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Chapter 6
Historical Data Logging and Extraction
6-12
©
National Instruments Corporation
How Do You Change the Timespan
of Data Displayed?
The timespan indicator displays the amount of relative time between the
start and end points of the time axis. To change the amount of time between
these points, you either can manually reenter data in the start or end point
on the time axis, or pull down the ring for the timespan indicator.
By default, the timespan ring contains the values 1:00, 5:00, 10:00, and
30:00. Select Enter New… in the timespan ring if you would like to enter
a different amount of data to display.
How Do You View the Value of a Tag
at a Specific Point in Time?
The Data Display table on the HTV, shown in Figure 6-2, shows the tags
displayed in the trend, the tag description, and, for analog tags, the
engineering units associated with the tag. The two rightmost columns show
the values of the tags at the two cursor locations in the trend. For discrete
tags, the values in these columns are either
On
or
Off
. To move the cursors,
grab their pointers at the bottom of the trend display.
How Do You Change the Y Axis?
The HTV displays two Y axes at any time. Each Y axis displays the color
of the tag associated with it. All discrete tags show their ranges as going
from
On
to
Off
. Click on the Y axis to make it rotate through the tags
displayed in the trend.
To change the range in the Y axis for analog and bit array tags, select the
text at the top or bottom of the scale and type in the desired value. When
you enter the value, that trend scale changes and the trend display updates.
Discrete tags are displayed without Y axis scales, and ranges are shown as
On
or
Off
.