Author Topic: vibration 10-20khz, which sensor?  (Read 686 times)

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Offline RogerThat

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vibration 10-20khz, which sensor?
« on: November 02, 2019, 09:37:34 am »

Spent all morning googling/searching/looking for which sensor to use. Anyone have a good ide? Am I dreaming about the bandwidth?? The highest bandwidth I found is around 5khz for a MEMS accelerometer.

I would like to have a very small sensor with analog output. The idea is to drill a hole in a bolt and pot the sensor in to it.
The bolt will then be fastened to the car engine which I would like to measure and output will be feed to a spectrum analyser.
The idea is to create a baseline FFT for the healthy engine and then being able to spot issue before it goes boom.

Offline branadic

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Re: vibration 10-20khz, which sensor?
« Reply #1 on: November 02, 2019, 09:56:06 am »
Though not metrology related, what about using a piezo accelerometer?

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Offline voltsandjolts

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Re: vibration 10-20khz, which sensor?
« Reply #2 on: November 02, 2019, 10:07:20 am »
Sounds like you are trying to re-invent the engine knock sensor, standard part made by bosch etc. They are piezo sensors.

Seems like MEMS is trying to get into this market though:
« Last Edit: November 02, 2019, 10:13:26 am by voltsandjolts »
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Offline RoGeorge

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Re: vibration 10-20khz, which sensor?
« Reply #3 on: November 02, 2019, 11:04:40 am »
Another way would be to do LASER vibrometry, it can sense vibrations without physical contact, from a distance, on all 3 axes and with very high precision, but much more expensive.

Offline RogerThat

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Re: vibration 10-20khz, which sensor?
« Reply #4 on: November 02, 2019, 11:58:57 am »
Knock sensor, why didn't I think about that, perfect  :-+

Offline DaJMasta

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Re: vibration 10-20khz, which sensor?
« Reply #5 on: November 02, 2019, 03:51:04 pm »
MEMS accelerometers are not the right kind of technology, you definitely want the piezo stuff - either IEPE or charge mode (for higher temperature operation).  You can find pretty high sensitivities to maybe 10kHz worth of bandwidth, but  higher frequency options are available.  Just remember that your attachment method will mean a HUGE amount to your bandwidth.  For such a high frequency range you will need a solid physical connection to the DUT - so like integrated metal mounting studs or similar.  Not affiliated with any companies, but I'd look at stuff by PCB Piezoelectronics, Endevco (Meggitt), Dytran, Bruel & Kjaer, etc - that's likely the class of measurement device you're looking for.

Generally a measurement system looks like:
Accelerometer -> Charge converter/signal conditioner -> acquisition device, though especially with IEPE sensors, you can find some digitizers with the current source integrated that are designed for accelerometer measurement.

Offline Henrik_V

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Re: vibration 10-20khz, which sensor?
« Reply #6 on: November 04, 2019, 12:31:10 pm »
Common metrology grade sensors for this frequency range are Bruel & Kjaer type 8305-001 or Endevco type 2270WH. These are the single ended versions of the back to back types, both uses for secondary calibration. 
Primay calibration is done via laser interferometry, nowadays mostly with the obove mentioned laser dopppler vibrometers with a digital, RF or IQ  output.
(commonly an analog voltage output proportional to velocity is provided, but that isn't primary anymore ;) )

For a cost effective informational measurement a knocking sensor and a DIY charge amplifier and a soundcard is fine:)
For a good and easy measurements The Modal Shop ('PCB') had a vibration pickup with a USB connector (with internal 'Soundcard') .. I had one for some weeks to play with ....   

« Last Edit: November 04, 2019, 02:08:59 pm by Henrik_V »
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