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AgendaIntroduction
Standard Protocols
What is Modbus?
Modbus in Detail
Comparison Modbus and OPC
Implementation of Modbus for Siemens PLC
Security in Modbus
Conclusion
IntroductionSlow controller (PLC) and Fast Controller(PXIe) system are the two key controllers of Local control unit for the Gyrotron system.
All auxiliary systems and power supplies are to be controlled by PLCs. Sequence control and soft interlock functions are to be implemented in PLCs.
High voltage and Magnet power supplies, Fast Local Protection and Data Archiving are performed by Fast Controller.
Hence, Many process variables will be exchanged between slow and fast controller for the operation of Gyrotron. So Standard communication protocols will be used for the same.
In this presentation, various protocols available are mentioned and Compared. Finally Modbus communication is discussed mainly.
Available Protocols OLE for Process Control (OPC)
Modbus Communication
Direct Access
Standard
Non‐Standard
Industrial Communication (Modbus)
Direct Access
OPC
What is Modbus?It is simple, reliable and efficient Communication protocol across a variety of controllers.
Application layer messaging protocol for client/server communication between devices connected on different types of buses or networks
Server/Client protocol and offers services specified by function codes.
(Client) (Server)
MODBUSMODBUS
RS485RS485
RS232RS232
TCP/IPTCP/IP
MODBUS TCP•MODBUS TCP is Client/Server serial communication that uses TCP/IP as a transmission medium
•The client establishes a connection and sends request frames to the server. The server processes this request and sends the appropriate answer to the request back to the client.
•The MODBUS protocol defines a simple Protocol Data Unit (PDU) independent of the underlying communication layers. The mapping of MODBUS protocol on specific buses or network can introduce some additional fields on the Application Data Unit (ADU).
Modbus TCP Implementation in STEP‐7For Siemens PLC, Modbus can be implemented in ◦ Integrated CPU PN Port◦ Extra Communication Processor PN Port(CP‐343‐1 Lean)
Siemens provides additional function blocks for Modbus TCP via PN CPU. These blocks are to be purchased and licensed for one particular CPU only. ◦ FB102, FB103,FB104,FB105, DB2
These blocks are then to be configured as per the user application. ◦ Server or Client, ◦ Local IP and Port settings◦ Memory area allotment in CPU◦ Data Types of Variables to be exchanged
Siemens PLC, as an Modbus server, defines a stack of memory area where all incoming and outgoing data will be stored.
Test of Communication : PLC ServeroData which is to betransferred is stored inDBs.
Similar, Data fromOther controller isstored here in thesame DBs at particularaddress
PLC is set as ModBUSserver at IP address192.168.23.239 andPort No. 502
Variable to be Communicated
MODBUS Connection Settings
Test of Communication : PC ClientoThis is computerbased Modbusclient. But it couldbe any othercontroller capableof Modbuscommunication.
ComparisonParameters OPC Server Modbus TCP
Open standard Open Protocol
Extra Software 1. Vendor dependent servers are available
1. No special software needed
Use of PC 2. Use of PC is needed to install it. PLC talks to OPC server PC and then PC talks to FC
1. No PC is Required. PLC directly talks to FC
Security 3. Less as OPC server can access any memory area of PLC e.g. input, output, internal registers w/o any information to PLC CPU.
1. Only those data which PLC intentionally wants to transfer are accessed by remote controllers. PLC knows what it is sharing with other controller
Continued…Parameters OPC Server Modbus TCP
Operating Systems Windows based standard ‐
Amount of work Quite less More, so suitable for one time installation
Flexibility and upgradability Quite Simple Much effort needed.
Application dependency? Independent of process Application
Dependent of process application.
Debugging? What data available, in which form, at what place available
More effort needed.
Cost High, depends on no. of tags, Quite less, no variable limitation
SummaryMODBUS is open protocol which can be used across variety of networks and between variety ofcontrollers and/or PC
Even though it is inferior to OPC standard communication, but for small amount of processvariables exchange directly between two controllers, this protocols can be adopted whicheliminates need of OPC computer application.
Time and speed response of Modbus is comparable to that of OPC communication (~100ms)
Additional Modbus Blocks from Siemens need to be purchased and can be used for oneparticular CPU only.