Damages, accelerometers

Downhole Shocks Measurements. An accelerometer in the MWD telemetry tool measures transverse accelerations, or shocks, that may be damaging for the bottomhole assemblies. When acceleration exceeds a certain threshold, the event is signaled to the surface as being a shock. These events versus time or depth are displayed as shock count. This information is used as a warning against excessive downhole vibrations and to alert the driller to change the rpm or weight on the bit [106]. 

A benefit of the use of accelerometers is that they do not require a calibration program to ensure accuracy. However, they are susceptible to thermal damage. If sufficient heat radiates into the piezoelectric crystal, it can be damaged or destroyed. However, thermal damage is rare since data acquisition time is relatively short (i.e. less than thirty seconds) using temporary mounting techniques. 

In addition to impact forces, transmission of vibrations to the product can result in damage. Characteristic vibration transmissibility plots for foams are also available, which can be matched with the product s susceptibility to damage. Of course, the design process should be followed by the preparation of a model package and suitable testing of the producl/package system, or in case of a very expensive product, a mock-up used with accelerometers to determine actual performance. 

An example application of a sensor network system equipped with MEMS accelerometers is the measurement of restoring force characteristics of strucmres subjected to strong ground motion. Right after a severe earthquake, the damage level of the structures in disaster-stricken region has to be quickly identified. For this... 

To prevent damage to the accelerometers, the shear force sensors and electrical eqnipment contained in the vibrating head from exposure to high temperatures, a layer of resin-bonded fiberglass insulation was mounted between each aluminum plate and vibration welder fixture. A schematic of the SPR fixture is shown in Figure 1. 

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