microDXP Technical Reference Manual
Version 3.15
October 7, 2019
25
2.3.1.2
Decay Time: TAURC
If using an RC-feedback type preamplifier you must set the DSP parameter TAURC, which
is expressed in units of the ADC sampling period. The decay time constant
RC
in
microseconds is:
RC
[
s] = TAURC / DSPSPEED
Equation 2-1
In ProSpect, TAURC is set via the
Decay Time
field in the
Detector
tab of the
Settings
panel. Simply enter the desired value in microsecond units and press the
[Apply / Save]
button.
The RS-232 command to set and save TAURC to nonvolatile memory is 0x89. Please refer
to the RS-232 Command Specification for details.
2.3.1.3
Reset Interval: RESETINT
If using a reset-type preamplifier you must set the DSP parameter RESETINT to the reset
delay time or reset interval. This is the period after each preamplifier reset that the
microDXP waits before re-enabling data acquisition. RESETINT, expressed in
microseconds, is set based on the settling time of the preamplifier reset transient waveform,
which typically ranges from hundreds of nanoseconds to hundreds of microseconds.
Setting the delay shorter than the transient settling time typically degrades the energy
resolution and may even introduce ‘reset artifact’ events, i.e. a false peak, into the
spectrum. Setting the delay longer than necessary introduces additional processor dead
time, which will reduce the data throughput at high count rates.
In ProSpect, RESETINT is set via the
Reset Interval
field in the
Detector
tab of the
Settings
panel. Simply enter the desired value in microsecond units and press the
[Apply
/ Save]
button.
The RS-232 command to set and save RESETINT to nonvolatile memory is 0x8A. Please
refer to the RS-232 Command Specification for details.
2.3.1.4
Preamplifier Signal Polarity
Preamplifier signal polarity denotes the polarity of the preamplifier output signal. Please
review §4.1 for a description and figures relating to the preamplifier signal polarity.
Briefly, a positive polarity preamplifier produces a voltage step with a rising edge. The
DSP parameter POLARITY must be set correctly.
In ProSpect, POLARITY is set via the
Polarity
field in the
Detector
tab of the
Settings
panel. Select the desired polarity and press the
[Apply / Save]
button.
The RS-232 command to set and save POLARITY to nonvolatile memory is 0x87. Please
refer to the RS-232 Command Specification for details.
2.3.2 Advanced Processor Settings
The advanced processor settings enable and disable various Digital X-ray Processor
functions, and correspond to bits of the DSP parameter RUNTASKS. Typically these
settings should only be modified as directed by XIA support staff.
In ProSpect, the advanced processor settings are accessed in the
Advanced
tab of the
Settings
panel.
