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SA2007P 数据表(PDF) 9 Page - Sames |
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SA2007P 数据表(HTML) 9 Page - Sames |
9 / 12 page sames sames SA2007P 9/10 http://www.sames.co.za TYPICAL APPLICATION The analog (metering) interface described in this section is designed for measuring 230V/60A with precision better than Class 1. The most important external components for the SA2007P integrated circuit are the current sense resistors, the voltage sense resistors and the bias setting resistor. The resistors used in the metering section should be of the same type so temperature effects are minimized. Current Input IIN1, IIP1, IIN2, IIP2 Two current transformers are used to measure the current in the live and neutral phases. The output of the current transformer is terminated with a low impedance resistor. The voltage drop across the termination resistor is converted to a current that is fed to the differential current inputs of the SA2007P. CT Termination Resistor The voltage drop across the CT termination resistor at rated current should be at least 20mV. The CTs have low phase shift and a ratio of 1:2500. The CT is terminated with a 3.6W resistor giving a voltage drop of 86.4mV across the termination resistor at rated conditions (I for the meter). max Current Sensor Input Resistors The resistors R10, R11 and R12, R13 define the current level into the current sense inputs of the SA2007P. The resistor values are selected for an input current of 16µA on the current inputs of the SA2007P at rated conditions. For a 60A meter at 2500:1 CT the resistor values are calculated as follows: R10 = R11 = ( I / 16µA ) x R / 2 LSH = 60A / 2500 / 16µA x 3.6W / 2 = 2.7kW I = Line current L RSH = CT Termination resistor 2500 = CT ratio The two current channels are identical so R10 = R11 = R12 = R13. Voltage Input IVP The voltage input of the SA2007P (IVP) is driven with a current of 14µA at nominal mains voltage. The voltage input saturates at approximately 17µA. At a nominal voltage current of 14µA allows for 20% overdriving. The mains voltage is divided with a voltage divider to 14V that is fed to the voltage input pins via a 1MW resistor. Voltage Divider The voltage divider is calculated for a voltage drop of 14V. Equations for the voltage divider in figure 4 are: RA = R1 + R2 + R3 RB = R7 || R5 Combining the two equations gives: ( RA + RB ) / 230V = RB / 14V Values for resistors R5 = 24kW and R7 = 1MW is chosen. Substituting the values result in: RB = 23.437kW RA = RB x ( 230V / 14V – 1 ) RA = 362kW. Standard resistor values for R1, R2 and R3 are chosen to be 120kW each. The capacitor C1 is used to compensate for phase shift between the voltage sense inputs and the current sense inputs of the device, in cases where CTs with phase errors are used. The phase shift caused by the CT may be corrected by inserting a capacitor in the voltage divider circuit. To compensate for a phase shift of 0.18 degrees the capacitor value is calculated as follows: C = 1 / (2 x p x Mains frequency x R5 x tan (Phase shift angle)) C = 1 / ( 2 x p x 50 x 1MW tan (0.18 degrees )) C = 1.013µF Reference Voltage Bias resistor R6 defines all on chip and reference currents. With R6 = 24kW optimum conditions are set. Device calibration is done with calibration data. PRELIMINARY |
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类似说明 - SA2007P |
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