78M6612 Maxim, 78M6612 Datasheet - Page 18

• Manufacturer Part Number: 78M6612
• Description: The Teridian™ 78M6612 is a highly integrated, single-phase, power and energy measurement and monitoring system-on-chip (SoC) that includes a 32-bit compute engine (CE), an MPU core, RTC, and flash
• Manufacturer: Maxim

78M6612 Data Sheet
2 Functional Description
2.1 Theory of Operation
The energy delivered by a power source into a load can be expressed as:
The following formulas apply for wide band mode (true RMS):
•
•
•
•
•
For actual measurement equations, refer to the applicable 78M6612 Firmware Description Document.
For some applications, not only voltage and current amplitudes, but also phase angles and harmonic
content may change constantly. Thus, simple RMS measurements are inherently inaccurate. A modern
solid-state electricity measurement IC such as the 78M6612 functions by emulating the integral operation
above, i.e. it processes current and voltage samples through an ADC at a constant frequency. As long
as the ADC resolution is high enough and the sample frequency is beyond the harmonic range of
interest, the current and voltage samples, multiplied with the time period of sampling will yield an accurate
quantity for the momentary energy. Summing up the momentary energy quantities over time will result in
accumulated energy.
Figure 5
50 samples of the voltage and current signals over a period of 20 ms. The application of 240 VAC and
100 A results in an accumulation of 480 Ws (= 0.133 Wh) over the 20 ms period, as indicated by the
Accumulated Power curve. The described sampling method works reliably, even in the presence of
dynamic phase shift and harmonic distortion.
18
P = ∑ (i(t) * v(t))
Q = √(S
S = V * I
V = √∑v(t)
I = √∑i(t)
shows the shapes of V(t), I(t), the momentary power and the accumulated power, resulting from
E
2
2
– P
=
2
∫
0
t
-100
-200
-300
-400
-500
2
500
400
300
200
100
)
V
Figure 5: Voltage, Current, Momentary and Accumulated Energy
0
) (
0
t
I
) (
t
dt
Current [A]
Voltage [V]
Energy per Interval [Ws]
Accumulated Energy [Ws]
5
10
15
20
DS_6612_001
Rev 2