Can a data file be made to "wrap" to always contain newest data?

[MBS]

We are writing Fieldpoint data to a text file every 1.5 seconds to use as a "blackbox" file for evaluating failures. A failure will shut down the unit under test and terminate the write to file loop.
Is there a way to log for a given period of time and then have old data "fall off" as new data is written?
We want to always have the last half-hour of data to use for analysis if the unit fails without having multiple files.
The data is mostly pressure data from an FP-AI-111 and RPM calculated from an FP-CTR-500; The application is programmed in Labview 7.0.

[Ray.R]

Depending on the size of the file, you could "read" the entire file, have the stored items indexed by time and feed that (initialize) the Shift Register within the loop which stores the data.

Inside the loop, have a Case Structure that verifies if the data is too old and drop that from your file.

When a "failure" occurs, you step out of the loop and write back the entire file.

-JLV-

[preston_johnson]

National Instruments LabVIEW Datalogging and Supervisory Module has such a file, citadel. It is very easy with the tag wizard to browse the I/O module to browse the I/O points and add them to the historical file list.

I would be interested in learning more about the unit under test. I would also to coach you through or show you an internet demonstration of these tools. Its really simple, and can save you a lot of time.

Preston Johnson
preston.johnson@ni.com
512-683-5444