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# problems of the Inductive NPN sensor

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#### Munyua44

##### Member level 1
hello all,
I have made a purchase of two Inductive proximity sensor 18mm- LJ18A3-8-Z/AX from [moderator action: removed link to commercial site] and i have come across a different problem from each of this sensors. When i supply them with 12 V the first sensor has a voltage difference of between + and the signal of 12 the LED reacts with the metal surface that is approaching the sensor but here the difference remains 12V since it does not drop to zero. The other sensor has the difference between + and signal and also between - and the signal and the sum becomes 12V an we dont get continuity between the - and the signal for this second observation. How ca i fix this?
thanks

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Hi,

sorry your description is some how confusing.

I assume you are using your proximity sensor as a low side switch (minus terminal is connected to ground).
You are talking about a LED, so I assume you have connected a LED and a resistor in series to the plus terminal of your sensor, and the +12 V to the other end of this series connection. Or is there a LED bulit in, as indicated by a small note in the construction drawing saying "action display light (RED)". Further, the picture of the sensor I have found shows 2 wires, whereas the datasheet talks about 3 wires.

According to the datasheet your sensor is normally closed (NC), so if there is no mateal in its vicinity the LED should light and stops to light

Please show us a sketch of your circuitry, indicate where you are performing the measurements. Based on your description I'm not able to give any advice how to solve your problem, or clearly identify your problem.

BR

In case you are measuring with a DMM, the results may be misleading. You should load the output with a resistor to +, e.g. 1 kOhm.

In case you are measuring with a DMM, the results may be misleading. You should load the output with a resistor to +, e.g. 1 kOhm.
can you share a simple circuit on how i should do the resistor connection?

Try doing the test again with an led and a 1k resistor, as already implied there may be some protection components within the proxy giving you misleading results using a high impedance multimeter.

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Try doing the test again with an led and a 1k resistor, as already implied there may be some protection components within the proxy giving you misleading results using a high impedance multimeter.
this one worked so well. I already achieved the result. the LED and the resistor offered well results

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