If you work for a large company, you probably have test equipment that is routinely calibrated. Some companies have their own metrology labs and others send out to an external lab. In a garage lab, you are less likely to do calibrations and — in our experience — that isn’t usually a problem. Still, it is nice to be able to do at least a sanity check on your gear. Also, if you buy old test gear and repair it, it would be nice to be able to check it, as well. [IMSAI guy] built his own little calibration setup, adding to it over the years, and he shares the details in a recent video, which you can see below.
The board started out simply as one voltage regulator and some 0.01% resistors. Over time, though, he added a few more bells and whistles. The setup isn’t going to rival a NIST-traceable lab setup, but for your garage it is perfectly fine.
The regulators are really precision voltage reference ICs that are readily available, so they should be better than your old bench supply. However, we didn’t think you’d really want to slavishly copy this design, but the idea of having a single calibration kit on a board is something you can grow organically out of your junk box and hamfest finds.
Among the additions to the board are a precision oscillator module from an old GPS and a second voltage reference. The initial reference was a 10V device that is specified to have a maximum error at room temperature of +/- 0.05%. He might have wanted to put some diode protection on the device, though, since reverse wiring it destroyed it. On the plus side, it caused him to look to see if any new better devices.
So when he replaced the reference he also added an AD587 as a second 10V reference which is just as accurate and has an ability to trim the output (although he doesn’t use that capability).
Of course, if you get obsessed with calibration, you might want to get a rubidium standard — in fact, one shows up in the video. There are also a variety of precision resistors we’ve looked inside of in the past.