Structural design and application advantage analysis of heating network monitoring solution using ADSL technology

“Urban heat network monitoring and control is an important part of urban municipal engineering. The control nodes of the heat network monitoring system are generally geographically distributed in a wide range, and it is difficult to use one access method to realize the access of all nodes. At present, the more common access methods include PSTN access, GPRS access, digital radio access, and dedicated line access.

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1. The overall structure of the heating network monitoring system based on ADSL

1.1 Overview

Urban heat network monitoring and control is an important part of urban municipal engineering. The control nodes of the heat network monitoring system are generally geographically distributed in a wide range, and it is difficult to use one access method to realize the access of all nodes. At present, the more common access methods include PSTN access, GPRS access, digital radio access, and dedicated line access.

These access methods all have their applicable occasions, but all have the disadvantages of low bandwidth and high operating costs. This paper proposes a heating network monitoring system based on ADSL, which realizes the communication access of nodes by ADSL. Its advantages are:

(1) Easy access, which can be provided in places covered by telephone networks in general cities; (2) High bandwidth, the maximum can reach 2Mbps, which can greatly improve the real-time monitoring; (3) Investment small;

(4) Low operating cost.

1.2 The overall structure of the system

The overall structure of the heating network monitoring system based on ADSL is shown in Figure 1. A typical heating network monitoring system consists of a monitoring center and multiple control nodes. The monitoring server is responsible for data communication with each control node, receives the working condition data sent by the control node, and sends instructions to the control node according to the operation status of the heat network to adjust the heat supply balance of the entire heat network. The database server saves the current and historical working condition data to provide support for data analysis and decision-making; the WEB server Displays the monitoring interface for the operating conditions of the heating network.

There are several thermal power stations under the thermal power company. Generally, each thermal power station is set with a control node, and the control node is composed of an embedded system. On the one hand, the control node collects on-site supply/return water temperature, flow, pressure and other working condition data through sensors, and controls solenoid valves, regulating valves and frequency converters to adjust on-site operating parameters; on the other hand, it connects to the Internet through ADSL Modem, The working condition data is transmitted to the monitoring center through the Internet, and the control node can also receive the instructions issued by the monitoring center to adjust the operating parameters of the on-site working conditions.

Figure 1: Structure diagram of ADSL-based heating network monitoring system

2. Key technologies of ADSL-based heating network monitoring system

The latest achievements in the field of control technology, computer technology and communication technology are effectively used in the ADSL-based heating network monitoring system. The key technologies used are:

2.1 Design and implementation of monitoring interface based on WEBGIS in monitoring center The development of GIS (Geographic Information System) technology has put forward higher requirements for the interface of thermal network monitoring, not only to be able to Display working condition data in tables, curves, etc., but also to be able to The data query and display of the thermal station is realized in the browser by means of Electronic map navigation. At present, there are two ways to realize WEBGIS, one is to carry out secondary development on the basis of commercial GIS software. The second method is to complete the secondary development on the basis of the open source WEBGIS server. In practical applications, due to the high cost of commercial GIS, the open source Mapserver is used as the GIS server.

2.2 Research on control algorithm of networked control system

The thermal network remote monitoring system is a network control system (NCS), and its control object is a large lag object. At present, there is no good mathematical model and control algorithm to solve this control problem. At present, the general method adopted by thermal companies is to adjust the balance of the heat network through human experience, to study a control algorithm suitable for monitoring of the heat network, and to fully consider the impact of ambient temperature, which is of great significance to saving energy and improving heating efficiency. . In the network control system, there will be time delay due to the limitation of bandwidth, and it is also a problem that needs to be solved to study the influence of time delay on the control algorithm.

2.3 Control node software and hardware system design

If the control node of the thermal power station is realized by technology such as industrial computer and PLC, the cost of the control node is relatively high. Adopting the embedded system design to realize the control node will reduce the cost of the whole system, which is conducive to large-scale promotion.

2.4 Design and Implementation of VPN Protocol

After adopting the node access mode of ADSL, there is a problem of data security due to the use of the Internet to transmit control data. In order to ensure data security, VPN (Virtual Private Network) technology can be used to ensure the security of data transmission.

