ADE7758_15 datasheet(48/72 Pages) AD

48 / 72 page

ADE7758

Data Sheet

Rev. E | Page 48 of 72

VARCFNUM

VARCFDEN

VARCF

%VARCF

xVAROS

EXPECTED

ERROR

⎟

⎠

⎞

⎜

⎝

⎛

100

–

(57)

where Q is defined in Equation 58 and Equation 59.

For xWATTOS,

25 ×

= CLKIN

(58)

For xVAROS,

[11

202

⎟

⎠

⎞

⎜

⎝

⎛

FREQ

CLKIN

(59)

where the FREQ (0x10) register is configured for line period

measurements.

Step 7: Repeat Step 3 to Step 6 for xVAROS calibration.

Example: Offset Calibration of Phase A Using Pulse Output

For this example, IMIN = 50 mA, VNOM = 220 V, VFULLSCALE =

500 V, IFULLSCALE = 130 A, MC = 3200 impulses/kWh, Power

Factor = 1, Frequency = 50 Hz, and CLKIN = 10 MHz.

With IMIN, VNOM, and unity power factor, the example ADE7758

meter shows 0.009789 Hz on the APCF pulse output. When the

power factor is changed to 0.5 inductive, the VARCF output is

0.009769 Hz.

This is equivalent to 0.1198% for the watt measurement and

−0.0860% for the VAR measurement. Using Equation 56

through Equation 59, the values 0xFFD and 0x3 should be

written to AWATTOS (0x39) and AVAROS (0x3C), respectively.

0xFFD

–

–2.8

277

0.01863

0.009778

100

0.1198%

–

⎟

⎠

⎞

⎜

⎝

⎛

AWATTOS

2.6

277

0.01444

0.009778

100

0.0860%

–

⎟

⎠

⎞

⎜

⎝

⎛

AVAROS

For AWATTOS,

01863

= E

For AVAROS,

0.01444

2083

202

Calibration Using Line Accumulation

Line cycle accumulation mode configures the nine energy

registers such that the amount of energy accumulated over an

integer number of half line cycles appears in the registers after

the LENERGY interrupt. The benefit of using this mode is that

the sinusoidal component of the active energy is eliminated.

Figure 81 shows a flowchart of how to calibrate the ADE7758

using the line accumulation mode. Calibration of all phases and

energies can be done simultaneously using this mode to save

time during calibration.

START

CAL IRMS OFFSET

CAL VRMS OFFSET

CAL WATT AND VA

GAIN ALL PHASES

@ PF = 1

CAL VAR GAIN ALL

PHASES @ PF = 0,

INDUCTIVE

CALIBRATE PHASE

ALL PHASES

@ PF = 0.5,

INDUCTIVE

CALIBRATE ALL

PHASES WATT

OFFSET @ IMIN AND

PF = 1

CALIBRATE ALL

PHASES VAR

OFFSETS @ IMIN

AND PF = 0,

INDUCTIVE

END

Figure 81. Calibration Using Line Accumulation

ADE7758 Datasheet(PDF) 48 Page - Analog Devices

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