NVH kit accelerometer

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NVH kit accelerometer

Postby Valhalla » Sat Aug 01, 2015 11:31 pm

I'm keen to explore the potential of the NVH kit, having seen the two (currently) published case studies. Has anyone got anything further to add regarding the potential of this equipment to isolate suspension-system clonks/rattles/etc. etc.?

What I am assuming, because it is not explicitly stated in the documentation, is that the accelerometer is sensitive in one axis - presumably the axis normal to the plane of the surface to which the magnetic mount and accelerometer are mounted? Has anyone got any data, measured or implied, regarding the relative sensitivities of the three axes, and subsequently, what the rejection is likely to be of lateral acceleration over vertical acceleration (using the normal axis as the vertical).

The reason I ask these questions is that;
a) it would help to site the accelerometer in the best place to receive noise (centre of a steel panel, for example) for general measurement
b) it would help to justify a mounting block that allowed the sensor to be angled in one plane or another (ie. away from vertical) to read vibration from one direction in particular, so helping to isolate a faulty component amongst many parts without having to make multiple measurements with the sensor placed at different points around the car.

Any thoughts?

Stuart
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Re: NVH kit accelerometer

Postby Technician » Sun Aug 02, 2015 9:01 am

Not sure if this will help.

The Pico Diagnostics NVH Kit from Pico Technology is the cost-effective answer to the many NVH problems facing technicians today. Providing real-time diagnosis to the technician in the form of either: a bar graph, a frequency chart, a 3D frequency chart, RPM order or road speed view. :)
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Re: NVH kit accelerometer

Postby Steve Smith » Mon Aug 03, 2015 8:38 am

Hello and thank you both for the posts.

To answer your questions surrounding suspension knocks, rattles and creaks etc.

I would be very careful about sporadic noise location and detection using a single accelerometer/ microphone as I have had mixed success locating particular noises that are very infrequent or of low sound level.

From experience I have found multiple microphones placed about the area of concern have helped to locate the source. I refer here to “Chassis Ear” or a similar device in these scenarios.

For example, looking for a single “Knock” sound over uneven road would most certainly be detected by the accelerometer but due to the infrequent nature, this would not be transferred to the frequency display. (We need vibrations/noise present for around 3 seconds)

This is an area under review here at Pico and I have no doubt we will produce a solution at some point in time where these noises will be detected using multiple “clip on devices”

Moving onto the NVH kit accelerometer sensitivity and axis measurement, the accelerometer included in the NVH kit is in fact a 3 axis device capable of measuring vibration in 3 directions X, Y, and Z or to put this another way, X axis vibration Fore/Aft, Y axis vibration Vertical, and Z axis vibration Lateral.

However all three axis are summed together inside the NVH interface box in such way as to give the end user an overview of all axis. Here then there is no rejection of a particular vibration in a specific axis/direction, everything is accounted for.

The real beauty of such a feature is that with one scope channel, the end user will pick up a vibration present even when the direction of vibration is unknown.

For example, mounting the accelerometer vertically on a chassis member will detect all vibrations in all axis/directions, as will mounting the accelerometer horizontally on the same chassis member.

What you may experience is a reduction or an increase in the amplitude of a particular vibration, but the frequency will remain the same and this is what we need to identify. (The frequency of a vibration)

I agree with all you are saying Stuart regarding “multiple measurements” to attempt to identify the direction of a vibration and we are working towards a solution where all 3 axis can be measured and displayed individually.

I hope some of this helps, take care…….Steve
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Re: NVH kit accelerometer

Postby Valhalla » Mon Aug 03, 2015 10:33 pm

Steve,
Many thanks for your reply. It answers so many questions. Not least, the validity in mounting the accelerometer by magnet to the seat fixings.

Do you see the future "Chassis Ear" systems dovetailing into the NVH kit, or becoming a product in its own right? I'm still pretty keen to try an NVH kit for some of my work, not least that I also spend a lot of time with engines and rotating systems, but I would prefer to hang-on if the kits are mutually exclusive to one another - not least the declaration that once an oscilloscope has been keyed for the NVH kit, it cannot be transferred. Better to wait and save-up for all the new kit in one, then! I'm still smarting over missing out on the 4425 features with my, nearly new, 4423!
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Re: NVH kit accelerometer

Postby Steve Smith » Tue Aug 04, 2015 12:14 pm

Hello Stuart thank you for the feedback.

