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Pulse Response Examiner

This VI simulates the pulse response of a simple RLC circuit. The small graph shows the ideal pulse input, and the large graph shows the resulting output. Using the R (resistance), L (inductance), and C (capacitance) sliders, you can instantly see the change in the output waveform that results from a change in R, L, or C.

Applications:

--simulate signal transmission through cable and connector into a high-impedance analog input

--diagnose triggering problem where dominant inductance causes spurious triggers due to ringing

--diagnose triggering problem where dominant capacitance causes missed triggers due to reduced pulse height or slow rise

--examine effect of loop inductance that can be significant when a signal's outgoing current path is physically separated from its return current path.

Calculation Method:

The VI employs the 'fourier method' for inversion of the Laplace transform. The method has been presented by multiple authors including Sven Lindhardt. It's a practical approximation of inverse Laplace for systems close to stability, whether a little overstable or understable, when the rightmost pole is not greater than zero. Labview's fast Complex FFT is used in this application to generate a fast inverse Laplace transform.

User Interface:

I tried a color scheme and other front panel features that are unusual for LabVIEW VIs. Graphs are without frames. Two buttons look like webpage hyperlinks. The mouse cursor is a pointer finger only when positioned over something you can click, otherwise it's the standard Windows arrow.

--Joe Czapski

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Joe Czapski
Automation Software & Instrumentation Engineer
Thermo Fisher Scientific
Tewksbury, Mass.
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