Design of multi-channel temperature monitoring system based on ARM

introduction

Temperature is an important measurement and control parameter in the industrial production process. Temperature monitoring systems are widely used in metallurgy, steel, petrochemical, cement, glass, medicine and other industries. The effective measurement and control of temperature has important practical significance. At present, the temperature measurement and control systems on the market are based on single-chip microcomputers or industrial computers as control platforms. The single-chip microcomputer has limited hardware resources and performance, and more peripheral circuits need to be expanded, which is complex to design; the industrial computer is used as the control platform, which is larger in size. If ARM9 is used as the control platform of the temperature measurement and control system, it will not only have fast speed, high performance, low power consumption, high chip integration, but also rich peripheral interfaces, and can also transplant embedded real-time operating systems, simplifying the design and development of LCD display, storage, network communication, etc. In view of this situation, this paper designs a multi-channel temperature measurement and control system based on ARM9 and MAX6675. The system can realize automatic temperature measurement and control of 24 loops. It can display the set temperature value and actual temperature value of each loop on a page of four loops, and can also switch from digital display to bar graph display. It can access the Internet and store historical data in a USB flash drive. Qt/Embedded can also be used to create a GUI graphical user interface, which can be displayed on the LCD display with a friendly graphical interface.

1 System Hardware Design

The temperature measurement and control system designed in this paper requires the processor to have a very high operating speed. ATMEL's processor AT91RM9200 is a cost-effective, low-power, 32-bit ARM chip based on the ARM920T core. When the clock frequency is 180MHz, its computing speed can reach 200MIPS. It is an industrial-grade chip that can run stably for a long time in an industrial environment.

1.1 Overall system design

The overall design block diagram of the system is shown in Figure 1:

The system uses AT91RM9200 as the core of the control system, and expands two 32M SDRAMs and one 2M Flash. The SDRAM chip selected is HY57V281620 with a 16-bit data width, which is used to set the program stack and store various variables. The Flash chip used is AT49BV1614, whose data width is 16 bits, which is used to store the startup code. The RS232 serial port is used to communicate with the PC, and the DM9161 that supports the IEEE802.3 standard is used to access the Internet. The USB interface can be connected to a U disk or a USB mouse, etc. The LCD display can be used to display various states of the system operation. Since the AT91RM9200 processor does not have an integrated LCD controller, it needs to be equipped with a dedicated display controller S1D13806 to realize LCD display.

The keyboard can set various parameters of the system and control the operation of the system. The system implements four function keys through interruption mode, namely: shift key, plus key, minus key and confirm key. The temperature acquisition unit collects the temperature data of 24 circuits in real time, sends it to the CPU for calculation and processing, and the control execution unit uses thyristor power adjustment to change the output power of the heater. The following mainly focuses on the design and analysis of the temperature acquisition unit, the control execution unit and the control algorithm.