Journal of Electric Power? computer application?
Application of Microcomputer Technology to Realize Automatic Group Control of Air Compressor Yang Tao (Taiyuan Electric Power College) Li Xuemei (Supply Department of Shanxi Electric Power Bureau) automatic control, automatic protection and automatic data recording. The application, design ideas and effects of the device in industrial production.
Introduction Air compressors (hereinafter referred to as air compressors) are indispensable wind power equipment for power, mining, metallurgy, chemical, machinery manufacturing, textile, food and other industries. There are dozens of large and medium-sized enterprises producing air compressors in China. The output is in the thousands. Because the air compressor is a large noise mechanical device, it is not only complicated to operate, but also has a noise of about 90 decibels. Especially in the summer factory, the temperature is up to 40 °C. In this harsh environment, the operation is extremely fragile and often has operational errors. Coupled with some inexperienced workers, when the machine is abnormal, it can not be handled correctly in time, often with varying degrees of machine damage, directly affecting production, and noise for the long-term operation of the air compressor workers' hearing nerve health Larger damage. To this end, we have adopted the microcomputer technology, and developed the YW 302 single-computer microcomputer control device and the YW 302/ 4 type and YW 302/8 type computer group control device series (YW 302/4 type can simultaneously control 4 air pressures) Machine, YW 302/8 type can control 8 air compressors at the same time). This series of suitable secondary gas compressors, soft and hardware can be applied to 60 m machine. Let's take the YW 302/4 microcomputer group control device as an example to introduce the main performance indicators of the system. The device is designed as 64 analog input, 17 switch input, 16 switch output, and can be used for 1~4. Taiwan two gas compressor stations and pneumatic air compressor station is equipped with water supply equipment author: female, born in August 1963, college lecturers, 030 013 centralized detection and control.
1.1 Automatic detection function a) First-stage cylinder pressure, temperature b) Two-cylinder pressure, temperature c) Cylinder slide temperature 2 d) Lubricating oil pressure e) Total gas tank pressure f) AC voltage, current g) Water volume h) oil temperature (oil temperature limit is switching amount) i) lubricating oil, oil droplets.
For the first six parameters, the timed face-to-table simultaneous display can be performed on the green display, and the record can be automatically printed once every hour using the Chinese character table, or the parameters of a certain machine can be manually and randomly printed.
1.2 Control function a) The number of consoles can be arbitrarily set by the user according to the production requirements. b) The limit value of the control parameters can be raised by the user, and can be satisfied at any time in the program. c) The water pump and water valve that can be used for each compressor are based on the working conditions. Automatic start and stop is required d) Automatic start and stop can be performed for each compressor (the switch process meets the operation requirements) e) The standby machine can be automatically opened or stopped according to the requirements of the user's production wind. When the running machine fails, it can automatically start the standby machine to realize the substitute f) Timing discharge of waste oil wastewater function g) Automatic unloading and automatic loading function h) Timing recording function of each working condition parameter i) Clock display and automatic time counting function j) Fault handling function.
1.3 Automatic protection function When any machine has abnormal or over-limit, it can be processed according to the fault prompt in time to protect, and simultaneously emit sound and light alarm signal, and automatically record the cause of the fault and the time when the fault occurred.
1.4 Detection accuracy Pressure: Temperature: Current and voltage: 2 The hardware composition of the system is shown in Figure 1.
In order to adapt to different users, the building block structure is adopted. Under the condition of basic system guarantee, the user can purchase the control board according to the existing number of air compressors. When the production is increased and the air compressor is added, the system can be inserted into the system with the corresponding template, the hardware system is unchanged, and the software is common.
