Hall sensor as limit switch

Discussion in 'The Projects Forum' started by k9electroman, Nov 2, 2011.

  1. k9electroman

    Thread Starter New Member

    Nov 2, 2011
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    I am driving a axis with a stepper motor and want an accurate home switch. The problem is my work environment is 77 Kelvin. The hall sensor i am using the FH-301-040 by FW BELL. This is because it works in extreme cold and cheap ones don’t. The motor controller needs digital input (>2.2volts) to sense "home" but the hall sensor only outputs 30ma. :confused:

    What kind of control circuit can I use?

    Here are the specifications of the hall sensor.
    fwbell.com/file/FH-300_500.pdf

     
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    That's one of the worst datasheets I've seen. Even on their website I didn't see much more information about it.

    The only thing that is quite explicit is that the output is a voltage output.

    "With field direction (+B) as shown <obs. shown where?> and Ic entering the Ic (+) terminal, the positive Hall voltage will appear at the VH(+) terminal"

    Are you sure you mean 77 KELVIN ??? This sensor works down to -55 Celsius, that's 218K so it would not work anyway.
     
  3. k9electroman

    Thread Starter New Member

    Nov 2, 2011
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    I agree the spec sheet is lacking. Yes I am sure about the temperature "77.36K". That is liquid nitrogen’s boiling temp. Most component specifications only go to -55F (224.8K) so I must do my own testing down to 4K. Some things work, most don't. I hear this hall sensor works cold, down to 30K. I just can’t figure out how to drive it accurately.
     
  4. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    Me neither. It's not described in the datasheet. You could try to pass the nominal current through the Ic terminals and see what happens to the output voltage when applying a magnetic field.
    I would contact the manufacturer directly. Also, according to the datasheet it works only down to -55 Celsius.
     
  5. bertus

    Administrator

    Apr 5, 2008
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  6. John P

    AAC Fanatic!

    Oct 14, 2008
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    Could you replace the magnetic switch with an optical one, with the transmitted and received light beams traveling down optical fibers? That way the electronics could stay in a warm environment. I doubt if there are any components specified for temperatures below 100K.

    Edited to say: If the electrical properties continue to work at very cold temperatures, could you use an inductive or capacitive sensor? I can imagine ways to do either of those.
     
    Last edited: Nov 3, 2011
  7. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    In our company we are using electronics on very low temperatues to reduce the noise:

    So it is possible to use special electronics at very low temperatures.

    Bertus
     
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