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Hall Effect sensor "sticks" on

Discussion in 'Electronic Design' started by MikeremlaP, Jan 29, 2005.

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  1. MikeremlaP

    MikeremlaP Guest

    Built a tachometer transducer using a Hall Effect sensor. Has worked well many
    years but now is failing. Have discovered that the Hall Effect sensor tends to
    "stick" on, even when no magnetic field around, as long as power is on.

    On the assumption it's not the hysteresis circuit inside the device, I tried
    degaussing the sensor. No success so far. Anyone ever heard of this happening
    before and anyone got a fix? Could make a new transducer with a new part, but
    the whole thing is potted in epoxy. If there's an easy fix, would like to try
    that first.


    Mike Palmer <><
    Excellence in Ergonomics
  2. Chris

    Chris Guest

    Hi, Mike. Assuming there have been no other physical changes, the only
    other "quick fix" I can think of is degaussing the mounting bracket or
    whatever is being used to keep the sensor in place. Sometimes that
    will cause this problem, and it can be accentuated by the positioning
    of the mounting bracket relative to the sensor.

    You could always try plastic, too.
    Good luck, and sorry for your troubles.
  3. James Meyer

    James Meyer Guest

    There is no easy fix. Hall sensors are a cross between electronic ICs
    and microminiature mechanical devices. The whole thing is very sensitive to
    heat and physical stress on the package. I suspect that the sensor has degraded
    and is now effectively "dead".

    Potting compounds, especially simple epoxys meant for adhesive purposes,
    can generate enormous strain on IC packages especially when combined with heat

    When (not if) you rebuild the assembly, take care to either use potting
    compounds meant expressly for sensitive electronics or use a flexible buffer
    coat over the hall sensor before potting the entire assembly.

  4. Yukio

    Yukio Guest

    Sounds like a bad Sensor. However last "Sample Changer " I serviced , was
    "acting up" intermittantly, and was restored to service after I wiped away
    some metallic dust on the Hall-Effect Sensor. Hall-effect Sensor, instead
    of an Opto-electronic Sensor to avoid dust problems !! Just made the problem
    worse !! hmm!

    Yukio YANO
  5. Jamie

    Jamie Guest

    Yup, i have seen it happen.,
    replace the component.
  6. You may want to double check the type of sensor you have. Some are made
    to latch on, and be turned off with the other poll of a magnet.

    Also, you may check to be sure that you do not have excessive current
    through the device. Sometimes, this can cause a device to latch up.

    You may also check to be sure that the strength of the magnet is not
    to powerful to damage the sensor. Some mfg. do not like to see
    excessive magnetic fields.

    The third thing may try to place a 0.1 uF cap across the power leads as
    close to the sensor as possible. Sometimes, a sensor will misbehave
    without this.

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