FPM conversion

Hello all. I have a clumsy way (I think it is) of converting my rpm to feet per minute and wanted to see if someone here might have a more precise way of doing it. I ran the drive for 30 seconds and measured the displacement then divided the frequency fed-back by the drive by that value and multiplied by 2. Does anyone have a more precise way? Thank you

If you know the diameter of the head shaft pulley you can calculate the circumference of the pulley and multiply by the rpm.

For our calibrations, we just run the drive at 100%, and physically tach the driven element. Drop that into the scaling block, done.

Tom Jenkins said:

If you know the diameter of the head shaft pulley you can calculate the circumference of the pulley and multiply by the rpm.

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This will give inches per minute, correct?

I just remembered, this pulling system has the motor encoder feeding back to the PF755 however, I also have an encoder direct connected to the chain pulley. I am thinking the separate encoder might be a better way calculate the fpm. Any thoughts? Thank you

Additionally, I am using the PF755 in torque mode, when speed becomes important. I have a conveyor that is run by a separate VFD and I must synchronize the speed of both drives.

You can calculate the RPM from the encoder feedback, then just multiply by the circumference of the pulley wheel to end up with inch/min, mm/min m/min dependent on your unit of measure.

Rob... said:

You can calculate the RPM from the encoder feedback,

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Is this possible if not using the Z pulse? I am not sure how to take changing of A and B and convert that to an RPM.

If I was using a tacho with an analogue output I would agree with all the methods above, but you have an encoder that gives out pulses. So you can measure a length, drive the system that length and see how many pulses you get. The number of pulses gives the system length. Then divide the measured length by system length to get the correct distance per rev for the encoder. To make it easy I create a calibration page on an HMI.

I installed time ago a metal mesh in a 400ºC tunnel of about 30 meters with an encoder on the entrance roller, that has no traction.

I used the nominal diameter = roller diameter + mesh thickness.

A PID loop regulate the VFD frequency depending on the distance traveled, the setpoint was increasing and the difference with the encoder counter was regulated.

To avoid overflow when it reached a large number, the same amount was subtracted from both the setpoint and the counter.

When the system is stopped both quantities are initialized to zero.

The system continues to operate with great precision.

ceilingwalker said:

This will give inches per minute, correct?

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Yes, if circumference is in inches