ade7953 Analog Devices, Inc., ade7953 Datasheet - Page 24

• Manufacturer Part Number: ade7953
• Description: Single Phase, Multifunction Metering Ic With Neutral Current Measurement Ade7953
• Manufacturer: Analog Devices, Inc.

ADE7953
ACTIVE ENERGY CALCULATION
As described in the Active Power Calculation section, power
is defined as the rate of energy flow. This relationship can be
expressed mathematically as shown in Equation 8.
where:
P is power.
E is energy.
Conversely, energy is given as the integral of power.
The ADE7953 achieves the integration of the active power
signal in two stages. In the first stage, the active power signals
are accumulated in an internal 48-bit register every 143 μs
(6.99 kHz) until an internal fixed threshold is reached. When
this threshold is reached, a pulse is generated and is accumu-
lated in 24-bit, user-accessible accumulation registers. The
internal threshold results in a maximum accumulation rate
of approximately 210 kHz with full-scale inputs. This process
occurs simultaneously on Current Channel A and Current
Channel B, and the resulting readings can be read in the 24-bit
AENERGYA (Address 0x21E and Address 0x31E) and
AENERGYB (Address 0x21F and Address 0x31F) registers.
Both stages of the accumulation are signed and, therefore,
negative energy is subtracted from positive energy.
This discrete time accumulation, or summation, is equivalent
to integration in continuous time. Equation 10 expresses this
relationship.
where:
n is the discrete time-sampled number.
T is the sample period.
The discrete time sample period (T) for the accumulation
registers in the ADE7953 is 4.76 μs (1/210 kHz). This is
illustrated in Figure 46, which shows the energy register
roll-over rates with full-scale inputs.
P =
E
E
= Pdt
=
∫
dE
∫
dt
P(t)dt
=
Lim
T
→
0
⎧
⎨
⎩
n
∑
∞
=
1
P(nT)
×
T
⎫
⎬
⎭
(10)
Rev. 0 | Page 24 of 68
(8)
(9)
Note that the energy register contents roll over to full-scale
negative (0x800000) and continue to increase in value when the
power or energy flow is positive. Conversely, if the power is
negative, the energy register underflows to full-scale positive
(0x7FFFFF) and continues to decrease in value.
AENERGYA and AENERGYB are read-with-reset registers
by default. This means that the contents of these registers are
reset to 0 after a read operation. This feature can be disabled
by clearing Bit 6 (RSTREAD) of the LCYCMODE register
(Address 0x004).
The ADE7953 includes two sets of interrupts that are triggered
when the active energy register is half full (positive or negative)
or when an overflow or underflow condition occurs. The first
set of interrupts is associated with the Current Channel A active
energy, and the second set of interrupts is associated with the
Current Channel B active energy. These interrupts are disabled
by default and can be enabled by setting the AEHFA and
AEOFA bits in the IRQENA register (Address 0x22C and
Address 0x32C) for Current Channel A, and the AEHFB and
AEOFB bits in the IRQENB register (Address 0x22F and
Address 0x32F) for Current Channel B.
Active Energy Integration Time Under Steady Load
The discrete time sample period (T) for the accumulation
registers is 4.76 μs (1/210 kHz). With full-scale sinusoidal
signals on the analog inputs and the AWGAIN and BWGAIN
registers set to 0x400000, a pulse is generated and added to
the AENERGYA and AENERGYB registers every 4.76 μs. The
maximum positive value that can be stored in the 24-bit
AENERGYA and AENERGYB registers is 0x7FFFFF before
the register overflows. The integration time under these
conditions can be calculated as follows:
0x7FFFFF
0x3FFFFF
0x000000
0x400000
0x800000
AENERGYx[23:0]
Time = 0x7FFFFF × 4.76 μs = 39.9 sec
Figure 46. Energy Register Roll-Over Time for Active Energy
19.95
39.9
59.85
TIME (Seconds)
xWGAIN = 0x200000
xWGAIN = 0x400000
xWGAIN = 0x600000
(11)