[time-nuts] Rb Mag sensitivity

[Don Latham]

Actually, Hp made a Rb vapor magnetometer in the '60s. We had one
attempted to measure the total electric charge moved by lightning strokes.
A sensitive compass can be used too...
Don

Bruce Griffiths
> Bob Camp wrote:
>> Hi
>>
>> I finally found a number listed for the external magnetic field
>> sensitivity of a fairly small Efratom rubidium. It's specified as 3
>> x10^-11 per 0.1 mili tesla.  I did *not* make up those units, that's the
>> way they stated it. If that's correct *and* my very rusty physics is
>> also right:
>>
>> A 1 A change in a wire one inch away will produce  0.08 mili tesla of
>> field change. That should produce  2.36x10^-11 frequency change.
>> Obviously it's not quite that simple since the wire is a lot closer to
>> the device than the device is large. I suppose a more proper measure
>> would be 1" away from the physics package. Even then the field is not
>> uniform over the entire physics package.
>>
>> The reasonable conclusion would seem be that amp or multi amp conductors
>> at an inch or more from the package might indeed be an issue at the
>> 1x10^-11 level. At the very least twisted paris for DC in the area sound
>> like a good idea as opposed to random wire routing. It also sounds like
>> a good idea to simply not have that sort of current running right by the
>> physics package.
>>
>> Ok, what did I miss that time. Hand calculating DC fields is something I
>> haven't done in ... ummm,... errr ... let's leave it at "quite a while".
>>
>> Bob
>> _______________________________________________
>>
> Yes, its about 80uT at 1" radial distance from an infinite length of
> straight conductor carrying 1A.
> B~ 2E-7(I/r)
>
> Smaller for finite wire lengths (but in this case one has to consider
> the geometry of the other conductors forming the loop).
>
> Since the earths field lies in the 30uT to 60uT range, one may be able
> to use the Rubidium standard as an insensitive compass.
>
> Bruce
>
>
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-- 
Dr. Don Latham AJ7LL
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