ADE7758 Analog Devices, ADE7758 Datasheet - Page 44

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

ADE7758
is approximately 16 kHz. A sample set of meters could be tested
to find a more exact value of the pulse output at full scale.
To calculated the values for APCFNUM/APCFDEN and
VARCFNUM/VARCFDEN use the following formulas
where MC is the meter constant, I
the nominal voltage that the meter is tested at, and V
and I
correspond to the full scale ADC inputs of the ADE7758. θ is
the angle between the current and the voltage channel, and the
APCF
under the test conditions.
The equations for calculating the VARCFNUM and
VARCFDEN during VAR calibration are similar, with one
exception
Because the CFNUM and CFDEN values can be calculated
from the meter design, these values can be written to the part
automatically during production calibration.
Step 5: Set the test system for I
factor. For VAR calibration, the power factor should be set to 0
in this step. For watt and VA, the unity power factor should be
used. VAGAIN can be calibrated at the same time as WGAIN
because VAGAIN can be calibrated at the unity power factor,
and both pulse outputs can be measured simultaneously.
However, when calibrating VAGAIN at the same time as
WGAIN, the rms offsets should be calibrated first (see the
Calibration of IRMS and VRMS Offset section).
Step 6: Measure the percent error in the pulse output, APCF
and/or VARCF, from the reference meter:
where CF
meter.
FULLSCALE
VARCF
%
APCF
APCF
APCFDEN
EXPECTED
Error
REF
NOMINAL
EXPECTED
EXPECTED
= APCF
are the values of current and voltage, which
=
value is equivalent to the reference meter output
APCF
=
= 16
INT
=
CF
EXPECTED
=
MC
–
REF
⎛
⎜
⎝
MC
CF
kHz
, 1
APCF
APCF
×
000
REF
, 1
×
= the pulse output of the reference
I
×
000
TEST
TEST
×
V
×
EXPECTED
I
NOMINAL
TEST
100
FULLSCALE
, 3
V
×
, V
×
TEST
600
NOM
, 3
V
%
×
600
NOM
NOM
is the test current, V
V
⎞
⎟
⎠
, and the unity power
NOM
×
×
cos
I
FULLSCALE
×
I
TEST
( )
sin
θ
( )
θ
FULLSCALE
(27)
(28)
(29)
(30)
(31)
NOM
Rev. A | Page 44 of 68
is
Step 7: Calculate xWG adjustment. One LSB change in xWG
(12 bits) changes the WATTHR register by 0.0244% and
therefore APCF by 0.0244%. The same relationship holds true
for VARCF.
When APCF is calibrated, the xWATTHR registers have the
same Wh/LSB from meter to meter if the meter constant and
the APCFNUM/APCFDEN ratio remain the same. The
Wh/LSB constant is
Step 8: Return to Step 2 to calibrate Phase B and Phase C gain.
Example—Watt Gain Calibration of Phase A
Using Pulse Output
For this example, I
I
and Frequency = 50 Hz.
Set APCFNUM(0x45) and APCFDEN(0x46) to the calculated
value to perform a coarse adjustment on the imp/kWh ratio.
Using Equations 27 through 29.
With I
ADE7758 meter shows 1.92 Hz on the pulse output. This is
equivalent to a 2.04% error from the reference meter value
using Equation 31.
FULLSCALE
%
APCF
APCF
xWG =
APCF
APCF
APCFDEN
LSB
Wh
TEST
Error
= 130 A, MC = 3200 impulses/kWh, Power Factor = 1,
, V
=
NOMINAL
EXPECTED
NOMINAL
EXPECTED
NOM
4
=
–
. 1
. 0
×
%
, and the unity power factor, the example
= INT
92
0244
Error
, 1
TEST
×
M
Hz
. 1
=
000
=
=
APCFNUM
96
C
APCFDEN
16
%
= 10 A, V
, 3
⎛
⎜
⎜
⎝
–
, 1
. 1
542
Hz
200
. 1
kHz
×
000
96
96
×
Hz
APCFNUM
Hz
APCFDEN
Hz
×
×
10
, 3
1
220
500
⎞
⎟
⎟
⎠
NOM
×
600
×
[
[
=
11
11
220
100
277
×
0 :
= 220 V, V
0 :
130
%
10
×
]
]
cos
=
×
×
=
. 2
⎛
⎜
⎝
( )
. 0
1
WDIV
0
04
542
+
%
=
1
FULLSCALE
xWG
. 1
kHz
96
2
Hz
[
12
11
= 500 V,
0 :
(32)
(33)
(34)
]
⎞
⎟
⎠