摘要
气相色谱仪是一种高效、快速的分离分析仪器,在分析化学、生命科学、材料科学、环境科学、医药科学及食品安全等领域有广泛的应用。气相色谱仪的控制系统水平体现了一台仪器的层次和水平。电子技术、材料科学的发展促进了色谱技术的发展,随着应用领域的不断扩大,对色谱仪控制系统也提出了越来越高的要求。新型便携式智能化色谱仪需要具备分析精度高、可灵活配置功能模块、计算机工作站控制、携带方便、操作简单等特点。因此,对便携式色谱仪控制系统的研究对加强仪器智能性、提高仪器的层次和水平具有重要意义。
本文首先对气相色谱原理、微型色谱技术进行了概括分析,然后采用模块化设计思想,选用TI公司LM3S系列ARM微控制器完成了色谱仪控制系统数据通信主控板模块和温度控制板模块的软硬件设计。在充分考虑了便携式仪器结构特点的基础上,根据新型气相色谱仪控制系统功能需求和嵌入式控制系统设计特点进行了模块划分,模块之间通过RS-485总线连接,具有一定的通用性。
数据通信主控板设计选用完全集成(MAC+PHY)遵循IEEE 802.3规范的工业级以太网控制器的嵌入式微控制器芯片,简化了嵌入式以太网硬件电路设计,提高了模块的稳定性。在嵌入式以太网通信协议栈实现方面,轻量级TCP/IP网络协议栈lwIP不仅具备完善的网络通信协议功能,而且ROM/RAM占用量少、通用性好,特别适合于资源十分有限的嵌入式系统。TCD、FID传感器信号直接由数据通信主控板的A/D电路采集,得到的数字信号通过以太网传输到运行工作站软件的计算机完成结果分析和存储。内置工作站数据采集器实现了传感器检测数据、仪器状态数据、工作站控制数据通过同一端口传输,使仪器的使用更加方便。RS-485总线模式降低了控制系统设计复杂度,定义了RS-485软件通信协议,提高了简单串行通信方式的可靠性。
温度控制是气相色谱控制系统的必须功能,直接影响仪器的性能。温度控制器硬件电路由PT100铂电阻测温电路、过零检测电路、双向固态继电器热丝加热功率控制电路构成。并采用了模糊PID控制算法。实验结果表明控温精度达到0.05℃,实现了设计预期目标。
Gas chromatography (GC) is a kind of highly efficient and rapid separation and analysis instrument, which is widely used in many fields such as analytical chemistry, life sciences, material science, environmental science, medical science and food safety. The GC’s control system level reflects the level of the instrument. Electronic technology and material science development promote GC technology development. With the expansion of application fields, GC’s control system must meet more and more high requests. Portable intelligent GC requires high analytical precision, flexible function module, computer workstation control, simple operation, etc. Therefore, the significance of research portable GC’s control system is to enhanceing its intelligence and improving its level.
Firstly, this dissertabion generally introduces chromatography theory and micro GC technology, and then implments the circuits and embedded software of data communication board and temperature control board based on TI’s LM3S series ARM microcontroller. Taking full account of the structural features of a portable GC, we design function modules according to GC’s control system function requirements and embedded technology fetures. RS-485 bus is used to communicate among modules.
An embedded microcontroller with fully integrated ethernet controller (MAC plus PHY) is selected when we design the data communication board. And the ethernet controller conforms to IEEE 802.3 specifications. This simplifys the ethernet hardware design and makes it more reliable. We select light-weight TCP/IP protocol stack named lwIP, which not only implements full network protocol but also consumes little ROM and RAM. So it especially suits for embedded system with limited resources. The data communication board onboard A/D circuit converts TCD and FID sensor signals directly, and the digital signal is transfered to workstation via ethernet. Built-in workstation data acquisition enables the sensor digital signal, instrument status information and workstation control commands to be transfered through the same port. This lets the instrument become more convenient. The RS-485 bus mode efficiently degrades the complexity of the control system. And definition of the RS-485 bus communication application layer protocol improves the reliability of a simple serial communication.
Temperature control is the necessary function module of GC’s control system, which directly affects the instrument’s performance. The temperature controller hardware circuit consists of PT100 platinum resistance measurement circuit, zero-crosing detection circuit and bi-directional solid state relay circuit. And we adopt fuzzy PID control algorithm. The experimental results indicate that temperature accuracy more than 0.05℃. We achieve our design target.
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