71M6545HT-IGTSLASHF datasheet(22/66 Pages) MAXIM

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71M6545T/71M6545HT

Energy Meter ICs

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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

phasedifference,Ф,introduceserrors.

delay

360

f 360

ϕ =

⋅° =

⋅ ⋅°

Where f is the frequency of the input signal, T = 1/f and

tdelay is the sampling delay between current and voltage.

Traditionally, sampling is accomplished by using two A/D

converters per phase (one for voltage and the other one

for current) controlled to sample simultaneously. Our

Single Converter Technology, however, exploits the 32-bit

signal processing capability of its CE to implement “con-

stant delay” allpass filters. The allpass filter corrects 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” allpass filter provides a broad-band

delay360°–θ,whichispreciselymatchedtothediffer-

ence 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.

Figure 4. Multiplexer Sequence with Neutral Channel and Remote Sensors

Figure 5. Multiplexer Sequence with Neutral Channel and Current Transformers

CK32

MUX STATE0

SETTLE

MULTIPLEXER FRAME

MUX_DIV[3:0] = 6 CONVERSIONS

CROSS

MUX_SYNC

UNUSED

CK32

MUX STATE0

1234

MUX_DIV[3:0] = 7 CONVERSIONS

SETTLE

MULTIPLEXER FRAME

CROSS

MUX_SYNC

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