Abstract: This article focuses on the composition and types of industrial Ethernet, and takes the network communication of Siemens SIMATIC S7 series PLC as an example to introduce the application of industrial Ethernet in basic network communication and programming debugging in PLC.
Keywords: Industrial Ethernet; PLC; Network communication; E-mail
Chinese Library Classification Number: TM921 Document Identification Code: A
XUWeiFeng
(Zhejiang QiLongcranesco.,Ltd, Shaoxing, Zhejiang Province, China)
Abstract:This article introduces with emphasisindustrycontentsandsoonEthernet'scompositionandtype,andwestoffamilyhouseholdSIMATICS7theseriesPLCnetworkserviceisanexample,introducestheindustryEthernet'sinPLCbasicnetworkcorrespondenceandtheprogrammingdebuggingapplication.
Keywords:IndustryEthernet;PLC;Networkservice;E-mail
I. Introduction
With the development of information technology, information exchange technology has permeated all industries. In the field of automation, more and more enterprises need to establish comprehensive automated network management platforms encompassing all levels, from factory field equipment to control and management layers, and to build enterprise information systems based on industrial control network technology. Industrial Ethernet provides an Ethernet standard for data transmission in manufacturing control networks. Based on industrial standards and utilizing a switched Ethernet architecture, this technology offers high network security, operability, and effectiveness, maximizing the satisfaction of the needs of users and manufacturers. Industrial Ethernet, with its unique advantages of low cost, high efficiency, high scalability, and high intelligence, is attracting an increasing number of manufacturing companies.
In the field of industrial Ethernet, Siemens' SIMATICNET industrial Ethernet is based on field-proven technology, conforms to the IEEE 802.3 standard, and offers 10 Mbit/s and 100 Mbit/s Fast Ethernet technologies. It can be used in harsh industrial environments, including areas with high levels of electromagnetic interference. SIMATICNET includes the following: the medium constituting the communication network, medium accessories and transmission components, and corresponding transmission technologies; data transmission protocols and services; and communication modules for connecting to PLCs (Programmable Logic Controllers) or PCs (Personal Computers).
II. SIMATICNET Industrial Ethernet
2.1 Basic Types
2.1.1 10Mbit/s Industrial Ethernet application baseband transmission technology, based on IEEE 802.3, utilizes the CSMA/CD media access method for cell-level and control-level transmission networks. The transmission rate is 10Mbit/s, and the transmission medium is coaxial cable, shielded twisted pair, or optical fiber.
2.1.2 100Mbit/s Fast Ethernet is based on Ethernet technology, with a transmission rate of 100Mbit/s and the transmission medium is shielded twisted pair or optical fiber.
2.2 Network Hardware
2.2.1 Transmission Media The physical transmission media of a network is primarily selected based on network connection distance, data security, and transmission rate. Commonly used transmission media in Siemens networks include: 2-core unshielded untwisted pair cable (e.g., AS-interfacebus); 2-core unshielded twisted pair cable; 2-core shielded twisted pair cable (e.g., PROFIBUS); coaxial cable (e.g., Industrial Ethernet); optical fiber (e.g., PROFIBUS/Industrial Ethernet); and wireless communication (e.g., infrared and radio communication). In PLC industrial Ethernet, commonly used physical transmission media are shielded twisted pair cable (TP-Twisted pair), industrial shielded twisted pair cable (ITP-Industrial Twisted pair), and optical fiber.
2.2.2 Network Components
a. Industrial Ethernet link modules OLM, ELM, and OMC
The OLM (Optical Link Module) has three ITP interfaces and two BFOC interfaces. The ITP interfaces can connect three terminal devices or network segments, while the BFOC interfaces can connect two optical path devices (such as an OLM), with a speed of 10 Mbit/s. The OMC (Optical Media Converter) module is used to extend network distance by converting fiber optic cables to electrical cables, and can also serve as a backup connection to redundant ring networks. The ELM (Electrical Link Module) has three ITP interfaces and one AUI interface. Through the AUI interface, network devices can be connected to the LAN at a speed of 10 Mbit/s.
b. Industrial Ethernet switches OSM, ESM, and ELS
The basic functions of OSM/ESM (Optical/Electrical Switch Module) include: improving network performance; simplifying network configuration and expansion; limiting the impact of erroneous frames; address learning; address deletion; setting transmission baud rate and adaptive switching; and VLAN priority labeling of data packets. Furthermore, OSM/ESM industrial Ethernet switches can connect more sites, extending Ethernet coverage to a wider range. For example, OSMITP62-LD, where "ITP" indicates that the OSM has ITP cable interfaces, "6" represents the number of electrical interfaces, "2" represents the number of fiber optic interfaces, and "LD" indicates long distance. ELS (Electrical Lean Switch) is also a type of switch device, but it only has TP interfaces and its functionality is simpler than that of OSM/ESM.
III. PLC Network Communication
Network communication requires adherence to specific protocols. Services that can run on Industrial Ethernet include: standard communication, S5-compatible communication, S7 communication, and PG/OP communication. These services are network-independent and can operate on different networks. Each service incorporates different network protocols to adapt to different networks. Standard communication is a protocol running at the application layer of the OSI reference model, including the MMS-MAP3.0 protocol for Industrial Ethernet subnets and the FMS protocol for PROFIBUS subnets. MAP (Manufacturing Automation Protocol) provides MMS services, primarily used for transmitting structured data. MMS is an industrial Ethernet communication standard conforming to ISO/IEC 9506-4. The MAP3.0 version provides an open and unified communication standard, allowing connection to products from various manufacturers, but it is now rarely used. S7 communication is integrated into every SIMATIC S7/M7 and C7 system. It belongs to the application layer of the OSI reference model and is network-independent, applicable to various networks (MPI, PROFIBUS, Industrial Ethernet). S7 communication ensures the correctness of network messages by continuously and repeatedly receiving data. In SIMATIC S7, S7 communication is achieved by establishing an S7 connection through configuration. On a PC, S7 communication requires the use of SAPI-S7 interface functions or OPC (Object Linking and Embedding for Process Control). In STEP 7, S7 communication requires calling function blocks SFB or FB, and the maximum communication data size can reach 64KB. In S5-compatible communication, when the subnet is IndustrialEthernet, the protocols used include ISOtransport, ISO-on-TCP, UDP, and TCP/IP; while when the subnet is PROFIBUS, the FDL protocol is used.
