Listening to Accelerometers

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Steve Smith
Pico Staff Member
Pico Staff Member
Posts: 1016
Joined: Sun Aug 25, 2013 7:22 am

Listening to Accelerometers

Post by Steve Smith »

When it comes to the diagnosis of illusive noises (Wheel bearings spring to mind - topic17901.html?hilit=wheel%20bearing).

It occurred to me how useful it would be if we could listen to accelerometers as we may be attached to the source of the noise. (I.e. the accelerometer could be attached to the hub with the offending bearing)

The advantage here would be an audio recording of offending noises at the point of contact, insulated from ambient noise (unlike an Omni-directional mic)

There is an option that we can use in the form of a "cheat" for now but rest assured work is always in progress at Pico to update software for such features

If we connect our accelerometer in Multiple Sensor Mode but inform the software a mic is connected instead of the accelerometer, we can obtain an audio recording of whatever the accelerometer is mounted too!
NVH Set up
NVH Set up
Please see a typical Single to Double BNC adapter below
Single to Double BNC adapter
Single to Double BNC adapter
Note the connection set up below using the double BNC adapter above. Channel A and D are connected to the same accelerometer/interface.
Channel A set up as an accelerometer, Channel D set up as Mic
Hardware Set Up
Hardware Set Up
Channel B and C are also set up using another accelerometer in the same fashion

Below we have an NVH capture from a Range Rover set up follows (using only 2 x accelerometer and no microphones)

Channel A Accelerometer (LH Front Wheel)
Channel B Accelerometer (RH Front Wheel)
Channel C Microphone (RH Front Wheel)
Channel D Microphone (LH front Wheel)
NVH Screen shot using Accelerometers as Mic
NVH Screen shot using Accelerometers as Mic
The vehicle was then driven at the relevant speeds and the results above speak for themselves
TEST 1 ALAN 2 X ACCEL AND MIC MARKER = KNOCK.pddata
Range Rover Wheel Bearing failure
(18.09 MiB) Downloaded 419 times
Please open the file above and hide the relevant channels:
To hide channels, right click on screen and select “Channel in View” to deselect the channels you wish to hide leaving only those you wish to analyse.

This will enable you to listen/playback each accelerometer (CH C & D) and so determine the offending bearing.

N.B.

Whilst the dB level will not be accurate when using the accelerometer in this fashion, we can use multiple accelerometers to carry out relative measurements.

The use of the NVH microphone remains essential as a cabin reference or to evaluate noise levels and frequencies beyond the detection zone of the accelerometer

To add to the above:

1. We simplify the analysis/diagnosis as the audio capture resembles the vibration capture in the spectrum thanks to the reduction in the noise floor.

2. During playback background noise is eliminated

3. This technique improves our audio analysis techniques

4. The number of cable runs from hub to cabin are reduced where no external mic is required

5. Accelerometer is capable of producing audio up to 1500 Hz which covers many of the nuisance noise issues for automotive

6. Reduces the risk of inadvertently recording conversations that could be deemed “awkward” during playback with customers.

Just to elaborate on this point 6 whenever we record cabin noises with a Mic, be aware it is a mic and it records EVERYTHING!!!!

I hope this helps, take care…….Steve

P.S Here is the offending bearing:
Offending bearing
Offending bearing
And again under the microscope:
Bearing race
Bearing race
Bearing Roller
Bearing Roller

Martinjensen
TwoWaves
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Posts: 54
Joined: Wed Feb 13, 2013 6:22 pm
Location: Denmark

Re: Listening to Accelerometers

Post by Martinjensen »

Hello Steve.

This is a great tip, and i will try this the next time a car with a failed bearing rolls into the shop.
This seems to be a much better way to confirm a failed bearing (And to document the repair)
If we just want to listen to the bearings, could we then skip the use of channel a and b in your example? then we would have the opportunity to listen to all 4 bearings at the same time (If we by 2 additional accelerometers)

Thank you for your continued support.

Regards Martin

victor2k
TwoWaves
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Posts: 310
Joined: Thu Jan 28, 2016 7:17 am

Re: Listening to Accelerometers

Post by victor2k »

Hello Steve,
Can be used "the listening to acceleromer" step to choose the better point of listening/capture in setup of the desired vibration? :)
How many accelerometers/microphones can be used with a NVH Starter kit/licence?
Thank you

Steve Smith
Pico Staff Member
Pico Staff Member
Posts: 1016
Joined: Sun Aug 25, 2013 7:22 am

Re: Listening to Accelerometers

Post by Steve Smith »

Hello and thank you for the feedback.

You are correct Martin, you could connect 4 x accelerometers to a 4 channel scope and use them as "listening devices" if you inform the software you have connected 4 x microphones.

This will most certainly speed up your wheel bearing diagnosis with documented data which includes audio playback for the customer.

Victor, that is a good catch too, "using the accelerometer like a stethoscope" to listen and locate the intense point of noise/vibration, thank you.

The number of accelerometers/Mic's that can be used with your scope is governed by the number of channels on your scope. This is either 2 or 4 in the case of Automotive Scopes using NVH software (4 devices is the max)

There is a useful kit comparison chart which can be viewed here https://www.picoauto.com/products/noise ... ccessories but I will add the image below.
Compare Kits
Compare Kits
If you click on "Compare NVH Kits" and then "Help Me Choose" it will guide you to what kit/accessories are suitable for you.

I hope this helps, take care.......Steve

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