The hottest mixing plant control system based on P

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Mixing plant control system based on PLC and configuration software

1. Introduction

with the continuous development of modern urban construction, infrastructure construction and real estate industry are booming day by day, and the quality requirements for construction projects are becoming higher and higher, and high-quality building materials are the guarantee of the high quality of the whole project. The traditional way of producing concrete on the construction site by itself is difficult to ensure its quality, and the noise and dust pollution are large. Therefore, it will be replaced by the automatic concrete mixing plant. The automatic concrete mixing plant has the characteristics of excellent product quality, high production efficiency and good environmental protection performance, and is becoming the mainstream of concrete production

the control system is stable and reliable. It can automatically and continuously control the measurement, feeding, mixing and discharging of all parts of materials according to the set formula. At the same time, the system also has a series of management functions such as browsing, querying, statistics, printing and so on. In addition, the drop is automatically corrected by dividing N and taking remainder oscillation curve method, and the accuracy problem is accurately controlled

2. System structure

2.1 hardware structure

the control system is composed of upper computer and lower computer. The system hardware structure is shown in Figure 1

Figure 1 hardware structure diagram of the mixing plant control system

due to the requirements of the system on operation speed, sensitivity, stability, dust prevention, earthquake resistance and noise resistance, the upper computer selects Yanxiang ipc-810p/fsc-1621vd industrial control computer as the upper computer, which has stronger i/o expansion function than ordinary PC, built-in 8MB independent video memory supports 3D graphics acceleration, so that it can intuitively monitor the site, and the board is equipped with ISA bus high drive, The maximum driving capacity is up to 64ma, with the serial port 15000V electrostatic protection function. On this industrial computer, the design and development of configuration software, the development of PLC program and the transmission of software to the CPU unit of PLC through serial port can be completed

the lower computer adopts Omron cqm1h PLC, a programmable controller with powerful function, high reliability, convenient maintenance and strong anti-interference ability, to realize the acquisition and control of mixing plant parameters. OMRON PLC is a strict and high-speed program controller composed of power supply, central processing unit and i/o components. As mechanical control constantly needs more advanced functions and processing speed, cqm1h is such a compact PLC with perfect functions. It provides value-added machine control and has the ability to upgrade through various advanced built-in boards. Large program capacity and storage unit. In addition, the CPU unit is equipped with RS-232C interface, which can realize timely data collection, and then the data is processed by the upper computer program

since the system must have manual operation function while meeting full-automatic production, weight instruments and power cabinets should be configured. The weight instrument adopts the wc-2000c weight display of Tianheng Fuzhong, which is an intelligent instrument controlled by a single-chip microcomputer and integrates weighing, setting and control. Due to the use of highly integrated integrated circuits, the circuit is simpler and more reliable. Unique anti-interference measures are added to the road. The instrument can be used stably and reliably in the harsh field environment. The instrument is simple in operation and accurate in measurement. In addition to the additives accurate to 0.01kg, other instruments 9. The fasteners of the electro-hydraulic servo universal testing machine should be locked regularly: the vibration after the specimen is broken will often make some fasteners loose, and the accuracy is 1 kg with low manufacturing cost

figure 2

the power control part is usually composed of circuit breaker (air switch), AC contactor, control transformer, intermediate relay, etc. The main circuit composed of circuit breaker and AC contactor is shown in Figure 2. The circuit breaker has short-circuit and overload protection functions. The contactor is only a high-power switch, which can directly drive motors and other electrical appliances. The control transformer provides various isolated power supplies required by the secondary circuit (control circuit), such as 220V, 24V, etc. Intermediate relay is the control object of weak current system (computer system) or master electrical appliance. Its function not only plays the role of electrical isolation between weak current and strong current, but also expands the control power and control signal. Schematic diagram:

the industrial control computer is connected with two epson300k + 24 pin printers for printing delivery vouchers and grading reports

2.2 software structure

industrial control configuration software is a software package that can collect data in real time from programmable controllers, various data acquisition cards and other devices, issue control commands and monitor whether the system operates normally. The configuration software can make full use of the powerful graphics function of windows, The operation status of the monitoring equipment is displayed by animation, which can easily form the monitoring screen and realize the control function, and can generate reports, historical databases, etc., which provides a convenient software development platform for the development of industrial monitoring software, and improves the quality of industrial control software as a whole. Centurystar5.0 developed by Beijing jinjialuo company is a configuration software running on window98/nt, which is composed of Engineering browser csmaker and image operation system csviewer. Csmaker is the core part and management development system of Century Star software. Its function is to establish an animation display window. Through the tool box provided by it, it is convenient to establish real-time curve chart, historical trend chart and alarm record display. Csviewer is a running environment that displays the graphic window established in csmaker. In the mixing plant control system, the structure of the control software is shown in Figure 3. The upper computer uses l driver to communicate with PLC and accesses the corresponding registers through serial port to obtain the actual value of the parameters of the equipment on the site of the mixing plant or control the on-site switching and analog quantities such as the opening of each control valve. In this system, dm0 ~ DM100 of PLC is set as the read-write area, that is, the upper computer can read and write the area of the lower computer; Set dm101 ~ dm399 as a read-only area, that is, the upper computer can only read the value of this area of the lower computer and cannot change it

