Elekta Neuromag NM21283A, User Manual

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Basic measurements 8
NM21283A-A 43
C H A P T E R 8
Basic measurements
The tuning program is a versatile tool that can be used measure several
characteristics of a SQUID sensor. These measurements are used with
suitable adjustment routines to perform various optimization and charac-
terization operations. This chapter describes the basic measurements that
can be made.
The basic measurements available are the following:
I/Phi
Measure flux to current transfer function of the SQUIDs. This mea-
surement is used to view the SQUID characteristics, to measure
modulation depths for detecting flux trapped sensors, and to mea-
sure I-V curves of the SQUIDs.
Noise
Measure the white noise level of the sensors. This provides a fast
measurement of the white noise levels. Also the dc and line fre-
quency level of disturbances are measured. These can be viewed
manually or used in automatic noise level tuning.
FFT
Measure the spectrum of the sensor signal. This gives more detailed
information about the noise compared to the “Noise” measurement,
but is slower. Spectra can be shown on a display and noise values in
selected bands can be printed.
Signal
Measure a sample of the time trace of the sensor signal. This mea-
surement can be used to get a sample of signal to visually examine
its quality.
8.1 Setting the expert level
In order to use features described in this part, the “expert level” must be
set to 1. The setting defaults to zero but it is saved in the preferences of the
user so that once it has been changed it is kept from session to session.
To change the expert level setting:
1. Select File > Preferences from the menu. A dialog box containing all
the values regarded as preferences is popped up.