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Calculating Distance Using Velocity Command

Calculating Distance Using Velocity Command

Calculating Distance Using Velocity Command

(OP)
   I have a hypothetical question.  Lets say that I have a  project where I have a motor drive that sends a 0-10V signal to an Allen-Bradley PLC that represents the motor's speed (0 - 4000 RPMs).  I'm not planning on using an encoder or a high speed proximity sensor w/ a high speed input card (unless there is no other way).
My plan:
   1. Scale the 0-10V signal to figure out motor RPMs  
   2. Divide RPMs by 60 to figure RPS (Revolutions/Second)
   3. Calculate the time for 1 motor revolution
   4. Move this calculation into a Timer Preset
   5. Use the Timer Done bit to increment a counter

Now, this looks like it may work untill you take the PLC's scan time into account.  If the motor is going 4000RPM, the time it takes for 1 revolution to occur is 15ms.  Is there anyway I would be able to accurately keep track of the number of motor revolutions using this method?

RE: Calculating Distance Using Velocity Command

Could you define your perception of "accurate" ?
If your scan time would be 5 ms then you have ca. 30% error (in best case) without taking other factors into account.

Regards,

Jacek

Do it right or don't do it at all.

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