Siemens pa module p03-01 manual Acquisition and Storage of Curve Values, Designing Curve Displays

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Acquisition and Storage of Curve Values

For the displayed course to reflect the actual course, the sampling rate of the process value has to correspond at least to twice the change frequency of the process value. In most cases, this requirement can be met with cyclical acquisition every 1s [2].

In PCS 7, the sampling rate corresponds to the acquisition cycle of a process value. As long as a process value is not archive, only the pre-history of the process value can be displayed. By archiving a process value (refer to chapter P02-03) the history can be displayed also, since archive variables are resorted to.

When curves are displayed, the pre-history differs from the history as shown in Table 1.

Table 1: Visible Differences between Prehistory and History [2]

	Prehistory	History
Position of the time span	Always relative to the	Through an absolute point
shown in the curve field	present	in time and a selected time
		span or through two
		absolute points in time
Labeling of the time axis	Relative time indications; if	Absolute time indications
	needed, can be switched to	can be switched to time
	absolute time indication	indications relative to a
		defined point in time of an
		event
Updates	Curve is updated during the	Curve does not change
	display whereby all curve
	points are shifted
Value axis	The value axis is usually	The value axis is located on
	located at the point in time of	the left margin of the display
	the present (at the right
	margin of the display)

Designing Curve Displays

In [2], guidelines for designing curve displays are provided. PCS 7 implements the basic design details by default; for that reason, they are described here only briefly. There are design rules, however, that you can implement yourself by means of the settings at OS engineering. To do this in a specific way, a few details are introduced here.

The curve display is displayed in the working area of the display area (refer to P02-01). It consists of the title field, the curve labeling field, and the curve field. The title field should contain the information for the unambiguous assignment to the process environment. In the curve labeling field, it should be possible to read off the relationship of displayed the curve and the process value. The curve display field is used to display the curve and should be as large as possible. To implement the curve display field, the following information is provided.

To facilitate reading off the values, grid lines have to be available. The value axis in this case should display several lines as an extension of the scale marks, and the time axis several lines according to the current time grid. The number of grid lines should be low and optically remain in the background. To this end, they should not be shown in color or blue. Reading rulers can provide additional support.

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