Rectifying a single wire AC signal

Discussion in 'General Electronics Chat' started by arudzki, Apr 25, 2012.

  1. arudzki

    Thread Starter New Member

    Sep 25, 2011
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    All,

    I have an application where I am checking for a broken wire. I am impressing 32VAC (60 hz) where the wire exits my box, goes through box #2 and returns to my box. What I would like to do is bridge rectify the incoming signal to test for a couple of conditions including consecutive pulses (120 Hz).

    Is there a way to make the negative going portion of the AC signal, positive using just the one input signal? I could use a bridge, but I don't have the normal 2 wires (AC Hot and AC N) to connect to the opposite sides of the bridge.

    Am I overlooking something simple here?

    Thanks

    Tony
     
  2. crutschow

    Expert

    Mar 14, 2008
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    You can connect the bridge to the wire and the 32Hz generator common. You then measure across the bridge output with an isolated meter.

    But what do you expect the rectified output to show you that just measuring the AC voltage wouldn't show?
     
  3. arudzki

    Thread Starter New Member

    Sep 25, 2011
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    The "rest of the story" is that box#2 has a diode in it and there is a possibility that the wire in the outside world can come into contact with 120VAC. So I'm scheming to be able to detect: 1) broken wire (no signal) 2) intact wire (60 Hz pulsed signal) 3) shorted with external voltage (120Hz signal).

    Does that make sense?

    Tony
     
  4. crutschow

    Expert

    Mar 14, 2008
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    So how will running the signal through a bridge help that determination?

    If you just measure the AC and DC values of the signal you should be able to determine whether the diode is working or not. A shorted diode will give little or no DC value.
     
  5. arudzki

    Thread Starter New Member

    Sep 25, 2011
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    0
    I'm wanting to use the bridge to convert the sine wave of the AC to a positive pulsed signal referenced to ground. My measuring device is going to either be a microcontroller or a CPLD/FPGA determining if pulses are there (no broken wire), happening at 60 Hz (good) or 120 Hz (must be an external 60 hz short).

    I'm over simplifying here and probably muddying the waters.

    Tony
     
  6. crutschow

    Expert

    Mar 14, 2008
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    To use a bridge you would need a floating (differential) measurement of the bridge output.

    To detect that the diode is working why not add a small capacitor on the output and measure the DC voltage. If the diode is working the cap should charge to the peak AC voltage. If the diode is shorted you will measure an AC voltage but little DC.
     
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