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SA2002D Scheda tecnica(PDF) 7 Page - Sames |
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SA2002D Scheda tecnica(HTML) 7 Page - Sames |
7 / 10 page sames SA2002D 7/10 http://www.sames.co.za TYPICAL APPLICATION In figure 7, the components required for stand alone power metering application, are shown. The application uses a shunt resistor for the mains current sensing. The meter is designed for 220V/40A I operation. The most important external components for the SA2002D integrated circuit are the current sense resistors, the voltage sense resistors as well as the bias setting resistor. R13 defines all on-chip and reference currents. With R13=24k , optimum conditions are set. Device calibration is done on the voltage input of the device. The voltage drop across the shunt resistor at rated current should be at least 20mV. A shunt resistor with a value of 625µ is chosen. The voltage drop across the shunt resistor is 25mV at rated conditions (Imax). The power dissipation in the current sensor is: P=(40A)² x 625µ = 1W. The resistors R6 and R7 define the current level into the current sense inputs of the device. The resistor values are selected for an input current of 16µA on the current inputs of the SA2002D at rated conditions. According to equation described in the Current Sense inputs section: R6 = R7 = ( I / 16µA ) x R / 2 = 40A / 16µA x 625µ / 2 = 781.25 A resistor with value of 820 is chosen, the 5% deviation from the calculated value will be compensated for when calculating resistor values for the voltage path. MAX LSH BIAS RESISTOR SHUNT RESISTOR CURRENT SENSE RESISTORS W W W W W W VOLTAGE DIVIDER The voltage divider is calculated for a voltage drop of 14V + 5%(14.7V). Equations for the voltage divider in figure 7 are: R1+R2+R3=RA and R12 || (R11+P1)=RB. Combining the two equations gives: (RA + RB) / 220V = RB / 14.7V A 5k trimpot will be used in the voltage channel for meter calibration. The center position on the pot is used in the calculations. P1 = 2.5k and values for resistors R11 = 22k and R12 =1M is chosen. Substituting the values will result in: RB = 23.91k and RA = RB x (230V/14.7V - 1) resulting in RA = 333k so the resistor values of R1, R2 and R3 are chosen to be 110k WW W W W W. PROGRAMMING The resistor values are calculated for a 40A rated meter. The LED pulse rate must be set accordingly by programming pins R0, R1 and R2. Using the table Rated Conditions Select (On page 5) pins R0 and R2 is set to V and R1 set to V . These settings will configure the SA2002D for 220V/40A operation with a LED pulse rate of 1600 pulses/kWh. The FAST pin is set to V for normal operation. SS DD SS |
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