How to write a paper on LAN installation and maintenance?

In industrial control system, the application of fieldbus technology and Ethernet technology can realize the networking of the system and improve the performance and openness of the system, but these control networks are generally based on wired networks. The wired network is high-speed and stable, meeting the needs of industrial networking in most occasions. However, wired networks can only transmit data along one-dimensional lines, and transmission requires conductive media, which brings a series of work related to transmission channels, such as planning and wiring, preset interfaces, line detection, line expansion and so on. And these jobs inevitably have some disadvantages, such as destroying buildings, wasting interfaces, and being difficult to maintain and expand. In the modern control network, many automation devices require higher flexibility and maneuverability. When industrial equipment is in an environment where wiring cannot be done, or when industrial equipment is loaded on mobile machinery such as vehicles, it is difficult to use wired networks. Accordingly, wireless networks can transmit data to three-dimensional space without transmission media, and local area networks can be established as long as access point devices are installed in networking areas; As long as the wireless network card is installed, the mobile terminal can freely access the network within the receiving range. In a word, wireless network has unique advantages in flexibility, convenience and expansibility of network construction, so wireless LAN technology has been developed and applied. With the continuous development of microelectronics technology, wireless local area network technology will play an increasingly important role in industrial control network.

I. Introduction of WLAN

Generally speaking, any local area network using wireless transmission media can be called wireless local area network. The wireless media here can be radio waves, infrared rays or lasers. Wireless local area network technology can connect the network devices in wireless local area network very conveniently, and people can access network resources at any time, anywhere and at will, which is an important direction of the development of modern data communication system. Wireless local area network can provide network interconnection function without using network cable.

1. Introduction to Wireless Fidelity

The protocol standard of WLAN has been established for a long time, but WLAN has not been widely used because of its slow speed, inconsistent protocol standard and high price, and users are unwilling to use WLAN for protection investment. In recent years, with the introduction of high-speed wireless communication protocols, wireless local area networks have developed rapidly.

IEEE802. 1 1 is the first international standard for wireless LAN adopted by IEEE 802 standards committee in 1997. 1September, 1999, the Committee promulgated the IEEE802. 1 1b standard, which includes the physical layer and the media access control layer (MAC) of the ISO/OSI model. The standard works at 2.4 GHz, and the transmission rate can reach 1 1 Mbps. According to the IEEE802. 1 1b standard, node devices are divided into base stations and client stations, which can communicate directly or under the unified management of base stations. The connection between a base station and a group of client stations is called a basic service set (BSS), and two or more BSS form an extended service set. IEEE802. 1 1b standard stipulates three methods to realize the physical layer, namely, frequency hopping spread spectrum method FHSS, direct sequence spread spectrum method DSSS and infrared technology IR. At the MAC layer, CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) technology is used for communication medium access. In order to minimize conflicts. 802. 1 1b has designed a unique MAC sublayer, as shown in figure 1. The lower layer is called the distributed coordination function (DCF) sublayer, which enables each node to use the channel in a competitive way and provide contention services upwards. This channel access mode may lead to conflicts, but the channel utilization rate is high. The upper layer is called PCF (Point Coordination Function).

Figure 1 MAC sublayer1IEEE 802.11+0

In the sub-layer, centralized control access algorithm is adopted, and the base station gives the communication rights to each client station in turn by polling, thus avoiding conflicts. However, the base station needs to poll all the client stations periodically, which takes up a lot of time, so it is suitable for small and medium-sized networks. Wireless LAN technology is still developing. RADIA-TA and Atheros announced that they will launch IEEE802. 1 1a chipset respectively. 802. The data transmission rate of11a is 54 Mbps. Atheros claims that its chipset can reach 72 Mbps in Turbomode. For 802. 1 1a, it can not only improve the transmission rate, but also work at the frequency of 5 GHz, thus avoiding the crowded 2.4 GHz frequency band. 200 1115, IEEE initially approved a new technology, 802. 1 1g, which can improve the wireless internet access speed of homes, companies and public places, and make the transmission speed of wireless networks reach 54 Mbps per second.

