Signal ground and DC ground

Discussion in 'The Projects Forum' started by francoisC, Jun 29, 2010.

  1. francoisC

    Thread Starter New Member

    Jun 29, 2010
    3
    0
    Hi,

    I currently have a video camera that has the following pinout:

    Power (24VDC)
    GND
    Signal

    It takes 24VDC as input and outputs a video signal. Shouldn't there be a separate Signal GND as a reference? Or is it acceptable to use the DC GND as my Signal GND reference?
     
  2. John P

    AAC Fanatic!

    Oct 14, 2008
    1,632
    224
    Obviously, it's what they're doing. To them, there's only one Gnd. Hopefully, their internal circuit does use separate grounds and joins them at the incoming connector. If I had to work with this device, I'd wire my system the same way, but in reverse--a dual system with 24V Gnd and signal Gnd, connected only at the outgoing connector.
     
  3. francoisC

    Thread Starter New Member

    Jun 29, 2010
    3
    0
    I'm using 24V GND and Signal GND as the same throughout my entire system, and when I input the RCA jack into a monitor, I'm getting horizontal lines the slowly move upward in my video...

    Any clue what could be causing this? Would isolating them and only connecting them at the outgoing connector make a difference?

    EDIT: http://www.deepsea.com/pdf/specs/Multi-SeaCamManual010810.pdf

    That's the camera being used.
     
    Last edited: Jun 29, 2010
  4. flat5

    Active Member

    Nov 13, 2008
    403
    17
    Put a 'scope on the 24v and ground and see if it has signal on it. It should be very clean.
    Is it an old camera? Check for slightly bad solder connections on the print. Maybe a bad ground connection. You might have a cap failing.
     
  5. francoisC

    Thread Starter New Member

    Jun 29, 2010
    3
    0
    When I plug my camera directly into my system (using DC Ground as the same as Signal Ground), it works fine.

    However, when I connect the camera to a ~600 ft long umbilical then into my system, I'm getting the "hum" in the video signal...

    Any ideas to offset perhaps the umbilical?

    edit - the video signal in the umbilical is through coax cable with the shield connected to the "GND" pin.
     
    Last edited: Jun 30, 2010
  6. flat5

    Active Member

    Nov 13, 2008
    403
    17
    I would try a three wire cable. If hum is still there, I would try to connect the shield at one end only.

    Can you run one end on battery power and see what happens?
     
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