control response

[wew044]

Hello experts,

I am currently learning labview and my goal is to do the following:

1. control dial that constantly outputs values. For example sake, say this is a motor speed (have done that through state machine where I can adjust the knob and it will output the value with time continuously).

2.this motor speed value needs to respond to pressure values. Say if pressure increases, then the motor speed needs to decrease.

3. implement a pressure setpoint so that the motor speed will always be <= this setpoint (say you turn on the motor, and base on this setpoint the motor speed increases until the pressure is at this setpoint).

**I dont think PID is what I am looking for right now because I dont need any response characteristics.

Any tips on how I can get started or find more information regarding to #2 and #3 is appreciated.

[GerdW]

Hi wew,

1. control dial that constantly outputs values.

All you need is THINK DATAFLOW! You don't need a "state machine" to read a control at regular intervals…

2.this motor speed value needs to respond to pressure values.

3. implement a pressure setpoint

This just screams at "use a PID function"!

Any tips on how I can get started or find more information regarding to #2 and #3 is appreciated.

Examine the example VIs for the PID functions in LabVIEW…

[wew044]

Hi GerdW,

Thanks for the response.

The way I understand PID is that it is used to control response characteristics of a particular variable. For example: pressure setpoint -> PID -> pressure output -> feedback loop. 

Would the "motor speed responding to pressure" part be implemented based on the pressure output? such as: pressure setpoint -> PID -> pressure output -> some correlating function -> motor speed

Thanks!

[GerdW · Accepted solution]

Hi wew,

The way I understand PID is…

wrong IMHO…

Would the "motor speed responding to pressure" part be implemented based on the pressure output?

No, motor speed should depend on pressure reading and setpoint!

such as: pressure setpoint -> PID -> pressure output -> some correlating function -> motor speed

More like:

pressure reading ("current value", cv), pressure setpoint (sp") and PID gains

-> PID

-> motor speed

-> feedback loop by next pressure reading…