The Ultimate Guide To Vibration Sensors

Tips for selecting the correct vibration sensor for your application and budget.

Vibration sensors are versatile tools used to measure the acceleration or vibration of a device or system.
These sensors use the piezoelectric effect, which measures changes in pressure, acceleration, temperature, strain or force by converting them to an electrical charge. A vibration sensor can also be used to determine aromas in the air by simultaneously measuring resonance and capacitance.

Ideal for measuring the amount and frequency of vibration in machines and equipment, vibration sensor measurements can be used to detect and monitor certain issues like imbalances to help mitigate the risk of future breakdowns of machines or equipment.

Used in a wide range of industries including medical, engineering, vehicle design and nuclear energy production, the various applications of vibration sensors include process control systems, aerial navigation and underwater.

What are the different types of vibration sensors?
The general types of vibration sensors include displacement sensors, velocity sensors and accelerometers. Accelerometers are the best choice for most industrial assets because they are simple, easy to apply and very sensitive to the high frequency vibrations typically generated during force failure. Industrial accelerometers are typically based on one of two technologies:

⦁ Piezoelectric accelerometers
⦁ Micro electromechanical systems (MEMS) accelerometers

Piezoelectric accelerometers
A piezoelectric vibration sensor (also known as piezo sensors) uses the effect of mechanical strain caused by high-frequency motion of the equipment to detect acceleration and vibration. These vibration sensors are very effective, flexible and work with a variety of applications.

Under acceleration, the seismic mass of the accelerometer causes the piezoelectric element to ‘displace’ a charge, producing an electrical output proportional to acceleration. Piezoelectric accelerometers are AC responsive, meaning the output is AC coupled. An AC coupled device is only suitable for measuring dynamic events and cannot be used to measure static acceleration such as gravity.

Piezoelectric vibration sensors are a popular design as they have high-level output, simple customer interface and wide bandwidth. They operate with frequencies of up to 20 kHz and accuracies of 1%. There are two types of piezoelectric accelerometers available on the market: charge output type and voltage output type.

Most piezoelectric sensors are based on lead zirconate titanate ceramics (PZT) which offer very wide temperature range, broad dynamic range, and wide bandwidth (usable to >10kHz). When housed in a hermetic, welded metal case, a charge mode accelerometer is considered one of the most durable sensors because of its ability to tolerate hostile environmental conditions.

The other type of piezoelectric accelerometer provides voltage output instead of charge. Unlike a charge mode device that only contains ceramic sensing elements, a voltage mode device includes a microelectronic circuit which limits the operating temperature of the device to the maximum operating temperature of the electronics, which usually tops at +125°C.

Inherently analog, piezoelectric vibrations sensors require additional processing electronics to digitise the signal. Though this does enable the user to define the frequency properties through their choice of analog to digital converter, the external electronics add complexity and size as well as increasing power consumption. Higher power consumption can present an issue for wireless vibration sensors which are battery powered. If a facility has hundreds of these sensors, changing the batteries frequently can consume a significant amount of time. Another downside is the cost – piezoelectric accelerometers are very expensive. MEMS based accelerometers provide an alternative.

Micro electromechanical systems (MEMS) accelerometers
MEMS accelerometers are used whenever there is a need to measure linear motion, either movement, shock or vibration but without a fixed reference. MEMS DC response sensors have true DC measurement capability, meaning they can measure static or very low frequency (<1Hz) acceleration. They are also capable of measuring dynamic events. MEMS-based vibration sensors have become increasingly popular because of advances in data analysis and signal processing. These vibration monitoring systems are compact, robust and economical. MEMS technology does not require A-D conversion, instead it has embedded electronics and therefore lower power consumption, enabling wireless vibration sensors to run for an extended period without battery change. They also provide good stability under variable temperature conditions. Things to consider
Vibration range
The range of vibration can vary greatly so you should always specify vibration sensors to measure the maximum vibration range of your application. If a machine produces high amplitude vibrations, a low sensitivity sensor is better.

Frequency
Frequency of various vibration sensors ranges from 0.2 up to 2500 Hz, so it is imperative to consider the frequency span you need to measure.

Temperature
High temperatures can affect the performance of the sensor.

Exposure
Contact with chemicals or debris can affect the reliability of the measurements and monitoring.

Environment
Hazardous atmospheres require specifically designed devices for use in dangerous areas.

Positioning
Where will the vibration sensor be positioned? We have top exit, side exit or low profile devices from TE available.

Talk to the sensor experts
As with most engineering activities, choosing the right tool may have serious implications on the measurement results. Each accelerometer sensing technology has its advantages and compromises. Before making a selection, it’s important to understand the basic differences of the various types and the test requirements.

Designed for application durability in harsh environments, TE Connectivity (TE) manufactures various board mounted silicon MEMS accelerometers and piezoelectric accelerometers. These sensors are available in standard packages and custom designs to meet customer design requirements. At Applied Measurement, we offer both DC-response (static) and AC-response (dynamic) types of accelerometer sensors to meet your application needs.

As industry leaders in test and measurement, Applied Measurement has been providing innovative and effective solutions for applications that involve measurement of physical parameters since 1976. We have the experience and expertise to supply the correct sensor for your application.

If you want to talk to someone about sensor solutions, contact us to discuss your requirements or application, we are always happy to help!