FS7755

Rev. 1.1

19/22

1.

Frequency Output CF

The pulse output CF (Calibration Frequency) is intended for use during calibration. The output pulse rate on CF

scaling (except for the high frequency mode SCF = 0, S1 = S0 = 1). Table Ⅳ shows how the two frequencies

are related, depending on the states of the logic inputs S0, S1, and SCF. Because of its relatively high pulse

rate, the frequency at this logic output is proportional to the instantaneous real power. As is the case with F1

and F2, the frequency is derived from the output of the

low-pass filter after multiplication. However, because the output frequency is high, this real power

information is accumulated over a much shorter time. Hence, less averaging is carried out in the digital to

frequency converter. With much less averaging of the real power signal, the CF output is much more

responsive to power fluctuations (see Fig2, Signal Processing Block Diagram).

SCF

S1

S0

(Hz)

CF Max for AC Signals

(Hz)

1

0

0

1.7

128×F1, F2 = 43.52

0

0

0

1.7

64×F1, F2 = 21.76

1

0

1

3.4

64×F1, F2 = 43.52

0

0

1

3.4

32×F1, F2 = 21.76

1

1

0

6.8

32×F1, F2 = 43.52

0

1

0

6.8

16×F1, F2 = 21.76

1

1

1

13.6

16×F1, F2 = 43.52

0

1

1

13.6

2048×F1, F2 = 5570

Table Ⅳ

Maximum Output Frequency on CF

2.

Selecting a Frequency for an Energy Meter Application

As shown in Table II, the user can select one of four 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 only four different output frequencies can be selected, the available

frequency selection has been optimized for a meter constant of 100imp/kWhr with a maximum current of

line voltage of 220V. In all cases the meter constant is 100imp/kWhr.

Table Ⅴ

F1 and F2 Frequency at 100imp/kWhr

F1 and F2 (Hz)

12.5

0.076

25

0.153

40

0.244

60

0.367

80

0.489

120

0.733