15A.4 Limit Testing Analysis

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This Appendix discusses using the polymorphic SVT Limit Testing VI located on the Limit Testing

palette.

You can use Limit Testing to perform analysis on any type of measured result produced by the Sound

and Vibration Toolkit, including the following measurements:

* Waveform

* Spectrum

* Peak

* Octave

* Swept sine

* Scalar

15A.4.1 Limit Testing Overview

You can use the SVT Limit Testing VI to analyze almost any measured result produced by the Sound and

Vibration Toolkit. Refer to Table 15A.4 for examples of data-types supported by the SVT Limit Testing VI

and VIs that generate supported data-types.

15A.4.2 Using the SVT Limit Testing VI

Limit testing allows one to specify an envelope around the data to define a pass range. You can enter a

scalar to the upper limit, lower limit, or both to specify a constant ceiling and floor for the data to perform

tests such as range detection. You can enter an upper limit mask, lower limit mask, or both to the SVT

Limit Testing VI to define a pass range that varies in shape and level based on acceptable results at any

given point in the measurement. You also can create a discontinuous mask which allows you to perform

limit testing on only a part of the results while ignoring the rest.

FIGURE 15A.6 Measuring the DUT propagation

delay.

15-82 Vibration and Shock Handbook

© 2005 by Taylor & Francis Group, LLC

You must enter at least one limit, or the SVT Limit Testing VI returns an error. You can visually display the

input signal, failures, upper limit, and lower limit by creating an indicator from the output values terminal.

The upper limit and lower limit inputs to the SVT Limit Testing VI must be compatible with the input

signal. Table 15A.5 lists the criteria that must be met for each input signal type that is compatible with the

SVT Limit Testing VI.

In Table 15A.5, the following abbreviations apply:

* dt is the time spacing, in seconds, between elements.

* df is the frequency spacing, in hertz, between elements.

* N is the number of elements in the array.

* f ðiÞ is the ith frequency element.

* S is the signal.

* U is the upper mask limit.

* L is the lower mask limit.

Limit testing covers a broad range of data testing from range detection to discontinuous mask

testing of a swept-sine frequency response spectrum. Figure 15A.7, Figure 15A.9, Figure 15A.11, and

TABLE 15A.4 Compatible Data Types for SVT Limit Testing VI

Data-type Output VIs

Waveform

measurement

AI read, DAQmx read, waveform

generation, weighting, integration,

vibration level, sound level

Frequency spectrum

measurement

Baseband FFT, baseband subset FFT,

zoom FFT, extended measurements

XY data ANSI and IEC octave, swept sine

Peak measurement Distortion, single-tone,

extended measurements

Scalar measurement Calibration, vibration level, sound level,

ANSI and IEC octave, distortion,

single-tone, extended measurements

TABLE 15A.5 Criteria for Upper and Lower Limits

Input Signal Type Criteria on Input Limit Masks

Waveform data type ðt0; dt; ½signal􀀉Þ dt . 0; dtS ¼ dtU ¼ dtL , NS ¼ NU ¼ NL

Frequency spectrum ðf 0; df ; ½spectrum􀀉Þ f 0S ¼ f 0U ¼ f 0L, dfS ¼ dfU ¼ dfL , NS ¼ NU ¼ NL

Octave spectrum, swept-sine spectrum, XY data ([X ], [Y ]) [X ]S ¼ [X ]U ¼ [X ]L, NS ¼ NU ¼ NL

Identified peaks, harmonic components, multitone phases

([frequency, amplitude])

f(i)S ¼ f(i)U ¼ f(i)L, NS ¼ NU ¼ NL

Virtual Instrumentation for Data Acquisition, Analysis, and Presentation 15-83

© 2005 by Taylor & Francis Group, LLC

Figure 15A.13 illustrate some, but not all, of the

different ways one can use the SVT Limit Testing

VI in your application.

Figure 15A.7 illustrates a range-detection test.

Scaled waveform data and upper and lower

limits are input to the SVT Limit Testing VI. The

VI checks that the data fall within the envelope

specified by the upper and lower limits. Figure

15A.8 shows the output results for the range

detection test.

Figure 15A.9 shows a pass/fail test on the

measured THD. This test only checks the upper

limit of the measurement, therefore, only the

upper limit is wired to the VI. The upper limit

should have the same units as the input measurement.

In this case, both the THD and the upper

limit are expressed as percentages. Figure 15A.10

shows the THD test output results.

Figure 15A.11 shows a continuous mask test on a power spectrum. Formula nodes define both the

upper and lower limits in this VI, making this a more complex test than the one in Figure 15A.9.

Figure 15A.12 shows the output graph for the power spectrum continuous mask test.

Figure 15A.13 shows a discontinuous mask test on a swept-sine frequency response. A discontinuous

mask test can track and test the results at different magnitudes and ranges, as well as stop testing at

defined intervals. For example, one might use the envelope defined by the upper and lower limit masks in

this example for a DUT such as a notch filter. Figure 15A.14 shows the output graph for the

discontinuous mask test.

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