indicated, such as the peak value of the measured LI/SI test voltage, the front and
tail time and occasionally the chopping time.
Basically, the measuring uncertainty is affected by both the hardware and the
software. Due to the comparatively high quantization rate of nowadays available
digital recorders, which is usually 14 bits and even more, as well as the high
sampling rate of 100 MS/s and above, the contribution of the hardware to the
measuring uncertainty is much lower than that of voltage dividers. As the quantization
error is given by 50 % of the least significant bit (LSB), this is approx.
0.012 % for a slow-rising signal for a quantization rate of 14 bit. However, the
deviation from the true value becomes much higher if a front-chopped LI voltage
according to Fig. 7.58 is measured using a sample rate of 100 MS/s. This is
because the voltage difference .d Vs between each sample is inversely proportional
to the sampling rate fs· For an assumed chopping time Tc= 0.5 μs and crest
voltage Ve, the voltage difference between each sample can be approximated by
Vs= Ve/(Tc ·ls)= Ve/50 = 0.02 ·Ve. Thus, the maximum deviation of the
measured value from the true value, which is given by 0.5 LSB, becomes 1 % of
the crest value Ve. Generally, it has to be taken care that the classical Shannon
theorem is accomplished, i.e. the sampling rate should exceed twice the maximum
frequency content of the signal to be measured where the analogue bandwidth