TABLE OF CONTENTS Process control electronic systems use both analog and digital circuits. The study of electronic circuits, where the input and output current and voltage amplitudes are continually varying, is known as analog electronics. In digital electronics, the voltage amplitudes are fixed at defined levels, such as 0V or 5V, which represent high and low levels, or "1"s and "0"s. This chapter deals with the analog portion of electronics.
In a process control system, transducers are normally used to convert physical process parameters into electrical signals, so that they can be amplified, conditioned, and transmitted to a remote controller for processing and eventual actuator control or direct actuator control. Measurable quantities are analog in nature; thus, sensor signals are usually analog signals. Consequently, in addition to understanding the operation of measuring and sensing devices, it is necessary to understand analog electronics, as applied to signal amplification, control circuits, and the transmission of electrical signals.
The basic building block for analog signal amplification and conditioning in most industrial control systems is the operational amplifier (op-amp). Its versatility allows it to perform many of the varied functions required in analog process control applications.
Op-amps, because of their versatility and ease of use, are extensively used in industrial analog control applications. Their use can be divided into the following categories.
Instrumentation amplifiers are typically used to amplify low-level dc and low frequency ac signals (in the millivolt range) from transducers. These signals can have several volts...
