Silicone vacuum grease, heavy machine oil, or bees wax are commonly used. The block diagram of the typical IEPE accelerometer and signal conditioning circuit 16.The PE transducer is comprised of a mass m and piezoelectric element often called a crystal. Under acceleration, the mass displaces and exerts a force ( F ma kx ) in the piezoelectric element, which is tensioned or stretched, according to acceleration direction. The piezoelectric element is attached to the seismic mass and to the spring. This coating aids in the transmissibility of the higher frequency vibrations and improves high frequency response of sensors. Figure 5.40 shows the basic structure of a piezoelectric accelerometer. In addition to surfaces being as flat as possible, clean and free of debris, and the mounting holes to be perpendicular, the mounting surfaces should be lightly coated with a lubricant. One last point worth noting regarding mounting involves surface preparation. However, when operating AC coupled signal conditioners with readout devices that have an input impedance of less than 1 megohm, the low frequency range may be affected. This roll-off behavior is typically fixed by the built-in sensor electronics. Common piezoelectric materials include quartz, lead zirconate titanate (PZT), and polyvinylidene fluoride (PVDF). Furthermore, the IEPE type accelerometers can be popular in the general-purpose testing market, while charge output piezoelectric accelerometers dominate applications where temperatures above about 150C are involved. Confusion often arises when selecting the proper accelerometer for a given application. These sensors are extremely rugged, provide a wide dynamic range, and are available in a variety of configurations to meet individual installation requirements. Note: The low frequency response is unaffected by the mounting technique. This effect was first discovered by Jacques and Pierre Curie in 1880. Charge output sensors can operate at temperatures as high as 700C. Industrial accelerometers have become the workhorse in the Predictive Maintenance market. Charge output accelerometers are typically used in high temperature environments, which would. ICP® accelerometers typically come in one of two sensitivities: 10 mV/g (+/- 500 g) or 100 mV/g (+/- 50 g) ranges. By examining the mounting configurations and corresponding graph, it can be seen that the high frequency response of the accelerometer may be compromised as mass is added to the system and/or the mounting stiffness is reduced. Generally, ICP® accelerometers are preferred, due to ease of use, easier data system calibration setup, and lower system cost.
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