Secondly, the transient must have died out when the simulation ends. A suitable input signal is therefore a step with an exponential decay. Another demand is that simulation start time and stop time have been chosen so that there is 1024 calculation points. It contains data that are suitable for frequency analysis. Begin by making one simulation in the time domain.
Figure shows the reference position and the corresponding piston position.
The grid can be obtained by clicking on any of the numbers in the diagram. The user is then requested to specify input and output variable and a variable name that will be assigned to the transfer function. If we are to obtain the open loop transfer function, it is necessary to have the position error. This is, however, not a plot variable in the example shown here. When a frequency analysis is performed it is important to realise that the transfer function concept is valid only for linear systems.