ADE7758 Analog Devices, ADE7758 Datasheet - Page 45

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

The AWG value is calculated to be 84 d using Equation 33,
which means the value 0x3F should be written to AWG.
Phase Calibration Using Pulse Output
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). Because a current transformer is a
source of phase error, a fixed nominal value may be decided on
to load into the xPHCAL registers at power-up. During
calibration, this value can be adjusted for CT-to-CT error.
Figure 78 shows the steps involved in calibrating the phase
using the pulse output.
Step 1: Step 1 and Step 3 from the gain calibration should be
repeated to configure the ADE7758 pulse output.
Step 2: Set the test system for I
Step 3: Measure the percent error in the pulse output, APCF,
from the reference meter using Equation 31.
END
xWG
YES
=
Figure 78. Phase Calibration Using Pulse Output
–
PHASE ERROR
CALIBRATED?
. 0
. 2
PHASES
0244
START
04
ALL
FREQ REGISTER
PERIOD USING
%
MEASURE
%
=
84
NO
NO
TEST
CALCULATE PHASE
STEP 1
STEP 2
STEP 3
STEP 4
ERROR (DEGREES)
PHASE A, B, OR C
FOR I
AND ENABLE CF
SET UP SYSTEM
ERROR IN APCF
SET UP PULSE
, V
OUTPUT FOR
MEASURE %
PERIOD OF
OUTPUTS
KNOWN?
PF = 0.5
SYSTEM
NOM
TEST
, and 0.5 power factor.
, V
NOM
,
CALCULATE AND
STEP 5
YES
WRITE TO
XPHCAL
Rev. A | Page 45 of 68
Step 4: Calculate the Phase Error in degrees using the following
equation:
Step 5: Calculate xPHCAL
If it is not known, the period is available in the ADE7758’s
frequency register, FREQ (0x10). Equation 37 shows how to
determine the value that needs to be written to xPHCAL using
the period register measurement. In Equation 37, the 2.4 µs is
for phase errors that are negative. For positive phase errors, the
2.4 µs is replaced by 4.8 µs (see the Phase Compensation
section).
Example—Phase Calibration of Phase A Using Pulse Output
For this example, I
I
inductive, and Frequency = 50 Hz.
With I
ADE7758 meter shows 0.9821Hz on the pulse output. This is
equivalent to 0.215% error from the reference meter value using
Equation 31.
The Phase Error in degrees using Equation 35 is −0.07°.
If at 50 Hz the FREQ register = 2083d, the value that should be
written to APHCAL (0x15) is 0x15 using Equation 37.
Power Offset Calibration Using Pulse Output
Power offset calibration should be used for outstanding
performance over a wide dynamic range (1,000:1). Calibration
of the power offset is done at or close to the minimum current
where the desired accuracy is required. The ADE7758 has
power offset registers for watts and VAR (xWATTOS and
xVAROS). Offsets in the VA measurement are compensated by
adjusting the rms offset registers (see the Calibration of IRMS
and VRMS Offset section). Figure 79 shows the steps to
calibrate the power offsets using the pulse outputs.
FULLSCALE
Phase
xPHCAL
Phase
APHCAL
xPHCAL
TEST
= 130 A, MC = 3200 impulses/kWh, Power Factor = 0.5
1
, V
Error
Error
NOM
=
=
=
, and 0.5 inductive power factor, the example
( )
( )
Arc
. 0
–
°
°
TEST
07
2
=
=
4 .
sin
× °
–
–
= 10 A, V
μs
Arc
Arc
Phase
⎛
⎜ ⎜
⎝
9
2
Error
6 .
4 .
×
1
sin
sin
µ
µ
360
3
s
s
⎛
⎜ ⎜
⎝
⎛
⎜ ⎜
⎝
×
Error
⎞
⎟ ⎟
⎠
CF
°
. 0
2083
×
360
NOM
×
00215
ERROR
9
2
Period
3
6 .
4 .
3
°
( )
= 220 V, V
°
µ
µ
=
s
s
1
⎞
⎟ ⎟
⎠
20
⎞
⎟ ⎟
⎠
×
=
( )
.
66
s
FREQ
–
. 0
=
07
360
FULLSCALE
21
°
[
11
°
ADE7758
0 :
]
= 500 V,
(37)
(35)
(36)