The proportional plus derivative element (PD element)

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The PD element shows both proportional and derivative behaviour and is described by the transfer function

(4.39)

Apart from the gain factor

this element is the inverse of the

element. Hence for

one obtains the magnitude and phase response by mirroring at the 0-

axis and the

line, respectively (compare Figure 4.12 with 4.10). The locus of the frequency response

(4.40)

is a semi-line, which starts for

on the real axis at

and progresses parallel to the imaginary axis for increasing values of

**Figure 4.12:** (a) Magnitude and phase response (b) Nyquist plot of the frequency response of a PD element

Next: The derivative lag element Up: Some important transfer function Previous: The 1st-order lag element Contents

Christian Schmid 2005-05-09