A modern measurement and control system A modern measurement and control system[1] could be set up as in Figure 1; in such a system, a great number of sensors collect information about the processes available in the system being monitored. Although sensors are employed in many different applica- tions, the more complex the system being monitored becomes, the more powerful, comprehensive or intelligent are the sensors required. In the digital sensor bus of Figure 1, a central computer is connected to a number of input and output devices. It picks up information from different sensor systems via a digital bus and either makes some signal processing before sending them out or directly sends them to actuators again after some basic conversion operations. For instance, the output signal of the sensor is first amplified and corrected for offset, non-linearity, and other types of sensor errors before trans- ferring it to the bus system. In the second group of sensors , the signals are treated in separate signal-con- ditioning circuits for offset, non- linearity, temperature sensitivity, and so on. Then a single multiplexing circuit feeds these signals one after the other into a single A/D converter and from there the signals are sent to the digital bus. This second solution is preferable, because several sensors are positioned quite close together to form one unit. In the last example, the sensor is connected by an A/D converter to a microprocessor. The microprocessor has stored the sensor’s specific data in its memory, ROM, and also the sensor signal, and the microprocessor transfers a corrected signal to the bus. An interesting property of this subsystem is that the microprocessor also permits the central computer to send data back to the sensor, which can be used to change the measurement range, to effect a recalibration or to adjust offset. In such a subsystem, each sensor or group of sensors also contains a circuit that can recognize addresses; this means the circuit can detect when communication between sensor and central computer is wanted. “Today, most of the described components of a bus system are still separate and have their own housing. However, in the future the integration of these com- ponents on a single chip will be the norm. This is indicated by the broken lines in Figure 1. Intelligent sensors and intelligent transducers In the existing systems, intelligence is still centralized, but the more the systems become decentralized the more the intelligence will be distributed, and as a result the more efficient and effective the systems will become. This will need what is called an intelligent sensor. A modern micro- processor-based intelligent sensor[1] could be composed of a sensing element, a signal-processing part, and a microprocessor as shown in Figure 2. If we combine a sensing element with a signal processor on a single chip then what we get is an intelligent sensor. In the near future it will be possible to put an intelligent sensor on a microprocessor, but much local signal conditioning can be taken over via a microprocessor used in a system. Intelligent transducers are a result of recent developments in large scale integration (LSI) and very large scale integration (VLSI) technology. Transducers can be integrated with signal-processing circuits on the same chip to perform active functions. These are defined as intelligent trans- ducers[2], in a broad sense, and are shown in Figure 3. Sensor Review, Vol. 15 No. 3, 1995, pp. 31-35, MCB University Press, 0260-2288 SR Vol. 15 No. 3, 1995 31 Intelligent sensors: structure and system E.T. Powner and F. Yalcinkaya S A S B 1 Signal conditioning Amplifier Correction S B 2 Signal conditioning S B 3 Signal conditioning A/D Multiplexer A/D S C Microprocessor A/D Bus Amplifier A/D Actuator Bus controller Central computer Storage Display or printer Telecommunicaion Figure 1. Schematic of a digital sensor bus interface structure