Understanding how energy is calculated inside a meter requires revisiting some electrical fundamentals. This page covers the math and the physical reality behind the numbers on your bill.

Active, Reactive, and Apparent Power

Three types of power exist in any AC circuit:

• Active Power (P) — the real work done. Measured in watts (W). This is what heats your kettle and spins your motor.
• Reactive Power (Q) — the energy stored and released by inductors and capacitors (motors, transformers). Measured in VAr. It does no net work but loads the grid.
• Apparent Power (S) — the vector sum of P and Q. This is what the utility must supply. Measured in VA.

title "Active vs Reactive Load — Phase Difference"
time start=0 end=20 unit=ms divisions=10

V: sine label="Voltage" amplitude=1 cycles=1 unit="pu"
I_R: sine label="Current (resistive, PF=1)" amplitude=0.9 cycles=1 unit="pu"
I_L: sine label="Current (inductive, PF=0.7)" amplitude=0.9 phase=45 cycles=1 unit="pu"

The power triangle relates them:

S² = P² + Q²
Power Factor (PF) = P / S

A PF of 1.0 means all drawn power is doing useful work. A PF of 0.7 means 30% is reactive — the utility still carries that current but earns no revenue from it. Industrial consumers are penalized for low PF.

Harmonics — The Hidden Problem

Non-linear loads (VFDs, SMPS, LED drivers) draw current in pulses rather than a smooth sine wave. These pulses decompose into harmonics — multiples of the fundamental 50 Hz frequency (100 Hz, 150 Hz, 200 Hz…).

title "Fundamental vs Harmonic Distorted Current"
time start=0 end=20 unit=ms divisions=10

F: sine label="Fundamental 50Hz" amplitude=1 cycles=1 unit="pu"
H3: sine label="3rd Harmonic 150Hz" amplitude=0.3 cycles=3 unit="pu"

Harmonics cause transformer heating, neutral conductor overload, and meter measurement errors if the meter is not designed for them. Modern meters measure Total Harmonic Distortion (THD) and energy across harmonic frequencies.

How a Metrology IC Computes Energy

The IC samples voltage (V) and current (I) simultaneously at very high rates (typically 3,900 to 8,000 samples/second). It multiplies each pair and accumulates the result:

Energy = Σ (V[n] × I[n]) × Δt

This gives instantaneous power integrated over time — which is exactly the definition of energy.

Tamper Detection

Meters must detect attempts to steal energy:

All tamper events are time-stamped and stored in the meter's event log.

Key Takeaway

A metrology IC is essentially a very fast, very precise multiplier and accumulator. The accuracy of the meter depends on the quality of the voltage divider, current sensor, and the calibration constants burned into the IC at the factory.