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FMCG/Operating procedure: Difference between revisions
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=FPGA and Arduino "Reset"=
Both the FPGA and Arduino microcontroller tend to behave somewhat strangely after a computer restart, so it is a good idea to "reset" both of them before beginning.
# Open up the Arduino code. The file is in the upper-right corner of the desktop and is named '''Decoupling Code (with LCD)'''. Click the '''right arrow''' (under the "Edit" menu) to upload the code to the Arduino.
# Once you receive an "Upload Complete" message in the program, the code is ready. The LCD screen should read all zeroes (or whatever values the user specified). However, because of a feature of the code, the outputs of the Arduino (and consequently, the current outputs of the current supplies) are all sent to the rail.
# To truly set the currents to zero, turn any one of the '''Field Adjust''' knobs on the current supply box by one click. Then turn the knob ''back'' one click to return all supplies to zero.
## A PreScan Dwell of '''10 s''' will allow the laser temperature to stabilize at the start temperature before the ramp begins.
# Clicking the LabVIEW '''Run''' button will begin the ramp. Results for each trace will be plotted in the XY Graph window. A .dat file containing all of the data collected (Thermistor resistance and 4 channels of voltage data) is recorded on the file in '''Path Out'''.
=Balancing the Detector=
Before magnetometry can be performed, the detector on each channel should be balanced, ie adjusted so equal light is incident on each photodiode. '''Make sure the pump laser is off when the following is being performed'''.
# On the array, switch the detectors to DIFFERENCE mode. This is the middle set of header pins, and is indicated by a '''Δ''' or '''-''' symbol. The signal being sent out of the room to the current to voltage converters is now the ''difference'' in currents from the two photodiodes.
# Return to the I-V converters and dial the gain way up to increase sensitivity. For ~500 μW of total laser power, 1-2 μA/V is appropriate. If the detectors have not been balanced in some time, the imbalance of laser light will likely cause the output of the I-V converter to rail.
# Connect a long BNC cable (the one passing through the port of the MSR is idea for this) to either the output of the I-V converter or to the green "monitor" BNC port of the detector you'd like to manage.
# Take a DMM into the room and plug the other end of the BNC cable into it. Switch it on to DC-voltage mode. Now, carefully adjust the balance of the detector by rotating the body. This can be '''VERY TOUCHY'''. At this level of gain, I usually try to get the voltage level down to ±0.2 V.
# Repeat on the other detectors as needed.
=Nulling
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