[volt-nuts] Homebrew DVM

[Andreas Jahn]

Ok Fred,

thats the ADC im currently using too.
Although he has internally a readout of 28 Bits due to noise only 18-19 Bits 
are usable.
To further reduce noise you will have to average many measurement values.
On the other side against many other sigma delta chips the LT2400
has very low offset and gain drift over temperature. And the main advantage
is the Overrange feature of +/-12% which makes offset and full scale 
adjustment easy.

Im still hoping that someone knows a ADC chip with less noise
and true 0..5V (or even 0..10V) input with the overrange feature.

With best regards

Andreas

----- Original Message ----- 
From: "Fred" <pa4tim at gmail.com>
To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
Sent: Wednesday, November 16, 2011 1:20 AM
Subject: Re: [volt-nuts] Homebrew DVM


> The ADC I am gonna use is the LTC2400. A friend who is a digit-nut made
> the pcb and will make the software for me.
>
> About the dual slope experiment. I could look better as it is. The
> arduino died before I could do more tests but first results amazed me.
> Remember it was just breadboard, no Vref (just resistive divider from
> Vcc and, I do not dare to say, but the measurement pictures were taken
> after I blew up my last 4066, so I used optocouplers to switch and
> strange enough that went very well.
>
> The drift you see in the measurements is more because the powersupply I
> measured the voltage from, is not realy stable. Noise I do not know.
>
> The experiment was after a discussion on a Dutch forum. There was some
> talk about multimeters and ADCs and the a member who works at ST as an
> EE told the top meters used dual slope about how easy it is to make a
> dual slope ADC. He told us to just try it on a breadboard and gave some
> tips. A few of us including me started experimenting with it and I was
> trilled it was so easy to get it working like it did. Was fun too. I'm
> now reading a lot of literature and your interesting discussions to
> learn more before I build my meter using the LTC2400. So thanks for all
> the valuable information. As a beginner I    appreciateitverymuch.
>
> Fred PA4TIM
>
>
> Andreas Jahn schreef op di 15-11-2011 om 23:19 [+0100]:
>> Hello Fred,
>>
>> I asked for the 26 bit (24 bit usable) ADC.
>> Do you really get this (noiseless) resolution with a simple dual slope 
>> ADC?
>>
>> With best regards
>>
>> Andreas
>>
>> >
>> > http://www.pa4tim.nl/?p=2482 there you see the schematic and some 
>> > pictures
>> > ( the top one is from the circuit that, i was told, turned out to be a 
>> > VF
>> > converter)
>> >
>> > Fred PA4TIM
>> >
>> >> I am looking now for a converter with less noise.
>> >> So what ADC are You using?
>> >>
>> >>>
>> >>> Now I have a 26 bit ( 24 bit usable) ADC waiting to be used 
>> >>> interfaced
>> >>> to the arduino, I am making/experimenting with some Vrefs and have 
>> >>> parts
>> >>> for a compound chopper based on a LT1052. But the realisation will be 
>> >>> up
>> >>> in the future, first gathering more knowledge about percision and 
>> >>> micro
>> >>> volt techniques.
>> >>>
>> >>> Fred PA4TIM
>>
>>
>>
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>
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