Figure 5-1. Trend Tool Trace Example 1 - Woodward 2301D Installation And Operation Manual

Manual 26247
6. Disable the Reset (integral) and Compensation (derivative) dynamic actions
by setting both to 0.01.
7. Disable Window Width by setting the Gain Ratio at 1.0 and the Window
Width at 60 rpm.
8. Disable Gain Slope by setting it at 0.0.
9. The engine should still be stable. If it is not, reduce the gain further.
10. With the engine running at no load, idle speed; increase the gain one click at
a time until a sustained speed oscillation is only just obtained. In between
clicks, use the actuator bump feature to introduce a very small bump to the
system (1% fuel demand, 0.020 seconds works well). The system oscillations
will either die out in a short amount of time (stable), stay at the same
amplitude for a long time (marginally stable), or keep increasing in amplitude
(unstable). To start with, you will most likely be in the stable range, where the
oscillations die out with time. As you increase the gain, you will eventually go
into the unstable region, where you might need to switch back to 2nd
dynamics to get the engine under control. Reduce the gain and switch back
to 1st dynamics. Keep slightly adjusting the gain up or down until you find the
setting that gives you the point of marginal stability. When you are there, the
oscillations will neither decrease nor increase in amplitude. If you can
maintain a constant amplitude for 30 seconds to a minute, you have found
the point. If the oscillations die out, your gain is too low. If they keep getting
bigger, your gain is too high. Adjust if required. The following trace (Figure 5-
1) is an example. Write down the Gain setting (5.92 in this example) and call
it Ku. This is needed to calculate final settings.
11. After recording the speed oscillations for 30–60 seconds, reduce the gain to
stop the oscillations.
12. Measure the elapsed time for several speed cycles and calculate the time
per cycle in seconds and call this value Pu. In the above trace, each vertical
grid line represents 3 seconds elapsed time, so 15 speed cycles occur in 47
seconds. Pu in this example is 47 divided by 15, which equals 3.133 seconds
per cycle.
13. Calculate dynamic settings as follows:
Gain = Ku divided by 1.7. In the above example this is 5.92/1.7 = 3.48.
Reset = 2 divided by Pu. In the above example this is 2/3.133 = 0.64.
Compensation = Pu divided by 8. In the above example this is 3.133/8 = 0.39.
14. Enter the calculated Reset, Compensation, and Gain setting into the control.
Save these settings in the control. The assumption is these settings will
produce good performance as shown in Figure 5-2. If this is not the case,
recheck all readings and calculations or repeat this entire procedure.
Woodward

Figure 5-1. Trend Tool Trace Example 1

2301D/2301D-EC Digital Control
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