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Auto Bed Leveling - Sensor Overheating - anyone else? Solution?

Posted by djzman 
Auto Bed Leveling - Sensor Overheating - anyone else? Solution?
November 24, 2016 10:17AM
Hello all ... I downloaded and configured Marlin 1.0.2 for auto-bed leveling. I used an LJ12A3-2-Z/AX sensor with aluminium tape on glass.

After I worked out all of the numbers in configuration.h, it worked great ... UNTIL, I heated up the bed to 70 deg C to make the final Z nozzle offset measurement.

After about 10-20 minutes, the sensor overheats and goes into the "triggered" mode, even if I move it away from the metal. After a while, it cools and works again. This symptom is repeatable.

Do note, this sensor has a 2mm sensing distance, so it's pretty close to the heat (I had these in my junk box). Also, in doing some research, the max temp on these sensors is 50 deg C. More expensive ones that go up to 70 and even >150 are available for ~$150.

My question ... has anyone seen this symptom when actually trying to use inductive proximity sensors?

Does anyone have specific experience using, say, an 8mm sensing distance and not having this issue?

If anyone has seen this issue and has fixed it, please pass along your wisdom.

Thanks to all and especially to the developers of Marlin ... this is really useful functionality !

Re: Auto Bed Leveling - Sensor Overheating - anyone else? Solution?
December 03, 2016 09:07PM
Hi all ... kept working on this with the following result:

I looked around and found EZAutomation.net and they had a very wide variety of sensors.

I picked up on with a 10mm sensing distance and 70 deg C spec. (EZ-M12-NPNNC-NMW-TS).
This is an NPN sensor which is normally closed (NC). You may need something different depending on
how you wire it. The main thing is the longer sensing distance. It cost $24.99 with $11.79 in shipping (kind of ridiculous shipping cost !!!)

Honestly, I don't know how much better it is than the $8 ones the above sensor is, but at least the spec's are better.

It was a wire-color compatible drop in ... wired it in/mounted it and ran the G28/G29 sequence with a cold bed ... perfecto !

I heated up the bed and ran it through some more paces ... no issues at all ... I couldn't get it to trip because of heat like the old one.

After fine tuning the offsets, it seems to be working great. I have run a few test prints so far ... it's so cool to see the Z-axis move slightly
to compensate for the (very) minor bed tilt. First layer beads look really nice.

I'll report if anything goes bad, but looks good so far.

Thanks to Tom Sanladerer and his YouTube video on this topic !
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