aacury
Posts: 2
Joined: Wed Jun 12, 2019 5:20 pm

Connecting a commercial accelerometer to RaspPi

Wed Jun 12, 2019 5:45 pm

Hey guys,

I've been using RaspPi along with MPU accelerometers (6050 and 9250) to assess structural vibration, mainly in laboratory. Even though the results in frequency domain analyses were acceptable - compared to commercial accelerometers - the MPU's signal-to-noise ratio for small amplitude readings in the time domain is very low in my applications.

Thus, in order to circumvent this limitation, I'm considering to connect commercial accelerometers that I've got such as Kyowa AS-1GA (https://bit.ly/2X9upl5) and Bruel 4507B (https://bit.ly/2Rc3Zde) to RaspPi 3 and to RaspPi Zero W. The idea is to gather the "best of two worlds': sensitive accelerometers with Wi-Fi data transmission.

So, I'm seeking help to clarify these two aspects:

1) Is it possible to connect commercial accelerometers to RaspPi 3 (ou Zero W) directly? For instance, the Kyowa accelerometer's cable has 4 wires (E,+,-,Ground). As for the Bruel's, it is a coaxial cable.

2) Which libraries would I need to tackle the readings from the accelerometers?

Sorry for the long post and thanks in advance.

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omegaman477
Posts: 145
Joined: Tue Feb 28, 2017 1:13 pm
Location: Sydney, Australia

Re: Connecting a commercial accelerometer to RaspPi

Fri Jun 14, 2019 2:25 pm

These type of Laboratory Accelerometers are usually either voice coil or piezo in construction. Both outputting low ANALOGUE DC signals, typically around 1vdc/g. THey send a raw signal, allowing your instrumentation to see peaks curves and spikes. Unlike the chip style accelerometers (usually a Hall Effect Gaussmeter) which produce a digital signal, but of much lower resolution and sensitivity (And cost).

So you need to use a high precision Analogue to Digital ADC Hat to convert these analogue signals into a digital value. Like this guy for the RPI Zero https://thepihut.com/products/adc-pizero You are looking for an instrumentation grade ADC.

You may also need some filtering and signal conditioning as well. These type of transducers produce very low voltages and hence are subject to stray EMF and electrical interference (hence the coax connectors)

As you sampling vibration you will need blistering sample rates (like 100-200 samples per second) and reasonable resolution (12-16 bits).

All good ADC hats and modules will have at least a Python library.

getting the data into your application is one thing, analysing large amounts of complex sample data is another. COmmercial units will often employ DSP chips to take on the workload.

Depending on your requirements (accuracy, resolution and sample range) you may be pushing the limits of a RPI.
..the only thing worse than a stupid question is a question not asked.

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Pekka
Posts: 20
Joined: Mon Nov 19, 2012 4:11 pm

Re: Connecting a commercial accelerometer to RaspPi

Mon Jun 17, 2019 5:07 am

We use SiliconDesigns accelerometers for various vibration measurements in traffic. They output an analogue voltage signal which needs to be digitsed. For this we use a MCP3208 ADC chip (on the Baart ADC board), which communicates over SPI interface. For communication we use C/C++ and the BCM2835 library (see this example application for sampling accelerations of a bicycle). The achievable sample rates are up to 500 SPS for simultaneously sampling 8 analogue channels.

aacury
Posts: 2
Joined: Wed Jun 12, 2019 5:20 pm

Re: Connecting a commercial accelerometer to RaspPi

Tue Jun 25, 2019 7:48 pm

Thank you omegaman477 and Pekka for your inputs. Much appreciated!

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