VARIABLE_DELAY

Block Screenshot

Contents

• Description
• Parameters
• Default properties
• Interfacing function
• Computational function
• Example

Description

The Variable Transport Delay block can be used to simulate a variable time delay between an action and its effect. The block might be used, for example, to model a system with a pipe where the speed of a motor pumping fluid in the pipe is variable.

The block accepts two inputs and one output: the first input is the signal u(t) that passes through the block (data input); the second input is the variable time delay τ(t).

At the current time step t, the block outputs the delayed data input u(θ) where θ is the current simulation time t minus the time delay parameter τ.

The equation of the output signal is:

y(t) = y(θ) - u(t - τ(t))

Parameters

• Max delay

  It defines the largest value the time delay input can have. The value cannot be negative.

  Properties : Type 'vec' of size 1.

• Initial input

  The output generated by the block until the simulation time first exceeds the time delay input. If it is not set to the y(τ) value, a linear approximation will be calculated between the initial input at t0 and the y(τ) value.

  Properties : Type 'vec' of size 1.

• Buffer size

  The number of points the block can store.

  Properties : Type 'vec' of size 1.

Default properties

• always active: yes

• direct-feedthrough: no

• zero-crossing: no

• mode: no

• regular inputs:

  - port 1 : size [1,1] / type 1

  - port 2 : size [1,1] / type 1

• regular outputs:

  - port 1 : size [1,1] / type 1

• number/sizes of activation inputs: 0

• number/sizes of activation outputs: 0

• continuous-time state: no

• discrete-time state: no

• object discrete-time state: no

• name of computational function: variable_delay

Interfacing function

• SCI/modules/scicos_blocks/macros/Linear/VARIABLE_DELAY.sci

Computational function

• SCI/modules/scicos_blocks/src/c/variable_delay.c (Type 4)

Example

In this example, the max time delay in the Block Parameters dialog box is set to 4. The input signal is a sine wave with amplitude 1 and frequency 0.2 Hz.

The constant block is set to 2 to introduce a delay of 2 second. The input and output waveforms of the VARIABLE_DELAY block are shown below: