Chapter 4 Unit Setup
80
The DISC#_###.CSV files containing the Discriminator Plot data contains the
following:
a. 1
st
row “Discriminator Plot”, Collect Time
b. 2
nd
row has channel number, 3
rd
column for Gamma description
c. 3
rd
row “Detector”, detector number
d. 4
th
row has High Voltage and ULD
e. 5
th
row has Dwell Time
f. 6
th
row has “Board ID”, board ID number
g. 7
th
and 8
th
rows have data column labels
h. 9
th
row to end has discriminator plot data (Discriminator Voltage and
Count Rate)
Upon opening the screen the high voltage for all detectors are turned on and
stabilized. Messages “Ramping HV” and “Stabilizing Detector” are shown on top
right of graph and the former appears until HV is ramped for all detectors (or 30 s
elapses). The latter appears for 2 s after HV is ramped.
The most recent plot is retrieved and displayed for the detector and channel currently
selected. The Date/Time, High Voltage, and Dwell Time in effect at the time of the
plot are indicated at the bottom right, along with data points (Discriminator Voltage,
DAC setting and measured Count Rate). Step through the data points by changing
the Discriminator setting (+/-, Ctrl +/- keys); however be sure to restore the setting
before exiting, for example by pressing Ctrl+F7.
The Discriminator Plot test sweeps the discriminator voltage through the specified
range in increments of Step Volts and plots the count rate at each setting. At low
settings, the count rate is high as electronic noise and detector noise are counted as
pulses.
Line Items
Discriminator: sets the discriminator voltage for normal operation. This value is
displayed as a vertical yellow line. The default is 0.1 V for Channel 3 Gamma.
Minimum Volts: Starting discriminator level for the sweep (default is 0.000 V).
Maximum Volts: Maximum discriminator level for the sweep (default is 0.250 V).
Step Volts: Voltage increment between data collection points (default is 0.005).
Dwell Time: Time spent at each voltage level during sweep (default is 1.000).
Maximum Rate: Sets a cut-off count rate for the display (default is 1000 cps).
Scale Type: Choices are “Linear” or “Sqrt” (Square root). Default is Sqrt.
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