ADE7762_15 datasheet(23/28 Pages) AD

23 / 28 page

ADE7762

Rev. 0 | Page 23 of 28

TRANSFER FUNCTION

FREQUENCY OUTPUTS F1 AND F2

The ADE7762 calculates the product of six voltage signals (on

current channel and voltage channel) and then low-pass filters

this product to extract active power information. This active

power information is then converted to a frequency. The

frequency information is output on F1 and F2 in the form of

active high pulses. The pulse rate at these outputs is relatively

low, for example, 2.09 Hz maximum for ac signals with SCF =

S0 = 0; S1 = 1 (see Table 6). This means that the frequency at

these outputs is generated from active power information

accumulated over a relatively long period. The result is an

output frequency that is proportional to the average active

power. The averaging of the active power signal is implicit to

the digital-to-frequency conversion. The output frequency or

pulse rate is related to the input voltage signals by the following

equation:

(

)

313

REF

Freq

(12)

where:

Freq is the output frequency on F1 and F2 (Hz).

VAN, VBN, and VCN are the differential rms voltage signal on

voltage channels (V).

IA, IB, and IC are the differential rms voltage signal on current

channels (V).

VREF is the reference voltage (2.4 V ± 8%) (V).

f1 to 7 is one of seven possible frequencies selected by using the

logic inputs SCF, S0, and S1 (see Table 5).

Table 5. f1 to 7 Frequency Selection1

SCF

f1 to 7 (Hz)

2.24

4.49

1.12

4.49

5.09

1.12

0.56

1 f1 to 7 is a fraction of the master clock and therefore varies if the specified

CLKIN frequency is altered.

Example 1

In this example, with ac voltages of ±500 mV peak applied to

the voltage channels and current channels, the expected output

frequency is calculated as follows:

()

value

reference

nominal

rms

peak

500

REF

SCF

(13)

Note that if the on-chip reference is used, actual output fre-

quencies can vary from device to device due to a reference

tolerance of ±8%.

230

313

Freq

(14)

As can be seen from these two example calculations, the maximum

output frequency for ac inputs is always half of that for dc input

signals. The maximum frequency also depends on the number

of phases connected to the ADE7762. In a 3-phase, 3-wire delta

service, the maximum output frequency is different from the maxi-

mum output frequency in a 3-phase, 4-wire Wye service. The

reason is that there are only two phases connected to the analog

inputs, but also that in a delta service, the current channel input

and voltage channel input of the same phase are not in phase in

normal operation.

Example 2

In this example, the ADE7762 is connected to a 3-phase, 3-wire

delta service as shown in Figure 18. The total active energy

calculation processed in the ADE7762 can be expressed as

Total Active Power = (VA − VC) × IA + (VB − VC) × IB

(15)

where:

VA, VB, and VC represent the voltage on Phase A, Phase B, and

Phase C, respectively.

IA and IB represent the current on Phase A and Phase B,

respectively.

With respect to the voltage and current inputs in Equation 7

and Equation 8, the total active power (P) is

(

)

(

) (

)

()

⎟

⎠

⎞

⎜

⎝

⎛

⎟

⎠

⎞

⎜

⎝

⎛

⎟

⎠

⎞

⎜

⎝

⎛

−

⎟

⎠

⎞

⎜

⎝

⎛

⎟

⎠

⎞

⎜

⎝

⎛

⎟

⎠

⎞

⎜

⎝

⎛

−

cos

(16)

ADE7762 датащи(PDF) 23 Page - Analog Devices

ADE7762 датащи(HTML) 23 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

датащи скачать

ссылки URL