rscott9399
Member
Hey Guys and Gals
Just want to spitball some things in regards to closed loop control.
If i were to ask you all the different between indirect feedback and direct feedback what would you tell me?
I want to chat a little bit about the different types of feedback specifically related to a some kid of process control.
Could be flow could be rpm could be temperature. Doesn't really matter
What i am further interested in discussing is the matching of units so to speak and do we really have to do that.
Lets look at a speed control for a second.
a motor accepts a 4-20 speed signal, the setpoint is rpm and the tachometer reports rpm back to the controller.
If someone asks me if that is direct vs indirect feedback i would say direct.
So the output of the controller is a signal directly proportional to RPM. It is ramping up and down partly based on the motor load.
The input is a setpoint in rpm obviously.
the feedback is also reporting back in rpm.
This is what i mean by consistent units.
Now the other case, Say we have an indirect control system.
Lets say for example a controller is moving a linear actuator. For the sake of the argument this linear actuator has the ability to place load on or off the shaft of the motor from the above example. (stupid i know but bare with me)
The controller is moving the actuator in and out and can increase or decrease the load which is also of course effecting the rpm
The feedback is still the tachometer.
If it were to be direct control i would say since the controller is controlling the stroke of actuator, the feedback should be an instrument that knows the position of the actuator stroke.
However, its not, its the tachometer. So we are reading RPM, and controlling an actuator.
How do these two scenarios effect our controller.
Questions....
Are both scenarios possible?
Considerations for each?
Why do this you ask?
Say you have a customer that does not want to buy an instrument to read the actuator feedback and wants to use the tach instead because they already have it.
I know this is a bizarre example but i want to stimulate some thought on direct vs indirect control.
Just want to spitball some things in regards to closed loop control.
If i were to ask you all the different between indirect feedback and direct feedback what would you tell me?
I want to chat a little bit about the different types of feedback specifically related to a some kid of process control.
Could be flow could be rpm could be temperature. Doesn't really matter
What i am further interested in discussing is the matching of units so to speak and do we really have to do that.
Lets look at a speed control for a second.
a motor accepts a 4-20 speed signal, the setpoint is rpm and the tachometer reports rpm back to the controller.
If someone asks me if that is direct vs indirect feedback i would say direct.
So the output of the controller is a signal directly proportional to RPM. It is ramping up and down partly based on the motor load.
The input is a setpoint in rpm obviously.
the feedback is also reporting back in rpm.
This is what i mean by consistent units.
Now the other case, Say we have an indirect control system.
Lets say for example a controller is moving a linear actuator. For the sake of the argument this linear actuator has the ability to place load on or off the shaft of the motor from the above example. (stupid i know but bare with me)
The controller is moving the actuator in and out and can increase or decrease the load which is also of course effecting the rpm
The feedback is still the tachometer.
If it were to be direct control i would say since the controller is controlling the stroke of actuator, the feedback should be an instrument that knows the position of the actuator stroke.
However, its not, its the tachometer. So we are reading RPM, and controlling an actuator.
How do these two scenarios effect our controller.
Questions....
Are both scenarios possible?
Considerations for each?
Why do this you ask?
Say you have a customer that does not want to buy an instrument to read the actuator feedback and wants to use the tach instead because they already have it.
I know this is a bizarre example but i want to stimulate some thought on direct vs indirect control.