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Scilab manual >> xcos > palettes > Continuous time systems palette > VARIABLE_DELAY


Variable delay

Block Screenshot


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:

Dialog box

  • 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.

    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


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:

Interfacing function

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

Computational function

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


Ramine Nikoukhah - INRIA


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Last updated:
Wed Jan 26 16:23:47 CET 2011