Use of Dial Gauge,Telescopic Gauge and Bore Gauge
Measuring instruments are also used in automobile serviceability. 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. We will try to understand the handling and usage of these measuring equipments.Dial Gauge
A dial gauge is like a fine watch. It consists of a graduated dial, pointer, plunger and a clamp. It measures the displacement of its plunger on a circular dial by means of a rotating point.
It is used as a measuring device to measure the accuracies in alignment, eccentricity of the parts/components.
Works
It works on the rack and pinion principal. The plunger has gear teeth cut on it and when it reciprocates it actuates a pinion attached to the pointer shaft. Thus any movement of the plunger causes a corresponding movement of the main pointer on a graduated dial. In addition to the main pointer the dial gauge has a secondary scale and a small pointer for indicating the number of revolutions made by the main pointer. Zero setting of the main pointer of the dial gauge can be done by rotating the dial face until ‘0’ line coincide with the pointer.
Dial Gauges are one of the most commonly used instruments in all types of automobile related industry.
Bore Gauge/Cylinder Gauge
Bore gauge or cylinder gauge is used to measure hole diameter or internal diameter or bore, ovality and taperness in the IC Engine cylinder.The bore/cylinder gauge has a dial indicator mounted on a sledge which acts or a guide when the instrument is in use. There are two contact points and a extension roads of varying length as per requirement.
To make a measurement a suitable length rod is fitted and the gauge is inserted in the cylinder where it is carefully traversed up and down in several positions while the movement of dial gauge pointer is observed. In this way we can detect the variations along the bore/internal diameter of engine cylinder.
Vernier Caliper
A vernier is a graduated short scale that is mounted on the measuring instrument that its graduations subdivided the divisions on the main scale of the instrument. A vernier calliper is used to make both inside and outside measurement with the help of its specially designed jaws.
Parts of a vernier caliper:
1. Outside jaws: used to measure 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.
7. Vernier scale: gives interpolated measurements in fractions of an inch.
8. Retainer: used to block movable part to allow the easy transferring of a
measurement.
About
The vernier, dial, and digital calipers give a direct reading of the distance measured to high accuracy. They are functionally identical, with different ways of reading the result. These calipers comprise a calibrated scale with a fixed jaw, and another jaw, with a pointer, that slides along the scale. The distance between the jaws is then read in different ways for the three types. The simplest method is to read the position of the pointer directly on the scale. When the pointer is between two markings, the user can mentally interpolate to improve the precision of the reading. This would be a simple calibrated caliper; but the addition of a vernier scale allows more accurate interpolation, and is the universal practice; this is the vernier caliper.
Vernier, dial, and digital calipers can measure internal dimensions (using the uppermost jaws in the picture at right), external dimensions using the pictured lower jaws, and in many cases depth by the use of a probe that is attached to the movable head and slides along the centre of the body. This probe is slender and can get into deep grooves that may prove difficult for other measuring tools. The vernier scales may include metric measurements on the lower part of the scale and inch measurements on the upper, or vice versa, in countries that use inches. Vernier calipers commonly used in industry provide a precision to 0.01 mm (10 micrometres), or one thousandth of an inch. They are available in sizes that can measure up to 1,829 mm (72 inches).
Measurement with a Vernier Calliper
Taking measure an outside diameter of cylinder:
1. The sliding jaw is moved along the beam until the sliding jaw almost contact the cylinder kept against the fixed jaw. In this way the cylinder is held between the fixed jaw and sliding jaw.
2. Then the sliding jaw assembly that carries the fine adjustment screw should be clamped to the beam with the help of fine adjustment clamp.
3. The two jaws are now brought into contact with the work piece by moving the sliding jaw with the help of fine adjustment screw.
4. The jaws should make definite contact with the surface of the cylinder but should not be tight.
5. The main slide assembly is then locked to the beam with the help of clamp.
6. The calliper is carefully removed from the work piece to prevent springing of the jaws.
Reading
Least count is the minimum possible measurement which can be measured by the
measuring instruments.
Least count = Main scale reading / Vernier scale reading
(1) Take that least main scale reading just ahead of which zero of the vernier scale
takes place. Assume that the zero of vernier scale is just ahead of 32mm
reading of main scale. So take note of 32 mm.
(A) Main scale reading = 32mm
(2) Now note the least count (L.C) of the vernier calliper. Least count is the
minimum possible measurement which can be measured by the measuring
instruments. Assume in this case L.C is .02 mm
(B) Least count = 0.02 mm
(3) Now look for the graduation mark of the vernier scale that coincides with any
graduation mark of the main scale.
