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Z31980_00_03
Configuration
DAC-Value:
Shows the current value of the Fine DAC. If the PI control is active, this is an indication
of what the lock is actually doing. When the lock is stable, this value should be close to
the centre of it operating region (ie. around 2000) and can vary by up to ±10 counts
(each count represents 0.025 Hz). When Auto-ranging is anabled, when the fine DAC
gets to below 500 or above 3500, the coarse DAC is incremented or decremented by
one step, to bring the fine DAC back nearer the center of its operating region
Magnitude
This is a “magnitude” value of the lock signal and corresponds to the sum of the squares
of the real and the imaginary part. Since there is no square root, taken at this point, it is
strictly speaking a power value.
Real
This is the real part of the lock signal, which is used for the lock monitor
Imaginary
This is the imaginary real part of the lock signal, which is used for the PI control
Search
This performs a search over the entire Fine DAC range looking for the maximum signal
in the 100 Hz or so (1H) covered by this range.
The Wide DAC will stay constant during this search function. It searches the range given
by “sweep width” (default 4000) around the “Field DAC center” (default 2047) value
in “steps” (default 40) number of steps, waiting dwell time (default 500ms) at each step.
At the end of the search (which with the above defaults takes about 20 seconds), the
maximum signal found is displayed in “Magnitude Max” and the DAC value shown in
DAC val. A search is considererd successful, if the maximum value is above the value
set in Minimum Amplitude (Default 100000), and if the corresponding DAC value was
between 500 and 3500 (i.e. not too close to its limits). If the search was unsuccessful,
the “AUTO LOCK procedure of TopSpin varies the coarse DAC in steps of ±10, ±20, ±30,
±40 and ±50 in order to find a good lock. If there still is no good lock result, the automatic
routine flais, and the lock has to be found manually using the sweep mode.
Sweep
This function sweeps the wide DAC with a range of “sweep width” (default 1000, i.e.
about 5 kHz range) around the currently set “Field DAC Wide” value, in steps of “step
size” (default 1).
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