Elekta Neuromag NM21283A, Руководство пользователя

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Manual tuning 7
NM21283A-A 33
C H A P T E R 7
Manual tuning
This chapter deals with the manual tuning procedure. We assume here that
the user is familiar to SQUID working principles (see “Principles of
SQUID operation” on page 27) and to basic Tuner operation (see “Basic
Usage” on page 3). The manual tuning can be done using two different
programs and both are described here only as much as it is needed to per-
form the manual tuning.
7.1 Need for manual tuning
When the system is cooled down for the first time, a manual tuning must
be performed for all channels. The tuning settings are strictly valid only
for a certain SQUID sensor-electronics card pair. Therefore, if a SQUID
sensor is changed or if an electronics card is changed, new settings must
be searched manually. Note that each electronics card drives 12 SQUIDs;
if a card is changed, all channels belonging to that card must be adjusted.
After major service operations, e.g., warm up – cool down cycle, it is
advisable to check the tuning settings by going through the manual tuning
cycle.
If you encounter degraded performance, try first heating (see “Heating
sensors” on page 13), then loading a previously loaded setting file that
corresponds most closely to the actual Helium level (see “About saving
and loading settings” on page 14). If that does not help, point of operation
should be tuned manually.
7.2 Tools for manual tuning
Since Vectorview flux locked loop electronics are digital, all tuning dis-
plays are computer generated and no physical tools are needed. What is
needed is a x-y -display to show the flux vs. current (I- ) characteristics,
a display to show real time signal or noise level, and controls to alter the
bias, offset, and gate settings of a SQUID. There are two tools for manual
tuning. You can either use the SQUID tuning program in expert level 1, or
Squiddler, which is a small controller dialog accessing the electronics set-
tings directly. The SQUID tuning program provides more auxiliary func-
tionality to ease the tuning, but the Squiddler works faster (has better
response times) since it does not make any measurements. Squiddler is
used in conjunction with the normal acquisition program to make the
required measurements. The tuning program is used for both measuring
and adjusting.
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