FMCG/Data Acquisition with LabVIEW Software

This part of the guide will cover the actual data acquisition with the LabVIEW software. It will assume the user has N operational magnetometers which have been field-nulled and optimized. The first part will explain how to use the program to acquire data in DC-SERF mode, the second part in Z-mode.

DC-SERF mode data acquisition

In DC-SERF mode, the magnetometers are sensitive to magnetic fields in the Y direction. The program is set up to calibrate the magnetometers' response using the shell-mounted Y coils, and then collect data.

1. From the FPGA Magnetometer.lvproj project, under Main Programs, open the Magnetometer_16.1_chirp-calibration.vi program.
2. The front panel can be somewhat intimidating, but a lot of it is not used. We'll hit on the parts that are necessary to take a measurement.
3. In the top left, under Y Channel Settings are controls for the calibration. Depress the yellow Select? button under the channels that you wish to measure. The other three inputs will tell the program how large of a chirp signal should be sent to the magnetic field coils, as well as calculate the size of the field in magnetic field units for calibration purposes.
   1. The Amp. (V) determines the amplitude of the chirp. This voltage will be output from the FPGA to the current supplies. This voltage must be at least .02 V for noise reasons. To keep electronic noise down, large SR570 I-V gain is generally used so using too large of a calibration signal will cause the magnetometer to rail during calibration. Generally I keep this at .02 V.
   2. The R(out) value should match the chosen output resistor on the Y shell coils, most likely 5000 Ω.
   3. The Field Coils input simply points the LabVIEW program to a particular coil calibration number which calculates how large of a calibration field (in T) is being applied. This should almost always be left on Printed Y - Coil, which tells the program that a coil calibration of 4.3 x 10^-5 T/A should be used.