What is the heating network monitoring solution based on ADSL technology?

1. Overall structure of heating network monitoring system based on ADSL

1.1 Overview

Urban heating network monitoring and control is an important part of urban municipal engineering. The control nodes of the heating network monitoring and control system are generally widely distributed geographically, and it is difficult to achieve access to all nodes using one access method. At present, the more common access methods include PSTN access method, GPRS access method, data transmission radio access method, dedicated line access, etc.

These access methods have their applicable occasions, but they all have the disadvantages of low bandwidth and high operating cost. This article proposes a heating network monitoring system based on ADSL, which implements node communication access in ADSL mode. The advantages are:

(1) Access is convenient. Generally, places with telephone network coverage in cities can provide this access method; (2) High bandwidth, up to 2Mbps, can greatly improve the real-time nature of monitoring; (3) Investment Small;

(4) Low operating cost.

1.2 Overall system structure

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, receiving the operating condition data sent by the control node, and sending instructions to the control node according to the operating status of the heating network to adjust the heating balance of the entire heating network. The database server saves the current day and historical working condition data to provide support for data analysis and decision-making; the WEB server displays the heating network operating condition monitoring interface.

There are several heating stations under the heating company. Generally, each heating station is equipped 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 is connected 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 instructions from the monitoring center and adjust the on-site working condition operating parameters.

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

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

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

2.1 Design and implementation of the monitoring interface of the monitoring center based on WEBGIS The development of GIS (geographic information system) technology has put forward higher requirements for the interface of heating network monitoring. It must not only be able to display working condition data in tables, curves, etc., but also be able to The data query and display of thermal stations are realized in the browser through electronic map navigation. Currently, there are two ways to implement WEBGIS. One is to conduct secondary development on the basis of commercial GIS software. The second method is to complete secondary development based on the open source WEBGIS server. In practical applications, because commercial GIS is expensive, the open source Mapserver is used as the GIS server.

2.2 Research on control algorithm of network control system

The heating network remote monitoring system is a network control system (NCS), and its control object is an object with a large lag. Currently, there is no good mathematical model and control algorithm that can solve this control problem. At present, the method generally used by heating companies is to adjust the balance of the heating network through human experience. Researching a control algorithm suitable for heating network monitoring and fully considering the impact of ambient temperature is of great significance to saving energy and improving heating efficiency. . In network control systems, time delays will occur due to bandwidth limitations, and studying the impact of time delays on control algorithms is also a problem that needs to be solved.

2.3 Control node software and hardware system design

If the thermal station control node is implemented using industrial computer, PLC and other technologies, the cost of the control node will be relatively high. Using embedded system design to implement control nodes will reduce the cost of the entire system and is conducive to large-scale promotion.

2.4 Design and implementation of VPN protocol

After adopting the ADSL node access method, there is a problem of data security because the Internet is used 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 an ARM7 (Advanced RISC Machine) core produced by Samsung. It has an 8-channel ten-bit A/D converter and other hardware resources. The chip has low cost and is very suitable for use in heating network monitoring systems. The power supply uses 5v/24v switching power supply to power embedded systems and sensors. The crystal oscillator uses a 10MHZ crystal oscillator module. The S3C44B0X has a phase-locked loop inside, which can generate a stable output frequency of 66MHZ based on the crystal oscillator.

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

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

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

The working principle of the actuator part is as follows:

By expanding the D/A converter, the analog signal is output to adjust the opening of the regulating valve. Control the switching action of the solenoid valve through general I/O and optical isolation. The communication with the frequency converter is completed by the RS-232 serial port, and instructions are sent to the frequency converter through the serial port to adjust the working status of the pressure pump.

3.2 Control node software system design

As shown in Figure 3, the entire system architecture adopts a hierarchical architecture design pattern. Each layer provides calling services for the layer above it. This design pattern has good scalability and maintainability.

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

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

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 module. This layer is implemented by calling services provided by the middleware layer and services provided by the operating system kernel.

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

The data acquisition module is a periodic task that collects data every 100ms and uses the operating system kernel to achieve precise timing. When an alarm occurs, interrupt is used to handle it. The communication between the data acquisition module and the other two modules is implemented by message queue and shared memory.

The automatic control module controls the action of the actuator and adjusts the operating conditions of the heating network based on real-time data. It 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 control instructions from the monitoring center.

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

4 Conclusion

The ADSL-based heating network monitoring system proposed in this article is a cheap, reliable, high-bandwidth heating network monitoring solution. This solution is also suitable for monitoring other urban pipe networks (such as water and gas) and has a wide range of applications. At present, the system still has some technical problems that need to be solved, such as the control algorithm and time delay issues of the network control system, which need to be continued to be studied in future work.