The total control panel of the unit: mainly consists of three CTCs, one PIO, address decoding circuit, multiple sets of debounce circuits and bus drive circuits (see Figure 2). It is mainly used for time control and system timing of each machine in the system. The P port of PIO works in the position control or interrupt mode. The warm oil, oil drop, water and manual signal B port of each compressor or each compressor are used for the position control input/output mode (or interrupt). The machine number is determined by the number of bits, and the sound and light alarm for the failure of a certain machine is output. The bus driver circuit is mainly used to provide bus load capacity to a single control board.
Single machine control board: The circuit block diagram is shown in Figure 3. It is mainly composed of address decoding circuit, analog switch sample and hold A/D conversion circuit, power journal switch output optical isolation circuit and fault diagnosis circuit.
Each board has 16 analog inputs (for converting each machine's operating parameters) and 4 digital inputs (for fault diagnosis), 8 switching outputs (for machines, pumps, sewage, Water supply valve). The stand-alone control board 1 can be interchanged and used as long as the corresponding address switch is dialed.
Signal Processing Board: The reason why the system is less invested is mainly the use of its own analog signal processing unit. Analog signals are divided into two categories. One type is a resistive signal sensor, all of which are pressure and temperature values ​​and the other is all alternating current and voltage signals.
When the sensing signal is a resistance signal, the Wheatstone bridge measurement method is usually used in the measurement, but this method generally shows nonlinearity, and as the sensitivity increases, the nonlinearity becomes more and more serious, often according to mathematics. The linearization compensation of the relationship requires a more complicated compensation circuit, and the software compensation is also complicated. This circuit is designed with a linearized bridge circuit as shown in Figure 4(a).
Let the variable bridge arm resistance R(1 Δ) itself be linear, and the mathematical relationship is: derivation: then the output is: in equation (3), K is the amplification factor of the second stage amplifier.
It can be seen from equation (2) that after linearization, the variable bridge arm can reach a linearity for changing the range of 200 or the same value as its reference voltage value, and satisfactory results are obtained in practical applications.
In order to convert the voltage and hundreds of amps of AC current into a computer-acceptable accurate linear analog signal, an AC signal with a variable voltage of 0 V to 2.5 V, 50 Hz is designed to be sent to the accurate AC-DC. Conversion circuit. The current is an alternating current of 0 A to 300 A, which is converted into an AC voltage signal of 0 V to 2.5 V through a current transformer and a current-to-voltage converter, and is sent to an accurate AC-DC conversion circuit.
Since the diode is only turned on when the applied voltage is greater than the tube voltage drop, passive full-wave rectification is not competent. This circuit is designed with an active full-wave rectification and smoothing circuit. As shown in Figure 4(b), it can accurately convert signals in millivolts or even millivolts. The conversion accuracy is based on sinusoidal signals. The first three terms of the Fourier expansion after full-wave rectification, using the equation: determine the cutoff frequency of the smoothing filter. The cutoff frequency I/RC radians of this circuit is one order of magnitude lower than the signal frequency ω, and the conversion accuracy reaches 1 , which satisfies the accuracy requirements of the working conditions, and satisfactory results are obtained in the measurement.
3 The software system is clear in structure and convenient to expand. The application program is divided into the following modules: data acquisition, fault processing, real-time clock carry, print processing, display processing, and switch-on interrupt processing. After the system is powered on, perform a self-test. After that, the 8 segments display the number, prompting to enter the control state, and type the year, month, day, hour, minute, and second. Then press the run key, the system performs initialization and data acquisition processing, and the interrupt is opened. System initialization includes: accumulator clearing, flag unit clearing, display clearing, initializing the interface chip, printing boot time, and so on.
3.1 Data acquisition and processing The data is collected into the accumulator A through the analog switch and the A/D converter data. Each data is sampled multiple times for filtering processing, scale conversion, and second to decimal conversion. Decimal ASCII code conversion, stored in the data area for display, print call, if the sample value exceeds the limit, set the error flag, call the fault handler. When there is no fault, the sampling program loops.