Table 1 Technical Standards, Frequency Allocation and Transmission Rate

technology standard

Formulated year

Frequency occupation

Maximum rate

Modulation technology

802. 1 1

1997

2.4GHz

2Mbps

FHSS

802. 1 1b

1999

2.4GHz

1 1Mbps

DSSS

802. 1 1a

1999

5GHz

54Mbps

Orthogonal frequency division multiplexing (short for orthogonal frequency division multiplexing)

802. 1 1g

2000

2.4GHz

54Mbps

DSSS

Description:

1.802. 1 1, 802.1b, 802. 1 1g all work in 2.4GHz ISM (industry, science and medical). However, 802. 1 1a works in the 5GHz band and is temporarily closed, so an application is required.

2.802. 1 1a and 802. 1 1g both have the highest physical layer rate of 54Mbps and the highest transport layer rate of 25Mbps, but the stability needs to be further improved and the cost is high. 802. 1 1b has a maximum rate of 1 1Mbps, which will be the most promising wireless LAN standard in the future due to its early start, mature technology and low cost. The following focuses on the 802. 1 1b standard.

Ii. IEEE 802. 1 1b wireless network standard

1. Physical layer of WLAN

The difference between wireless LAN and traditional wired LAN is that wireless LAN generally uses radio as transmission medium instead of traditional cable. For IEEE 802. 1 1b WLAN, there are three optional physical layers: frequency hopping spread spectrum (FHSS), direct sequence spread spectrum (DSSS) and infrared (IR). The choice of physical layer depends on the requirements of practical application. Frequency hopping spread spectrum and direct sequence spread spectrum are two commonly used spread spectrum technologies in communication technology, which are used to improve the utilization rate of wireless channels and the security of data communication. At present, the physical layer media of most WLAN products based on IEEE 802. 1 1b work in the radio frequency band (ISM band) of 2.4000~2.4835GHz, and direct sequence spread spectrum technology is adopted to provide data transmission rate as high as 1 1Mbps.

2. MAC protocol of WLAN

In principle, there is no essential difference between the MAC protocol of wireless LAN and the MAC protocol of wired LAN. However, due to the inherent characteristics of wireless transmission media and the influence of mobility, the MAC protocol of WLAN cannot follow the original LAN protocol. For example, the MAC layer of IEEE 802.3 uses CSMA/CD to make different sites * * * share the same physical channel. An important prerequisite to realize CSMA/CD is that each site can easily realize the conflict detection function. In the case of wired LAN (such as Ethernet), collision detection can be easily realized according to the change of DC component on the tested cable. However, when wireless transmission media is used, it is difficult to achieve conflict detection for the following reasons.

1) collision detection requires each station to send (send its own signal) and receive (decide whether the transmission of other stations interferes with its own transmission) at the same time, which will increase the cost of the channel.

2) More importantly, because of the hidden terminal problem, even if a station has the ability to detect conflicts and has detected conflicts during transmission, there will still be conflicts at the receiving end.

In view of the above reasons, the wireless LAN protocol standard IEEE 802. 1 1b adopts the carrier sense multiple access (CSMA/CA) protocol with collision avoidance to realize wireless channel sharing.

A simple CSMA/CA can be implemented as follows: Before sending a data packet, a wireless device will listen to see if other wireless devices are sending. If the transmission is in progress, the device will wait for a randomly determined time and then listen. If no other device is using the medium, the device will start transmitting data. Because it is likely that one device is sending data while another device is sending data, in order to avoid data loss caused by this conflict, the receiving device will detect the CRC of the received packet, and if it is correct, it will send an acknowledgement to the sending device, indicating that there is no conflict. Otherwise, the transmitting device will repeat the above CSMA/CA process.

In order to minimize the possibility of collision caused by simultaneous transmission of two wireless devices, 802. 1 1 The designer used a mechanism called send request/clear send (RTS/CTS). For example, if data arrives at a wireless access point (AP) designated by a wireless node, the AP will send an RTS frame to the wireless node, requesting a certain amount of time to send data to it, and the wireless node will respond with a CTS frame, indicating that it will block any other communication until the AP sends the data. Other wireless nodes can also hear the ongoing data transmission and delay its transmission after this time. In this way, when transmitting data between nodes, the possibility of collision on the medium caused by equipment is the least. This transmission mechanism also solves the problem of hiding terminals in WLAN.

