lthough the microprocessor and digital network technologies have fundamentally reinvented the ways in which today's data acquisition systems handle data, much laboratory and manufacturing information is still communicated the "old" way, via analog electrical signals. And a fundamental understanding of how analog signal transmission works must first begin with a discussion of electrical basics.
To understand the ways in which an analog signal is transmitted over a circuit, it is first important to understand the relationships that make analog signal transmission possible. It is the fundamental relationship between voltage, current, and electrical resistance (Figure 3-1) that allow either a continuously varying current or voltage to represent a continuous process variable.
Electric Circuit