motor speed sensing

Look at the DT-207L laser tachometer. This is a very precise unit. I doubt you can build one yourself at home, but you will find this interesting.

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Jerry G. =====

Any suggestions?

Is this a 1-time deal? Will you need an unsupervised (no human) technique? Will this be used for feedback/control?

If not, see Jerry's post and

snipped-for-privacy@posting.google.com (This is an optical technique, but not reflective. It requies a human.)

it depends./ if your only looking for absolute motion sensing to ensure the unit is fully stopped there are a couple of ways, i have done them both. on AC sync type when you turn off the contactor it will spin down thus giving you a regenerative output of AC voltage. not much current how ever but enough for electronics to know if the unit is at near stop. i use a TL082 chip with some zener input clipping to protect it. its a comparator circuit and will detect down to 0.002 volts of output which is not much of a rotation at all in the motor. the reason why we need this?, is because if the direction was to change on the motor we must make sure it is at near stop, or in our case you have some other unit that tends to randomly fire off a clutch that is connected from the output of this motor thus causing an unexpected jerk in machine parts if the operator happens to turn off the unit and restart it before the motor spins down. the other way was for us to use an LED and PHoto Detector both side by side aimed close to a shaft point. the rotation of the shaft caused the IR to get modulated. we made what you may call a AM detect or a slop detector on the signal, that can be done using an OP-amp with both inputs decouple via a resistor and small cap on the other side to delay the remote input .. this will generate a pulse output when surfaces change just alittle. you can then run this into a one shot timer to hold the output on..

Jaja wrote: