.

Question 1) Can the rectified L1 and N, as shown in the picture, operate the 110V DC coil?

Question 2) I don't understand this part. When the controller output is ON, I read 110VAC across B and N, and the DC coil is energized. But when the controller output is OFF, I still read 110VAC across B and N, and the DC coil de-energized.

Your using a/c to control a d/c coil?

Well that's not quite true it's rectified AC so not true AC or DC looking at the circuit it is not a bridge rectifier and so you will be getting a half sinewave to the coil also 110v AC when rectified and smoothed will be above 110v for example a full bridge rectifier on 110v will give 1.4 x the AC voltage so is likely to be 150v plus. I don't think the circuit could be correct as drawn as i would not expect the readings you are getting are you sure the contact is truly a relay or is it a solid state.
Thinking of 110v whereas I see it's 120v but same principal.
I assume the controller is a Eurotherm 2300 so it sounds like the controller needs setting up.

1. Yes, an AC signal through a rectifier will power a DC coil.

2. Since it is half-wave rectification the reverse half of the wave is blocked, and that might be letting a solid state output on the 2300 to show 120V from some leakage current.

To be sure see if you can find a bridge rectifier and let full wave DC get to the coil, thus shutting down both sides of the AC output when off.

If the heater contactor opens and closes correctly according to the controller output, then you have no problem with the coil and its power supply and therefore that is not the problem that causes the temperature to exceed.

A varistor (VDR) or whatever the controller has to protect the output contact can produce the voltage reading you have with the coil off.

You probably have the problem in the PID parameters of the controller, surely you would have to increase the derivative factor D.

Some thermal systems may have a slow response.

I agree with the full wave but any capacitance in the wiring may make the voltage above a safe level for the coil.but if you are getting overshoot that is locking out then it sounds like you need to look at tuning the loop to stop the overshoot, It's been some years since using the 2300 controller and I have not used a lockout feature within the controller as far as I can remember but I believe there is one. I suggest you do a auto tune on the controller it could be that it has been replaced without setting it up. as a termporary measure you could set a higher alarm lockout to see how far it overshoots, however, think safety first for example what are the consequences of going over temperature so I suggest you tune it with the lockout margin kept as is.

Another (quick) option is to add an AC dummy relay to bleed any leakage current in parallel with the DC setup.

unsaint33 said:

I need help troubleshooting an oven controller unit. Once in a while (not always) temp increases steadily 20 degrees above SP causing the unit to shut down.

Here is the two of the main components.
-Honeywell UDC2300 temp controller. SP 170. HL at 190.
-AMF RP11DY0 (110VDC) This is a DC coil contactor.

Click to expand...

While it was not one of your questions, it sounds like you are trying to correct the overshoot/shutdown problem with your oven controls. Since it typically works OK, there may be an issue with the controller tuning, as already suggested.

Your options to improve performance (e.g., reduce overshoot) include:
1. Run the "Accutune" procedure built into the UDC2300. As with any auto-tune procedure you want to minimize any external disturbances while the tuner is running (e.g., don't open the oven door), and it can be helpful to have a typical load in the oven. Sometimes these auto-tuners work well if your process can tolerate the output changes needed for good results.
2. Determine a process model using open-loop output steps. Calculate PID tuning from the observed response. You will need to know details about the UDC2300 PID algorithm (A or B) beyond what is in the user manual.
3. Make some trial-and-error tuning adjustments to reduce overshoot. Often times overshoot and oscillation come from too much proportional and/or integral gain. You might first try reducing integral, but you must be very careful with the UDC2300 because it lists two sets of units for integral gain -- presumably whether the A or B algorithm is selected -- where one of them is repeats per minute (RPM) and the other is minutes per repeat (MPR). If RPM, a smaller number is less integral, if MPR a larger number is less integral. It is a similar situation with proportional action, a smaller gain number is less proportional, a larger proportional band (PB) is less P-action. The fact that they use the term "repeat" implies changing the P-action also affects integral tuning.

All UDC 2300's had Accutune. You need to run it and let it tune the process.

You need to enable the Accutune function first by enabling the Auto Tune key. Then press the button and run it (when you have a load).

A few thought on this
A few things don’t make sense to me. You have a 110 VAC power source and only one DC contactor coil
Why would you use a DC coil when AC coils are much more common and cheaper.
Having said that your voltages don’t sound right to me
Full wave rectified 110-120 VAC is 90VDC not 110, I know that not a lot of difference but it is important
Half wave rectified 110-120 VAC is 50VDC
You should measure the voltage across the coil when it both energizes and not energized just make sure it not being held in.
So we must first know what rectifier we are dealing with I would think is a full wave.
I have seen what’s called economizer ‘s used on DC coils both contactors and brake coils
They reduce the holding current on the coil a few seconds after the coil is energized. The way that is usually done is by opening half the full wave rectifier bridge using a timer .
With DC coils while it takes full current in the coil to pull in the contactor it only takes half the current to hold it in. Less power = less heat = longer coil life.
The economizer is usually a little module that can be mounted on the coil or external someplace.
The are sometimes mistaken for simple rectifiers you need to check them carefully.
From your description I have to wonder if the coil is really a DC coil at all.
AC coils usually have a laminated iron core with a shade pole to reduce the noise and help them release when power is removed. Yes I have seen AC coils work on DC power they are not reliable but do sometimes work.
DC coils usually have a solid iron core with a shade pole to again to help them release when the power is removed. If a DC coils is powered for long time it is possible for the coil core to become magnetized so even when the power is removed it will still hold the contacts closed for a little while.
I have seen circuits where they momentarily reverse the polarity on the coil to release the contactor.

If you try to use AC current on a DC coil they usually buzz as the current changes polarity.

If it were me I would change the relay / contactor to an AC type and eliminate the problem altogether