Interesting question surrounding the Chassis Ear system, as to incorporate such a feature into NVH would be ideal and logical.

I have carried out some testing recently with a view to "listening devices" linked into PicoScope!
I must stress though this is early days and development is continual, not just in NVH territory.
Once the new hardware can deliver acceptable data the next step is software and how we choose to display/present test results.

I am huge fan of NVH along with the Chassis Ear as they compliment one another perfectly, it would be difficult to imagine them as separate products.

I would like to see them somehow incorporated so as to enable the additional features of PicoScope within Chassis Ear.(I think a must have tool for sure)

You have raised a valid point surrounding NVH licensing and the purchase of your nearly new 4423. I guess the timing there was not in your favour when the new 4425 was launched but this should not deter you from upgrading or prevent you from licensing your current scope.

At present you appear in limbo with an excellent scope that can release all the benefits of NVH diagnosis yet you are holding out. Rest assured should you go ahead and purchase an NVH kit and license your 4423 we would assist you in an applicable fashion to transfer your license to your new scope.

I hope this is of some help, take care.......Steve
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Re: NVH kit accelerometer

Postby Valhalla » Tue Aug 04, 2015 10:12 pm

Thanks Steve,
I'm looking at the finances over the next couple of weeks. I'd like to do a bit of research anyway with the NVH kit, although it has to pay for itself over the next couple of years to be viable. I have one or two projects that may benefit from the application of this sort of tool. One of those may well be a useful "add-on" to the NVH kit software for the near-future;

Way back in the mid-90's, I did some OEM research in timing-belt oscillations and subsequent cam/injection mis-timing in a 2-belt system (one after another) on a Diesel injection system. As well as studying the modes of oscillation for various belt tensions and engine speeds, I looked at the effect on injection duration (start to end of true injection) at full-load (ie. max torque line on the engine). What became apparent at the time was that a clavis gauge was a useful device for getting the fine tune on a belt tension when the engine was stationary, but a microphone could impart even more information when listening to the belt on a running engine. The NVH kit could provide a useful way to a) set a timing belt to its correct tension, where the static frequency is known by the manufacturer - Renault is one that includes the frequencies in its workshop data, and b) highlight belt mis-tension and/or impending failure on a system before it is even disturbed, where a baseline has been established (through waveform data) on a known good system.

Cheers, Stuart
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Re: NVH kit accelerometer

Postby Steve Smith » Thu Aug 06, 2015 11:11 am

Hi Stuart, thanks for your feedback, I did not see that coming!

Microphone application for timing belt tensioning! WOW

I think this brings engineering level measurability and practices direct into the workshop which is something that has been missing for a long time.

I know from experience when struggling with diagnosis that there are tools out there with the ability to resolve issues but their expense and the training required simply renders them unreachable.

I am sure vibration/sound analysis whilst in its infancy at present will form part of any diagnosis as technology marches on.

This is another string to our bow and not to be ignored for sure.

I will add your post into the Ideas funnel here at Pico as it seems a very logical application.

Take care......Steve
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Re: NVH kit accelerometer

Postby Valhalla » Sat Aug 08, 2015 10:02 pm

Steve,
Well, I didn't look at the finances too much. I just took the plunge. Lots of things to try now, if I can ever get the couriers to deliver here....!

Stuart
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Re: NVH kit accelerometer

Postby Technician » Sat Aug 08, 2015 10:24 pm

Steve,

I'll have a look at my old Gates electronic timing belt tool which I bought from them some 15 years ago, it cost me if I remember correctly about £750 + Vat at the time, Gates advised back then that anyone who bought this electronic belt tension tool who experienced an engine fail because of incorrect belt tension, Gates advised that they would without quibble pay for the new engine.

I have not used this belt tool for a long long time, I am sure it measures frequency of the belt using a sensor on the end of a lead, but not attached to a scope.
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Re: NVH kit accelerometer

Postby Valhalla » Sat Aug 08, 2015 10:56 pm

If memory serves me correctly, these sensors are made up of two opposing microphones, attached to a C-shaped holder that is passed over the belt to measure it? Definitely no scope output in those days, but maybe a BNC on the sensor head that would allow a scope to be attached?
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