urvish soni government polytechnic ahmedabad · the vapour-pressure thermometer is also a...

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Process Instrumentation-2

READING NOTES

URVISH SONI Government Polytechnic

Ahmedabad

2 G P Amdavad PI_II

LEARNING: 1

AIM: To study Temperature scales and relationship between them.

APPARATUS: Different Ranges Temperature scale, thermometer.

Theory:

Temperature scales:

Centigrade (Celsius) and Fahrenheit Temperature scale:

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Kelvin and Rankine temperature scale:

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The Reaumur Scale:

Conclusion: Questions:

1) Write the name of different range temperature scales? 2) Explain different between Fahrenheit scale and centigrade scale? 3) Explain different between Kelvin scale and Rankine scale? 4) Explain about Reaumur scale?

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LEARNING: 2

AIM: To study Expansion Thermometers. Apparatus: Different types thermometers, Temperature scale, Mercury, Gas, Bimetallic strip, Theory: Expansion Thermometers: Expansion thermometer are classified according to the nature of substance which expands. They may be describe under three heading as follows. 1). Expansion of solids (a) bimetallic thermometers 2). Expansion liquids (a) liquids in glass thermometers (b) liquid in metal thermometers 3). Expansion of gases (a) gas thermometers 1). Expansion of solids: (a) bimetallic thermometers: The expansion of solids is employed mainly in bimetallic elements by utilizing the differential expansion of bonded strips of two metal. It consists of two strip of metal such as invar and brass welded together, each strip made from a metal heavy a different coefficient of thermal expansion . whenever the welded strip is heated ,the two metals change length in accordance with their individual rates of thermal expansion. The two metals expands to different lengths as the temperature rises. This forces the bimetallic strip to bend with towards the side with low coefficient of thermal expansion As shown in figure. Figure:

Bimetallic strips: 2). Expansion liquids: (a) liquids in glass thermometers: The liquid in glass thermometer is one of the simplest temperature measuring device ,widely used in both laboratory and industry . its operation is based on the fact that liquid expands as the temperature rises .in this type of thermometers, the expansion causes the liquid to rise in the tube, indicating the temperature.

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Figure:

Liquid in-Glass Thermometer The simplest form of the liquid in glass thermometer is shown in figure .it consist of a small bore glass tube with a thin wall glass bulb at its lower end . the liquid that fills the bulb and part of the tube is usually mercury. As heat is transferred through the well and metal stem and into the mercury , the mercury expand, pushing the column of mercury higher in the capillary above which indicates the temperature. The liquid in glass thermometer is commonly used for the temperature range of -18.4 to 608o f .but when mercury is used as liquid, it freezes at -38.2of .thus, for measuring very low temperature, alcohol is used as liquid. for measuring high temperature, the thermometers glass stem above the mercury can be charge with nitrogen at a pressure of 30 to 300 psi. this helps in preventing the mercury from evaporating or boiling. even with the nitrogen, liquid in glass thermometers are usually limited to temperatures below 1100o f .temperatures is higher than 600oC can affect the glass and cause permanent changes in the volume of the bulb, thus destroying the accuracy of the instrument. The liquid in glass thermometers have got certain disadvantages also. They are fragile and not easily adapted to automatic recording or transmission of temperature data. this limits their use in modern industries. they can be difficult to read also .in the mercury in glass thermometer , a large error may be introduced by changes in the size of the bulb due to ageing. The industrial mercury in glass thermometer is used in application such as open tanks containing liquids, cooking kettles, certain molten metal baths, stems lines, pipe lines for fluid flow, and air ducts. It should not be employed when rapidly fluctuating temperature are to be measured with high accuracy. 3). Expansion of gases: (a) gas thermometers:

