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

Comparator A comparator works on the relative measurement It gives only dimensional differences in relation to a basic dimension A comparator has to compare the unknown dimensions of a part with some standard (Basic Size) These are commonly used for linear measurement in mass production Classification Depending on the amplification system, Comparators are classified as Mechanical Comparators Electrical Comparators Optical Comparators Pneumatic Comparators

Mechanical Comparators : Mechanical comparator s are extremely convenient to use It does not require any external power for its operation The measuring head consists of the work contact plunger(Stylus) The movement due to size difference between standard and work piece operates a pointer The pointer moves over a dial This movement of the plunger is magnified by means of the gear train or levers The magnification of mechanical comparators is limited to 1000 These are cheap and intended to measure external surfaces However the mechanical devices are subjected to wear Types of Mechanical Comparators Dial indicator Reed type mechanical comparator The Sigma comparator

Comparator A comparator works on the relative measurement It gives only dimensional differences in relation to a basic dimension A comparator has to compare the unknown dimensions of a part with some standard (Basic Size) These are commonly used for linear measurement in mass production Classification Depending on the amplification system, Comparators are classified as Mechanical Comparators Electrical Comparators Optical Comparators Pneumatic Comparators

METROLOGY Metrology is the science of measurements. In manufacturing industry the dimensions are measured to control the shape and sizes of an object Controlled measurements are necessary in the manufacture of interchangeable parts Linear Measuring Instruments Slip gauges Dial indicator Angle Measuring Instruments Bevel Protractor Sine bar Angle gauge Slip gauges Slip gauges are used for precise measurement of parts and for verifying measuring tools such as micrometers,comparators and various limit gauges Slip gauges are rectangular blocks made of alloy steel having a cross-section of about 32mm by 9mm The distance between two opposite faces determines the size of the gauge During use, the required number of gauge blocks are used together to know the required dimension. Dial Indicators Dial indicators are used to test and inspect the size and trueness of a finished work It is measured to an accuracy of 0.01mm They are also used in conjunction with other measuring instruments like

Reed type Mechanical Comparator The instrument used to measure linear displacement of spindle with the help of the reed mechanism is known as reed type Mechanical comparator. It is a device magnifying small motions of spindle. Constructional details : The reed mechanism is frictionless device for magnifying small motions of the spindle It consists of a fixed block `A` which is rigidly fastened to the gauge head case The floating block `B` carries the gauging spindle The floating block is also connected horizontally to the fixed block by reeds `C` A vertical reed is attached to each block with upper ends jointed together These vertical reeds are shown in fig by letter `D` A pointer is attached to this joint Working principle A linear motion of the spindle moves the floating block vertically upwards This vertical movement causing the vertical reed on the floating block to slide past the vertical reed on the fixed block The movement causes both reeds swing through an arc As the point is