Amprobe DM-4 Power-Quality-Recorder - Manual (Page 56)

15.4 MEASURING METHOD: OUTLINES
The instrument is able to measure: voltages, currents, active powers, inductive and
capacitive reactive powers, apparent powers, inductive and capacitive power fac-
tors, analog or impulse parameters. All these parameters are analyzed in a digital
way: for each phase (voltage and current), 6 x 128 samples are acquired on a mod-
ule of 16 x 20ms, repeated for the three phases.
15.4.1 Integration Periods
The storage of all the data would require a huge amount of memory. Therefore,
we’ve tried to find out a storage method that compresses the information to be
memorized, while still providing a significant amount of data. The chosen method
is that of integration. After a certain period called the “integration period”, which can
be set from 5 seconds to 60 minutes, the instrument extracts from the sampled val-
ues the following:
• Minimum value of the parameter during the integration period (harmonics excluded)
• Medium value of the parameter (intended as arithmetic average of all the values
registered during the integration period)
• Maximum value of the parameter during the integration period (harmonics excluded)
Only this information (repeated for each parameter to be memorized) is saved in the
memory along with starting time and date of the integration period. Once these data
are memorized, the instrument restarts to take measurements for a new period.
15.4.2 Power Factor Calculations
According to the standards in force, the medium power factor can’t be calculated as
average of the instantaneous power factors. It must be obtained from the medium val-
ues of active and reactive power. Each single medium power factor (of phase or total)
is therefore calculated, at the end of each integration period, on the medium value of
the corresponding powers independently on the fact that they must be registered or
not. Besides, for a better analysis of the type of load present on the line and in order
to have terms of comparison when studying the invoicing of the low cosj, the values
of inductive and capacitive cosj are treated as independent parameters.
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DM-4 Power Quality Recorder