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Proximity switch/sensor testing?

Discussion in 'Electrical Engineering' started by Alistair Ross, Mar 16, 2005.

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  1. New to the group, so apologies if this question has been asked before.

    My car is fitted with a sensor that tells the ECU that manages the auto
    gearbox what RPM's the engine is running at.
    The error code on the car points to the sensor not sending the RPM's to the
    ECU
    Before I fork out £60 for another sensor is there a way of using digital
    multimeter to test it?
    The unit is a plastic moulding with two wires, and has quite a strong
    magnetic field.

    Anyone know of a layman's guide to testing gadgets and gizmos found on
    modern cars on the web??

    My level of expertise?....Novice!

    All help appreciated.......ttfn........Alistair
     
  2. Firstly, it may not be the sensor but the electronics pack
    to which it is connected. However:

    The simplest of these just has a magnet with a coil of wire
    wrapped around it and works by producing a small electrical
    output as the teeth of a gear wheel rotate into and out for
    the magnetic field produced by the magnet. As this couldn't
    be a lot simpler, they seldom go wrong - but their position
    relative to the gear wheel is very critical. It may be that
    it doesn't require replacement but simply needs to be set
    correctly in relation to the gearwheel teeth. It may have
    vibrated out of adjustment. The vehicle maintenance manual
    will have the setting up instructions.

    One of these sensors can be tested for basic functionality
    by simply by putting it across the terminals of an analogue
    microammeter and moving the sensor towards and away from a
    steel object - the needle of the meter should swing as you
    do so. It is less easy to do with a digital meter but you
    may be able to see that the meter is reading /something/ as
    you move the sensor.

    You may have a different type of sensor though - some use
    the two wires to power an active electronic,
    self-compensating, sensor from a constant current supply.
    The sensor gives an output by varying the impedance of the
    device as seen by the power supply and hence changes the
    supply output voltage. These units can only be tested whilst
    connected to a suitable supply. I can't think of any harm
    you can do to one by simply connecting it across a
    microammeter, though - to see what it does. These more
    complicated sensors are used because their exact positioning
    is not so critical and their output is amplified and low
    impedance and thus far less effected by ambient electrical
    noise - of which a lot exists in an engine compartment.
    Because they produce a much larger output, the electronics
    pack to which they connect can be made correspondingly
    simpler and less likely to go wrong.

    Testing these needs special equipment - although a 'scope
    will do the job nicely.

    In my experience, these seldom go wrong but much more
    frequently are knocked or vibrate out of position.
     
  3. Roy Q.T.

    Roy Q.T. Guest

    Sue };-) I have a whole new respect for you .

    From: (Palindr☻me)
    Alistair Ross wrote:
    New to the group, so apologies if this question has been asked before.
    My car is fitted with a sensor that tells the ECU that manages the auto
    gearbox what RPM's the engine is running at. The error code on the car
    points to the sensor not sending the RPM's to the ECU
    Before I fork out £60 for another sensor is there a way of using
    digital multimeter to test it?
    The unit is a plastic moulding with two wires, and has quite a strong
    magnetic field.
    Anyone know of a layman's guide to testing gadgets and gizmos found on
    modern cars on the web??
    My level of expertise?....Novice!
    All help appreciated.......ttfn........Alistair
    Firstly, it may not be the sensor but the electronics pack to which it
    is connected. However:
    The simplest of these just has a magnet with a coil of wire wrapped
    around it and works by producing a small electrical output as the teeth
    of a gear wheel rotate into and out for the magnetic field produced by
    the magnet. As this couldn't be a lot simpler, they seldom go wrong -
    but their position relative to the gear wheel is very critical. It may
    be that it doesn't require replacement but simply needs to be set
    correctly in relation to the gearwheel teeth. It may have vibrated out
    of adjustment. The vehicle maintenance manual will have the setting up
    instructions.
    One of these sensors can be tested for basic functionality by simply by
    putting it across the terminals of an analogue microammeter and moving
    the sensor towards and away from a steel object - the needle of the
    meter should swing as you do so. It is less easy to do with a digital
    meter but you may be able to see that the meter is reading /something/
    as you move the sensor.
    You may have a different type of sensor though - some use the two wires
    to power an active electronic, self-compensating, sensor from a constant
    current supply. The sensor gives an output by varying the impedance of
    the device as seen by the power supply and hence changes the supply
    output voltage. These units can only be tested whilst connected to a
    suitable supply. I can't think of any harm you can do to one by simply
    connecting it across a microammeter, though - to see what it does. These
    more complicated sensors are used because their exact positioning is not
    so critical and their output is amplified and low impedance and thus far
    less effected by ambient electrical noise - of which a lot exists in an
    engine compartment. Because they produce a much larger output, the
    electronics pack to which they connect can be made correspondingly
    simpler and less likely to go wrong.
        Testing these needs special equipment - although a 'scope
    will do the job nicely.
    In my experience, these seldom go wrong but much more frequently are
    knocked or vibrate out of position.
     
  4. LOL. Thanks. Eau de gasoline doesn't do much for my love
    life though..Neither does being better at mending a range
    than actually /using/ it.
     
  5. Yes.....Thanks Sue best answer to a question I've ever had. Also thanks to
    other's who replied direct.

    ttfn.....Alistair
     
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