Model SR715 Model SR720 LCR Meters

SR715/720 LCR METERHow the SR715/720 WorksThe SR715/720 measures the impedance of acomponent by measuring the voltage across thepart and the current through it. This is done forboth the real and imaginary (90° phase shifted)components of the signals. The complex ratio ofvoltage to current is equal to the compleximpedance. The processor calculates the variousparameters that are displayed, R, C, L, Q or D.The voltage across the part is generated by Vs.Both the amplitude and frequency of Vs can beset. This voltage is applied to the device under test(DUT) through source resistance Rs, which variesaccording to the measurement range. The currentflows to the virtual ground of A1, and through Rr,the current conversion resistor. The output of A1provides a signal proportional to the current, I x Rr.The voltage across the DUT is measured with aseparate signal path providing a 4-wire Kelvinconnection.The real and imaginary signals are obtained bymultiplying the voltage and current signals with areference signal in phase with Vs and one shifted90 degrees from Vs. These signals are measuredby an integrating A/D converter which is read bythe microprocessor. These values are corrected bycalibration factors, converted to impedances andfinally converted to the appropriate parameters fordisplay by the processor.xi