Campbell-scientific CR800 and CR850 Measurement and Control Systems Manual de usuario descargar pdf (Pagina 265)

100

101

Section 7. Installation

265

Figure Running-Average Frequency Response (p. 266) is a graph of signal

attenuation plotted against signal frequency normalized to 1/(running average

duration). The signal is attenuated by a synchronizing filter with an order of 1

(simple averaging): Sin(πX) / (πX), where X is the ratio of the input signal

frequency to the running-average frequency (running-average frequency = 1 /

time length of the running average).

Example:

Scanperiod=1ms,

Nvalue=4(numberofpointstoaverage),

Running‐averageduration=4ms

Running‐averagefrequency=1/(running‐averageduration=250Hz)

Input‐signalfrequency=100Hz

Inputfrequencytorunningaverage(normalizedfrequency)=10

0/250

=0.4

Sin(0.4π)/(0.4π)=0.757(orreadfromfigureRunning‐Average

FrequencyResponse

(p.266),wheretheXaxisis0.4)

Fora100‐HzinputsignalwithanAmplitudeof10‐Vpeaktopeak,a

runningaverageoutputsa100‐Hzsignalwithanamplitudeof7.57‐V

peaktopeak.

There is also a phase shift, or delay, in the AvgRun() output. The formula for

calculating the delay, in number of samples, is:

Delayinsamples=(N‐1)/2

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.

1 2 ... 260 261 262 263 264 265 266 267 268 269 270 ... 565 566

Comentarios a estos manuales

Sin comentarios

Campbell-scientific CR800 and CR850 Measurement and Control Systems Manual de usuario Pagina 265

Comentarios a estos manuales

Relacionado con productos y manuales para Instrumentos de medición Campbell-scientific CR800 and CR850 Measurement and Control Systems