Appendix A
HMI Function Reference
A-62
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National Instruments Corporation
Trend Tags
Use the Trend Tags VI to set data for a real-time trend chart in your HMI. The Trend Tags VI
supports analog, discrete, and bit array tags. The Trend Tags VI formats data for one or more
tags such that it can be wired directly to a trend (waveform chart). The Trend Tags VI returns
after each time interval with the next set of points for the trend.
Place each Trend Tags VI in its own While Loop, assuming that each loop is running at a
different time interval.
tag names is the name of each tag to be trended.
scale to % determines how the trend data is scaled. If scale to % is FALSE,
trend data is in engineering units. If scale to % is TRUE, trend data is in
% of full scale (0 to 100%). The default setting for scale to % is FALSE.
time interval (secs) (1) is the time interval in seconds for reading the tag
values for the real-time trend. The default time interval is 1 second.
trend data contains the data from each tag, formatted for wiring to a
waveform chart. These values are either in engineering units, or scaled, as
specified by scale mode.
error indicates that an error occurred when executing Trend Tags, or that
one or more tag values could not be accessed.
shutdown indicates that the BridgeVIEW Engine is shutting down. In this
case, Trend Tags returns immediately with shutdown TRUE, and trend
data might no longer be valid. You can use shutdown to exit any loop that
uses the Trend Tags VI.
config change indicates that configuration of the Trend Tags VI has
changed since the last execution. This could be because of a change in the
list of tags in the trend, the time interval input, or the scale to % input.
Optionally use this output to reinitialize your waveform chart because past
history data will be no longer valid.
