IIS3DWB sensitivity and resolution

[Sudhir]

I would like to find out the if the following assumptions are correct. It offers 16 bit (65K) level resolution. The sensitivity in mV/g would about 3000/2g for the 2g range? That seems rather high because typically you see 500 mv/g values. Also I am not sure how the 26.6 K data rate translates into 6 KHz bandwith specified in the datasheet.

[Eleon BORLINI]

Hi @Sudhir​ ,

the IIS3DWB is a digital sensor, so it's sensitivity is defined in terms of mg/LSB (and it's value is 0.061 for the +-2g FS).

It's not so straightforward to convert the LSB into analogic voltage, since it passes through the internal ADC.

About the 6kHz bandwidth, this limitation comes from the Sensor resonant frequency (see datasheet, p.5), that is around 7kHz for the 3 axis. For this reason, the bandwidth is limiter below the resonance, to guarantee a linear frequency response. Using the acquisition frequency to 26.6kHz increases the temporal resolution of the acquired data (for example, for FFT conversion).

-Eleon

[Sudhir]

Thanks for the detailed answer. I guess +-2g= 4000 mg, and 4000mg/65K (16 bit)=0.061LSB.

I am trying to pick from the variety of acceleration/vibration sensors that you offer and it is proving a bit difficult.

The IIS is industrial perhaps from temperature and wide bandwidth reasons but you also have sensors in the sensortile.box that seem equally good.

How do I find the mg/LSB and the resonant frequencies and the max ODR rate for your products in a comparison grid?

What is the difference between labels vibration sensor and acceleration sensor?

I love ST products and thanks for your response.

[Eleon BORLINI · Accepted solution]

Hi @Sudhir​ ,

>> I love ST products and thanks for your response.

First thank you very much for your endorsement, it's well appreciated 🙂

>> I guess +-2g= 4000 mg, and 4000mg/65K (16 bit)=0.061LSB

Right.

>> How do I find the mg/LSB and the resonant frequencies and the max ODR rate for your products in a comparison grid?

Unfortunately, I cannot share the for all the sensors, if not reported in the datasheets...

However, I can surely tell you that the ST accelerometers with the maximum (real) bandwidth is the IIS3DWB.

This actually defines the difference between a standard accelerometer, in the framework of applications like the predictive maintenance: beyond 1k/2k frequency, you can define an accelerometer as a vibrometer.

-Eleon

[Chubs]

@Sudhir,

Apart from IIS3DWB, almost all the MEMS Accelerometers from ST are bandwidth limited to 400Hz except 2-3. 

I have had to do the detailed comparison of all currently active MEMS accelerometers from ST & found only a few with Noise Density less than 100µg/√Hz to be of any real value for Vibration based monitoring.

LISDTW, IISDPLC, LISDW12 for instance.