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Hey guys, noob technician here.
I'm pretty new to PLC stuff, but I'm having a ridiculously hard time understanding why my PLC behaves like this. The definition of the PID function block I'm using says that it uses an incremental algorithm. That's great, I'm totally comfortable with that. My problem seems to be though, there is never any proportional action from the start. Here's what I mean by that. The documentation for this blocks says that ProportionalComponent= kp*(change in error). So lets say I have a setpoint of 100 and a PV of 0. If I run that PLC - with a Kp=1 and say Ki >0, I should end up with an output of 100 right off that bat. But what actually happens is, my output starts from 0, and as I increase my PV, my output decreases (like should happen with an incremental controller).
Can anyone explain why this happens? All through college was taught that if I have an error of 100, my controller output should have a proportional component of 100*Kp; but with this block (and another one I've seen as well), I actually only take away from my output as I decrease my error. This isn't a direction problem, because the integral component accumulates in the correct direction.
Basically, my PID doesn't seem to operate like any control systems "textbook" would suggest. Any help to a PID noob? I'd be forever grateful if someone could get me out of this rut!
I'm pretty new to PLC stuff, but I'm having a ridiculously hard time understanding why my PLC behaves like this. The definition of the PID function block I'm using says that it uses an incremental algorithm. That's great, I'm totally comfortable with that. My problem seems to be though, there is never any proportional action from the start. Here's what I mean by that. The documentation for this blocks says that ProportionalComponent= kp*(change in error). So lets say I have a setpoint of 100 and a PV of 0. If I run that PLC - with a Kp=1 and say Ki >0, I should end up with an output of 100 right off that bat. But what actually happens is, my output starts from 0, and as I increase my PV, my output decreases (like should happen with an incremental controller).
Can anyone explain why this happens? All through college was taught that if I have an error of 100, my controller output should have a proportional component of 100*Kp; but with this block (and another one I've seen as well), I actually only take away from my output as I decrease my error. This isn't a direction problem, because the integral component accumulates in the correct direction.
Basically, my PID doesn't seem to operate like any control systems "textbook" would suggest. Any help to a PID noob? I'd be forever grateful if someone could get me out of this rut!