Elekta Neuromag NM21283A, User Manual

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NM21283A-A 17
4
C H A P T E R 4
Troubleshooting
This chapter describes how to deal with the most common problems with
the sensors. For a more detailed description of the manual tuning and
trouble shooting, see “Manual tuning” on page 33. Also some more
advanced features available are explained including viewing the noise his-
tory during the tuning and how to tune only some specific channels.
4.1 Basic checks
If the noise level is very high before fine tuning, try following operations
until the situation looks better:
• Check that the door of the shielded room is closed.
• Check that there is no strong source of disturbance inside the room,
like a moving patient.
• Load a well known tuning file. See “About saving and loading settings”
on page 14.
• Heat suspicious or all sensors. See “Heating sensors” on page 13.
Try tuning even if all previous fail, system may be just in some non typi-
cal state, like just after powering up the system or helium level may be
very low. If this does not help, you need to contact the system administra-
tion or to tune manually to find out what is wrong.
If all channels are mostly out of lock (small negative bars), check that
there is helium in the dewar. If not, inform the system administrator
immediately to prevent system to warm up completely. If there are
helium, try loading a known tuning file. If this does not help, manual tun-
ing is needed.
If just some channels are noisy, try heating the channels. See “Heating
sensors” on page 13.
4.2 Viewing noise history of a channel
If some particular channel is misbehaving in tuning, you can study the
noise values of a channel in previous noise measurements, e.g. how the