A Feeler gauge is used to measure the clearance between two parallel flat faces for example piston and cylinder. As the name suggests, feeler gauge called as to measure neither tide nor freely.
Watch the video of feeler gauge
Feeler gauges are used for measurement of clearances.
It is a tool that measures air or narrow gap widths between two surfaces in engines and machinery.
Size of Feeler gauge
Feeler gauge available in no. of the blade like 10,13,20 and 28. With a step of 0.05 and 0.10 mm.
The thickness of the blades are in fractions of mm and inches, usually ranging from 0.03 mm to 1mm.
Parts of Feeler gauge
The feeler gauge has two major parts, a body or block which acts like a protective case or shealth and a large number of blades of different thickness.
The body is the base that holds the blades together. Feeler gauges
are made entirely of steel so that they are corrosion free and the
blades do not rust easily.
In machinery and engine service, it is important to predict accurate measurement of gaps for smooth performance and to avoid any faulty operations.
It is extensively and mostly used for measuring the gap between an engine cylinder and piston.
When there is extra gap even after a blade is inserted then the blades of the feeler gauge can be used in various combinations as per the requirement, that is different blades having different thickness can be stacked together and used.
How to use Feeler gauge?
The working of feeler gauge is easy. The blades are kept on the
vacant gap that needs to be measured, initially one blade of standard
thickness is kept, then if there are extra gaps other blades are
adjusted and joined together and used.
Ensure that the blades can be easily pushed to and fro and are not tight nor free to move.
In order to have a problem-free measurement, the blades should be free of dirt and grease.
Simple D’Arsonval Type to Measure Current or Voltage
It essentially consists of components like a permanent
magnet, coil, hairsprings, pointer, and scale. The coil assembly is mounted on a shaft, which in turn is hinged on a hair spring.
To concentrate the magnetic fields, initially, the iron core is placed inside the coil.
The curved pole pieces are then attached to the magnet to ascertain if the torque increases as the current increases.
This means that electromagnetic energy is used to move the meter.
Volt-Ohm Milliammetersor Multimeters
The typical volt–ohm milliammeter employs switching provisions for connecting multipliers, shunt resistors, and rectifier circuits.
The current flowing through the resistor can easily be determined by switching over to the ohm-meter function, wherein the leads can be connected to the unknown resistance that causes the meter movement.
The advantage is that direct measurement is possible since the current flow indication is calibrated in terms of resistance
The vacuum tube voltmeter, popularly known as VTVM, is basically used to measure voltage.
To control the grid of the tube, proper multiplier resistors are employed through which the AC or DC input is given to the meter.
The input resistance of a VTVM is usually very high, when compared to that of a simple meter, due to high grid circuit resistance. This minimizes the loading of the signal source.
Cathode Ray Oscilloscope
A CRO is a voltage-sensitive device that is used to view, measure, and analyse waveforms.
Its advantage is that a beam of electrons with low inertia strikes the fluorescent screen, generating an image that can rapidly change with varying voltage inputs to the system.
The cathode ray tube (CRT) is the basic functional unit of CRO. The electron gun assembly comprises a heater, a cathode, a control grid, and accelerating anodes. When a cathode is heated, electrons are generated.
The accelerating anodes, which are positively charged, provide the necessary striking velocity to the emitted electron stream.
The electron beam, after gaining necessary acceleration, passes through horizontal and vertical deflection plates, which provide the basic movements in the X and Y directions.
The XY plotters generate Cartesian graphs, which are obtained by two DC inputs, in X and in the Y-axis. It consists of two self-balancing potentiometers, one to control the position of the paper and others to control the position of the pen.
In XY plotters, the output is generated by plotting one emf as a function of the other emf.
Further, the emf, which is the output signal of transducers, may be a value of displacement, force, pressure, strain, or any other parameter.
Measurement is a Natural part of everyday life. We express daily needs in size & weights, water and electricity are also metered.
A number of blood samples, active sub-stain in medicine also needs to be precise.
I think it is Impossible to describe anything without measuring it.
Room temperature, body weight, sunshine,chest width and so on..
Almost every company are concerned with Quality management in the process of Introducing their work
First, we try to understand what is Metrology!
What is Metrology?
Metrology word derived from the Greek words Metro(means Measurement) and Logy(means Science).
Metrology includes all aspects with reference to measurements, whatever their level of accuracy.
Some technical terms are difficult to understand, so the following terminology is quite helpful for further studies
Accuracy is the closeness between a test result and accepted value.
Bias is the difference between the expected value and the accepted reference value.
Calibration is the set of operations that establish under specified conditions, the relationship between values of quantities indicated by a measuring instrument or values represented by a material measure and the corresponding values realized by standards.
Drift is slow to change of a metrological characteristic of measuring instrument.
The output result from a measuring device to be magnified many times to make it more readable, called Magnification.
Precision is the closeness of agreement between independent test results obtained under stipulated conditions.
The smallest change of the measured quantity which changes the indication of a measuring instrument is called Resolution.