3. Control node software and hardware system design

3.1 Control node hardware system design

The hardware system of the control node is implemented based on Samsung’s ARM7 processor S3C44B0X, as shown in Figure 2:

S3C44B0X is a 32-bit microprocessor with ARM7 (Advanced RISC Machine) core produced by Samsung, with 8-way ten-bit A/D converter and other hardware resources. The chip has low cost and is very suitable for heat network monitoring system. The power supply adopts 5v/24v switching power supply to supply power for embedded systems and sensors. The crystal oscillator adopts a 10MHZ crystal oscillator module, and the S3C44B0X has a phase-locked loop inside, which can generate a stable output frequency of 66MHZ on the basis of the crystal oscillator.

The display part adopts VFD high-brightness display screen, which has the advantages of dot matrix output, high brightness and wide viewing angle. This screen is used to display the temperature, flow, pressure and other working conditions data on site. In addition, in order to meet the requirements of human-computer interaction, the indicator light and keyboard are also expanded, and this part is realized through the general I/O of S3C44B0X.

The system expands 2 RS-232 serial ports through the MAX232 chip, one is used for debugging and the other is used for communication with the frequency converter.

Since the S3C44B0X does not have a network interface, the network interface is realized by expanding the RTL8019A network control chip. The communication rate of this chip is 10Mbps, which can fully meet the system requirements. The chip communicates with ADSL MODEM through the network isolation transformer and RJ45 interface to complete the functions of dial-up and network communication.

The realization principle of the data acquisition part is as follows: the six-channel 4-20mA analog signals of supply/return water temperature, flow rate and pressure are converted into the 0-2.5v signal required by the internal A/D of the S3C44B0X through the I./V conversion Circuit to complete the data acquisition.

The actuator section works as follows:

By extending the D/A converter, the analog signal is output to realize the adjustment of the opening degree of the control valve. Control the switching action of the solenoid valve through general-purpose I/O and optical isolation. The communication with the inverter is completed by the RS-232 serial port, and the command is sent to the inverter through the serial port to adjust the working state of the booster pump.

3.2 Control node software system design

As shown in Figure 3, the whole system architecture adopts the design pattern of hierarchical architecture, and each layer provides invocation services for its upper layer. This design pattern has good scalability and maintainability.

The structure design and application advantage analysis of the thermal network monitoring solution using ADSL technology The bottom layer is the operating system layer, which uses the vxWorks real-time operating system. This layer also provides the encapsulation of the TCP/IP protocol for the middleware layer to call.

Above the operating system layer is the middleware layer, which provides services for the application layer. Including hardware driver module and communication protocol module two parts.

Above the middleware layer is the application layer, which is the application software of the system, including three Modules: data acquisition module, automatic control module and remote communication. This layer is implemented by calling the services provided by the middleware layer and the services provided by the operating system kernel.

The three modules of the application layer have high real-time requirements, which are realized by designing several independent tasks.

The data acquisition module is a periodic task. It collects data every 100ms and uses the operating system kernel to achieve precise timing. When an alarm occurs, it is handled in an interrupted manner. The communication between the data acquisition module and the other two modules is realized by means of message queue and shared memory.

The automatic control module controls the action of the actuator according to the real-time data, adjusts the operating conditions of the heating network, and can also accept instructions from the remote communication module to adjust the operating conditions.

The remote communication module transmits real-time data to the monitoring center through the network, and accepts the control instructions from the monitoring center.

The inter-task communication between the remote communication module and the automatic control module is achieved through message queues.

4 Conclusion

The heating network monitoring system based on ADSL proposed in this paper is a cheap, reliable and high-bandwidth heating network monitoring solution. At present, there are still some technical problems to be solved in the system, such as the control algorithm and time delay of the network control system, which need to be further studied in the future work.

The innovation of this paper is to use ADSL technology as the communication method for remote monitoring of the heat network, and to use the embedded system design to realize the control node, which has the advantages of low cost and good real-time performance. The system has been operated for two heating periods in a certain city, which proves that the system operates stably and reliably. By reducing energy consumption, reducing staff and increasing income, the annual economic benefit is 5.27 million yuan.