ADE7752B
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). Because 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 maxi-
mum current of between 10 A and 100 A. Table 8 shows the
output frequency for several maximum currents (I MAX ) with 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
When selecting a suitable f 1 to 7 frequency for a meter design, the
frequency output at I MAX (maximum load) with a 100 imp/kWhr
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 1 to 7 ). For example, if a 3-phase, 4-wire
Wye meter with a 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 0.46 Hz.
Therefore, f 1 to 7 = 4.49 Hz is selected for this design.
FREQUENCY OUTPUTS
Figure 2 shows a timing diagram for the various frequency
I MAX (A)
10
25
40
60
80
100
F1 and F2 (Hz)
0.18
0.46
0.73
1.10
1.47
1.83
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 1 ) is set at
120 ms, and the time between the rising edges of F1 and F2 (t 3 )
is approximately half the period of F1 (t 2 ). If, however, the
period of F1 and F2 falls below 550 ms (1.81 Hz), the pulse
The f 1 to 7 frequencies allow complete coverage of this range of
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
Frequency on F1 and F2
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 4 ) at a frequency proportional
to active power. The CF output frequencies are given in Table 7.
As in the case of F1 and F2, if the period of CF (t 5 ) falls below
190 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.
SCF
0
1
0
1
0
1
0
1
S1
0
0
0
0
1
1
1
1
S0
0
0
1
1
0
0
1
1
f 1 to 7 (Hz)
2.24
4.49
1.12
4.49
5.09
1.12
0.56
0.56
(Half-Scale AC Inputs) (Hz)
0.23
0.46
0.12
0.46
0.52
0.12
0.06
0.06
Rev. 0 | Page 22 of 24
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