Appendix A HMI Function Reference
© National Instruments Corporation A-11 BridgeVIEW User Manual
Read Event History
Use the Read Event History VI to display all the alarms and events that have occurred for a
set of tags or tag groups within a given alarm priority range. You also can filter out
acknowledged tags. The Read Event History VI formats the event history information for
display in an Event History Display indicator in your HMI. If you specify a timeout value
greater than 0, this VI returns when the event history information changes, or the timeout
value is exceeded, whichever occurs first. The changed? output alerts you as to whether the
event history information has been updated.
The format and color codes inputs tell the Read Event History VI how to format and color
code event history information. The Read Event History VI returns all the information needed
to update the Event History Display indicator. Part of the Event History Display indicator
formatting is done through attribute nodes which only can exist in your diagram. The column
headers display the table column header information and must be wired to your table Column
Headers[] attribute if you are displaying column headers. Normally this is updated only when
the VI is executed for the first time, assuming you do not change the format control during
program operation. The initialize headers output is TRUE when you need to update the
Column Headers attribute.
Wire the history data output directly to your Event History Display. Wire the row colors
output to the Active Cell and Cell FG Color attributes inside a While Loop. Wiring the Event
History Display attributes formats the table to show different line colors for different alarm
states or events. You can generate this code automatically by using the HMI G Wizard.
The entire Event History Display, including attributes, is updated only if the event history
information changes, and there was no timeout. Table indicator updates can be slow for large
tables, so it is usually a good idea to update the table only if the changed? indicator is TRUE.
Notice that the changed? indicator is always TRUE after the first execution of the VI.
read parameters is a cluster of parameters for filtering out the alarms read.
min priority is the minimum priority of alarms read. If left
unwired, alarms corresponding to priority level 1 and above are
reported.