请问spectrum mask是何意

myyear1984

不是学射频的，可最近项目需要，看芯片资料中看到了这个名词，不懂何意，还有前辈指点一下spectrum mask的来龙去脉[em13]

kinpoagilent

The Spectrum Mask



As we have seen, healthy machines will show minor deviations in their vibration spectra because of small load variations, temperature variations, line voltage variations, and background noise level fluctuations. These variations in vibration signatures can cause false alarms to be generated if the raw spectrum is directly compared to a valid reference spectrum. For this reason, it is desirable to generate a so-called mask spectrum from the reference spectrum. The mask is a new spectrum made by increasing the levels in the reference spectrum by various amounts at different frequencies. For instance the mask might be 6 dB above the reference at 1X, but only 4 dB above the reference at 2X.

A good staring point for establishing the mask is to add one standard deviation in level at each spectral peak to the averaged reference spectrum. A large class of machines will be found to produce averaged spectra with fairly small standard deviations, and with these machines in particular it is a good idea to perform the spectrum averaging and then generate the mask by adding one standard deviation to the average spectrum at each frequency. A group of machines which exhibits large standard deviations in level when making the reference will be more difficult to deal with in generating the mask, and the mask levels will have to be higher than one standard deviation above the reference.

The determination of the shape of the mask spectrum can be fairly complicated, and it depends on the machine in question and normal variation in its vibration spectral levels at different frequencies. This can only be determined by looking at a series of historical spectra and applying good judgment and a good knowledge of the machine itself.

kinpoagilent

The Spectrum Mask

As we have seen, healthy machines will show minor deviations in their vibration spectra because of small load variations, temperature variations, line voltage variations, and background noise level fluctuations. These variations in vibration signatures can cause false alarms to be generated if the raw spectrum is directly compared to a valid reference spectrum. For this reason, it is desirable to generate a so-called mask spectrum from the reference spectrum. The mask is a new spectrum made by increasing the levels in the reference spectrum by various amounts at different frequencies. For instance the mask might be 6 dB above the reference at 1X, but only 4 dB above the reference at 2X.
A good staring point for establishing the mask is to add one standard deviation in level at each spectral peak to the averaged reference spectrum. A large class of machines will be found to produce averaged spectra with fairly small standard deviations, and with these machines in particular it is a good idea to perform the spectrum averaging and then generate the mask by adding one standard deviation to the average spectrum at each frequency. A group of machines which exhibits large standard deviations in level when making the reference will be more difficult to deal with in generating the mask, and the mask levels will have to be higher than one standard deviation above the reference.
The determination of the shape of the mask spectrum can be fairly complicated, and it depends on the machine in question and normal variation in its vibration spectral levels at different frequencies. This can only be determined by looking at a series of historical spectra and applying good judgment and a good knowledge of the machine itself.