MODBUS Master/Slave interface...need DSC & OPC?

[jonathanupr]

I've been reading up on the DSC & OPC modules looking at reasons on why I would or wouldn't need these modules for my particular application.

I have a custom designed PLC that I need to communicate with.  We are looking at pros/cons in regards to using MODBUS ethernet communication for sending control commands & receiving around a 100 channel count DAQ input (1-2 times per second).   LabVIEW on the Windows system is the Master device, and the PLC sits as the Slave device.  Will we need the DSC or OPC modules?  We are looking at creating our custom MODBUS code.  Question here is, what do the DSC & OPC modules really do?  More of a plug and play option so customers don't have to develop custom code?  Is developing custom code that extensive?  It seems that I could just get by with the MODBUS drivers provided thru LV...though would like to hear feedback on this.

Also, is MODBUS ethernet fairly easy to configure on deployed applications (desktop/laptop) ?  Presently we are using a CAN I/O for connection & this works fairly well and is easy to  install & deploy...but is a bit expensive.

Thanks

[charris · Accepted solution]

Hello

The main advantage of the DSC module is that it allows you to use shared variables as tags to communicate on multiple industrial protocols (like MODBUS or OPC), which eliminates a lot of hassle involved with the communication side of things. Additionally, it allows you to log any and all of your variables to a relational database, along with alarms and events with a minumum of difficulty. I won't get into the full feature list here, but if you're interested, you can read more on the DSC Module info page.

For your application, it sounds like your PLC will do MODBUS Ethernet communication, so NI OPC Servers shouldn't be neccessary unless you really want to publish the PLC data over OPC for some reason (without doing any programming). Additionally, if you want to use NI OPC Servers, you'll likely want to make sure it will work with your PLC. There is a hardware compatibility page that lists compatible devices.

The primary benefit of using DSC over the MODBUS library is ease of use and deployment. Since all of your MODBUS I/O is on your shared variables, your application data sources are all handled from the LabVIEW project, and can be edited centrally.

If you're looking for a cheaper alternative, the MODBUS Library is definitely worth looking into. My recommendation is to try out the DSC Module and the MODBUS Library and see which works better for you.

Good luck!

[jonathanupr]

Thanks for the info, it was helpful.