Engineeringdev

Measurement of Engineering Components Gauges are used mainly to check the Engineering Components produced on mass scale, where the job is usually handled by semi-skilled workers.   This type of measurement cannot be relied upon where accuracy is more important.   The different methods and instruments used for precision & accurate (linear & angular) measurements are discussed in this unit. Comparator It is a precision instrument employed to compare the dimension of a given component with a working standard (generally slip gauges).   It does not measure the actual dimension but indicates how much it differs from the basic dimension (working standard). Uses of Comparator : For calibrating the working gauges Used as working gauges  Used as final inspection gauges Essential characteristics of a good Comparator : Robust design and construction Linear chara cteristics of scale High magnification Quick in results Versatility Minimum wear of contact point Free from back lash Quick inser

Terms of measuring systems: (i) Sensitivity (ii) Readability (iii) Calibration (iv) Repeatability Sensitivity Sensitivity may be defined as the rate of displacement of the indicating device of a instrument, with respect to the measured quantity. In other words, sensitivity of an instrument is the ratio of the scale spacing to the scale division value. For example, if on a dial indicator, the scale spacing is 1.0 mm and the scale division value is 0.01 mm, then sensitivity is 100. It is also called as amplification factor or gearing ratio. If we now consider sensitivity over the full range of instrument reading with respect to measured quantities as shown in Fig., the sensitivity at any value of  y = dy/dx where dx and dy are increments of x and y, taken over the full instrument scale, the sensitivity is the slope of the curve at any value of y. The sensitivity may be constant or variable along the scale. In the first case we get linear transmission and in the second non-linear transmi

Precision and Accuracy: The agreement of the measured value with the true value of the measured quantity is called accuracy. If the measurement of a dimensions of a part approximates very closely to the true value of that dimension, it is said to be accurate. Thus the term accuracy denotes the closeness of the measured value with the true value. The difference between the measured value and the true value is the error of measurement. The lesser the error, more is the accuracy. Precision, The terms precision and accuracy are used in connection with the performance of the instrument. Precision is the repeatability of the measuring process. It refers to the group of measurements for the same characteristics taken under identical conditions. It indicates to what extent the identically performed measurements agree with each other. If the instrument is not precise it will give different (widely varying) results for the same dimension when measured again and again. The set of observations wil

Classifications of Methods of Measurements In precision measurements various methods of measurement are followed depending upon the accuracy required and the amount of permissible error. There are numerous ways in which a quantity can be measured. Any method of measurements should be defined in such a detail and followed by such a standard ​practice that there is little scope for uncertainty. The nature of the procedure in some of the most common measurements is described below. Actual measurements may employ one or more combinations of the following. (i)  Direct method of measurement:  In this method the value of a quantity of obtained directly by comparing the unknown with the standard. It involves no mathematical calculations to arrive at the results, for example, measurement of length by a graduated scale. The method is not very accurate because it depends on human insensitiveness in making judgement. (ii)  Indirect method of measurement:  In this method several parameters (to wh

Table of Contents (toc) C lassification of measurements: In the precision measurements, various methods of measurement are followed depending upon the accuracy required and the amount of permissible error. The various methods of measurement are classified as follow : 1. Direct method of measurement 2. Indirect method of measurement 3. Absolute method of measurement 4. Comparative method of measurement 5. Contact method of measurement 6. Contact less method of measurement Direct method of measurement: The direct method of measurement is one in which the measurement value in determined directly where as in the indirect method of measurement the dimension in determined by measuring the values functionally related to the required value. The direct method of measurement is simple and most widely employed in production. Indirect measurement: In many cases, for example, as when checking the pitch diameter of treads, the direct method may lead to large errors in measurement. In this c

Table of Contents (toc) BASICS OF METROLOGY Metrology  is the name given to the science of pure measurement.  Engineering Metrology  is restricted to measurements of length & angle. Need  for Measurement: • To ensure that the part to be measured conforms to the established standard. • To meet the interchangeability of manufacture. • To provide customer satisfaction by ensuring that no faulty product reaches the customers. • To coordinate the functions of quality control, production, procurement & other departments of the organization. • To judge the possibility of making some of the defective parts acceptable after minor repairs. Precision & Accuracy of Measurement Precision :  It is the degree which determines how well identically performed measurements agree with each other. It is the repeatability of the measuring process. It carries no meaning for only one measurement. It exists only when a set of observations is gathered for the same quantity under identical condit

Table of Content (toc) ​ What is property of thermodynamic system? • A property of a system is an observable characteristic of the system. • The quantities which define the state of the system are called properties. • Whose value must be independent of the process • The property is a point function ​ Classification of properties Thermodynamic properties are generally divided into two classes 1. Intensive properties: These are independent of mass of the substance Eg: pressure, temperature, density, specific gravity, specific volume, surface tension, thermal conductivity etc. ​ 2. Extensive properties: These are dependent on mass of the substance Examples: mass, weight, enthalpy, entropy, internal energy etc. ​ State: • State of the system is a condition and is identified through certain observable properties such as pressure, volume, temperature, density etc. • Two independent properties are sufficient to represent the state. ​Path: • The path is the series of states thr