传统电缆测井的机械多臂井径仪在高速旋转的随钻条件下难以完成测量,而基于超声测距的随钻井径测量系统,具有利用超声测距的非接触、速度快、信息处理简单、抗干扰能力强等优点,通过采用3个换能器等角距圆周分布,在存在“偏心”时可有效测量井径以及井筒轴心到仪器轴心的距离矢量。本文借鉴国内外现有超声波随钻井径测量系统及技术经验,设计了以单片机为核心的模块化超声随钻井径测量系统。从超声换能器特性、硬件电路以及程序控制3个方面入手进行协同设计,精度高、具偏心修正功能。根据理论计算和超声换能器产品参数特点,采用1MHz的超声换能器进行测距。采用增益可编程的反射波信号检测电路,通过多次增益校正,使得首个反射波信号前沿被比较器捕捉到,把超声波传输时间检测精度提高到一个换能器振荡周期以内,有效提高了测距精度,实现高速高精度测量与井径计算,其测量精度达到毫米量级。

Caliper measurement by using the traditional wireline multi-finger caliper tools is very difficult under the condition of while drilling. The Logging While Drilling (LWD) caliper tool based on ultrasonic distance measurement possesses the advantages of non-contact, high speed, easy process, and strong anti-jamming. By using three ultrasonic transducers which are equidistantly mounted on the surface, the caliper and the eccentricity are effectively measured. The modular design is utilized for the entire system with the MCU as the core, by drawing lessons from the domestic and international research results of the LWD caliper tool based on ultrasonic distance measurement. In order to design a high precise and eccentricity correcting caliper measurement system, the characteristics of ultrasonic transducer, hardware circuit, and program control are together considered and the collaborative design is used. According to the result of calculation and the parameter characteristics of the real ultrasonic transducers, 1MHz ultrasonic transducers are chosen. Since the variable gain detection circuit and the several gain calibrations are utilized, the first echo signal frontier is captured by the comparator, and the time precision of ultrasonic flight is improved to one period of the ultrasonic transducer oscillation. Finally the measurement precision is effectively improved and the measurement deviation is reached at 1mm.