ADE7758_15 datasheet(52/72 Pages) AD

52 / 72 page

ADE7758

Data Sheet

Rev. E | Page 52 of 72

If it is not known, the line period is available in the ADE7758

frequency register, FREQ (0x10). To configure line period

measurement, select the phase for period measurement in the

MMODE[1:0] and set LCYCMODE[7]. Equation 72 shows how

to determine the value that needs to be written to xPHCAL

using the period register measurement.

360

]

[

μs

FREQ

Weight

LSB

PHCAL

Error

Phase

xPHCAL

(72)

Example: Phase Calibration Using Line Accumulation

This example shows only Phase A phase calibration. All three

PHCAL registers can be calibrated simultaneously using the

same method.

For this example, ITEST = 10 A, VNOM = 220 V, power factor = 0.5

inductive, and frequency = 50 Hz. Also, LINECYC = 0x800.

With ITEST, VNOM, and 0.5 inductive power factor, the example

ADE7758 meter shows 7318d in the AWATTHR (0x01) register.

14804d in the AWATTHR register. This is equivalent to

−1.132% error.

132

01132

14804

–

7318

−

Error

The Phase Error in degrees using Equation 66 is 0.374°.

()

⎟

⎠

⎞

⎛ − 01132

⎜

⎝

374

sin

–Arc

Error

Phase

Using Equation 72, the value written to APHCAL (0x3F), if at

50 Hz, the FREQ (0x10) register = 2085d, is 17d. Note that a

PHCAL_LSB_Weight of 1.2 μs is used because the %Error is

negative.

360

2085

374

APHCAL

For unity power factor (after gain calibration), the meter shows

STEP 1

SET MMODE,

LCYCMODE,

LINECYC AND

MASK REGISTERS

STEP 2

SET UP SYSTEM

FOR IMIN,VNOM

@PF = 1

STEP 3

RESET STATUS

STEP 4

READ ALL

xWATTHR

REGISTERS AFTER

LENERGY

INTERRUPT

END

FOR STEP 8

READ ALL xVARHR

AFTER LENERGY

INTERRUPT

FOR STEP 8, CALCULATE

xVAROS FOR ALL PHASES

STEP 5

CALCULATE

xWATTOS FOR ALL

PHASES

FOR STEP 8, WRITE TO

ALL xVAROS REGISTERS

STEP 6

WRITE TO ALL

xWATTOS

REGISTERS

STEP 7

SET UP SYSTEM

FOR ITEST,VNOM @

PF = 0, INDUCTIVE

STEP 8

REPEAT STEP 3 TO

STEP 8 FOR

xVARHR, xVAROS

CALIBRATION

Figure 84. Power Offset Calibration Using Line Accumulation

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