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  • EEVblog #38 2of2 – Seismic Survey Boats & Insulation Resistance Measurement

    Posted on October 16th, 2009 EEVblog 11 comments

    Dave explains errors and problems associated in insulation resistance measurement through a relay test matrix.
    Betcha no one else has covered that one before!

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    • Ramzi

      interesting blog, and yeah i bet no one else covered that.

      Thanx.

    • http://www.danielbjohnson.net septer012 – Daniel

      Hey great, really feel like im learning something now! I have never gotten the chance to utilize a relay, do you remember what your first project was involving relays Dave?

      • http://www.eevblog.com EEVblog

        Oh wow… I would have been under 10yo at the time I worked with relays for the first time, so I don’t quite remember the project or application!

    • http://www.mastrogippo.it Mastro Gippo

      Interesting! But… When you said “bang, bang”, I thought: “poor fishes”. This brings me to a question: How do you feel about our passion, and the way it impacts our enviroment? I’m always on a fight against myself, because I love electronics but I also love.. well, being alive!!! And all the stuff that we build, and trash, and “consume”, it’s all going to kill us. I know, it’s a big question, but I’d like to know your opinion!

      • http://www.eevblog.com EEVblog

        Great question!
        I worked for more than a decade on oil exploration equipment and marine military systems which were pretty horrible environmental wise, and looking back on that I’m certainly not proud of that aspect of it.
        I’m quite an environmentalist myself, so I do feel rather guilty having had worked on this stuff, I greatly doubt I could ever work on such thing again. I’d love to have a job that could actually help the environment in some way for a change!
        I felt less bad because the new “solid” streamers I worked on were actually fairly “environmentally friendly” compared to existing oil filled streamers.

        • http://www.mastrogippo.it Mastro Gippo

          I think you should do some talk about this matter! Sometimes we are too busy playing with our toys to see things in a different perspective. Look at this:
          http://www.storyofstuff.com
          It impresses me everytime I watch it, and I watch it regularly to keep in mind that I must try to lower my impact on the environment every day.
          Want to feel even more guilty? There was a documentary from Laura Ling, but it seems to be vanished: http://current.com/items/76355482_toxic-villages.htm . I’m trying to contact one of the producers to get a copy. Meanwhile, if you can stand all the journalist sensationalism, you can watch this similar video: http://www.cbsnews.com/video/watch/?id=4586903n

          Please talk about it, people need to know.

          • http://www.eevblog.com EEVblog

            @Mastro
            http://www.storyofstuff.com

            Thanks, I hadn’t seen that one. Most excellent.
            I love Home project:

    • Michael Thompson

      I love relays.
      There are a lot of things I don’t understand, but I understand relays. LOL

      :D

    • Timothy Tee

      I keep wondering why there is a need for a 100Mohm meter.

      Now I see why insulation meter is so useful for cables.

    • Andrew

      You can roughly measure multi 100 M? resistances with a bog standard $10 no-name, 3 1/2 digit multimeter with the same trick.

      The highest resistance range of a 3 1/2 digit multimeter is usually 2 M?. You need to get a resistor as close to that value as possible. Lets say Rr = 1.8 M? (best would be one giving you a 1.999 M? reading, but that would be like winning the lottery). You connect that reference resistor Rr to the multimeter and measure it. Best would be if you fix the resistor with some screw terminals to the meter.

      The you connect the unknown high resistance resistor Rx in parallel to Rr and measure the resulting resistance Rp. Rp is less than Rr.

      The value of the unknown resistor Rx is

      Rx = (Rr * Rp) / (Rr – Rp)

      Lets say you measure

      Rr = 1.800 M?
      Rp = 1.790 M?

      -> Rx = 320 M?

      You have just measured a 320 M? resistance with a $10 multimeter and a 5ct resistor, 160 times larger than the specified maximum value the meter is supposed to be good for. The error gets larger, the larger the unknown resistance Rx is.

      If only the last digit differs between Rr and Rp you are in the Giga ? range, but you really can’t say if it is one, two or three Giga ?.

    • Neil

      Great explanations, although one thing did make me smile. High resistance is all a matter of perspective. My first task in my current job was to help design an insulation tester. It measures 35T?. Mind you, one of my colleagues remarked that it was