Campbell-scientific CR1000 Measurement and Control System Instrukcja Użytkownika Pobierz pdf (Strona 265)

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Section 7. Installation

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Note N = Number of points in running average)

To calculate the delay in time, multiply the result from the above equation by the

period at which the running average is executed (usually the scan period):

Delayintime=(scanperiod)(N‐1)/2

For the example above, the delay is:

Delayintime=(1ms)(4‐1)/2=1.5ms

Example:

Actualtestusinganaccelerometermountedonabeamwhoseresonant

frequencyisabout36Hz.Themeasurementperiodwas2ms.The

runningaveragedurationwas20ms(fre

quencyof50Hz),sothe

normalizedresonantfrequencyis,

36/50=0.72,SIN(0.72π)/(0.72π)=0.34.

Therecordedamplitudeforthisexampleshouldbeabout1/3ofthe

input‐signalamplitude.Aprogramwaswrittenwithtwostored

variables:Accel2andAccel2RA.Therawme

asurementwasstoredin

Accel2,whileAccel2RAwastheresultofperformingarunningaverage

ontheAccel2variable.Bothvalueswerestoredatarateof500Hz.

FigureRunning‐AverageSignalAttenuation

(p.266)showthetwovalues

plottedinasinglegraphtoillustratetheattenuation(therunning‐

averagevaluehastheloweramplitude).

Theresultantdelay(delayintime)=(Scanrate)(N‐1)/2=2ms(10‐1)/2=

9ms.Thisisabout1/3oftheinput‐signalperiod.

Figure 83: Running-average frequency response

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