Jul 082011
 

I’m a big fan of lock-in amplifiers; I’m always scanning eBay for a good deal. Recently I got a pair of EG&G 5207 lock-ins. Both were busted. One seemed to have ended up in the auction chain due to some bad buttons and the other one booted up with error messages. I bought both cheap and was able to Frankenstein a working unit of of the two of them. The main issue was the sticky buttons on the good unit causing the control computer to be unresponsive. That was the unit I saved. All I had to do to get it working was to swap in the good switch array board from the unit with the bad computer. Lots of screws and standoffs, but it wasn’t too bad.

Here’s the organ donor:

I might be able to get this one working too. I’ll have to fiddle with the CPU card on the far left.

The organ donor had cards in it for two frequency ranges: 0-20 kHz and 0-100kHz. I pulled the broadband card and put it into the working unit. Even better, the local reference oscillator card from the donor was moved over to the new unit too. So now I have nice single phase lock-in with two front ends optimized for audio and 0-100kHz inputs. I’ve got almost all of the available options in the good unit now.

How well does it work? I’m feeding a 90 kHz 1V peak-to-peak sine wave into the lock-in reference and signal inputs. The correct RMS voltage is 0.354 V. It’s not too far off for a 24 year old instrument that I saved from from the junk pile. I haven’t tested the GPIB or RS232 interfaces, but I bet they work too. I’m not sure how to calibrate the thing, and I’m not even sure I want to try. A few percent absolute accuracy is fine and I’ll mostly be doing relative measurements anyhow.

All that’s left to do is clean the front panel.

 Plans? Well, I’m going to try building a phase-switched radio interferometer so I can do some radio astronomy.

 Posted by at 11:15 PM

  2 Responses to “Lock-in Amplifier”

  1. [...] The author picked up his lock-in amplifer – an EGG 5207 – for cheap on eBay, which he discusses in this blog post. [...]

  2. Nice demo, Scott!

    This seems like a cool updating of a technique written up in the 1960s in a book called “Seeing Sound” by Winston E. Kock. He used a neon bulb and ultrasonic transducers, along with long-exposure photograph film.

    For a similar low-tech technique, you might find my website interesting: http://www.seagraveinstruments.com .

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