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Tab.1 Measured values R Measured values with AC bridge 3.38 kΩ Rx= 6.811 kΩ 3.38 kΩ 21.6 kΩ 21.6 kΩ 21.6 kΩ 3.38 kΩ 3.38 kΩ Cx=0.3064 µF Rx=110Ω Rx=7.245 kΩ Cx=0.3181 µF Rx=132Ω Cx=0.1291 µF Rx=328Ω Lx=0.931 H Rx=93 Ω Lx=1.912 H Rx=222 Ω Measured values with insruments 6.84 kΩ 0.33 µF 7.25 kΩ 0.33 µF 0.12 µF 1.0 H 105 Ω 2.0 H 215 Ω Weights w1=-2.0152 w2=-0.0003 w1=-0.038 w2=1.537 w1=-0.3354 w2=-0.0001 w1=-0.0061 w2=0.2310 w1=-0.015 w2=0.569 w1=-0.027 w2=-0.346 w1=-0.073 w2=-0.711 Magnitude of Ur [LSB] 800 800 1200 1000 1000 700 700 500 400 300 200 am plitude 100 0 -1 0 0 -2 0 0 -3 0 0 -4 0 0 -5 0 0 0 500 1000 1500 s a m p le s Fig.6 Variation of E voltage REFERENCES IV. CONCLUSIONS [1] M. Dutta, A.Rakshid, S.N.Battacharyya and J.K.Choudhury, "An application of the LMS adaptive algorithm for a digital AC bridge," IEEE Trans.Instrum.Meas.,vol.36, pp.894-897, 1987 [2] Selim S. Awad, Natarajan Narasimhamurthu and Wiliam H. Ward, "Analysis, Design, and Implementation of an AC Bridge for Impedance Measurements, IEEE Trans.Instrum.Meas.,vol.43, pp.894-899, 1994 [3]L. Angrisani, A.Baccigalupi and A.Pietrosanto, "A digital Signal-Processing Instrument for Impedance Measurement" IEEE Trans.Instrum.Meas.,vol.45, pp.930-934, 1996 [4]B. Widrow, S.Stearns, "Adaptive Signal Processing", Prentice Hall, New Jersey, 1985 [5] Lab-PC+ User Manual, National Instruments, 1994 This paper presented implementation of an virtual AC bridge for impedance measurement using an IBM-PC which contains a data acquisition board with two DAC's and one ADC. This virtual instrument works in real-time using a C-language program. Experimental tests were carried out on resistors, capacitive impedances and inductive impedances. The obtained results have very small errors. 26
