The Process Analyst control typically uses analog pens to represent variable or numerical data. Only analog pens have a value (vertical) axis, which the data is plotted against.

Analog pens have two types of interpolation that allow you to specify how to connect data samples on a trend line:

• Straight - a line is drawn directly between the points or sample values like this:



• Stepped - the lines drawn always maintain the value of the previous sample until a sample with a different value arrives, in which case a vertical line is drawn:

See Also Interpolated Samples.

The Process Analyst control typically uses digital pens to represent binary data. Values on the pen are restricted to 0 or 1. Any value equal to or greater than 0.5 is set to 1; other values are set to 0. A fill color is used to indicate where the data is 1, as shown here:

By default, the layout of digital pens is stacked. For details, see Pen Layout.

The Process Analyst uses alarm pens to graphically display the history of Citect SCADA alarms over time. The alarm's on/off transition state changes and acknowledgment are represented graphically in the alarm pen display.

When an alarm is on, it is represented by a bar filled with color. The color indicates different states. The line above represents operator acknowledgment of the alarm.

The diagram below illustrates how an alarm pen displays the information of an alarm tag:

1. The alarm is turned on in its initial state and is unacknowledged.
2. The alarm changes to a different state, but is still unacknowledged.
3. The alarm is acknowledged.
4. The alarm is turned off.