Twidec/M12 Approach Sensor Inductive Proximity Switch NPN NO DC 6-36V, 4mm Detecting Distance LJ12A3-4-Z/BX

I purchased this inductive sensor as a bed leveling sensor for my Monoprice Select V2. After upgrading the Marlin firmware and making a few changes in the Configuration.h tab I got the sensor to work. I connected the sensor to an Arduino Uno powered with a 9v battery. The sensor is being powered with the input voltage (9v) which gives the sensor enough of a sensing distance that the sensor could be places slightly higher than the hotend nozzle (.12mm). This setup supplied enough voltage to the sensor to get it to detect the aluminum print bed. The higher the input voltage to the sensor the greater the detection distance. I will be trying a voltage divider where the sensor connects to the the Arduino Uno so I can get a higher voltage through the sensor and a lower voltage to the arduino and MKS Gen L board.

TLDR, Doesnt work as expected. It doesnt drop voltage fully, it leaks voltage. I am not new to 3D printers, been building them and using them for over 5 years. Lately my 4 yr old Z probe sensor quit in my CoreXY, so i got this as a replacement. After wiring this sensor trusting it will work, it didnt and crashed my bed. The 10k ohm internal resistance seems ok, being NO, the output voltage seems ok, but when triggered it leaks voltage and wont trigger the end stop. Pulled an old LJ18A3 i had in a drawer and that one works fine as expected. Bad batch, not happy it didnt work.

Installed it the moment I got it but what a let down. I cut the wires to fit my printer and now I can’t return it. I needed it to detect 4mm or higher but this only detects 2mm. DO NOT BUY if your printer has a removable non-metal build surface like my printer does.

Bought two of these for a cnc project to use as a homing limit switch which it didn't work. It is NPN because the signal line does connect to the negative wire and it is NO because it switches when metal approaches it but the voltage doesn't drop to 0.....it just stays at 5v which is the voltage I have running it. I have tried it at higher voltages and I get the same results. Same results for both sensors purchased...not happy.

This thing is very inconsistent. I have had numerous prints fail due to its unreliable measuring of the distance. I have to constantly change the Z-offset in order to get a good first layer.

Passed it 12v, it returned 8.5v.

Part was a perfect replacement.

There's nothing wrong with the sensor itself, it functions exactly as it is supposed to. It just doesn't have the right specs for use on a 3D printer with an aluminum bed. The detection distance is far too small and the sensor makes contact with the build surface before triggering.