Simple PID control

[Neutone]

This is turned out to be a really easy way to impliment a PID control.
All variables are floats

//PID PWM calculation routine for SupplyTemperature

errorNOW = Setpoint - SupplyTemperature;
PWMonTIME = PWMonTIME + (PWMp * errorNOW ) + (PWMi * (errorNOW - (PWMd * (errorNOW - errorLAST))));
errorLAST = errorNOW;
if (PWMon > 190) PWMon = 190; //maximum on time
if (PWMon < 10) PWMon =10; //minimum on time
PWMoff = 200 - PWMon;
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This message was ported from CCS's old forum
Original Post ID: 427

[valemike]

Neutone,
Since i have to maintain temperature at around 405 degrees F, i looked at your past post. I'm new to PID, and am wondering the following:
1. PWMp*errorNOW is obviously your Proportional Term.
2. PWMi * (errorNOW)
3. PWMd*(errorNOW -errorLAST) looks like your Derivative Term.

What I don't understand is why do you multiply PWMi with the Derivative stuff too?
Looking at a bunch of ESP magazines, I see that the Integral Term is theoretically calculated by: Ki*sum_of_errors.

Is this a "quasi PID" algorithm you simplified that is good for your particular application?

Thanks,
Mike

[Neutone]

[falleaf]

Yes mike, normally, we can compute PID like Kp, Ki, Kd, but in some case, they use Kp (1 + Ki' (...) + Kd' (...)). But in this case, it's so strange. And it must be something wrong.

I finished my PID position controller with great results, and I think with uC software controller, we should compute directly.

[sonicdeejay]

thx..