ADE7758 Analog Devices, ADE7758 Datasheet - Page 50

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

ADE7758
Figure 82 shows the steps involved in calibrating the phase
using the line accumulation mode.
Step 1: If the values were changed after gain calibration, Step 1,
Step 3, and Step 4 from the gain calibration should be repeated
to configure the LCYCMODE and LINECYC registers.
Step 2: Set the test system for I
Step 3: Reset the interrupt status register by reading RSTATUS
(0x1A).
Step 4: The xWATTHR registers should be read after the
LINECYC interrupt. Measure the percent error in the energy
register readings (AWATTHR, BWATTHR, and CWATTHR)
compared to the energy register readings at unity power factor
(after gain calibration) using Equation 49. The readings at unity
power factor should have been repeated after the gain
calibration and stored for use in the phase calibration routine.
Step 5: Calculate the Phase Error in degrees using the following
equation.
Error
Phase
Figure 82. Phase Calibration Using Line Accumulation
Error
=
xWATTHR
( )
°
=
–
SET UP SYSTEM FOR
READ ALL XWATTHR
ERROR IN DEGREES
XPHCAL REGISTERS
Arcsin
LINECYC AND MASK
I
STEP 1
STEP 2
STEP 3
STEP 4
STEP 5
CALCULATE PHASE
STEP 6
TEST
REGISTERS AFTER
xWATTHR
FOR ALL PHASES
CALCULATE AND
SET LCYCMODE,
RESET STATUS
WRITE TO ALL
PF
REGISTERS
INTERRUPT
, V
REGISTER
LENERGY
=
NOM
⎛
⎜
⎝
5
Error
–
TEST
2
, PF = 0.5
xWATTHR
3
, V
PF
⎞
⎟
⎠
NOM
=
1
2
, and 0.5 power factor.
PF
=
1
(50)
(49)
Rev. A | Page 50 of 68
Step 6: Calculate xPHCAL and write to the xPHCAL registers
(0x3F to 0x41).
The period is available in the ADE7758 frequency register if it is
not known. Equation 37 shows how to determine the value
written to xPHCAL using the period register measurement (see
the Phase Calibration Using Pulse Output section). In Equation
37, the 2.4 µs is for phase errors that are negative. For positive
phase error, the 2.4 µs is replaced by 4.8 µs (see the Phase
Compensation section).
Example—Phase Calibration Using Line Accumulation
This example shows only Phase A phase calibration. All three
PHCAL registers can be calibrated simultaneously using the
same method.
For this example, I
inductive, and Frequency = 50 Hz.
With I
ADE7758 meter shows 12036d in the AWATTHR (0x01)
register. For unity power factor (after gain calibration), the
meter shows 24020d in the AWATTHR register. This is
equivalent to 26 LSBs of error.
The Phase Error in degrees using Equation 50 is −0.07°.
Using Equation 37, the value written to APHCAL (0x3F), if at
50 Hz the FREQ (0x10) register = 2083d, is 21d.
Power Offset Calibration Using Line Accumulation
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.
The ADE7758 has power offset registers for watts and VAR,
xWATTOS (0x39 to 0x3B) and xVAROS (0x3C to 0x3E).
Offsets in the VA measurement are compensated by adjusting
the rms offset registers (see the Calibration of IRMS and VRMS
Offset section). Figure 83 shows the steps to calibrate the power
offsets using the line accumulation mode.
Phase
xPHCAL
APHCAL
TEST
, V
Error
NOM
=
=
, and 0.5 inductive power factor, the example
2
–
( )
°
4 .
TEST
2
4 .
µ
=
s
= 10 A, V
–Arc
µ
×
Phase
s
360
×
360
sin
× °
.
Error
07
⎛
⎜
⎝
°
⎛
⎜
⎜
⎝
NOM
. 0
×
2083
°
00215
Period
( )
= 220 V, Power Factor = 0.5
3
°
×
1
1
9
⎞
⎟
⎠
6 .
( )
=
s
µ
–
s
. 0
⎞
⎟
⎟
⎠
07
=
21
°
(51)