User Manual Siemens Water System Pa Module P03-01 [5/42 Pages]

Siemens water system pa module p03-01

Industry Sector, IA&DT

SCE Training Curriculum Page 5 of 42 To be used only at Educational and R&D Facilities

P03-01_AdvancedLayout_R1309_en.doc

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].