[Abstract]: This article mainly introduces the application of the latest product "Integrated Controller OCS" of the United States HORNER Co., Ltd. with the GPRS device in the district heat exchange system.
[content]:
I. Introduction
The winter weather in the north is cold and every household needs heating for the winter. Therefore, residential heat exchange stations must be established in all residential areas. The heat exchange station is mainly used in a centralized heating system. The central heating system has the characteristics of large thermal inertia, obvious lag, and large interference from temperature and weather factors, which makes the adjustment and control of the entire system more difficult, and the traditional heat transfer control Most of them use relays, inverters, etc. for simple control. The system adjustment is based entirely on past experience. The cost of operation and maintenance is too high and the efficiency is low. In view of the above-mentioned situation in the heating network regulation, it is an effective method to adopt a computer monitoring and management system to implement centralized monitoring of the heating network. The system has the following remarkable features:
The monitoring center computer collects field data in real time through various field control devices, monitors the key data of the entire heating system, comprehensively analyzes the hydraulic conditions and thermal conditions of the heating network, and then adjusts the parameters such as the heating temperature in time according to the thermal compensation conditions. Coordinate the stable and reliable operation of the entire system, give full play to the maximum efficiency of the system, and reduce costs.
In the heat exchange stations with relatively dispersed geographical positions, the integrated controller (OCS) of the American HORNER Company was used for field control. By using advanced PID algorithm, the time constant of traditional PID controllers was overcome, and the inertia of adjustment was large and easy. Overshooting has the disadvantages of large amplitude oscillations, and at the same time it is convenient to display and operate on the spot through an integrated human-machine interface.
Through real-time communication with multiple frequency converters in the field through serial communication protocol, the key parameters of the frequency converter are collected and continuously adjusted so that the water pump works in the best condition.
In terms of data transmission, real-time communication with the central computer through the advanced GPRS network saves a lot of time, manpower, and money consumed by the wired network.
The following is a detailed description of the above sections.
Second, a highly integrated integrated OCS controller
Did you encounter this problem during the application of the PLC: I/O devices, PLCs, display devices, and networks come from different manufacturers, we spend a lot of time, the funds will integrate them together, and may also need to There are several packages purchased and many trainings can be completed. These undoubtedly increase the complexity of our work, slow down the speed of product R&D, increase the cost of products, and reduce the competitiveness of companies. So what is the solution to these problems?
The American Horner integrated controller (OCS) integrates traditional PLC controllers, human-machine interface HMIs, input/output I/Os, and network networks together. Only one set of software can be used to configure the hardware of the entire system. Programs, network connections, and human-machine interfaces are configured and edited, greatly reducing the time and cost of engineers' program development. Horner's OCS products have a very wide range of applications in developed countries such as Europe and the United States. They are particularly suitable for equipment manufacturing, automated production lines and various DCS systems. The integrated control concept proposed by American Horner Company is increasingly accepted by the industry and is gradually becoming the mainstream product in the automation control industry.
In this heat exchange system, two main products of the HORNER X series are used, the compact and compact XLE103, and the LX300 with a 5.7-inch color touch screen. The programming software uses Horner's own Cscape and is free. The system configuration diagram is as follows, where the XLE103 has a small operator interface (128x64 backlit display with 16 function keys) with built-in I/O: 12-point DC input (positive/negative logic) compatible with 12/24 Volt, 12-point DC output (max. 0.5A per channel), 2-channel 10-bit analog input (0-10V/4-20mA). 2-pulse/PWM output function, and 4 high-speed counters (10kHz) . XLE103 comes with two RS232/485 interfaces, supports PLC/Drive communication protocol and a large-capacity removable memory slot (supports standard SD card). Xle has an integrated CsCAN network port for high-speed communications and I/O expansion. Each Xle is DC powered. Xle can be mounted on a DIN rail. The LX300 comes with a 5.7-inch standard color touch screen. Supports CsCAN network interface and remote I/O modules (SmartStix).
Third, OCS controller has flexible PID control function and rich computing power Modern heat exchange station needs to achieve automatic constant temperature water supply, so PLC should adjust the frequency converter according to parameters such as temperature and pressure feedback from field transmitter. Frequency of. Control the speed of the two circulation pumps and one make-up pump to control the temperature and pressure of the secondary heating.
