When is adhesive accelerometer mounting appropriate?
The most desirable accelerometer mounting method is using a screw, stud or the bolt supplied by, or recommended by the manufacturer. But, for many measurements, adhesive mounting is often the most convenient and sometimes the only option available. Adhesive mounting is most commonly accomplished using cyanoacrylate or Epoxy. Other methods are sometimes used and are discussed in Endevco Technical Papers TP319 and TP312 (available on the Endevco web site).Cyanoacrylate Mounting
These adhesives are available from a number of suppliers and are commonly found in hardware stores under the name of "Super Glue." This is a one-part adhesive that sets-up quickly making it very convenient. Since only a very thin layer is applied to the accelerometer's base, one can expect excellent transmissibility. Cyanoacrylate mounting is usually considered a semi-permanent type of mounting.
When removing the accelerometer, use a releasing agent (e.g., Loctite X-NMS and acetone) to soften the adhesive, then twist off the accelerometer with a wrench. Never strike the accelerometer or remove it with a chisel or pry it off with a screw driver. Once the accelerometer is removed, clean off the residue using a solvent. Never scrape the residue off of the sensor.
There are many excellent suppliers of cyanoacrylate adhesives. Loctite 430, Eastman 910 and Master Bond are among some of the popular choices. Suppliers offer the adhesives with different properties. A convenient reference showing the available properties can be found at this link:www.masterbond.com/sg/masterbond_cyanosg.pdf
As with any type of mounting, always ensure a clean, smooth, flat, clean mounting surface. Never use too much cyanoacrylate, or it will become very difficult to remove the sensor.Epoxy Mounting
In cases where a permanent mounting is required and the use of screws or stud mounting is impractical, epoxy offers an excellent alternative. Two-part epoxy adhesives offer the stiffness required to maintain the high-frequency response required in many tests as well as long-term reliable service.
The rules for surface preparation and removal are the same as those described above for cyanoacrylate mounting. When using epoxy, try to keep the adhesive layer between the accelerometer and UUT as thin as possible to ensure maximum transmissibility.
There is a wide selection of epoxy types available with differing properties. The Endevco Applications Engineering Department has found the tables on the following website to very useful:www.masterbond.com/sg/masterbond_htsg.pdfGeneral Considerations
When adhesively mounting a stud-mount accelerometer, always use an adhesive mounting base. This will prevent the adhesives from entering the threaded hole and also make removal easier.
Post-test clean-up cannot be overemphasized. Many accelerometers do not perform properly due to excess adhesive residue from past tests. The bottom surface of the accelerometer must be flat and smooth to ensure high frequency performance.
Temporary mounting can be accomplished using Petro Wax and magnets. Other mounting materials include dental cement and hot glue.
Following these simple guidelines will ensure years of accurate measurements from your accelerometers. Assistance is always available from Endevco at email@example.com
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