Introduction

Introduction

The measurement of any quantity plays very important role not only in science but in all branches of engineering, medicine and in almost all the human day to day activities. The technology of measurement is the base of advancement of science. The role of science and engineering is to discover the new phenomena, new relationships, the laws of nature and to apply these discoveries to human as well as other scientific needs. The science and engineering is also responsible for the design of new equipments. The operation, control and the maintenance of such equipments and the processes is also one of the important functions of the science and engineering branches. All these activities are based on the proper measurement and recording of physical, chemical, mechanical, optical and many other types of parameters.

The measurement means, to monitor a process or a operation and using an instrument, express the parameter, quantity or a variable in terms of meaningful numbers. Such a measurement gives in depth knowledge of the process and the parameter and helps in further modifications, if required. Thus the measurement provides us with a means of expressing a natural phenomena or the various processes, in quantitative terms. The feedback information is possible with the help of measurement techniques, which helps in achieving goals and objectives of various engineering processes and systems.

The measurement of a given parameter or quantity is the act or result of a quantitative comparison between a predefined standard and an unknown quantity to be measured.

For the result to be meaningful, there are two basic requirements :−

1. The comparison standard is accurately defined and commonly accepted, and

2. The procedure and the instrument used for obtaining the comparison must be provable.

The major problem with any measuring instrument is the error. Hence, it is necessary to select the appropriate measuring instrument and measurement procedure which minimises the error. The measuring instrument should not affect the quantity to be measured.

Key Point The measuring instrument may be defined as a device for determining the value or magnitude of a quantity or variable.

An electronic instrument is the one which is based on electronic or electrical principles for its measurement function. The measurement of any electronic or electrical quantity or variable is termed as an electronic measurement.

1. Advantages of Electronic Measurement

The advantages of an electronic measurement are

1. Most of the quantities can be converted by transducers into the electrical or electronic signals.

2. An electrical or electronic signal can be amplified, filtered, multiplexed, sampled and measured.

3. The measurement can easily be obtained in or converted into digital form for automatic analysis and recording.

4. The measured signals can be transmitted over long distances with the help of cables or radio links, without any loss of information.

5. Many measurements can be carried either simultaneously or in rapid succession.

6. Electronic circuits can detect and amplify very weak signals and can measure the events of very short duration as well.

7. Electronic measurement makes possible to build analog and digital signals. The digital signals are very much required in computers. The modem development in science and technology are totally based on computers.

8. Higher sensitivity, low power consumption and a higher degree of reliability are the important features of electronic instruments and measurements.

But, for any measurement, a well defined set of standards and calibration units is essential. This chapter provides an introduction to different types of errors in measurement, the characteristics of an instrument and different calibration standards.

Key Point The physical, chemical, electrical quantity, property, process, variable or a condition to be measured is referred as measurand.

The various physical measurands are pressure, level, force, strain, velocity, etc. while the important electrical measurands are voltage, current, power and frequency.

Review Questions

1. What is measurement ? What are the two basic requirements of any measurement?

2. List the advantages of an electronic measurement.