INTRODUCTION

GMT METROLOGY DIVISION has been in the field of Metrology for the past 30 years, concentrating in design, development and manufacturing of all sort of metrological calibration items made of Granite (Dolerite). Before studying about GMT METROLOGY product and their features, we need to know what is meant by Metrology. On coming lines give you an idea about GMT METROLOGY and their contribution in this regard.

METROLOGY

Lord Kelvin said, “I often say that when you can measure what you are speaking about and express it in numbers, you know something about it. But when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind”. It is clear from the words of Lord Kelvin that, how vital to engineers is the knowledge of the Science of Measurements (called Metrology).

All engineers, regardless of their branch of specialization, are constantly faced with the problem of measurement. It may be of time, mass, force, temperature, length, angle and so on. Almost invariably, the results of such measurements will determine the course of action the engineer takes there after. All such measurements form part of the science of Metrology.

The mechanical and production engineers are, however, especially concerned with the measurement of length, angle, surface, etc. Before World War-I, Metrology had been applied to engineering to a limited extent only. Since that time, however considerable progress has been made in the application of scientific principles to the dimensional control of engineering products. The accurate control of standards of measurements is essential function in every precision engineering production plant. Knowledge of Metrology and practice in its application is of utmost importance in industry today.

Systems of Measurement
Linear measurements are basically comparisons of a given dimension with a particular standard of length. Different standard systems of measurements are discussed below,
(1)The English system:  It is also known as British Standard. The system makes use of yard as the standard system of measurement.

(2)The Metric system: In metric system the meter replaces the yard (of English system). The metric system is essentially decimal, all multiples and submultiples of the basic units being related by the factor of 10. As decimeter, centimeter, millimeter, micrometer and so on.

(3)The International System of units (SI): Earlier CGS (centimeter, gram, second) system was in use for specific work. The MKS (meter, kg, sec) system followed it. This MKS system is very convenient to use and to handle rational, coherent, comprehensive systems at ease.

The main features of SI are that the meter and kilogram supersede the centimeter and gram of the old system. The Newton, unit of force, is independent of the earth’s gravitation and g need no longer be introduced in equations. The joule (Newton X meter) is the unit of energy, and of power, the joule per second (watt). Units such as meter, kilogram, second and ampere is of maximum interest to engineers.

Standards of Measurements
 Standards of measurement of length are,
(1)Fundamental or primary standards: The length is defined as the distance between two standard lines, and hence these standards are called Line Standards. The length of the workpiece is compared with a scale, which can be a yard or a meter. Scales are subject to parallax errors. It is also not convenient for close tolerance length measurement with unaided eye.

(2)Secondary or working standards: These standards are derived from primary standards. The length is the distance between two flat parallel end faces. Thus, they are known as End standards. They consists of slip gauges, micrometer, vernier calliper, etc. End measurement is more accurate because it is possible to detect much smaller variations by feel than can be seen with the unaided eye. But this method is time-consuming in use and is subject to wear on their measuring faces.

(3)Wavelength standards: In these standards, the wavelength of the monochromatic light is used as a unit of length.

ERRORS IN MEASUREMENT
 There is a true fact that, no measurement is exact. All measurements are subject to some error. It is therefore necessary to state not only the measured dimension, but also the accuracy of determination to which the measurement is made. As for as possible the errors inherent in the method of measurement used should be kept to a minimum, and having minimized the error, its probable magnitude, or accuracy of determination should be stated.

 Along with the actual gauge block size details, there should be details regarding the measured error in the block and the accuracy of determination with it enclosed. The accuracy of determination can be improved by repeating the measurement a number of times and stating the mean value.

Types of errors:
 There are two types of errors,
Those which should not occur and can be eliminated by careful work and attention.
Those which are inherent in the measuring process.

 Misreading an instrument, arithmetic errors, alignment errors, parallex error, errors due to temperature were some of the errors that we can eliminate on proper procedural handling of the system.

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