ADE7758 Analog Devices, ADE7758 Datasheet - Page 21

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

di/dt CURRENT SENSOR AND DIGITAL
INTEGRATOR
The di/dt sensor detects changes in the magnetic field caused by
the ac current. Figure 42 shows the 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. The ADE7758 has a built-
in digital integrator to recover the current signal from the di/dt
sensor. The digital integrator on Channel 1 is switched on by
default when the ADE7758 is powered up. Setting the MSB of
the GAIN[7:0] register turns on the integrator. Figure 43 to
Figure 46 show the magnitude and phase response of the digital
integrator.
–10
–20
–30
–40
–50
20
10
0
10
Digital Integrator and Phase Compensator
Figure 43. Combined Gain Response of the
Figure 42. Principle of a di/dt Current Sensor
100
FREQUENCY (Hz)
MAGNETIC FIELD CREATED BY CURRENT
(DIRECTLY PROPORTIONAL TO CURRENT)
+ EMF (ELECTROMOTIVE FORCE)
– INDUCED BY CHANGES IN
MAGNETIC FLUX DENSITY (di/dt)
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89.80
89.85
89.90
89.95
90.00
90.05
90.10
80
81
82
83
84
85
86
87
88
89
90
91
–1
Digital Integrator and Phase Compensator (40 Hz to 70 Hz)
Digital Integrator and Phase Compensator (40 Hz to 70 Hz)
5
4
3
2
1
0
10
40
40
Figure 44. Combined Phase Response of the
Figure 46. Combined Phase Response of the
Digital Integrator and Phase Compensator
Figure 45. Combined Gain Response of the
45
45
100
50
50
FREQUENCY (Hz)
FREQUENCY (Hz)
FREQUENCY (Hz)
55
55
1k
60
60
65
65
ADE7758
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70