ADE5166_08 AD [Analog Devices], ADE5166_08 Datasheet - Page 51

• Manufacturer Part Number: ADE5166_08
• Description: Single-Phase Energy Measurement IC with 8052 MCU, RTC, and LCD Driver
• Manufacturer: AD [Analog Devices]

RMS CALCULATION
The root mean square (rms) value of a continuous signal V(t) is
defined as
For time sampling signals, rms calculation involves squaring the
signal, taking the average, and obtaining the square root. The
ADE5166/ADE5169 implement this method by serially squaring
the input, averaging them, and then taking the square root of
the average. The averaging part of this signal processing is done
by implementing a low-pass filter (LPF3 in Figure 56, Figure 57,
and Figure 58).
I
V
I
P
/I
I
V
V
PA
N
P
N
I
V
rms
PGA1
PGA2
=
V
60Hz
T
1
×
ADC 2
T
ADC 1
0.1°
∫
0
V
Figure 55. Phase Calibration
2
(
t
)
dt
1
–231.93µs TO +48.83µs
7
1
DELAY BLOCK
0
1.22µs/LSB
PHCAL[7:0]
0
1
HPF
0
1
1
24
1
0
CHANNEL 2 DELAY
REDUCED BY 4.48µs
(0.1°LEAD AT 60Hz)
0x0B IN PHCAL[7:0]
24
V
60Hz
I
LPF2
Rev. 0 | Page 51 of 148
(1)
This LPF has a −3 dB cutoff frequency of 2 Hz when MCLK =
4.096 MHz.
where V is the rms voltage.
When this signal goes through LPF3, the cos(2ωt) term is attenu-
ated and only the dc term, V
through.
The I
ting the WAVMODE register (Address 0x0D) and setting the
WFSM bit (Bit 5) in the Interrupt Enable 3 SFR (MIRQENH,
Address 0xDB). Like the current and voltage channels waveform
sampling modes, the waveform data is available at sample rates of
25.6 kSPS, 12.8 kSPS, 6.4 kSPS, and 3.2 kSPS.
It is important to note that when the current input is larger than
40% of full scale, the I
represent the true processed rms value. The rms value processed
with this level of input is larger than the 24-bit read by the wave-
form register, making the value read truncated on the high end.
V
V
rms
( )
2
t
) (
V (t ) = √2 × V sin(ωt )
signal can be read from the waveform register by set-
INPUT
t
=
=
V
2
2
×
−
V
V
Figure 56. RMS Signal Processing
sin(
2
V
rms
cos
2
ω
(t ) = V
waveform sample register does not
t
(
)
2
ω
rms
2
t
– V
)
2
(shown as V
2
cos(2ωt)
LPF3
ADE5166/ADE5169
V
2
(t) = V
2
2
in Figure 56), goes
V
(2)
(3)