Thanks for asking a question on our blog.

It sounds like the peaks your seeing are the natural frequencies of the structure your exciting.

Your Finite Element Analysis is giving you a natural frequency of 2700Hz, from the practical testing you have carried out it would appear to be inclusive. You say you have performed the test twice, but you have quite different results each time. Any practical test should be repeatable, no matter how many times you carry out the same test you should get the same results. I would suggest carrying out the practical tests again, perhaps repeating the test three times to make sure no experimental error is creeping into the testing.

Please feel free to come back and let us know your new results.

Benjamin Franklin,
Chennai, India.

Thank you for asking a question on our blog.

Torque measurement is basically the measure of force being applied in turning a shaft. When a turning force is applied to a shaft the shaft twists by a very small amount. This twisting produces some deformation in the material of the shaft. This twisting is in a direction at 45 degrees to the axis of the shaft. The shaft effectively stretches slightly in that direction.

The shaft also exhibits a compressive force in the opposite 45 degree direction.

So if you mounted strain gauges at both +/- 45 degrees perpendicular to the shaft axis you should see both the compression and the extension forces.

With regards as to how to measure this whilst the shaft is moving is a more difficult question, it depends on the shaft itself and what you’re doing.

Generally we would use some wireless strain gauges for this application, but that might not be practical for your application.

I’m PhD student and I need to measure the torque transmitted to right and lift wheel by using strain gauges on each shaft connecting between differential and each wheel. without using torque transducers.

Do you can explain the correct direction for bonding the gauge and How I can measure the reading while it rotating.

thank you.

Thanks for asking a question on our blog.
I think you may have hit a technical barrier there, you have to pass the signals through a medium that allows for the mechanical rotation, if you just used cables they would soon become twisted and fail.

I have colleagues who have used wireless sensors, but these are even more expensive.

I would suggest that you need to find a mechanism in your budget.

I need a conversion table or formula for vibration units, say microns, mm/sec or whatever. My mail address will do.

Thanks.

Abiye Zerfu

I expect you’ve already had a look around the rest of the blog, but there are a couple of other posts that might help.

There is the article Notes On Fourier Analysis by Dr Mercer. This has some good illustrated examples and also looks at the mathematics behind the Fourier Transform.

Also, you may find 10 Great Fourier Transform Links helpful. This collects together several good WWW resources. One of the best links there is a series of lectures by Professor Brad Osgood of Stanford University. There are about 30 hour long lectures, but maybe the first few will help you.

Anyway, good luck with your thesis. If you have any specific questions then feel free to post a comment somewhere on the blog and one of our posters may be able to help.

I am a final year engineering student and I am doing my thesis on damage detection using distributed accelerometer. In this I will be using the Fast fourier transforms and know very little about the topic. Is there any chance you have any information that will help me understand the basic? Any help at all would be greatly appreciated.

Emma

I read about your article. I am currently doing a project, on the business & marketing side, on torsional vibration analysis. I really have a very limited knowledge on it so I want to know where can I use torsional vibration analysis apart from Motors and gearboxes. It is said that it can be used to any machine that rotates, could you perhaps provide me an example of other possible machine?

Best Regards,

Jasmin

http://machinesvideo.blogspot.com

thanks!

Interpolation could help if you have enough samples.
“Linear interpolation” from figures above is the simplest but with sin(x) and cos(x) is better.

May be the following papers will help to understand better the topic:

1. “ET 4 CO 198.pmd”, http://www.ieindia.org/pdf/88/88ET104.pdf

2. “9 CP PE 8.pmd”, http://www.ieindia.org/pdf/89/89CP109.pdf

3. “Revaluation and replacement of basic terms in the sampling theory”,
http://www.pueron.org/pueron/nauchnakritika/Th_Re.pdf

4. http://www.knowledgerush.com/kr/jsp/db/board.jsp?id=54913
A note about the definitions of “sine/cosine wave”, “sinusoidal/co-sinusoidal signal” and the “simplest band limited signals”.

Best regards
Petre Petrov

I am looking for a software to perform torsional vibration analysis of a mass elastic system ( engine + coupling elastic + pump). Does your software do such calculation?

Thanks,

Ademar.

Thank you for asking a question on our blog.

You pose an interesting question.

Strain and Acceleration are not commonly compatible types.
I am sceptical that you will be successful in this endeavour.

Acceleration, Displacement and Velocity are all related. For example an accelerometer will traditionally measure displacement and convert it to acceleration internally. The strain in the material is not really related to the acceleration.

A Strain Gauge will measure the strain in the material it is adhered to. This is not necessarily the acceleration of the component.

There may be a relationship between strain and vibration. You could measure the strain and draw a conclusion on the possible acceleration level. But you would need to first measure and categorise the relationship between the strain and vibration.

In my experience I would advise against it and try to find a way to use an accelerometer for your application.