4.1 Method for measuring technical factors
The measuring method with non-invasive instruments, for example kV
p
/t
meter, is accepted, even if it generally provides less accuracy. In fact, the
measurement of the high voltage at the tube with non-invasive
instruments is closely correlated to the method selected by the
instrument manufacturer; in general, this method is more inaccurate
than the direct method and may also require two subsequent exposures.
In the same way, the method of measuring the anodic current with the
indirect method is affected by systematic errors, as they are often based
on the measurement of the current/time product, dividing the
measurement by the time measured with the said method.
• High voltage value at the tube (kVp)
The kVp value is defined as the stationary value of the high voltage
applied at the tube that is stabilised under load after the pre-heating
time.
Measure the value of the kVp with a non-invasive instrument (with
2% accuracy), setting the exposure time to 1 second.
• Measuring the exposure time
The exposure time must be measured using a non-invasive
instrument.
In compliance with standard IEC 60601-2-7, the exposure time is
measured as the interval of time between the moment in which the
high voltage has reached for the first time a value equal to 75% of the
peak value and the moment in which it goes down below this value.
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