ST Mems Acceleromoters vs PiezoResistive sensor for Vibration sensing, advice needed

[Jvan .13]

Hi All

As suggestion stated this question relates to the choice of mems accelerometer vs piezoresistive sensors with amplification and the pitfalls to look for.

I looking to build a battery powered device that will be used for sensitive vibration on a pole. Frequency seems to be ranging from 0-1000hz maximum. I know from experience that piezoelectric sensor is/was best at low frequency detection but there has been alot of improvement in the mems range as of late and was hoping someone could share their opinion on the latest options from ST as it compares and relates to this application.

[Eleon BORLINI]

Hi @Jvan .13​ ,

ST MEMS technology for accelerometers and inertial measurement units is capacitive, and evolved improving bandwidth and noise level.

In particular, the class of vibration sensors such as the one of the IIS3DWB, can go far over 1kHz: it has an ultra-wide and flat frequency response range from dc to 6 kHz (±3 dB point) and ultra-low noise density: down to 75 µg/√Hz in 3-axis mode.

Moreover, all ST accelerometers have the capability to detect DC / low frequency, and can be configured with specific high-pass and/or low-pass filters to optimize the acquisition sensitivity in a particular frequency range of interest.

And, differently from PR devices, they are almost all digital and can be acquired without particular acquisition stages.

I know little about piezoresistive technology applied to accelerometers / vibrometers, but form literature they are used for shock detection (for example, PCB piezotronics smt ones), where the MEMS capacitive accelerometer is less accurate and can be potentially damaged (according to the shock intensity).

Of course, if you are searching for very high performances of frequency > 10kHz and shocks detection for your application, the PR device is the right choice, even if I believe that the price of the two kinds of accelerometers is not comparable...

This is a very vast field, but if my reply was somehow useful for your decision, please click on Select as Best at the bottom of this post. This will help other users with the same question to find the answer faster. 

-Eleon

[Jvan .13]

Hi Eleon
Thank you for the detailed reply. I looked at the PR accelerometer you are referring to and agree the price is not comparable. I was however not comparing it to those types of PR sensors but general purpose piezoelectric element (disk) with a front end amplifier and analog output into a ADC. The advantage of this setup is power consumption. With opamp running below 1uA and piezoelectric element using no power its ideal for battery.
I do like the St Mems accelerometer listed but at 1.1mA current is difficult for an always on application.
All this aside my question really referred to the sensitivity/accuracy aspect between Piezo and Mems sensors with the limiting factor of being low power.

[Eleon BORLINI]

Hi @Jvan .13​ ,

ok understood, but in the "analogic" case of the PR you have also to consider the current consumption of the ADC you need to digitalize the analogic signal coming from the PR microphone.

If you are interested only in the band below 1kHz, the IIS2DH is an accelerometer that consumes 185uA for ODR 5376Hz (but the mechanics cuts the sensitivity below ODR/2).

A true wide-band accelerometer is the LIS25BA, which goes up to 2.5kHz but consumes more than 1mA.

Also the LIS344ALH analogic accelerometer current consumption is very high compared with the Piezo sensor...

-Eleon

[YAlic.1]

Yes, I agree. LIS25BA is generally used for earbuds solution.

-- JH Park