In order to ensure that data will not be lost in transmission, CSMA/CA also introduces an acknowledgement (ACK) mechanism. After receiving the data, the receiver sends a confirmation notification ACK to the sending unit. If the sender does not receive an ACK, it indicates that the data is lost and the data will be transmitted again.

3. Real-time performance analysis of WLAN.

IEEE 802. 1 1b wireless LAN standard adopts CSMA/CA protocol in the media access control layer to realize the enjoyment of wireless channels. In the case of light network load, the probability of conflict is very small, and some wireless network products take some additional measures, or even completely avoid conflicts. For example, AWE 120-24, a wireless product of Wi-LAN, adopts the way of dynamic time allocation polling: when multiple wireless remote devices communicate with the base station, the base station will ask each remote station in turn whether there is any data to send according to the ID of the remote station, and if there is any data to send, it will be allocated a time slice. If not, it will continue to ask, and so on. The so-called dynamic polling here means that users can set the polling mode of base stations to reduce the number of inquiries to inactive sites to ensure that time slices will not be wasted. Dynamic time allocation polling technology completely avoids conflicts and can obtain better real-time performance than CSMA/CA. This makes the application of wireless technology in industrial control network possible.

3. Introduction of networked intelligent sensor based on wireless technology.

The combination of computer network technology, wireless technology and intelligent sensor technology has produced a brand-new concept "networked intelligent sensor based on wireless technology". The intelligent sensor integrates data acquisition, data processing and wireless network interface module. The bottom network interface (hardware interface) of wireless network interface module adopts the network interface chip based on IEEE 802. 1 1b, and the high-level network interface (software interface) adopts TCP/IP protocol, which is an embedded application, that is, the TCP/IP protocol is solidified into the ROM of intelligent sensors to make the field data. This networked intelligent sensor based on wireless technology enables industrial field data to be directly transmitted, published and appreciated on the network through wireless links.

Wireless local area network can be realized by wireless hub, wireless access point (AP), wireless bridge, wireless modem and wireless network card on the basis of ordinary local area network.

In the field of industrial automation, there are thousands of sensors, detectors, computers, PLC, card readers and other devices, which need to be interconnected to form a control network. Usually, the communication interface provided by these devices is RS- 232 or RS-485. Wireless LAN equipment uses isolated signal converter to convert RS-232 serial signal of industrial equipment into signals of wireless LAN and Ethernet, which conforms to IEEE802. 1 1b of wireless LAN and IEEE 802.3 of Ethernet, supports standard TCP/IP network communication protocol, and effectively expands networking communication capability of industrial equipment.

Fourthly, the application of WLAN in industrial control network.

The networking of industrial control system provides the foundation and possibility for the application of wireless technology in industrial control system. In recent years, many researchers have also carried out research work in this field. Ceng Peng and others of Shenyang Institute of Automation, Chinese Academy of Sciences built a field-level wireless communication protocol stack based on FFHSE (High Speed Ethernet) promulgated by FF (Fieldbus Foundation) and the wireless Ethernet standard IEEE 802.11b. This protocol stack maintains the communication model of Foundation Fieldbus, and can complete the time synchronization and real-time communication between wireless devices. Kyung Chang Lee of Busan National University in South Korea and others designed a protocol conversion model to realize the interconnection between PROFIBUS-DP network and IEEE802. 1 1 WLAN. Mario Alves et al. estimated the message transmission delay time of hybrid network based on broadcast fieldbus/wireless network. C.Koulamas and others studied the performance of combining Profibus with DSSS physical layer based on IEEE 802.11b.

In addition to theoretical research, wireless communication technology has been applied in some industrial control networks. For example, in the three-layer control network system based on DeviceNet, Control-net and Ethernet/IP, Rockwell Company of America added wireless Ethernet to realize wireless communication. Siemens Germany combined wireless Ethernet technology into the control network based on PROFIBUS-DP and Profinet, which made the control network have wireless communication function. Due to the unparalleled advantages of wireless network, it can avoid a large number of line connections, save the construction cost and maintenance cost of the system, and meet the needs of some special occasions. At the same time, the flexibility of system composition is greatly enhanced. Coupled with the continuous improvement of wireless communication technology itself, wireless communication technology will have broad development space and application prospects in the field of industrial control.

