Fluke Biomedical 8000 Victoreen User Manual
Page 28
Victoreen 8000
Operators Manual
2-16
Positive Measurement Delay
0
20
40
60
80
100
120
0
10
20
30
40
50
60
msec
kV
A positive delay
is used to skip
overshoots
Exposure time measured with positive delay
10 millisecond
delay
An example showing this use of a measurement delay can be found in troubleshooting Section 4.5--
Waveforms - Overshoot.
When a positive measurement delay is used in making a measurement in the Radio or Mammo mode,
the measured exposure time may be slightly longer than the exposure time between the selected %kV
points on the kV waveform. This is because the Model 8000 does not store the leading edge of the x-ray
output waveform when a measurement delay is used; it waits for the specified delay time before acquiring
waveform data. As a result of this, the %kV point on the rising edge of the kV waveform is not stored and
the time from exposure start to this point cannot be subtracted from the total time.
When exposure time is measured in pulses (1ØPULSE), use of a measurement delay may cause an error
in the pulse count because no pulses are counted during the delay time. The polarity of the delay has no
effect on pulse counting; for example, the number of pulses counted with a -10 millisecond delay is the
same as the number counted with a +10 millisecond delay.
When using a measurement delay in pulsed and single-phase applications, care must be used in
determining the correct delay period. If x-rays are detected at the end of the delay period, such as during
a pulse, the NERO mAx begins timing immediately. If no x-rays are detected at the end of the delay
period, such as between pulses, the NERO mAx waits up to one second for the beginning of the next
pulse to begin timing. As a result of this, the delay period should terminate prior to the first x-ray pulse to
be included in data analysis.
The NERO mAx Excel Add-In should be used to view radiation and kV waveforms to determine the
optimum measurement delay to use. Information on using the NERO mAx Excel Add-In to view
waveforms may be found in the NERO mAx Toolkit for Excel Instruction Manual. In addition, a digital
storage oscilloscope may be connected to the scope output on the rear panel of the NERO mAx readout
to view radiation output waveforms. Information on using the NERO mAx scope output may be found in
Section 1.6 of the NERO mAx instruction manual.