Measuring instruments NSQF Automobile Unit-3 session-1

 

Measuring Instruments

Measuring Instruments

All of us are totally surrounded by measurements, no matter what we may be doing. A measurement is assigning a value to length, mass and time. The importance of measurements in science is the exactness. You can not verify laws, properties or science experiments without having exact measurements. If measurements are not given, and you try and recreate a project someone else did, you will not come up with the same result they did. Accurate measurement is important because it helps in quality assurance and giving of accurate calculations in almost every field. Lack of accurate measurement causes errors which may be quite costly and dangerous.


Source:IndiaMART

        Instruments used for measuring basic units such as mass, length and time or derived units such as speed, acceleration, pressure etc; are called measuring instruments or equipment. 

Source:Slideplayer

An automobile require regular care and maintenance so that its working life and efficiency can be increased, and the cost of operation, which includes unnecessary breakdowns and spares, can be reduced. An automobile technician must know the measuring instruments and techniques, which is a basis for repair & maintenance and inspection of parts and require different measuring tools, instruments and gauges.

Source:Slideshare



HANDLING AND USAGE OF DIRECT AND INDIRECT MEASURING INSTRUMENTS

"LINEAR MEASURING INSTRUMENTS"

Source:Slideshare

These instruments help in measurement of important dimensions of components. Important measuring instruments used are Dial gauge, Bore Gauge, Vernier caliper, Depth Gauge, Micrometer, Hydrometer and Multi meter etc. We will try to understand the handling and usage of these measuring equipment's.

Measuring Instruments

 Measuring instruments used in automotive can be classified as below:

 1. Linear measurement

a. Direct measuring instruments

b. Indirect / instruments for transferring measurements

2. Angular measurement

3. Plane surface measurement


       Direct measuring instruments

Source:SlideShare

The measuring instruments, which do not require the help of other instruments for measuring are called direct measuring instruments. Usually these instruments have a line, which is divided in equal parts, called graduated scale.

Indirect measuring instruments

Source:SlideShare

 There are situations where direct measuring instruments cannot be used. The simple calipers can be used in these situations. For measuring, the object is held between the ends, object removed and the ends are placed on steel scale to determine the distance. These calipers can be used to measure the length, outside and inside diameters.

 Commonly used direct measuring instruments are:

Source:BlogMech

Steel scale/rule: 

Source:tenor

It is a line measuring device. It is the simplest and most common measuring instrument used in inspection. It works on the basic measuring technique of comparing an unknown length to the one previously calibrated.

Source:Giphy

Vernier caliper: 

Source:Vivax Solution

The meter scale enables us to measure the length to the nearest millimeter only. Automobile technicians need to measure much smaller distances accurately. For this a special type of scale called Vernier scale is used. The Vernier Caliper is a precision instrument that can be used to measure internal and external distances extremely accurately. The vernier caliper is usually a manual caliper. Measurements are interpreted from the scale by the user.

Vernier caliper and its parts Parts of a Vernier caliper:

Source:Technolgy Student

1. Outside jaws: used for measuring external diameter or width of an object

2. Inside jaws: used to measure internal diameter of an object

3. Depth probe: used to measure depths of an object or a hole

4. Main scale: scale marked every mm

5. Main scale: scale marked in inches and fractions

6. Vernier scale gives interpolated measurements to 0.1 mm or better Vernier scale gives interpolated measurements in fractions of an inch

7. Retainer: used to block movable part to allow the easy transferring of a measurement.

Source : HowMechanisumWorks ?

In the vernier calliper sliding jaw containing the vernier scale, moves over the main scale. When the two jaws are in contact, the zero of the main scale and the zero of the vernier scale should coincide. If both the zeros do not coincide, there will be a positive or negative zero error.

Dial caliper:


               

                                                                   Source: PURI Tools & Steel Trader

Instead of using a vernier mechanism, which requires some practice to use,the dial caliper reads the final fraction of a millimeter on a simple dial. In this instrument, a small, precise gear rack drives a pointer on a circular dial, allowing direct reading without the need to read a vernier scale.

Digital caliper: 

               

                                                                                     Source : IndiaMart

It is refinement or replacement of the analog dial with an electronic digital display on which the reading is displayed as a single value. Some digital calipers can be switched between centimeters or millimeters. All provide for zeroing the display at any point .

Vernier depth gauge: 

              

                                                                                 Source:IndiaMart

 For measuring the depth of holes, recesses and distances from a plane surface to a projection, the vernier depth gauge is employed. For use of vernier. depth gauge, its base or anvil is rested on or against a reference surface and the scaled beam or tongue is pushed beyond the base to contact the measured point.

Screw gauge / Micrometer: 

                                                                            Sourcer:MSC industrial Supply 

The micrometer is a measuring instrument, used by engineers and technicians for inspection and measuring two faces. The object to be measured is placed between the anvil face and the spindle face. The ratchet is turned clockwise until the object is ‘trapped’ between these two surfaces and the ratchet makes a ‘clicking’ noise. This means that the rachet cannot be tightened any more and the measurement can be read.

                                              Source:Open source physics @ Singapoure

Digital Micrometer: 

                                                                 Source: Travers Tools

The digital micrometer is shown is the figure and display the final reading. There are many types of micrometers which depend on the type of anvil and spindle faces such as gear tooth micrometer, sheet metal micrometer etc.

  Micrometer head can be part of any measuring instrument which makes the instrument known with prefix as micrometer such as micrometer depth gauge, micrometer bore gauge etc.

Indirect measuring instruments

Source:SlideShare

 There are situations where direct measuring instruments cannot be used. The simple calipers can be used in these situations. For measuring, the object is held between the ends, object removed and the ends are placed on steel scale to determine the distance. These calipers can be used to measure the length, outside and inside diameters. Some of the calipers are as below:

Firm Joint Calipers: 


                   

                                                                                              Source:IndiaMart 

These are the devices for comparing measurements against known dimensions. The firm joint caliper has two legs and working ends are suitably hardened and tempered, the legs are joined together by a rivet. The legs are set correctly so that the working ends meet evenly and closely when brought together. The capacity of the caliper is the maximum dimension which can be measured by it. The nominal size of 100,150, 200 and 300 mm are commonly used. Different calipers are shown in figure.

 Spring joint calipers: 


                   

                                                                                                    Source:Pinterest

The spring joint calipers are shown in the figure. The functions these calipers are similar to firm joint calipers. The legs of caliper can be opened and closed with the help of screwing the nut in and out on the bolt.


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