Elekta Neuromag NM21283A, Руководство пользователя

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4 Troubleshooting
18 NM21283A-A
noise evolved during the tuning process. To do this select one channel to
be displayed.
Selecting a channel can be done in three ways:
• By entering the channel number into the channel number box of the
operating point controls. The number should be the ordinal number,
not the number in the sensor name. See Figure 2.1
• By inserting the channel name into the channel name box of the operat-
ing point controls. See Figure 2.1.
• By clicking the noise bar of the channel in the noise display with the
left mouse button while pressing the
C
TRL
key.
The display will now show the name of the channel and a curve that indi-
cates the noise level at each noise measurement made during the session.
You can scale the noise history display same way as the bar display. See
“Noise display” on page 15.
To change back to view all channels:
1. Enter 0 into the channel number box or
2. Click anywhere in the display with right mouse button having the
C
TRL
button simultaneously pressed down.
You can also view the previous operating point tuning values by clicking
with the left mouse button any particular measurement time. The bias, off-
set, and gate values are shown in the information area. This is especially
useful if the tuning has for some reason failed and the noise has been
lower with some other parameters than the current ones. You can read the
old parameters by clicking the noise history curve at the point where the
noise was low and then write the tuning values into the operating point
control area at the left top corner. This way you can easily get back the
good values.
Another typical usage for reading old tuning values is to check that some
abrupt change in noise is not due to change in tuning values but because
of a change in the sensor or environment.
The Command menu contains buttons that can be used to show noise his-
tories of all channels at the same time and to clear the history records.
4.3 Tuning selected channels
In some cases it may be useful to tune only some selected channels. This
is possible by “locking” some channels. When channels are locked they
are ignored in all automatic tuning operations. Locked channels are shown
as black bars in the noise displays and their noise values are not taken into
account when the average value shown on top of the display is calculated.