microDXP Technical Reference Manual
Version 3.15
October 7, 2019
31
In ProSpect select the
MCA
tab in the
Main
panel.
2.7.1 Starting a Run
Data acquisition runs can be configured to automatically terminate the run after a preset
time or number of input or output counts has elapsed, as described below in §2.7.5. By
default (i.e. PRESET = 0) the run continues until a ‘stop run’ command is issued.
In ProSpect, simply press the
[Start Run]
button. Normally, spectrum data and statistics
are cleared at the beginning of a data acquisition run. To preserve data and statistics from
the previous run, check the
Resume
checkbox before pressing the
[Start Run]
button.
The RS-232 command to start a data acquisition run is 0x00. Please refer to the RS-232
Command Specification for details.
2.7.2 Stopping a Run
By default (i.e. PRESET = 0) a run in progress continues until a ‘stop run’ command is
issued. The microDXP can be configured to automatically terminate until a preset time or
number of input or output counts has elapsed, as described below in §2.6.5. In such cases
the ‘stop run’ command overrides the run preset.
In ProSpect, simply press the
[Stop Run]
button.
The RS-232 command to stop a data acquisition run is 0x01. Please refer to the RS-232
Command Specification for details.
2.7.3 Reading a Spectrum
The ‘read spectrum’ command supports readout of any contiguous region of the MCA data,
extending, of course to the entire spectrum. Each MCA bin is represented in DSP program
memory as a 24-bit word (i.e. 3 bytes), supporting up to 16,777,215 counts per bin. In some
cases (i.e. for short runs and/or low count rates) the upper bits of each bin word will always
be zero. The readout speed can be increased by opting to read out a fewer number of bytes
per bin, or DEPTH. At DEPTH=2 up to 65,535 counts per bin are supported. At DEPTH=1
up to 255 counts per bin are supported. Note: If the number of counts in a bin exceeds the
DEPTH, the resulting distribution will display sharp discontinuities. The data is however
always stored internally in the DSP at the full 24 bits. It is thus not necessary to restart the
run when the DEPTH is exceeded: Simply change DEPTH and re-read the spectrum.
In ProSpect, the spectrum and statistics can be updated automatically or manually. Check
the
Continuous
checkbox for automatic updates. If the checkbox is unchecked press the
[Update]
button to manually update the spectrum and statistics. Select
Save MCA Data…
from the
File
menu to save the data to file in ASCII format.
The RS-232 command to read the MCA spectrum is 0x02. Please refer to the RS-232
Command Specification for details.
2.7.4 Reading (and Calculating) the Run Statistics
The ‘read run statistics’ command retrieves the
Livetime
(48-bit LIVETIME) of the
triggering filter, the
Realtime
(48-bit REALTIME), the number of input counts (32-bit
FASTPEAKS) and the number of output
Events
(32-bit EVENTSINRUN). These
parameters can be used to directly calculate the input count rate (
ICR
), output count rate
(
OCR
) and the
Deadtime
percentage:
