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Can I Convert a Continuous Transfer Function (TF) To a Discrete TF in LabVIEW?

Primary Software: LabVIEW Toolkits>>PID Control Toolset
Primary Software Version: 6.0
Primary Software Fixed Version: N/A
Secondary Software: N/A

Problem: I have a continuous TF model in the s-domain, and I want to convert it to discrete TF in the z-domain. Are there any VIs that I can use in LabVIEW?

Solution: Currently, LabVIEW does not have a VI that can be used for this conversion. But, the LabVIEW PID Control Toolset includes the Discrete Transfer Function VI that allows you to simulate discrete models in the z-domain. There are different analytic methods that can be used for continuous-to-discrete conversion. The simple method is to replace s with (1 - z^-1) / T_s, where T_s is the sampling interval. For example, if you have a TF model of
H(s)= 1/(s2 + s + 1), and Ts=0.01 sec, then replacing s with (1 - z-1) / Ts, H(z) is obtained as
H(z)= 0.0001z2/(1 - 2.01 z + 1.0101 z2)

The VI attached below shows the step response of both the continuous and the discrete TF models given in this example.


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Report Date: 11/13/2003
Last Updated: 05/10/2004
Document ID: 33CBHOVS

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