In the previous chapters you have created three variables in the "BoilerPlant/Boiler1/Data" object, namely "Temperature", "Power" and "Status". You write a number generated in the script of the timer "Emul" every second into the "Temperature" object. You change and influence the value of the power by moving the slider of the PmiSliderPane item that you've placed in the window named "Panel".
In real devices, the values of temperature, pressure, flow, speed, etc. are usually accessed via the PLCs. The PROMOTIC system is designed in order to comminicate with such devices - exchange the data.
There are several ways the computers communicate with the surrounding world. By the serial port, via network or by specific communication hardware cards, also by reding/writing the files or databases.

From the PROMOTIC point of view, we can divide the communications into following types:

- communication via the communication drivers of the PROMOTIC system
- these drivers allow to communicate with devices connected by serial link or by Ethernet.
- if there is a communication driver available for your device we recommend using it, otherwise use for example the OPC communication
- the main advantage of such communication is the absence of any mediator between the device and the PROMOTIC system which means the communication setup is much easier and the communication itself is more reliable
- communication by OPC
- communication between the PROMOTIC system and the OPC server is unified regardless if the communication between the OPC server and the device uses the serial link, Ethernet or special communication cards, etc.
- the main advantage of such communication is the fact that OPC servers are available almost for all PLCs on the market
- the disadvantage of such communication is the necessity of purchasing/installation of the corresponding OPC server
- communication via ActiveX
- some manufacturers prefer not to provide OPC servers for their devices, but to use communication items in the form of ActiveX. PROMOTIC can use this type of communication for example with Johnson Controls, Amit, etc.
- other communication methods - these options are mentioned here in order to give you the full overview, their description goes beyond the purpose of this coursebook
- Communication via DLL libraries
In the following chapters you wil learn:
- how to add and configure the PmComm and PmCommData objects, that allow communication via the selected communication protocol or via OPC communication.
- how to define the data extension that reads the values from communication
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