开云体育

Sometimes simple is all you need. Based on a cheaply available AD584 module with some mod's to capacitor values and the addition of an Opamp to counteract? the shunt voltage (burden) of the meter being tested for the current ranges.? I could have added trimming for the reference , current setting resistors, and opamp offset, but all should be within about 0.1% from data sheets. I felt that it was better to have it close enough and stable rather than introducing other possible items to drift just to get some more zero's. There are probably better opamps out there, but I used what I had, minimal/stable offset voltage and input current probably most important parameters. The BAT48 is to protect the opamp input from potential over voltage when no meter is attached to the current outputs.? I used ten 10K 0.1% resistors in parallel for the 1K because I had a box of them. Comments, suggestions for improvements, etc. invited.
Paul McMahon
VK3DIP

I have personally never made anything like this - instead just comparing values to a 6.5 digit multimeter. But recently I bought a cheap(ish) 20,000 count Chinese multimeter, and wanted to check it. On DC around a few volts and resistance it was excellent. However, I wanted to check AC volts and amps too. That brings a whole lot of challenges. The AC mains is not stable enough, so comparing a 20,000 count multimeter with a 6.5 digit HP 3457A is totally impossible.?

I actually bought a 100 W Tandy PA amplifier from eBay, that was designed to run into 4 ohm speakers. My plan was to put that into a high voltage transformer to allow me to generate AC that should be more stable than the 50 Hz mains. Other projects go in the way, so I never got around to testing the multimeter properly on AC.?

You can expect any multimeter to be most accurate on DC voltages around its reference voltage, so most are probably going to be mist accurate on a 3 V or 10 V DC scale. To do a proper check, one really needs to test at high and low voltage DC too.?

You could consider adding AC calibration.

Fluke multifunction calibrators are extremely expensive. There’s probably a lot of work into making some produce a wide range of voltages and currents.?

Dave

If you can find a HP3245A - they can be had for about $1000 if you are lucky - you can can use it as a source for DC volts, DC current, AC volts and AC current (up to 1MHz). The main drawback is it's limited to 10V output unless you have the elusive 002 option which takes it to 100V. It's not intended as a calibrator but then it's not $25k like a Fluke 5720.

- Keith