Cable tester project, need to place conditions based upon resistance

Discussion in 'The Projects Forum' started by Cleevo, Apr 7, 2009.

  1. Cleevo

    Thread Starter New Member

    Apr 7, 2009
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    I am an electronics newbie. I have been tasked with creating a cable tester to test a 2 wire cable for shorts or breakage. The meters that are normally connected to the cable read information very quickly (milliseconds) so I need to tell if there is a fault on the cable that could interupt the data for even a very small time period. I have purchased a latching relay that fires in 18 ms. I need some sort of device that can energize the coil on the relay when the resistance is either too high (indicative of break?) or too low (indicative of short). the relay will in turn switch from a green lamp to a red one. I have attached the iagram of the project as i envision it. Sorry I don't know much about diagrams, so it is probably not up to specs.

    Any help would be appreciated...
     
  2. Cleevo

    Thread Starter New Member

    Apr 7, 2009
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    Forgot to mention the relay is 12 vdc. I presume this is important. Again, thanks in advance.
     
  3. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,172
    397
    Do you have control of both ends of the cable under test? Might try a Wheatstone bridge with an OP amp, several comparaters, a few LEDs with drivers. If you need to know where a break is, use a Wien bridge to measure capacity. It does work, 'been there - done that with 1320 ft, 13 pair cables, just a long time ago, early '50s.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    With what little time I have available, my suggestion would be to use a window comparator that will latch when there is a fault.

    A relay simply won't be fast enough to capture small transients.

    Google "Window comparator" for quite a few hits.
     
  5. Cleevo

    Thread Starter New Member

    Apr 7, 2009
    3
    0
    Bernard - I don't understand. I am not looking to locate the fault as my cables are only about 2 feet long and only have 1 pair. I am just interested in a quick "go/no-go" guage. Sorry, but I am really new to this.

    SgtWookie - according to the spec sheet for the relay, it can latch in 18ms, This suits my purpose, my further question is, can I use the window comparator in addition to the latching relay? If this is the case can I use set it up like this diagram.

    Ω rates are guesses and any suggestions are appreciated

    Thanks so much for your help - both of you
     
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