Has anybody seen a PID controller with only 'I'?

[Speakerguy]

Topic says it all! Thanks.

 

[Leftyretro]

Topic says it all! Thanks.

Well I worked with PID controllers for decades, but I don't recall any of them having the ability of running with only I (or only D for that matter) operation. Most let you switch out the I & D terms for sure but I think the P term is fundemental to the feedback function, while I & D just modify the response.

https://en.wikipedia.org/wiki/PID_control

 

[SPDCHK]

I agree with Leftyretro.

Most PID controllers give the option of combination selections such as P, PI, PD or PID, but I've ever seen the I or ID options standalone.

 

[Speakerguy]

Well, here is the control loop I am looking at:

**broken link removed**

It is to convert a voltage supply into a constant current supply using a current monitor pin. It sort of looks like only the 'I' portion is implemented unless I am misunderstanding the top opamp ckt.

 

[Leftyretro]

Well, here is the control loop I am looking at:

**broken link removed**

It is to convert a voltage supply into a constant current supply using a current monitor pin. It sort of looks like only the 'I' portion is implemented unless I am misunderstanding the top opamp ckt.

Well it looks to me like R11/R9&R12 on U1:A (lower amp) would set the gain (P-term) with R10/C3 giving some D-term action. I see no obivious I-term action but of course I could be wrong

U1:B (top amp) looks to me like it's just running as an full open loop gain error amp that just compares output of gain amp (lower amp) with the remote setpoint voltage, full positive or full negetive output unless P-term output = remote setpoint voltage.

Looks like a classic feedback circuit, but can't tell if it is implemented as a general purpose PID tunable controller.

Lefty


Lefty

 

[mneary]

Given that any output capacitor on the "regulated high voltage supply" creates a pole (Integral term, at relevant frequencies), this is a full PID control.

 

[Speakerguy]

Yes, these guys do have significant output capacitance (perhaps a few nF, which is huge at 30kV).