Datasheet

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
register (0x14). For example, clearing Bit 1 and Bit 0 selects
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?
NO YES
STEP 0
SET
APCFNUM/APCFDEN
AND
VARCFNUM/VARCFDEN
STEP 1
STEP 2
CLEAR
xWG/xVAR/xVAG
STEP 3
SET LYCMODE
REGISTER
STEP 4
SET ACCUMULATION
TIME (LINECYC)
STEP 5
SET MASK FOR
LENERGY INTERRUPT
STEP 6
SET UP SYSTEM FOR
I
TEST
,V
NOM
,PF=1
STEP 7
READ FREQ[11:0]
REGISTER
STEP 8
RESET STATUS
REGISTER
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
I
TEST
,V
NOM
,
PF = 0, INDUCTIVE
STEP 12
RESET STATUS
REGISTER
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
04443-081
SELECT PHASE
FOR LINE PERIOD
MEASUREMENT
CONFIGURE
FREQ[11:0] FOR A
LINE PERIOD
MEASUREMENT
Figure 82. Gain Calibration Using Line Accumulation