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  • Digital tachometer wiring question

    I got a digital tachometer from ebay, trying to understand how to wire it.

    There are three components:
    1. Power supply (my VFD suplies 24V DC).
    2. The magnetic sensor (black, blue, brown wires).
    3. The tachometer display (flat cable with five leads, numbered 1 through 5).

    So it seems that the 24V+ goes to the lead 1 of the display and brown lead of the sensor.
    Looks like the black lead of the sensor goes to lead 5 of the display unit.
    The 24V- goes to the blue lead of the sensor.

    What I'm confused about are the leads 2 and 3 of the display unit. 2 is marked "power ground", and 3 is marked "blue" and "signal earth".

    So do I connect 24V- to BOTH the blue lead of the sensor AND the lead 3 of the display unit?

    What do I connect to the lead 2 of the display unit?

    Below are the pictures fromthe ebay page:
    Click image for larger version

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    Click image for larger version

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  • #2

    Re: Digital tachometer wiring question

    Don't blame me if it goes up in smoke since it isn't totally clear!

    Brown and pin 1 of display go to the + voltage as you said. Black goes to pin 5, this is the detector signal, as you said.
    Blue is the negative voltage common for the probe and you need it on pin 2 with the - voltage from the VFD for the power circuit of the display.

    Electronic instruments often have a signal ground that is not exactly the same as the power ground to keep electrical noise levels down, sometimes they are referred to as a high-quality ground. They are usually connected at the same point in the device so it should work; if it doesn't work with nothing connected to it (pin 3), then I think pin 3 signal ground needs to be connected to the pin 2. It may well work with the probe's blue wire connected to the signal ground rather than the power ground on pin 2. It just depends on how the circuit inside the display is configured.

    Power ground most likely means power common - not the safety ground as mentioned in house wiring.

    Maybe somebody who has actually wired one will come along.

    billh
    Last edited by billh; 11-16-2017, 02:26 PM.

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    • #3

      Re: Digital tachometer wiring question

      Randy in Calgary has done this I believe.
      Erik

      Canada's Island Paradise - Prince Edward Island

      Proud member of the Wadkin Blockhead Club

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      • #4

        Re: Digital tachometer wiring question

        My sensor had a pin connector so I didn’t have to deal with that.
        Cheers
        Randy

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        • #5

          Re: Digital tachometer wiring question

          Looks like the same one I installed a couple of years ago:
          Sensor black to pin 5 on Display
          Sensor blue to pin 3 on Display
          Sensor brown to +24v source
          Pin 2 on Display to 0v source
          Pin 1 on Display to +24v source
          Pin 4 is not used.

          Comment


          • #6

            Re: Digital tachometer wiring question

            Originally posted by Kenneth View Post
            Looks like the same one I installed a couple of years ago:
            Sensor black to pin 5 on Display
            Sensor blue to pin 3 on Display
            Sensor brown to +24v source
            Pin 2 on Display to 0v source
            Pin 1 on Display to +24v source
            Pin 4 is not used.
            The mystery of Pin 3 is solved, thanks!

            Comment

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