Pulse Height Spectroscopical Measurements
3.2.9 Offset
Offset is normally set automatically. The internal offset DAC can be adjusted such that the
input range goes from 0V to +U
max
or from -U
max
to 0V. Typically it is set such for positive
signals the base line is at 10% of the ADC range and for negative signals the base line is
at 90% of the ADC range.
35
Figure 16: Dependence of resolution on flattop setting using a NaI detector. As a NaI
detector exhibits slower rise times, a bit longer flattops yield best results.
0
1
2
3
4
5
5,0
6,0
7,0
8,0
9,0
FWHM @ 663keV [%]
Flattop [µs]
F
W
H
M
@
66
2k
eV
[%
]
Figure 17: Spectrum with extremely wrong offset setting. The spectrum just cuts off
somewhere in the middle.
