11 responses to “EEVblog #38 2of2 – Seismic Survey Boats & Insulation Resistance Measurement”

• Ramzi October 17th, 2009 at 04:46

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

  Thanx.

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• septer012 - Daniel October 17th, 2009 at 17:49

  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?

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  • EEVblog October 18th, 2009 at 22:07

    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!

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• Mastro Gippo October 17th, 2009 at 23:33

  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!

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  • EEVblog October 18th, 2009 at 22:06

    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.

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    • Mastro Gippo October 21st, 2009 at 06:04

      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.

      Reply

      • EEVblog October 22nd, 2009 at 15:25

        @Mastro
        http://www.storyofstuff.com

        Thanks, I hadn’t seen that one. Most excellent.
        I love Home project:
        http://www.youtube.com/watch?v=jqxENMKaeCU

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• Michael Thompson October 17th, 2009 at 23:47

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

  

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• Timothy Tee October 19th, 2009 at 11:19

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

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

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• Andrew October 20th, 2009 at 04:11

  You can roughly measure multi 100 MΩ 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 MΩ. You need to get a resistor as close to that value as possible. Lets say Rr = 1.8 MΩ (best would be one giving you a 1.999 MΩ 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 MΩ
  Rp = 1.790 MΩ

  -> Rx = 320 MΩ

  You have just measured a 320 MΩ 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 Ω range, but you really can’t say if it is one, two or three Giga Ω.

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• Neil October 23rd, 2009 at 06:10

  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 35TΩ. Mind you, one of my colleagues remarked that it was “only 20kV. That’s nothing.”

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