Basics of Accelerometer Mounting Explained

Overview
In this blog post, we'll examine the advantages and disadvantages inherent in various mounting methods for accelerometers or piezo-velocity sensors. By better understanding these basic principles, analysts will be better able to decide which hardware and techniques to use depending on the type of data you require for a given application.

Accelerometer Mounting Options
There are four general categories of mounting styles which we will focus on:

1. Magnet Mount with a curved or flat-surface magnet
2. Specialty Mounting Pads such as motor fin mount pads
3. Epoxy Pads including quick disconnect studs, targets for flat magnets, and permanent mounting pads
4. Stud Mount

There are advantages and disadvantages to each method of sensor mounting. Generally speaking, an analyst will capture better data when the mounting method adds minimal mass (or weight), maximizes surface area contact, maximizes stiffness (how firmly the sensor is attached to the machinery), and is located closer to the source of the vibration.

Magnet Use
One of the most common methods of portable data collection is through the use of a curved surface (also known as "two-bar") magnet system. The contact area of these magnets is not as good as a quick disconnect system or a flat magnet with a mounting target, and its mass tends to be higher; therefore, analysts should not depend on data above 2 kHz (120,000 CPM).

Flat magnets and quick disconnect systems offer a far better response range due to the increased surface area in contact with the source of the vibration. A flat magnet on a well-installed target can yield reliable data up to 8 kHz to 10 kHz (480,000 to 600,000 CPM).

MH112-1A Multipurpose 2 Rail Magnet Mounting Base with 1/4-28 integral stud, 30 lbs. (14 kg) pull strength, 1.00 in. (25.4 mm) OD, 0.68 in. (17.27 mm) height

MH103-1B Flat Surface Magnet Mounting Base with 1/4-28 integral mounting stud, 40 lbs. (18 kg) pull strength, 1.00 in. (25.4 mm) OD, 0.46 in. (11.68 mm) height

MH133-1A Low Profile Magnet Mounting Target, 1.00 in. (25.4 mm) diameter, 0.25 in. (6.4 mm) height

MH107-1A Quick Disconnect Receptacle, with 1/4-28 tapped sensor mounting hole
and
MH107-1B Quick Disconnect Stud

Specialty Mounts
Specialty mounts such as grease fitting mounts (also known as "Zerk adapters") and motor fin mount pads tend to add a bit of mass and lack some stiffness. However, they are designed to be positioned in good proximity to the source of bearing vibrations; therefore, they tend to provide good data, typically in the 2 kHz to 5 kHz range (120,000 to 300,000 RPM). Most specialty mounts can either be used for magnet targets or permanent mounting.

MH134-1A Accelerometer Mounting Pad with Zerk Grease Fitting Adapter, 1/4-28 tapped hole, 1/4-18 NPT mounting thread

MH118-1A Motor Fin Mount Probe Pad, with 0.50 in. x 1.25 in. (12.70 mm x 31.75 mm) probe tip

Permanent Monitoring
Assuming proper techniques have been employed to mill the surface of the machine and affix the sensor, permanent mounting options will tend to produce good results at higher frequency ranges (up to the full scale of the sensor). The data in general will be cleaner, more accurate, and highly repeatable. However, to achieve these results, the initial installation requires more care and time than some portable methods. Permanent mount installations initially also tend to be more expensive due to dedicating a sensor to each monitoring point. This additional investment can easily be recouped when analysts are able to gather better data more efficiently. 

MH117-1B Accelerometer Installation Tool Kit, 1.25 in. (31.75 mm) end mill diameter for 1/4-28 thread, with tap set

MH101-1B Adhesive Pad Mounting Disk, with 1/4-28 integral mounting stud, 1.00 in. (25.4 mm) diameter