Calibration; System Parameters; Rms Calibration; Phase Calibration - Analog Devices ADE9000 Technical Reference Manual

ADE9000 Technical Reference Manual

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
Total and Fundamental IRMS and
VRMS
Total and Fundamental WATT,
VAR, and VA
Fast RMS½
10 Cycle RMS/12 Cycle RMS
Resampled Data

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 = 220 V rms
NOMINAL
•
I = 10 A rms
NOMINAL
•
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 = 0.067/0.707 = 9.47%.
FSP
The nominal voltage as a percentage of full scale is
V = 0.220/0.707 = 31.1%.
FSP

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 × full-scale rms codes = 0.0947 × 52,702,092 = 4,801,488
FSP
ADE9000 using
Full-Scale Codes (Decimal)
52,702,092
20,694,066
52,702,092
52,702,092
18,196
Rev. 0 | Page 51 of 86
Therefore, the following gain must be applied to reach the
expected value:
AIRMS
= EXPECTED =
GAIN
AIRMS
MEASURED
The AIGAIN register is calculated as follows:
AIGAIN = (GAIN − 1) × 2
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 × Full-Scale RMS Codes
FSP
= 0.0002 × 52,702,092 = 10,540.
The AIRMSOS register is calculated as
AIRMS
EXPECTED
=
AIRMSOS
2 − 2
10 , 540 70 , 431
= = −
147
15
2
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
Phase Error ( )

AWATTHR _ HI

−
= − 1
tan

A WATTHR _ HI

( )

× −
10356 sin 60 17585

−
= − 1
tan

( )
+
10356 cos 60 17585

Therefore, the phase calibration register is

ϕ − +
sin( ω )

=
APHCAL0

× −
sin( 2 ω


−
sin( RADIAN ( . 0 49 )

=

× −
sin( 2 . 0 039 RADIAN

= − =
13265997 0xFF3593B3
APHCAL0 = 0xFF3593B3
Follow similar steps to obtain the BPHCAL0 and CPHCAL0
calibration constants.
UG-1098
, 4 801 , 488
=
. 0 907
, 5 294 , 441
27 = −12,482,248 = 0xFF418938
2 − 2
AIRMS
MEASURED
15
2
=
, 992 0xFFFDBDE8
( )
× − ×
sin 60 AVARHR _ HI cos
( )
× + ×
cos 60 AVARHR _ HI sin
( )

×
cos 60

= − °
. 0 49

( )
×
sin 60


sin ω

× 27
2

ϕ
)


− +
. 0 039 ) sin( . 0 039 )

× 27
2

−
( . 0 49 )

( )

60


( )
60
