Elekta Neuromag NM21283A, User Manual

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3 Basic tuning operations
12 NM21283A-A
If the noise values look good you can press the “stop button”, exit the pro-
gram, and go on measuring with the acquisition program. If not, proceed
to tune the channels. This is explained in the next section.
3.2 Fine tuning
Normally the program is used to tune slight offsets from a good operating
point that is set after the installation of the system or thermal cycling. This
is referred as fine tuning.
Before tuning one should measure the noise level. See “Measuring the
sensor noise level” on page 11. If it is abnormally high, check that the
door of the shielded room is closed. If the noise still looks very high, or
some channels are saturated (small black bars appear in the display), try
heating the noisy channels. See “Heating sensors” on page 13. If the over-
all noise level is very high, you probably need to load suitable tuning set-
tings from a file before doing the fine tuning. See “About saving and
loading settings” on page 14. Contact your administrator to find out the
correct tuning file.
When the channels seem to work properly, but the noise level is higher
than normally, running the auto-tuning routine of the tuning program
should be able to fine tune the noise levels to normal.
To tune sensors automatically:
1. Start a noise level measurement.
2. Press the “start button” again (the same button that was used to start the
noise measurement). The button should now have text
Tune
on it.
3. Wait until the tuning has obtained good noise values. (Or, hopefully
not, failed to tune the noise.) The tuning does not stop automatically. It
continues until it is explicitly stopped.
4. Press
Stop tuning
button.
5. Press Stop collector button (the same stop button as before which now
has different text on it), to release the acquisition system for normal
measurements.
Warning: All measurements should be made with the doors of the
shielded room closed.
Warning: Heat single noisy channels before tuning. Tuning may success
even with flux trapped SQUID but then the tuning is off when the sensor
is later returned to its normal state.