How to use DSC to perform PLC triggered, high speed DAQ tasks

[Kenneth]

I have an application that needs to perform high speed acquisitions using a DSA for a few channels. The trigger for each acquistion is a status register from a PLC. The acqusition lasts for a few hundred milliseconds at max speed, then hands the data to an analysis VI.

I am considering implementing the entire application in LabVIEW as this problem only benefits from DSC's monitoring capabilities of a PLC. Does anyone have applications of a similar nature?

My first obstacle is to understand how can I use DSC to communicate with the PLC and start a DAQ task. DAQ OPC is not an option. So I want to avoid having PLC values cross the DSC Engine to LabVIEW process boundary.

I considered that writing
a custom DAQ server might address this problem. In the DSC Engine process, a custom DAQ server could monitor the PLC registers and start its task when appropriate. However, that solution requires that DSC support a waveform tag data type. Can a memory tag be used for waveform data?


Thanks,
Kenneth

[steven@ni]

Kenneth,

Usually communication to plc's or rtu's are done through an add-on called Industrial Automation OPC Servers (also called Lookout Protocol Drivers). This add-on basically contains drivers for various plc's that are accessed through a standard opc server (called OPCLookoutDrivers). 

In response to your second question, currently we do not have a memory tag that can store waveform data. This is being considered for future versions.

[preston_johnson]

Kenneth,

Steve from NI addresses the PLC communications part. You monitor the PLC register/tag with the OPC server for the PLC. A loop in DSC, via tag change notification (use the read tag vi with a large timeout), sleeps until the tag us updated. You DAQ VI captures the waveform and processes it say with an FFT, Harmonic Analysis, or our Sound and Vibration Order Analysis routines. The results can then be written to memory tags in DSC for other OPC clients to see. If you need to store the raw waveforms, you can write the data to a number of file types for viewing later or by other programs.

I am curious, what waveform are you capturing? Is it a Vibration?

Thanks

Preston Johnson
Business Development Manager
Industrial Applications
Nati
onal Instruments
512-683-5444
preston.johnson@ni.com