[time-nuts] OT: AC voltage standard
didier at cox.net
Tue Nov 6 07:08:05 EST 2007
I suggest you use a CMOS multiplexer driven by a clock and a flip-flop (to
guarantee 50% duty cycle) to switch the Weston cell's output voltage on and
off at 50% ratio. Knowing the ON resistance of the CMOS multiplexer will
allow you to calculate the effect of loading if you know the impedance of
the meter you are driving. Other than that, the output voltage will be an AC
voltage with a peak-to-peak value equal to the cell voltage. Possible
problem: the output will be chopped DC, not true AC.
Alternately, you could make the circuit a little more complicated and build
a full bridge with the multiplexer, so that the output voltage is either the
cell voltage or the cell voltage reversed, for a DC coupled true AC (+/-)
If you don't see what I mean, I can draw a schematic for you.
> -----Original Message-----
> From: time-nuts-bounces at febo.com
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Joe McElvenney
> Sent: Tuesday, November 06, 2007 5:57 AM
> To: time-nuts at febo.com
> Subject: [time-nuts] OT: AC voltage standard
> Excuse the topic but is does push the same buttons as it were.
> After calibrating my old HP54502A 6-bit digitizing scope I'm
> left with an error I can't quite believe and so am trying to
> determine which of my instruments is telling me lies.
> Anyone know of a simple way of producing an AC voltage
> standard suitable for general workshop use without reference
> to another one? About one percent would be good enough, wave
> shape and frequency accuracy not important (wash my mouth
> out). I have a Weston Cell for DC voltage calibration, a Rb
> one for frequency but nothing for AC volts. Perhaps there is
> a chip out there that clocks between accurate limits that I
> could use as a source?
> Thanks - Joe
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