Performing measurements
40
4.7
Evaluation of the measurement results
The following three measured values appear permanently in the upper part of the
measurement screens, and can be used for an evaluation of the PD activity:
Level (in dB or dBµV)
The signal level is measured continuously, and the value displayed is updated every
second. The highest respective value measured during the last second is displayed. The
colour of the text indicating the value of the level is based on the thresholds entered in
the settings (see page 49).
Pulse per cycle (PpC)
The PpC value describes the number of pulses measured during a mains frequency
period (20 ms or 16.67 ms). The signals evaluated as pulses are determined in two
stages. Once noise suppression has been performed by the hardware filter, the pulses
that were not suppressed by the noise suppression are filtered again in the memory by
means of an algorithm, and the remaining number is used for the calculation of the PpC
value. Because this process is repeated multiple times before the display is updated,
this may also result in PpC values that are not integers.
Criticality
The values for the criticality can vary from 0 to 100, whereby 0 is considered absolutely
uncritical. An increasing criticality value means that a PD weak point is more and more
likely in the measurement object being examined. A distinction is made between
acoustic measurements and the TEV/HFCT measurements to determine the criticality.
The level measured and the PpC value are used as a basis for the calculation. Over the
course of the calculation, the level is standardised and evaluated using a weighting
factor, which is based on empirical values measured on different measurement objects.
The internal weighting factors are modified in accordance with the sensors used and
may, in part, differ. While the measured values are added up when acoustic
measurements are made, the values are multiplied when TEV and HFCT measurements
are made.
