Chapter 4
Human Machine Interface
©
National Instruments Corporation
4-31
This example illustrates the use of dataflow programming to enforce the
order of two structures that otherwise are not related by data flow. By
wiring the time interval (secs) constant through the Sequence structure and
into the While Loop, the While Loop does not begin execution until the
code in the Sequence structure has completed execution. Another way to
enforce this order of execution is to put the While Loop inside the second
frame of the Sequence structure. Both techniques are correct. The
advantage of the technique used in Figure 4-6 is that it is easy to see the
entire diagram at a glance.
How Can You Use Tag Attributes to Configure
HMI Indicator Attributes Programmatically?
Use the Tag Attributes VI library to read or change specific configuration
details of a tag. Anything you have configured in the Tag Configuration
Editor can be queried programmatically using the Tag Attributes VIs. Use
these VIs when you want to control attributes programmatically for your
front panel controls or indicators, or to display configuration information
on your HMI. Setting attributes programmatically for front panel controls
and indicators is an alternative to changing attribute values for the control
or indicator through the various front panel pop-up menus or by typing into
various control and indicator fields.
Handling attributes programmatically is most useful when you use the
same indicator or control for different tags. For more information on tag
configuration, see Chapter 3,
. For more information
about the Tag Attributes VIs, see the section
in
Appendix A,
.
Figure 4-7 shows a simple case where the scale range for all the front panel
level and temperature indicators are set to the engineering scale that is
configured for the tag. A unit string display for each
L1
and
Temp
indicator
is initialized to the engineering unit for the respective tag. The Get Tag
Range and Units VI returns the engineering scale range information in a
form that can be wired directly to a control or indicator scale range attribute
node. The VI also returns the engineering units configured for the tag.
