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PEM (General)
tatsuki.washimi - 11:42 Monday 02 March 2020 (13263) Print this report
Consideration of current PEM injection analysis

To check the validation of current PEM injection method, I analyzed the acoustic component in REFL table accelerometer signal.

In this result (plot), it is over estimated.

In my hyposesic, it's coming from the direct vibration from the speaker.


The microphone detects the enviromental sound (Senv) and the injected sound (Sinj).

The accelerometer detects the enviromental vibration (Venv) , the vibration from speaker (Vinj), and the total sound with coupling function CA.


From injected data and background data for MIC and ACC, the coupling function CA is caliculated as


If we ignore Vinj, the coupling function and acoustic component are overestimated as

The same situation occurs in other channels.

So it is difficult to evaluate any valid environmental noise budget from the acoustic injection by large speaker, and we need to do local shaking test.

However, anyway, the fact that the area around REFLEX is delicate against environmental noise (sound and seismic) is true.



I  tried to swap the main channel and sub channel  from (table ACC, booth MIC) to (booth MIC, table ACC).

The result is here. Overestimation is not occures. From this plot, the vibration of REFL table may be direct one, rather than acoustic coupling.

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tatsuki.washimi - 13:55 Tuesday 03 March 2020 (13295) Print this report

In the previous discussion, the microphone channel was not correct. (See
So I reproduce the same analysis (evaluation for acoustic components in accelerometer signal) for the correct channel (K1:PEM-SENSOR_BOOTH_IMC_BNC3)


(1) White noise 60-3000 Hz, DAC amplitude = 2000 counts
 - Background data : from GPS 1266985700, 100sec
 - Injection data :  from GPS 1266985880, 64sec

Projected acoustic noise is almost same with ACC signal. So the ACC signal is occupied by the sound and is is well evaluated. 


(2) White noise 60-3000 Hz, DAC amplitude = 5000 counts
 - Background data : from GPS 1266986785, 64sec
 - Injection data :  from GPS 1266986945, 100sec

We can see many overestimated peaks.They are near-miss of the resonant peaks. [See]

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