71M6511 Maxim, 71M6511 Datasheet - Page 14

• Manufacturer Part Number: 71M6511
• Description: The 71M6511 and 71M6511H are highly integrated SoCs with an MPU core, RTC, flash, and LCD driver
• Manufacturer: Maxim

71M6511/71M6511H
Single-Phase Energy Meter IC
A Maxim Integrated Products Brand
DATA SHEET
NOVEMBER 2010
There is no correlation between the line signal frequency and the choice of PRE_SAMPS or SUM_CYCLES (even though when
SUM_CYCLES = 42 one set of SUM_CYCLES happens to sample a period of 16.6ms). Furthermore, sampling does not have to
start when the line voltage crosses the zero line.
Delay Compensation
When measuring the energy of a phase (i.e., Wh and VARh) in a service, the voltage and current for that phase must be
sampled at the same instant. Otherwise, the phase difference, Ф, introduces errors.
t
φ
=
⋅
=
⋅
⋅
delay
o
o
360
t
f
360
delay
T
Where f is the frequency of the input signal and t
is the sampling delay between voltage and current.
delay
In traditional meter ICs, sampling is accomplished by using two A/D converters per phase (one for voltage and the other one
®
for current) controlled to sample simultaneously. Teridian’s Single-Converter Technology
, however, exploits the 32-bit signal
processing capability of its CE to implement “constant delay” all-pass filters. These all-pass filters correct for the conversion
time difference between the voltage and the corresponding current samples that are obtained with a single multiplexed A/D
converter.
The “constant delay” all-pass filters provide a broad-band delay β that is precisely matched to the difference in sample time
between the voltage and the current of a given phase. This digital filter does not affect the amplitude of the signal, but
provides a precisely controlled phase response. The delay compensation implemented in the CE aligns the voltage samples
with their corresponding current samples by routing the voltage samples through the all-pass filter, thus delaying the voltage
samples by β, resulting in the residual phase error β – Ф. The residual phase error is negligible, and is typically less than ±1.5
milli-degrees at 100Hz, thus it does not contribute to errors in the energy measurements.
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