[time-nuts] OT: AC voltage standard

Neon John jgd at johngsbbq.com
Tue Nov 6 16:57:17 EST 2007

On Tue, 6 Nov 2007 13:52:13 -0500, Didier Juges <didier at cox.net> wrote:

>The problem with a mercury relay is that the switching delay is significant and not well controlled, so the duty cycle of the resulting waveform is not well controlled, and so would be the RMS value.

Not at all. The early edition of the Berkeley Nucleonics precision pulser, capable of
delivering a monotonic amplitude pulse to a 4096 multichannel analyzer, used a pair
of off-the-shelf Claire MWRs, one to switch the reference voltage to a capacitor and
another to switch the charge to the pulse forming network.  In later models they
changed to a complicated solid state circuitry that never was quite as stable.

None of that is particularly relevant here because he needs a simple circuit to check
the accuracy of a 6 bit ADC in a scope.  The RMS value doesn't matter, as the output
is a simple square wave that swings between 0 volts and precisely the value of the DC
source.  Neither does the frequency.

The advantage of the reed relay approach, in addition to precision, is that the
circuit can be thrown together on a bench using jumper clips in 5 minutes, assuming a
MWR is on hand.  A voltage source (battery even), a good DVM, the relay and a 6 volt
filament transformer to drive the coil is all that is needed.  More than good enough
for a 6 bit application.
John De Armond
See my website for my current email address
http://www.johndearmond.com <-- best little blog on the net!
Tellico Plains, Occupied TN
Democracy is three wolves and one sheep voting on what to have for supper.

More information about the time-nuts mailing list