IEVref:351-50-03ID:
Language:enStatus: Standard
Term: second-order lag element
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Definition: linear time-invariant transfer element the transfer function of which has exactly two poles with negative real parts which may be real or complex conjugate and no zeros

Note 1 to entry: The transfer function of a second-order lag element is given as

$\frac{V\left(s\right)}{U\left(s\right)}=\frac{{K}_{\text{Ρ}}}{\left(1+{T}_{1}\cdot s\right)\cdot \left(1+{T}_{2}\cdot s\right)}$ for two real poles

and as

$\frac{V\left(s\right)}{U\left(s\right)}=\frac{{K}_{\text{Ρ}}}{\frac{{s}^{2}}{{\omega }_{0}^{2}}+2\cdot \vartheta \cdot \frac{s}{{\omega }_{0}}+1}$ for a complex conjugate pair of poles

where
 KP is the proportional action coefficient; T1, T2 are the time constants; $\vartheta$ is the damping ratio; ω0 is the characteristic angular frequency; s is the complex variable of the Laplace transform; U(s) is the input transform; V(s) is the output transform.

Note 2 to entry: This entry was numbered 351-28-14 in IEC 60050-351:2006.

Publication date:2013-11
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Internal notes:2013-12-16: de term corrected in accordance with mail from "Seeger, Anne" <anne.seeger@vde.com>, 2013-12-16. JGO

2017-08-28: <mstyle displaystyle=true'> corrected to <mstyle displaystyle='true'>. LMO
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