position feedback

Hello people,
I'll start to take course in process controll soon. I already have some knowleadge with process control systems theory (Laplace transform,
closed loop, stability...), but I'm interested to know what therm "Position feedback" really means. Is it there that is used only when using motor actuators or....? Can you explain what is meant under position feedback?
Thanks
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snipped-for-privacy@yahoo.com wrote:

Position feedback is a physical measurement of the position being controlled to a setpoint specification. Any positioning system can, in principle, have a measurement made that can be used as feedback for the position control system. This includes spacecraft to single atom micro positioners. Motors and motor driven mechanisms are just typical applications.
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Another very common example in the process control field: Position feedback on a control valve. Just because you have commanded the valve to move doesn't mean that it has moved! With position feedback, you can uncover valve problems, such as stiction and hysteresis.
To find out more about how to handle valve issues on PID Loops, visit ExperTune's on-line library:
http://www.expertune.com/r2.asp?f=Newsgroup&l=articles.html#PIDOptValves
Good luck!
george.buckbee AT expertune.com
snipped-for-privacy@yahoo.com wrote:

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