🚀 go-pugleaf

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.

I happen to know the answer to that question.  The very best battery for
that use is the  Duracell RM-42R mercury cell, a 1.35 volt "D" sized cell
made by a variety of manufacturers.  

It's rated at 14 ampere/hours, and if the current consumption is kept in
the microamp region, it has a noise resistance of about 2 ohms.

-- 

Norm Strong  (strong@tc.fluke.com)
2528 31st S.   Seattle WA 98144