A proper AC voltmeter ?

A project log for Mains protection box

Work more safely with mains power

Yann Guidon / YGDESYann Guidon / YGDES 05/17/2019 at 22:340 Comments

I also received a front-panel AC voltmeter.

It was a bet because the specs were not very precise but for less than 8$ on eBay, it was worth a try.

I like that this model seems to be "old school", based on the venerable ICL7107, so there is headroom for "adaptation". The box looks like it was stored 10 or 20 years (or more ?). It is rated at 500V max (peak ? RMS ?) and can work from an independent power supply though there is less than 2M Ohms of isolation. The integrated diode bridge makes the power easy to supply, with a small 9Vac transformer for example.

I just need to find the proper transformer and I'll test it, and even probably compare with my multimeters.

And of course I'll have to build a stand/support to fit the display on the fraim...

Tests with the PM5715 signal generator show that it's pretty biased ! The display changes a lot with the offset, duty cycle etc. but it shouldn't. That thing is crazy. It's obvious its power supply must float well...

Anyway the display draws 50mA @ 12Vdc, it's good to know.