Vibration Accelerometer

February 19, 2016

Vibration accelerometer is a device that measures the vibration, or acceleration of motion of a structure. Vibration accelerometer has been a popular choice for rotating machinery vibration monitoring.

Vibration accelerometer is a rugged, compact, light weight transducer with a wide frequency response range. This transducer is typically attached to the outer surface of machinery. Generally, this machinery will have parts that generate high frequency signals, such as, rolling element bearings or gear sets. Meanwhile, its application and installation must be carefully considered for an accurate and reliable measurement.

Vibration accelerometer is inertial measurement device that converts mechanical motion to an electrical signal. This signal is proportional to the vibration’s acceleration using the piezoelectric principle.

There are two types of vibration accelerometer (vibration sensor). The first type is a “high impedance” charge output accelerometer. In this type of accelerometer, the piezoelectric crystal produces an electrical charge which is connected directly to the measurement instruments. The charge output requires special accommodations and instrumentation most commonly found in research facilities.

This type of accelerometer is also used in high temperature applications (>120C) where low impedance models can not be used.

Meanwhile, the second type of vibration accelerometer is a low impedance output accelerometer. A low impedance accelerometer has a charge accelerometer as its front end but has a tiny built-in micro-circuit and FET transistor that converts that charge into a low impedance voltage that can easily interface with standard instrumentation. This type of accelerometer is commonly used in industry.

Choosing the right vibration accelerometer for your application can be a daunting task. So, there are several steps you should consider in the selection process. The first step is to determine the type of measurement to be made. In this case, there are three popular technologies used for acceleration measurements: Piezoelectric (PE) accelerometers (the most widely used accelerometers for test and measurement applications), Piezoresistive (PR) accelerometers (desirable for shock measurements and less useful for vibration measurements), and Variable capacitance (VC) (among the newer accelerometer technologies).

However, before talking about the technologies and applications of vibration accelerometer, you should consider a few general considerations associated with frequency response. It is an important parameter when considering any accelerometer. The frequency range will usually be determined by the test specifications or by the user. It is usually specified within ±5% of the reference frequency (usually 100 Hz). Many devices will have the specifications extended

Another consideration is the number of axes to be measured. Vibration accelerometer comes in single-axis and triaxial (3-axis) versions. An alternative approach to making a three-axis measurement is to mount three accelerometers on a triaxial mounting block. Both methods allow for the measurement of three orthogonal axes simultaneously.

Other things you should take into account in the selection process ofvibration accelerometer are vibration and shock. Related to shock, it is important to know the expected shock level because this will determine the type of accelerometer to be used. For low-level shock measurements, a general-purpose accelerometer will usually do the job, while for automotive crash testing, a rather specialized area of shock testing, piezoresistive accelerometer is usually used.

Meanwhile, for far-field shock measurements, a special shear-mode accelerometer with a built-in electronic filter is often adequate.

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