Two Lags in Series

Applets

• Single Lag Frequency Response
• Two Lags in Series Frequency Response
• Single Lag Bode Diagram
• Two Lags in Series Bode Diagram

Exercise

• First look at the Frequency Responses for the single lags with the following parameters:
  • Gain 1 = 1.8, Time Constant 1 = 3
  • Gain 2 = 0.9, Time Constant 2 = 1.5

  Note in particular what the AR and PA are at various frequencies.

• Now try these values for Two Lags in Series, again noting AR and PA.
• Compare values from the Frequency Response with the Bode Diagram (note that it is not possible to alter the process parameters).
• Finally try varying the gains and time constant for the Frequency Response.

Questions

• What is the relationship between the Amplitude Ratios and Phase Angles for the two lags when separate and when they are joined in series?
• What value does the Phase Angle approach with two lags in series?

Answers

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