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Clutch Drag detector.

i have made a design in the pass using motors as tension drag and was able to detect the tension so that one could detect the absence of no tension and thus turn off the machine.

now we have a case using magnetic drag (not friction) clutches and must be able to detect using only the 2 DC lines used to energies the field. i haven't disassembled one of these units yet but it appears they may have a PM (permanent magnet) in the rotor and Fixed coil in the back plate, from what i can gather from the feel if it there must be poles because it feels like what a stepping motor would feel like if you were to have low current in the stepping more and manually turned the shaft. in any case, this brake unit is part of the mounting plate where mylar tape is loaded, cable is past through the center of a rotating shaft. when the tap has tension (not broke or run out), the clutch is also slipping with a drag in it. this unit is powered by 2 slip rings. we can not put any more slip rings and because of how the surroundings are set up, we can not use a strobe tach of any kind and can mount any wireless devices on the plates. the solution must be of no devices hanging out in the open in the way.. other attempts of such devices has proven to not work well or just get broke by the machine operators.

I have already tested for current and voltage changes when the unit is being dragged, there is no noticeable effects that can be used. what i purpose is to modulate the DC current slightly at a freq where the moving PM's over the poles will cause change effects in the wave that can be detected as a phase shift offset. when the rotor is spinning and not slipping in the field the phase should not be showing any phase timing shifts. of course the modulation level is only going to be no more than abt 5 % of the DC current being applied to the brake field. what do you think about this idea ?

Reply to
Jamie
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In article , Jamie wrote: [...]

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Does this include there not being an AC waveform imposed on the DC when you rotate it? At low speeds it would be small.

I expect that this clutch works like an induction motor in reverse. The magnetic field is non-rotating and thuse makes a torque when the shaft is rotated. If that is the case and there is no evidence of AC, you will have to do something a bit trickier. If there is some AC it could be as simple a putting a transformer in one wire.

I think that if you measure the impedance vs frequency of this critter, it will be slightly different when it is rotating. I suggest you jig up something that will let you measure it while it is contantly being turned. This will geive you an idea of what you have to work with,

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kensmith@rahul.net   forging knowledge
Reply to
Ken Smith

Thanks for replying. i have done some more research and it appears the initial method of testing could have been flawed. i was using an incandescent lamp as the shunt (because it was handy at the time). it was suggested that maybe the fact that the filament changes R, this could be suppressing the effect. i can say that i did notice at the start and end of rotor movement, there seem to be an effect, but it balances out as it runs. in other words it only seems to be showing effects on the start and stop. The brake field is static and rotor has a PM in it. i am next going to try using a xformer (current config) transformer. by passing the DC current through one field, i may be able to see small levels of AC/Pulses appear on the other field. this would be good to also isolate the dc. if that does not work, then i am thinking of modulating DC line also via the Xformer with around 5K hz or better monitoring phase shift and load effects to see if i can detect the PM in the pole line. I think that a PM should make some inductive change effects when the PM is in the pole lines. with this, i can convert the stream of pulses to form a Logic train signal using a Capacitor Decoupler to generate Pulses which would indicate the rotor is moving. we will see how that goes. Thanks, for replying.

Reply to
Jamie

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