The environment in which equipment is to be located will affect the overall performance of the measuring system. It is beneficial to analyze the environment in which the equipment will be placed, and choose the most ideal location. There are many factors to consider when evaluating a vibration system and its performance. The building, as well as the room must be evaluated before placing equipment into operation. As we saw in the previous section, a passive isolation system placed in an environment where the building resonance is near the isolation system resonance would result in amplification instead of isolation. The VA-2 vibration sensor can be used to evaluate the environment. The VA-2 can be purchased or leased from Herzan. We also conduct site analysis and vibration surveys.

The varied foundations, such as granite, sand, clay and landfill, can greatly affect the stability of a building. If a solid building is not built into bedrock, the ground will be soft. When a train or car passes near the building, low frequency vibration may occur and negatively impact the performance of the isolator. A large mechanical press operation near the building may cause the same result. Softer ground may transmit vibrations more readily.

Vibration Spectrum - 2nd Floor

The properties of building vibrations are highly affected by building materials and methods of construction. Depending the resolution requirements of the equipment, the system may need to be placed in a building with rigid construction. Fig. 4 shows the difference in vibration in two different types of building construction.

Vibration Spectrum - 2nd Floor

Ideally buildings would be constructed to the precise specifications of the equipment that will be used within them. Unfortunately, this can often be prohibitively expensive and time-consuming. And sometimes, even though the requirements of the equipment are taken into account, construction companies can have trouble completely meeting specifications or anticipating unexpected sources of vibrations. When this happens Herzan is happy to work with construction companies or the researchers themselves to bring their sites up to desired specifications.

Natural phenomena like the wind and waves must also be considered. Wind gusts may occur at 2-3 Hz, predominantly in the horizontal direction. These gusts will cause the building to sway, inducing rotational and translational movement. Therefore, an isolation system must be capable of damping out the building vibrations in the translational and rotational modes. The active TS and AVI isolation systems isolate ALL six degrees of freedom.

As waves break against the shore, their forces cause ground-disturbing vibrations. Much of the land along the seashore is very soft so buildings within two kilometers of the ocean may be affected by the surf. Rivers can be troublesome as well. Waves and wakes caused by traffic on the river can cause vibrations that are transmitted to nearby buildings.

Road traffic also presents a problem for sensitive equipment. Large vehicles and trains can cause ground disturbances and heavy traffic creates a great deal of noise interference. Additionally, airplanes flying within hearing range of the building can cause unwanted vibrations and acoustic interference.

The top curve represents vibrations of the floor far from the support beams.

The bottom curve represents vibrations of the floor under the support beams.

Figure 6.

Vibrations emanating from the floor can be caused by forces from outside the building and from within the building itself. A common source of vibrations is machinery operating within the building. There is a wide range of machinery that causes offending vibrations: everything from air conditioners and heaters to manufacturing equipment to other laboratory machines. It is not necessary that the machines be located near the sensitive equipment; often vibrations will resonate through walls, between floors, or throughout an entire building.