Fluke Biomedical 8000 Victoreen - Manual (Page 29)

2
Operation
Modes of Operation
2-17
Using %kV and Exposure Time Measurements
The %kV setting determines how the NERO mAx measures exposure time. When 75%, 80%, or 90% kV
is selected, the NERO mAx measures exposure time between the 75%, 80%, or 90% points on the kV
waveform. For best results when selecting 75%, 80%, or 90% kV, make sure that the percentage of the
kV waveforms peak kV is within the selected filter range. If the %kV or the measured kV is too low, a
"%kV TOO LOW" error message will be displayed.
When zero crossing (ZERO) is selected, the NERO mAx measures radiographic exposure time from the
moment x-rays are detected by the NERO mAx until they are no longer detected. This corresponds to the
time between first and last passage through the NERO mAx internal radiation detection threshold of the
channel A radiation signal. When using zero crossing, measured exposure times may be lengthened by
cable charging or by output filter capacitors used in some single phase generators to smooth the
generator’s output waveform.
When 1ØPULSE is selected, the NERO mAx counts the number of x-ray pulses in a pulsed or single-
phase radiographic exposure. Pulses are detected by counting each passage through the NERO mAx
internal radiation detection threshold of the rising and falling edges of the pulses on channel A radiation
signal. This is primarily for use with single-phase full and half-wave rectified generators. Pulse counting
may not function properly on single-phase generators employing output filter capacitors to smooth the
generator’s output because the generator’s output may not drop to zero between pulses. Additionally,
use of a measurement delay may cause an error in the pulse count. For more information, see "Using a
Measurement Delay".
When calculating kVp average, the NERO mAx only includes peaks that are above the selected %kV in
the kVp average calculation. When ZERO or 1ØPULSE are selected, the NERO mAx includes all
detected peaks in the kVp average calculation.
2.5.2 Mammo Mode
Mammo mode is used to make measurements on mammographic generators. Mammo mode
simultaneously measures kVp, exposure time and mAs from a single mammographic exposure.
Exposure time in the Mammo mode is measured between the first and last passage through the 90%
points on the kV waveform. A measurement delay of up to 999 milliseconds may be used to delay the
start of kV data acquisition in order to skip over waveform anomalies at the beginning of an exposure.
See "Using a Measurement Delay" (at the end of this section) for more information on using a
measurement delay.
To make a mammographic measurement
Make sure that the NERO mAx is turned off. Plug one end of the NERO mAx’s detector cable into the
NERO mAx detector. Plug the other end of the detector cable into the NERO mAx’s detector connector.
Insert the MAMMO filter card into the detector and place the filter card in the correct position for the x-ray
tube target material. Place the NERO mAx detector on the x-ray table with the top of the detector facing
the x-ray tube. Position the detector so that the detector is centered in the beam and is aligned with the
x-ray tube axis. If mAs measurements are to be made, plug the mAs cable into the NERO mAx detector’s
mAs input and connect the mAs leads to the generators mAs terminals. For more information on
positioning the NERO mAx detector, see section "Positioning the Detector".
WARNING
Extreme caution should be used when making
connections to the mAs terminals of the X-ray
generator or detector. Improper connections may
result in injury, damage to the NERO mAx, and/or
damage to the x-ray generator.