ADE7752B_15 datasheet(23/24 Pages) AD

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ADE7752B

Rev. 0 | Page 23 of 24

NO-LOAD THRESHOLD

The ADE7752B includes an innovative no-load threshold detection

scheme that detects if a current input, when multiplied with any

of the three voltages inputs, cannot create power larger than a no-

load threshold. This threshold represents 0.0075% of the full-

scale output frequency.

For example, if the A, B and C voltage phases are 50% of full-

scale input and 120° apart, and Current Phase A is 10% of full

scale with a PF = 0, this detection scheme detects that VA × IA is

below the no-load threshold but that VB × IA and VC × IA are not.

Therefore, the ADE7752B does not detect a no-load threshold

for VA × IA and lets this phase contribute to the total power.

However, in the same voltage conditions, if current Phase A is

0.0075% of full scale with a PF = 1, this detection scheme detects

that VA × IA is below the no-load threshold and because VB × IA

and VC × IA are as well, VA × IA is detected as below the no-load

threshold and its contribution to the total power is stopped.

The no-load threshold is given as 0.0075% of the full-scale output

frequency for each of the f1 to 7 frequencies (see Table 10). For

example, for an energy meter with a 100 imp/kWhr meter

constant using f1 to 7 (4.49 Hz), the minimum output frequency

at F1 or F2 is 1.38 × 10−4 Hz. This is 2.21 × 10−3 Hz at CF

(16 × F1 Hz). In this example, the no-load threshold is equiva-

lent to 4.8 W of load, or a start-up current of 20.7 mA at 240 V.

Table 10. CF, F1, and F2 Minimum Frequency at No-Load

Threshold

SCF

F1, F2 Minimum (Hz)

CF Minimum (Hz)

6.92E − 05

1.11E − 03

1.38E − 04

1.11E − 03

3.46E − 05

1.11E − 03

1.38E − 04

2.21E − 03

1.57E − 04

2.51E − 02

3.46E − 05

5.53E − 04

1.73E − 05

5.53E − 04

1.753 − 05

2.77E − 04

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