Help getting started with auto tunning

[celer]

#3575

Hi,

So I’ve finally gotten around to hooking my osPID up to a toaster oven for use as a reflow oven and I have a few questions.

I have not yet performed any auto-tuning or tuning of the PID controller at all yet.

With the default, untuned settings the toaster oven I’m using seems to be able to gain temperature very quickly, a little quicker then needed for reflow, which mostly works, except that it far over-shoots the desired temperature when waiting. So if ramping from 30C to 100C the toaster oven keeps up with the desired ramp and then when shut off keeps gaining temperature until about 130C, and then slowly cools down to 100C, and the ospid controller moves to the next step. At higher temperatures the toaster oven has to work harder to ramp up, so the gain from 100C to 230C isn’t so quick, but still acceptable, but it overshoots less.

I assume that I need to tune the PID for the toaster oven – but based upon reading the posts here I’m not sure what the best way to do that is.

What is the general procedure for auto-tuning? Do I just set a temperature, and then do auto-tuning?

Also in this screen shot, what does the “Relay output window” setting do?

http://www.ospid.com/docs/images/thumb/f/fe/Configtab.png/800px-Configtab.png

[celer]

#3936

BTW, here is the toaster oven I’m using: http://www.walmart.com/ip/Black-Decker-4-Slice-Toaster-Oven/20564668

[rhys]

#3937

The “Relay Output Window” is the frequency at which the PID updates the state of the relay output. The output switching frequency is independent of the PID algorithm loop in the firmware. The lower the window, the more frequently the PID can switch the output relay on or off. There is a hard coded .5s minimum in the firmware. According to Brett “the 0.5 is to protect the relay mainly. but there is also the issue of computation speed. there’s a lot of stuff going on in there, and things start misbehaving if you ask for too much.”

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