Rank: Guest 
|
Posted By Telstar
Looking for a laymans terms definition of how vibration magnitude is arrived at. I need something really basic that explains how a value of m/s2 is arrived at.
Thanks
|
|
|
|
|
|
Rank: Guest
|
Posted By RP
Vibration is measured in m/sec, ie. how far it will travel in a straight line, so if you move your hand up then down .5m the straight line would be 1m. Obviously equipment vibrates at a higher frequency than this but over a shorter time. So if vibration is measured using special equipment along the x and y axis, that is up/down, side to side, (you can also measure in a z axis diagonally) you would need to add up the figures and square it to get a value which is usable. This then is mulitplied by the average 8 hour working day (A8) to give you an exposure. Standards suggest, I think, 2.5m/s averaged over an 8 hour day. Equipment manufacturers are obliged to print this in their operators handbooks. So if they say a chainsaw produces 4.5 m/s it would mean that a person could use it for about 4 hours before being exposed to higher risks of injury. Now I have a head ache. HSE have a tool on their website that makes the task easy using a spread sheet to calculate the exposure time.
|
|
|
|
|
|
Rank: Guest
|
Posted By Smurfer
Ignore everything above by RP - sorry RP but it's complete rubbish.
Vibration is measured as acceleration whicvh is m/s^2.
|
|
|
|
|
|
Rank: Guest
|
Posted By Alan Hoskins
Smurfer is correct - vibration is cyclical acceleration and its units are metres per second per second. The only way to arrive at the value is to measure it using an accelerometer.
Manufacturers will already have done that and provide the information, but beware! Their testing will most likely have been on a new and unloaded tool. Once the tool begins to wear and when used on a job - say an angle grinder - the figures will be much higher.
Alan
|
|
|
|
|
|
Rank: Guest
|
Posted By Ken Dickson
Wel said both Smurfer and Alan.
Also keep in mind that the vibration data provided by tool manufacturers will not be in any way relevant to the vibration experienced in use. It is the task that generates at least 95% of vibration not the tool.
Ken
|
|
|
|
|
|
Rank: Guest
|
Posted By Advanced Safety
Telstar
I will avoid the mechanics, and just advise that you go on to the HSE website and download a free Vibration Calculator! Get the vibration impact level for the plant and the hours works and tap it into the Excel Calculator.
if you cant find it, e-mail me and i will send it to you
|
|
|
|
|
|
Rank: Guest
|
Posted By Advanced Safety
Ooops! sorry, think i misread the request. Although the definition can probably be found on the Vibration Website also.
|
|
|
|
|
|
Rank: Guest
|
Posted By Adrian Watson
Three quantities are available which could be used to assess vibration. Vibration can be measured in terms of acceleration, velocity or displacement. To describe these measurements fully, the direction must be known as well as the magnitude. Displacement is measured in millimetres, velocity in metres per second (m/s) and acceleration in metres per second squared (m.s-2). Of the three quantities, acceleration is the one normally measured.
As vibration levels are rarely constant, the equal energy principle is used to measure a long-term average for assessing vibration levels.
Regards Adrian Watson
|
|
|
|
|
|
Rank: Guest
|
Posted By Ron Hunter
thrum a ruler off the side of a desk. the oscillation is a fair approximation of what is happening with a vibrating tool. Draw a sine wave on a chart and explain that this is the changing velocity over time. Relate this to your oscillating ruler. The rest is SI Units. Velocity equals metres per second, acceleration is a rate of change of velocity, hence metres per second per second. Surprising the amount of people who go blank at this, but the sine wave picture usually helps. Draw a straight line across the sine wave at the r.m.s point (0.707 if I recall correctly)if you want to go into the science a bit more, also explain that this is happening in 3 axes (or vectors)and we are usually interested in the vector sum.If you want to demo the vector sum, you'll need something like a rectangular fish tank to show the 3 axes and aa piece of string or coloured cord for the resulting vector.
Bring in an electric toothbrush, Playstation vibrating controller etc., discuss anecdotal use of DIY power tools etc.
|
|
|
|
|
|
You cannot post new topics in this forum.
You cannot reply to topics in this forum.
You cannot delete your posts in this forum.
You cannot edit your posts in this forum.
You cannot create polls in this forum.
You cannot vote in polls in this forum.