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FSS Review
28th August 2009
Overview of what I’ve worked on…
• Stabilising voltage supply 0-200V with a
Peltier Cooler
• Shield rubidium vapour cell from ambient
magnetic fields
• Testing system that will stabilise 110 MHz
Voltage Control
• Source providing a stabilised DC signal:
0-200V
• Varies due to the lock-in amplifier’s signals
• Stabilisation at 3 kHz level≡ no ambient
variations above 70 µV
• Temperature stabilisation of internal circuit
Peltier Cooler
•‘Heat pump’
•Connected to
Evaluation board to
control set voltage
and power
•NTC thermistor
•Progressive power
adjustment to see if
it operated efficiently
•Examined heat
sinks
•~-60ºC/V in linear
region
•Promising about
room temperature
• Recent tests examine shielding voltage
tuning control from environment
• PT100 thermistor sensitive 20-30°C
Temperature Control
aluminium box
PT100 temperature
sensor
to voltage
supply
to Peltier
cooler
4.7 Ω + 5% resistor
blocks
to Peltier
cooler
PT100 temperature
sensor
4.7 Ω +5%
resistor
probe tip encased in
aluminium grip
• Current on,
temperature rises
• Switched off, short
delay before starting
to decay
• Blocks led to less
extensive and slower
cooling
• Exponential decay
Temperature profile for aluminium unit
to encase the temperature sensor
Module with lid
• Temperature
span reduced
by factor of 3 Two blocks
•Time constant
increased by
factor of 9
Magnetic Field Shielding
• Lock into 5²S1/2 → 5²P3/2
• Spin angular momentum and external field
interaction produce energy level shifts
• 780 nm transition wavelength known less
accurately
• Test cylindrical shield lined with mu-metal
Results of test with Hall Probe
Fine tuning
frequency
•~110 MHz
•Opto-isolator: 31
FBs and 8 ABs
•Set DIP switches
on opto-isolator
•Apply small
voltages to ADC
•Spectrum Analyser
to locate peak
frequency
• On adjustment of voltage, we get ~-1.65 MHz/V
(maximum +1V)
• Limitations on voltage gives ~2.5 MHz tuning range
•Need to understand how opto-isolator input mapped to DDS
output
•Use of schematic diagram