Operating point plot

The compressor operating point plot is drawn on the basis of recorded operating point data (the (x,y) coordinates).

The plot provides a visual indication of the following information for each (x,y) point plotted:

• Flow conditions associated with the operating point sample.

• Age of the operating point sample with respect to number of operating points plotted.

Operating Point Data Quality

The data quality conditions supported are described in Flow conditions status and data quality.

Operating Point Flow Conditions

Flow conditions for a plotted operating point are represented by a symbol. The symbols selected to represent particular flow conditions are fixed. Ten different symbols are available in easy eXtended Operator Station (ezXOS) for the purposes of plotting the operating point, thus allowing for up to ten different flow conditions to be represented. The Flow Conditions supported are described in Flow conditions status and data quality.

Operating Point Age

The age of a plotted operating point is represented by a color and color shade. The color and shade selected are based on the number of operating points plotted.

To ensure that compressor performance plots represent the age of the plotted points consistently, the color of the operating points is determined using easy eXtended Operator Station (ezXOS) Color Mapper function. The color map set used for the compressor performance plot provides the following functions:

• Configurable by the System Administrator.

• Assigned to each plot individually at display configuration time.

• May be altered for each plot individually at display run time through OBEL.

A map set specifies a numeric value that is cross-referenced to a color index used by ezXOS to color an object. The color index specifies a color to ezXOS.

Based on the number of operating points plotted, the compressor performance plot determines the color of each point by referencing it against the color map specified for the plot. The newest operating point plotted is colored according to the first entry in the color map set, the next operating point is colored according to the second entry in the color map set, and so on.

The color map set table used for a compressor performance plot requires that the following information be specified:

• Color map set name

• Reference value(s)

• Color index value(s)

A sample table is shown below:

Using the above table as an example, if four operating points were plotted, then the first four entries of the color map set assigned to the plot would be used to color the plotted points.

The color map sets are loaded into ezXOS at login time. This means that for changes to the color map set to take effect, you must log out of ezXOS and then log in again.

To minimize login time, the number of color map sets used for compressor performance plots should be minimized and each set should be restricted to 24 entries.

Current Operating Points

The current operating point plot shows the four most recently acquired or calculated values for head pressure (y) and flow rate (x). The current operating point on the compressor performance plot is updated when a new operating point is sampled or calculated.

Historical Operating Point

The Historical operating point plot shows the operating points recorded within the start and end times that you specify as values for head pressure (y) and flow rate (x). The Historical operating point is updated when you specify a different time frame or selects a different compressor.

The Historical operating point plot allows you to specify the Historical data to plot as either short term (minute-by-minute) or long term (hourly).

Current Performance Curve Set

The performance curve set currently associated with a compressor is shown on a station schematic display as a separate text field configured using the tools provided with the ezXOS Display Editor. The text field references the current curve set that is maintained for the compressor in the RealTime database (RTDB). The text field may be added to station and compressor schematics on a project-by-project basis. The associated curve set name is not shown on the compressor performance plot directly.

The Controller can reassign a performance curve set using ezXOS and the Plot Action menu. The Plot Action menu is accessible from an ezXOS display through selection of the right mouse button while the mouse pointer is over the compressor plot object. The Plot Action menu provides an item for the Controller to select to perform a curve set assignment. When selected, a list of available curve sets are presented to the Controller.

When a different curve set is selected, the compressor performance plot display is redrawn with the selected curves.

Operating Point Table

The operating point plot provides a data cursor (dipstick) function. A menu item on the Plot Action menu allows the Controller to select the current operating point table display. The operating point table display, when called up by yourself, displays the following information for each point currently plotted in a tabular arrangement:

• (x,y) coordinate value

• Date/time stamp

• Data quality

  Note: The color of each row indicates the age of the operating point.

Freeze/Thaw

The current operating point plot provides a freeze/thaw function. The freeze/thaw function, when you invoke it, enables or disables the current operating point plot from being updated with new data.

Zoom

The operating point plot provides a zoom-in and zoom-out function which allows you to zoom in on a specified area of a compressor performance plot display.

Legend

The legend function on the Plot Action menu allows the Controller to select the operating point legend display. The Performance Plot Legend displays the flow condition mapping.

Window Resize

The operating point plot supports resizing functions. When you resize the window, the system regenerates the plot, according to the new size of the window.