Technical Report: Vibration and its Sensors 2

The gap (displacement) is measured from the capacitance of the capacitor formed by the sensor and the object being measured. Therefore, the object being measured is limited to a conductor. The capacitance C is a function of the opposing area S of the conductors and the gap D, and the above relationship holds when the sensor and the opposing conductor (object being measured) are parallel plates. If the area S is constant, the gap D is inversely proportional to the capacitance C. Therefore, if the capacitance C can be measured, the gap D can be determined.

Advantages	Non-contact detection Any conductor can be used without calibration. High precision and high stability Measurement possible from near zero gap. Measures down to DC
Points to note	Electrical connection to the object being measured is required. The measurement is affected by oil, water, etc. on the surface of the object being measured. The area to be measured is relatively large.

When a force is applied to a single crystal of quartz or titanium sambalium, an electric charge is generated on its surface. This is called the piezoelectric effect. Materials that exhibit the piezoelectric effect are called piezoelectric materials (piezoelectric elements). A piezoelectric Accelerometer is a sensor that uses a piezoelectric element as a spring in a seismic system and simultaneously as a mechanical-electrical conversion element. It outputs an electrical signal proportional to the vibration acceleration. Piezoelectric Accelerometer are basically classified into two main types based on how force is applied to the piezoelectric element: compression type and shear type (shear type). The structural diagrams of each are shown on the right. In the compression type, the piezoelectric element is sandwiched between the sensor base and a weight. In the shear type, the piezoelectric element is fixed between a post that is erected perpendicularly to the base and a weight. While the compression type was conventionally used, recently, the shear type, which is less affected by base strain and rapid temperature changes, has become popular. Our piezoelectric Accelerometer are of the shear type, with some exceptions.

Advantages	Measurement is relatively easy The system can be implemented at low cost. High stability and minimal deterioration over time.
Points to note	Because it is a contact type, be careful of mass effects and contact resonance. Measurement of uniformly accelerated motion is not possible.

The frequency characteristics of the sensor change depending on the method used to fix it to the object being measured. Please refer to the diagram below. It is necessary to choose the optimal fixing method according to the measurement frequency range.