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FMCG/Data Acquisition with LabVIEW Software: Difference between revisions
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FMCG/Data Acquisition with LabVIEW Software (view source)
Revision as of 15:56, 25 August 2016
, 25 August 2016→DC-SERF mode data acquisition
(Created page with "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-null...") |
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## The R(out) value should match the chosen output resistor on the Y shell coils, most likely '''5000 Ω'''.
## 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<sup>-5</sup> T/A should be used.
# The only other settings that may need to be adjusted (though the default values are normally fine) are those under '''Run/Calib Settings'''.
## Regardless of the number of channels you are using, always leave '''Max Chans''' at '''4'''.
## '''Sample Rate (Hz)''' will set the FPGA acquisition rate. Sampling faster and then later downsampling (see below) can give better averaging and lower noise, but generally this type of noise is not what limits a measurement. '''100000 Hz''' is usually sufficient.
## '''Downsample (Hz)''' sets the downsampling rate. To save space and take advantage of signal averaging, the signals collected by the FPGA are downsampled by an averaging procedure which takes blocks of ''N'' points (where ''N'' = f<sub>sample</sub>/f<sub>downsample</sub>) and averages them to a single value. The Nyquist frequency of the downsample rate must still be larger than our bandwidth of interest (DC-100 Hz), thus we've generally set this to '''1000 Hz'''.
## The '''Run Time (s)''' will determine how long of a post-calibration time series is made. For noise-measurement purposes, usually a short scan ('''6-10 s''') is used. For a patient measurement, a much longer sample ('''60-180 s''') is more common.
## '''Chirp Iterations''' sets the number of calibration chirps sent to each magnetometer during the calibration. The responses to these chirps are averaged when calculating the response. Historically we have used '''5''' chirps for this purpose.
## I'm not 100% sure what '''Calib Freq Max''' does, but I think it should be set equal to the Downsample frquency, or '''1000 Hz'''.
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