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1. System overview
The absolute drying quantity of pulp is an important index affecting the quality of paper making. The main line of the absolute drying quantity control system is the concentration regulation. The pulp concentration is detected by the concentration sensor before the pulp mixing box. The central controller realizes the concentration control to ensure the pulp concentration is stable and accurate. The electromagnetic flowmeter is used to measure the pulp flow rate. According to the absolute dryness set by the system and the pulp concentration detected from the concentration sensor, the absolute dry pulp flow rate per unit time in the pulp conveying pipe and the system setting value are basically the same by controlling the flow electric ball valve, so as to achieve continuous and stable control of the absolute pulp flow rate per unit time. The purpose of dry sizing is to get online.
At present, there are four sets of absolute drying control system for coated white board production line in a paper mill, including concentration transmitter, electric regulating ball valve, electromagnetic flowmeter, electric ball valve and DPS absolute drying measurement and control instrument. There are several defects in the system, resulting in unstable pulp quality, seriously affecting the continuous and stable production of paper machine.
1). DPS pulp absolute drying measurement and control instrument has poor adaptability to the environment. Environmental temperature, humidity, vibration and so on often lead to poor control effect of the instrument.
2). The instrument belongs to a special system. The system has poor exploitability and maintainability. It is difficult to judge the cause of the fault when the control system fails.
3). The monitoring function of the measuring and controlling instrument is relatively closed, and the function can not meet the needs of the real-time monitoring of pulp absolute drying quantity in the steady and continuous production.
4). The instrument is self-contained and can not realize the networking and communication with other control systems, and can not meet the user's desire to connect the flow and paper cutting, forming a closed-loop control requirements.
Therefore, it is urgent to reform the original control system, overcome the problems in the system, and meet the needs of production for stability, reliability and versatility.
1). The selected control system adopts a general design scheme, which is universal, reliable and maintainable.
2). the control software has good flexibility, which is convenient for adjusting and modifying the control mode.
3). The system should have good expansibility, simple and convenient expansion of system scale, and little modification to the original control software.
4). The system has good network function and can be connected with the paper machine control system to realize the synchronization of paper cutting and flow.
3. system configuration and function realization
1). This control system is composed of SIEMENS CPU315-2DP and UniMAT I/O module of UniMAT company. It realizes density signal, flow signal and field control state. After digital filtering, signal conversion and other signal processing, the concentration and flow of pulp are closed-loop controlled to achieve the purpose of absolute dryness control.
2). SIEMENS Operating Panel OP270 is used for centralized monitoring of dry-out capacity, which accomplishes two tasks. One is to display the current parameters of the flow system in the form of system flow chart, tables, trends, etc. The other is to set the parameters of the dry-out capacity control system, including concentration setting, dry-out capacity setting and so on.
3). The dry weight control system is connected with the paper machine control system by PROFIBUS DP mode. On the one hand, the real-time parameters of the dry weight control system are transmitted to the paper machine control system for display and storage on WinCC. On the other hand, the paper machine control system sends the adjustment signal of the paper machine to the dry weight controller, and the dry weight controller is automatically suitable. It is necessary to adjust the process to realize the synchronization of the paper machine control and the flow control, and realize the dynamic realization of the whole paper-making process. Thus, the whole control process can be formulated to manage, different varieties and speed of paper for rapid system synchronization, reduce process adjustment time, provide production efficiency.
4). Dry-out control system can realize many practical functions which can not be realized before, including concentration adjustment cycle setting, manual automatic construction switching, pulp concentration multi-point calibration, sensor fault protection, concentration detection filtering and so on.
5). Through this control system, the control of slurry pump and the control of dry-out can be integrated, and the frequency converter of slurry pump can be directly controlled by this control system
4.Application effect analysis
Moisture quantitative control system has been put into operation so far. It works stably and reliably. Its regulation precision is better than the original DPS absolute drying measuring and controlling instrument. It also realizes the linkage with the paper machine control system. It is of positive significance to the continuous and stable production. It is the most competitive and cost-effective cost control solution.
Abstract：This paper introduces the application of UniMAT PLC in pH value online detection and control system. In the process of printing and dyeing, the monitoring of PH value is an important link. The environment of printing and dyeing enterprises is special. There are two difficult problems in the testing of PH value: how to improve the reliability and accuracy. The PH value of mercerizing machine cloth surface is one of the most important factors affecting color difference in pretreatment. The PH value of finished cloth has strict standards. The PH value must be controlled within a reasonable range. The introduction of UniMAT PLC into the on-line detection and control system of PH value as its automatic control core effectively realizes the on-line detection and fault diagnosis of PH value, achieves the purpose of fault-tolerant testing, realizes the transformation of PH value from manual measurement to quantitative control, improves the testing accuracy of PH value, and meets the requirements of high-grade products.