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The operation of gas thermometer depend upon on the Ideal gas law which states that the volume of a gas increases with temperature, if the pressure is maintained constant; and the pressure increases with temperature, if the volume is maintained constant. Therefore, if a certain volume of inert gas is enclosed in a bulb, capillary and bourdon tube, and most of the gas in the bulb, then the pressure indicated by the bourdon tube may be calibrated in terms of the temperature of the bulb. Nitrogen is the favourite fill for a gas-filled thermometer because it is almost inert and inexpensive. It does react somewhat with the steel bulb material at temperatures exceeding 427oC, and it does act less like a perfect gas at extremely low temperatures. Under these conditions helium should be used. Different ranges are obtained by selecting the correct filling pressure. An advantages of the gas filled thermometer is that the gas in the bulb has a low thermal capacity then a similar quantity of liquid, so that the response of the thermometer to temperature changes will be more rapid than that for a liquid –filled system with a bulb of the same size and shape. Conclusion: Questions:

1) Write the Classification of Expansion Thermometers? 2) Explain in detail Expansion of solids Thermometers? 3) Explain in detail Expansion liquids Thermometers? 4) Explain Gas Thermometers?

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LEARNING: 3 AIM: To study Bimetallic thermometers. APPARATUS: Different Ranges Temperature scale, Bimetallic strip. Theory: Expansion thermometer are classified according to the nature of substance which expands. They may be describe under three heading as follows. 1). Expansion of solids (a) bimetallic thermometers 2). Expansion liquids (a) liquids in glass thermometers (b) liquid in metal thermometers 3). Expansion of gases (a) gas thermometers Bimetallic thermometers The expansion of solids is employed mainly in bimetallic elements by utilizing the differential expansion of bonded strips of two metal. It consists of two strip of metal such as invar and brass welded together, each strip made from a metal heavy a different coefficient of thermal expansion . whenever the welded strip is heated ,the two metals change length in accordance with their individual rates of thermal expansion. The two metals expands to different lengths as the temperature rises. This forces the bimetallic strip to bend with towards the side with low coefficient of thermal expansion As shown in figure.

Bimetallic strips: If one end of the bimetallic strip is fixed so that it can not move, the distance the other end bends is a directly proportional to the square of the length of the metal strip, as well as to the total change in temperature, and is inversely proportional to the thickness of the metal. The movement of the bimetallic strip is a utilized to deflect a pointer over a calibrated scale. The deflection of the tip is small if the strip is short, and is large if the strip is long, since deflection increases with the square of strip length. A longer strip can be contained in a relatively small space if the strip is long in spiral, helix or multihelix form. If the bimetallic element is a wound in the form of a spiral, the spiral coil is tightened with increase in temperature. As it coil, the counter post rotates clockwise, and thus a pointer attached to the post also moves on a calibrated temperature scale. Figure:

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Spiral Bimetallic Element:

Fig. is shown a spiral element with an attached pointer mounted in a housing with a scale. This type of temperature indicator is often used in homes and offices for indicating ambient air temperature. the bimetal can also be used in the form of a helix to indicate temperature. This type of industrial bimetallic thermometer is shown in fig. below .

Helical Bimetallic Element: It a consists of a tightly wound helical bimetallic strip located inside the stem of

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the thermometer with one end fastened permanently to the outer casin This causes the pointer to move on the dial to indicate the measured temperature. A thermal well is used with the thermometer for protection against corrosion and breakage. The material of thermal well may be brass, steal, stainless steal or other alloys, depending upon the requirements of the installation. Bimetallic thermometer inexpensive , relatively rugged, and easy to read. They are also reasonably accurate if handled carefully. They are available of the temperature range from (-75 to 540c)

Advantage: Following are the advantage of bimetallic thermometer 1. Their cost is low. 2. They are tough, and cannot easily be broken. 3. They are easily installed and maintained 4. They have good accuracy relative to cost. 5. They have fairly wind temperature range

Disadvantage: Following are the disadvantage of bimetallic thermometer.

1. They are limited to local mounting. 2. Only indicating type of available. 3. They are always a possibility of calibration change due to rough handling 4. Their accuracy is not as high as glass stem thermometer


1) Bimetallic thermometer is which type of thermometer? 2) Explain bimetallic thermometer in detail?


