4. Measurement Principles & Theory
Waveforms and Triggers
Piranha & QABrowser Reference Manual
2014-06/5.5C
82
Waveforms and Triggers4.5
To get an understanding of how triggers, delays, and windows work, take a look at the
waveform below. This is what happens during a standard exposure:
1. The radiation starts, i.e. it goes over the detector's lowest trig level.
2. The signal reaches 50 % of its maximum. This is the starting point for the irradiation
time calculation. (The level is user adjustable.)
3. The signal reaches its maximum.
4. The Delay time is reached. (User adjustable.) kV integration window starts.
5. The Delay+Window time is reached. (User adjustable.) kV integration window stops.
6. The signal goes below 50 % of its maximum. This is the end point for the Irradiation
time calculation. (The level is user adjustable.)
7. The radiation ends, i.e. it goes under the detector's lowest trig level.
8. If the signal has been below the trig level during all of Post delay, the exposure is
considered finished. All exposure readings are calculated.
Integrated signal (dose, mAs, etc.)
Is the integration of all signal which means the area below the curve above from point 1
to 7. During the measurement (exposure) the accumulated signal (dose, etc) is
displayed where applicable.
Signal rate (dose rate, tube current, etc.)
During the measurement the mean signal for the last second is displayed. When the
measurement (exposure) is over, point 8 above, the mean signal for the whole
measurement is displayed. This signal rate is calculated as all integrated signal (as
described above) divided by the irradiation time. If no irradiation time is possible to
calculate, the radiation time is used instead.
This means that for long measurements you may see a change in the rate value (dose
rate, etc) when the measurement is finished, if the signal level was changed during the
measurement.
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