Measurements in accordance to ISO 5349
Hand-arm vibration occurs when one or both of the upper limbs is in contact with a vibrating surface (e.g. power tools, steering wheels and levers to control vehicles). Changes in the human body resulting from contact with mechanical vibrations are recognized as an occupational disease called “vibration syndrome” (or “vibration disease”). The only effective way to avoid vibration disease is by prevention.
The ISO 5349 contributes to the gathering of consistent data in order to improve occupational safety. In particular, ISO 5349 specifies the general requirements for the measurement and evaluation of human exposure to hand-transmitted vibration. It is supplemented by the information given in ISO 5349-2, which gives practical guidance for the implementation of appropriate measurement and evaluation techniques at the workplace.
Instrumentation to be used for measurements made in accordance with ISO 5349 is fully specified in ISO 8041.
The fundamental parameter used in the evaluation of hand-arm vibration is the vector sum of tri-axial vibration called ahv which is the basis for the calculation of daily exposure A(8). To identify the daily exposure it is necessary to identify all the sources of vibration, which means identifying all working modes of tools (e.g. drilling with hammer and without), and changes in the conditions of use of the device. This information is necessary for the proper organization of measurement and to include as many common tasks of the operator during which he is exposed to hand-arm vibration. Daily exposure should be calculated for each source of vibration.
After determining the sources of mechanical vibrations affecting the employee, the next step is to choose the most appropriate accelerometer mounting. According to ISO 5349, hand-arm vibration should be measured in place, or at the point of contact with the hand tool. The best location is the centre of the handle which is the most representative location. ISO 5349 suggests using lightweight sensors to reduce measurement errors. Measurements directly at the hand are performed using special adapters and measurement in all three axes is recommended.
Typical vibration exposure consists of short periods in which the operator is in contact with the tool. Measuring time should include a representative tool operation time and the measurement should start from the moment the vibrating device is touched and should end when the contact is broken or the vibration stops (ISO 5349-2:2001).
Human Vibration Meter
Hand-arm vibration meter meeting specification of ISO 5349 and ISO 8041.
Thanks to the FORCE DETECTION it became possible to automatically obtain information about the period that the hand is in contact with the vibrating surface and to evaluate the total contact time per day.
One-third Octave Band
Frequency analysis such as 1/3 octave provides information on dominant frequencies and harmonics, which may help engineers to identify effective vibration control measure as well as detection of artifacts.
Tri-axial MEMS accelerometers from Svantek are extremely robust, SHOCK RESISTANT, uses very low power and is free of the DC-shift effect that adversely affects systems based on piezoelectric accelerometers.
Improved methods of hand-arm vibration exposure measurement have been defined by ISO 5349 as the ones using additional factors such as contact force in order to decrease the uncertainty of exposure time. Contemporary, very small force transducers can be fitted right next to the MEMS-technology-based vibration accelerometer in a form of hand-arm adapter as specified by ISO 5349-2 and ISO 10819. With such an effective solution it became possible to perform continuous measurements through the whole working day which decreases the uncertainty of the sample limitation. The time-history of contact force values proved important in determining the true exposure time by simple selection of the force threshold level and this was backed up by the analysis of spectrograms.
Simultaneous measurement of coupling forces and vibration is necessary because different coupling forces applied by operators on handheld vibrating tools influence differently the stage of transmission of vibration in the upper limbs. Coupling forces modify exposure to vibration and the health effects it causes. Moreover, the synergic impact of force and vibration on the cardiovascular system, nervous system and the joints and muscles should be considered.
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