ADE7758_15 datasheet(46/72 Pages) AD

46 / 72 page

ADE7758

Data Sheet

Rev. E | Page 46 of 72

PHASE CALIBRATION USING PULSE OUTPUT

The ADE7758 includes a phase calibration register on each phase

to compensate for small phase errors. Large phase errors should

be compensated by adjusting the antialiasing filters. The ADE7758

phase calibration is a time delay with different weights in the

positive and negative direction (see the Phase Compensation

section). Because a current transformer is a source of phase error,

a fixed nominal value can be decided on to load into the xPHCAL

registers at power-up. During calibration, this value can be adjusted

for CT-to-CT error. Figure 79 shows the steps involved in

calibrating the phase using the pulse output.

START

ALL

PHASES

PHASE ERROR

CALIBRATED?

END

YES

STEP 1

SET UP PULSE

OUTPUT FOR

PHASE A, B, OR C

AND ENABLE CF

OUTPUTS

STEP 2

SET UP SYSTEM

FOR ITEST,VNOM,

PF = 0.5, INDUCTIVE

STEP 3

MEASURE %

ERROR IN APCF

STEP 4

CALCULATE PHASE

ERROR (DEGREES)

STEP 5

PERIOD OF

SYSTEM

KNOWN?

MEASURE

PERIOD USING

FREQ[11:0]

YES

CALCULATE AND

WRITE TO

xPHCAL

SELECT PHASE

FOR LINE PERIOD

MEASUREMENT

CONFIGURE

FREQ[11:0] FOR A

LINE PERIOD

MEASUREMENT

Figure 79. Phase Calibration Using Pulse Output

Step 1: Step 1 and Step 3 from the gain calibration should be

repeated to configure the ADE7758 pulse output. Ensure the

xPHCAL registers are zero.

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

inductive.

Step 3: Measure the percent error in the pulse output, APCF,

from the reference meter using Equation 49.

Step 4: Calculate the Phase Error in degrees by





















100

–

%Error

Arcsin

Error

Phase

(53)

Step 5: Calculate xPHCAL.







360

)

(

Period

Line

Weight

LSB

PHCAL

Error

Phase

xPHCAL

(54)

where PHCAL_LSB_Weight is 1.2 μs if the %Error is negative or

2.4 μs if the %Error is positive (see the Phase Compensation

section).

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 55 shows how

to determine the value that needs to be written to xPHCAL

using the period register measurement.











360

]

[

FREQ

Weight

LSB

PHCAL

Error

Phase

xPHCAL

(55)

Example: Phase Calibration of Phase A Using Pulse Output

For this example, ITEST = 10 A, VNOM = 220 V, VFULLSCALE = 500 V,

IFULLSCALE = 130 A, MC = 3200 impulses/kWh, power factor = 0.5

inductive, and frequency = 50 Hz.

With Phase A contributing to CF, at ITEST, VNOM, and 0.5

inductive power factor, the example ADE7758 meter shows

0.9668 Hz on the pulse output. This is equivalent to −1.122%

error from the reference meter value using Equation 49.

The Phase Error in degrees using Equation 53 is 0.3713°.

























3713

100

1.122%

–

– Arcsin

Error

Phase

If at 50 Hz the FREQ register = 2083d, the value that should be

written to APHCAL is 17d, or 0x11 using Equation 55. Note

that a PHCAL_LSB_Weight of 1.2 μs is used because the

%Error is negative.

360

2083

μs

3713

APHCAL











Power Offset Calibration Using Pulse Output

Power offset calibration should be used for outstanding

performance over a wide dynamic range (1000:1). Calibration

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

where the desired accuracy is required.

The ADE7758 has power offset registers for watts and VAR

(xWATTOS and xVAROS). Offsets in the VA measurement are

compensated by adjusting the rms offset registers (see the

Calibration of IRMS and VRMS Offset section). Figure 80

shows the steps to calibrate the power offsets using the pulse

outputs.

ADE7758 Datasheet(PDF) 46 Page - Analog Devices

ADE7758 Datasheet(HTML) 46 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72

Datasheet Download

Link URL