ADE7754 Analog Devices, ADE7754 Datasheet - Page 22

• Manufacturer Part Number: ADE7754
• Description: Poly-phase Multi-Function Energy Metering IC with Serial Port
• Manufacturer: Analog Devices

ADE7754
ENERGY CALCULATION
As stated earlier, power is defined as the rate of energy flow.
This relationship can be expressed mathematically as
Equation 7.
Where P = Power and E = Energy.
Conversely Energy is given as the integral of Power.
The ADE7754 achieves the integration of the Active Power
signal by continuously accumulating the Active Power signal
in an internal non-readable 54-bit Energy register. The
Active Energy register (AENERGY[23:0]) represents the
upper 24 bits of this internal register. This discrete time
accumulation or summation is equivalent to integration in
continuous time. Equation 9 below expresses the relationship
Where n is the discrete time sample number and T is the
sample period.
The discrete time sample period (T) for the accumulation
register in the ADE7754 is 0.4µs (4/10MHz). As well as
calculating the Energy, this integration removes any sinusoi-
dal component which may be in the Active Power signal.
Figure 26 shows a graphical representation of this discrete
time integration or accumulation. The Active Power signal
is continuously added to the internal Energy register. This
addition is a signed addition, therefore negative energy will
be subtracted from the Active Energy contents.
The 54-bit of the internal Energy register are divided by
WDIV. If the value in the WDIV register is equal to 0 then
the internal Active Energy register is divided by 1. WDIV is
an 8-bit unsigned register. The upper 24-bit of the result of
the division are then available in the 24-bit Active Energy
register. The AENERGY and RAENERGY registers read
the same internal Active energy register. They differ by the
the state in which they are leaving the internal Active energy
P =
TOTAL ACTIVE POWER
E= Pdt
E=
∫
dE
∫
dt
p(t)
00000h
26667h
dt Lim
=
T 0
→
T



∑
n 0
∞
=
T
time (nT)
p nT
(
Active Power
Signal - P
+
Σ
)
+
PRELIMINARY TECHNICAL DATA
×
WDIV
T
53
53
23



AENERGY[23:0]
TOTAL ACTIVE POWER ARE
ACCUMULATED (INTEGRATED) IN
THE ACTIVE ENERGY REGISTER
0
0
0
(7)
(8)
(9)
–22–
register after a read. Two operations are held when reading
the RAENERGY register: Read and reset to zero the internal
Active Energy register. Only one operation is held when
reading the AENERGY register: read the internal Active
Energy register.
Figure 26 shows the energy accumulation for full scale
signals (sinusoidal) on the analog inputs. The three displayed
curves, illustrate the minimum time it takes the energy
register to roll-over, when the individual Watt Gain registers
contents are all equal to 3FFh, 000h and 800h. The Watt
Gain registers are used to carry out a power calibration in the
ADE7754. As shown, the fastest integration time occurs
when the Watt Gain registers are set to maximum full scale,
i.e., 3FFh.
Note that the Active Energy register contents roll over to full-
scale negative (80,0000h) and continue increasing in value
when the power or energy flow is positive -See Figure 26.
Conversely if the power is negative the energy register would
under flow to full scale positive (7F,FFFFh) and continue
decreasing in value.
By using the Interrupt Enable register, the ADE7754 can be
configured to issue an interrupt (IRQ) when the Active
Energy register is half full (positive or negative).
3F,FFFFh
7F,FFFFh
40,0000h
00,0000h
80,0000h
AENERGY[23:0]
44
88
132
Time
(seconds)
176
220
264
REV. PrG 01/03
AWG = BWG = CWG = 3FFh
AWG = BWG = CWG = 000h
AWG = BWG = CWG = 800h