Datasheet

ADE7758 Data Sheet
Rev. E | Page 50 of 72
Step 5: Set the LENERGY bit, MASK[12] (0x18), to Logic 1
to enable the interrupt signaling the end of the line cycle
accumulation.
Step 6: Set the test system for I
TEST
, V
NOM
, and unity power factor
(calibrate watt and VA simultaneously and first).
Step 7: Read the FREQ (0x10) register if the line frequency is
unknown.
Step 8: Reset the interrupt status register by reading
RSTATUS (0x1A).
Step 9: Read all six xWATTHR (0x01 to 0x03) and xVAHR
(0x07 to 0x09) energy registers after the LENERGY interrupt
and store the values.
Step 9a: Calculate the values to be written to xWG registers
according to the following equations:
()
WDI
V
APCFNU
M
APCFDEN
AccumTimeθcosVIMC
WATTHR
NOM
TEST
EXPECTED
1
36001000
4
×
×
×
×××××
=
(60)
where AccumTime is
[]
SelectedPhasesofNo.FrequencyLine
:LINECYC
××2
015
(61)
where:
MC is the meter constant.
θ is the angle between the current and voltage.
Line Frequency is known or calculated from the FREQ[11:0]
register. With the FREQ[11:0] register configured for line period
measurements, the line frequency is calculated with Equation 62.
6-
109.60]:[11
1
××
=
FREQ
FrequencyLine
(62)
No. of Phases Selected is the number of ZXSEL bits set to Logic 1
in LCYCMODE (0x17).
Then, xWG is calculated as
12
21 ×
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−=
MEASURED
EXPECTED
WATTHR
WATTHR
xWG
(63)
Step 9b: Calculate the values to be written to the xVAG registers
according to the following equation:
VADIVVARCFNUM
VARCFDEN
AccumTimeVIMC
VAHR
NOM
TEST
EXPECTED
1
36001000
4
××
×
××××
=
(64)
12
21 ×
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−=
MEASURED
EXPECTED
VAHR
VAHR
xVAG
Step 10: Write to xWG and xVAG.
Step 11: Set the test system for I
TEST
, V
NOM
, and zero power
factor inductive to calibrate VAR gain.
Step 12: Repeat Step 7.
Step 13: Read the xVARHR (0x04 to 0x06) after the LENERGY
interrupt and store the values.
Step 14: Calculate the values to be written to the xVARG
registers (to adjust VARCF to the expected value).
()
VARDI
V
VARCFNU
M
VARCFDEN
AccumTimeθsinVIMC
VARHR
NOM
TEST
EXPECTED
1
36001000
4
×
×
×
×××××
=
(65)
12
21 ×
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−=
MEASURED
EXPECTED
VARHR
VARHR
xVARG
Step 15: Write to xVARG.
Step 16: Calculate the Wh/LSB, VARh/LSB, and VAh/LSB
constants.
()
xWATTHR
AccumTimeθcosVI
LSB
Wh
NOM
TEST
×
×
×
×
=
3600
(66)
xVAHR
AccumTimeVI
LSB
VAh
NOM
TEST
×
×
×
=
3600
(67)
()
xVARHR
AccumTimeθsinVI
LSB
VARh
NOM
TEST
×
×
×
×
=
3600
(68)
Example: Watt Gain Calibration Using Line Accumulation
This example shows only Phase A watt calibration. The steps
outlined in the Gain Calibration Using Line Accumulation
section show how to calibrate watt, VA, and VAR. All three
phases can be calibrated simultaneously because there are nine
energy registers.
For this example, I
TEST
= 10 A, V
NOM
= 220 V, Power Factor = 1,
Frequency = 50 Hz, LINECYC (0x1C) is set to 0x800, and MC =
3200 imp/kWhr.