Datasheet
ADE7758 Data Sheet
Rev. E | Page 48 of 72
VARCFNU
M
VARCFDEN
Q
VARCF
%VARCF
xVAROS
EXPECTED
ERROR
××
⎟
⎠
⎞
⎜
⎝
⎛
×
=
4
2
%100
– (57)
where Q is defined in Equation 58 and Equation 59.
For xWATTOS,
4
1
2
1
4
25
××=
CLKIN
Q
(58)
For xVAROS,
4
1
4
0]:[11
202
2
1
4
24
×
⎟
⎠
⎞
⎜
⎝
⎛
××=
FREQ
CLKIN
Q (59)
where the FREQ (0x10) register is configured for line period
measurements.
Step 7: Repeat Step 3 to Step 6 for xVAROS calibration.
Example: Offset Calibration of Phase A Using Pulse Output
For this example, I
MIN
= 50 mA, V
NOM
= 220 V, V
FULLSCALE
=
500 V, I
FULLSCALE
= 130 A, MC = 3200 impulses/kWh, Power
Factor = 1, Frequency = 50 Hz, and CLKIN = 10 MHz.
With I
MIN
, V
NOM
, and unity power factor, the example ADE7758
meter shows 0.009789 Hz on the APCF pulse output. When the
power factor is changed to 0.5 inductive, the VARCF output is
0.009769 Hz.
This is equivalent to 0.1198% for the watt measurement and
−0.0860% for the VAR measurement. Using Equation 56
through Equation 59, the values 0xFFD and 0x3 should be
written to AWATTOS (0x39) and AVAROS (0x3C), respectively.
0xFFD3– –2.8
1
277
0.01863
2
0.009778
%100
0.1198%
–
4
===××
⎟
⎠
⎞
⎜
⎝
⎛
×
=AWATTOS
32.6
1
277
0.01444
2
0.009778
%100
0.0860%–
–
4
==××
⎟
⎠
⎞
⎜
⎝
⎛
×=AVAROS
For AWATTOS,
01863.0
4
1
2
1
4
610
25
=××=
E
Q
For AVAROS,
0.01444
4
1
4
2083
202
2
1
4
610
24
=×××=
E
Q
Calibration Using Line Accumulation
Line cycle accumulation mode configures the nine energy
registers such that the amount of energy accumulated over an
integer number of half line cycles appears in the registers after
the LENERGY interrupt. The benefit of using this mode is that
the sinusoidal component of the active energy is eliminated.
Figure 81 shows a flowchart of how to calibrate the ADE7758
using the line accumulation mode. Calibration of all phases and
energies can be done simultaneously using this mode to save
time during calibration.
START
CAL IRMS OFFSET
CAL VRMS OFFSET
CAL WATT AND VA
GAIN ALL PHASES
@ PF = 1
CAL VAR GAIN ALL
PHASES @ PF = 0,
INDUCTIVE
CALIBRATE PHASE
ALL PHASES
@ PF = 0.5,
INDUCTIVE
CALIBRATE ALL
PHASES WATT
OFFSET @ I
MIN
AND
PF = 1
CALIBRATE ALL
PHASES VAR
OFFSETS @ I
MIN
AND PF = 0,
INDUCTIVE
END
04443-080
Figure 81. Calibration Using Line Accumulation