Reply To: PID questions

Soolocks5779George Barnette
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Rank: Jedi

Thank you, Fred. Yes, it is a sawtooth oscillation, I think it’s  because of some of the scaling on their graphs. I don’t have any of those graphs right now or I’d send you one. The temp stays pretty steady, they’re worried about “wearing out” the valve. Go figure.

Anyway, I just don’t get that “min/repeat when in dependent mode for the integral. So, if I’m figuring this right, if I have an Ki value of 0.016, then does that mean I’m repeating the integral control function once every 16 thousandths of a minute? I would say that a tenth of a minute is 6 seconds, a hundredth is a little over a half a second, so a thousandth would be much faster than that.

I’ll try making Kp a value larger than 1 and increasing the value of Ki and see what happens. When I was tuning the PID’s for the fans, I had to have a very slow increase on output % from the PID because they don’t want them ramping up fast at all. And if you program in an accel time in the drive, then whenever the PID makes a positive change in the output %, then there’s a long delay before any drive response, which increases the output, on and on. So we took out all pre-programmed accel time and they work pretty good with those values I gave you. I’m just looking for those water valves to be a little more stable so I’ll try what you suggested. Thanks, Fred.