I am working on a control system(picture uploaded) . I need to I have calculated the required transfer function G(s) which is 1/(Js^2+Ds) . That is the relationship between required rotational speed and the torque. I need to calculate critical gain for the PID controller . I have found some articles online and one formula to found critical gain by changing Kp till the system start oscillating.(another picture uploaded). I am a little confused about what is the plant and what should i consider a plant in my system

 

The transfer functiom is 1/Js+D . Not sure where i got that extra s from

 

The "plant" in control system theory is the transfer function of whatever is in the forward path from the error signal to the output variable(s). There is also the difference operator that looks at the difference between the input command signal and the output (in the case of unity gain in the feedback loop) to produce the error signal.

 

So in my case the plant if we are looking at the red square marked loop would ve G(s)/s?

 

So in my case the plant if we are looking at the red square marked loop would ve G(s)/s?

Yes.

The word "plant" comes from common industrial usage; for instance an "automobile plant" is a factory that makes automobiles while a "munitions plant" is a factory that makes munitions. So a "plant" takes one or more inputs and produces some kind of output that we are interested in. Its origins are reasonably related to the notion of a plant in the ground -- it is something that takes inputs (nutrients in the soil, water, air) and makes something (fruit, vegetable, wood, whatever) that is of value.

Another equivalent word is "works", such as "iron works" or "ship works" -- a place where people work to produce something, but "plant" is the pretty universal term used in control systems.

 

Thank you guys that was helpful