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Sensing on rotating parts.

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Renate:
I don't know your application, but sometimes the best solution to a specific problem is fixing the general problem.

Years ago, the Ampex VPR-3 video tape recorder had an innovative capstan motor.
It used a "printed armature" or printed circuit or pancake motor.
The rotor looked like a copper web that had been squashed to a disk.
You can see some photos here (and of other motors): http://www.et.byu.edu/~chasek/ME%20472/Motors/electric_motors-USoW.pdf
The advantage was that it had very low inertia for high acceleration.
Because this motor was so powerful and the rotor (or armature) so light weight it could overheat easily some thermostatic protection needed to be included.
Instead of actually measuring the temperature, they decided to make a circuit to model the thermal characteristics.
And that's how they implemented thermal protection.

vini_i:

--- Quote from: Renate on April 26, 2020, 02:41:12 pm ---I don't know your application, but sometimes the best solution to a specific problem is fixing the general problem.

Years ago, the Ampex VPR-3 video tape recorder had an innovative capstan motor.
It used a "printed armature" or printed circuit or pancake motor.
The rotor looked like a copper web that had been squashed to a disk.
You can see some photos here (and of other motors): http://www.et.byu.edu/~chasek/ME%20472/Motors/electric_motors-USoW.pdf
The advantage was that it had very low inertia for high acceleration.
Because this motor was so powerful and the rotor (or armature) so light weight it could overheat easily some thermostatic protection needed to be included.
Instead of actually measuring the temperature, they decided to make a circuit to model the thermal characteristics.
And that's how they implemented thermal protection.

--- End quote ---

The application is a wire reel. It's a large portable piece of equipment with a built-in extension cord. The reel holds about 3 layers of wire. At full load, the equipment consumes 100A of 3 phase 480VAC. At full load, the reel needs to be unspooled down to the bottom layer. To keep the cable from overheating. At light load, all 3 layers can be on the reel.

We could use an absolute position encoder to check how far the reel is spooled out and combine that with a loading model to predict the cable temperature. That sounds too much like work and doesn't account for all conditions like burst loading. I want to just have a bimetallic switch on the inside of the reel up against the inner row of wire. When it gets too hot the switch opens and the equipment shuts down.

wizard69:
slip rings would be dead simple and would work with the temperature switch already there.   This would also work at zero revolutions per minute which might be an issue if this something that dwells in one place for long.   I don't see how transformer coupling would work here.  Also slip rings can be made to be very rugged which sounds like an important feature if you are winding up a 100 amps extension cord on this drum.

As for anything industrial you will have to implement debounce in some manner or form as the hardware will likely get knocked about a lot.   Also I wouldn't run anything less than 24 VDC across the rings.

jbb:
Texas Instruments does 'Inductance to Digital' converters which might be able to sense the change in impedance when the switch opens.  But they may not be suited to an industrial electrical noise environment.

duak:
If the reel turns only three or four times per actuation and returns, I might consider a high flex cable inside the hub if there is room.  These cables are used in CNC machines and are rated for hundreds of thousands of actuations.

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