Verb (abbreviation of verb) Application scheme and equipment of wireless technology in industrial control network

1. Wireless industrial control method

By using networked intelligent sensors based on wireless technology and combining various wireless LAN bridges based on IEEE 802. 1 1b, the application scheme of wireless LAN technology in industrial control network can be realized. A wireless LAN bridge is used as a wireless access point (AP). The networked intelligent sensor based on wireless technology collects and processes the field data, encapsulates the data with TCP/IP protocol, and sends it to AP through wireless link. Because the high-level wireless link and wired Ethernet adopt TCP/IP protocol, and the low-level protocol is transparent to the high-level protocol, the seamless connection between wireless network and wired network is realized. Through the Internet, remote monitoring can be realized.

2. Selection of wireless devices

To realize wireless network, there are generally two devices to choose from. One is wireless LAN bridge, which can connect multiple wireless stations to the existing LAN; The other is wireless communication equipment, such as wireless network card, wireless modem, etc. Next, we will introduce Advantech's wireless devices.

A.WLAN-9200 series 1 1Mbps industrial wireless LAN access equipment.

WLAN-9200 is an enhanced 1 1Mbps wireless LAN bridge for outdoor use. It can connect multiple remote workstations to the LAN without any physical wiring.

Features:

Support IEEE 802. 1lb standard 2.4GHz ISM band.

Support advanced user authentication, provide strong security WEP 128, MAC address control.

With a rust-proof shell conforming to IP 66/NEMA 4x standard, the system is protected from damage.

Provide cooling fans and heaters to prevent the system from overheating and supercooling.

The temperature can be easily set by providing buttons and LED display.

IP66 waterproof interface is adopted to protect power supply, local area network and wireless interface.

Provide various antennas to increase the transmission distance.

WLAN-9200 is an enhanced 1 1Mbps wireless LAN bridge for outdoor use. It can connect multiple remote workstations to the LAN without any physical wiring. This saves the cost of maintaining and establishing the corresponding wired network. WLAN-9200 has a solid shell, which can prevent water, acid, lightning, low temperature and high temperature from damaging the system. Because of these characteristics, WLAN-9200 is very stable and reliable, and it is an ideal choice for outdoor applications. Therefore, WLAN-9200 is very suitable for use in harsh places such as reservoirs and buildings where wiring is difficult. WLAN-9200 is compatible with IEEE 802. 1lb standard and has various powerful functions. At the same time, it provides high security protection (WEP: 128 bit), DHCP client, SNMP agent, etc. , which can provide high transmission speed of 1 1Mbps. In addition, in order to meet the requirements of harsh outdoor environment, WLAN-9200 also provides advanced system protection functions: luminous protection, cooling fan, heater, waterproof interface, industrial equipment box, power supply/LAN coaxial cable, etc.

Low cost and simple installation.

WLAN-9200 can connect different distributed sites together to form a larger wireless network. It can save wiring costs in remote locations. WLAN-9200 is specially designed, so users can install or disassemble it conveniently and quickly. In addition, WLAN-9200 also provides buttons and LED display screen for displaying and setting high/low temperature. Users can use it to quickly establish their own wireless networks. In order to be used in a longer range, WLAN-9200 also provides various antennas to extend the transmission distance.

Reliable, stable and robust design

WLAN-9200 adopts advanced design and has a rust-proof and waterproof shell, which can effectively protect the system. It conforms to IP 66/NEMA 4x standard and has the characteristics of corrosion resistance, ultraviolet protection, safety and automatic fire extinguishing. In order to prevent WLAN-9200 from overheating or supercooling, Advantech also designed a cooling fan and heater inside, and users can set high/low temperature settings. When the operating temperature is higher or lower than the temperature specified by the user, the cooling fan or heater will start to work. In addition, WLAN-9200 also provides waterproof interface and lightning protection, which can protect power supply, LAN and antenna interface.

Fast data transmission between remote sites

WLAN-9200 is fully compatible with IEEE 802. 1 lb, providing the speed of 1 1Mbps (in the air) and supporting faster data transmission. WLAN-9200 adopts DSSS technology in ISM band of 2.4 GHz, so it will not be disturbed by noise, and the data transmission is more secure and reliable.

