ADE7761ARS-REF View Datasheet(PDF) - Analog Devices
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ADE7761ARS-REF Datasheet PDF : 28 Pages
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ADE7761
Table 9. F1 and F2 Frequency with Half-Scale AC Inputs
No-Load Threshold
S0 S1 F1–4
0
0
1.72
0
1
3.44
1
0
6.86
1
1
13.5
Frequency on F1 and F2,
Ch 1 and Ch 2,
Half-Scale AC Inputs (Hz)
0.085
0.17
0.34
0.68
The ADE7761 includes a no-load threshold and startup current
feature that eliminates creep effects in the meter. The ADE7761
is designed to issue a minimum output frequency. Any load
generating a frequency lower than this minimum frequency
does not cause a pulse to be issued on F1, F2, or CF. The mini-
mum output frequency is given as 0.0045% of the full-scale
output frequency. (See Table 7 for maximum output frequencies
When selecting a suitable F1–4 frequency for a meter design, the
for ac signals).
frequency output at IMAX (maximum load) with a meter constant
For example, an energy meter with a meter constant of
of 100 impulses/kWh should be compared with Column 4 of
Table 9. The frequency that is closest in Table 9 determines the
best choice of frequency (F1-4). For example, if a meter with a
maximum current of 40 A is being designed, the output
frequency on F1 and F2 with a meter constant of
E 100 impulses/kWh is 0.266 Hz at 40 A and 240 V (from
Table 8). Looking at Table 9, the closest frequency to 0.266 Hz
in Column 4 is 0.17 Hz. Therefore, F2 (3.4 Hz; see Table 5) is
selected for this design.
T Frequency Outputs
Figure 2 shows a timing diagram for the various frequency
outputs. The high frequency CF output is intended to be used
E for communications and calibration purposes. CF produces a
90 ms wide, active high pulse (t4) at a frequency that is propor-
tional to active power. The CF output frequencies are given in
L Table 7. As in the case of F1 and F2, if the period of CF (t5) falls
below 180 ms, the CF pulse width is set to half the period. For
example, if the CF frequency is 20 Hz, the CF pulse width is
OBSO 25 ms.
100 impulses/kWh on F1, F2 using SCF = 1, S1 = 0, and S0 = 1,
the maximum output frequency at F1 or F2 is 0.68 Hz and 43.52
Hz on CF. The minimum output frequency at F1 or F2 is
0.0045% of 0.68 Hz or 3.06 × 10–5 Hz. This is 1.96 × 10–3 Hz at
CF (64 × F1 Hz).
In this example, the no-load threshold is equivalent to 1.1 W of
load or a startup current of 4.6 mA at 240 V. Compare this value
to the IEC61036 specification, which states that the meter must
start up with a load equal to or less than 0.4% IB. For a 5 A (IB)
meter, 0.4% of IB is equivalent to 20 mA.
Note that the no-load threshold is not enabled when using the
high CF frequency mode: SCF = 0, S1 = S0 = 1.
NEGATIVE POWER INFORMATION
The ADE7761 detects when the current and voltage channels
have a phase shift greater than 90°. This mechanism can detect
wrong connection of the meter or generation of negative power.
The REVP pin output goes active high when negative power is
detected, and active low when positive power is detected. The
REVP pin output changes state as a pulse is issued on CF.
Rev. A | Page 24 of 28
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