ade7169f16 Analog Devices, Inc., ade7169f16 Datasheet - Page 51

• Manufacturer Part Number: ade7169f16
• Description: Single-phase Energy Measurement Ic With 8052 Mcu, Rtc And Lcd Driver
• Manufacturer: Analog Devices, Inc.

Preliminary Technical Data
where IRMS
Voltage channel RMS Calculation
Figure 36 shows the details of the signal processing chain for the
rms calculation on Voltage channel. The Voltage channel rms
value is processed from the samples used in the Voltage channel
waveform sampling mode. Voltage channel rms value is stored
in the unsigned 24-bit VRMS register.
The update rate of the Voltage channel rms measurement is
MCLK/5. To minimize noise in the reading of the register, the
Vrms register can also be configured to be updated only with
the zero crossing of the voltage input. This configuration is
done by setting ZXRMS bit in the MODE2 register (0x0C).
With the specified full-scale ac analog input signal of 0.5 V, the
output from the LPF1 swings between 0x28F5 and 0xD70B at
60 Hz—see the Voltage Channel ADC section. The equivalent
rms value of this full-scale ac signal is approximately
0d1,898,124 (0x1CF68C) in the VRMS register. The voltage rms
measurement provided in the ADE7169F16 is accurate to
within ±0.5% for signal input between full scale and full
ACTIVE POWER CALCULATION
Active power is defined as the rate of energy flow from source
to load. It is defined as the product of the voltage and current
waveforms. The resulting waveform is called the instantaneous
power signal and is equal to the rate of energy flow at every
instant of time. The unit of power is the watt or joules/sec.
Equation 9 gives an expression for the instantaneous power
signal in an ac system.
where:
V is the rms voltage.
I is the rms current.
IRMS =
v(t) =
i(t) =
p
p
) (
(
t
t
)
VI
v
0
2
2
(
is the rms measurement without offset correction.
t
)
IRMS
I
VI
V
sin(
t i
sin(
cos(
(
)
0
t
2
2
)
t
)
t
)
IRMSOS
VOLTAGE CHANNEL
32768
Figure 36. Voltage channel RMS Signal Processing
LPF1
VOLTAGE SIGNAL (V(t))
0xD70B
0x28F5
0x0
Rev. PrD | Page 51 of 140
(4)
(7)
(8)
(9)
LPF3
scale/20. The conversion from the register value to volts must
be done externally in the microprocessor using a volts/LSB
constant.
Voltage channel RMS Offset Compensation
The ADE7169F16 incorporates a voltage channel rms offset
compensation register (VRMSOS). This is a 12-bit signed
register that can be used to remove offset in the voltage channel
rms calculation. An offset could exist in the rms calculation due
to input noises and dc offset in the input samples. The offset
calibration allows the contents of the VRMS register to be
maintained at 0 when no voltage is applied. One LSB of the
voltage channel rms offset is equivalent to 64 LSB of the rms
register. Assuming that the maximum value from the voltage
channel rms calculation is 0d1,898,124 with full-scale ac inputs,
then one LSB of the voltage channel rms offset represents 3.37%
of measurement
error at –60 dB down of full scale.
where VRMS
The average power over an integral number of line cycles (n) is
given by the expression in Equation 10.
where:
T is the line cycle period.
P is referred to as the active or real power.
Note that the active power is equal to the dc component of the
instantaneous power signal p(t) in Equation 9, i.e., VI. This is
the relationship used to calculate active power in the
ADE7169F16. The instantaneous power signal p(t) is generated
by multiplying the current and voltage signals. The dc
component of the instantaneous power signal is then extracted
by LPF2 (low-pass filter) to obtain the active power
information. This process is illustrated in Figure 37.
VRMS = VRMS
sgn
P =
2
16
VRMOS[11:0]
nT
2
1
15
0
+
is the rms measurement without offset correction.
0
2
nT
8
+
2
p
7
) (
0x28F5C2
t
2
6
0
dt
+ 64 x VRMSOS
VRMS[23:0]
0x00
VI
ADE7169F16
(10)
(6)