ADE9078ACPZ datasheet(53/108 Pages) AD

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ADE9078

Data Sheet

Rev. 0 | Page 52 of 107

error. It can be checked if the phase angles correspond to the

ones in the phasor diagrams given in the Applications

Information section.

The times between negative to positive zero crossings are

measured using a CLKIN/24 = 12.288/12 = 512 kHz clock. The

time between the zero-crossing on Phase A and Phase B is

stored in the ANGL_VA_VB register. The resolution of the

ANGLx_x2x register is (1/512000)/20 ms × 360° = 0.03515625°

at 50 Hz.

The time between the zero crossing on Phase B and Phase C is

stored in the ANGL_VB_VC register and the time in between

the zero crossings on Phase A and Phase C is stored in the

ANGL_VA_VC register, as shown in Figure 75.

PHASE A

PHASE B

PHASE C

ANGL_VA_VB ANGL_VB_VC

ANGL_VA_VC

Figure 75. Voltage to Voltage Phase Angle

The angle in degrees can be calculated from the following

equation with a 50 Hz line period:

Angle (degrees) = ANGL_VA_VB × 0.03515625/LSB

For a 4-wire wye configuration, the expected ANGL_VA_VB

and ANGL_VB_VC is 120°/0.03515625 = 3413d. Note that the

expected ANGL_VA_VC from Phase A voltage to Phase C

voltage is 240°/0.03515625 = 6826d, which corresponds to a

120° angle between Phase C and Phase A.

The current to current zero crossings are also measured. This

measurement is done similarly to the voltage to voltage phase

angle described previously, except the current channel zero

crossings are used as the reference. The time between the zero

crossing on Phase A and Phase B is stored in the ANGL_IA_IB

Phase C is stored in the ANGL_IB_IC register and the time in

between the zero crossings on Phase A and Phase C is stored in

the ANGL_IA_IC register.

The voltage to current phase angles are measured as well. Use

these measurements to determine the power factor at the

fundamental. ANGL_VA_IA reflects the phase angle between

the Phase A voltage and current, as shown in Figure 76.

ANGL_VB_IB holds the Phase B voltage to current phase angle,

whereas ANGL_VC_IC holds the Phase C voltage to current

phase angle.

PHASE A

CURRENT

ANGL_VA_IA

PHASE A

VOLTAGE

Figure 76. Voltage to Current Phase Angles

Note that if the magnitude of the voltage channel is below the

user configured zero-crossing threshold, the zero-crossing

output for that phase is not generated. In this event, the

corresponding ANGLx_x2x measurements are not updated—

the last value remains in the register. The current channel does

not have these thresholds. When low input signal levels occur,

spurious zero-crossing events may be generated on the current

channel, which results in ANGLx_I2I and ANGLx_V2I

readings that are not meaningful.

Phase Sequence Error Detection

4-Wire Wye and 4-Wire Delta

For 4-wire wye and 4-wire delta meters, the normal phase

sequence is shown in Figure 77.

ZXC

ZXB

PHASE A

PHASE B

PHASE C

A,B,C PHASE

VOLTAGES AFTER

LPF1

ZXA

NORMAL PHASE SEQUENCE

SEQERR = 0

Figure 77. 4-Wire Wye and 4-Wire Delta Normal Phase Sequence

For a 4-wire wye or 4-wire delta system, VCONSEL = 000, 010,

or 011 as described in the Applications Information section. In

these 4-wire systems, the negative to positive transitions on ZXVA,

ZXVB, and ZXVC are monitored to determine if there is a phase

sequence error as shown in Figure 79. To detect a phase sequence

error, set how many sequences to observe in the SEQ_CYC register.

It is recommended to set SEQ_CYC to 1.

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