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FMCG/Operating procedure: Difference between revisions
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# '''Nulling notes'''
## During the above two steps, the DC value of the magnetometer signal will likely swing wildly. Use the '''Y''' current supply to attempt to keep the DC value close to zero. Actually, it's a decent idea to keep sweeping the Y field anyway...as the X and Z fields get closer to zero, the dispersive shape when scanning the y field should become more and more apparent.
## It is possible for the response to [X, Z] fields to decrease even if the [Z, X] fields are not approaching zero. In fact, if the transverse fields grow huge, the response to the transverse fields will grow small simply because the magnetometer gets worse at detecting **any** field. During the nulling procedure, when you're approaching the "true null point", the response to the transverse field will actually "slowly" get ''larger'' as you approach the optimum point and then "quickly" shrink to a very small value, only to begin quickly increasing when the optimum point is passed. If instead, you're approaching a "false null point", the response will "slowly" get smaller but never quite reach the "very small response value" of the true null point.
## As you continue to iterate and bring the X and Z fields get closer to their null points, the process will get easier and the wild DC swings associated with adjusting the transverse fields will get smaller (obviously, as the magnetometer is also becoming less sensitive to DC transverse fields). You can probably begin increasing the I-V gain and decreasing the applied field (on the BK fungen).
# Once the optimum '''(X,Y,Z)''' fields are applied, check to see if larger output resistors can be used. Use a DMM to measure the DC voltage on the monitor outputs (white BNC ports). The voltage range on the monitor output is roughly '''-25 V to +25 V''' on each channel. So, for example, if 1 kΩ resistors are being used and the monitor voltage reads 2 V, a switch to the 5 kΩ output resistors is possible as long as the DC voltage is increased to 10 V (maintaining the same current). Larger output resistors have historically given us lower magnetic noise (leading us to believe we are voltage-noise limited on the current supplies).
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