4.2 Sensors

As discussed above, the term sensor can be interpreted broadly as a provider of data. In the military framework, vital information may be provided by a variety of channels and it is there that the interpretation is broadest. For the purposes of this review, a more restricted definition of sensor may be adopted without loss of generality. A sensor will be understood to be some physical construct which translates an environmental or structural variable into an electrical signal which can be quantified. (There is little point in attempting further precision as this may lead to discussions bordering on philosophy.) In most structural dynamic applications, the sensor signals are processed either in software or hardware and used to formulate some decision about the structure. This may be a control decision, where it proves necessary to alter the state of the system, or it may be a health management decision where the system is taken off-line for more detailed inspection or repair.

The processing chain for an individual sensor is therefore as summarised in Fig. 4.1. The elements of the chain can be summarised as follows:

• Sensor Provides an electrical ^[*] signal proportional to the structural or environmental variable of interest. For example, an accelerometer could be placed on the outer casing of a gearbox in order to monitor its condition or state of health.

• Pre-Processing In most circumstances, the time-varying voltage from the sensor will contain too much data, much of which is redundant. The goal of...