Keep communication private.

WLAN-9200 adopts various security functions to protect your wireless network (WEP 128 encryption, MAC address control and password security). By adopting advanced WEP 128 encryption, you can choose WEP key to protect your data and prevent unauthorized wireless users from viewing it. Only the access point and the wireless adapter are accessible, and various security mechanisms work together to effectively prevent unauthorized access to wired and wireless networks.

B.ADAM-4550 series 2.4GHz wireless modem (RS-232/485 interface)

ADAM-4550 is a direct sequence spread spectrum wireless modem. It works in the ISM band of 2.4GHz and can be used all over the world without application. Through the RS-232 or RS-485 serial port, ADAM- 4550 can communicate with computers or other devices at a speed as high as 1 15.2Kbps.

ADAM-4550 works in half-duplex mode and transmits wireless data at the rate of 1Mbps. The output power is 100mW, and the transmission distance can reach150m if the self-contained small antenna is used, and it can exceed 20km (line of sight) if the high-gain outdoor antenna of Advantech is used.

RS-485 standard supports half-duplex communication. This means that you can use a twisted pair to send and receive data. The direction of data flow is usually controlled by handshake signal RTS (Request to Send). But ADAM-4550 has a special I/O circuit, which can be used to detect the direction of data flow and automatically switch the transmission direction without handshake signal.

ADAM-4550 wireless modem provides reliable "point-to-point" or "point-to-multipoint" network wireless connection. The typical application is to connect an ADAM-4550 module with the host computer through RS-232, and place other ADAM-4550 modules in a remote site. Each ADAM-4550 module can be connected with remote equipment through RS- 4550 network. The remote ADAM- 4550 module transmits remote data to the main ADAM-4550 module, and the main ADAM-4550 module sends control commands to the remote ADAM-4550 module through wireless transmission.

standard

Rs-232/RS-485 transmission rate (bps): 1200, 2400, 4800, 9600, 19.2K, 38.4K, 57.6K,1/5.2k.

RS-232 interface connector: hole DB-9

RS-485 interface connector: Plug-in screw terminals support AWG 1-# 12 or 2-# 14-#22 (wire diameter 0.5 to 2.5mm2) cables.

Wireless transmission rate: 1Mbps

Wireless transmission frequency: 2.45GHz (nominal value)

Wireless transmission power: 100mW (nominal value)

Wireless modulation: direct sequence spread spectrum PSK

Wireless transceiver address: The software can configure 254 different addresses.

Communication distance: 550 feet effective distance (in the case of using 2dBi omni-directional antenna in open space), the actual distance depends on environmental conditions, antenna type and location.

Working temperature:-10? 0? 2 to 70℃( 14? 0? 2 to 158 F)

Power requirements:+10 ~+30v DC.

Power consumption: 4W

Size: 60mm×120mm (2.36 inches× 4.41inch)

trait

RS-232 or RS-485 can be configured by software, and the data transmission rate can reach 1 15.2kbps.

With external antenna and amplifier, the transmission radius can exceed 20km.

Built-in watchdog timer and automatic RS-485 data flow control

Spread spectrum wireless modulation

Working in the global frequency band (2.4GHz), no application is needed.

Inter-module 1Mbps wireless data transmission rate

Software configurable wireless transceiver address

Convenient installation of DIN rails, panels or stacks

EEPROM for storing communication settings.

Support point-to-point or point-to-multipoint applications

Transparent IEEE802. 1 protocol and 10K cache to ensure data integrity.

Power and data flow indicators for fault diagnosis

Diagnostic software with wireless connection test

Comply with FCC Part 15 and ETSI 3000.683/300.328 standards.

Conclusion of intransitive verbs

It is easy to control industrial equipment through WLAN, but the cost is slightly higher. At present, most wireless control protocols adopt IEEE802. 1 1 series, which can be seamlessly connected with Ethernet adopted by most of our local area networks. Therefore, it has no influence on the user layer measurement and control program, and only needs to simply configure the physical layer equipment in the original scheme. For example, the wireless products of Advantech mentioned above are selected to replace the original wired communication equipment, and other hardware and software configurations are not affected.