Elekta Neuromag NM21283A, Руководство пользователя

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10 Measuring characteristics
54 NM21283A-A
Offs drift (Not used)
He level helium level.
Operating point settings, modulation depth, and fraction are updated in
every I-
measurement. Helium level is automatically checked when the
program starts. The flux quantum sizes can be estimated after a I- mea-
surement by selecting
Commands > Estimate phi0
from the menus. The
derivative information must be measured with a separate routine
described in next section.
10.2 Measuring derivative information
To measure the operating point derivative information:
1. Check that the current operating point is correct.
2. Check that all I- traces are on the screen, and none of them is very
near saturation (near highest or lowest signal level available).
3. Select Job > Meas. derivatives from the menus.
4. Press the “start button” and wait until the measurement is finished.
This measurement calculates also estimates for the flux quantum sizes.
Note that the dV/dB value is not needed in any of the current optimization
of characterization routines, and that the dV/dO value is independent of
the operating point, so in many cases the operating point does not matter,
as long as the signals do not saturate during the measurement.
10.3 Measuring and using current-voltage characteristics
To measure the I-V curve of the SQUIDs:
1. Check that derivative information is available, If not measure it (See
Section 10.2).
2. Select
Job > I-V curve
from the menus.
3. Press the “start button” and wait until the measurement stops.
The I-V curves are displayed using three curves: two showing the extre-
mum values, and one showing the modulation depth. A cursor cross hair
shows the current operating point in the graph. The curves are available
until the end of the session.
One usage for the I-V curves is a quick initial tuning. When the I-V
curves have been measured, one can set the operating point of the SQUID
by clicking a point in the graph with the left mouse button, having both
S
HIFT
and
C
TRL
buttons pressed.
Φ
Φ
Φ