What is a vibration sensor?
A vibration sensor is a device used to measure the level of mechanical vibration. It is installed on equipment or systems to measure the vibration or oscillatory motion at that location. By analyzing the amplitude and frequency of the vibration, it detects issues such as imbalance or looseness in the machinery and predicts future faults.
The vibration sensor can measure the levels of displacement, velocity, and acceleration. If the measured values exceed the normal threshold, it indicates potential issues with the machinery, such as bearing wear, misalignment of components, or other conditions.
Why do you need to monitor vibrations?
The requirements for motors and other equipment are increasing in industrial production processes. Managers not only need to ensure their normal operation but also their long-term functionality. During the operation of the equipment, issues such as component detachment, equipment aging, and inadequate fastening can result in abnormal vibrations. Various vibration sources exist in any equipment, such as bearing defects, imbalance, and gear meshing, each causing vibrations with different frequencies and directions. The vibration signals of the equipment provide information about its condition, with different signals representing different operational information. Therefore, by analyzing and detecting the vibration signals of the equipment, potential faults can be identified, preventive measures can be taken in a timely manner, and accidents can be avoided or minimized.
How does a vibration sensor work?
A vibration sensor does not simply convert mechanical quantities into electrical energy. Instead, it uses the original mechanical quantity as an input signal and then converts it into a suitable mechanical quantity through the mechanical receiving component. Finally, it is converted into electrical energy through the electromechanical conversion component. Therefore, the data depends on the working condition of its mechanical receiving component and electromechanical conversion component.
How many different types of vibration sensors are there?
There are multiple types of vibration sensor. Next, I will introduce seven of the most commonly used vibration sensors, along with their advantages, disadvantages, and applications.
1. Strain Gauges
The working principle of strain gauges is based on the strain effect, which means that when a conductor or semiconductor material undergoes physical deformation under external forces, its resistance also changes. This phenomenon is known as the “strain effect.” The working principle of a strain gauge is to convert the received tensile or compressive changes into changes in resistance, thereby outputting measurable electrical signals. The structure of a strain gauge involves bonding a thin metal foil onto a flexible substrate material. Two wires are welded to the resistance foil to transmit the current, and as the surface of the measurement device is stretched or compressed, the resistance changes. This resistance change is directly proportional to the surface changes of the measured device. Due to the thinness of the metal foil in the strain gauge, even small changes in resistance can be accurately measured.
Pros:
No moving parts, hence no wear and tear.
Small in size and low cost.
Very sensitive to changes in resistance, enabling measurement of even small changes.
Cons:
Highly sensitive to temperature.
Requires regular calibration.
Requiring high installation precision.
Application: Strain gauges are used for various purposes in mechanical engineering, such as stress analysis, structural testing, and quality control. In stress analysis, strain gauges help determine the internal forces and moments acting on structures or components and identify critical areas, failure modes, and safety factors. For structural testing, strain gauges measure the actual strain, deformation, and displacement of samples and compare them with expected values. In terms of quality control, strain gauges can detect defects, flaws, or variations that may impact the quality or functionality of materials or the manufacturing process.
2. Accelerometers
Accelerometers operate based on the principle of converting mechanical vibrations or forces (acceleration) into proportional electrical charges using piezoelectric materials. When a mechanical device is stationary, accelerometers can measure static acceleration (continuous gravitational force from the Earth) and analyze the device’s tilt angle relative to the Earth. During device operation, accelerometers can measure dynamic acceleration (vibration or rotation) and analyze the device’s displacement and vibration frequency. There are single-axis accelerometers and triaxial accelerometers depending on the measurement direction. Single-axis accelerometers measure vibration along a single axis, while triaxial accelerometers can measure vibration along three mutually perpendicular axes. Single-axis and triaxial accelerometers can be configured with specifications such as sensitivity, temperature, frequency response, and amplitude response.
Pros:
Various installation methods.
Wide range of applications.
They can simultaneously monitor equipment temperature.
They can be used for both high-frequency and low-frequency measurements, offering good stability.
Cons:
Accelerometers need to be in contact with the equipment to measure vibrations.
They require secure fixation before use.
Noise can impact the monitoring results.
Application: Vibrations of rotating machinery are monitored using accelerometers. They are used in devices such as tablets and digital cameras to ensure that the images on the screen are always displayed upright. In unmanned aerial vehicles, accelerometers contribute to stabilizing flight.
