Justin Richards gmail.com> writes: > > My problem is when I read about PID controllers , = (in > > an attempt to improve the precision) they discuss that fo= r > > the proportional part the output is basically given by > > > > Pout =3D Kp x (SP - PV) > > > > Which makes sense, but in my case I fail to equate Pout to a PWM value= .. > > This is the bit I cant get my head around. > > > > i.e When Pout =3D 0 that is there is no error, I still need some level= of > > PWM which is non zero. For example an approx actual value for PWM, for= my > > setup is 211 for 61 deg C with an ambient temp of 23 deg C. There is n= o > > value I can multiply by an error of 0 to get 211. > > > > So it looks to me that my process of accumulating the Error and adding = it > > to the PWM value is actually calculating only the Integral Term. But > > intuitively I think I am applying proportional control. > > > > Any chance anyone can set me straight on how to produce a Proportional = and > > Intergral PWM control value based on SP and PV > > > > Justin The bit you are missing is that a proportional only control scheme will almost always have some residual error, since it is the error that drives the output. The higher the gain, the less the error, but of course too muc= h gain will lead to instability. A proportional term is used in conjunction with an integral term if minimising error is important. The P terms gives you fast response, the I term reduces the residual error to zero some time later. -- Mike --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .