Inductive sensor detection distance incredibly low

Hi everyone,
I am still trying to get my Prusa i3 clone to work reliably. I have calibrated the z-axis endstop, which is an inductive sensor, and everything worked fine until today, where I noticed the printhead crashing into the heatbed when I sent a G29, which did not happen before. So I tried to move the sensor a bit further down, but I can't seem to get it to trigger correctly, unless it is below the printhead, such that it triggers only when it practically touches the bed.
If anyone has seen something similar, it would be of great help. Thanks in advance

Could you provide us with more information;

I would like to know which Proximity sensor you are using, the voltage an if any external circuit is being used in conjunction with the proximity sensor.
It could help to know about what bed you are using is it 3mm aluminum or something else.

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Computer Programmer / Electronics Technician

Hi,
I am using this (6-36V NPN) inductive sensor, with this voltage adapter. The sensor is supposed to have a 2mm detection range, which it seemed to have until recently. I have a 3mm aluminium heatbed.

Edited 1 time(s). Last edit at 10/16/2019 04:20AM by bathal.

I know that the voltage stated is 6-36V though I have a SN04-N and a TL-W3MC2 proximity sensor with the same voltage specs.
I have them connect to 5vdc from the Controller and they have been correctly working for going on 3 years now...


If more voltage is needed then think about this method
I supply 24volts to the Ramps 1.5 controller then using the DC - DC Converter set to 12 volts for the Arduino Mega 2560 by replacing D1 power source with the DC - DC Converter.
This requires that D1 be removed from the circuit when installing the DC-DC converter.

Then on the Arduino replacing the 5 volt regulator with a 2nd DC -DC Converter to supply sufficient current to power the controller and any accessories.

Edited 6 time(s). Last edit at 10/16/2019 12:09PM by Roberts_Clif.

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Computer Programmer / Electronics Technician

Ok this is even weirder than I thought. The probe seems to fail to detect the heatbed at a ~2mm distance, but detects other objects such as a screwdriver or a metal ruler just fine. I had the Z axis home over a metal ruler, and it homed as expected, stopping at a ~2mm distance over the ruler. But when I remove the ruler, it needs to get much much closer to be triggered, almost touching the bed.

Tensions are fine though, so I doubt the adapter board is the issue here.

That's because inductive sensors detect steel at much greater distance than aluminium.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Ok so I got a replacement probe from the store I bought the former one from, plus I bought a 5V one on amazon. I get the same problem as before with both sensors, so obviously this is not the sensors fault. Loosing my mind here...

Have you tried test using this M119 - End-stop States

If this does not help I guess then we need more information.

Has it ever worked, Did you install the firmware, If so upload the source code to a share like Google Drive and post a link here.

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Computer Programmer / Electronics Technician

Really you need a sensor with at least 8mm detection range for aluminium,2 mm is just too small.

This could be true!

I have been using a Omron TL-W3MC2 {" Inductive Proximity Sensor, TL-W Series, Flat, 3mm, NPN, 10 V to 30 V "} now for 3 years.
It has been powered via the Controllers +5v source an have never had any problems.

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Computer Programmer / Electronics Technician

Thanks for your answers.
M119 shows what it is supposed to. The problem is not that the probe doesn't detect the bed, but that it detects it at a distance so short that it is impossible to adjust the probe's height properly. Before I started this thread, the detection distance was greater, and the printer was functioning perfectly fine, with the offset between probe and nozzle correctly calibrated. Then one day, when homing the z axis, the nozzle crashed in the bed, and it hasn't worked properly since. As I said in my previous message, I have this issue with 3 probes, 2 of which are identical to that which used to work before. Here is the Configuration.h file from my firmware. I am using Marlin (branch 1.1.x)
Thomas Sanlanderer used a similar sensor on his i3 clone, and had no issue with it.

Edited 1 time(s). Last edit at 11/08/2019 04:19AM by bathal.

One thing i noticed in your config

#define Z_PROBE_OFFSET_FROM_EXTRUDER 0.1 // Z offset: -below +above [the nozzle]

In marlin firmware this should be a negative value for a inductive probe , as the probe trigger point is below the nozzle.

Thanks for pointing that out. This should not influence the detection distance when homing though right? If I understand correctly, this define is used to position the nozzle properly when printing.

Ok!

Have you tried to reset your controllers firmware's defaults.
M502: Factory Reset - Marlin Firmware
M500: Save Settings - Marlin Firmware

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Computer Programmer / Electronics Technician