| Parameter | Description |
|---|
| Spectral Measurement | Contains the following options:
- Magnitude (peak)—Measures the spectrum and displays the results in terms of peak amplitude. You typically use this measurement with more advanced measurements that require magnitude and phase information. The magnitude of the spectrum is measured in peak values. For example, a sine tone of amplitude A yields a magnitude spectral value of A at the sine tone frequency. You can unwrap the phase spectrum or convert it from radians to degrees by setting Phase to Unwrap phase or Convert to degree, respectively. If you place a checkmark in the Averaging checkbox, the phase of the spectrum is zero for averaging.
- Magnitude (RMS)—Measures the spectrum and displays the results in terms of root-mean-square (RMS). You typically use this measurement with more advanced measurements that require magnitude and phase information. The magnitude of the spectrum is measured in RMS values. For example, a sine tone of amplitude A yields a magnitude spectral value of 0.707*A at the sine tone frequency. You can unwrap the phase spectrum or convert it from radians to degrees by setting Phase to Unwrap phase or Convert to degree, respectively. If you place a checkmark in the Averaging checkbox, the phase of the spectrum is zero for averaging.
- Power spectrum—Measures the spectrum and displays the results in terms of power. All phase information is lost in the computation. You typically use this measurement to examine the various frequency components of a signal. While averaging to compute a power spectrum does not reduce the unwanted noise in a system, averaging is useful because it provides a reliable statistical estimate of the level of random signals measured.
- Power spectral density—Measures the spectrum and displays the results in terms of power spectral density (PSD). Power spectral density is a scaled version of Power spectrum, where the power present within each spectral bin is normalized by the frequency bin width. You typically use this measurement to examine the noise floor of a signal or the power in a specific frequency range. Normalizing the power spectrum by the bin width makes this measurement independent of the signal duration, or number of samples.
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| Result | Contains the following options:
- Linear—Returns the results in terms of the original units.
- dB—Returns the results in terms of decibels (dB).
|
| Window | Specifies the window to apply to a signal. - None does not apply a window to Signals.
- Hanning applies a Hanning window to Signals.
- Hamming applies a Hamming window to Signals.
- Blackman-Harris applies a Blackman-Harris window to Signals.
- Exact Blackman applies an exact Blackman window to Signals.
- Blackman applies a Blackman window to Signals.
- Flat Top applies a flat top window to Signals.
- 4 Term B-Harris applies a 4 Term Blackman-Harris window to Signals.
- 7 Term B-Harris applies a 7 Term Blackman-Harris window to Signals.
- Low Sidelobe applies a low sidelobe window to Signals.
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| Averaging | Specifies if the Express VI performs averaging. |
| Mode | Contains the following options:
- Vector—Computes the average of complex quantities directly.
- RMS—Averages the energy, or power, of the signal.
|
| Weighting | Contains the following options:
- Linear—Specifies linear averaging, which averages over the number of packets you specify in Number of Averages in a non-weighted manner.
- Exponential—Specifies exponential averaging, which averages over the number of packets you specify in Number of Averages in a weighted manner. Exponential averaging gives the most recent packets more weighting in the average than older packets.
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| Number of Averages | Specifies the number of packets to average. The default is 1. |
basis.