MEASURING VIBRATION

Vibration is a disturbance that is put onto a system. Causes of vibration can be categorized as: continuous, impulsive, and intermittent.

Accelerometers (made of piezoelectric material) are used to measure vibration. Accelerometers gives off a small voltage when they are moved. This voltage is magnified and processed by a signal analyzer – generally in a computer.  The system is calibrated using a shaker. Calibration is performed by connecting the accelerometer to a calibrated shaker that moved up and down at a specific frequency and amplitude.

There are different size accelerometers for different uses.  Large ones are used for low frequency ground vibration.  Smaller ones are attached directly to a surface and measured how much the surface is moving and at what frequencies.  The accelerometer can not be too large or it will affect the movement of the surface because of its mass.

Vibration is measured in acceleration (G’s, m/s2, ft/s2) or velocity (m/s, ft/s).

VIBRATION REGULATIONS

OSHA has a vibration guidelines for vibration to workers (hand and arm and entire body).

There are some guidelines that state when vibration is noticeable and could be a nuisance but there are very few regulation.

As consultants, we sometimes measure vibration that potentially could cause a structural problem.  One example is a residential building being constructed near a heavy rail track. Sometimes vibration is addressed for worker exposure. Long term exposure to vibration from mechanical equipment.

Noise Expert frequently measures the vibration levels on the floors where proposed MRI machines were going to be located – various types of medical centers. The manufacturers require that the sites meet certain vibration limits so that imaging from the MRIs are not affected.

Vibration measurements include steady state spectrum and time decay after an impact. For the steady state measurements, expected activities are simulated, such as: an elevator operating, people walking in corridors, people in the control room, and HVAC equipment operating.

If the site does not meet the vibration requirements, the vibration source is identified and treated. If further mitigation is needed, a vibration isolation system is installed.

VIBRATION CONTROL

Lessening vibration relies on upon the cause of the vibration and the where it is found. For example:

Ordinarily, the producer will have vibration isolation systems for their products. Such as for MRI machines. Contacting the manufacturer is a good begining step.

For mechanical systems, such as rooftop units, it is helpful to know the type, size, speed, roof spans, …  From that information you can determine what vibration isolation system will be most effective: rubber pads, spring isolators, inertia bases, curb mounted bases…

For floor-roof systems and roof-ceiling systems, vibration isolation can be achieved by improving the floor (or roof) or the ceilinng. It is best if the floor and roof can be detached. Treating the floor can include installing a cushoning layer under a completed floor. Treating the roof can incorporate mounting a gypsum board roof on springs or channels.

In either case, it is easier and less costly to put these systems in the design than to install them in after construction. After construction can involve removing floors and/or ceilings and installing a new one.

We have, as of late, evaluated the vibration for several cross fit gyms situated alongside office spaces. In these locations, huge individuals frequently lift overwhelming weights and drop them on the floor. This effect shakes the contiguous spaces. We have been able to significantly reduce the vibration by installing different thickness and density rubber matts.

We have not discovered the mix of thicknesses and densities for each circumstance. We have gotten the best results by testing an assortment of elastic mats of different thicknesses and densities.

Vibration detachment for pipes normally involves the way the channels are mounted to the studs. Wrapping the channels in closed cell foam and mounting the system to the studs or utilizing resileient mounts (that do likewise).

Thank you for visiting Noise Expert Acoustical Consulting – Please let us know if you have any questions or if you would like our assistance with acoustical evaluations. 480-332-9325, info [at] noiseexpert.com, www.noiseexpert.com.  We now have offices in Phoenix, San Diego, Las Vegas, and Salt Lake City.

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