Design Of High Precision Data Acquisition System Based On TMS320F2812

Through Casing Formation Resistivity Logging is mainly used for measuring variations of formation resistivity in cased hole outside, due to the small effects of casing, borehole, geological environment and other factors, which has important practical value and broad application prospect evaluation in evaluation remaining oil saturation,dynamic monitoring of the oil gas reservoir, positioning the oil-water interface and other factors. Directing at weak signal detection of Through Casing Formation Resistivity Logging, the heat resisting and high precision data acquisition system based on TMS320F2812and ADS1274is designed combining with the practical application in the paper.The principle of Through Casing Formation Resistivity Logging is introduced in the paper, which adopts three electrodes on the casing to measure tiny voltage drops for formation resistivity. Through the analysis of frequency and amplitude characteristics of the logging signal, the signal amplitude of Through Casing Formation Resistivity is very weak in microvolt level and the signal frequency is lower than lOHz; Then according to the characteristics of the logging signal, the hardware design of ultra low noise preamplifier circuit and data acquisition circuit is introduced in detail in the paper. The preamplifier circuit is divided into three stage amplifying circuit for signal conditioning to improve the signal to noise ratio. The data acquisition circuit includes four part of ADC driver, ADC conversion, DSP control and data transmission module. This acquisition system with high precision differential amplifier forming a single-ended to differential circuit, utilizes the McBSP (Multi-channel Buffered Serial Port) of DSP to achieve24-bit high precision data, and makes use of the eCAN (enhanced Controller Area Network) module of DSP connecting with CAN transceiver to transmit data and to communicate information, with the SCI(Serial Communication Interface) as spare commissioning and testing interface; Finally, the program of DSP is completed in CCS2.2development environment, which accomplishs data acquisition with McBSP and makes communication with eCAN.The test software is programmed in VB6.0development environment,which completes acquisition data to upload computer for processing and analyzing with the SCI of DSP.By experimental verification, the precision of the acquisition system can reach0.5%, and can work continuously in high temperature environment for more than8hours, and this system has been applied in Through Casing Formation Resistivity Logging instrument. In simulation system with measuring scale box including resistor1to200, the relative errorof logging instrument is less than7%. So acquisition system can meet the requirements ofdesign acquisition system.