Author Topic: DIY AC Voltage reference  (Read 5374 times)

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Offline krish2487Topic starter

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DIY AC Voltage reference
« on: May 07, 2012, 07:00:43 pm »

I have a fluke 111 TRMS that i would like to calibrate
(It is fairly accurate even now as when compared against a new calibrated Rish 16S True RMS (rebranded gossen metrawatt).
it is off only in the decimal readings. i wanted to perform a at home calibration to see if
1) I could "tune up" the fluke to perform as well as the Rish
2) If i could develop a fairly accurate reference for resistances/voltages/currents at the lowest cost possible to get a 0.1 % or thereabouts standard.

The semiconductors available seem as a pretty good compromise considering a true calibration from a government body would cost more than my annual salary so would getting a Reference itself off ebay.
Passives in 0.05% tolerance range are about 4 times the cost of a 1% tolerance passive.

Throw in a bunch of Ics and resistances and caps and inductances. It is by no means negligible cost but still a LOT cheaper than getting it calibrated by a Institution ( which i feel is not required for hobby purpose).
I got my hands on the service/calibration manual and saw that the calibration itself was done at 6V,6A etc, you get the point right.

So getting a DC voltage reference, capacitors, resistors, inductors seems pretty straightforward.
I am stumped at a 6V RMS AC reference which is holding me back at the moment. I have no clue as to how to generate a 6V AC RMS reference

So I request all the guys present on this forum to help me with this roadblock. Maybe we can come up with a solution that might be a poor-mans reference calibration, much like the uCurrent.

Or putting it another way
So i sound as if I am talking out of my head or is there a geniune need for such a thing??
I figured not everybody can afford a bench reference (even used).
If god made us in his image,
and we are this stupid

Offline Jeff1946

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Re: DIY AC Voltage reference
« Reply #1 on: May 07, 2012, 08:25:33 pm »
One way.  Connect a suitable AC source (Wall wart or whatever) to a power resistor.   Connect your meter parallel to the resistor. Place the resistor into an insulated container (coffee mug?) with water and a temperature probe.   Gentlely stir and accurately measure time for the change between two temperatures.  Repeat with a known DC voltage similar to the RMS of your AC voltage.  Ratio of the time between the same two temperatures should be the inverse of the ratios of the square of the voltages.   I would expect this would be about 1% accurate if you are careful.  Thus an accurate value of the resistor or accurate temperatures doesn't matter as they are the same for both experiments.  Note you must coat any bare wires so you don't electrolyze the water.  Note this measures RMS of the AC.   It is a little tricky because home AC is often a little distorted due to non-resistive loading.  For example note the current rating printed on a compact fluorescent lamp is greater than you would calculate from the power rating.

Another way.  Measure peak to peak voltage on an oscilloscope and compare to known DC voltage.   Again at best 1% accurate.


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