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isolated motor feedback circuit


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Audioguru,

I've found from experience that the motor requires an inrush of full current for at least 10ms to get started. I'll have to wait for the spec sheet on the motor until monday.

I've managed to free up an analog channel for the sensing circuit and I am planning on using it to check the sensing circuit once every 100ms.

You said that the circuit you changed would output 3.03v if R2 was 910k, that works for me. I've wanted to get an optocoupler to work in it's linear range but could not figure it out. How do I get the output to follow the input?

Bob

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Bob,
Yes, the inertia of the motor causes a high start-up current, but its inductance will cause a current ramp-up for each current pulse while running at a constant speed/load. This will also delay the pulses and reduce their averaged level.

I am glad that you managed to free an analog channel to read the averaged voltage that will be equivalent to motor current.

The PS2501 has a broad range of coupling, for current that flows through its LED, to the current that flows through its coupled transistor, of 80 percent to 600 percent.
So the PS2501's transistor will need an opamp with an adjustable gain, for you to match the PS2501's coupling. Then the output will follow the input with a predictable scale. See page 6 on the data sheet here:
http://www.csd-nec.com/opto/english/pdf/PN10225EJ01V0DS.pdf

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This seems to be an impossible task. Trying to adjust for the wide range of CTR, loss of LED integrity and temperature changes. I seems to me that tranfering the information is still best done digitally and then converting it to an analog signal or a timed digital signal on the other side. So I've decided to add a small micro (12F675) to supervise the circuit and send the data digitally.

Thanks for all your help. I've learned alot from your comments and suggestions.

Bob

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