Datasheet
ADE7116/ADE7156/ADE7166/ADE7169/ADE7566/ADE7569
Rev. B | Page 55 of 152
Fault with Inactive Input Greater Than Active Input
If the difference between I
PB
, the inactive input, and I
PA
, the
active input (that is, being used for billing), becomes greater
than 6.25% of I
PB
, and the FAULTSIGN bit (Bit 6) of the
ACCMODE register (Address 0x0F) is cleared, the FAULTSIGN
flag (Bit 5) in the Interrupt Status 1 SFR (MIRQSTL, Address
0xDC) is set. The I
PB
analog input becomes the active input.
Again, a time constant of about 3 seconds is associated with this
swap. I
PA
does not become the active channel again until I
PA
is
greater than I
PB
and the difference between I
PA
and I
PB
—in this
order—becomes greater than 6.25% of I
PB
. However, if the
FAULTSIGN bit (Bit 6) of the ACCMODE register (Address 0x0F)
is set, the FAULTSIGN flag (Bit 5) in the Interrupt Status 1 SFR
(MIRQSTL, Address 0xDC) is set as soon as I
PA
is within 6.25%
of I
PB
. This threshold eliminates potential chatter between I
PA
and I
PB
.
Calibration Concerns
Typically, when a meter is calibrated, the voltage and current
circuits are separated, as shown in Figure 49. Current passes
through only the phase circuit or the neutral circuit. Figure 49
shows current being passed through the phase circuit. This is
the preferred option because the ADE7116/ADE7156/
ADE7166/ADE7169 start billing on the I
PA
input on power-up.
The phase circuit CT is connected to I
PA
in the diagram.
Because the current sensors are not perfectly matched, it is
important to match current inputs. The ADE7116/
ADE7156/ADE7166/ADE7169 provide a gain calibration
register for I
PB
, IBGAIN (Address 0x1C). IBGAIN is a 12-bit,
signed, twos complement register that provides a gain
resolution of 0.0244%/LSB.
For calibration, a first measurement should be done on I
PA
by
setting the SEL_I_CH bits to 0b01 in the CALMODE register
(Address 0x3D). This measurement should be compared to the
measurement on I
PB
. Measuring I
PB
can be forced by setting the
SEL_I_CH bits to 0b10 in the CALMODE register (Address 0x3D).
The gain error between these two measurements can be evaluated
using the following equation:
()
() ()
()
A
AB
ItMeasuremen
ItMeasuremenItMeasuremen
Error
−
=%
(2)
The two channels, I
PA
and I
PB
, can then be matched by writing
−Error(%)/(1 + Error (%)) × 2
12
to the IBGAIN register
(Address 0x1C). This matching adjustment is valid for all
energy measurements made by the ADE7116/ADE7156/
ADE7166/ADE7169, including active power, reactive power
(ADE7169 only), apparent power, and I
rms
.
AGND
I
PB
I
N
I
PA
R
F
R
F
C
F
C
F
CT
CT
R
B
R
B
0V
V
A
0
I
PB
PHASE
NEUTRAL
R
F
R
A
V
P
R
F
V
N
C
T
C
F
V
TEST
CURRENT
240V rms
06353-025
Figure 49. Fault Conditions for Inactive Input Greater Than Active Input
di/dt CURRENT SENSOR AND DIGITAL
INTEGRATOR FOR THE ADE7169/ADE7569
A di/dt sensor, a feature available for the AD7169/ADE7569 but
not for the ADE7116/ADE7156/ADE7166/ADE7169, detects
changes in the magnetic field caused by ac currents. Figure 50
shows the principle of a di/dt current sensor.
MAGNETIC FIELD CREATED BY CURRENT
(DIRECTLY PROPORTIONAL TO CURRENT)
+ EMF (ELECTROMOTIVE FORCE)
– INDUCED BY CHANGES IN
MAGNETIC FLUX DENSITY (di/dt)
06353-026
Figure 50. Principle of a di/dt Current Sensor
The flux density of a magnetic field induced by a current is
directly proportional to the magnitude of the current. The
changes in the magnetic flux density passing through a conductor
loop generate an electromotive force (EMF) between the two
ends of the loop. The EMF is a voltage signal that is proportional
to the di/dt of the current. The voltage output from the di/dt
current sensor is determined by the mutual inductance between
the current-carrying conductor and the di/dt sensor. The current
signal needs to be recovered from the di/dt signal before it can
be used. An integrator is, therefore, necessary to restore the
signal to its original form.