Years ago I acquired a Sangamo J4S Cat No 76003 meter. I have it wired for 120 volt using the jumper method from the back of the meter to neutral. In my infinite wisdom, I got bored one day and wanted to see how fast I could make it go by adjusting the calibration screws! Needless to say, it didn't have the desired effect...
On to my request, is there any way I can get this meter back to where it's fairly accurate? I've read several posts with calculations, and aren't super great with math, but do understand basic Ohm's Law and how these meters work. Is there a calculation that would tell me how far off the meter is by plugging a known load into it and counting the rotor revs for a set time?
I have a multimeter with the ammeter clamp, so can measure AC amps and volts.
It's only used for my workshop, so it doesn't need to be super accurate, but I'd like to fix my blunder from years past
The Sangamo J4S meter has an Kh of 7.2, which means that 1 revolution of the disc equals 7.2 Watthours. Best is to have a known load connected to the meter and perhaps purchase a plug in killawatt electronic meter to see what the actual load is drawing. For example a 2000 Watt heater is only 2000 Watts at the specified voltage 120 or 240 volts.(check the heater nameplate) Do a 10 rev test with a known load (electric heater) and measure the time in seconds. In 1 hour (3600 seconds) the meter records 2 kWh and the disc has done 277.7 revs To do 10 test revs 72 Wh of electricity is used. The time for 10 revs equals 3600 / 27.7 = 130 seconds. Then the meter has a zero error provided the 2 kW load remained the same. If the 10 rev test yields in a longer time the meter runs slow. If the 10 rev test yields in a shorter time then the meter runs fast. A matter of readjusting the brake magnet to get the meter back within specs. Hope it helps.
Many of my meters are turning around on the web.
Have a look on YouTube