文档介绍：哈尔滨工业大学工学硕士学位论文
摘要

在石油化工等行业中迫切需要一种能实现多层面全程检测,能指示出油
水不同界面和混合层厚度的新型液位测量仪表。基于分段式电容传感器的液
位测量仪恰恰能够满足这种需求。分段式液位测量是利用等结构物理电极把
整个测量范围分成不同层面,每个层面对应着固定的空间高度,用模拟电路
技术、数字电路技术及单片机技术相结合,逐层测量电容。如果测量的是同
一介质,各段采集的数字量应该一致或接近,反之则有较大差异,利用该现
象可以判断出介质分界面的层段,就能计算出界面或液面高度。
分段式液位测量系统中的变送器部分是本论文的主要研究内容。首先对
变送器部分进行了整体的方案设计,变送器由电容/电压转换、纹波控制电
容切换、放大倍数切换、A/D 转换、单片机、光电隔离和 RS485 串口通讯
等几部分组成。其中微小电容测量是变送器部分的关键技术,在比较了多种
电容测量方法后,采用了基于充放电法的抗寄生干扰的微小电容测量方法,
因此重点在理论上分析了这种测量方法的原理和优点。
在整体设计和理论分析的基础之上,从硬件和软件两方面对各部分进行
了具体的设计,包括硬件电路和软件流程等。通过现场调试实验和数据分
析,验证了此变送器具有良好的性能,达到了要求的技术指标,同时指出了
需要改进和完善的地方。

关键词分段式液位测量;变送器;微小电容测量;充放电法
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哈尔滨工业大学工学硕士学位论文
Abstract
Some industries such as petrochemistry imminently need a new kind of
liquid-level measuring instrument, which can detect whole range of many lays,
can indicate the oil-water interface and the thickness of mixed lay. The liquid-
level measuring instrument based on divided-into-segments capacitor sensor just
satisfies this kind of need. Divided-into-segments liquid-level measuring
instrument divides measuring range into different lays(every lay corresponds to a
fixed space height) using equal-structure physical electrodes, combines analog
circuit technology, digital circuit technology and singlechip technology to detect
capacitor lay by lay. If same mediums are measured, the digital collections from
every lay should be same or near, otherwise should be rather different. Utilizing
this phenomenon, the lay where the interface is can be judged, the interface or
liquid-level height can be calculated.
The transducer in divided-into-segments liquid-level measuring instrument
is the main research content of this paper. Firstly, the whole scheme of the
transducer is designed, the transducer includes capacitance/voltage converting,
ripple-control capacitor switching, magnify-multiple switching, A/D converting,
singlechip, photoelectric isolation and RS-485 munication, etc. The
measurement of microcapac