Thank you for asking a question on our blog.

Your question is quite simple, if there is a piece of metal which is vibrating does this vibration induce any strain in the metal?

The answer is not so simple, it might be and it might not be inducing some strain. It depends on the vibration and if the metal is supported well or not, the size of the metal mass and so on.

The basic rule is this is the metal is bending in anyway then there will be some stress/strain.

I would expect any piece of any metal that is vibrating to move around as it’s own structure and therefore I would expect various amounts and directions of stress and strain in the material.

I hope this answers your question

I am working with strain gauge measurement on the electrical steel lamination, any effect with strain if while I am measuring the lamination vibrate ?

Thanks.

You are quite correct, thank you for pointing this out.
I have corrected the article.
The formula is only an example and is not actually correct in any case it just intends so show the process in action rather than any hard results.

I don’t think being correct is being pedantic!

Sorry to be pedantic, but the second equation for resistance of a piece of copper wire appears to be incorrect. The wire is stretched to 2m and its diameter decreases to 0.5mm^2, which equates to 0.0005m^2, not 0.005m^2. So the resistance is 0.144 Ohms, not 0.00144 Ohms.

Yours sincerely,

Bruce Hefford

http://www.datatel-telemetry.de/en/

It sounds like your using the strain gauges as part of a weigh scale.

Basically the strain gauges are put under load by the item your measuring, this changes their resistance values. The load puts the material the gauges are on under strain.

When you put a known mass, like 1 kg for example, on the scale you monitor the voltage change and therefore the resistance change in the elements of the bridge, hence you have a known voltage change for a known mass. Thus you can calculate how the voltage will change for any mass and therefore you have a linear sensitivity in volts per kg or unit.

Thanks for making a note on our blog.
You are quite correct, we have updated the article, thank you for pointing this out.

If you have any further comments or questions, please feel free to share them.

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.

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.

Thank you for your helpful article about the strain gauges.

I would like to ask you a question. Is it possible to measure vibrations with the strain gauges? I do not want to use an accelerometer because they are too big for my application (I wanted something like the surface bonded strain gauges).

Thank you in advance!

Thank you for asking a question on our blog.

Strain gauges are effectively wires and long wires at that. They can behave like aerials and pick up electrical signals from any other sources, for example mains electricity at 50Hz is quite a common source of noise.

The sample rate you choose is very important. You must use a sample rate that reflects what you’re looking for. If you are studying the human body and motion on a bicycle we are talking a few Hz at most. For example, an effective bandwidth of 10Hz would need a sample rate of 24Hz. If you sample higher you will simply be collecting noise, you will gain no useful information below 10Hz.

Now perhaps 24Hz is not high enough for your application or is not practically possible. In this case you should consider using a low pass filter on your captured data. This will remove the effects of the high frequency noise you are seeing. The result will be the dynamic strain you are looking to study.

Thank you for your question.

It really sounds like your trying to do it all in one giant step. Perhaps you should break the problem down into smaller chunks.

A strain gauge is like a resistor, a strain gauge bridge is made of 4 resistive elements.

All the resistors in the bridge should be of the same value, 120 Ohms is often used in industry. The resistors must be the same value to balance the bridge. There are other techniques to balance a bridge, but for clarity in this case we’ll assume the bridge must be balanced by the four resistors having the same resistance.

When you have setup your bridge you should attach the active strain gauge (assuming you have only one active element in your bridge) to the area where you are interested in knowing the strain. I am afraid we cannot offer advice about where to attach your gauge.

You should then be able to read back a value of zero volts from your bridge, then when your material under test has some forced applied, which produces a strain in the area your gauge is attached, you’ll see the voltage from the bridge change to something other than zero. This voltage change is proportional to the strain in that gauge.

You simply then use the bridge and gauge factor, supply voltage, output voltage and non-deformed and deformed gauge resistance values to calculate the strain.

Thank you for your comments.

Your points are well made and correct sir. The picture was intentionally a 2 wire system in order to illustrate that the strain gauge at a very basic level is a very long single piece of wire, or more simply a resistor. The first part of the article attempts to explain to the reader what a strain gauge is and how they work in a very basic sense before moving on to more complex actual real world issues.

As the article tries to show in figure 4 the classical quarter bridge configuration is in fact a 3 wire system. The wires connecting to the gauge in figure 4 should be the same length and as your rightly state they should follow the same route, for the reasons you state. By following these points the bridge will be balanced by virtue of the fact the resistance of the lead wires will be the same.

Your point about the lead wiring running together is a valid point, in most cases this sort of point is glossed over, but with experience and wisdom with strain gauges these things are learnt. Thank you for sharing your knowledge with our readers.