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Metering Math for the Open Source Meter –

Metering Math for the Open Source Meter

Metering Functionality of the Open Source Meter

The Open Source Meter is based on the CS5463 metering chip. The basic Theory of operation of the CS5463 is it is a dual-channel analog-to-digital converter (ADC) with a complex computational engine that performs power calculations and energy-to-pulse conversions. The metering chip has a number of measurement functions that are applicable to both power monitoring and power quality monitoring.

Voltage and Current Measurements
The meter can perform Vrms and Irms calculations. The calculation is the root mean square calculation performed on N instantaneous voltage and current samples.
Voltage Current Calculation
Active Power
The meter can perform Active power calculations by taking the instantaneous voltage and current samples and multiplying them to obtain the instantaneous power. The product is averaged over N conversions.
Reactive Power
The meter can perform reactive power calculations by using QTrig (Trigonometric Identities) with the formula
Reactive Power Formula
The average reactive power is obtained QAVG by averaging the voltage multiplied by the current with a 90deg phase shift difference between them.
Apparent Power
The apparent power is the combination of the active power and the reactive power, without reference to an impedance phase angle
Apparent Power Formula
Power Factor
The power factor (PF) is the active power (PActive) divided by the apparent power (S)
Power Factor Formula
Fundamental Active/Reactive Power
The Fundamental active and reactive power (PF) and (QF) is calculated by performing the discrete Fourier transform (DFT) at the relevant frequency on the instantaneous voltage and current. Epsilon is used to set the frequency of the internal sine (imaginary) and cosine (real) wave form generator. Epsilon is used to achieve unity gain at the line frequency and to attain accurate QAVG results over line-frequency variation.
Harmonic Active Power
The Harmonic active power (PH) is calculated by subtracting the fundamental active power (PF) from the active power (PActive) inversely reactive power can be calculated.
Sag and Fault Detect
Voltage and Current Sag thresholds can be set to the average of the absolute instantaneous voltage and current respectively.
Sag and Fault Detect
Temperature readings can be obtained in the Celsius scale.
It is important to note that the OpenSource Meter is not a real-time device and should not be used in highly deterministic applications. Time lags can be expected no larger then 20 milliseconds.