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[joecos]

Hello. I have two high temperature furnaces that I am controlling using ramp/soak PID controllers. The first furnace is maintained at 1000 deg C using the SYL-2352 controller with an N-type thermocouple. After using the auto-tune step, the system is very stable: +/- 1 deg at the setpoint.

The second furnace is heated to 1400 deg C using the SYL-5352 controller with an R-type thermocouple. With the default PID parameters (P=0, I= 500, D=100) and with the cycle time set to 2 s, the furnace temperature oscillates ~ +/- 6 deg after reaching the setpoint (1400). In this case, however, the temperature oscillation gets worse (+/- 10-15 deg) after running the auto-tune step. The PID parameters after auto-tuning are P=8, I = 2283 and D = 2. Any help would be greatly appreciated.

Thanks, Joe

[Kkane]

Your auto-tune result seems strange to me.

You can set the PID back to the default value (P=0, I= 500, D=100) then run auto-tune again.

Before you start the auto-tune, change your step 1 and 2 as the following.

r01 = 2000, t01 = 0, C01 = 100
r02 = 1, t02 = 60, C02 = 1400 (your most important temp in your profile).

Restart the program then start auto-tune.

[joecos]

Kkane, thanks for your quick response.

Is the very short r02 of 1 minute required? We have to be careful that we don't thermally shock the heating elements (silicon carbide) in our furnace

Joe

[Kkane]

No, you can use any none-zero number as R02. If you set R02 to 0, the controller will bypass this step, so I put 1 here. If you like to slow down the ramp up rate to protect your element, you can use a large number there.

The rule is, the auto-tune is based on your set temperature and also your oven, so it is recommended to run the auto-tune at your most important temp in your profile. If you run auto-tune at a different temp, the result may not be good.

I just updated my previous reply. Once the program is restarted and running, you can start the auto-tune. You don't need to wait until the temp is 1400.

[joecos]

Kkane OK thanks I will give this a shot. Joe