[time-nuts] cesium clocks..
cfharris at erols.com
Sat Jun 28 10:47:54 EDT 2008
Bruce Griffiths wrote:
> Chuck Harris wrote:
>> This is a chicken vs egg sort of problem. When I took apart the oven
>> on my 5065A rubidium, it looked to me as though the enamel insulated
>> nichrome wire developed a short about 50% into the coil, and wiped out
>> the transistor. It also heated the rubidium lamp hot enough to reflow
>> the solder on its circuit board and thoroughly char the PCB's epoxy.
>> I am not sure how the quartz ovens are wound (I suspect they are the
>> same), but with the rubidium ovens, the nichrome wire is wound as a
>> bifilar loop. This is done for two reasons, 1) to cancel the magnetic
>> fields, and 2) to make the start and finish wires of the winding happen
>> at the end of the oven where the terminals are.
>> -Chuck Harris
> An Ayrton-Perry style winding will also have low magnetic field.
There are no doubt hundreds of ways of achieving the same result,
but HP used a single layer bifilar winding of enameled nichrome wire
that was shorted on the far end.
When I replaced the oven winding on my Rubidium, I used a shielded coaxial
winding that was also shorted on the far end.
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