Assume in this case the 11th graduation of vernier scale coincides with any
graduation of the main scale. So note it down as C=11
Now calculate the reading as follows
Actual measurement = A + (BX C)
= 32 + (0.02 X 11)
= 32 + 0.02
= 32.22 mm.
Micrometer
Micrometer is a measuring instrument used to measure very fine and precise dimensions of length, width, thickness, diameter etc. Micrometer measure the cylindrical component like shaft, bolt, coin, boll etc. This is more accurate and precise than a vernier calliper.
It consists of a rigid frame which carries a hardened and optically flat anvil face at one end. At the other hand the micrometer head is attached which a spindle of accurate flat face. The micrometer head consists of thimble which can be rotated with the thumb and finger. The rotating thimble gives rotating movement to the simple.A micrometer sometimes known as a micrometer screw gauge is a device having a calibrated screw used widely for precise measurement of small distances in mechanical engineering and machining as well as most mechanical trades, along with other metrological instruments such as dial, vernier, and digital calipers.
composed
Frame :The C-shaped body that holds the anvil and barrel in constant relation to
each other. It is thick because it needs to minimize flexion, expansion, and
contraction, which would distort the measurement. The frame is heavy and
consequently has a high thermal mass, to prevent substantial heating up by the
holding hand/fingers. It is often covered by insulating plastic plates which further
reduce heat transference.
Anvil :The shiny part that the spindle moves toward, and that the sample rests
against.
Sleeve / barrel / stock :The stationary round part with the linear scale on it.
Sometimes vernier markings.
Lock nut / lock-ring / thimble lock :The knurled part (or lever) that one can
tighten to hold the spindle stationary, such as when momentarily holding a
measurement.
Screw :The heart of the micrometer is inside the barrel. The shiny cylindrical part
that the thimble causes to move toward the anvil.
Thimble :The part that one's thumb turns. Graduated markings.
Ratchet stop :Device on end of handle that limits applied pressure by slipping at
a calibrated torque.
For taking measurements the work piece should be held between the anvil face and
the spindle face. The rotating spindle should not be tightened hardly. For this
purpose the ratchet is used to give proper pressing of the spindle against the work
piece. Now locked the micrometer with the help of lock nut and removed from the
work piece very precisely.
Least Count = Pitch / Number of divisions on circular scale (thimble)
Where pitch is distance travelled by thimble on a linear scale in one rotation.
Now take readings as follows-
1. Take note of the least count (L.C) of micrometer. In this case L.C = 0.01mm
2. Take note of Major division on barrel ‘A’
3. Take note of Minor division on barrel ‘B’
4. Take note of thimble division ‘C’ X L.C =D
5. Now to read the micrometer, a circular scale on the sleeve is provided.
The circular scale has each graduation represent 0.002 mm and each
graduation is marked with a number 0,2,4,6,8 etc to help in the reading.
Now look for which no. of division of circular scale is coincides with the
division of vernier scale coincides with the any division of thimble then
vernier division on barrel = 3 X .002 = .006 mm =E
Total reading = A+B+D+E.
Hydrometer
Hydrometer is used to measure specific gravity of the electrolyte of the battery. It consists of a glass tubular body with a rubber bulb at the top and a sampler tube at the bottom. There is a glass float inside the glass body. There is a mark inside the glass (red & green).
This glass float has a vertical density scale. To test the specific gravity of the electrolyte :
1. Immerse the sample tube in the cell containing electrolyte. (Mixture of water and sulphuric acid)
2. Squeeze the rubber bulb and release the same which would cause a sample of the electrolyte to be drawn inside the glass body. Let the float inside rise and then read off the scale drawn at the surface of the sampler tube. The specific gravity of a fully charged battery is 1.280. If the specific gravity is less than 1.200 then it should be charged.
Multi Meter
Multi Meter
A multimeter or a multi tester, also known as a VOM (Volt-Ohm meter), is an electronic measuring instrument that combines several measurement functions in one unit. A typical multi meter may include features such as the ability to measure voltage, current and resistance. A multi meter can be a hand-held device useful for basic fault finding and field service work or a bench instrument which can measure to a very high degree of accuracy. They can be used to troubleshoot electrical problems in a wide array of industrial and household devices such as electronic equipment, motor controls,
domestic appliances, power supplies, and wiring systems.
domestic appliances, power supplies, and wiring systems.
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