3.2 Interrupt Arrangement The system's various functions are implemented by means of interrupts. In the programming, we consider the nesting, protection and reentrant interrupts of multiple interrupts. A two-second period pulse is provided in series with the two channels of the CTC. On the one hand, as the system real-time clock carry and update the screen interrupt request signal, on the other hand, as an external trigger input of the extended two CTCs, the timing of starting, shutting down, venting, and discharging the four compressors is realized. In addition, the CTC provides 8 minute and 1 hour timed interrupts.
3.3 Fault Handling Faults are classified into two types: the over-limit error subroutine and the interrupt request-to-interrupt service routine. Because the interrupt source (no water, oil temperature limit, manual start and stop, etc.) is after the debounce processing phase or logic, the PIO is requested to interrupt, so after the interrupt service is transferred, the signal latched by the read command is read back. , a bit by bit query to determine the source of the interrupt. Since both the sampling period and the response interrupt are completed within a few hundred milliseconds, any faults can be processed in a timely manner.
3.4 block diagram data acquisition, loop program block diagram shown in Figure 5.
4 Measures against system interference The device works in the presence of strong electromagnetic field interference, high-power relays, frequent contactors, power fluctuations and mechanical vibrations, and the system itself has many AC and DC solenoid valves and hundreds of A large motor of kilowatts, so the anti-interference problem is a very important issue. The device is considered to have a reasonable arrangement of the same power journal to find out which device is used for a long time, and which device is used for a short time, which is very vivid. (See Figure 2).
3.4 System Window This window mainly completes the modification password option and includes daily remarks on the use of the instrument or other conditions in the laboratory.
The above functions are completed by the memo window and the password modification window. spare parts. The user can fill in the content to be recorded on the day, or view the previous record. In the password window, enter the new password belonging to the SinglineEdit control and determine the new password. The Enabled property is False. Enter the original password and press the Enter key to confirm. If the password is incorrect, the user is prompted to re-enter the password correctly. The Enabled property changes to T rue. After entering the password twice, press the Enter key. If the two inputs are different, the system will prompt to re-enter.
The functions and functions of the basic window and the book window are implemented similarly to the device window, and are omitted here.
4 Conclusion Using Powerbuilder5.0 to develop the process of the laboratory management system, is the editing process under Windows, its object-oriented editing allows developers to write programs only for a certain control or an event, without having to make a mistake The full program looks up and down, but only changes the program of each window button or other events of the control. At the same time, Powerbuilder is a distributed database front-end development tool with graphical interface. The developed laboratory management system is intuitive. Practical, clear and beautiful interface.
2 Luo Yunmo editor. Beijing: Beijing University of Aeronautics and Astronautics Press. Getting Started with Powerbuilder 5.0, 1998.
At the time, the following measures were taken: an anti-interference AC stabilized power supply was adopted to ensure that the voltage fluctuation was between V and 230 V. The AC-DC two-stage filter switch signal was adopted. The photoelectric isolation and the breaker isolation simulation were adopted. Network, line laying, separate the signal line and the power line, try to avoid the grounding of the chassis of the reasonable connection system between the simulated ground and the digital ground, shield the internal circuit of the chassis, and the ground wire of the power supply for the microcomputer is suspended at the two ends of the inductive load. A RC absorption network or a freewheeling diode is added.
5 Conclusion The system is installed in Chongqing Air Compressor Factory and Shanxi Changcun Coal Mine respectively. After on-site operation, the performance is stable and reliable, meeting the various testing, control and protection indicators of the compressor. And won the "Shanxi Province Science and Technology Progress Third Prize" and "Chongqing Computer Application Achievements Third Prize".
1 week Mingde. Microcomputer principle application. Beijing: Higher Education Press, 1995.
2 Li Zheying, Xiao Haiqiao. The principle and application of single chip microcomputer. Beijing: Tsinghua University, 3 Zhao Changde, Lei Tianyu. Microcomputer principle and interface technology. Beijing: Mechanical Industry Press, 1998.
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