Suppose that there are several air conditioners to be monitored in the industrial site. First, we need to monitor its temperature, humidity and operating status; second, we need to start and stop it; then we need to accept its non-stop accident alarm information; finally, we often need to analyze the operating parameters of a certain period to judge the state of the air conditioner. Using the idea of object-oriented programming, we create a class air conditioner. In this class, we define the corresponding attributes, methods and events. The attributes can be simple data or complex structure. This class can be understood as the information model of opcua. Opcua manages these real-time data (DA), historical data (HDA) and accident alarm data (A & E) on the same platform, which is called unified architecture.
What’s the effect of using this mode to communicate? Now let’s do a simple demonstration. Several air conditioners have been defined in demoserver produced by unified automation company. We monitor them through uaexpert, a client produced by the company. On the left side of the menu bar, the properties, methods and events of the air conditioner are listed; on the right side, only the temperature, humidity and operation status of the air conditioner are monitored. At this time, the air conditioner is in the off state. If you need to start the air conditioner and set the operating target temperature to a comfortable 25 ℃, just call the startwithcheckpoint method and enter the target value in the dialog box.
When monitoring event and alarm information, create an event and try to subscribe to the event of the air conditioner. An event will be triggered when the air conditioner is in the start stop state, and an alarm will be triggered when the air conditioner is in the stop state. At the same time, the alarm can be confirmed on the client.
Finally, on the server side, if you turn on the historical storage function of an attribute of the air conditioner, after a period of storage, you can read the historical data on the client side.
This is the charm of information model and unified architecture, which makes a communication software feel like HMI.
Of course, the information model of opcua is not unique in the industrial control field. The thing model in thingworx, PTC’s Internet of things platform, and Rockwell’s CIP protocol are all similar object-oriented models. So good design is similar, bad design has its own shortcomings.
Editor in charge: LQ