Key words: pH online detection, UniMAT PLC, automatic control, PID
Most of the domestic printing and dyeing wastewater PH value control is basically completed by manual operation, its shortcomings: measurement value is not easy to grasp, poor real-time, poor reproducibility of production process, so many factors restrict the further improvement of product quality. Therefore, it is particularly important to develop a pH online control system. PH value on-line detection and control system is a new technology which sprang up in the 1980s and is widely used in all walks of life of construction machinery. In recent years, China has accelerated the development and innovation of PH value on-line detection and control system. Perfect monitoring system, stable operation and precise PID control characteristics have become the key points of excellent printing and dyeing PH treatment equipment.
The system consists of UniMAT PLC, detection electrode, PH value control instrument, frequency converter, metering pump, control box, touch screen and other parts. According to PH probe detected PH value, output detection signal to the control instrument and PLC, touch screen display actual PH value, PLC use PID control, according to the set PH value control speed of the feeding speed pump, automatically add acid to the pool to neutralize alkali, so that sewage to reach the set pH value. The whole system is precise, stable and reliable. It adopts PLC intelligent design and has powerful functions, such as automatic zero stabilization, digital display, over-limit alarm, transducer output, current regulation output or time proportional output, RS485 communication and so on. The working principle is shown below
The system consists of detection electrode, PH value control instrument, frequency converter, metering pump, control box, UniMAT PLC, touch screen and other parts. The electronic control system consists of UniMAT PLC system, HMI system, low-voltage electrical apparatus, sensors and actuators. The configuration of UniMAT PLC system is shown in table 1
|No.||Model name||Series No.||Unit||Qty|
Table 1: configuration of UniMAT PLC system
Comparing with the similar products on the market, UniMAT CPU 124XP-2R has the following excellent characteristics: CPU itself comes with 10DI/8DO, 4AI/2AO, DC 24V power supply. Four channels of AI and two channels of AO are added. The system saves an analog input module and an analog output module for customers because of the need for an analog input and an analog output module. Additional PPI ports have been added to save customers from the trouble of using touch screens and programmed cable ports at the same time, which can only be plugged in and out of ports continuously; no batteries are needed to provide more than 10 years of power-down data to maintain; faster instruction execution speed, a single Boolean operation instruction is three times that of similar Siemens products. The appearance of CPU 124XP-2R products is shown in figure 2...
The electric control system of PH value on-line detection and control system is PLC control system, the core is composed of upper computer and lower computer. The subordinate computer is billionaire CPU124XP-2R PLC, and the upper computer is LCD touch screen or HMI. The user interface is friendly and easy to operate. The device monitors the PH value in all directions; the LCD touch screen can display all kinds of setting parameters and running state of the system; the user can change the local mode, remote mode, test mode, etc. of the system; the user can also modify the PH value according to the actual needs to ensure that the sewage discharged can meet the discharge requirements; when there is a failure, the system may be. Display the location of the fault and alarm, in addition to password protection function also requires the user to change the system settings parameters to confirm identity, to ensure that the system is not random operation. The control process diagram is shown in figure 3..
ig. 3 control technology
Main technical parameters:
1). PH measurement range: 0pH - 14pH;
Display resolution: 0.01pH;
(3) pH control accuracy: + 0.3pH;
The suitable environment for sensors is less than 80 degrees Celsius.
Power supply: three phase AC 380V + 10% 50Hz + 2%<1.5KVA;
2). Ambient temperature: 0~50 C;
3). Ambient humidity: no more than 95%RH (no condensation).
4).Altitude: not more than 1000m;
5).Working mode: continuous.
5 system effectiveness
The protection effect and economic benefit of the PH value on-line control system are obvious. The main effects are as follows:
(1) change the traditional transformation from the operator's titration pH value to the system intelligence measurement.
(2) To reduce the randomness of titration, the whole process of measuring the PH value of the system is completely realized by the process room.
(3) improve product quality and success rate.
(4) reduce the problem of dyeing, cylinder difference and batches.
(5) shorten dyeing time and increase output.
(6) the dyeing and dyeing rate is increased, and the dye is saved. The color stability and color fastness are high, and the quality is ensured.
(7) environmental protection and energy saving.
6 concluding remarks
The application of UniMAT PLC in the PH value on-line control system shows the high compatibility with Siemens PLC and the excellent characteristics of stable performance. UniMAT PLC can completely replace Siemens products, ensuring the stability of the product while reducing the manufacturer's production costs.