Current transducer

Discussion in 'General Electronics Chat' started by mik3, Apr 7, 2010.

  1. mik3

    Thread Starter Senior Member

    Feb 4, 2008
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  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Did you see this at the last page of the datasheet?

    [​IMG]

    It looks like there is a "transformer" that make ± 7.5 mA from the ± 15 A max.

    The output is converted to a voltage using the opamp.

    Bertus
     
  3. mik3

    Thread Starter Senior Member

    Feb 4, 2008
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    Can the current to be measured pass though pins 123 to 456 or does it have through the hole on the device?
     
  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Both are possible, the pins 1 - 6 have a table.
    The hole is an extra (not calibrated) pass through.

    [​IMG]

    Bertus
     
  5. mik3

    Thread Starter Senior Member

    Feb 4, 2008
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    We have tried some brand new by using the second recommended connection for a current of 1A but they do not work. The supply voltage is 5V as shown.

    One of them output 2.5V when the current was zero, which is correct, but its output did not change when a 1A current was flowing.

    The other, was drawing 0.6A when the 5V supply was connected.

    Another one, output 0V with zero current through it.

    I think these current sensors do not work at all.

    Has anyone ever used one?
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    Hi Mik3,

    Yes, it's a Hall-effect sensor, with a built-in current loop.

    That would be a very easy way to monitor the current in an H-bridge drive.

    You could even use it for higher currents by using a resistance in parallel with it. The internal resistance of the +/-15A loop is 0.18mOhms, which is extremely low.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Oh boy, I'm slow. :( No, I haven't used one. However, current through the loops should create a response on the output side. :confused:
     
  8. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    When you say the set-up was as in 2, the current range is ± 7.5 A.
    The output at 1A will be 2.5 ± (1 / 7.5) * 0.625 = 2.5 ± 0.08333 Volts.
    So there is "only" a change of 0.08333 Volts.

    What was the load at the moment of testing?
    The datasheet says it must be larger as 2kΩ.

    Bertus
     
  9. mik3

    Thread Starter Senior Member

    Feb 4, 2008
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    It should but it doesnt.
     
  10. rjenkins

    AAC Fanatic!

    Nov 6, 2005
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    I've used those and various other of the LEM current sensors without problems.

    They do different styles, some with large center holes to take serious cables.

    If you want to measure a higher current with one of the small sensors, the best method is to make up a multi-strand cable using a number of lengths of insulated wire, all *exactly* the same length, then connect them in parallel with only one passing through the sensor.

    eg. if you used ten lengths of (say, 22g, 0.5mm2) with one of them through the sensor, the 7.5A scale would then be reading to 75A.

    As long as the wires are exactly the same length the current will be equally distributed.
     
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