Modbus vs OPC

OPC

• OPC stands for OLE for Process Control. OPC is communicating software-to-software for operator display.

• OPC is mostly a standard interface software between a driver, mostly for networks and device hardware, and also a databases, and the application display for example software of HMI/process visualization.

• You use OPC between a hardware driver software (OPC server) and a process visualization software (OPC client) on a Windows computer, or another client such advanced control, statistics etc. If the server and client applications are in different computers they communicate across Ethernet.

• OPC is principle within the environment of Windows to get data from the server I/O to other applications for example process control, soft alarms, graphics, trend, advanced control, auto tuning, statistical etc. anyway if the applications are implementing on the different or same computers.

• OPC is not the finest option for interlock communication and closed loops between controllers. Because it is not completely deterministic or real-time.

• For OPC you can browse the data, see what is available, without having to worry where it is located and in what data type. This makes it a whole lot easier to use. OPC runs on Windows operating system so OPC depends on the reliability of computers.

MODBUS

• Modbus is communicating hardware-to-hardware for control.

• Modbus/TCP is idyllic for interlock communication and closed loops between controllers.

• It is all software driven and does not need any cards of scanner, Just RS-485 or RS-232.

• You can use either Modbus, Profibus, or any other fieldbus for closed loop control.

• Modbus/TCP is not the most excellent option for communications between computers or between applications software. It is because the Modbus/TCP simplicity comes from a lack of logical object structure and a standard data types.

• Modbus breaks data down to the lowest feasible denominator. That’s why it can move to anywhere, but once it takes there it gets many user configuration attempt to plan registers Modbus back into names of parameter and group them rationally in objects and separating what all the types of data are thought to be after all has been changed to words of Modbus. For some parameters it is feasible, but with the great amount of information accessible in up to date systems it does not fly.

• For Modbus you find data in registers. Every device use different registers, and if the device is programmable the registers will also be different for each application. Some devices use integers while other use floating point. Some devices use percentage while others use engineering unit. You need to refer to device documentation to find which information is in which register and what format is used. This is quite tedious. Making changes often create a lot of work.