A wide range of functions are accomplished by microelectronics, and one important measurement made by them is vibration. Vibration sensors measure what is known as oscillatory motion, a movement that continuously goes back and forth. The direction can be indicated using a coordinate system with axes, and the force in relation to gravity can be measured as well. Vibration analysis is done by measuring displacement and velocity as well as acceleration, which is primarily analyzed by vibration-monitoring sensors. The different types include piezoelectric, integral electronics piezoelectric, piezoresistive, variable capacitance, and servo sensors.
Vibration sensors are usually called accelerometers. Piezoelectric accelerometers operate on the energy of the forces that act on them, so there is no need for extra power sources in the system. The displacement of electron charges on either side of the sensor is used to generate measurements. Common types of this sensor include a shear design, which is built to handle large temperature differences, and a beam-type design that is often preferred because it is typically available at a low cost.
Integral electronics piezoelectric sensors include small amplifiers of their own, so a special cable is not needed like in a piezoelectric product. The input and output signals pass through a single cable connected to the sensor, and the overall design is protected from electrical noise. This device can also incorporate electronic filters, electrical overload protection, and a variety of accessory functions.
A piezoresistive sensor is configured in either a single- or multiple-arm design for producing a more complex output. It is powered by outside power sources, allowing an output signal to be used to monitor vibration conditions that are stable instead of changing in direction or force. For high acceleration conditions, variable capacitance vibration sensors often integrate silicone wafers with gaps in between for durability. They can tolerate accelerations up to 1,000 times their defined operating range.
Unlike other sensors which rely on displacement of crystals or other elements in an open-loop configuration, a servo, or force balance, accelerometer uses a closed-loop design. Servo-driven vibration sensors have a higher accuracy and can be used in inertial guidance systems. Other common forms of sensors for vibration analysis include proximity sensors. These often reside inside machinery to monitor the movement of internal components by measuring their electrical conductivity. While these are non-contact, other vibration sensors rely on contact to accurately gauge motion or distance.
