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APPENDIX A
Additional information for accurate kVp Measurement.
Height (distance from instrument to x-ray head)
This instrument can measure kVp accurately over the specified range and is
relatively independent of the height of the x-ray tube above the instrument. However,
there are limitations that must be taken into account. Please note, that when we
refer to height, we are discussing the height above the instrument to the actual x-ray
head, not the collimator. The intensity of any x-ray is proportional to kV, to x-ray tube
current (mA) and distance (height), so all three parameters are important. To simplify
this discussion, please refer to the chart below:
The chart below shows the maximum kV and mA. This instrument can accurately
measure at kV / mA combinations below the three curves at the particular height.
Two examples will clarify the use of the chart. If the user anticipates measuring a kV
of 100 at a tube current of 200 or 250 mA, The height should be 24 or 25 inches
(about 64 cm). If the user tries to make the measurement at a height of 12 or 13
inches (31 cm) the unit will read overscale. As another example, at 60 kV, the
instrument can measure up to 400 mA at a height of at least 9 inches (23 cm). Keep
in mind that for low mA, and low kV there is also a sensitivity issue, and that lower
heights will be helpful in getting readings at low kV / mA settings.
Here are some more guidelines:
