SENSING AND SAMPLING STRATEGIES 43 Sensing element Signal conditioning and processiing A/D converter Sensor-bus interface To PC Figure 2.3. Block diagram of a classical integrated sensor. 3. SENSOR FUNDAMENTALS A sensor is a device designed to acquire information from an object and transform it into an electrical signal. The signal from a sensor can be grouped into six energy domains: electrical, thermal, mechani- cal, chemical, radiant, and magnetic. Since electrical signals are the most preferred signal form, in this chapter only this category of sensors is discussed. A block diagram of a classical integrated sensor is shown in Figure 2.3. The first stage has a sensing element, which could be a resistor, capacitor, transis- tor, piezoelectric material, etc. This signal is often influenced by interference and noise. Therefore, signal conditioning and signal processing techniques such as filtering and amplification are required. The signal is then fed to an ADC, because the data acquisition system needs the signal to be in either serial or parallel digital format. When a large number of sensors are being used, a multiplexer is required to derive information from one sensor at a time. However, this would require long cables running to the multiplexer from the sensors. Therefore, a bus interface is needed, with all sources and receivers con- nected to a common bus. This system handles all the data ports from different sensors and transfers all the collected data to the computer. A block diagram of a smart sensor is shown in Figure 2.4. In this case, the microcontroller performs most of the digital signal processing, analog-to-digital conversion, and also interfacing functions. The main advantage of smart sensors is the potential to modify performance using the capabilities of the microcontroller. Due to its smart sensing capabilities, the measuring process can be tuned to provide optimum accuracy, speed, and power consumption. Signal sampling and data processing stages of these sensors are discussed in detail in the next section. Sensing element Signal conditioning Microcontroller To PC Figure 2.4. Block diagram of a smart sensor. 4. SENSOR TEST METHODS Sensor response measurements can be classified as (2) AC or DC measurements or (2) steady-state or dy- namic measurements. DC measurements consist mostly of measuring steady-state currents when a DC voltage is applied to the sensor. AC measurements can be either steady-state or dynamic measurements. In steady-state measurements, input is applied to the sensor and the response of the sensor is measured