The PID of this system is completely realized by software programming. It does not need to add any peripheral equipment and can realize up to 8 independent PID control. And LX300 scan rate is about 0.2ms, the response speed to PID is very fast. One of the most advantageous is that it has the function of self-tuning parameters, so that even if the end user does not have PID theory knowledge can quickly adjust the PID, users only need to open the PID self-learning function, PLC can automatically find out the proportion according to the working conditions Coefficient, integration time, differential time and other parameters. After the PID parameter is found, it will automatically enter the control program. The specific screen of PID adjustment is as follows:
This heat exchange system requires a total of 3 PID control:
1. Realize outdoor temperature compensation and automatically control the secondary water supply temperature function. The controller can automatically control the secondary outlet temperature according to the set heating curve and the change of outdoor temperature, and can also maintain the secondary outlet temperature according to the set fixed outlet temperature. The outlet water temperature is constant to meet the user's best energy efficiency requirements.
2. The secondary side circulation variable flow regulation function, the controller can adjust the rotation speed of the circulation pump according to the change of the system thermal load, maintain the secondary supply and return water temperature difference (can be adjusted) constant, achieve the best heating efficiency and energy saving effect. There is a period of time (adjustable) delay alarm before the new start-up to remind the staff who may be in the field to pay attention to their own safety.
3. Adjust the flow of the secondary water supply according to the pressure of the secondary return water, detect the pressure of the secondary pipe network return water in real time, and timely control the flow valve of the secondary pipe network through PID adjustment. Ensure the constant pressure of the secondary water supply.
IV. Communication between OCS Controller and Inverter In the industrial automation control system, the most common is the combination application of PLC and frequency converter, and there are a variety of ways to control the frequency converter by PLC, among which RS-485 communication is adopted. The implementation of the control scheme has been widely used because of its strong anti-interference ability, high transmission rate, long transmission distance and low cost. However, RS-485 communication must solve a series of technical problems such as data encoding, checksum calculation, framing, sending data, parity check of received data, timeout processing, and error retransmission. A simple inverter operation instruction is required. It is sometimes necessary to write dozens of PLC ladder instructions to achieve programming. The workload of programming is large and cumbersome, which makes designers daunting.
But in the OCS this all becomes very simple, we only need one function block to realize all functions of Modbus, namely has retained the advantage of RS485 communication, but also saved the complicated programming work. The following is an example of compiling a communication program. It can be seen that the OCS is very simple to obtain the desired parameters from the inverter:
Fifth, the perfect combination of GPRS and OCS DTU refers to the data terminal equipment (Data Terminate unit), can be understood as the lower GPRS transmitter terminal. The advantage of using GPRS is real-time online, which is charged by traffic when there is data transmission. It can save a lot of wiring, debugging and maintenance work, and it has obvious advantages for data transmission with relatively long geographical distance. However, there are some weaknesses in the system itself. For example, the delay time of the system is long (about 10 seconds), the signal is affected by the surrounding environment, and the operator supports it.
For this heat exchange system, the real-time data required by the calculation center is not high (about 1 minute), and each heat exchange station is relatively far away from the geographical location, so it is particularly suitable for the application of this transmission method for communication between the PLC and the host computer. The basic diagram is as follows:
The heat exchange control center monitoring screen is as follows:
Six, OCS other protection and alarm function protection features include conventional over-voltage protection, undervoltage protection, missing protection, leakage protection, over-current protection and other functions. Alarm functions include circulating pump fault alarm, make-up pump fault alarm, make-up water overpressure alarm, system softened water tank pressure too low alarm, secondary net return water pressure too low alarm, heat exchange station shutdown alarm and other functions.
For the first time, HORNER OCS products use mobile storage technology and support ordinary SD cards or CF cards (up to 2G) for storing historical data and alarm information. In this system, we use a 1G memory SD card to store alarm information and back up data in real time. When we need to check, we can simply open the SD card and plug it into a computer to open all files, and all files can be saved. For EXCEL format.
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