Cognition And Realization Of NMR Signal Detection Circuit For Oil Well-Logging System

With the guidance of low level signal detection method and low noise design theory, this thesis has cognized and developed a low level signal detection circuit used in Nuclear Magnetic Resonance Logging Tool, which can realize the reliable detection of the n-volt level Nuclear Magnetic Resonance Signals.The thesis introduces the basic theory of Nuclear Magnetic Resonance Logging, the mechanism and character of the Signals. The scheme of the circuit is planned in total.On this basis, the concrete realizing scheme and the hardware block diagram of this signal detection platform are proposed, the emphases of description are put on the key techniques adopted to improve the performance of signal detection, including the design of low noise amplifier module based on MAT02, the amplifier module based on OP160, the power filter and the application of common-mode inductance. Go a step further to simulate in bias point detail, AC sweep and transient analysis, in order to perfect the preamplifier realizing scheme with PSpice. In the course of the circuit realization, the selection of parts of the apparatus, composition and wiring of PCB, argument adjustment of each module, electromagnetic shielding and ground connection are token into account, in order to make sure the low noise of circuit. Then the design of the filter amplifier and DPSD software are introduced concisely.At last, the thesis introduces the test result of the preamplifier, the filter amplifier and the low level signal detection platform, then expands and verifies on obtaining of the lowest level signal. The experiment proves that, the bandwidth of platform is 400kHz to 850kHz and peak to peak value of the signal caught is below 50nV.