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Sensing on rotating parts.

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vini_i:
I need to sense a temperature threshold on a component that rotates. If the component gets too got the bimetallic switch opens.

My idea for doing this is with inductive sensing. Have two coils that act as loosely coupled inductors. The coil on the rotating side would be connected to a resistor and the thermal switch with a resistor. The idea is that there would be four distinct states.

* Switch closed
* Switch open
* Open in the circuit (Fault)
* Short in the circuit (Fault)
These states would be sensed by the current consumption of the stationary coil.

Does a device exist that can both excite the coil and have built-in current sensing and thresholding?
If it was in an industrial DIN rail mounted package that would be great but I'm more than willing to work around other form factors.
My issue is that I'm not even sure how to search for a device like this.



Thanks

duak:
Two ideas come to mind:

A rotary transformer could do what you want: https://en.wikipedia.org/wiki/Rotary_transformer  Google gives a number of hits.

The second would have two coils mounted on opposite sides of the rotating part connected electrically by the thermal switch.  The coils would pass over a stationary magnet .  Opposite the magnet would be a stationary pickup coil with a sensitive amplifier.  The idea would be to have a voltage pulse induced in one coil by passing by the magnet that would be passed to the other coil if the switch were closed.  If the rotating part turns too slowly, the induced voltaged would be small.  However, the magnet could be replaced by another coil driven by an AC source.  Please note that the signal amplitudes would be quite small and it would take a bit of electromagnetic engineering to work out.

cur8xgo:

--- Quote from: vini_i on April 24, 2020, 01:41:43 pm ---I need to sense a temperature threshold on a component that rotates. If the component gets too got the bimetallic switch opens.

My idea for doing this is with inductive sensing. Have two coils that act as loosely coupled inductors. The coil on the rotating side would be connected to a resistor and the thermal switch with a resistor. The idea is that there would be four distinct states.

* Switch closed
* Switch open
* Open in the circuit (Fault)
* Short in the circuit (Fault)
These states would be sensed by the current consumption of the stationary coil.

Does a device exist that can both excite the coil and have built-in current sensing and thresholding?
If it was in an industrial DIN rail mounted package that would be great but I'm more than willing to work around other form factors.
My issue is that I'm not even sure how to search for a device like this.



Thanks

--- End quote ---

Drive the stationary coil with AC through a fixed appropriate series R

Use something to monitor that AC signal

The impedance of the rotating circuit will be reflected and you will see changes in your AC signal depending on what is open/closed etc.. on the rotating circuit

Can try this with a function generator and scope

Then can implement it with a microcontroller (entirely) or a few comparators/RC filters and a 555

As an alternative, have you considered using a thermopile non-contact sensor to scan the surface of the rotating object as it spins? Not sure if thats what you are measuring or not. But they have fast enough time constants and great sensitivity at close ranges to where you could possibly use that. Not expensive either

m98:
If you aren't looking to make it yourself, this is exactly the product you're looking for: https://mesa-systemtechnik.de/en/inpud-produkteigenschaften/

vini_i:

--- Quote from: m98 on April 25, 2020, 05:36:22 pm ---If you aren't looking to make it yourself, this is exactly the product you're looking for: https://mesa-systemtechnik.de/en/inpud-produkteigenschaften/

--- End quote ---

I was not looking to make it myself. That looks like exactly what I wanted. Even more so than what I wanted. Thanks

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