Using 2 Inductive Z-Probes



  • Hello,

    I'm about to start assembling my custom IDEX (Independent Dual Extrusion) machine and I plan to use inductive probes to calibrate the Z offset for each tool head. My question is how to wire two PNP inductive sensors and configure the firmware for them.

    For leveling I plan to probe the bed at 3 points with the first tool head to compensate for tilt and to gauge the Z offset, then use the second tool to probe the center of the bed to calculate the Z offset for the second tool head. I'd like to use the calculation of the tilt done by the first head for both tools (i.e. instead of probing 3 points with both tools which might give slightly different tilt calculations)

    This will essentially allow me to use tools with different Z heights (i.e. E3D V6 and Volcano). I understand that I give up the ability to dual print.


  • administrators

    The only input that is suitable for use with PNP output sensors is the Z probe input (with 2 resistors to reduce the voltage). So you would need external circuitry to switch between them. Whereas NPN output sensor can be connected to 3 different endstop inputs, which you can select using M558.



  • @dc42 said in Using 2 Inductive Z-Probes:

    The only input that is suitable for use with PNP output sensors is the Z probe input (with 2 resistors to reduce the voltage). So you would need external circuitry to switch between them. Whereas NPN output sensor can be connected to 3 different endstop inputs, which you can select using M558.

    Okay so lets say I use two NPN sensors instead. How would I go about wiring and configuring them both if I'm using the E0 input for the U axis limit switch?



  • You could also just mount the sensor on your bed and probe both tips on the same sensor. Then you only need one sensor. The goal is to find out the difference between the 2 hotends.



  • @timcurtis67 said in Using 2 Inductive Z-Probes:

    You could also just mount the sensor on your bed and probe both tips on the same sensor. Then you only need one sensor. The goal is to find out the difference between the 2 hotends.

    That could work but I want to probe 3 points to calculate tilt of the bed for auto-leveling which means I would need 3 probes, instead of just two.



  • I mount a probe on one of my heads to check the bed mesh. Then I remove it and use the probe on the bed to set the nozzles when I have to change them.

    I only run a bed mesh every so often to make sure nothing has changed. It really shouldn't change unless you have some sort of crash.


  • administrators

    @asteinmark said in Using 2 Inductive Z-Probes:

    @dc42 said in Using 2 Inductive Z-Probes:

    The only input that is suitable for use with PNP output sensors is the Z probe input (with 2 resistors to reduce the voltage). So you would need external circuitry to switch between them. Whereas NPN output sensor can be connected to 3 different endstop inputs, which you can select using M558.

    Okay so lets say I use two NPN sensors instead. How would I go about wiring and configuring them both if I'm using the E0 input for the U axis limit switch?

    Use the E1 endstop input for one of them. For the other, use the Z endstop input if it is free, or the Z probe input.


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