Inductive sensor - Magnetic bed - Mesh bed levelling

  • Hello Everyone,

    I completed my new custom build and i am running into some trouble. I installed a spring metal surface on top of my bed and magnets below the silicone heater. Thus when i mesh bed level i get peaks in some points that show there is some problem. To my understanding the magnetic field of the magnets interferes with the inductive sensor.

    0_1552583015426_Screenshot_2019-03-13 GCORE(2).png 0_1552583020361_Screenshot_2019-03-13 GCORE(1).png

    How does RRF handle these peaks?

  • This is rather easy for you to test. You'll see the bed moving up and down.

    I don't entirely understand how using magnets below an inductive sensor is a good idea at all. The magnetic field is escaping from the metal.

  • Moderator

    That would result in a rather poor first layer as the Duet would try to compensate for those large spikes.

    You have a few options. You could open the heightmap.csv file on your PC and edit out the spikes to better match the surrounding area. Or you could change probes. Or if you could remove the magnets during probing, and ensure that when you are homing Z the probe is lined up with an area that doesn't have a magnet below it.

  • have a look at this.
    its not sensitive to interference at all.

  • What sensor would you prefer? I hear a lot about the IR. But not tried one yet and not sure how it works. I have seen the info page on that but scared of small pcbs 😛

  • Moderator

    The IR sensor can work great, but it is also effects by the material of the bed surface. Reflectivity, etc.

    Every probe type has it's pros and cons.

    The BLTouch is popular because it's a contact probe, not very expensive, but some people find the setup a little complicated.

  • @gpetropoulos I'm using an inductive NPN sensor LJ12A3-4-Z/BX. Sort what you already got and I must say connecting and using it is EZ PZ, as long you don't use magnets. There is a comparison table in the Duet3D docs posted above.

    In my case I simply took the best probe with the shortest setup instructions:

    I then broke the bank on an overpowered, really good 24V power supply so that the voltage is stable and it worked perfectly ever since.

    Is there any reason you can't use an adhesive for the silicone heater? The heater runs inefficiently without full contact due to air gaps.

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