Sensitivity accelerometers

The advent of new, more reliable, and sensitive vibration instrumentation such as the eddy-current sensor and the accelerometer coupled with modern... 

For measurement ranges from 0 to 180°, three accelerometers mounted orthogonally must be used as shown in Figure 4-224. The x and y accelerometers are mounted with their sensitive axis perpendicular to the tool axis. The z accelerometer is mounted with its sensitive axis lined up with the tool axis. 

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. 

Abstract The techniques of atom cooling combined with the atom interferometry make possible the realization of very sensitive and accurate inertial sensors like gyroscopes or accelerometers. Below earth-base developments, the use of these techniques in space, as proposed in the HYPER project (ass.stud), should provide extremely-high sensitivity for research in fundamental physics. 

Miniaturized and integrated sensor systems were developed early for pressure and accelerometer sensors. The technology of silicon micromachining leads to sensitive pressure sensors which were marketed early [4]. Also accelerometers were developed mainly driven by the huge market of air bag application and crash sensors [5]. 

The complex mechanical impedance can be obtained by measuring force, velocity, and their phase difference using probes or pickups attached to the transducer at suitable points [144], This method is very convenient with solids [52] (sometimes the most accurate), but not with liquids, although in this case it can be a convenient method of checking the performance of a transducer. The output from an accelerometer or strain-sensitive pickup gives information on resonant frequency and vibrational amplitude. However subsequent correlation with the power transmitted to the sonicated medium is not straightforward. 

Accelerometers generally fall into two application categories of impact or motion measurements. The specifications for each type of application vary with regard to sensitivity, zero-g offset, frequency range and noise. In all cases there is a desire to have the smallest possible package size and lowest power consumption. 

Stephens M 1993 A sensitive interferometric accelerometer . Rev Sci Instrum 64,2612 - 4 and refererwes therein... 

A gravimeter is a device used to measure the local gravitational field. They are much more sensitive than accelerometers. Measurements of the surface gravity of the earth are part of geophysical analysis, which includes the study of earthquakes. 

Other devices are the ambulatory accelerometer-based foetal activity monitor (Mesbah et al., 2011) and the foetal movement acceleration measurement (Qi, 2013) recorder. They use accelerometers to detect foetal movement. Although their sensitivity is limited and they are prone to artefacts, they present a promising approach for objective foetal movement monitoring (Brown et al., 2014). 

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... 

Acceleration is the time derivative of velocity and the second derivative with respect to time of displacement. Thus, sensors of displacement and velocity can be used to determine acceleration when their signals are appropriately processed. In addition, there are direct sensors of acceleration based on Newton s second law and Hooke s law. The fundamental structure of an accelerometer is shown in Figure 2.3. A known seismic mass is attached to the housing by an elastic element. As the structure is accelerated in the sensitive direction of the elastic element, a force is applied to that element according to Newton s... 

Surveyors always try to verify their results with independent, redundant measurements. They use the redundant measurements for finding a statistically significant result, for raising the accuracy and for increasing the signal to noise ratio. As an independent sensor in our problem we need a second sensor, which can react on high-frequency movements which have a short relaxation time. The sensor can have a one dimensional sensitivity, because we want to measure only movements in the direction of the brake power. Therefore we used an accelerometer, which we mounted on the abutment with its sensitive axis in the direction of the brake power (Fig. 7). 

Porous Si shows a much lower thermal conductivity than bulk crystalline Si. The measured difference is more than two orders of magnitude at room temperature, while it exceeds four orders of magnitude at cryogenic temperatures. This makes porous Si very appropriate for use as a local thermal isolation platform on the Si wafer for the integration of sensitive thermal and other devices. Existing devices to date include flow sensors, accelerometers, bolometers, gas sensors. 

---