Piezoelectric accelerometer

Since acceleration is the second derivative of displacement, a piezoelectric accelerometer sensor with an integrator becomes a velocity transducer. This arrangement is gradually superseding the self-generating mo ing-coil velocity sensor (where a coil of wire moves relative to a magnetic field). 

The damping of such vibrations may also heat the detectors. For this reason, the vibration spectrum of the cryostat has been measured with piezoelectric accelerometers placed on the 1 K pot, the Still, the mixing chamber and the crystal copper frame [98],... 

Angular displacement sensed by piezoelectric accelerometers frequency from vibrator input G M G M... 

In a separate trial 24 h later, the animals are presented with a startle stimulus (e.g., loud noise 70-80 db, or air puff) and their activity is recorded as a baseline. The startle stimulus can be presented in four blocks of five startles each, with 30-35 s between each startle stimulus (7). Peak and amplitude of the startle response can be recorded (e.g., using a piezoelectric accelerometer) and digitized (18). 

Niitsuma et al. [1993] Kamaishi mine, Japan 30 m triaxial piezoelectric accelerometers 234 during four hydraulic fracturing tests 10 kHz not available... 

FIGURE 18.5 Seismic accelerometers (a) rectilinear acceleration transducers, (b) rotary accelerometer, (c) force-balance accelerometer, (d) piezoelectric accelerometer. 

Here, the whole shear cell is located on a vibrating plate, mounted on vertical leaf springs, see Fig. 3. On the shear base and the shear ring, there are located one piezoelectric accelerometer each for measuring the vibration acceleration a and a, respectively. The arrangement whole shear cell vibrated can be used for investigations on the resonance and damping characteristics of cohesive powders. 

The dynamic tests were carried out in Jrme 2007, using a 16-channel data acquisition system and WR 731A piezoelectric accelerometers (10 V/g sensitivity and 0.5 g peak acceleration). Each accelerometer was coimected with a short cable (1 m) to a WR P31 power unit/amplifier, providing the constant current needed to power the accelerometer s internal amplifier, signal amplification, and selective filtering. 

Few weeks after the execution of the second AVT, a simple dynamic monitoring system was installed in the tower. The system is composed by a 4-channel data acquisition system (24-bit resolution, 102 dB dynamic range, and anti-aliasing filters) with three piezoelectric accelerometers (WR model 731A, 10 V/g sensitivity, and 0.50 g peak). The response of the tower is measured in three points, belonging to the cross section at the crowning level of the tower. Furthermore, a temperature sensor is installed on the S-W front, measuring the outdoor temperature. 

Passia H, Staniek A, Szade A, Motyka Z, Bochenek W, Bartmanski C (2008) Comparative studies of principal vibration parameters of a building using an LDV, laser tilt and vibration sensors and piezoelectric accelerometers. In Tomasini EP (ed) 8th international conference on vibration measurements by laser techniques advances and applications, Proc. of SPIE vol 7098, 70980J, (2008) 0277-786X/08/S18 doi 10.1117/ 12.803001... 

The system studied in this example is the 2-DOF pick-and-place mechanism mentioned earlier (Fig. la). The random vibration response is measured in the same direction as the excitation, using lightweight piezoelectric accelerometers. During a single experiment a single cycle is performed, in which the linear motors move from their rightmost to their leftmost position and back. The measured vibration response is conditioned and driven into a data acquisition... 

The fracture of a brittle material is often accompanied by acoustic emission, which results from the release of energy.This acoustic emission has both an energy and a frequency spectrum, Acoustic emission may be used as one indication of the onset of failure. For example, in the testing of adhesion by the scratch test, the coated surface is scratched by a rounded diamond point and the load on the point is increased while monitoring the acoustic emission using a piezoelectric accelerometer to detect the onset of fracture. 

Also the vibrational motion of the milling head has been measured by a piezoelectric accelerometer mounted horizontally on the milling head close to the cutter. The output of this accelerometer is fed to a conditioning amplifier whose calibration factor is 10 g/V. 

If the acceleration is variable, as in sinusoidal movement, piezoelectric systems are ideal. In case of a constant acceleration, and hence a force that is also constant, strain gages may be employed. For petroleum applications in boreholes, however, it is better to use servo-controlled accelerometers. Reverse pendular accelerometers and single-axis accelerometers are available. 

The transducer most commonly used to obtain vibration measurements is an accelerometer. It incorporates piezoelectric (i.e., pressure-sensitive) films to convert mechanical energy into electrical signals. The device generally incorporates a weight suspended between two piezoelectric films. The weight moves in response to vibration and squeezes the piezoelectric films, which sends an electrical signal each time the weight squeezes it. 

Acceleration is perhaps the best method of determining the force resulting from machine vibration. Accelerometers use piezoelectric crystals or films to convert mechanical energy into electrical signals and Figure 43.23 is a schematic of such a device. Data acquired with this type of transducer are relative... 

Figure43.23 Schematic diagram of accelerometer (l)Base (2) Piezoelectric crystals (3) Mass (4) Case...

A benefit of the use of accelerometers is that they do not require a calibration program to ensure accuracy. However, they are susceptible to thermal damage. If sufficient heat radiates into the piezoelectric crystal, it can be damaged or destroyed. However, thermal damage is rare since data acquisition time is relatively short (i.e. less than thirty seconds) using temporary mounting techniques. 

Accelerometers use a piezoelectric crystal to convert mechanical energy into electrical signals. 

In addition, accelerometers can be used to measure acceleration directly, and speed can be derived through integration. However, piezoelectric models have no steady-state response and may not be useful for slower movements. Single accelerometers are used to measure linear motion. Simple rotatory motions require two accelerometers. Triaxial accelerometers are commercially available that contain three premounted accelerometers perpendicular to each other. Multiple accelerometer outputs require appropriate processing to resolve the vector component corresponding to the desired speed. Accelerometers are most appropriately used to measure acceleration when they are mounted on rigid materials. Accelerometers... 

Quartz and piezoelectric ceramic crystals have more temperature independent constants than PVDF, so they are used for force and acceleration transducers. However, PVDF films can be used for large area flexible transducers. Their sensitivity to stress or strain allows the construction of pressure sensors (using the J33 coefficient), and accelerometers by mounting a seismic mass on the film. PVDF electrets are particularly suited for large area hydrophones (Fig. 12.21) that detect underwater signals. Their... 

The most common sensor is the activity sensor, which uses any of a variety of technologies (e.g., piezoelectric crystals and accelerometers) to detect body movement. Systems using a transthoracic-impedance sensor to estimate pulmonary minute ventilation or cardiac contractility are also commercially available. Numerous other sensors (e.g., stroke volume, blood temperature or pH, oxygen saturation, and right ventricular pressure) have been researched or market-released at various times. Some systems are dual-sensor, combining the best features of each sensor in a single pacing system. 

Above these frequencies the range of AE measurement in rock begins with applications in mines as well as in laboratory studies. In the frequency region of about 1 kHz up to 100 kHz accelerometers or typical piezoelectric AE sensors are used in mines. The t5q)ical distances between sensors may amount up to 50 m the covered areas may have linear dimensions of up to 200 m. 

A simpler seismic accelerometer utilizes one electrode of a piezoelectric crystal as the seismic element (Fig. 18.5(d)). Similarly, another simple accelerometer utilizes the common plate of a differential capacitor (Fig. 18.3(a)) as the seismic element. 

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