Comparing Options for RS-485 Communications with NI LabVIEW

The Process Controller Communication Libraries for LabVIEW provide a simple, drag and drop, instrument driver-style interface to DIN-sized, panel-mounted, process or temperature controllers, which have the capability to communicate via RS-485 serial bus. This style of interface is familiar to many LabVIEW™ programmers, who already use it for communicating to data acquisition hardware, stand-alone instruments and other devices.

There are other options for interfacing to these controllers, however. Here is a comparison:

  • Free software provided by the manufacturer: Many of the devices supported by the Process Controller Communication Libraries for LabVIEW can be obtained with a freely downloadable software package for setting up and communicating with the controller. While this software provides many useful functions, the obvious difference is that it does not include the ability to interface with LabVIEW.
  • MODBUS Library for LabVIEW: Freely downloadable from National Instruments this provides some VIs that can be used to implement communications to RS-485 devices using raw register access via Modbus. This is an example program and not an official NI Product.

    The MODBUS Library for LabVIEW is a generalized solution. It is not used by our libraries and was not used as a basis for our development. While it does provide (Modbus only) RS-485 communications to a wide array of Modbus devices, which can include the controllers supported by the Process Controller Communication Libraries for LabVIEW, it lacks the time-saving, customized, device and command-specific pallettes of VIs and friendly typedefs and controls offered by Process Controller Communication Libraries for LabVIEW.

  • OPC Server Communications: In many automation environments, RS-485 communications is implemented using an OPC Server, such as the National Instruments’ OPC Server. This communications method also allows for integration with other automation devices, such as PLCs. For interfacing with LabVIEW, this option requires the LabVIEW Datalogging and Supervisory Control (DSC) Module in order to create and I/O server and implement communication using tags.

    The main considerations between the OPC Server option and the instrumentation driver-style communications offered by the Process Controller Communication Libraries for LabVIEW are cost, scope of the application and familiarity with OPC. The Process Controller Communication Libraries for LabVIEW are not intended to be a replacement for an OPC Server.

    In larger automation applications, especially if OPC communications are already implemented or desired, you may wish to consider OPC. As a National Instruments Alliance partner, Integrated Pro can help with the implementation of the NI OPC Server and LabVIEW Datalogging and Supervisory Control (DSC) Module.

In conclusion, if integrating a controller into a large scale operations, especially if OPC is already in use, you may wish to consider using OPC. However, for dedicated RS-485 applications with an instrument driver-style approach to programming, integrating a supported process controller into a test application or controlling a small process, for example, you may be more comfortable with Process Controller Communication Libraries for LabVIEW.

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