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With the advent of semiconductor and other microtechnologies, the basic principles applied at the time were generally retained:
Resistive systems used the change in resistance as a change in measuring value. The temperature sensitivity of the resistance in a wire was used as a thermometer to measure temperature. The principle of detuning of a measuring bridge was utilized as a piezoresistive effect by implementing p-n transitions in a semiconductor crystal.
Capacitive and inductive processes are primarily used for thickfilm methods. In thickfilm processes, the measuring bridge is applied by screen printing; whereas in thinfilm processes, the bridge is applied by vaporization or metalizing, for instance.
Optical processes are often based on changes in light intensity due to diffusion or diffraction of external effects. The change in the refraction index or the transmission of special materials can also be utilized – thus implementing fibre-optic methods.
An important motor for innovation is the need for improvement of reliability, cost cutting, and miniaturization of measuring systems. Catchwords, such as SMT, ASIC, or even microelectronics, are associated with this development.
The demand to miniaturize applied not only to electronics, but increasingly also to the other components in a sensor system. Semiconductor sensors played a major role in developing microsensors, which were subsequently coupled to microelectronics to realize the first microsystems.
Parallel to this continual miniaturization, a trend emerged towards increasing the intelligence of these measuring systems.
The AMA polls showed that most of the suppliers of sensor systems today provide some kind of connection to a bus system, while integrated bus systems have only been implemented in about 5% of the produced units, but with increasing tendency. The reason for this discrepancy can be found in the cost-per-unit problem. Microsystem technology will provide considerable changes within the next years to alleviate this problem. Another approach may be found in the AMA’s “modular microsensors” concept, which includes a definition of a bus interface.
