ML0035 September 27, 2017 - 84 - Copyright 2017 Bitronics, LLC
6.9 Frequency
The M650 monitors the change in Phase Angle per unit time using the Phase Angle
measurement for the fundamental generated by the FFT. The System Frequency is
the frequency of the input used for synchronizing the sampling rate.
6.10 Demand Measurements
The traditional thermal demand meter displays a value that represents the logarithmic
response of a heating element in the instrument driven by the applied signal. The
most positive value since the last instrument reset is known as the maximum demand
(or peak demand) and the lowest value since the last instrument reset is known as the
minimum demand. Since thermal demand is a heating and cooling phenomenon, the
demand value has a response time T, defined as the time for the demand function to
change 90% of the difference between the applied signal and the initial demand value.
For utility applications, the traditional value of T is 15 minutes, although the M650 can
accommodate other demand intervals (Section 6.10.5).
The M650 generates a demand value using modern microprocessor technology in
place of heating and cooling circuits, it is therefore much more accurate and
repeatable over a wide range of input values. In operation, the M650 continuously
samples the basic measured quantities, and digitally integrates the samples with a
time constant T to obtain the demand value. The calculated demand value is
continuously checked against the previous maximum and minimum demand values.
This process continues indefinitely, until the demand is reset or until the meter is reset
(or power removed and reapplied). The demand reset and power-up algorithms are
different for each measurement. These routines are further described in following
paragraphs. The maximum and minimum demand values are stored in non-volatile
memory on the Host Processor module.
NOTE: Changing VT or CT ratios does NOT reset demand measurements to
zero.
Demand Quantit
Phase Reference Function
mperes Phase, Residual Present, Max
Fundamental Amperes Phase, Residual Present, Max
Volts
Phase - Neutral,
Phase - Phase Present, Max, Min
Total Watts
, B, C, Total
Phase, Total Present, Max, Min
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