MR8740、MR8741_user_manual_eng_20191016H.pdf - 第294页
12.8 FFT Analysis Modes 282 W aveform Example T ransfer Function From the input and output signals, the transfer funct ion (frequency cha racteristic) of a measurement system can be obt ained. It can also be displayed as…
12.8 FFT Analysis Modes
281
11
Chapter 12 FFT Function
12
Waveform Example
LPC (Power Spectrum Density )
When the spectrum shape is complex and hard to comprehend with either linear or power spectra, a
rough spectrum structure can be obtained.Main uses:
To obtain a spectral envelope using statistical methods
See: About the Functions"12.8.2 Analysis Mode Functions" (p.293)
Axis Display Type Description
X axis
Linear Frequency is displayed with equal spacing
Log Frequency display of logarithm interval
Y axis
Lin-Mag The analysis data is displayed linearly.
Log-Mag(logarithm)
Analysis values are displayed as dB values. (0 dB reference value: 1eu
2
/Hz)*
* eu: engineering units that are currently set are the standard (e.g., when the unit settings is volts, 0 dB = 1 V
2
/Hz)
X axis: Log
Y axis: Lin-Mag
X axis: Log
Y axis: Log-Mag
• Always specify the order (from 2 to 64). Higher orders can expose finer spectral details.
• Amplitude values provided by LPC are not always the same as the power spectrum density.
• If an error occurs during analysis, no waveform is displayed.
• Noise-like phenomena can strongly affect the spectrum shape.
12.8 FFT Analysis Modes
282
Waveform Example
Transfer Function
From the input and output signals, the transfer function (frequency characteristic) of a measurement
system can be obtained. It can also be displayed as a Nyquist plot.
Main uses:
• To inspect a filter’s frequency characteristic
• To inspect the stability of a feedback control system (using the Nyquist plot)
• To inspect the resonance characteristic of an object using an impulse hammer and pick-up sensor
See: About the Functions"12.8.2 Analysis Mode Functions" (p.293), "Linear Time-Invariant Systems" (p.A14)
Axis Display Type Description
X axis
Linear Frequency is displayed with equal spacing
Log Frequency display of logarithm interval
Nyquist display
Displays the real-number component of the input-output ratio.
Y axis
Lin-Mag
Displays the input-output ratio linearly (dimensionless units).
Log-Mag(logarithm)
Displays the input-output ratio as dB values.
Lin-Real
Displays the real-number component of the input-output ratio (dimensionless
units).
Lin-Imag
Displays the imaginary component of the input-output ratio (dimensionless
units).
Nyquist display
Displays the imaginary component of the input-output ratio.
Normal display
X axis: Log
Y axis: Lin-Mag
Normal display
X axis: Log
Y axis: Log-Mag
Normal display
X axis: Log
Y axis: Lin-Real
Normal display
X axis: Log
Y axis: Lin-Imag
Lin-Imag
Nyquist display
12.8 FFT Analysis Modes
283
11
Chapter 12 FFT Function
12
Waveform Example
Cross Power Spectrum
The product of the spectra of two input signals can be obtained. The common frequency components
of two signals can be obtained.
Using the voltage and current waveforms as input signals, active power, reactive power and apparent
power can be obtained at each frequency.
Main uses:
To inspect common frequency components of two signals
See: About the Functions"12.8.2 Analysis Mode Functions" (p.293)
Axis Display Type Description
X axis
Linear Frequency is displayed with equal spacing
Log Frequency display of logarithm interval
Nyquist display
Displays the real-number component of the input-output ratio linearly.
Y axis
Lin-Mag
Displays the squared value of amplitude contents of analysis data linearly.
Log-Mag(logarithm)
Displays the amplitude contents of analysis data as dB values. (0 dB reference
value: 1eu
2
)*
Lin-Real
Displays the squared values of the real component of analysis data linearly.
Lin-Imag
Displays the squared values of the imaginary component of analysis data linear-
ly.
Nyquist display
Displays the imaginary component of analysis data linearly.
* eu: engineering units that are currently set are the standard (e.g., when the unit settings is volts, 0 dB = 1 V
2
)
Normal display
X axis: Log
Y axis: Lin-Mag
Normal display
X axis: Log
Y axis: Log-Mag
Normal display
X axis: Log
Y axis: Lin-Real
Normal display
X axis: Log
Y axis: Lin-Imag
Lin-Imag
Nyquist display