Main Menu

See All Acoustic End-of-Line Test Systems See All DAQ and instruments See All Electroacoustics See All Software See All Transducers See All Vibration Testing Equipment See All Academy See All Resource Center See All Applications See All Industries See All Insights See All Services See All Support See All Our Business See All Our History See All Our Sustainability Commitment See All Global Presence

Main Menu

See All Actuators See All Combustion Engines See All Durability See All eDrive See All Production Testing Sensors See All Transmission & Gearboxes See All Turbo Charger See All Industrial electronics See All S&V Signal conditioner See All DAQ Systems See All Power Analyser See All S&V Hand-held devices See All High Precision and Calibration Systems See All Test Solutions See All nCode - Durability and Fatigue Analysis See All ReliaSoft - Reliability Analysis and Management See All Test Data Management See All DAQ Software See All Drivers & API See All Utility See All Vibration Control See All Acoustic See All Current / voltage See All Displacement See All Load Cells See All Pressure See All Strain Gauges See All Vibration See All Torque See All LDS Shaker Systems See All Vibration Controllers See All Power Amplifiers See All Accessories for Vibration Testing Equipment See All Training Courses See All Acoustics See All Asset & Process Monitoring See All Custom Sensors See All Data Acquisition & Analysis See All Durability & Fatigue See All Electric Power Testing See All NVH See All Reliability See All Smart Sensors See All Vibration See All Weighing See All Automotive & Ground Transportation See All Calibration See All Installation, Maintenance & Repair See All Support Brüel & Kjær See All Release Notes See All Compliance See All Our People

Main Menu

See All QuantumX See All LAN-XI See All SomatXR See All MGCplus See All CANHEAD See All Optical Interrogators See All GenHS See All API See All Microphone Cartridges See All Microphone Sets See All Microphone Pre-amplifiers See All Sound Sources See All Acoustic Calibrators See All Special Microphones See All Accessories for acoustic transducers See All Experimental testing See All Transducer Manufacturing (OEM) See All CCLD (IEPE) accelerometers See All Charge Accelerometers See All Rotating See All Non-rotating (calibration) See All Electroacoustics See All Noise Source Identification See All Environmental Noise See All Sound Power and Sound Pressure See All Noise Certification See All Industrial Process Control See All Structural Health Monitoring See All Electrical Devices Testing See All Electrical Systems Testing See All Grid Testing See All High-Voltage Testing See All Vibration Testing with Electrodynamic Shakers See All Structural Dynamics See All Machine Analysis and Diagnostics See All Dynamic Weighing See All Calibration Services for Transducers See All Calibration Services for Handheld Instruments See All Calibration Services for Instruments & DAQ See All On-Site Calibration See All Resources See All Software License Management

Avoiding Vibration Measurement Errors

Avoiding errors is part of the measuring vibration introduction which answers some of the basic questions asked by the newcomer to vibration measurement. It gives a brief explanation of the following: avoiding errors due to accelerometer resonance, how to choose a mounting position for the accelerometer, and how to mount it.

Download Handbook


  1. Accelerometer Mounting Position
  2. Mounting the Accelerometer

Accelerometer Mounting Position

The accelerometer should be mounted so that the desired measuring direction coincides with its main sensitivity axis. Accelerometers are also slightly sensitive to vibrations in the transverse direction, but this can normally be ignored as the transverse sensitivity is typically less than 5% of the main axis sensitivity.

The reason for measuring vibration on the object will usually dictate the position of the measuring point. Take the bearing housing in the drawing as an example. Here, acceleration measurements are being used to monitor the running condition of the shaft and bearing. The accelerometer should be positioned to maintain a direct path for the vibration from the bearing.

Accelerometer "A" thus detects the vibration signal from the bearing predominant over vibrations from other parts of the machine, but accelerometer "B" detects the bearing vibration, probably modified by transmission through a joint, mixed with signals from other parts of the machine. Likewise, accelerometer "C" is positioned in a more direct path than accelerometer "D".

The question also arises — in which direction should one measure on the machine element in question? It is impossible to state a general rule, but as an example, for the bearing shown, one could gain valuable information for monitoring purposes by measuring both in the axial direction and one of the radial directions, usually, the one expected to have the lowest stiffness.

The response of mechanical objects to forced vibrations is a complex phenomenon so that one can expect, especially at high frequencies, to measure significantly different vibration levels and frequency spectra, even on adjacent measuring points on the same machine element.

Accelerometer sensitivity

Mounting the Accelerometer

The method of mounting the accelerometer to the measuring point is one of the most critical factors in obtaining accurate results from practical vibration measurements. Sloppy mounting results in a reduction in the mounted resonant frequency, which can severely limit the useful frequency range of the accelerometer.

The ideal mounting is by a threaded stud onto a flat, smooth surface as shown in the drawing. A thin layer of grease applied to the mounting surface before tightening down the accelerometer will usually improve the mounting stiffness and thereby ensure a mounted resonant frequency close to the specification.


The tapped hole in the machine part should be sufficiently deep so that the stud is not forced into the base of the accelerometer. The upper drawing shows a typical response curve of a general-purpose accelerometer mounted with a fixing stud on a flat surface. The resonant frequency attained is almost as high as the 32kHz mounted resonant frequency attained under calibration where the mounting surface is dead flat and smooth.

A commonly used alternative mounting method is the use of a thin layer of beeswax for sticking the accelerometer into place. Remember to squeeze the layer of wax as much as possible to get a very thin layer! As can be seen from the response curve, the resonant frequency is only slightly reduced (to 29kHz). Because beeswax becomes soft at higher temperatures, the method is restricted to about 40°C. With clean surfaces, bees-wax fixing is usable up to acceleration levels of about 100 m/s2.

Where do vibrations come from
Where permanent measuring points are to be established on a machine and it is not wished to drill and tap fixing holes, cementing studs can be used. They are attached to the measuring point using hard glue. Epoxy and cyanoacrylate types are recommended as soft glues can considerably reduce the usable frequency range of the accelerometer.

A mica washer and isolated stud are used where the body of the accelerometer should be electrically isolated from the measuring object. This is normally to prevent ground loops, but more about that under "Environmental Influences". A thin slice should be peeled from the thick mica washer supplied. This fixing method also gives good results, the resonance frequency of the test accelerometer only being reduced to about 28 kHz.

A permanent magnet is a simple attachment method where the measuring point is a flat magnetic surface. It also electrically isolates the accelerometer when an isolating disk is used. This method reduces the resonant frequency of the test accelerometer to about 13 to 20 kHz depending on whether isolation disk is used and on whether silicon grease is used for the mounting, and consequently cannot be used for measurements much above 7 to 13 kHz. The holding force of the magnet is sufficient for vibration levels up to 1000 m/s2 depending on the size of the accelerometer.

Mounting the Accelerometer


A hand-held probe with the accelerometer mounted on top is very convenient for quick-look survey work but can give gross measuring errors because of the low overall stiffness.

Repeatable results cannot be expected. A low-pass filter should be used to limit the measuring range to about 1000 Hz.

Use the buttons below as we continue to the next chapter on environmental effects on measurements.