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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)
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## The program can be set up to output the ''demodulated'' signal so that signal can be optimized. To do so, locate the row of four switches on the FPGA breakout box near the red '''ANALOG OUT''' BNC ports. Flip the switch(es) up for the channel(s) you are optimizing. This will connect the FPGA AO channels 0-3 (normally outputting the chirp) to the top row of red BNC ports. Connect these outputs to a second scope triggered by the source of the 20 Hz modulation (likely the BK precision generator). In the LabVIEW program, make sure that '''AO Type''' is set to '''X Magnitude''' and then in the '''Chan Settings''' box, click the buttons in the '''chans?''' column to send the demodulated X Magnitude signal to the second scope.
## The optimization and field-nulling processes are a little different than the DC-SERF mode process, but if you're optimized for SERF operation, you'll be pretty close to the required settings for z-mode. Essentially, you goal is to have the modulation "bulbs" all be roughly the same size and in a nice straight line with a DC value near zero.
### First, optimize the z-modulation amplitude by dragging the '''Amplitude (V)''' bar up and down until the size of the demodulated signal on the second scope becomes largest. The reference phase can be optimized likewise. If you're optimizing multiple channels simultaneously, you'll probably find that you'll have to iterate between channels with the field amplitudes - the decoupling matrix only works with the applied DC nulling fields, so the Z-mode fields from one channel will affect the size of the modulation field the others.
### To set the
## Once you are satisfied with the performance of each channel, note all of the modulation amplitudes and demodulation phases. The amplitudes can be copied directly into the main magnetometer program under the '''Modulation Settings''' box. Note again, the modulation frequency applied to all channels is the one in the top (channel 1) box, all others are irrelevant. Unfortunately, the size of the FPGA memory does not allow for independent demodulation phases in the main program, but generally they are all pretty close, so pick an "average" of the values and put it in the '''reference phase''' box below the '''Modulation Settings''' box.
## Click the '''STOP''' button in the '''XY Modulation+Z-mode v1.5.vi''' program. You can leave the program open. '''If you were using the analog outputs from the FPGA box to output the demodulated X signal to the scope, make sure to flip the corresponding Analog Output switches DOWN to reconnect the analog outputs (which will be sending chirp signals now) to the current supplies).'''
# With that, you're ready to take data in Z-mode. To enable z-mode, you need to select the appropriate channels in the '''X Channel Settings''' box on the far left. This will tell the program that both x and y directions must be calibrated before taking a noise measurement. The '''Field Coils''' should be set to '''Printed X - Coil''' and the R(out) will likely be '''5000 Ω'''. By default, the chirp size is '''0.05 V'''. The larger chirp size is to compensate for the fact that the printed X coils have more than a factor of two smaller current-to-field calibration, as well as the fact that in Z-mode, the response to X fields is often smaller than the response to Y fields.
# Now you're ready to go! Click the '''Run''' button to start the program.
## Again, the first prompt will be one regarding the heaters. Click '''Yes'''.
## You'll first be asked if you want to calibrate the Y coils. Again, make sure the '''Chirp''' selector on the main box is flipped to '''Y''' and the
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