3. Eddy Current or Capacitive Displacement Sensors
An eddy current sensor can accurately detect the distance or defects of metal objects without direct contact. The main component of an eddy current sensor is the induction coil, which is a coil of wire located at the probe’s tip. When the alternating current emitted by the probe passes through the coil, it generates an alternating magnetic field. This magnetic field can sense the distance to the target. As the measured metal moves, the strength of the magnetic field changes, causing a change in the coil’s impedance. The farther the distance between the sensor and the target, the greater this change. Eddy current sensors can non-contact measure the state of rotating shafts, providing data on mechanical issues such as rotor imbalance, misalignment, bearing wear, shaft cracks, and friction.
Pros:
Non-contact measurement
High sensitivity for detecting surface-defective workpieces.
Can detect through different layers.
Good in harsh environments with pressure, temperature, dirt, and oil.
Cons:
Measurement targets must be conductive metals.
Susceptible to changes in magnetic permeability.
Not suitable for large-area measure.
Eddy current sensors can measure the shaft displacement of rotating machinery and monitor whether the machinery is in optimal working condition. This type of vibration sensor exhibits excellent performance in environments with oil, dirt, dust, moisture, and magnetic field interference. It is one of the best non-contact sensors for measuring displacement and position in harsh industrial environments.
4. Laser Displacement Sensors
A laser displacement sensor is used for precise non-contact measurement of the position, displacement, and other changes of an object. It is mainly applied in measuring geometric quantities such as displacement, thickness, vibration, distance, and diameter of objects. Based on the measurement principles, laser displacement sensors can be categorized into laser triangulation and laser echo analysis methods. Laser triangulation is generally suitable for high-precision and short-distance measurements, while laser echo analysis is used for long-distance measurements.
Pros:
Non-contact measurement, leading to longer lifespan and no wear.
Short response time.
High precision.
Capable of measuring small objects.
Cons:
The laser emitter and receiver windows and lenses of the sensor are susceptible to contamination from dust and oil.
The proper installation angle is required, as being too close or too far can affect measurement results.
Triangulation Method
In the triangulation method, a laser emitter projects visible red laser light onto the surface of the object to be measured. The scattered laser light from the object is received by a lens and detected by an internal CCD linear camera. Based on the different distances, the CCD linear camera “sees” the light spot at different angles. With this angle and a fixed distance (between the laser and the camera), the digital signal processor can calculate the distance between the sensor and the object being measured.
Echo Analysis Method
The echo analysis principle is used to measure the distance. The sensor consists of a processor unit, echo processing unit, laser emitter, laser receiver, and other components. The laser displacement sensor emits one million laser pulses per second towards the object and receives the reflections back to the receiver. The processor calculates the time required for the laser pulse to encounter the object and return to the receiver, and uses this information to calculate the distance value.
Application: Laser displacement sensors are well-suited for environments that require high speed, high measurement accuracy, and long-distance measurement of numerous targets.
5. Gyroscopes or Angular Rate Sensors
A gyroscope, also known as an angular rate sensor, measures the rate of change of angular velocity around an axis, typically in degrees or radians per second. Gyroscopes can track the twisting, rotation, and rolling of objects in motion, providing more accurate information about displacement. These devices use vibrating structure gyroscopes and are often used in combination with accelerometers to measure vibration.
Pros:
Small size and lightweight.
Fast operation, capable of measuring angular velocity.
High resolution and low drift.
Cons:
Requires high calibration accuracy, resulting in longer production time.
Low stability concerning temperature, humidity, and stress.
Application: Gyroscope sensors are primarily used in the automotive industry to determine the yaw angle (rotation of a vehicle around its vertical axis) or roll angle (rotation of a vehicle around its longitudinal horizontal axis) during vehicle motion.
6. Microphones or Acoustic Pressure Sensors
The working principle of acoustic pressure sensors, or microphones, is to detect mechanical waves or sound waves. When sound waves propagate through a material or on the surface of a material, any changes in the propagation path can affect the velocity and/or amplitude of the waves. Acoustics is a major field in vibration testing.
Pros:
Cost-effective method for high-frequency vibration measurement.
Low cost and easy to operate.
Can accurately represent the frequency content in vibrations.
Cons:
Susceptible to environmental interference.
Limited application range.
