| Portable Digital Storage Oscilloscope (DSO), as a kind of basic measuring tool, is applied to many fields. Due to the expansion of measuring fields, DSO has to be embedded with more functions. Modern DSO usually has digital multimeter, which can be used to measure electric elements. Based on the portable DSO and transmission line theory, this design claims that utilizing Time-Domain Reflectometry (TDR) into it, by which can it be extended to cables'fault location measuring field.In this design, it uses the method of low voltage pulse reflection which is implemented in FPGA by making up a programmed-control pulse signal generator having variable pulse width and delay time. The source and reflected pulses will be displayed on the screen after sampled. Using the cursors can measure the time difference of two pulses and compute the length or fault location of cables. It also can get the NVP value by measuring a cable of constant length and decide the fault type through viewing the phase difference between two pulses. This thesis mainly introduces the software design, using LPC2138 as the MCU, which is produced by NXP and based on core ARM7TDMI-S. The development of software is under ADS v1.2 tool.In this thesis, the software system is divided into modules of pulse signal generator, signal sampling, cursor measuring, analog channel control and screen display. Pulse signal generator introduce the way to control the width and delay time of pulses; signal sampling has two ways including peak-peak and equivalent, and primarily introduces the principle of constructing waves after equivalent sampled; parameter measuring introduce that how to use cursors to measure the signals and get the distance value by selecting different NVP; channel control module introduce how the serial-parallel transformation and digital-analog signal converter chips work, and channel auto calibration; display module introduce the hardware interface circuits, and the man-machine interface uses multilevel pop-up menus. |
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