ADE7758 Analog Devices, ADE7758 Datasheet - Page 52

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

ADE7758
Step 11: Calculate the value written to the xVAROS registers
according to the following equations.
Example—Power Offset Calibration Using Line
Accumulation
This example only shows Phase A of the phase active power
offset calibration. Both active and reactive power offset for all
phases can be calibrated simultaneously using the method
explained in the Power Offset Calibration Using Line
Accumulation section.
For this example, I
Power Factor = unity, Frequency = 50 Hz, and LINECYC =
0xFFF.
At I
AWATTHR (0x01) register after gain calibration at 0xFFF line
cycles. At I
register. By using Equation 52, this is equivalent to the 6 LSBs of
offset, therefore, using Equation 53, the value written to
AWATTOS is 94d.
TEST
Offset
Offset
xVAROS
AWATTOS
, the example ADE7758 meter shows 192489d in the
MIN
=
=
, the meter shows 1919d in the AWATTHR
1919
xVARHR
[
11
=
:
] 0
TEST
13
×
10
.
+
65
= 10 A, I
0
AccumTime
×
1 .
6
–
×
×
10
192
I
–
I
TEST
4
MIN
10
MHz
,
Offset
489
MIN
–
–
xVARHR
I
×
TEST
×
= 100 mA, V
2
×
×
0
29
1 .
4
CLKIN
=
=
94
. 5
.
95
39
×
I
×
MIN
NOM
2
29
= 220 V,
(54)
(55)
Rev. A | Page 52 of 68
Calibration of IRMS and VRMS Offset
IRMSOS and VRMSOS are used to cancel noise and offset
contributions from the inputs. The calibration method is the
same whether calibrating using the pulse outputs or line
accumulation. Reading the registers is required for this
calibration since there is no rms pulse output. The rms offset
calibration should be performed before VAGAIN calibration.
The rms offset calibration also removes offset from the VA
calculation. For this reason, no VA offset register exists in the
ADE7758.
The low-pass filter used to obtain the rms measurements is not
ideal, therefore it is recommended to synchronize the readings
with the zero crossings of the voltage waveform and to average a
few measurements when reading the rms registers.
The ADE7758 IRMS measurement is linear over a 500:1 range,
and the VRMS measurement is linear over a 20:1 range. To
measure the voltage VRMS offset (xVRMSOS), measure rms
values at two different nonzero current levels, for example,
V
(IRMSOS), measure rms values at two different nonzero current
levels, for example, I
test conditions: I
V
measurements.
NOM
NOM
/20. Figure 84 shows a flow chart for calibrating the rms
and V
NOM
/20. To measure the current rms offset
TEST
TEST
and V
and I
NOM
MAX
, I
MAX
/500). This translates to three
/500 and V
NOM
, I
TEST
and