Application and discussion of the hottest flow mea

Application and discussion of flow measurement network management system

I. system requirements and technical background

China is a country with relatively scarce water resources, especially in the northwest and northeast regions: the contradiction between existing water resources and daily production and domestic water is more prominent. In this context, the rational development and effective use of water resources, especially tap water, has become a very important topic. In this subject, we should first master the raw data of the production and use of tap water. However, due to the limitations of the instruments currently used and the constraints of the existing management methods, it is impossible to accurately obtain the actual water use situation of these users, which brings difficulties to further strengthen the operation management of the flow instruments in use and improve the external service quality and modern management level of the water company

in order to solve this problem, the solution of instrument cluster has been adopted by foreign counterparts and other domestic industries. The main purpose of the water company's group monitoring of the instruments in use is to monitor the water consumption of many tap water users scattered in the business area in real time (including the water consumption and pipe pressure of the user), and send the data back to the management center - to obtain statistical data, so as to master the water consumption of their incoming water users, and then combine the "geographical distribution" of the pipes of these measurement points, Calculate the requirements of each business area for water supply and the corresponding pipe load in different periods of time, so as to provide raw data for more effective use of the existing tap water production capacity and planning pipe reconstruction

in technology, with the rapid development of the sensor industry and the computer measurement and control field, now the use of advanced sensors as the front-end, computer technology as the core of high-performance price ratio remote metering instruments has been mature, as long as the appropriate type selection, the function of the network terminal can be completed; However, it is still a problem worth discussing how to construct the basic trunk network

II. Selection of communication group mode

in this system, the basic trunk network mainly provides the data transmission channel between the on-site monitoring point and the central control room. In the selection of network scheme, the reliability of the system, the realizability of the project and the economy of system operation should be mainly considered

we know that there are usually two ways of data communication group, namely, wireless mode and wired mode. Among them:

the one-time construction cost (including infrastructure and equipment costs) of the wireless system is relatively large; Moreover, with the increase of system coverage, the complexity and construction cost of the system will increase in the square order, and the reliability will decrease at the same time. On the other hand, the wireless system has high call rate, fast call response speed, good real-time performance, and the operating cost is not affected by the amount of communication data. Therefore, the wireless system is suitable for applications with small geographical range and high communication density, such as the real-time monitoring of instruments in the general scale factory

wired mode is divided into special line mode and public line mode. Among them, the special line mode requires that a dedicated communication line be laid between each endpoint of the communication. When the communication line is long, its construction cost will increase and its reliability will decrease. Its characteristics are similar to the wireless mode, and it is generally used in small-scale occasions. The public line mode is to use the existing communication lines, such as ordinary dial-up line, narrowband ISDN, ads. this product is based on the impact structure in line with national standards. Its characteristic is that it does not need to lay communication lines, only needs to pay a certain rent and royalties, and professional communication business operation companies (Chinatelecom, etc.) provide communication physical lines and daily maintenance services. In a certain scale, the operation cost of this mode has nothing to do with distance, but only with the time and frequency of communication; It is generally suitable for occasions with wide communication coverage and low communication frequency. Due to the use of public communication lines, the call rate of communication is slightly poor and the real-time performance is poor

in this application, the monitoring points are mostly located at the pipe node and the user entrance end; This leads to the wide geographical distribution and uneven density of the monitoring points in the network. At the same time, the site conditions are relatively complex and different. If wireless mode is adopted for such a scale network, it is uneconomical from the perspective of construction cost. In addition, since the monitoring points are distributed in urban areas with many high-rise buildings, if the wireless group method is adopted, it needs to consider avoiding the shelter of high-rise buildings between antennas; Moreover, with the development of urban construction, when new high-rise buildings appear on the transmission path to highlight the main role of enterprises and give play to the decisive role of the market in resource allocation, the erection of antennas needs to be readjusted. Therefore, the wired transmission mode is more appropriate for this application

for water supply business companies, the data they care about are the flow and pressure of users and pipes. These data do not need to be monitored in real time, but only:

1. When the water supply is normal and the instruments are normal, the data they care about can be collected in time

2. When the water supply is abnormal (such as pipe failure or abnormal water use by users, etc.) or the instrument is abnormal, the abnormal situation can be understood in time

therefore, the network involved in this application is a remote reading of the flow meter in the metropolitan area, and the clamping force on the film 4 blows is uniform. It is not easy to produce the sliding of the sample during the impact, which will affect the accuracy of the experimental results and the fault monitoring network. Because the amount of communication data required by the network is not large, and the communication density is not high, there is no need to set up a special communication line, and there is no need to choose a broadband network suitable for large amount of data

to sum up, it is appropriate for this application to choose a wired network communication scheme based on ordinary dial-up lines

III. selection of communication access equipment

after determining the basic network scheme, one problem that needs to be considered is the access of instruments. Modem (modem) is a necessary device for network communication based on ordinary dial-up line. However, since the standard modem only provides RS-232C connection with the computer interface, it requires that the connected instruments have this type of interface. This is no problem for new instruments, but most of the instruments in use do not have this interface, so data acquisition and conversion modules need to be installed. This problem can be solved by using special equipment (such as the special data acquisition communication machine of some professional manufacturers), or by using general industrial field equipment (such as PLC) plus modem

in the case of large network scale, the connection time of a single point will become the bottleneck of network system performance. In most people's concept, as long as the modem speed is fast enough, it will shorten the communication time of a single point. This concept is right, but it has its scope of application - in the communication of large amount of data, the transmission speed plays a decisive role; In low data communication, the bottleneck is the connection time of the modem

Figure 1 lists