Inductive NPN sensors problem

Thread Starter

NikMav

Joined Nov 19, 2021
3
Hello,

I have purchased two of these "Inductive Proximity Sensor 18mm - LJ18A3-8-Z/AX" sensors and I have a different problem with each of them.
I supply them with 12V. The first one has a voltage difference between + and signal of 12V, the led reacts to metal surfaces approaching the sensor, but the difference doesn't drop to 0 (it stays 12V). The second one has voltage difference between + and signal but also between - and signal, the sum of which are 12V. There is also no continuity between signal and - for the second instance. Does anyone know whether I could fix any of them?
 

Alec_t

Joined Sep 17, 2013
12,477
Welcome to AAC!
Do you have the datasheet, or full specification for the sensors?
Are you sure you have the pinout correct?
If they are of the open-collector output type, do you have a pull-up resistor (say 10k or so) between V+ and signal?
 

Thread Starter

NikMav

Joined Nov 19, 2021
3
Welcome to AAC!
Do you have the datasheet, or full specification for the sensors?
Are you sure you have the pinout correct?
If they are of the open-collector output type, do you have a pull-up resistor (say 10k or so) between V+ and signal?
I cannot find any datasheet. The pinout is correct and the only thing I can find for the output type is NPN normally closed. I have not used any resistor though. Wouldn't a pullup negate the effect of the internal switch though?
 

KeithWalker

Joined Jul 10, 2017
2,095
I can't find a detailed spec sheet either but I would suspect that the output is an open collector circuit. Try it with a10K resistor connected from the output to the + supply. I think that may solve your problem.
 

sghioto

Joined Dec 31, 2017
2,749
From what I have read the output is between the blue - and black signal. Output should measure 12 volts with no metal present and 0 when detecting metal.
 

Alec_t

Joined Sep 17, 2013
12,477
Depending how you want to use the output signal voltage it could be taken between the output wire and either supply rail. However, an open collector NPN output does require a pull-up resistor. Without that you may well get flakey output measurements.
 

sghioto

Joined Dec 31, 2017
2,749
The "AX" on the model number indicates a NPN NC output.
In this diagram a load or resistor (say 10K) is required between black and brown.
Measuring from 0V (blue) the black should read 0V with no metal present and 12 volts with metal.
1637343709527.png
 
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