OPC UA/DA Overview

理解OPC UA/DA過程中的簡易筆記。

OPC

Without OPC:

With OPC:

使用OPC，軟體(SCADA、人機介面)開發商就不需特地為了各種不同的PLC通訊界面製作各種驅動軟體，擷取任何的資料，只需要建立OPC Client，並向OPC Server發送資料請求並擷取資料即可。而現今大多數中高端的PLC已經內建OPC Server。

Client and Server Fundamental Interactions:

• A Client initiates communications(sending request) with a Server.
• A Server's behaviour depends on Clients.
• A server waits for incoming requests from Clients.
• Interacting like a simple web service.

OPC Server config:

• Channel: protocol being used
• Device: device type like part number of PLC and its hierarchy path.
• Tag: data of interest.
  • Tag name: fan speed RPM, boiler temperature, tank level, …etc
  • PLC memory address (not sure is this is correct)
  • tag properties: mostly data type(boolean, integer, float…)

OPC DA(1995~2009)

• Only works on same Windows Domain or Workgroup.
• Only works with Windows OS via COM/DCOM.
• Opening DCOM also open a big hole on firewall, impossible route over Internet.
• Security was not a concern dates back to when this protocol designed.

OPC UA(2009~now)

• based solely on IP-based standards. (ex: opc.tcp://ServerIP)
• Crossing platforms.
• Established crossing LAN, WAN and Internet.
• Passing data through router and firewall.
• Security
  • Key exchange from Client to Server and from Server to Client.
  • Surpporting HTTPS/SSL/TCP.
  • RSA data encryption.
• Not sure if it's fully open or not.

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Reference:

OPC Server & Client Data Communications – Introduction and Overview (Kepware, KEPServerEX)

【物聯網線 08】簡化工業裝置的聯網利器：Azure IoT + OPC UA

OPC Proxy by Microsoft

OPC Publisher by Microsoft

OPC Foundation Official Website

Open OPC UA

FreeOpcUa