Figure 3 control software structure diagram

the configuration software of the upper computer of the mixing plant control system basically realizes the requirements of the mixing plant measurement and control. The site process flow of the mixing plant is simulated concisely and vividly, and the operators can understand all the operating conditions of the mixing plant, including various alarms, on the computer screen in the control room. The operator who has obtained the permission can modify the formula parameters and moisture content in the control room, and all switches between automatic and semi-automatic are undisturbed. Each control button and each automatic and semi-automatic switching button have further confirmation or cancellation to prevent misoperation

the lower computer of the mixing plant control system is a PLC controller. The system adopts modular design and is composed of a/d data processing, control parameter processing, input and output control, batching process control, feeding process control, mixing operation control, upper computer inching control and other program modules. The program is written directly with ladder diagram. Within the scope allowed by the program framework, you can arbitrarily increase the batching variety or set the feeding sequence. For example, aggregate is first put into the middle bucket, and then put into the mixer with powder and water in sequence to start mixing. At the same time, the system makes the feeding sequence into a window so that users can modify it in time

see Table 1 for the communication parameter settings between the upper computer and the lower computer. Table 1 device drive parameter setting table

3. Database structure

because the upper computer software is based on windows98/nt platform, the whole Chinese browsing interface, using event driven technology. Therefore, the database program design can use the open program interface of configuration to record data through API (dynamic connection Library), and can also be stored in acess. The customer information, project name, contract number, etc. are recorded for browsing and querying. 3. Plug the bulb of the microscope into the low-voltage transformer (6 ~ 8V). At present, VB is used to compile an access program to process the timely recorded data, so as to realize the statistical management of data. The specific functions are as follows:

recipe management: you can set and manage more than 1000 recipes, and set a password to prevent accidental modification and deletion

project management: it can be managed separately by proportion number, contract number, project name and construction unit, and it can also be counted by vehicle number and job number

print report: you can choose to print or not to print the report according to the actual needs, or you can choose which printing method

4. Main functions realized by the control system

1) display functions: process flow, measured value, equipment operation status, operation mode, alarm and other display, screen call and other functions

2) alarm processing and report generation function: there is a timely alarm function when a fault occurs. The report output of the system can be selected according to the time, proportion number, project name, construction unit, etc

3) database storage and access: realize the automatic creation of access historical database and record it in seconds every time the system runs, and the storage of on-site data

4) the picture system modifies and stores the control parameters and system calibration, and can realize the undisturbed switching between the automatic/semi-automatic/manual operation modes of the monitoring system

5) management authority: realize different levels of system management authority, the system operator can input and modify the formula, and the engineer with authority can modify the control software and lower computer software according to the actual situation

5. Other technical measures

5.1 measures to enhance reliability

in order to improve the reliability of the system, the following measures are taken in the design:

PLC adopts separate power supply and grounding wire is separately grounded

the industrial computer and weak current part are powered by 500W UPS, which not only purifies the weak current power supply, but also ensures that the industrial computer will not lose data due to sudden power failure

the grounding resistance of the whole system is required to be less than 1 Ω

the control output and alarm input of industrial computers and weight instruments all adopt photoelectric isolation technology to effectively prevent external interference signals from entering

all AC contactors are installed with resistance capacitance absorption

all intermediate relay packages are installed with diode absorption circuits

all kinds of weak current transmission cables adopt shielded wires, and the shielding layer is grounded at one end

5.2 measures to improve accuracy and production efficiency

adopt the method of dividing N and taking remainder oscillation curve to track and adjust the drop, which can be automatically corrected in the production process, and a fixed drop can also be set. This can ensure that the error of aggregate is within ± 2%, while that of other powders is within ± 1%. Through the pretreatment of data, the efficiency can be improved by weighing materials in advance in continuous production

take some other methods:

· adopt variable speed feeding for cement and fly ash to reduce the impact of impulse. When weighing, feed at high speed first, and when it reaches about 90% of the set value, it will automatically change to low-speed batching to realize fine weighing

· the fine weighing method of double bins and successive approximation is adopted for aggregates (stone and sand). During rough weighing, the two bins are fully opened, and the discharge door is closed after quickly reaching the closing value (formula value - drop). After stabilization, the pulse feeding time is automatically calculated according to the gap with the formula value, and then only the fine discharging door is opened. Generally, the fine weighing and batching can be completed after secondary feeding

· adopt the scheme of adding water in thick and thin pipes to realize the precise weighing of flow

through the above technical measures, not only the weighing accuracy is improved, but also the production efficiency is guaranteed

6, conclusion

the mixing plant control system based on PLC and configuration software studied in this paper makes use of the characteristics of PLC with strong anti-interference ability, which is suitable for industrial sites, and also makes use of the powerful data processing and graphic representation ability of configuration software, which integrates more advanced automation technology, computer technology, communication technology, fault diagnosis technology and software technology, with high reliability, simple operation and maintenance

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