ade7880 Analog Devices, Inc., ade7880 Datasheet - Page 39

• Manufacturer Part Number: ade7880
• Description: Polyphase Multifunction Energy Metering Ic With Harmonic Monitoring
• Manufacturer: Analog Devices, Inc.

Preliminary Technical Data
The mav values of full-scale sinusoidal signals of 50 Hz and
60 Hz are 209,686 and 210,921, respectively. As seen in Figure 42,
there is a 1.25% variation between the mav estimate at 45 Hz
and the one at 65 Hz for full-scale sinusoidal inputs. The accuracy
of the current mav is typically 0.5% error from the full-scale
input down to 1/100 of the full-scale input. Additionally, this
measurement has a bandwidth of 3.3 kHz. The settling time for
the current mav measurement, that is the time it takes for the
mav register to reflect the value at the input to the current
channel within 0.5% error, is 500 ms.
As stated in the Current Waveform Gain Registers section, the
serial ports of the ADE7880 work on 32-, 16-, or 8-bit words. As
presented in Figure 43, the AIMAV, BIMAV, and CIMAV 20-bit
unsigned registers are accessed as 32-bit registers with the 12
MSBs padded with 0s.
Current MAV Gain and Offset Compensation
The current rms values stored in the AIMAV, BIMAV, and
CIMAV registers can be calibrated using gain and offset
coefficients corresponding to each phase. It is recommended to
calculate the gains in PSM0 mode by supplying the ADE7880
with nominal currents. The offsets can be estimated by
supplying the ADE7880 with low currents, usually equal to the
minimum value at which the accuracy is required. Every time
the external microcontroller reads the AIMAV, BIMAV, and
CIMAV registers, it uses these coefficients stored in its memory
to correct them.
31
Figure 43. xIMAV Registers Transmitted as 32-Bit Registers
0000 0000 0000
20 19
20-BIT UNSIGNED NUMBER
VOLTAGE SIGNAL
FROM HPF
Figure 44. Voltage RMS Signal Processing
x
0xAEB86F=
-5,326,737
0
0x14791=
2
5,326,737
0V
Rev. PrE | Page 39 of 103
LPF
2
xVRMSOS[23:0]
7
Σ
Voltage Channel RMS Calculation
Figure 44 shows the detail of the signal processing chain for the
rms calculation on one of the phases of the voltage channel. The
voltage channel rms value is processed from the samples used in
the voltage channel. The voltage rms values are signed 24-bit
values and they are stored into the Registers AVRMS, BVRMS,
and CVRMS. The update rate of the current rms measurement
is 8 kHz.
With the specified full-scale analog input signal of 0.5 V, the
ADC produces an output code that is approximately ±5,326,737.
The equivalent rms value of a full-scale sinusoidal signal is
3,766,572 (0x39792C), independent of the line frequency.
The accuracy of the voltage rms is typically 0.1% error from the
full-scale input down to 1/1000 of the full-scale input. Additionally,
this measurement has a bandwidth of 3.3 kHz. It is
recommended to read the rms registers synchronous to the
voltage zero crossings to ensure stability. The IRQ1
can be used to indicate when a zero crossing has occurred (see
the Interrupts section).
The settling time for the V rms measurement is 580 ms for both
50 Hz and 60 Hz input signals. The V rms measurement is the
time it takes for the rms register to reflect the value at the input
to the voltage channel when starting from 0.
As stated in the Current Waveform Gain Registers section, the
serial ports of the ADE7880 work on 32-, 16-, or 8-bit words.
Similar to the register presented in Figure 32, the AVRMS,
BVRMS, and CVRMS 24-bit signed registers are accessed as
32-bit registers with the eight MSBs padded with 0s.
xVRMS[23:0]
ADE7880
interrupt