Help in identifying strange proximity switch component

[Messtechniker]

I have here a busted proximity switch consisting of two identical components
(one operative the one other busted ). More details in the enclosed pic.

Can anyone tell me what kind of component this is?

[ataradov]

What is the physical appearance of the switch? Any pictures? Markings on the device?

[Messtechniker]

Thanks for your assistance.

No markings on the device.
It's round. 11 mm in diameter and 13.5 mm long. Top surface is black.
Has two wires - black and blue - coming from the bottom.
It has been press-fitted into a white plastic surround having a diameter of 19 mm.

There are two of these devices wired in parallel.

Sorry no pics at the moment because I don't have it in my lab.
Was measured in the field.

[tautech]

A 2 wire hall effect sensor ?

[coromonadalix]

yep  my tought too   

[JFJ]

Unless a current was flowing through the piece of aluminium, there wouldn't be a magnetic field for a Hall effect sensor to detect. The device is more likely to be a 2 wire inductive sensor - NC (normally closed) type, as the presence of the aluminium increased the voltage drop across the sensor.

[Messtechniker]

Thanks for considering this question.
Here some more information:
The "Transistor Tester" measures with nothing in the vicinity, the isolated (i.e. not in-circuit) component as a diode with
Uf= 2.9 V
9.2 .... 8.2 nF @0...5 V
Ir = 21 nA (1.4 uA for the defective sensor)

And with the Al piece present it measures 9343 pF (and nothing for the defective sensor).

I'll be getting back to the sensor assy. in a day or two to see how the sensor responds to other materials (steel, magnet, finger, wood, brass and plastic).

[Messtechniker]

Sorry folks. Went down the wrong rabbit hole

Since the sensor responds to aluminium, steel and copper and not to a finger, wood or plastic it is not of the capacitive type.
Moreover, measuring with a coil connected to a scope, a 1.23 MHz sine at the sensor surface indicates that this is an inductive (eddy current) proximity sensor. Possibly even a hall effect sensor.
With the oscillation present it draws a current of 2.6 mA. I.e the voltage output is low at 2.1 V. With conductive material present the oscillation amplitude reduces more and more until it ceases completely. Current draw is then 0.6 mA and the output voltage is high at around 3.4 V.

Next step: sifting though data sheets to find an electrically and mechanically matching two-wire inductive sensor. This is going to be the non-fun bit.

[SeanB]

Look up intrinsically safe inductive sensors, commonly known under the generic NAMUR sensor. there will be one that fits there.

http://www.tektron.ie/namur1.htm

[Messtechniker]

Well, that pritty well nails it.