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ADE7752A Datasheet(PDF) 19 Page  Analog Devices 

ADE7752A Datasheet(HTML) 19 Page  Analog Devices 
19 / 24 page ADE7752/ADE7752A Rev. C  Page 19 of 24 MODE SELECTION OF THE SUM OF THE THREE ACTIVE ENERGIES The ADE7752 can be configured to execute the arithmetic sum of the three active energies, Wh = WhϕA + WhϕB + WhϕC, or the sum of the absolute value of these energies, Wh = WhϕA + WhϕB + WhϕC. The selection between the two modes can be made by setting the ABS pin. Logic high and logic low applied on the ABS pin correspond to the arithmetic sum and the sum of absolute values, respectively. When the sum of the absolute values is selected, the active energy from each phase is always counted positive in the total active energy. It is particularly useful in 3phase 4wire installa tion where the sign of the active power should always be the same. If the meter is misconnected to the power lines, (for instance, if CT is connected in the wrong direction), the total active energy recorded without this solution can be reduced by twothirds. The sum of the absolute values assures that the active energy recorded represents the actual active energy delivered. In this mode, the reverse power pin still detects when negative power is present on any of the three phase inputs. POWER MEASUREMENT CONSIDERATIONS Calculating and displaying power information always has some associated ripple that depends on the integration period used in the MCU to determine average power as well as the load. For example, at light loads, the output frequency may be 10 Hz. With an integration period of 2 seconds, only about 20 pulses are counted. The possibility of missing one pulse always exists since the ADE7752 output frequency is running asynchro nously to the MCU timer. This would result in a 1in20 or 5% error in the power measurement. 
