摘要人们在城市生活中时常有食物不新鲜的情况发生，对于和谐社会中提出的节约资源，合理利用资源的主题来说，食物浪费的现象违背了社会进步的主题。传统的保鲜方式由于成本高，能耗大的缺点也必然会被新型节能降耗的方法所取替，同时传统的保鲜方式对于一些昂贵的药物来说已经不适用了，保鲜的方法也逐渐向智能化、可靠性高、恒温的方向发展，所以应用PLC的温度闭环控制系统是社会发展的必然趋势。75058

本文选用的是以日本三菱公司生产的FX2N-48MR可编程逻辑控制器(PLC)为其主要部件，在其基础之上添加了温度模块，A/D转换模块，温度变送器，PID部分。制冷机构是以变频漩涡压缩机，蒸发式冷凝器，冷风机，电子膨胀阀为主加上一些辅助的设备（比如有油分离器，气液分离器，高压贮液器，截止阀和干燥过滤器）。变频漩涡压缩机启动后，制冷剂就会开始进入到毛细管处。因为毛细管自身结构的原因使得毛细管两边的压力相差很大，根据能量守恒的原则，所以在蒸发器处需要吸收大量的热，造成温度变化。这篇毕业论文有图12幅，表8 个，参考文献22篇。

毕业论文关键词：可编程逻辑控制器  温度变化  闭环控制

Temperature closed loop control system design based on PLC

Abstract In the urban life, the situation of food which is not fresh often occurs。 The phenomenon of food waste is contrary to the theme of social progress for the theme of saving resources and rational utilization of resources in the harmonious society。 Because of the high cost and large energy consumption, the traditional way of keeping fresh will be replaced by the new energy saving method, while the traditional way of keeping fresh is not suitable for some expensive drugs。 The method of preservation has gradually developed to the direction of intelligence, high reliability and constant temperature, so the temperature close-loop control system of PLC is the inevitable trend of social development。

In this paper, the FX2N-48MR programmable logic controller (PLC), which is produced by Japanese Mitsubishi Co, is used as its main component。 On this basis of FX2N-48MR, the temperature module, A/D conversion module, temperature transmitter and PID part are added。 The main bodies of the refrigerator are variable frequency swirl compressor, evaporative condenser, cool air machine, electronic expansion valve with some auxiliary equipments such as oil separator, gas-liquid separator, high pressure liquid storage, the cut-off valve and filter drier。 After starting the variable frequency compressor, the refrigerant will start to enter the capillary。 Because of the capillary structure, the pressure difference between the two sides of the capillary is very large。 According to the principle of conservation of energy, refrigerant needs to absorb a lot of heat in the evaporator, resulting in temperature changes。

This paper has figure twelve, table eight, twenty-two references。

Key words: programmable logic controller; temperature change; close-loop control

目 录

摘   要 I

Abstract II

1绪论 1

1。1概述 1

1。2国内外发展状况 1

1。3设计的目的及意义 1

2冷库的工作原理 2

3系统软硬件设计 3

3。1控制系统的组成 3

3。2制冷环节 12

3。3系统硬件的连接