What is Vibration Monitoring?

Vibration is movement or oscillation relative to a reference point. The frequency of this motion is measured in hertz (Hz). Vibration is a normal part of operating many machines but can become a concern if it goes beyond defined parameters. Vibration monitoring helps workers understand when a machine needs attention prior to failure. Predictive maintenance can prevent costly repairs, damage, and even injuries.

^{Figure 1: Vibration sensor}

The following list describes several types of sensors used to monitor vibration:

• Accelerometers—Vibration is usually measured with an accelerometer, many of which take advantage of the piezoelectric effect to sense vibration. The piezoelectric effect is a phenomena where certain types of crystals generate a voltage in response to a force. The voltage is proportional to the applied force, allowing the accelerometer to accurately measure vibration.
• Proximity probes—A proximity probe measures the distance to a target and is often used to measure the displacement of rotating machinery components. Proximity probes can be particularly useful where flexible fluid film bearings or heavy housings block the vibrations that accelerometers require to operate effectively.
• Velocity sensors—Also known as velocity transducers, these devices operate similarly to accelerometers but have an integrating circuit that converts acceleration to velocity. Velocity sensors are often used to monitor low frequency vibrations where other measuring devices could be susceptible to noise or distortion.

^{Figure 2: Wireless Vibration Monitoring Process}

Every machine component has a unique vibration signature under normal operation. Deviations from this baseline—such as increased amplitude, frequency shifts, or irregular patterns—can signal early signs of failure. Vibration monitoring systems combine sensors, data acquisition (DAQ) hardware, and analysis software to detect these changes in real time, enabling predictive maintenance before critical failures occur. Not only are there different types of sensors, but there are also different setups that enable vibration data collection and analysis, including the following list of some common options.

• Wireless vibration monitoring—Sensors placed on equipment transmit information to a data acquisition device connected to a computer for analysis. Wireless vibration sensors can be installed in difficult-to-reach or dangerous areas without concerns about running wires through a machine or sending a technician to take manual readings when equipment is running. Sensors can also be relocated without the removal and repositioning of wires. However, there are potential disadvantages to this approach, including wireless data security and signal range limitations.
• Wired vibration monitoring—Vibration sensors are connected to a data acquisition device and computer with wires or cables. Data is less susceptible to interference or interception than in a wireless setup, and wired sensors deliver real-time readings. On the other hand, installation may be complicated, and wires can be physically damaged. Redeploying sensors to other locations requires removal and reinstallation of wires.

Both wireless and wired vibration monitoring methods are examples of online monitoring, where data is gathered continuously.

• Offline vibration monitoring—A technician carrying a portable sensor measures vibration levels at each component. While this is a flexible approach to vibration monitoring, it’s periodic rather than continuous and can put a human at risk around operating machinery.

Vibration analysis refers to the review of sensor data by specialized software. There are various ways signals are analyzed, including fast Fourier transform (FFT), order analysis, time-frequency analysis, envelope analysis, and wavelet analysis. These methods can be combined for a more comprehensive analysis. Potential signs of trouble can be flagged for human review. Vibration monitoring systems may also be set up to automatically take action, such as shutting down a machine, if the situation is serious enough. 

Vibration monitoring is used on equipment in many industries, including automotive, aerospace, and energy. You’re likely to find vibration monitoring sensors in the following places:

• Rotating shafts
• Motors
• Gas turbines
• Reciprocating compressors
• Pumps
• Bearings
• Fans
• Engines

Vibration monitoring is an important part of designing and testing new components. For example, engineers need to confirm that rocket or jet engine parts operate safely when subjected to the extreme forces and conditions they’ll encounter in the real world.

Vibration monitoring includes the following potential benefits:

• Reducing unplanned downtime
• Decreasing predictive maintenance costs
• Keeping humans out of harm’s way
• Increasing the lifespan of machinery
• Optimizing maintenance schedules
• Improving machine reliability
• Gaining efficiency

NI sound and vibration hardware interfaces with accelerometers to acquire vibration signals for machine condition monitoring as well as noise, vibration, and harshness (NVH) applications. Our offerings go beyond DAQ to include software; the NI LabVIEW Sound and Vibration Toolkit enables vibration analysis within a powerful and widely used program.

NI solutions for vibration monitoring offer several advantages over other approaches:

• Our long history of measurements in many applications means that the measurements you take with NI equipment are higher quality than hardware designed specifically for condition monitoring. NI products are more accurate, with more stable timing, and more reliable measurements.
• NI platforms are built on a concept of modularity, so systems are more efficient to design and easier to maintain over the lifetime of the application. Unlike fixed-personality systems, you can easily expand systems by adding modules to gain new channels or measurements.
• NI high-speed systems can capture all of the data, not just periodic bursts. This means you can record events that other systems miss.