WBV Data Collection

Whole-body vibration data is collected and analyzed using the Vibration Analysis Tool Set (VATS) from NexGen Ergonomics, Inc. The key components of the Vibration Analysis Tool Set are shown in the figure below and consist of the Biometrics DataLOG (Model P3X8), DataLOG software, VATS analysis software and one of the two tri-axial accelerometers.

The DataLOG component of the VATS collects data from accelerometers and then onto a flash memory card. The data collection device has a sampling rate of up to 20,000Hz for each of the three channels used in vibration measurement.

The tri-axial accelerometers (X,Y and Z directions) have factory-set signal buffers, adjustable filters and adjustments for offset and sensitivity for each channel. The accelerometers connect directly to the DataLOG acquisition device. Each channel (X,Y and Z) is connected to the host instrument using a separate plug, so that each accelerometer is set up to use all 3 channels.

The VATS analysis software Version 3.4.4 (2006) allows the user to choose from several different standards to analyze whole-body vibration (WBV) which include the ISO 2631-1, ISO 2631-5, BS 6841, and ACGIH.  The VATS software also includes a whole-body vibration 8-hour equivalent (8-EQ) calculator which calculates the total exposure from partial exposure values of multiple tasks as in this analysis and/or different types of equipment within an 8-hour shift if needed.

Whole-body vibration data is collected separately by two (or more) accelerometers that measure vibration in all three orthogonal axes. The X-axis is positioned to measure vibration in the anterior-posterior direction, the Y-axis in the medial-lateral direction, and the Z-axis is positioned to measure in the vertical direction. Each accelerometer is calibrated and set to zero according to manufacturer guidelines prior to the collection of whole-body vibration data.

The guidelines listed in ISO 2631-1 (1997) are used to guide the mounting and installation of the vibration measurement equipment. A circular seat pad with an embedded tri-axial accelerometer is placed on and secured to the seat pan of the Operator's seat. The Operator sits on the thin-profile seat pad which makes contact with both ischial tuberosities of the inferior aspect of the pelvis during data collection of vibration exposure at the seat pad/operator interface.

A second tri-axial accelerometer is placed on the support components of the seat pan near the floor (or on the floor) and is typically mounted with a rare-earth magnet. Vibration data related to the seat-base is also collected in all three axes and is used to assess the amount of transmissibility of vibration from the floor to the seat pan.  Comparisons of vibration magnitudes at the floor (base of the seat) and at the seat pan help to determine how well a seat dampens vibration. 

The VATS software is used to analyze and process the WBV data using equations indicated in ISO 2631-1. The equations are used by the VATS software to evaluate the vibration signals and other steps in an assessment as detailed in the ISO 2631-1. The results of an analysis can include one-third octave band frequencies for each vibratory event that the Operator is exposed to during the operation of a machine or vehicle as well as weighted acceleration summaries for each event. The results can also include the use of the 8-hour Equivalent Calculator to determine the potential for negative health effects of vibration exposure levels.