TABLE OF CONTENTS Fred Cruger
Agilent Technologies
Lake Stevens, Washington
In the context of this chapter, data-acquisition systems are generally those products designed to capture basic electro-mechanical phenomena by measuring the electrical output from a variety of transducers. The dominant measurements include temperature, pressure, strain, flow, vibration, voltage, current, etc. These parameters represent the real (physical) world. In specialized applications, more esoteric measurements (field strength, chemical content, etc.) can become a necessary piece of a data-acquisition system; such special requirements often affect the final choice of system architecture. This chapter, therefore, presents the fundamental architectural choices and the factors that help to differentiate the alternatives.
Various forms of data acquisition have been commercially available for decades, but technologies and techniques continue to evolve. For example, voltmeters that periodically print results, tape recorders that are optimized for multi-channel recording, and strip chart recorders that make hard-copy graphs have been used in everything from measuring the durability of mechanical devices during life test, to in-flight recording of airframe structural movements, to measuring and recording changes in barometric pressure, river levels, or seismic events. These have evolved into complex, distributed, computer controlled, and reconfigurable systems.
Sensors, the devices that are actually used to measure physical phenomena, typically require some sort of signal conditioning to be compatible with measurement hardware. Such conditioning consists of amplifiers (for sensors generating very low-level signals), filters (to limit the amount of noise on the signal), isolation (to protect the sensors...
