There are many other sources of vibration that emanate from within buildings. The footfalls in a hallway or the slamming of a door can cause serious disturbance to sensitive equipment and can significantly distort results. Even the acoustic interference from voices talking can affect measurements.

When equipment is placed on floors above the ground, the rigidity of the floor must be taken into consideration. Even when high performance vibration isolators are used, the effect of the floor rigidity, and properties of the floor vibration can be seen in the precision equipment.

When choosing between the first floor and upper floors, it is generally better to utilize the first floor or basement of a building. If an upper floor is chosen, it is important to place the equipment near floor support beams. Typically, the vibration acceleration of the floor located near a support 'beam' is 1/5 smaller than the floor vibrations far from the support 'beam'. Fig. 6 shows the comparison of this point. If isolation equipment is placed on a floor where there are no support beams, it will be difficult to isolate the lower frequencies. When locating equipment on upper floors of a building, it is important to choose a location close to a support beam or pillar.

When placing precision equipment in a clean room environment or on a floor that is raised off the primary floor, special considerations and alterations should be made before placing the equipment in service. Typical clean room floors are raised off the primary floor. The isolation systems should be mounted directly to the primary floor with a support system that rigidly connects the isolation system to the primary floor. Please contact a sales engineer for more advice on clean room installations.

This section was written for users of extremely sensitive measuring equipment. Special precautions must be taken to eliminate acoustical as well as vibrational noise when making extremely sensitive measurements.

Sound, or acoustic energy can cause measurement error. Typically, this type of energy causes a 'quivering' interferometric image or reduction of measurement repeatability. Figure 7 shows an example of the effect of a cough, a common source of acoustical energy. Location and type of air conditioning ducts should be considered when installing equipment. Acoustic affects should be minimized whenever possible. It is possible to remove the effects of acoustic noise with simple precautions. For high resolution imaging the AEK Acoustic enclosures made by Herzan will provide the ultimate in acoustic isolation.

Effect of a human cough on surface prober measurement. Figure 7. The following may help to improve the performance of your measuring system: a. A makeshift acoustic baffle can be constructed of cardboard or wood, covering the outside with a thick cloth will reduce the acoustic pressure. b. Enclose the entire vibration isolation system in AEK acoustic enclosure, if the entire system is being affected by acoustic pressure or wind. When an enclosure is used, it should be mounted on the floor. If the enclosure is mounted to the isolation table it negatively impacts performance, by acting as an antennae for noise. When sound or wind hits an enclosure mounted on the table is acts as an obstacle, and reacts against the incoming pressure wave.

This, in turn, causes the isolation system to sway on the isolation system. If it is attached directly to the bench top, it transmits the energy directly into the table top.

c. In a clean room, an enclosure around the isolation system is recommended.

Thermal effects of the room environment can also affect the accuracy and repeatability of measurements. Keep the vibration isolation system away from a window, radiators and other heating and cooling sources, where thermal affects can alter measurements. When using an enclosure the enclosed system may need to be “normalized” before commencing measurements.

Reliable test and measurements results can always be obtained by precision measuring equipment if the proper isolation system/acoustic enclosure, and environment are chosen.

As the resolution of precise measuring equipment and laser research continues to improve, it will be important to address the 'measuring environment' and vibration isolation. Humidity, and magnetic field effects must also be addressed.

Unfortunately, there is no one solution for every measuring environment. Each situation must be addressed individually, for every application possesses different governing constraints. The environment strongly affects the measurements, and must always be taken into consideration, even with an isolation system.