CHAPTER 5 - Measurements

Abstract

This chapter discusses the various types of measurements. In any chemical process, there are several variable quantities that should be measured to effect proper control and, thus, ensure safe and efficient operation. Quantities frequently measured are time, temperature, pressure, volume, weight, density, and electrical current, voltage, and resistance. Measuring devices or instruments can be of the indicating type where the instantaneous value is shown or they can be of the recording type when the value is recorded continuously on a chart providing a permanent record. A clock, for example, is an indicating instrument for the measurement of time. At present, instruments are often grouped together on an instrument panel or in a control room adjoining the plant. A quantity is a meaningless number unless it is expressed in terms of units. When a measured quantity is recorded for process control purposes, it is misleading and possibly dangerous not to state the units in which it is measured.