\chapter{Twisted Pair cable models}

Twisted pair models have been developed with gauges 20, 22, 24, from 3 different standards \cite{3901/019},  \cite{3901/002} and \cite{3901/025} i.e. 9 models in total.

The process followed to obtain the parameters for the \textbf{.cable\_spec} file from information in the ESCC specifications is as follows (where we assume that all dimensions are converted to metres):

 \begin{enumerate}

 \item 
 \begin{equation}
 comnductor\_radius = \sqrt{\frac{nominal\_section}{\pi}}          
 \end{equation}          
 
 \item 
 \begin{equation}
 dielectric\_radius = \frac{core\_max\_diameter}{2}                        
 \end{equation}          

 \item 
 \begin{equation}
 conductor\_separation    = finished\_wire\_diameter -2* dielectric\_radius 
 \end{equation}          
 
 
 \item 
 The conductor in the model is a homogeneous cylindrical conductor so we need an effective 
 conductivity. This is based on the maximum resistance (quoted in ohms/km)
 
 \begin{equation}
 Conductivity = \frac{length}{(max\_resistance*nominal\_section)}
 \end{equation}          
 
 \item 
The dielectric surrounding each conductor is also assumed to be homogeneous and independent of frequency.
 
 polyimide: $\epsilon_r=3.4$
 
\end{enumerate}

 As an example, the cable specification for the 20AWG cable, variant 14 from \cite{3901/019}
 
 TP\_AWG\_20\_ESCC\_3901019\_V14.cable\_spec:

\begin{verbatim}
#MOD_cable_lib_dir
LIBRARY_OF_CABLE_MODELS
Twisted_pair
2                 # number of conductors
4                 # number of parameters
   4.370E-04      # parameter 1: inner conductor radius
   1.520E-03      # parameter 2: inner conductor separation
   7.400E-04      # parameter 3: inner dielectric radius
   4.762E+07      # parameter 4: conductivity
1                 # number of frequency dependent parameters
# Dielectric relative permittivity model follows
1.0        # w normalisation constant
0   # a order, a coefficients follow below:
   3.400E+00
0   # b order, b coefficients follow below:
1.0     
\end{verbatim}


\clearpage
