Finn's LabVIEW Goldmine:

Time-delay

LabVIEW file (subVI):

SubVI_Timedelay.vi

What is it?

The subVI implements a time-delay. The time-delay can be adjusted during run-time. A typical use is shown in Figure 1 (from inside a While loop).


Figure 1

Inputs to the function:

  • u is the input signal that is to be delayed.

  • timestep [s] is the time-step. For real time time-delay implemented in a While loop, timestep must be set equal to the cycle time of the While loop.

  • init_output is the value of y, the initial output of the function, that is: the value of y until the simulation time has passed the time-delay. If you want the init_output to be equal to the present input (u), you wire init_output to u.
  • timedelay [s] is the time-delay. It can be adjusted by the user during the simulation.
  • timedelay_max [s] is the assumed maximum value of the (adjustable) time-delay. timedelay_max is used to set the size of the internal array used to implement the time-delay in this subVI. It should not be changed during the simulation.

  • Init (boolean) can be used in the following alternative ways (the first of these can be used in most applications)

    1. By connecting a First Call? function to the Init input, y gets value y_init when the VI starts.
    2. By connecting a boolean terminal (which typically stems from a button on the Front panel) to the the Init input, y can be reset to init_output at any time by giving the boolean terminal a True value (typically by clicking a button).

Outputs from the function:

  • y which is the output of the function, i.e. the time-delayed input.

How to include the Time-delay in your block-diagram?

  1. Save the subVI LabVIEW file to any folder (do not open it directly in LabVIEW).

  2. Add the subVI to the block-diagram of your VI via Functions Palette / Select a VI etc. Then connect its inputs and its output to the proper signals (wires) in the block-diagram. (It is not necessary to copy the block-diagram code of the subVI explicitly into your program.)

Why this subVI?
The reason why I have developed this subVI, is that the inbuilt time-delay functions in LabVIEW do not have sufficient functionality for dynamic simulators, or can not be used, or are complicated to use, in ordinary While loops.

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Updated 30 August 2016 by Finn Aakre Haugen