Marine Dumont & Andy Cook
Acceleration Measurement Optimization: Mounting Considerations and Sensor Mass Effect
Norton Kinsley, Engineering Lab Supervisor, Kistler Instrument Corp. 75 John Glenn Drive, Amherst, NY 14228-2171 USA
Published: December, 16 2015
In the world of acceleration, a common topic is that of modal analysis. Within this topic, applications can range from the study of bridges as vehicles roll across them, to the qualification of very delicate space and aviation equipment. One can see that modal analysis contains a very large spectrum of applications. However, there is a small detail that is commonly overlooked, and that is the proper mounting of very sensitive accelerometers. Mounting options include direct stud mounting, wax mounting, magnetic mounting and a variety of options in-between. Although these options are diverse, they come with varying stiffness and sometimes with the cost of addition mass, termed the mass loading effect. The first part of this paper will take an in-depth look into some of the more common mistakes made during mounting, as well as a look into what can be done to optimize the mounting to avoid unwanted results. In the second part of this paper, there will be an exploration into the results of poorly mounted accelerometers; then a look in more detail at what the mass loading effect and stiffness are and how these can drastically change the measurement results.
A- Sensor Mounting Considerations – Introduction
To obtain useful measurement information, an accelerometer must be coupled so that complete event information is transferred. Mounting methods may vary, with some transferring event information more effectively than others. A high performance accelerometer will behave like a low performance accelerometer if the mounting method is inadequate. The transfer function behavior between the mechanical input properties and electrical output properties can be characterized by a “Single Degree of Freedom” (SDOF) system with a mounted resonance frequency, which will decrease if the mounting method becomes less stiff. This is illustrated in Figure 1 below.