Help in identifying strange proximity switch component - Page 1
Forum section: electronics / repair

author: Messtechniker
author_rank: Frequent Contributor
timestamp: November 20, 2018, 06:40:37 pm
content: 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?

author: ataradov
author_rank: Super Contributor
timestamp: November 20, 2018, 07:12:48 pm
content: What is the physical appearance of the switch? Any pictures? Markings on the device?

author: Messtechniker
author_rank: Frequent Contributor
timestamp: November 20, 2018, 08:18:55 pm
content: 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.

author: tautech
author_rank: Super Contributor
timestamp: November 20, 2018, 09:31:23 pm
content: A 2 wire hall effect sensor ?

author: coromonadalix
author_rank: Super Contributor
timestamp: November 20, 2018, 09:32:19 pm
content: yep my tought too

author: JFJ
author_rank: Regular Contributor
timestamp: November 21, 2018, 12:56:33 am
content: 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.

author: Messtechniker
author_rank: Frequent Contributor
timestamp: November 21, 2018, 06:30:52 am
content: 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 withUf= 2.9 V9.2 .... 8.2 nF @0...5 VIr = 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).

author: Messtechniker
author_rank: Frequent Contributor
timestamp: November 22, 2018, 03:54:39 pm
content: Sorry folks. Went down the wrong rabbit holeSince 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.

author: SeanB
author_rank: Super Contributor
timestamp: November 22, 2018, 07:48:02 pm
content: 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

author: Messtechniker
author_rank: Frequent Contributor
timestamp: November 23, 2018, 06:12:58 am
content: Well, that pritty well nails it.