[volt-nuts] MicroVolt meter

[shalimr9 at gmail.com]

There are 24 bits ADCs available. One I have used is the MSC1210 from TI. It is actually an ADC with an 8051 processor integrated (with Flash and RAM). There are many more. You can probably buy a cheap development kit. I paid $50 for mine.

Didier KO4BB
Q
Sent from my BlackBerry Wireless thingy while I do other things...

-----Original Message-----
From: Fred Schneider <pa4tim at gmail.com>
Sender: volt-nuts-bounces at febo.com
Date: Tue, 3 May 2011 18:59:40 
To: volt-nuts at febo.com<volt-nuts at febo.com>
Reply-To: Discussion of precise voltage measurement <volt-nuts at febo.com>
Subject: [volt-nuts] MicroVolt meter

Am I a dreamer if I think there must be a way to build a digital or analogue meter that has a resolution of 0,1 uVDC and a max input of 2 V in that range, and 1 uV at a 20 V range.
Used bench meters with that resolution are scares and new ones made of plain gold.

I was thinking of using a modern chopper opamp. LTC1051 with LT1007. Or a TL7652.
Maybe two that split up the voltage and then to two ADC's. Wilkinson version ? The result to an Arduino for the readout and combining of the most and least significant digits.
But I'm an RF head, i can make 1GHz oscillators, but digital stuff is rather new for me ( I can program a little in C).

Other idea
A 845AB meter can reach 1 uV full scale, but that is nice as null detector. You can not measure the voltage of a 1 V calibrator direct. There should be a way to use that thechnique. For instance make something for that meter, a sort attenuator or divider or subtractor and let it switch automatic through it ranges. The 845 stays in 1 uV range but the Attenuator switches from the 10 V to 1 uV range. The measurements from the recorder output to a uProcessor that combines all the results. 
So in the 10 V range it measures 3.53V, we keep the 3.  in the 1 V ranges it sees 0,534V. We keep the 5, in the 1 mV range it sees 0,0346, we keep the 3 ect upto 0.1 uV.
A sort of sample and hold that we use in a later stage to subtract from the next input.

Fred PA4TIM
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