Traceability means a measured result can be related to references.
We also measure depth through Vernier caliper, but Vernier caliper does not deliver as much as accuracy and precision, because extension rod of Vernier caliper has no standard, it used only for comparison purpose.
Depth micrometer used to measure the depth of an object with precision and accuracy with least count of 0.01 mm. The measuring span is 25 mm just like in micrometer, that can change by changing upsetting rod.
How to Measure with Micrometer?
Measuring Concept of Depth Micrometer is same as External Micrometer. The main differences are direction and position. Reading scale is Vertical in-depth micrometer and Direction of reading is opposite (starting from the end scale).
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Some normal characteristics of Depth Micrometer describe follows
The accuracy of Depth Gauge is 0.01 mm which is fair enough for linear measurement and also accurate than vernier caliper. You can choose Digital Depth Micrometer, in order to simplify observation only. Both types of Depth Micrometer delivers the same accuracy.
Depth Micrometer follows national or international measurement standard, while vernier caliper is not(in order to check depth through extension rod only).
The cost of Depth Micrometer is low than digital type. Cost may be
varied brands to brands, usually depend upon the quality of material
used. Some most famous Brands which are known for their quality promise
available in a market like Mitutoyo, baker etc.
The main use of depth micrometer is to check the depth of any objects. Basically used in industrial areas of manufacturing plants.
Inside Micrometer is used to measure the larger internal dimension. Inside Micrometer can measure internal Diameter of holes and registers.
Types of Micrometer
There are various types of micrometers available in the industry each used for a specific purpose. One such micrometer is the “Inside Micrometer”.The inside micrometer is used to measure the inner diameter of objects that are bonded by walls,cylindrical bore or hollow pipe.There are two types of Inside Micrometer
Analog type Inside Micrometer
Digital type Inside Micrometer
The least count is 0.01 mm for analog type and 0.001 mm for digital type.
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It can be measured by mm or inches and gives precise readings. The
inside micrometers are also available in different designs and sizes for
The general equipment comprises of a measuring head or a micrometer unit; extension rods; spacer or spacing collar and a handle.
The measuring head consists of a thimble, which has one way marking
and holds readings up to 50 mm which is the thimble division(TD)
The sleeve or barrel have the main or index scale and sub-scales,
they have two waymarking. The main scale can measure up to 25 mm and the
measured value is known as MSD(main scale division).
On the frontier end of the measuring head which is also known as the anvil is a hole through which the extension rods are inserted to the inside micrometer. On one side of the anvil is a locking screw that is used to adjust the extension rods and holds it firm. On the other side, there is a hole that is used to fit the handle.
The handle is used to insert the inside micrometer through objects
having depth. The posterior end also contains a screw that is used to
adjust the thimble.
Range of inside Micrometer
Good quality steel is used in measuring head and spindle, but for the
faces-high graded tool steel is used. The least count of the inside
micrometer is 0.01 mm. The extension rods can be of different sizes
ranging from 50 mm- 200mm, depending on the requirement.
The extension rods are classified as
.Extension rods are used for extensive objects having large
diameters, it is used along with the spacer. The spacer is used for
smaller diameter in addition to the measuring head. The spacer is of 12
How to measure inner diameter with Inside Micrometer?
The design of inside micrometers can also have jaws where one end is
fixed and the other is movable.The working of inside micrometer is very
simple.It basically consists of three steps
The construction of the radius gauge consists of two gauges having a number of steel strips or blades screwed together in one single holder. The screw is known as the lock screw.
The radius measurement is usually in metric form and measured in mm(millimeter). The material used is entirely made up of stainless steel, but a layer or finish of satin chrome can be added since it keeps the radius gauge corrosion free and gives them more rust resistance.
The blades used are of the concave and convex shape. It may be swung
out of the holder case when necessary readings need to be taken as per
The markings are inscribed on the upper surface of every individual blade
Types of radius gauge
Three sets of radius gauge are manufactured.
Set 1 measure the radius available from 0.6-0.8mm.
Set 2 measures 1-7mm,
Set 3 measures 3-8.25mm.
The object or workpiece whose radius is to be measured is taken and
the blades are inserted one by one to check which one fits in exactly by
comparing it with the radius on the object.
Specifications of radius gauge
The radius gauge is light in weight and has an attractive design. The world keeps evolving and new and advanced technologies are taking over the old methods, hence a more optimistic and advanced gauge known as “digital radius gauge” is also available.
It is used for obtaining a high level of precision. It is a
measuring tool that is user-friendly and the end user can operate it
with great ease, fast since it is digital and portable.
Construction of radius gauge
T he construction of a digital radius gauge is entirely different than that of a simple radius gauge. It has a digital screen that is used to display values and for adjusting them, a measuring head and a number of brackets or jaws of different sizes ranging from 5-100mm.
The digital screen, measuring head and jaws are connected together and used. Another important aspect to be noted is that the simple radius gauge is used for measurement of small radius objects whereas the digital radius is used for larger radius measurement.