Operation Techniques 57
4.2.2 Averaging
To split peaks, the PM295 offers a number of techniques for averaging real-time
quantities. Two main techniques are used: sliding averaging performed over the
predefined number of measurements, and time averaging performed within the
predefined demand interval.
Sliding averaging is applied to all real-time quantities except harmonic spectrum
measurements. The PM295 allocates storage registers (buffer) for each calculated
quantity sufficient to store the last 8, 16, or 32 measurements. These measurements
represent a sliding window that slides one step forward after each subsequent
measurement. At the end of each measurement, the oldest entry in the storage is
discarded, and the averaging is performed on the newest set of measurements. The
user can define the number of entries for averaging depending on industrial
conditions.
Time averaging is applied to phase voltages, currents, and all total powers. The
instrument uses three techniques of time averaging: block interval demand, sliding
window demand, and thermal demand. For each method, calculations are performed
within the user-defined DEMAND PERIOD. The measured quantity is integrated in
the demand storage register over a fixed time period as unit-second value. At the end
of the interval, the accumulated value is converted to watt, var, volt-ampere, volt,
and ampere demand values. They are stored in separate set of present demand
registers, and the accumulating registers are cleared before accumulating values for
the next demand interval.
4.2.3 Minimum/Maximum Logging
Standard Min/Max Log
The PM295 provides automatic recording of the extreme values for all real-time
quantities (except real-time harmonics) and demands measured by the instrument.
The minimum and maximum values for each parameter are recorded independently
with date and time stamp at a 1 second resolution.
The maximum demand readings can be viewed via the front panel of the instrument.
The others can be accessed via communications.
When a new minimum or maximum value is detected, the instrument announces an
internal event that can be used as a trigger for operating setpoints.
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