Fluke Biomedical 8000 Victoreen - Manual (Page 67)

Troubleshooting
Modes of Operation
4
4-5
Measured mAs is not what is expected
The measured mAs may appear to be low when the NERO mAx only “sees” only part of an x-ray
exposure. This happens when exposures are made near the NERO mAx’s minimum detectability and
only a portion of the exposure is above the instrument’s threshold. This also results in short measured
exposure times. To remedy this situation, switch to high sensitivity, switch to the next lower kV filter
range (if the kV is still within range) or decrease the distance between the detector and the x-ray tube.
See Section 4.6--Waveforms - Partial kV Waveforms.
The measured mAs will also be low if the x-ray exposure stops for more than 20 milliseconds. When this
occurs, the NERO mAx assumes that the exposure is complete after 20 milliseconds and proceeds with
data analysis.
4.2.2 Mammo Mode
For an explanation of error messages, see Section 4.3--Error Messages.
All of the explanations of perceived anomalies that may occur in the radio mode also apply to the mammo
mode. Please refer to those listed for the radio mode in addition to those listed for this mode.
Measured kV is not what is expected
In the mammo mode, improper menu selection of target or filter will result in inaccurate kVp
measurements. The amount and type of filtration in the x-ray beam greatly effects measured kVp in the
mammo mode. The filtration that the NERO mAx is calibrated with is printed on the NERO mAx
calibration report.
Measured exposure is not what is expected
Incorrect menu selection of target or filter may result in inaccurate exposure measurements. This is
because exposure measurements made in the mammo mode are corrected based upon calculated kV
and if the calculated kV is incorrect, the calculated exposure may also be incorrect.
4.2.3 Fluoro Mode
For an explanation of error messages, see Section 4.3--Error Messages.
The NERO mAx says “MAKE EXPOSURE” even after the stop key has been pressed
This can occur when the x-ray beam intensity is below the NERO mAx’s detectability limit. To overcome
this, switch to high sensitivity, switch to the next lower kV filter range (if the kV is still within range) or
decrease the distance between the detector and the x-ray tube.
This also occurs in the pulsed fluoro mode when pulse rates are less than 1 pulse per second. When this
happens, the displayed exposure per pulse may occasionally drop to zero also. To correct this problem,
increase the pulse rate above one pulse per second.
Measured kV is not what is expected
Inaccurate kVp measurements will result if the NERO mAx detector is not aligned properly in the x-ray
beam. The NERO mAx detector should be aligned along the axis of the x-ray tube, located in the center
of the beam. Also, the top of the detector must face the x-ray tube. For fluoroscopic use (under table x-
ray tubes), this usually means that the detector must be turned upside down. The beam should be
collimated to the detector. See section "Positioning the Detector" for more information.
The amount and type of filtration in the x-ray beam also effects measured kVp. The inherent filtration that
the NERO mAx is calibrated with is printed on the NERO mAx calibration report.
Inaccurate kVp measurements may occur when using high sensitivity with a filter card kV setting that is
too high for the kVp being used. Under these conditions, the NERO mAx may detect enough scatter to
induce it to take an exposure and calculate kVp incorrectly. To remedy this situation, switch to the next
lower filter card setting.