Event Trapping and Logging -- How?--

Don’t know if it’s possible or how to go about doing it? I’m looking to create some kind of event trapping and logging. The run down first, I’m using an slc5/04 interfacing with a Panelview 1000 through dh485 communication protocol. And what I would like to do is monitor certain data table elements and log any changes that have occurred. Which will be displayed on a particular screen, much like an alarm screen. With each occurrence being date & time stamp, and the current value and previous values displayed. Any help and advice would be appreciated.

Thanks
Heterodoxy

Here's a few links to some code snippets that you may find useful:

A FIFO system for tracking data + timestamps + whatever (You'll want to FIFO your log - the PLC just doesn't have enough memory to keep stuff forever
http://www.plctalk.net/qanda/showthread.php?s=&threadid=1751

And then there's my treatis on alarms (i.e, event capturing for operators)
http://www.plctalk.net/qanda/showthread.php?s=&threadid=1964

This should get you started. It sounds like you plan to monitor analog data points. Some questions to ask yourself:

- Should the change be logged for ANY change, or must it change by a set maount (deadband) for it to be logged?

- Once logged, should there be a time delay before the next capture is made, or should another data point get captured if the data changes on the next scan as well?