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current sense resistor

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ash

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Hi all,
How can i convert current data to velocity data from a current sense resistor in servo system? Actually, the system consist of a dc servo motor and pic-based controller.I can measure current but i don't know how to use it for closed loop servo system. It will be for current loop.
Thanks for your considerations.
Best regards.
 

Actually, the current provides info about the torque.
To measure the speed, you need to measure the back emf.

You could measure the voltage across the motor and subtract the voltage drop across its Ra (Ra*Ia) to get the back emf. You need to know Ra and Ia is the current you measure.
The drawback is lots of calculation and the fact that Ra varies with temperature.

The best way would be to measure the back emf directly, by using a chopper for the motor voltage and measure the back emf when the switch is off.
 

VVV is right. You can use rotary encoder as other alternative. You just count the pulses coming into your PIC.
 

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