Electronics > Metrology

An Experimental AC Voltage Calibrator

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I have completed the build of the AC Voltage Calibrator Ver2 and tested the LV at 10v and HV at 100v output. This final (?) version has a built-in 1KHz LD Audio Range Signal Generator mentioned in Reply #7 and has provision for an external signal generator.

Learnings from this project:
1) It is possible to build a stable 0-200vAC signal source at 100Hz to >30KHz frequency using readily available audio modules, voltage regulators and transformers.
2) Amplitude stability is almost entirely reliant on the signal source.
3) Low signal distortion is good but far more important is signal noise as this is amplified by up to x400.
4) Fan cooling of the audio amplifier is recommended and speeds up the settling time.
5) Separating the LV and HV output terminals allows the HV output to float above ground.

One application would be to calibrate up to 5.5 digit AC meters using a 6.5 digit or better reference meter.

As a follow up to this project, I found a cheaper solution for the power amplifier module.
A class AB MOSFET audio amp kit for less than $31AUD at:


This amp can be powered by up to +/-70v rails and deliver up to 40vRMS at the output.

As before, regulated rails improve amplitude stability. Also, for frequencies over 20KHz, the output stability capacitor should be reduced in value accordingly otherwise the 10R/1W series resistor will go up in smoke!

A heatsink is essential to assist with thermal tracking.

L7 mono MOSFET class AB audio amplifier board kit.
Output power of 150W 8R DC +/- 56V rails (this applications only needs a couple of watts)
Frequency response 4Hz-350KHz, -3dB
THD <0.01% 100W 1KHz
Slew Rate = 38V/uS
SNR> 99dB
Requires AC 50V(or less)x2 transformer, or DC ±70V(or less) power supply.
PCB size = 78 * 63 MM


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