ADE7758 Analog Devices, ADE7758 Datasheet - Page 49

• Manufacturer Part Number: ADE7758
• Description: Poly Phase Multifunction Energy Metering IC with Per Phase Information
• Manufacturer: Analog Devices

Step 8: Read all six xWATTHR (0x01 to 0x03) and xVAHR
(0x07 to 0x09) energy registers after the LENERGY interrupt
and store the values.
Step 8a: Calculate the values to be written to xWG registers
according to the following equation.
where Accumulation Time is
MC is the meter constant, θ is the angle between the current
and voltage, Line Frequency is read from the FREQ register or is
known, and the No. of Phases Selected are the number of ZXSEL
bits set to Logic 1 in LCYCMODE (0x17).
Step 8b: Calculate the values to be written to the xVAG registers
according to the following equation.
Step 9: Write to xWG and xVAG.
Step 10: Set the test system for I
(calibrate VAR gain).
Step 11: Repeat Step 7.
Step 12: Read the xVARHR (0x04 to 0x06) after the LENERGY
interrupt and store the values.
Step 13: Calculate the values to be written to the xVARG
registers (to adjust VARCF to the expected value).
Step 14: Write to xVARG.
Step 15: Calculate the Wh/LSB, VARh/LSB, and VAh/LSB
constants.
AccumTime
xWG
xVAG
xVAG
Wh
LSB
xWATTHR
xVAHR
xVAHR
AccumTime
AccumTime
2
2
2
12
AccumTime
12
12
=
=
=
=
[
[
I
11
11
TEST
4
4
4
0 :
0 :
×
[
11
×
, 3
×
MC
=
]
]
×
600
MC
0 :
MC
×
×
V
2
VADIV
VADIV
]
NOM
×
×
×
×
×
, 1
×
, 1
Line
WDIV
, 1
I
xWATTHR
000
I
000
TEST
I
000
TEST
×
TEST
AccumTime
×
×
Frequency
×
×
×
×
, 3
, 3
V
TEST
V
, 3
600
600
V
TEST
TEST
600
LINECYC
TEST
, V
×
×
NOM
×
sin
cos
×
cos
, and zero power factor
No.
( )
( )
θ
θ
( )
[
θ
15
×
of
×
×
0 :
Phases
]
Selected
(42)
(44)
(45)
(46)
(43)
Rev. A | Page 49 of 68
Example—Watt Gain Calibration Using Line Accumulation
This example only shows 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
Frequency = 50 Hz, LINECYC (0x1C) is set to 1FF, and
MC = 3200 imp/kWhr.
To set APCFNUM (0x45) and APCFDEN (0x46) to the
calculated value to perform a coarse adjustment on the
imp/kW-hr ratio, use Equation 27 to Equation 29:
Under the test conditions above, the AWATTHR register value
is 24008d after the LENERGY interrupt. Using Equation 42 and
Equation 43, the value to be written to AWG is 02d.
Using Equation 46, the Wh/LSB constant is
Phase Calibration Using Line Accumulation
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’s phase calibration is a time delay with different
weights in the positive and negative direction (see the Phase
Compensation section). Since a current transformer is a source
of phase error, a fixed nominal value may be decided on to load
into the xPHCAL (0x3F to 0x41) registers at power-up. During
calibration, this value can be adjusted for CT-to-CT error.
VAh
VARh
APCF
APCF
APCFDEN
AccumTime
xWG
Wh
LSB
LSB
LSB
=
NOMINAL
EXPECTED
=
=
=
, 3
10
I
2
TEST
12
600
I
TEST
×
= INT
×
=
220
×
TEST
×
, 3
4
2
, 3
=
×
0
V
=
24
600
×
×
600
16
1 x
V
NOM
×
= 10 A, V
50
, 3
. 1
, 3
541
,
NOM
008
, 1
1
kH
200
FF
, 1
95
200
×
×
7 .
000
×
000
×
3
xVAHR
Hz
Hz
z
xVARHR
×
×
=
AccumTime
=
×
×
×
10
AccumTime
×
1
. 4
10
, 3
=
220
500
7 .
, 3
NOM
×
33
600
227
s
×
600
220
×
×
220
= 220 V, Power Factor = 1,
130
10
10
×
5 –
cos
×
=
1
. 0
( )
θ
×
54
24
=
1
. 1
7 .
,
008
95
s
ADE7758
Hz
×
1
=
. 2
(47)
(48)
268