ADE7753 View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'ADE7753' PDF : 60 Pages View PDF
ADE7753
Phase Calibration
The PHCAL register is provided to remove small phase errors.
The ADE7753 compensates for phase error by inserting a small
time delay or advance on the voltage channel input. Phase leads
up to 1.84° and phase lags up to 0.72° at 50 Hz can be corrected.
The error is determined by measuring the active energy at IB
and two power factors, PF = 1 and PF =0.5 inductive.
Some CTs may introduce large phase errors that are beyond the
range of the phase calibration register. In this case, coarse phase
compensation has to be done externally with an analog filter.
The phase error can be obtained from either CF or LAENERGY
measurements:
Error = LAENERGYIB, PF=.5 − LAENERGYIB(expected) 2
LAENERGYIB(expected) 2
(56)
If watt gain and offset calibration have been performed, there
should be 0% error in CF at unity power factor and then:
Error = %ERRORCF(IB,PF = .5) /100
(57)
The phase error is
Phase
Error
(°)
=
−Arcsin
⎜⎜⎝⎛
Error
3
⎟⎟⎠⎞
(58)
The relationship between phase error and the PHCAL phase
correction register is
PHCAL=
INT
⎜⎝⎛
Phase
Error(°)×
PERIOD
360°
⎟⎠⎞
+
0x0D
(59)
The expression for PHCAL can be simplified using the
assumption that at small x:
Arcsin(x) ≈ x
The delay introduced in the voltage channel by PHCAL is
Delay = (PHCAL − 0x0D) × 8/CLKIN
(60)
The delay associated with the PHCAL register is a time delay if
(PHCAL − 0x0D) is positive but represents a time advance if
this quantity is negative. There is no time delay if PHCAL =
0x0D.
The phase correction is in the opposite direction of the phase
error.
Phase Correction (°) = −(PHCAL − 0x0D) × 360° (61)
PERIOD
Calibrating Phase Using a Reference Meter Example
A power factor of 0.5 inductive can be assumed if the pulse
output rate of the reference meter is half of its PF = 1 rate. Then
the %ERROR between CF and the pulse output of the reference
meter can be used to perform the preceding calculations.
SET ITEST = Ib, VTEST = VNOM, PF = 0.5
MEASURE THE % ERROR BETWEEN
THE CF OUTPUT AND THE
REFERENCE METER OUTPUT
CALCULATE PHCAL. SEE EQUATION 59.
WRITE PHCAL VALUE TO THE PHCAL
REGISTER: ADDR. 0x10
02875-A-010
Figure 84. Calibrating Phase Using a Reference Meter
For this example:
CF % Error at PF = .5 Inductive:
0.215%
PERIOD Register Reading:
%ERRORCF(IB,PF = .5) =
PERIOD = 8959
Then PHCAL is 11 using Equations 57 through 59:
Error = 0.215% / 100 = 0.00215
Phase
Error
(°)
=
−Arcsin
⎜⎜⎝⎛
0.00215
3
⎟⎟⎠⎞
=
−0.07°
PHCAL
=
INT
⎜⎝⎛
−
0.07° ×
8959
360°
⎟⎠⎞
+0x0D
= −2
+
13
=
11
PHCAL can be expressed as follows:
PHCAL =
INT
⎜⎜⎝⎛ − Arcsin⎜⎜⎝⎛
Error
3
⎟⎟⎠⎞ ×
PERIOD
2π
⎟⎟⎠⎞
+
0x0D
(62)
Note that PHCAL is a signed twos complement register.
Setting the PHCAL register to 11 provides a phase correction
of 0.08° to correct the phase lead:
Phase Correction (°) = − (PHCAL − 0x0D)× 360°
PERIOD
Phase Correction (°) = − (11 − 0x0D)× 360° = 0.08°
8960
Rev. C | Page 44 of 60
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