ADE7166_15 datasheet(55/152 Pages) AD

55 / 152 page

ADE7116/ADE7156/ADE7166/ADE7169/ADE7566/ADE7569

Rev. B | Page 55 of

152

Fault with Inactive Input Greater Than Active Input

If the difference between IPB, the inactive input, and IPA, the

active input (that is, being used for billing), becomes greater

than 6.25% of IPB, 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 IPB analog input becomes the active input.

Again, a time constant of about 3 seconds is associated with this

swap. IPA does not become the active channel again until IPA is

greater than IPB and the difference between IPA and IPB—in this

order—becomes greater than 6.25% of IPB. 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 IPA is within 6.25%

of IPB. This threshold eliminates potential chatter between IPA

and IPB.

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 IPA input on power-up.

The phase circuit CT is connected to IPA 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

signed, twos complement register that provides a gain

resolution of 0.0244%/LSB.

For calibration, a first measurement should be done on IPA by

setting the SEL_I_CH bits to 0b01 in the CALMODE register

(Address 0x3D). This measurement should be compared to the

measurement on IPB. Measuring IPB 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:

()

( )

()

Measuremen

Error

−

(2)

The two channels, IPA and IPB, can then be matched by writing

−Error(%)/(1 + Error (%)) × 212 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 Irms.

AGND

IPB

IPA

IPB

TEST

CURRENT

240V rms

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)

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.

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