How does a single speed controller differ from an on-off and a proportional controller?

Thread Starter

rudha13

Joined Sep 6, 2015
14
Hello everyone...
In process control systems, I recently came across this topic and wasn't quite clear about the difference between a single speed controller and the two controllers mentioned above. How do they differ and what are the characteristics of an error encountered in such a system?
 

MaxHeadRoom

Joined Jul 18, 2013
19,771
ON/OFF is exactly that, no in between.
Proportional can take several forms, the common popular one is PWM, Pulse Width Modulated DC.
Max.
 

Thread Starter

rudha13

Joined Sep 6, 2015
14
ON/OFF is exactly that, no in between.
Proportional can take several forms, the common popular one is PWM, Pulse Width Modulated DC.
Max.
oh, ok... thank you for your answer, but with all due respect, can you tell me a bit more regarding this topic. This has definitely got me piqued ... thank you..!
 

mcasale

Joined Jul 18, 2011
210
To clarify a bit - on/off control, or bang/bang, is when the plant (the thing you are controlling) is driven by a full-on or a full-off signal. For example, in an oven controller the heater would be full on or off, depending on the error signal. If the oven was too cold, the heater would turn full on. If the oven was too hot, the heater would turn off.

A "proportional controller", or more accurately a PID (Proportional/Integral/Derivative) drives the plant with a signal that can be anywhere between full-on and full-off. Nowadays, the calculations are done with an MCU, which usually generates a PWM output signal.

The toughest part about any controller is modeling the plant. You need to (at least) approximate the plant's poles and zeros to ensure it is stable under expected conditions. This is NOT trivial.
 
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