Elekta Neuromag NM21283A, User Manual, Page: 43 / 85

Manual tuning 7
NM21283A-A 37
• If the system has been tuned earlier start from the current value of
the gate setting. Otherwise start from 150. Increase the value by the
right arrow key. The noise on the falling slope diminishes, see
Figure 7.2(b), until an irregularity appears as in Figure 7.2(c). Stop
increasing the gate at that point. In the actual SQUID, the noise
might be difficult to distinguish on the 10V-scale; the appearance of
a hump in the current vs. flux characteristics is a clear sign indicat-
ing that the gate voltage has been increased too much.
• Decrease the gate voltage step-by-step back until the hump has
completely disappeared and the current vs. flux characteristics looks
again smooth
5. Adjust the offset voltage so that approximately one quarter of the cur-
rent vs. flux characteristics is below the zero line and three quarters
above it. See Figure 7.3 (c).
6. Change Squiddler/Tuner settings to make a noise measurement. Now
you should see a signal trace on the raw data display screen or the
noise level trace of Tuner. The noise seen should be minimized by fine-
tuning the gate and offset. At this point, you can either use automatic
Figure 7.2 Gate tuning
Φ
a
I
B
Φ
a
I
B
Φ
a
I
B
(a)
(b)
(c)