Back to Basics: Understanding Decibels and Vibration Sensor Orientation

Alan Friedman, Cat IV, CRL, CMRP, Author; Founder/CEO of Zenco Vibration Experts

Posted 4/17/2025

Understanding Decibels and Vibration Sensor Orientation (Introduction)

Are you new to vibration analysis, or do you just need a quick refresher on filters, sensors, or vibration data? These tips from Zenco Vibrations break down the core concepts of decibels and vibration sensor orientation. Watch the two short, easy-to-follow videos for insight into how decibel measurements relate to power and voltage, and why sensor orientation is necessary for accurate diagnostics.

Understanding Decibels

This is a very short video that describes the “half power point” in a filter in terms of decibels (dBs) as well as the 0.707 voltage point. It will also describe the linear range of a vibration sensor in terms of its +- 3dB points.

Decibel units are frequently used in vibration analysis and sound measurements. We will explore the simple dB formulas and how to solve them. After watching this video, you will have an understanding of decibels and how a dB change relates to both power and the voltage coming off a sensor.

Understanding Decibels Formulas

These are the formulas we will review in the video to help with you understand decibels

V = Volts, V1 = Initial voltage, V2 = New voltage

P = Power, P1 = Initial Power, P2 = New Power

dB = 20 log (V2/V1)

dB = 10 log (P2/P1)

V=√ (P2/P1) and P=(V2/V1)2

You will understand these formulas and you will understand why a drop of -3dB is called the “half power” point. You will also see how this change is reflected in vibration amplitude and how it relates to the voltages coming off of a sensor. This will also help you understand the use of the 3dB point in sensor calibration and in filters.

Now, test your knowledge with this short quiz!

Vibration Sensor Orientation

This short video by Alan Friedman from Zenco Vibration Experts explains the importance of defining sensor orientation for triaxial accelerometers. Whether you are taking readings on a route or using wireless sensors, this video has important information you need to know!

It’s not enough to know whether you are looking at data from the “X” or “Y” channel of the accelerometer. You have to know the sensor orientation with respect to the machine.

Vibration Faults and Axes

Different mechanical faults show up in different axes. For example, unbalance in a supported rotor shows up at 1x vertical and 1x horizontal whereas angular misalignment shows up at 1x and 2x axial. Not only do we need to know what test point the vibration data came from, we also have to know which axis. Vibration diagnostics are not possible without information about sensor orientation.

*Unbalance causes the shaft to vibrate vertically and horizontally*

angular misalignment on shaft — *Angular misalignment causes the shaft to vibrate in the axial direction*

What is the Orientation?

We need to know which direction the X, Y and Z sensors are facing with respect to the machine. What is the orientation of the sensor? Is the X sensor in the Vertical direction? Is the Y sensor in the Axial direction? This is what mean by sensor orientation, and this is what we need to determine.

Do you have a better understanding of decibels and vibration sensor orientation?

Check out ZENCO’s course schedule and sign up for a course online or in person with Alan Friedman today! https://zencovibrations.com/events/

Alan Friedman

Alan, aka the Vibe Guru, has over 30 years of vibration analysis experience, He has trained 1000’s of students around the world up to Category IV. One of the things that makes Alan a great teacher is his ability to teach people where they are at. Whether you are a math challenged millwright, an engineer or a PhD, Alan will challenge you without overwhelming you. If you are interested in condition monitoring you can also check out his book: Audit It. Improve It! Getting the Most from your Vibration Monitoring Program or hire him for an on-site program audit.

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Back to Basics: Understanding Decibels and Vibration Sensor Orientation