ADE7758_15 datasheet(49/72 Pages) AD

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Data Sheet

ADE7758

Rev. E | Page 49 of 72

Gain Calibration Using Line Accumulation

Step 2: Select Phase A, Phase B, or Phase C for a line period

measurement with the FREQSEL[1:0] bits in the MMODE

Phase A for line period measurement.

Gain calibration is used for meter-to-meter gain adjustment,

APCF or VARCF output rate calibration, and determining the

Wh/LSB, VARh/LSB, and VAh/LSB constant.

Step 3: Set up ADE7758 for line accumulation by writing 0xBF

to LCYCMODE. This enables the line accumulation mode on

the xWATTHR, xVARHR, and xVAHR (0x01 to 0x09) registers

by setting the LWATT, LVAR, and LVA bits, LCYCMODE[0:2]

(0x17), to Logic 1. It also sets the ZXSEL bits, LCYCMODE[3:5],

to Logic 1 to enable the zero-crossing detection on all phases

for line accumulation. Additionally, the FREQSEL bit,

LCYCMODE[7], is set so that FREQ (0x10) stores the line

period. When using the line accumulation mode, the RSTREAD

bit of LCYCMODE should be set to 0 to disable the read with

reset mode. Select the phase for line period measurement in

MMODE[1:0].

Step 0: Before performing the gain calibration, the APCFNUM/

APCFDEN (0x45/0x46) and VARCFNUM/ VARCFDEN

(0x47/0x48) values can be set to achieve the correct impulses/kWh,

impulses/kVAh, or impulses/kVARh using the same method

outlined in Step 4 in the Gain Calibration Using Pulse Output

section. The calibration of xWG/xVARG/xVAG (0x2A through

0x32) is done with the line accumulation mode. Figure 82 shows

the steps involved in calibrating the gain registers using the line

accumulation mode.

Step 1: Clear xWG, xVARG, and xVAG.

Step 4: Set the number of half-line cycles for line accumulation

by writing to LINECYC (0x1C).

FREQUENCY

KNOWN?

YES

STEP 0

SET

APCFNUM/APCFDEN

AND

VARCFNUM/VARCFDEN

STEP 1

STEP 2

CLEAR

xWG/xVAR/xVAG

STEP 3

SET LYCMODE

STEP 4

SET ACCUMULATION

TIME (LINECYC)

STEP 5

SET MASK FOR

LENERGY INTERRUPT

STEP 6

SET UP SYSTEM FOR

ITEST,VNOM,PF = 1

STEP 7

READ FREQ[11:0]

STEP 8

RESET STATUS

STEP 9

READ ALL xWATTHR

AND xVAHR AFTER

LENERGY

INTERRUPT

STEP 9A

CALCULATE xWG

STEP 9B

CALCULATE xVAG

STEP 10

WRITE TO xWG AND

xVAG

CALIBRATE WATT

AND VA @ PF = 1

STEP 11

SET UP TEST

SYSTEM FOR

ITEST,VNOM,

PF = 0, INDUCTIVE

STEP 12

RESET STATUS

STEP 13

READ ALL xVARHR

AFTER LENERGY

INTERRUPT

STEP 14

CALCULATE xVARG

STEP 15

WRITE TO xVARG

STEP 16

CALCULATE

Wh/LSB, VAh/LSB,

VARh/LSB

END

SELECT PHASE

FOR LINE PERIOD

MEASUREMENT

CONFIGURE

FREQ[11:0] FOR A

LINE PERIOD

MEASUREMENT

Figure 82. Gain Calibration Using Line Accumulation

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