Siemens pa module p03-01 manual The Purpose of Curves, Industry Sector, IA&DT

Industry Sector, IA&DT

The Purpose of Curves

Curves are displayed to show courses. By selecting different time horizons, different tasks can be implemented. Three variants exist in reference to the time the operator has the curve displayed.

1.The curve shows the past without the present. Such a curve is called history and is used for analysis. This can refer to a fault analysis but also to an analysis to optimize process control.

2.The curve shows the present with the recent past. This type is called pre-history. It can be used to display a trend. It is the most frequently used type of display regarding process control. From the course, the operator is able to read off qualitative values such as rising, falling, or steady and quantitative values such as the process value at a certain time, or the difference regarding a setpoint.

3.The curve shows the most recent past, the present and the future, and is called prediction display (refer to Figure 2). It is used to predict a process value and allows the user to intervene before the event occurs. To represent the future, the possible value course has to be calculated in advance.

Figure 2: Prediction display according to [2]

In general, the following values can be determined quite well through curves:

–Points in time where striking changes occurred in the course

–Process values at the points in time indicated before

–Gradients at certain points in time

–Dependencies between process values at simultaneous displays

–Extreme values (when and how large)

–Fluctuation ranges

–Deviations from the setpoint

–Frequencies

This variety of characteristics that can be read off shows the importance of curve displays. While the current process values and extreme values that occurred can be represented otherwise -for example, with analog or digital displays- the display of the other characteristics in such a compressed and immediately understandable form is difficult to conceive [3].

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