12 responses to “EEVblog #38 – LCR Meters, Transmission Lines, and Moving goal posts”

• Jeff Nichols October 16th, 2009 at 22:51

  Great video. It’s always interesting to see not just how things work, but how they were designed.

  Reply

• Jason October 17th, 2009 at 02:05

  I’m only a year in, so this may be an overly simple question. How do you get a full-wave rectified signal from a clamping amplifier?

  Reply

  • Tom October 17th, 2009 at 03:48

    I thought exactly the same, so I checked the high-res pictures again and downloaded the datasheet. I guess he is (ab)using the negative clamping voltage.

    You could connect the voltage to the negative input as wel as the negative clamping voltage. If the voltage is positive, the output is positive because it is the low clamping voltage. If the output is negative, the voltage get inverted because it is connected to the inverting input.

    Reply

    • Jason October 17th, 2009 at 04:24

      Nice! That seems to make some sense. Thanks!

      Reply

    • EEVblog October 17th, 2009 at 11:17

      The full-wave rectifier is a recommended app for this device. Check out the datasheet on page 19 figure 12.
      Curiously, the circuit is on the front cover of the Analog Devices “Practical Analog Design Techniques” book.
      All the sections of the book can be downloaded
      HERE
      Dave.

      Reply

      • Jason October 18th, 2009 at 13:09

        Thanks for the link! The positive cycle is still playing with my mind, but maybe if I look at it a while longer it’ll sink in.

        Reply

• Ingo Seidel October 17th, 2009 at 03:30

  Hi Dave,

  was the design a one man show or have you been part of a design team?

  Reply

  • EEVblog October 17th, 2009 at 07:26

    It was all a one man show. Concept, design, layout, construction, testing, manuals etc. Quite funny when you see most of the Drawn, Checked, and Approved boxes with your name in them!

    Reply

• TrentO October 17th, 2009 at 03:48

  After watching the latest two videos, I believe PeteB had a better answer than me… and he was one of the first respondents as well. Perhaps he’s more deserving of the prize? I really would not want to be the sneaky-bastard that stole it from the more serious contenders….

  -Trent “The Rookie” O.

  Reply

• Jacek May 12th, 2010 at 08:52

  Dave,

  I’m interested in the math behind the measurements and I’d like to read more about it. I tried to follow the calculations on the board, but I feel lost. Could you post a reference (book, website, book on a website, whatever) with more details (especially derivation of the formulas)?

  Reply

• NJC July 13th, 2010 at 07:12

  I know this is an old post, but I just wanted to say it is my favorite so far. I’ve been watching all your blogs starting with the first after finding your site a few days ago. I am an EE student and have been doing hobby EE related things for about 10 years. I generally like to think I know my stuff, and I really loved your description of the LCR meter. I was actually pondering this a few hours before I even saw this blog! Perfect timing. Very impressive and comprehensive explanation. Love it. Can’t wait to get up to speed with the blogs.

  @Jacek
  Dave mentioned this in an earlier blog, but the Art of Electronics goes over this pretty nicely. In general text books used in engineering school are quite expensive. I would recommend first understanding the simple version of Ohms Law (V = IR), then looking into simple complex algebra, then understanding V = I*Z, then look at theory behind frequency and phase and how Z can change them. It’s not too hard if you break it into smaller chunks even though its hard if you just look at the end equations.

  -NJC

  Reply

• Laichh December 31st, 2010 at 19:33

  Here is a simple utility that I wrote some years ago, you can go to download it from:

  http://www.utssb.com/index.php?page=emailrequested&dfile=LCR

  Best Regards,

  Laichh

  Reply