ADE7752BARW AD [Analog Devices], ADE7752BARW Datasheet - Page 24

• Manufacturer Part Number: ADE7752BARW
• Description: Polyphase Energy Metering IC with Pulsed Output
• Manufacturer: AD [Analog Devices]

Preliminary Technical Data
SELECTING A FREQUENCY FOR AN ENERGY METER APPLICATION
As shown in Table 5, the user can select one of seven
frequencies. This frequency selection determines the maximum
frequency on F1 and F2. These outputs are intended to be used
to drive the energy register (electromechanical or other). Since
seven different output frequencies can be selected, the available
frequency selection has been optimized for a 3-phase 4-wire
service with a meter constant of 100 imp/kWhr and a
maximum current of between 10 A and 100 A. Table 8 shows
the output frequency for several maximum currents (I
a line voltage of 220 V (phase neutral). In all cases, the meter
constant is 100 imp/kWhr.
Table 8. F1 and F2 Frequency at 100 imp/kWhr
I
10
25
40
60
80
100
The F
output frequencies on F1 and F2. When designing an energy
meter, the nominal design voltage on the voltage channels
should be set to half scale to allow for calibration of the meter
constant. The current channel should also be no more than half
scale when the meter sees maximum load. This allows
overcurrent signals and signals with high crest factors to be
accommodated. Table 9 shows the output frequency on F1 and
F2 when all six analog inputs are half scale.
Table 9. F1 and F2 Frequency with Half-Scale AC Inputs
SCF
0
1
0
1
0
1
0
1
MAX
(A)
1–7
S1
0
0
0
0
1
1
1
1
frequencies allow complete coverage of this range of
S0
0
0
1
1
0
0
1
1
F
2.3
4.61
1.15
4.61
5.22
1.15
0.58
0.58
1–7
(Hz)
F1 and F2 (Hz)
0.18
0.46
0.73
1.10
1.47
1.83
Frequency on F1 and F2
(Half-Scale AC Inputs) (Hz)
0.23
0.46
0.12
0.46
0.53
0.12
0.06
0.06
MAX
) with
Rev. PrA | Page 24 of 27
When selecting a suitable F
frequency output at I
meter constant should be compared with Column 5 of Table 9. The
frequency that is closest in Table 9 determines the best choice of
frequency (F
25 A maximum current is being designed, the output frequency on
F1 and F2 with a 100 imp/kWhr meter constant is 0.46 Hz at 25 A
and 220 V (see Table 8). Looking at Table 9, the closest frequency to
0.46 Hz in Column 5 is 0.53 Hz. Therefore, F
selected for this design.
FREQUENCY OUTPUTS
Figure 2 shows a timing diagram for the various frequency
outputs. The outputs F1 and F2 are the low frequency outputs
that can be used to directly drive a stepper motor or electro-
mechanical impulse counter. The F1 and F2 outputs provide
two alternating high going pulses. The pulse width (t
120 ms, and the time between the rising edges of F1 and F2 (t
is approximately half the period of F1 (t
period of F1 and F2 falls below 550 ms (1.81 Hz), the pulse
width of F1 and F2 is set to half of their period. The maximum
output frequencies for F1 and F2 are shown in Table 6.
The high frequency CF output is intended to be used for
communications and calibration purposes. CF produces a 90 ms-
wide active high pulse (t
power. The CF output frequencies are given in Table 7. As in the
case of F1 and F2, if the period of CF (t
pulse width is set to half the period. For example, if the CF
frequency is 20 Hz, the CF pulse width is 25 ms.
NO LOAD THRESHOLD
The ADE7752B includes no load threshold and start-up current
circuitry features that eliminate any creep effects in the meter.
The circuit is designed to issue a minimum output frequency.
Any load generating a frequency lower than this minimum
output frequency does not cause a pulse to be issued on F1, F2, or
CF. The no-load threshold is determined by the sum of all phases.
The minimum output frequency is given as 0.0075% of the full-
scale output frequency for each of the F
approximately 0.0029% of the F
example, for an energy meter with a 100 imp/kWhr meter
constant using F
F1 or F2 would be 13.35 × 10
at CF (16 × F1 Hz). In this example, the no load threshold would
be equivalent to 4.8 W of load or a start-up current of 20.03 mA
at 240 V.
1–7
). For example, if a 3-phase 4-wire Wye meter with a
1–7
(4.61 Hz), the minimum output frequency at
MAX
4
(maximum load) with a 100 imp/kWhr
) at a frequency proportional to active
1–7
–5
frequency for a meter design, the
Hz. This would be 2.13 × 10
1–7
frequency (see Table 10). For
5
) falls below 190 ms, the CF
1–7
2
). If, however, the
frequency selections, or
1–7
= 5.22 Hz is
ADE7752B
1
) is set at
–3
Hz
3
)