Datasheet

ADE7854/ADE7858/ADE7868/ADE7878 Data Sheet
Rev. G | Page 44 of 100
the integrator is enabled, that is, when Bit 0 (INTEN) in the
CONFIG register is set to 1, the equivalent rms value of a full-
scale sinusoidal signal at 50 Hz is 4,191,910 (0x3FF6A6) and at
60 Hz is 3,493,258 (0x354D8A).
The accuracy of the current rms is typically 0.1% error from
the full-scale input down to 1/1000 of the full-scale input when
PGA = 1. 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
inter-
rupt can be used to indicate when a zero crossing has occurred
(see the Interrupts section). Table 13 shows the settling time for
the I rms measurement, which is the time it takes for the rms
register to reflect the value at the input to the current channel
when starting from 0 to full scale. However, during the chip
power-up and DSP reset cases, it would typically take about
1.2 seconds for a FS/1000 signal to be settled.
Table 13. Settling Time for I rms Measurement
Integrator Status 50 Hz Input signals 60 Hz Input signals
Integrator Off 440 ms 440 ms
Integrator On 550 ms 500 ms
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 AIRMS,
BIRMS, CIRMS, and NIRMS (ADE7868 and ADE7878 only)
24-bit signed registers are accessed as 32-bit registers with the
eight MSBs padded with 0s.
0xA58AC0 =
–
5,928,256
0
x5A7540 =
5,928,256
0V
CURRENT SIGNAL FROM
HPF OR INTEGRATOR
(IF ENABLED)
LPF
x
2
√
2
7
xIRMSOS[23:0]
xIRMS[23:0]
08510-040
Figure 59. Current RMS Signal Processing