I recently purchased 2 little voltmeters they look like the sort that would go in a control or instrument panel they are connected with just 2 wires which provide the operating supply ( they light up green and red) however the green one states it will work between 20and 500 volts and the red one between 60 and 480 volts. When they are both on the green one indicates normally around 241 volts the red one shows 235 volts why the discrepancy I know it's not much but makes you wonder if one of them is lying. Secondly I've noticed that the green one tracks voltage changes faster than the red one and that a few times the green one jumps down to 238 then up to 241 multiple times while the red one stays the same and I think can see a slight flicker in my filament lamps when this is happening incidentally both meters are connected to the same plug a 2 pin 5 amp one
Thank you Mike that does help to be able to look at those scope traces did you do all those experiments yourself? I'm a bit short of test gear now although I do have a scope and certainly recognise the rectifier waveforms I remember ages ago reading an article about rectifier noise and how to cure it and have done it on a couple of linear PSUs that are used in the shack. Anyhow looking at the red trace on the bottom picture it's clear that the current it shows does go negative slightly just after the mains current goes positive and the other way on the next zero cross so I think I got it now maybe I need to do some more reading on it wanted to thank you for your efforts in explaining this
Thank you Mike that does help to be able to look at those scope traces did you do all those experiments yourself? I'm a bit short of test gear now although I do have a scope and certainly recognise the rectifier waveforms I remember ages ago reading an article about rectifier noise and how to cure it and have done it on a couple of linear PSUs that are used in the shack. Anyhow looking at the red trace on the bottom picture it's clear that the current it shows does go negative slightly just after the mains current goes positive and the other way on the next zero cross so I think I got it now maybe I need to do some more reading on it wanted to thank you for your efforts in explaining this