Measures relative changes.
Application: Acoustic pressure sensors are used for vibration measurements, assessing fluid flow and vibration. They are also used to detect imbalances between liquids and solids (such as temperature changes) and are applied in vibration analysis and measurement systems to measure machine vibrations. They can be used as liquid pressure sensors or in vibration compensation systems to measure machine vibrations.
7. Handheld Vibration Analyzer
A vibration analyzer is an instrument used to monitor the frequency of mechanical vibrations. It is typically handheld and used for vibration assessment, diagnostics, and quality control in equipment operations. A handheld vibration sensors provides real-time measurement data, allowing users to directly read vibration values by connecting the sensing end to the machine. Based on the data provided by the vibration analyzer, decisions can be made regarding maintenance or repairs. It enables quick testing of the vibration frequency of a machine.
Pros:
Portability and ease of use.
Fast and accurate measurement values.
Offers measurement, storage, diagnostics, and analysis functions.
Wireless operation, no need for installation.
Cons:
Expensive price.
Cannot provide continuous measurements.
Application: Handheld vibration analyzers can be used in various settings such as manufacturing plants, product development laboratories, construction sites, and other places. They are indispensable for advanced vibration measurement and analysis experts.
How to mount a vibration sensor?
Magnetic Mounting
In industrial applications, magnetic bases are commonly used when sensors require periodic point-to-point fast measurements. When using a magnetic base for installation, the magnetic force causes the adapter and sensor to move towards the mounting surface. However, upon contact, the magnetic force can create significant impact on the accelerometer, potentially damaging the sensor chip or its internal electronic components. Magnetic mounts are most suitable for low-frequency testing where the vibration frequencies are relatively small. When magnetic mounting is used for mid-frequency testing, it is necessary to treat the test surface effectively to increase its resonance frequency.
Bolt Mounting
The preferred method for vibration sensor installation is using bolts. By directly fixing the vibration sensor to the bearing with bolts, not only can vibrations in three directions at the top of the bearing housing be measured, but vibrations in two directions on the vertical plane can also be measured. This mounting method provides the most secure attachment.
Adhesive Mounting
In many cases, it is required to install the vibration sensor without damaging the mounting surface, for example, when threaded holes cannot be installed on the mounting surface (due to composite surface materials, insufficient structural thickness, small mounting surface, or multiple mounting points). Adhesive mounting is used in such situations. The hardness of the cured adhesive plays a crucial role in the testing of the entire system. The more adhesive between the sensor and the surface of the structure being tested the poorer the transmission performance. When using adhesive for sensor installation, the operating temperature is an important factor to consider. Adhesives include hot-melt adhesives, super glues, waxes, and double-sided adhesive tapes.
Where is the vibration sensor application?
Mechanical Industry
The vibration sensor can be used to monitor the vibration of rotating equipment such as motors, pumps, fans, and gearboxes. By measuring vibrations, it is possible to detect equipment failures in a timely manner, prevent damage to machinery, and avoid production losses caused by unexpected downtime. The vibration sensor can also be used to monitor the vibration of fixed equipment such as vibration screens and vibratory conveyors.
Aerospace Industry
The vibration sensor can be used to monitor the vibration of aircraft, rockets, and other flying vehicles. They can measure the vibration of the aircraft during flight, takeoff, and landing. This provides data support for normal flight operations, helps optimize designs, and extends the lifespan of the aircraft.
Automotive Industry
The vibration sensor can be used for fatigue and fault monitoring in automobiles. During vehicle operation, a vibration sensor can monitor the vibration of components such as wheels, brakes, and engines. They can predict component damage and faults, enabling timely repairs or replacements and improving the safety and reliability of vehicles.
Energy Industry
The vibration sensor can be used to monitor the vibration of power equipment such as generators and transformers. By providing vibration data, they ensure the proper operation and maintenance of these electrical devices.
Construction Industry
The vibration sensor can monitor the vibration of buildings. During the construction and operation of structures such as subways and high-rise buildings, vibration sensors can monitor the vibration data of the buildings, allowing for the prediction of deformation and damage.
Seismic Exploration
The vibration sensor can be used in seismic exploration. They monitor the vibrations of seismic waves, providing information about geology and underground structures. Vibration sensors can also monitor the vibration of structures such as buildings and bridges during seismic events, providing data support for disaster assessment and rescue operations.
