Datasheet

71M6513/71M6513H
3-Phase Energy Meter IC
DATA SHEET
AUGUST 2011
Page: 14 of 104 © 2005-2011 Teridian Semiconductor Corporation
A Maxim Integrated Products Brand
Figure 4: Samples in Multiplexer Cycle
The end of each multiplexer cycle is signaled to the MPU by the CE_BUSY interrupt. At the end of each multiplexer cycle,
status information, such as sag data and the digitized input signal, is available to the MPU.
Figure 5: Accumulation Interval
Figure 5 shows the accumulation interval resulting from PRE_SAMPS = 42 and SUM_CYCLES = 50, consisting of 2100 samples
of 397µs each (only one phase is shown) followed by the XFER_BUSY interrupt. The sampling in this example is applied to a
50Hz signal.
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.
VA
VB
IB
VC
IC
IA
1/2520.6Hz = 397µs
2/32768Hz =
61.04µs
13/32768Hz = 397µs
per mux cycle
A
C
B
VA
VB
IB
VC
IC
IA
1/2520.6Hz = 397µs
2/32768Hz =
61.04µs
13/32768Hz = 397µs
per mux cycle
A
C
B
XFER_BUSY
Interrupt to MPU
20ms
833ms
XFER_BUSY
Interrupt to MPU
20ms
833ms