XIA Pixie-4 Express, User Manual, Page: 12 / 76

PIXIE-4 User’s Manual V2.69
©
XIA 2015. All rights reserved.
xii
In addition there are buttons to copy settings between channels and modules, and to extract
settings from a settings file. Two large buttons at the lower left duplicate the buttons to call the
S
TART
U
P
panel and the O
SCILLOSCOPE
.
3.2.1.1 Trigger Tab
The Trigger tab contains controls to set the trigger filter parameters and the trigger threshold ,
together with checkboxes to enable or disable trigger, to control trigger distribution (see section
7.2.1), and to set time stamping options for each channel. Except for the threshold, the trigger
settings have rarely to be changed from their default values.
The threshold value corresponds to ¼ of the pulse height in ADC steps, e.g. with a threshold
of 20, triggers are issued for pulses above 80 ADC steps. This relation is true if the trigger filter
rise time is large compared to the pulse rise time and small compared to the pulse decay time.
A pulse shape not meeting these conditions has the effect of raising the effective threshold. For
a modeled behavior of the trigger, you can open displays from the O
SCILLOSCOPE
and the L
IST
M
ODE
T
RACES
panels that show trigger filter and threshold computed from acquired
waveforms using the current settings. The threshold value is scaled with the trigger filter rise
time , therefore it is not limited to integer numbers.
Figure 3.2: The Trigger tab of the P
ARAMETER
S
ETUP
panel.
3.2.1.2 Energy Tab
The E nergy tab contains the settings for the energy filter and the subsequent computation.
These settings are most important for obtaining the best possible energy resolution with a Pixie-
4 system. The energy filter
rise time (or peaking time) essentially sets the tradeoff between
throughput and resolution: longer filter rise times generally improve the resolution (up to a
certain optimum) but reduce the throughput because more time is required to measure each
pulse. The pulse decay time
Tau is used to compensate for the decay of a previous pulse in the
computation of the pulse height. You can enter a known good value, or click on Auto Find Tau
to let the Pixie-4 determine the best value.