What Are the Basics of Vibration Analysis?

When it comes to rotating and reciprocating machinery, making sure your machines are functioning properly is one of the most critical tasks necessary to keep you and your workers safe. Regardless of the industry, machinery vibration analysis is important for maintaining your equipment and keeping it functioning at maximum efficiency and reliability. Rotating and reciprocating machinery vibration measurements should be taken to ensure that the machine is safe and in working order.

What is Vibration Analysis?

Vibration analysis is a methodology of examining the vibration amplitude, frequency and phase emitted by a piece of machinery to determine the machine's functional condition. For rotating and reciprocating machines vibration sensors are strategically located to provide the best information regarding the machine’s condition. The different vibration patterns sensed can be interpreted to help reveal problems or irregularities with your machine. Some of the most common machines require evaluation at multiple vibration frequencies. Each rotating part can emit a different vibration frequency, so using a proper vibration sensor is crucial to understanding your machine’s behavior.

What Are the Different Kinds of Vibration? 

Vibration is measured in terms of amplitude, frequency and phase and can differ widely depending on the type of machine and the mode in which the data is taken. For example, when you start up or shut down a machine, you have major changes in speed. The vibration monitoring system has to be able to accommodate for that transient mode, or speed change. Another important vibration mode for the machine is its steady state loaded condition. Two other uncommon vibration modes are when the machine is slowly turning during a shutdown (no dynamic motion), and when the machine is stopped. Depending upon the machine, you may need vibration data from all four modes of operation.

Three different types of vibration measurements can be taken:

• Displacement – If your machine has fluid film bearings, the best measurement is usually two proximity probes mounted in X-Y orientation on or near each of the bearings. Displacement is also used for measuring thrust position and speed. Proximity probes provide a non-contact position measurement that can watch the relative rotor movement that may be invisible to casing sensors like velocity sensors and accelerometers.
• Velocity – Velocity measurements are made for those machines with rolling element bearings that operate at 60 Hz. or less. Velocity sensors are used because they have an excellent Signal to Noise Ratio (SNR) as compared to accelerometers in this frequency range. Proximity probes are not used with rolling element bearings because there is no relative motion between the rotor and the casing. Sometimes, in special applications, velocity sensors are used on fluid film bearing machines to measure casing vibration.
• Acceleration – Acceleration measurements are made for those machines with rolling element bearings that operate at greater than 60 Hz. Accelerometers are also used to measure casing vibration when higher frequencies are expected, usually above 2 KHz like gear mesh frequencies.

Combined, these three measurements can be used to accurately determine the vibrational output of your rotating or reciprocating machine. It is common to see more than one type of measurement on a machine. For example, in certain situations, proximity probes measuring vibration on fluid film bearings, coupled with velocity sensors measuring casing vibration on the same machine.

Vibration analysis provides deeper insight into the behavior of your machines. It allows you to move from a preventative maintenance methodology to a predictive or a proactive maintenance methodology. This in the long run, saves you money.

Early Warning Helps You to Know When Vibration Analysis is Necessary

It’s a waste of time to perform vibration analysis on a machine that is perfectly healthy. It’s analogous to going to see a doctor (other than your annual check-up), even though you feel well, and you have not even taken your temperature.

Metrix is in the business of providing early warning so that you know when to perform vibration analysis. Some of the most common forms of vibration measurement in machinery are performed by vibration switches. Vibration switches help bring your attention to a rotating or reciprocating machine that may need vibration analysis.

The two most common types of vibration switches are:

• Mechanical Vibration Switches - These switches are used to let you know that the machine behavior has changed in a significant way. These switches should be considered failure detection devices. When this type of switch is activated, often times you do not have early warning even though something significant has changed. This could include broken fan blades, broken impellers, piston rods or other mechanical failures. This device is used to protect people and the facility.
• Electrical Vibration Switches - In contrast to mechanical switches, they provide greater precision in the vibration measurement, as well as in many cases a 4-20 mA output that can be trended to provide early warning. The electronic switch can be setup to take advantage of the precise vibration output to provide alarm and shutdown levels. These alarm and shutdown levels provide the early warning necessary for you to conduct vibration analysis and avoid machinery failure.

Vibration switches are a critical component to help keep your machines in proper working order. They help protect the machine, while providing you an opportunity to conduct vibration analysis when needed. This saves you time and money. 

Where to Begin A Predictive or Proactive Vibration Measurement Program

Metrix Vibration is the industry’s premier vibration monitoring company. With various vibration switches and monitoring accessories to choose from, you can be sure you’re getting a monitoring system that fits your requirements. Metrix will provide you the early warning you need to conduct vibration analysis that helps you to prevent breakdowns, save time and money, and support safety measures. For more information, visit our Products section, and look through our Online Store today. You can still call us at 281-940-1802, we pick up the phone!

By Everett Jesse, Vice President of Sales and Marketing