Technical
Given the requirement for breaks, refuelling, changing cord and moving around on site, very few operators will achieve more than three or four hours trigger time in a normal working day
The measurement of vibration
Vibration is not good for the operator, and all vibration needs to be measured with exposure levels monitored and recorded. Vibration is usually recorded in two different categories,
- HAV (hand and arm vibrations) - WBV (whole body vibration) The unit of measurement is m/s2
” (metres per
second squared). Basically, a sensitive measuring device is attached to the part of the machine to be tested, usually the handles or the seat, and any movement is recorded. Movements will be very small, but very fast. The measuring device, or meter, will record the movement and give out a reading in m/s2
. The
legal daily limit for vibration exposure is 2.5m/s2
. The Operator’s book
There is a clear duty under CE certification for manufacturers to include the vibration data in the Operator’s Instruction book. A ride-on machine will have to show its HAV values (steering wheel) and WBV (seat and footplate area). Handheld machinery will include HAV values only.
The below chart, taken from a Jacobsen GP400 Operator’s Manual, shows the way the vibration values are shown in the operator’s instruction book, and quotes the relevant EN standards to which the machine was tested.
The effects of vibration
Vibrations damage the nerves in our skin, and any areas of the body which come into contact with the vibrations can be effected. Nerve damage can result in the loss of touch and
Noise is a vibration which has travelled through the air and reached your ears. The intensity and frequency of the vibration will determine what you actually hear.
Good vibrations?
Well, some of our machinery deliberately create vibrations in order to achieve an end result; vibrating rollers and some aerators are a typical example. Other machinery, like deep tine aerators, create considerable movement, or shaking due to the way they work (large rotating crank shafts and lots of fast moving parts). But, unless the vibration is a deliberate end result of using the machine, then most vibration is, in fact, bad and should be avoided if possible.
Vibration increases soil compaction, it reduces the working life of machinery and equipment, or causes manufacturers to build heavier and, therefore, more expensive machinery to cope with, or absorb, the vibrations created by using it.
PC DECEMBER/JANUARY 2016 I 127
sensation, making everyday tasks like doing up buttons more difficult. More extreme damage can result in intense pain during cold weather and severe dexterity problems.
Trigger time
With many powered hand tools, the measured HAV reading will be above the 2.5m/s2
normal working day. So, if a piece of machinery registered 5m/s2
total run time for that operator has to be reduced to four hours, giving the same exposure as eight hours at 2.5m/s2
.
Given the requirement for breaks, refuelling, changing cord and moving around on site, very few operators will achieve more than three or four hours trigger time in a normal working day.
For self-propelled machinery, the operator is sitting in the seat all day, so the exposure times are going to be much higher. Thankfully, the vibration levels on bigger machinery are very much lower, and the majority can be used all day, every day without any concern about vibration exposure levels.
limit, so
the only way to stop exceeding the legal limit is to reduce the actual usage, or trigger time. 2.5m/s2
is the daily max, taking eight hours as a , the
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