﻿ 20-sim webhelp > Editor > Interface Editor > Ports with more than one Terminal

# Ports with more than one Terminal

By default, an iconic diagram port is a port where power can be exchanged between a component and its environment in terms of an across variable and a through variable. Such a port is represented by one terminal (connection point). However, there are two special cases where it is desirable to define an iconic diagram port that has more than one terminal.

## Separate High / Low Terminals

Consider, as an example, an mechanical spring. The power that flows into such a component is uniquely determined by the velocity difference between the two terminals of the component and the common force that acts upon both ends. Because of this one could say that there is one port, whose power is determined by one across value (the velocity difference) and one through value (the common force), but is represented by two terminals. To support this, 20-sim allows you to define a special type of iconic diagram port by indicating that is has Separate High / Low Terminals. The two terminals of the connection are named high and low. If the port is named p, the formal equations are:

fixed in orientation:

p.F = p_high.F = p_low.F

p.v = p_high.v - p_low.v

fixed out orientation:

p.F = p_high.F = p_low.F

p.v = - p_high.v + p_low.v

In 20-sim these equations are automatically derived.

## Any Number of Terminals

Consider, as an example, a mass. A characteristic of this component is that you can connect many springs and dampers to it. Implicitly, one expects that the net force (i.e., the summation of the forces applied by the connected components) will be applied to the mass, and that it will have a single velocity. To support this, 20-sim allows you to define a special type of iconic diagram port by indicating the kind to be Any Number of Terminals. The terminals of the connection are named 1, 2, 3 etc.. If the port is named p, the formal equations are:

fixed in orientation:

p.v = p1.v = p2.v = p3.v = .....

p.F = sign1*p1.F + sign1*p2.F + sign1*p3.F + ....

fixed out orientation:

p.v = p1.v  = p2.v = p3.v = .....

p.F = -sign1*p1.F - sign1*p2.F - sign1*p3.F - ....

with

sign = 1 when p1 has a fixed in orientation etc.

sign = -1 when p2 has a fixed out orientation etc.

In 20-sim these equations are automatically derived.