HT instruments PQA820 - Manual (Page 30)

PQA820
EN – 29
12.4. INFORMATION ON THE MEASURING METHOD
The instrument is capable of measuring: voltages, currents, active powers, inductive and
capacitive reactive powers, apparent powers, inductive and capacitive power factors and
analogical or pulse parameters. All of these parameters are analyzed in a completely
digital way: for each phase (voltage and current) 128 samples per period are taken, then
repeating this operation for 18 consecutive periods.
12.4.1. Integration period
Saving all data would require a considerable memory capacity. Therefore, a saving method
has been chosen that, although supplying significant data, would allow compression of the
information to be saved.
After a time period called Integration period, which can be set upon configuration to a
value between 5 seconds and 60 minutes, the instrument extracts the following values
from the sampled values of each quantity to be saved:
 Minimum value of the quantity in the integration period (harmonics excluded)
 Average value of the quantity (intended as arithmetical mean of all values recorded in
the integration period)
 Maximum value of the quantity in the integration period (harmonics excluded)
These three values only (repeated for each quantity to be saved) are saved in the memory
together with the period start date and time.
Once these data are saved, the instrument starts acquiring data for a new period.
12.4.2. Calculation of the power factor
 According to the standards in force, the average power factor cannot be calculated as
an average of the instantaneous power factors. It must be obtained from the average
values of active and reactive power
 Each single average power factor, of phase or total, is therefore calculated, at the end
of each integration period, on the average value of the corresponding powers,
independently of the fact that they must be recorded or not
 Besides, for a better analysis of the type of load present on the line and in order to
obtain reference terms in the invoicing analysis of the "low cos
", the values of
inductive and capacitive cos
 are treated as independent parameters