| Large capacity, high voltage, and complicated structures associated with power system together with the development of modern industry and agriculture and the enhancement of customer importance require more and more stringent safety and reliability measures. As such, it is necessary to effectively monitor electrical equipments online. Online monitoring refers to managing the operation of equipments in such a way that, by using modern sensor technology and computer technology et al., the operating equipments are monitored periodically or continuously without disassembling the metal seal of the equipments to evaluate or diagnose their conditions. Based on this information, specific measures are then taken to fix the abnormal phenomenon or the breakdown to ensure that the system is working reliably. In the power system, the electrical equipment control panel is widely used, and is responsible for both powering electrical equipments on or off and keeping electrical equipments running safely. The characteristics of its internal connections have direct effects on the reliability of the control panel. The electrical equipment control plane is composed of many relays and the strong electric controller. In the equipment start and the generating process, the bad electronic contact, the wiring column becomes less crowded, the definite value protection malfunction, insulation aging and so on often causes partial part giving off heat, producing the electric arc what ablates the periphery part, makes the equipment trouble, the power cut accident even to have the fire, creates the huge economic loss. Therefore, accurately monitoring the temperature of key spots of control panel in an uninterrupted manner and responding quickly to overheat is an important approach to either avoid serious accidents or to keep the situation from deteriorating in case something does go wrong. To solve this problem, herein we report the design of an infrared based online temperature sensor system for electrical equipment control panel.The major problem involved in the infrared temperature sensor technology is the detection of signal. When measuring the temperature, the infrared radiation from an object enters the optical system where it will be modulated into alternation radiation by the modulator. This alternation radiation is then detected by the detector and transformed into electrical signal which is then amplified by the electronic amplifier and the temperature will be displayed on the monitor. In this system, MID10LT is selected as the temperature sensor. MID10LT is a two components non-contact infrared temperature sensor manufactured by Raytek. It is composed by a miniature probe and an independent electric circuit box. The probe, which can accurately detect the radiation energy from the object and transform it into temperature, is connected to the electric circuit box through a piece of 1m long electric cable.This temperature sensor system can monitor and display the temperatures of six electrical equipment control panels. According to preset parameters, it can also put the whole running process of the equipment under surveillance. The entire surveillance system was designed as such that a slave (SCM based) which is capable of controlling the temperature measurement of every spots (six spots for each control panel) and transferring data to the master was assigned to each control panel. The master computer is a PC which is responsible for the surveillance of the entire temperature monitoring system. It is also responsible for the paperless temperature recording, printing, analysis, and acousto-optic warning signals.Firstly, hardware implementation and software programming for the slave computer have been accomplished. The slave computer takes a SCM as core. Its other key components include infrared sensor, port expansion, human-computer interaction, data storage, acousto-optic warning, and network module and so on. Measuring temperature and responding to the inquiry from the master computer are the key responsibilities of the slave. Furthermore, the slave can also survey and give alarms independently, which improved the compatibility of the surveillance system.Based on this, we wrote the code for the master computer to control the temperature monitoring process. This code was installed on a PC and is responsible for the real-time processing and display of the temperature data collected by the slave. Additionally, it provided a way for operator to monitor and manage the system. This software receives temperature data collected by the slave through port. It also periodically samples temperature data and makes a graph out of these samples. Additionally, it also records all of the temperature data to enable the inquiry and printing of the temperature data history. In order to enable the operator to monitor each individual sensor temperature promptly, the software was programmed as such that the temperature have to stay in a certain range. Whenever the data collected is out of this range, the warning light will turn red and the generated message will be saved in a log file for abnormal events. The above-mentioned function will promptly and accurately feed collected data back to operator and ensure the surveillance and control of the entire system.Since the stability and reliability of the entire surveillance system depend on whether the master can receive the temperature data from the slave accurately, the selection of the bus type and the network protocol as well as the circuit design is essential. In the monolithic integrated circuit application system, the data communication mainly uses the asynchronous COM mode communication. In this system, RS-485 COM mode is used for data communication and RTU mode of Modbus is employed as the network protocol. For the hardware design, the requirements for the field are fully considered. As such, RS485 connection chip SN75LBC184 is used for the monolithic integrated circuit side due to its ability to effectively avoid the damages that can be potentially caused by thunder. Additionally, the match resistance, the bias resistance, the anti-thunder facility and the photoelectric coupler installed at the network terminal enhance system reliability enormously. On the PC side uses the MAX485 chip isolates after the photoelectric coupler again after the MAX232 chip to transform the circular electric signal into the RS232 level.Electromagnetic interference is one of the primary causes for the failure of SCM surveillance system. Since this system will be working under high electric current and high voltage, it is essential to have good capacity of resisting disturbance to ensure its reliability. To improve this capacity, we took both software and hardware into consideration. From the hardware point of view, techniques such as shielding, channel interference suppression, and PCB interference suppression and so on were adopted. Additionally, watchdog, digital filtering, and error control and so on were used during the design of the software process. With the adoption of those technologies, we minimized the influence of interference on the system.To develop this system, sensor technology, computer technology as well as communication technology was integrated. Additionally, the non-contact and remote surveillance of temperature was realized. This system is a good combination of simple hardware electric circuit structure, user-friendly software interface, and ease of operation. At this point, this temperature surveillance system has already been assembled and trial run in field is currently underway. So far the trial run has been very stable and reliable and provided very good results, and the preset goals have been achieved. |
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