Sensors and Signal Conditioning, 2nd Edition

8

DIGITAL AND INTELLIGENT SENSORS

The overwhelming presence of digital systems for information processing and display in measurement and control systems makes digital sensors very attractive. Because their output is directly in digital form, they require only very simple signal conditioning and are often less susceptible to electromagnetic interference than analog sensors.

We distinguish here three classes of digital sensors. The first yields a digital version of the measurand. This group includes position encoders. The second group relies on some physical oscillatory phenomenon that is later sensed by a conventional modulating or generating sensor. Sensors in this group are sometimes designated as self-resonant, variable-frequency, or quasi-digital sensors, and they require an electronic circuit (a digital counter) in order to yield the desired digital output signal. The third group of digital sensors use modulating sensors included in variable electronic oscillators. Because we can digitally measure the oscillation frequency, these sensors do not need any ADC either.

Digital computation has evolved from large mainframes to personal computers and microprocessors that offer powerful resources at low cost. Process control has similarly evolved from centralized to distributed control. Silicon technology has achieved circuit densities that permit the fabrication of sensors that integrate computation and communication capabilities, termed intelligent or smart sensors.