150
edits
FMCG/Data Acquisition with LabVIEW Software: Difference between revisions
Jump to navigation
Jump to search
FMCG/Data Acquisition with LabVIEW Software (view source)
Revision as of 21:32, 29 August 2016
, 29 August 2016no edit summary
(→Z-mode) |
No edit summary |
||
|
The setup and data acquisition for Z-mode is a little more involved, though not terribly so. Generally I do all of my field nulling and optimization in DC-SERF mode. Only small adjustments are then required to get Z-mode up and running. The process is aided by a "test" LabVIEW VI which allows one to play with the Z-mode parameters to optimize. All of the following will assume the magnetometer(s) are properly nulled and the laser powers and detunings are optimized.
==Z-mode Setup==
# Since Z-mode will involve applying a 1 kHz modulation to the atoms, and then using the LabVIEW code to demodulate that signal, it's necessary that there not be any low pass filters below 1 kHz between the photodiodes and the input to the ADC on the FPGA. It's likely that a ~300 Hz low pass filter was applied to data being taken in DC-SERF mode. Make sure to either move this filter up in frequency (10 kHz recommended for a 1 kHz modulation frequency) or disable it completely.
# Because the Z-mode modulation is quite large, it is necessary to reduce the output resistors on the shell coils. Using the 500 Ω resistors is sufficient for 1 kHz modulation, 2 kHz and above will likely require using the 100 Ω resistors. Remember that to maintain the correct field coupling, all channels should be adjusted to use the same Z output resistors.
# In order to allow the modulation to be sent to the current supplies, the '''Z-mode''' switch on the front of the main control box must be switched to '''ON'''.
# In the '''FPGA Magnetometer''' project, in the '''Main Programs''' folder, locate the '''XY Modulation+Z-mode v1.5 (Host).vi''' program. This program will help you set up and optimize Z-mode detection.
## First, make sure all of the buttons under '''Chan Settings''' are disabled, and click the LabVIEW '''Run''' arrow.
## Now, decide on a Z-mode frequency. Commonly used values are 1 kHz and 2 kHz. Enter your choice under '''Channel 1''' in the '''Z-mode Settings''' box. As the text at the top of the front panel notes, when operating in Z-mode, all four channels' z-modulation fields will be output with the frequency of Channel 1 - the other three frequency boxes (which are by default set to '''0''') are useless. For now, leave the '''Amplitude (V)''' sliders where they are. They can be varied later.
## Once you've decided on a frequency, in the '''Chan Settings''' box, click the buttons in the '''z-mode?''' column corresponding to the channels you wish to measure. You should notice the modulation "fuzz" appear on the scope when you do so. If not, make sure all of your connections are right, the '''Z-Mode''' switch on the main box is set to '''ON''', and there are no excessive low-pass filters on the SRS I-V converters.
## Use the room coils to apply a low-frequency (~ 20 Hz) signal in the '''X''' direction. You should now see the fuzz being modulated at that frequency. To optimize it may help to set up another function generator to output a sine wave at the modulation frequency and use the SYNC output to trigger the scope. Zoom in so there are a few cycles of the 1 kHz frequency visible on the scope. If done correctly, you should see a row of 20 Hz-modulated "bulbs" when looking at the magnetometer output.
## 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.
##
| |||