The Study Of Well Logging Cable DataTransmission System Based On USB

Well-logging cable data transmission system is an important component of well-logging equipment. With the rapid development of high performance well-logging tools, the data acquired by logging tools becomes more and more, so the data communication rate of hundreds of kilobits per second or even high is required in logging cable. Key aspects of well-logging cable data transmission system,such as cable transmission features,modulation technology,design of Manchester encoder and decoder based on complicated programmable logical device,USB interface design,micro-controller programming,and device driver programming,are described. The transmission feature of well-logging cable is varied with its material,length,manufacturing technique,and the temperature of application environment. As the frequency width of well-logging cable is about 100 kHz,it is necessary to realizing high rate data transmission to adopt multi-channel communication mode or high efficiency modulation techniques. To make full use of current downhole tools, the modulation technique of this system should be compatible with current downhole tools, so Manchester code is adopted. The power spectrum of Manchester code is irrelative with the feature of data stream, so frequency equalizer can be used to compensating the feature of communication channel of constant characteristics. The bandpass feature of Manchester code makes it adapt to cable telemetry system with transformer couple mode. As its time field waves have many edges, its timing clock for decoder is easy picked out. To get the best compensating cable features, a frequency equalizer is designed by mixing digital and analogy circuit techniques. According to the principle of Manchester code, Manchester coder and decoder with parallel interface are realized by in system programmable complicated programming logical device (CPLD) of Lattice Semiconductor. Compared to the old devices of serial interface, the CPLD device integrates serial to parallel shift register, parallel to serial shift register, data buffer, data register, control register, and address decoder, which can be directly used as interface components of computers and makes system design simplified. An USB interface device PDIUSBD12 of Phillips, and a micro-controller AT89C52 of ATMEL are also used to realize the USB interface with host computer. To lighten the burden of micro-controller,the output data of Manchester decoder is directly written to first-in-first-out (FIFO) memories. A direct memory access (DMA) controller is designed to read data from FIFO memories and write to PDIUSBD12. The realization of USB protocol and telemetry functions,the design of USB device driver based on Windows driver model (WDM),and the application program design are also described. An application example of transmission system is given at last.