Fluke Biomedical 8000 Victoreen - Manual (Page 78)

Victoreen 8000
Operators Manual
4-16
4.7 Waveforms - Self-Rectified
This example shows the effects of using an incorrect %kV setting when making measurements on a
single-phase, self-rectified dental x-ray machine. The x-ray machine was set for 70kVp, 15mA and 8
pulses (133 milliseconds). The NERO mAx %kV was set to 90% and no measurement delay was used.
Note that the measured exposure time is less than the actual exposure time. This is because the NERO
mAx finds peaks and calculates exposure time only between 90% of kVp on the kV waveform. Since the
first peak is 96.4 kV, any peaks below 86.8 kV (90% of the peak kV) will be ignored. Consequently, the
NERO mAx only bases its calculations on the first 4 peaks of the waveform. In this case, setting the %kV
to 1ØPULSE (pulse counting mode) is advisable since the generator’s exposure time is set in pulses. If
the exposure time is set in milliseconds, setting the %kV to a lower percentage or ZERO (zero crossing)
will also yield more accurate results. Generally, a %kV setting of ZERO or 1ØPULSE should be used for
single-phase, self-rectified x-ray machines.
The NERO mAx Excel Add-In should be used to view kV waveforms to determine the best %kV setting 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.
Exposure Results, High Sensitivity
kVp Avg kV Eff kV Peak mSec mR
40.4 39.9 42.2 10.9 2
kV Waveform
Self Rectified Dental
0
20
40
60
80
100
120
0 20 40 60 80 100 120 140
mSec
kV kV
4.8 Waveforms - Dental with Filament Preheat
The radiation waveform below is from a single-phase dental x-ray machine that utilizes a 14 pulse
filament preheat. The exposure time on this generator is set in pulses (instead of milliseconds) but does
not include the filament preheat pulses. For instance, when the exposure time control is set for 10
pulses, the generator actually outputs 24 pulses, 14 of which are filament preheat pulses.