Variable Time Delay

The Variable Time Delay unit delays the input signal for a variable amount of time.

The output data at the current time step is equal to the value of its input data at the previous time step. This step is the current simulation time minus the delay time specified by the time delay input.

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During the simulation, the block stores the time and input value pairs in an internal buffer. At the beginning of the simulation, the block outputs the value of the parameter Initial output until the simulation time exceeds the input time delay value. Then, at each simulation step, the block outputs the input signal received at a point in time that corresponds to the current simulation time minus the delay time.

If you want data at time points that are between the input storage times, and the solver is a continuous solver, the block performs linear interpolation between the points. If the time delay is smaller than the step size of the solver, the block extrapolates the output point based on the previous point. For example, consider a simulation with a fixed step solver with step size 1 and current time at t = 5. If the delay is 0.5, the block should generate a point at t = 4.5, but the most recently stored time value will be at t = 4. Thus, the block extrapolates the input data at time t=4.5 from the data generated at t=4 and then uses the extrapolated data in calculating the value at time t=5.

Extrapolating forwards from a previous time step may give a less accurate result than extrapolating backwards from the current time step. However, the block cannot use the current input to calculate its output value because the input port does not have a forward pass-through connection.

If the model specifies a discrete solver, the block does not interpolate between time steps. Instead, it returns the nearest stored value that precedes the desired value.