Datasheet

ADE7854/ADE7858/ADE7868/ADE7878 Data Sheet
Rev. G | Page 46 of 100
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 ±5,928,256.
The equivalent rms value of a full-scale sinusoidal signal is
4,191,910 (0x3FF6A6), 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 2 kHz. It is recommended
to read the rms registers synchronous to the voltage zero crossings
to ensure stability. The
IRQ1
interrupt can be used to indicate
when a zero crossing has occurred (see the Interrupts section).
The settling time for the V rms measurement is 440 ms for both
50 Hz and 60 Hz input signals. The V rms measurement settling
time 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 ADE78xx work on 32-, 16-, or 8-bit words.
Similar to the register presented in Figure 36, the AVRMS,
BVRMS, and CVRMS 24-bit signed registers are accessed as
32-bit registers with the eight MSBs padded with 0s.
0xA58AC0 =
–5,928,256
0x5A7540 =
5,928,256
0V
VOLTAGE SIGNAL
FROM HPF
LPF
x
2
√
2
7
xVRMSOS[23:0]
xVRMS[23:0]
08510-041
Figure 63. Voltage RMS Signal Processing