4-8 PID Control Concepts Models 2510 and 2510-AT User’s Manual
Long Lag and Tau time example
In order to demonstrate the benefits of response tuning, refer to the example of a system
with very long Lag and Tau times (shown in Figure 4-5). In this example, the load has a
Lag time of 11.0 seconds and a Tau of 107.0 seconds and is subjected to a +3°C step in
temperature setpoint. For the minimum settling time plot, the temperature overshoot
occurs at 26.495 seconds (with a peak value of 27.450°C). It settles to within ± 0.1% of
the final temperature (±.026°C) in 149.1 seconds. In the minimum overshoot case, the
temperature overshoot occurs at 20.847 seconds (with a peak value of 26.226°C). It settles
to within 0.1% of the final temperature (25.974°C) at 521.914 seconds (See Table 4-2).
Clearly the minimum settling time option settles much more quickly to 0.1% than does the
minimum overshoot version
Figure 4-5
Response comparison example 2 (long Lag and Tau times)
Table 4-2
Response time comparison example 2 (Lag Time 11.0sec, Tau Time 107.0sec)
Condition Minimum Settling Time Minimum Overshoot
Max Overshoot: 27.450°C @ 26.495 Sec after Step 26.226°C @ 20.847 Sec after Step
Settle to 0.1%: 26.025°C @ 149.100 Sec after Step 25.974°C @ 521.914 Sec after Step
Minimum Settling Time
Time (Sec)
Temp (Deg C)
27
26
25
28
23
0 100 200 400
24
300
Minimum Overshoot
Time (Sec)
Temp (Deg C)
27
26
25
28
23
0 100 200 400
24
300
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