ADE7761B
Frequency Outputs
For example, with an energy meter with a meter constant of
100 impulses per 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).
Figure 2 is a timing diagram for the various frequency outputs.
The high frequency CF output is intended for communication
and calibration purposes. CF produces a 90 ms wide, active high
pulse (t4) at a frequency that is proportional to active power. The
CF output frequencies are given in Table 8. As with 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 25 ms.
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 IEC 62053-21 specification, which states that the meter must
start up with a load equal to or less than 0.4% of IB. For a 5 A (IB)
meter, 0.4% of IB is equivalent to 20 mA.
No-Load Threshold
The ADE7761B includes a no-load threshold and start-up current
feature that eliminate creep effects in the meter. The ADE7761B
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 minimum
output frequency is given as 0.0045% of the full-scale output
frequency (see Table 8 for maximum output frequencies for
ac signals).
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 ADE7761B detects when the current and voltage channels
have a phase shift greater than 90°. This mechanism can detect
a wrong connection of the meter or the 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.
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