Fluke Biomedical 8000 Victoreen - Manual (Page 79)

4
Troubleshooting
Waveforms-Dental with Filament Preheat
4-17
Output Waveform
Dental With 14 Pulse Filament Preheat
0%
20%
40%
60%
80%
100%
120%
0 50 100 150 200 250 300 350 400
Exposure Time (ms)
Rel
a
ti
ve Rad
iati
o
n
Filament Preheat Pulses
Below is an example of what the NERO mAx “sees” when making a measurement without a
measurement delay on this type of generator. Note that the NERO mAx only acquires the two pulses
during the filament preheat period. This is because the intensity of the remaining filament preheat pulses
fall below the detectability limit of the NERO mAx. This causes the NERO mAx to stop acquiring data,
ending the measurement after the first two pulses resulting in a measured exposure time of 18.36
milliseconds. For this exposure, the x-ray generator was set for 10 pulses, which should result in a
waveform containing 24 pulses (including 14 filament preheat pulses).
Radiation Waveform
No Delay
0
50
100
150
200
250
300
350
400
450
500
0 2 4 6 8 10 12 14 16 18 20
mSec
c
ounts
Channel A
Channel B
To accurately assess this generator’s performance, a measurement delay should be used to skip over the
filament preheat pulses. The radiation waveform shown below illustrates the effect of using a -20
millisecond delay. Again, the x-ray generator was set for 10 pulses but the measurement delay caused
the NERO mAx to skip the first 2 preheat pulses, wait for the exposure to resume and only record the
desired portion of the generator’s output. For this x-ray machine, a delay from 20 milliseconds up to
approximately 230 milliseconds would yield the same measurement results. This is because the NERO
mAx waits for up to one second after the delay time has elapsed for its radiation detection threshold to be
exceeded, initiating data acquisition and measurement.