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3000AC Operation Manual - V2.0
Theory of operation
The 3000AC uses a high resolution audio DAC which is controlled via a PIC to generate 256
discrete steps of an AC Sine wave, going between +10V and -10V, generating an approximate 7.07V
quasi sine wave.
The DAC can be stopped at any point, allowing a measurement of each DC Voltage step to be
measured, squared, and then added to the squares of all measurements, divided by the number of steps
(256) and then the square root taken.
The long term stability of the DAC and voltage reference does not need to be considered, as the
intended use of the instrument is as a check standard, and to be checked against a suitable 8.5 digit
multimeter (with a total DC Voltage uncertainty of less than 10ppm on the 10V Range) at the time of
use.
When automated the AC Characterisation process takes no more than 30 minutes, and can be
used to calculate the AC Output to better than 20ppm. The total accuracy of the output is dependant
upon the measurement uncertainty of the DC Voltage steps, any short term drift of the 10V Reference
(less than 0.5ppm across the time of use and within a stable environment) and any glitches/step errors
in the DAC. Glitches/Step Errors often cancel each other out depending on the position of the sine
wave (rising or falling) and are also quite insignificant in the total uncertainty of the output.
Calculating the AC Value
Measure each DC Step as a DC Voltage and record in a spreadsheet for future use. To obtain the
RMS value of the AC output, perform the following calculation
Where Vx2 is each of the 256 DC Steps (0through 255), where the x is the DC step of the
measurement, and n is the number of steps in the waveform, 256. Taking the square root of this value
will provide the RMS value of the output, which is nominally 7.07V (10V pk)
