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Vibration sensor basics | Vibration sensor types, Vibration sensor applications

This article covers Vibration sensor basics and Vibration sensor types including its applications. It describes different types of Vibration sensor viz. pin and spring, Piezoelectric, chip based piezoelectric, mousetrap, magnetic, mercury etc.

What is a Vibration sensor?

Definition
Vibration sensors are sensors used to measure, display and analyze frequency, displacement, velocity or acceleration. There are various types but the most commonly used vibration sensor is accelerometer. It produces electrical signal proportional to acceleration of vibrating component.

Vibration sensors respond to repetitive mechanical motion. Most of the sensors are available with their contacts "normally open" type. The contacts close when the sensor vibrates in its designed frequency range. Frequency range and sensitivity are manually adjustable in some of the sensors.

Mechanical sensors or switches which respond to displacement are best suited for low frequency vibrations. Piezoelectric sensors are sensitive to acceleration and hence are best suited for high frequency vibrations.

Vibration sensor applications

Following are the applications of Vibration sensor:
• It is used as automatic shutdown switches due to excessive vibration of machinery.
• It is used to shut down domestic appliances such as washing machines (when it is out of balance during spin cycle).
• It is used in toys and games.
• It is used as shock sensor while device is being transported.

Vibration sensor Types

Based on their working principles and constructions, Vibration sensor types are as follows.
• Pin and Spring• Piezoelectric strip• Chip based piezoelectric• Mousetrap type • Magnetic• Mercury etc.

Pin and Spring Vibration Sensor

Pin and Spring Vibration Sensor

• It is simplest type of vibration sensor. It consists of small and thin pin in the center of a coil spring. The spring is anchored at its base and the other end is free to vibrate. If the vibration reaches sufficient amplitude, the spring touches the pin and completes the circuit between the two leads of the device. Figure-1 depicts one such sensor manufactured by chinese supplier Elecrow.
• Advantages: Low cost, ability to respond two out of three axes, no power supply requirement, ability to switch DC or AC.
• Disadvantages: It requires latching components such as flipflop or 555 timer as internal contact is extremely brief.

Piezoelectric vibration Sensor

Piezoelectric vibration sensor

• It is usually made of piezoelectric polymer film laminated to a polyester substrate. The film is designed to be anchored at one end and the other end is free to vibrate. The figure-2 depicts one such sensor developed by "Measurement Specialties".
• It is available in unweighted version and weighted version (as shown in the figure). The addition of weight changes the resonant frequency of the vibration sensor.
• It generates about 7 V DC between the two leads with deflection of mere 2 mm. Larger deflection produces higher voltages.
• It is possible to connect CMOS component with the sensor and Op-Amp may be used for signal conditioning purpose.
• Surface mount version of piezoelectric vibration (Murata PKGS series) sensor is available with analog output for connection through an op-amp.
• Advantage: It has resonant frequency of about 170 Hz when there is no weight attached to its free end.
• Disadvantage:It generates voltage during process of deflection. The output diminishes to zero when the strip is held in curved position.

Mousetrap type vibration Sensor

• This sensor rely on simple system of leverage, similar to mouse tap in which a relatively small stimulus releases a stong spring.
• It is used in power station cooling towers where a loss of large fan blade results into major vibration.

Magnetic vibration Sensor

• It is used to detect excessive vibration in machines or other devices which contain heavy rotating mechanical parts.
• These sensors may be larger in size and handle currents of 1 Ampere or significantly higher.

There are many other vibration sensor types such as vibrometer which measures vibration using laser beam and so on. Accelerometer, Velocity sensor, proximity sensor and small mercury switch are also used as vibration sensors. Refer advantages and disadvantages of vibration sensor >> for more information on merits and demerits of the different types of vibration sensors.



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