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Process Trends
Clicking the Process Trend button in the Normal Operating window brings you the Trend Data window
(figure 29), which records 90 seconds of position and its setpoint. The time range is fixed at 90 seconds
and the default range for Y-axis is 0 to 100%. You can adjust the Y-axis range precisely by entering Y-
axis limits into the boxes at the left-top window and pressing Tab (or click in another box in the window).
You can also drag the mouse over part of the graph to zoom in for more detail. To reset to the default
range, click the right mouse button.
Process trend can be used to monitor the performance of a positioner. With an enabled built-in process
controller, process variable and its setpoint are also recorded in the process trend. Therefore, the trend
can also be used to test, tune and monitor the process loop. Since the process trend update rate is 1 to
2 seconds, the trend recording does not accurately describe the fore-mentioned variables, especially
that of valve position during a transient state. To obtain a precise record of valve response to setpoint
change, run the step profile test described in Diagnostic Mode. (Chapter 11).
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Figure 29. Trend Data Window