The following section uses Siemens SIMATIC S7 series PLC network communication as an example to introduce the basic network communication and programming debugging of industrial Ethernet in PLC.
3.1 Basic Network Communication of PLC
The SIMATIC S7 series can provide industrial Ethernet communication through CP modules with IT functions, enabling email sending, device monitoring and data processing via the web, and FTP (File Transfer Protocol) functionality. Since implementing email communication is similar to implementing FTP and web functions, the following section focuses on implementing email communication.
3.1.1 Network connection for E-mail communication
First, let's briefly introduce the main protocols used in the email system: SMTP, or Simple Mail Transfer Protocol, is a standard host-to-host email sending protocol over Ethernet, using the dedicated port 25 by default. POP3 (PostOfficeProtocolV3) is an email receiving protocol used to delete emails after authorized users have downloaded them from the email server. However, these emails can usually be further preserved through certain operations, so POP can also be considered a store-and-forward service.
IT-CP can be used as an email client, supporting SMTP (Simple Mail Transfer Protocol). It can send emails but cannot receive them. Through the email function, the PLC can send operational information based on specific triggered events or at specific times, and its network connection is maintained.
3.1.2 Hardware and software requirements for E-mail communication
Hardware: CP343-1IT or CP443-1IT, PC (with Ethernet card).
Software: STEP7 V5.3, E-mailserver software, E-mailclient software.
3.1.3 Configuring E-mailserver and E-mailclient
Since IT-CP can only act as an email client and supports the SMTP protocol, an email server is needed to receive and forward emails from IT-CP. In this example, software is used to turn the PC into an email server. The cMailServer software is installed on the PC, and system settings and account creation are performed.
a. System Settings: Configure the system as a local area network (LAN) email server to receive emails sent from the control station within the enterprise intranet; configure the email domain name.
b. Create an account: The username and password are the email client account information.
Similarly, when configuring the E-mailclient, you can create an email communication account through the client software installed in the E-mailclient (such as Outlook) for receiving emails. The mailbox server specifies the server computer's IP address; for example, if the local machine is used as the server, the IP address would be set to 192.168.0.1.
3.1.4 PLC System Configuration for E-mail Communication
a. Create a new project: In the STEP7 software, right-click and select "New Project" from the pop-up menu. Name the project and select the PLC's CPU module in the next step. In this example, the CPU315-2DP module of the S7-300 series is selected. At the same time, in the hardware configuration "HWConfig", insert the "CP343-1IT" module (CP343-1Advanced-IT module in this example).
b. Configure CP343-1IT. In the properties of CP343-1IT, create a new Ethernet network “Ethernet(1)” and assign an IP address. In this example, the IP address is 192.168.0.9 (subnet mask is 255.255.255.0).
Open "NetPro" and configure network parameters. Select CPU and create a new connection in the connection list. Select "Email Connection" as the connection type. In the properties of the "Email Connection" tab, set the block parameters ID=1 and LADDR=W#16#0100. These two parameters will be used in later programming. In the "Address" tab, set the local PLC (SMTPClient) IP address to 192.168.0.9, the E-mailServer (SMTPServer) IP to 192.168.0.1, and the port number to 25. In this example, the sender's mailbox name is set to...
[email protected], as shown in Figure 1.
Figure 1
3.1.5 Email Communication Programming
First, create data block DB50.
In setting the initial value:
The 'TO:' string format represents the email receiving address; here, it's set to the PC's email address.
The 'CC:' string format represents the address to which an email is copied.
The 'FROM:' string format represents the email receiving address, which is set here to the email address of IT_CP: [email protected].
The 'SUB:' string format represents the filename (i.e., the email subject), such as "StatusStation7".
The 'TXT:' string format represents the email content, such as "FaultinplantSector2".
'BNY:' is a string format indicating a file attachment.
Call the FC5AG_SEND function block in the STEP software's instruction library to send an email.
Program code:
CALL "AG_SEND"(FC5AG_SEND) // Call the FC5AG_SEND function block
ACT:=M10.0
// Trigger signal, sent on rising edge
ID:=1
//Link number, please refer to the link frame
LADDR:=W#16#100
//CP address
SEND:=P#DB50.DBX0.0BYTE224 //Send area DB
LEN:=224 // Transmitting area length
DONE:=M10.1 //Executable code
ERROR:=M20.1 // Fault code
STATUS:=MW12 // Status code
After the program is written, the entire project is downloaded to the PLC, and an email is sent by triggering M10.1. When M10.1 is "1", the task is triggered, and the data in DB50 is sent out. On the PC side, the Outlook client can access the E-mailServer and receive the email, as shown in Figure 2.
Figure 2
4. Conclusion
Through the above content, we have gained a deeper understanding of the application of industrial Ethernet in PLCs, which enables data exchange between PLCs and PCs, as well as between PLCs and other PLCs. At the same time, PLCs can also establish connections and transmit signals to existing actuators/sensors, with short data transmission times. Under certain circumstances, PLCs can use the CP343-1IT module to send relevant information such as emails to managers to ensure that the factory's operation can be monitored in a timely manner.
