Accelerometers measure shock and vibration by providing an output signal proportional to the object to which it is attached. There are many methods of attaching accelerometers (magnetic, tape, epoxy and studs/screws). Where possible and practical, screw or stud mounting is preferred because this method provides the stiffest connection with the object under test. Accelerometers manufactured with holes or flanges for screw/stud mounting provide end users with the most effective way of attaching these sensors to obtain best quality of data possible. However, even the most experienced users end up with bad data because they forget or ignore one or more of the basic mounting guidelines below.
1. The mass of the accelerometer must be <1/10 of the mass of the object under study.
2. Mounting surfaces need to be clean, free of any residue from epoxies, waxes, paint or other foreign materials.
3. Mounting surface should be flat.
4. The surface roughness of mating surfaces should be 32 micro-inches RMS (MAX).
5. The mounting holes need to be perpendicular – within 1 degree.
6. The mounting hole must be checked to ensure it is longer than the mounting screw so as to prevent “bottoming out”.
7. Use a torque wrench for tightening screws to the manufacturer’s specifications. Do not use electric tools as their frequencies may damage the accelerometer.
8. Spread mating surface with a light coating of silicone grease, heavy machine oil or bees wax to ensure contact is secure thereby maximizing the usable frequency range.
9. Secure the cable using clamps, o-rings, tape or other materials most suited to the application. Ensure that you have sufficient slack to allow for free movement of the sensor.
10. Inspect mounting holes and remove any debris, burrs or other foreign materials.
There are many applications where holes cannot be drilled into the structure or the design of the accelerometer does not allow for screw/stud mounting. In these instances, adhesive solutions are the most practical. For best performance, end users suggest using cyanoacrylate adhesives – a generic name for methyl-2-cyanoacrylate, which can be purchased under such trademarks as Super Glue, Loctite® or Krazy Glue®. Another form, 2-octyl cyanoacrylate (trade name Dermabond®), has many medical uses and causes less irritation to one’s skin than methyl-2-cyanoacrylate. Cyanoacrylate sets in less than 60 seconds, with full strength reached in two hours. For temporary installation, it is recommended to use hot glue bees wax or double-sided tape
The guidelines below are suggested when using adhesives to mount accelerometers.
1. Mounting surfaces must be clean and free of any residue from epoxies, waxes, paint or other foreign materials.
2. The mounting surface should be flat and even.
3. Prolonged inhalation of vapors can be harmful!
4. Avoid contact with your skin.
5. Use acetone to soften cured cyanoacrylate for accelerometer removal.
6. Cyanoacrylate is available for temperature ranges from -18° C through 125° C.
7. Use the thinnest layer of cyanoacrylate possible for best frequency response.
8. Exposure to moisture in the air causes cyanoacrylate to set. Store the material in an airtight container with a package of silica gel.
9. Use a razor blade to remove the accelerometer after the cyanoacrylate has been softened by acetone. Prying the sensor loose with a screwdriver may damage the sensor unit.