Accelerometer Mounting Studs and Screws
To acquire the best sensor data the sensor must be rigidly affixed to the test article. By this means, maximum energy is transferred from the test article into the sensor. Rigid connection to the test article results in the highest frequency response possible within the limit of the sensor upper frequency response. Often a test person may loosely mount a sensor. Sometimes such an approach may result in off-axis orientation. To prevent this, a prerequisite to mounting the sensor is to “face” the mounting location. A flat (faced) surface is required to properly mount the accelerometer. Drill and tap a hole perpendicular to the flat (faced) surface. The mounting stud or screw mates to this hole.
Accelerometer mounting studs are used to secure the accelerometer to the test object. To ensure accurate measurements, always mount the accelerometer to the datasheets recommended mounting torque. Also, avoid bottoming the stud into the test object or accelerometer’s tapped mounting hole. A shoulder stud will usually prevent bottoming out. Ensure that the base of the sensor is counter-bored to accept the shoulder. Once installed, the accelerometer’s base should be flush with the test articles surface. In temperature environments below the upper temperature limit of a particular grease or light engine oil, a small amount of this grease or oil should “wet” the flat surface interface between the test article and sensor. This grease or oil is often referred to as a “Couplant”.
Is it always best practice to use vender manufactured mounting adaptors instead of end user made mounting devices.
Electrically, measurement systems may have more than one ground. This is often by mistake as a measurement system should only have one ground reference. The resulting “ground loop” is at power line frequency (60 Hz in the USA) and odd harmonics. Isolation studs do not allow continuity between the sensor case and the shell of a metallic test article. This prevents “Ground Loops” resulting in better data quality.