GBS Elektronik MCA-527 - Manual (Page 47)

Pulse Height Spectroscopical Measurements
3.6 Measurement Time Presets
For non-infinite measurements, the MCA527 offers 4 choices to limit the measurement
time.
Real Time
The simplest method. The measurement will take as long a the time given. This is also the
choice if doing repeat measurements.
Live Time
Often chosen if quantitative evaluation of the spectrum is done. Very similar to real time,
only with high count rates live time measurements will take a bit longer than real time
measurements, as live time is the real time with the dead time subtracted.
Integral
The measurement will continue until a certain number of counts in the spectrum or in a
ROI are achieved. This is a choice if a certain statistics is needed in a spectrum.
Area
The measurement will continue until a certain net area of a peak is reached. This is a
choice if the area of a distinct peak has to be measured with a defined accuracy.
3.6.1 Dead Time Calculation
Dead time calculation is a crucial task when doing high rate measurements and still
expecting accurate quantitative measurement results.
Dead time with MCA527 has several components. At first there is the limited pulse pair
resolution of the trigger filters. The pulse pair resolution (the minimum time distance
between two subsequent events which is needed to count them separately) depends on
trigger filter and has to be found out experimentally.
Next is the time interval which corresponds to the length of the digital filter within which no
other pulses are tolerated for correct calculation. Here different subsequent pulses can be
distinguished, but are rejected as pile-up.
Also the time where the input signal is out of range has to be considered as dead time. At
last, also the time where the processor is busy with other tasks and cannot process
events is dead time.
3.6.2 Repeat Mode
Repeat mode is basically a feature realized by software. It comprises just starting a new
measurement after the previous one has finished. Number of repetitive measurements are
determined by application software.
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