ADE7854AACPZ View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'ADE7854AACPZ' PDF : 96 Pages View PDF
ADE7854A/ADE7858A/ADE7868A/ADE7878A
Data Sheet
Voltage RMS Calculation
Figure 65 shows the detail of the signal processing chain for the
rms calculation on one phase 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 AVRMS, BVRMS, and CVRMS
registers. 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. Read the rms registers
synchronous to the voltage zero crossings to ensure stability. Use
the IRQ1 interrupt to indicate when a zero crossing has occurred
(see the Interrupts section).
The settling time for the voltage 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 ADE7854A, ADE7858A, ADE7868A, and
ADE7878A work on 32-, 16-, or 8-bit words. Similar to the
register in Figure 37, the AVRMS, BVRMS, and CVRMS 24-bit
signed registers are accessed as 32-bit registers with the eight
MSBs padded with 0s.
Low Ripple Voltage RMS
The ADE7854A, ADE7858A, ADE7868A, and ADE7878A also
provide the average of 1.024 sec of voltage rms data. The
averaged voltage rms values are signed 24-bit values that are
stored into the VARMS_LRIP, VBRMS_LRIP, and VCRMS_LRIP
registers. The low ripple registers remove the need for external
averaging and provide a stable reading. These average rms
registers are updated every 1.024 sec and contain an average of
the previous 8192 rms samples. The VxRMS_LRIP register
readings settle to within 99% after 2.048 sec.
xVRMSOS[23:0]
27
VOLTAGE SIGNAL
FROM HPF
x2
LPF
√
xVRMS[23:0]
0x5A7540 =
5,928,256
0V
0xA58AC0 =
–5,928,256
Figure 65. Voltage RMS Signal Processing
Rev. C | Page 46 of 96
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