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.
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.
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.
HANDLING AND USAGE OF
DIRECT AND INDIRECT MEASURING INSTRUMENTS
"LINEAR MEASURING INSTRUMENTS"
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
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
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:
Steel scale/rule:
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.
Vernier caliper:
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:
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.
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.
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
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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