Amprobe DM-111S Current-Data-Logger - Manual (Page 60)

DMIIIS
EN - 58
16.4. MEASURING METHOD: OUTLINES
The instrument is able to measure: voltages, currents, active powers, inductive and
capacitive reactive powers, apparent powers, inductive and capacitive power factors,
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 module of 16 x 20ms,
repeated for the three phases.
16.4.1. 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 values 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.
16.4.2. 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 values
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 cos

, the values of inductive
and capacitive cos

are treated as independent parameters.