ADE75 datasheet(55/148 Pages) AD

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Preliminary Technical Data

ADE75xx/ADE71xx

Rev. PrE | Page 55 of 148

When APSIGN in the ACCMODE register (0x0F) is set, the

APSIGN flag in the Interrupt Status Register 1 SFR (MIRQSTL,

0xDC) will be set when a transition from negative to positive

active power has occurred.

Active power no-Load detection

The ADE75XX/ADE71XX includes a no-load threshold feature

on the active energy that eliminates any creep effects in the

meter. The ADE75XX/ADE71XX accomplishes this by not

accumulating energy if the multiplier output is below the no-

load threshold. When the active power is below the no-load

threshold, the APNOLOAD flag in the Interrupt Status Register

1 SFR (MIRQSTL, 0xDC) is set. If the APNOLOAD bit is set in

the Interrupt Enable Register 1 SFR (MIRQENL, 0xD9), the

8052 core has a pending ADE interrupt. The ADE interrupt

stays active until the APNOLOAD status bit is cleared—see

Energy measurement interrupts section.

The No-load threshold level is selectable by setting bits

APNOLOAD in the NLMODE register (0x0E). Setting these

bits to 0b00 disable the no-load detection and setting them to

0b01, 0b10 or 0b11 set the no-load detection threshold to

0.015%, 0.0075% and 0.0037% of the full-scale output frequency

of the multiplier respectively. The IEC62053-21 specification,

states that the meter must start up with a load equal to or less

than 0.4% Ib. If the nominal voltage input and the maximum

current represent 50% of the full scale ADC input and Imax =

400% of Ib, the ADE75XX/ADE71XX no-load threshold

options translate to 0.24% of Ib, 0.12% of Ib and 0.06% of Ib

respectively.

WGAIN[11:0]

WDIV[7:0]

LPF2

CURRENT

CHANNEL

VOLTAGE

CHANNEL

TIME (nT)

CLKIN

ACTIVE POWER

SIGNAL

WATTHR[23:0]

OUTPUTS FROM THE LPF2 ARE

ACCUMULATED (INTEGRATED) IN

THE INTERNAL ACTIVE ENERGY REGISTER

UPPER 24 BITS ARE

ACCESSIBLE THROUGH

WATTHR[23:0] REGISTER

WAVEFORM

VALUES

WATTOS[15:0]

sgn

2-6 2-7 2-8

FOR WAVEF0RM

SAMPLING

DIGITAL TO FREQUENCY

CONVERTER

Figure 39. ADE75XX/ADE71XX Active Energy Calculation

Active Energy Calculation

As stated earlier, power is defined as the rate of energy flow.

This relationship can be expressed mathematically in Equation 12.

(12)

where:

P is power.

E is energy.

Conversely, energy is given as the integral of power.

∫

= Pdt

(13)

The ADE75XX/ADE71XX achieves the integration of the active

power signal by continuously accumulating the active power

signal in an internal non-readable 49-bit energy register. The

active energy register (WATTHR[23:0]) represents the upper 24

bits of this internal register. This discrete time accumulation or

summation is equivalent to integration in continuous time.

Equation 14 expresses the relationship.

()

(

)

p t dt

Lim

p nT

∞

→

⎧⎫

⎨⎬

⎩

⎭

∑

∫

(14)

where:

n is the discrete time sample number.

T is the sample period.

The discrete time sample period (T) for the accumulation

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