ADE7753ARS datasheet(46/60 Pages) AD

46 / 60 page

ADE7753

Rev. C | Page 46 of 60

Apparent Energy

Voltage rms compensation is done after the LPF3 filter (see

Figure 56).

Apparent energy gain calibration is provided for both meter-to-

meter gain adjustment and for setting the VAh/LSB constant.

VRMS = VRMS0 + VRMSOS

(64)

VAENERGY =

⎟

⎠

⎞

⎜

⎝

⎛ +

VAGAIN

VADIV

VAENERGY

initial

(68)

where:

VRMS0 is the rms measurement without offset correction.

VRMS is linear from full-scale to full-scale/20.

VADIV is similar to the CFDEN for the watt hour calibration. It

should be the same across all meters and determines the VAh/LSB

constant. VAGAIN is used to calibrate individual meters.

To calibrate the offset, two VRMS measurements are required,

for example, at Vnominal and Vnominal/10. Vnominal is set at half of the

full-scale analog input range so the smallest linear VRMS

reading is at Vnominal/10.

VRMSOS =

VRMS

−

(65)

Apparent energy gain calibration should be performed before

rms offset correction to make most efficient use of the current

test points. Apparent energy gain and watt gain compensation

require testing at Ib while rms and watt offset correction require

a lower test current. Apparent energy gain calibration can be

done at the same time as the watt-hour gain calibration using

line cycle accumulation. In this case, LAENERGY and

LVAENERGY, the line cycle accumulation apparent energy

interrupt. Figure 87 shows a flowchart for calibrating active and

apparent energy simultaneously.

where VRMS1 and VRMS2 are rms register values without offset

correction for input V1 and V2, respectively.

If the range of the 12-bit, twos complement VRMSOS register is

not enough, the voltage channel offset register, CH2OS, can be

used to correct the VRMS offset.

Current rms compensation is performed before the square root:

IRMS2 = IRMS02 + 32768 × IRMSOS

(66)

VAGAIN = INT

⎟

⎠

⎞

⎜

⎝

⎛

⎟

⎠

⎞

⎜

⎝

⎛

−

)

(

)

(

nominal

expected

LVAENERGY

(69)

where IRMS0 is the rms measurement without offset correction.

The current rms calculation is linear from full-scale to full-

scale/100.

LVAENERGYIB(expected) =

INT

⎟

⎠

⎞

⎜

⎝

⎛

(s)

s/h

3600

time

Accumulati

constant

LSB

VAh

nominal

(70)

To calibrate this offset, two IRMS measurements are required,

for example, at Ib and IMAX/50. IMAX is set at half of the full-scale

analog input range so the smallest linear IRMS reading is at

IMAX/50.

IRMSOS =

IRMS

−

32768

(67)

The accumulation time is determined from Equation 37 and the

line period can be determined from the PERIOD register accord-

ing to Equation 38. The VAh represented by the VAENERGY

where IRMS1 and IRMS2 are rms register values without offset

correction for input I1 and I2, respectively.

VAh = VAENERGY × VAh/LSB constant

(71)

The VAh/LSB constant can be verified using this equation:

LVAENERGY

time

Accumulati

constant

LSB

VAh

3600

(s)

(72)

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