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I am trying to do a noise/vibration profile on a piece of machinery in an incubator. Ideally, it should not be subject to vibration, but inevitably there will be some.

In addition to the internal vibration of fans there may be acoustic pickup and resonance in the metal supports.

So the methodology will be to glue a vibration sensor or microphone to the metal support and capture the signal on a PC. All expected frequencies are expected to be in the low audio band, with frequencies under (at a guess) 1kHz dominating.

The question is what types of pickups will be suitable? Initially I am thinking of using a moving coil microphone insert. Perhaps for lower frequencies (<50Hz) maybe a strain gauge. Has anyone done a project such as this that can offer suggestions?

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  • \$\begingroup\$ For a calibrated vibration profile, you should use an accelerometer designed for this purpose. The voltage output is very low, so you will need a preamplifier. This is how people measure the profile during vibration testing of products. These setups are not cheap. \$\endgroup\$
    – Mattman944
    Oct 18, 2022 at 16:00
  • \$\begingroup\$ @Mattman944 Maybe, but the vibration is so low that it is impossible to feel manually. Not tried biting the metal, but it's all going to be very low amplitude \$\endgroup\$ Oct 18, 2022 at 16:03

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Has anyone done a project such as this that can offer suggestions?

I've been involved in using strain gauges well beyond 100 kHz (plenty of times) looking for vibration and resonance on the turbines of aero engines. Because gauges have virtually zero mass (compared to the object vibrating), they introduce very little measurement effect. I designed the gauge excitation and signal processing circuits (along with other bits like the data acquisition). If this method is accepted by aero engine manufacturers then I would simply suggest it's "good enough".

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  • \$\begingroup\$ As I mentioned in a comment above, amplitudes are very low \$\endgroup\$ Oct 18, 2022 at 16:04
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    \$\begingroup\$ @DirkBruere it's probably still worth trying. Gauges don't cost much and, with frequencies below 1 kHz you can build very sensitive amplifiers at low cost from InAmps. Gains up to 1,000 should not be a problem. \$\endgroup\$
    – Andy aka
    Oct 18, 2022 at 16:13
  • \$\begingroup\$ Just did a quick "teeth test" ie I chewed the metalwork. Barely perceptible, but since we are measuring sub microgram loads it may be of significance. On Monday I will start with a microphone test and see what that picks up \$\endgroup\$ Oct 19, 2022 at 8:58

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