Abstract
IP or complex measurement of core sample or water with pollution is very important for exploration geophysics, engineering geophysics and environment geophysics. Current SIP measurement system for laboratory usage can work well for sample with high DC resistance because of using amplifier with high impedance as input buffer. But its inherent noise is high, and the precision of SIP measurement is poor when it measures the SIP of sample with low DC resistance. The situation is worse especially for environment problem when the resistance of water sample with high pollution is very low. Our development is to design and realize a precision SIP measurement system suitable to sample with very high resistance and very low resistance. We design three input buffers in a single board with switch option corresponding to low resistance, medium resistance, and high resistance of different sample. An ultra- low noise buffer with voltage noise as low as 1 nV/sqrt(Hz) is adopted for sample with low resistance (d 1000 :). An ultra-high input impedance buffer is adopted for sample with high resistance (t 1 M:). A general input buffer is adopted for sample with medium resistance (< 1000 : & < 1M:). Each b uffer is composed of 4 channels to measure current and voltage with differential input. Active shielding is used for each channel to prevent parasitic capacitance among measurement wires. A high precision data acquisition system with 4 channels is also developed. The data acquisition system is optimized for geophysical signal acquisition with frequency range from DC to 1000Hz. The calibration and compensation process are adopted to reduce measurement error. We tested our system on resistors with resistance as 0.1:, 1:, 10 :, 100 :, 1.2 K:, 10 K:, 100 K:, and 930 K: in frequency 1 Hz ~ 800 Hz, and the measurement error is less than 0.1 mrad. We also carried out a test on core samples with low resistance, high resistance, and medium resistance, the measure error was less than 0.1 mrad in most conditions.
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