Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!apple!apn
From: apn@Apple.COM (Alex Novickis)
Newsgroups: sci.electronics
Subject: Re: What is the noise voltage of a 1.5V cell
Message-ID: <48423@apple.Apple.COM>
Date: 24 Jan 91 06:31:39 GMT
References: <1991Jan3.001303.483@ae.chalmers.se>
Organization: Apple Computer Inc., Cupertino, CA
Lines: 40

In article <1991Jan3.001303.483@ae.chalmers.se> hogstedt@ae.chalmers.se (PER HOGSTEDT) writes:
>I need to produce a voltage that is going to be used to bias
>a high sensitivity magnetometer (intrinsic noise < 1 pT/sqrt(Hz)) exposed
>to the earth's magnetic field. The long term stability demands on this
>voltage source are moderate, but the voltage noise has to be extremly low.
>
>I have tried some "reference voltage" IC:s and they are indeed very stable,
>but the noise level is too high. The noise level would have to be below
>what corresponds to <1/2LSB of a 22 bit A/D converter to utilize this beast
>to it's full. Can you send me a dozen :-)
>
>As a kind of last resort, I would like to know what the noise is of a 
>regular 1.5V (e.g. alkaline) cell, assuming the cell is kept at
>room temperature and loaded only by some microAmps?
>
>Yes, if you have that super duper low noise circuitry I'm looking for at hand
>I'm certainly interested in any pointers. 
>
>The bandwidth of primary interest is DC to maximum 50 Hz.
>
>-------
>   Per Hogstedt               Internet:  hogstedt@ae.chalmers.se
>   Lindholmen R&D                   or:  hogstedt@plab.se
>   P.O. Box 8714              Phone...:  +46 3 50 70 50
>   S-402 75 Gothenburg        Fax.....:  +46 3 51 53 13
>   Sweden                     MiniCall:  +46 74 35 68 49
>-------

I don't recall as to waht purpose it was for, but I remember using
a mercury cell for a reference of this nature. Degradation of the cell
over long-term time can be _computed_ and therefore compensated out.
Short term noise was in the 22nd bit range.



-- 
Alex P. Novickis, Real Time systems demi-guru.  (W)   408-370-4541
ALINK:alex.n                                    (PAGE)    989-6678
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