Operational amplifier instruments, components

Operational amplifiers, which are the main components of an analog computer, were first used in electrochemical instrumentation at the beginning of the 1960s [26]. Because they are extremely useful in measuring and controlling the electrode potentials and the currents that flow at the electrodes, electrochemical instruments were completely modernized by their introduction. Today, most electrochemical instruments are constructed using operational amplifiers. Knowledge of operational amplifiers will help the reader to understand electrochemical instruments and to construct a simple apparatus for personal use. 

The rapid development of solid-state electronic devices in the last two decades has had a profound effect on measurement capabilities in chemistry and other scientific fields. In this chapter we consider some of the physical aspects of the construction and function of electronic components such as resistors, capacitors, inductors, diodes, and transistors. The integration of these into small operational amplifier circuits is discussed, and various measurement applications are described. The use of these circuit elements in analog-to-digital converters and digital multimeters is emphasized in this chapter, but modern integrated circuits (ICs) have also greatly improved the capabilities of oscilloscopes, frequency counters, and other electronic instruments discussed in Chapter XIX. Finally, the use of potentiometers and bridge circuits, employed in a number of experiments in this text, is covered in the present chapter. 

The left-hand side of this figure shows a well-understood standard symbol for the operational amplifier showing input (Pj and and output voltages (o ). The rigjit-hand side shows a component-level diagram of the archetypal 741 operational amplifier. (Courtesy of Texas Instruments.)... 

One of the most useful of digital IC components is the operational amplifier, or Op-Amp. Op-Amps contain transistor-based circuitry that boosts the magnitude of an input signal, either voltage or current, by five orders of ms nitude (100,000 times) or more, and are the basis of the exceptional sensitivity of the modern analytical instruments used in all fields of science and technology. 

Generally, laboratory instruments require dc power to operate amplifiers, computers, transducers, and other components. The most convenient source of electrical power, how ever, is the nominally 110-V ac. fiO-Hz line voltage furnished by public utility companies. As shown in Figure 2-20. laboratory pow er supply units increase or decrease the voltage from the house supply. 

Amplification by Operational Amplifiers. Although operational amplifiers (OAs) contain numerous electronic components, they can be handled themselves like a single component. Working with integrated OAs is so easy that untrained persons can solve their problems in this way. Sometimes, some do-it-yourself electronics is a better solution than to look for specialized commercial instruments. It is sufficient to understand the graphic symbol of the OA and its inherent functionalities. 

Therefore, when you open an analog Instrument, you will see inside discrete components, analog integrated circuits, like operational amplifiers, comparators, analog switches, and, more rarely, multipliers and possibly some digital integrated circuits. 

The general construction of an atomic absorption spectrometer, which need not be at all complicated, is shown schematically in Fig. 1. The most important components are the light source (A), which emits the characteristic narrow-line spectrum of the element of interest an absorption cell or atom reservoir in which the atoms of the sample to be analysed are formed by thermal molecular dissociation, most commonly by a flame (B) a monochromator (C) for the spectral dispersion of the light into its component wavelengths with an exit slit of variable width to permit selection and isolation of the analytical wavelength a photomultiplier detector (D) whose function it is to convert photons of light into an electrical signal which may be amplified (E) and eventually displayed to the operator on the instruments readout, (F). 

Since this is a book concerned primarily with applications, no further details are given concerning instrumentation. The reader is referred to Alpert et al. (1970), in which are discussed an optical diagram of a double-beam spectrophotometer operating variables (resolution, photometric accuracy) components of infrared spectrophotometers (sources, types of photometers, dispersing elements, detectors, amplifiers, and recorders) special operating features, such as optimization of scan time and available instruments and their specifications. The books by Martin (1966), Conn and Avery (1960), and Potts (1963), and the chapter by Herscher (1966) are also recommended for details on some of these topics. 

Defenses against common cause failures all involve "diversity" of one kind or another. One form, called equipment diversity, involves use of instruments operating on different principles to measure the same reactor variable. Use of different kinds of components in the amplifying and scram logic systems leading from the... 

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