ADE7758ARWRL datasheet(50/68 Pages) AD

50 / 68 page

ADE7758

Rev. A | Page 50 of 68

Step 6: Calculate xPHCAL and write to the xPHCAL registers

(0x3F to 0x41).

Figure 82 shows the steps involved in calibrating the phase

using the line accumulation mode.

STEP 1

SET LCYCMODE,

LINECYC AND MASK

REGISTERS

STEP 2

SET UP SYSTEM FOR

ITEST, VNOM, PF = 0.5

STEP 3

RESET STATUS

STEP 4

READ ALL XWATTHR

REGISTERS AFTER

LENERGY

INTERRUPT

STEP 5

CALCULATE PHASE

ERROR IN DEGREES

FOR ALL PHASES

STEP 6

CALCULATE AND

WRITE TO ALL

XPHCAL REGISTERS

()

Error

Phase

Period

xPHCAL

360

–

(51)

The period is available in the ADE7758 frequency register if it is

not known. Equation 37 shows how to determine the value

written to xPHCAL using the period register measurement (see

the Phase Calibration Using Pulse Output section). In Equation

37, the 2.4 µs is for phase errors that are negative. For positive

phase error, the 2.4 µs is replaced by 4.8 µs (see the Phase

Compensation section).

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.

Figure 82. Phase Calibration Using Line Accumulation

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

ADE7758 meter shows 12036d in the AWATTHR (0x01)

meter shows 24020d in the AWATTHR register. This is

equivalent to 26 LSBs of error.

Step 1: If the values were changed after gain calibration, Step 1,

Step 3, and Step 4 from the gain calibration should be repeated

to configure the LCYCMODE and LINECYC registers.

Step 2: Set the test system for ITEST, VNOM, and 0.5 power factor.

The Phase Error in degrees using Equation 50 is −0.07°.

Step 3: Reset the interrupt status register by reading RSTATUS

(0x1A).

()

⎟

⎠

⎞

⎜

⎝

⎛

–

00215

sin

–Arc

Error

Phase

Step 4: The xWATTHR registers should be read after the

LINECYC interrupt. Measure the percent error in the energy

compared to the energy register readings at unity power factor

(after gain calibration) using Equation 49. The readings at unity

power factor should have been repeated after the gain

calibration and stored for use in the phase calibration routine.

Using Equation 37, the value written to APHCAL (0x3F), if at

50 Hz the FREQ (0x10) register = 2083d, is 21d.

2083

360

⎟

⎠

⎞

⎜

⎝

⎛

APHCAL

–

xWATTHR

Error

(49)

Power Offset Calibration Using Line Accumulation

Power offset calibration should be used for outstanding

performance over a wide dynamic range (1,000:1). Calibration

of the power offset is done at or close to the minimum current.

The ADE7758 has power offset registers for watts and VAR,

xWATTOS (0x39 to 0x3B) and xVAROS (0x3C to 0x3E).

Offsets in the VA measurement are compensated by adjusting

the rms offset registers (see the Calibration of IRMS and VRMS

Offset section). Figure 83 shows the steps to calibrate the power

offsets using the line accumulation mode.

Step 5: Calculate the Phase Error in degrees using the following

equation.

()

⎟

⎠

⎞

⎜

⎝

⎛

–

Error

Arcsin

Error

Phase

(50)

ADE7758ARWRL Datasheet(PDF) 50 Page - Analog Devices

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