ADE9000 Technical Reference Manual
UG-1098
Rev. 0 | Page 51 of 86
CALIBRATION
The following section describes calibrating the
register readings. The expected register values at full scale are
used as the reference.
Table 29. Full-Scale ADC Codes
Parameter
Full-Scale Codes (Decimal)
Total and Fundamental IRMS and
VRMS
52,702,092
Total and Fundamental WATT,
VAR, and VA
20,694,066
Fast RMS½
52,702,092
10 Cycle RMS/12 Cycle RMS
52,702,092
Resampled Data
18,196
SYSTEM PARAMETERS
The system is calibrated at nominal operating voltage and current
using an accurate source. The accuracy of the calibration is less
than or equal to the accuracy of the source. The example shows
the calibration for Channel A. The calculations are similar for
Channel B and Channel C.
•
V
NOMINAL
= 220 V rms
•
I
NOMINAL
= 10 A rms
•
Line frequency = 50 Hz
•
Current transformer ratio = 3000:1
•
Burden resistor = 20 Ω
•
Voltage Divider R1 = 990 kΩ
•
R2 = 1 kΩ
The current transfer function is 20/3000 = 0.0067 V rms/A rms.
The voltage transfer function is 1/(900 + 1) = 0.001 V rms/A rms.
The input at the current ADC pins is 0.0067 × 10 = 0.067 V rms.
The input at the voltage ADC pins is 0.001 × 220 = 0.22 V rms.
The ADC full-scale voltage at gain = 1 is 0.707 V rms.
The nominal current as a percentage of full scale is
I
FSP
= 0.067/0.707 = 9.47%.
The nominal voltage as a percentage of full scale is
V
FSP
= 0.220/0.707 = 31.1%.
RMS CALIBRATION
AIGAIN and AVGAIN are the respective current and voltage
calibration registers for Channel A.
With the nominal voltage and current inputs, read the AIRMS
and AVRMS registers. It is recommended to read the rms values
at zero-crossings for 1 sec and average them for better accuracy.
For this example, the AIRMS register reading is 5,294,441.
The expected AIRMS register reading is
I
FSP
×
full-scale rms codes
= 0.0947 × 52,702,092 = 4,801,488
Therefore, the following gain must be applied to reach the
expected value:
907
.
0
441
,
294
,
5
488
,
801
,
4
=
=
=
MEASURED
EXPECTED
AIRMS
AIRMS
GAIN
The AIGAIN register is calculated as follows:
AIGAIN
= (
GAIN
− 1) × 2
27
= −12,482,248 = 0xFF418938
To calibrate AIRMSOS offset register, apply a small current
typically at 5000:1 or less dynamic range. In this example, the
offset calibration current is 20 mA.
After applying offset calibration current, the AIRMS register
reading is 70,431.
The expected AIRMS register reading is
Icalibration
FSP
×
Full-Scale RMS Codes
= 0.0002 × 52,702,092 = 10,540.
The AIRMSOS register is calculated as
0xFFFDBDE8
992
,
147
2
431
,
70
540
,
10
2
15
2
2
15
2
2
=
−
=
−
=
−
=
MEASURED
EXPECTED
AIRMS
AIRMS
AIRMSOS
Follow similar steps to obtain the AVGAIN and AVRMSOS
calibration constants.
PHASE CALIBRATION
APHCAL0 is the phase calibration register for Channel A.
To calculate APHCAL0, apply a nominal current and voltage at
a lagging 0.5 power factor such that the active and reactive
energy registers are positive. In this example, the energy
registers are configured such that EP_CFG = 0x0011 and
EGY_TIME = 7999 (1 sec accumulation).
Read the AWATTHR_HI and AVARHR_HI registers.
( )
( )
( )
( )
( )
( )
( )
( )
°
−
=
×
+
×
−
×
−
=
×
+
×
×
−
×
−
=
ϕ
−
−
49
.
0
60
sin
17585
60
cos
10356
60
cos
17585
60
sin
10356
tan
60
sin
_
60
cos
_
A
60
cos
_
60
sin
_
tan
)
(
1
1
HI
AVARHR
HI
WATTHR
HI
AVARHR
HI
AWATTHR
Error
Phase
Therefore, the phase calibration register is
0xFF3593B3
13265997
2
)
49
.
0
(
039
.
0
2
sin(
)
039
.
0
sin(
)
039
.
0
)
49
.
0
(
sin(
2
)
2
sin(
sin
)
sin(
27
27
=
−
=
×
−
−
×
+
−
−
=
×
ϕ
−
×
+
−
ϕ
=
RADIAN
RADIAN
ω
ω
ω
APHCAL0
APHCAL0
= 0xFF3593B3
Follow similar steps to obtain the BPHCAL0 and CPHCAL0
calibration constants.