LEARNING: 4 Aim: To Study Filled System Thermometry. Apparatus: Different Ranges Temperature scale, Two Dissimilar metal wire, Voltmeters, Heat Source,

Theory: Filled- system thermometer: Figure:

Filled-system Thermometer Working: Figure shown the basic components of a filled system thermometer. It consists of a bourdon tube, a capillary tube, and a thermometer bulb all Interconnected as shown. The entire system is sealed after filling with an appropriate liquid (known as the filling liquid) at a pressure at the normal ambient temperature. The common liquid that are used are mercury, ethyl alcohol, xylene and toluene. When in use, the thermometer bulb is installed inside the substance to be measured. This causes the filled liquid inside the bulb to heat or cool until its temperature matches the temperature of the measured substance. This change in temperature causes the filled liquid to expand or contract and thus the bourdon tube moves. With increase in temperature (heating) the liquid expands and this expansion forces the bourdon tube


to uncoil. With decrease in temperature (cooling) the liquid contracts and if forces the bourdon tube to coil more tightly. The movement of the bourdon tube may be used to drive a pointer for indicating temperature or to drive the pen on a strip- chart. Basically, there are four type of filled system thermometers:

(i) Gas-filled thermometer (which is already described in this chapter as gas thermometer ).

(ii) Liquid-filled thermometer. (iii) Mercury-filled thermometer. (iv) Vapour -pressure thermometer.

Liquid –filled Thermometer: These thermometers are completely filled with a liquid (other than mercury) and operate on the principle of liquid expansion with an increase of temperature. The filling fluid is usually an inert hydrocarbon, such as xylene (C8 C10) which has a co-efficient of expansion six times that of mercury and makes smaller bulbs possible. Other liquids (even water) are sometimes used. The criterion is that the pressure inside the system must be greater than the vapour pressure of the liquid to prevent bobbles of vapour from forming in the spiral. Also, the liquid should not be allowed to solidify even in storage, otherwise the calibration may be affected. Vapour-pressure Thermometers: The vapour-pressure thermometer is also a filled-system thermometer. In this system the bulb is partially filled with liquid, while the capillary and Bourdon tubes are filled with vapour. In this system some of the liquid vaporizes during operation. Various liquids used in vapour-pressure system are given with temperature range in Table.

Temperature Range of Liquid in Vapour-Pressure System A vapour-pressure thermometer is shown in fig. the liquid in a vapour pressure system boils and vaporizes during operation which creates a gas or vapour inside the capillary and Bourdon tube. The liquid inside the bulb continues to boil


until the pressure in the system equals the unless its temperature increases. Figure:

Vapour-Pressure Thermometer Now, when the temperature of the substance surrounding the bulb drops, the liquid and vapour inside the bulb also cool. This causes some of the vapour to condense. As the vapour condenses, the pressure inside the system decreases. This action continues until the pressure drops to the vapour pressure of the boiling liquid. Due to this change in pressure, the Bourdon tube uncoils as pressure increases and coils tightly as it decreases. This movement of Bourdon tube may be connected to a pointer, or a pen on strip-chart recorder, or to a transmitter to indicate temperature. Mercury – filled thermometer: Mercury is a liquid, and in this respect a mercury – filled thermometer is similar to the liquid-filled thermometer. These two are separated because of the unique characteristics of mercury and its importance as a temperature measuring medium. Mercury provides rapid response, accuracy, and plenty of power for operating control elements. Pressure within the working system is relatively high, as much as 1200 psig (8.3MPa) for the higher temperature dropping to 400 psig (2.8Mpa) for the two temperature end of the range. This high pressure reduces any


head effect error (different in elevation between bulbs and measuring element). A comparison table for various filling system thermometer is given in table The thermometer bulbs in filled systems are normally made of stainless steel. This increases their corrosion resistance and makes them compatible with the various kinds of gases and liquids used in industry. Also, this has good heat transfer properties and thus does not thermally insulate the filling fluid from the surrounding fluid. They many sizes and shapes of thermometer bulbs, used to improve their performance in specific applications. Source of error in filled system thermometers: The common source of error in the filled-system thermometer is: Ambient temperature effect. Head or elevation effect Barometric effect Immersion effect Radiation effect

Advantages:

1) They have a rugged construction. 2) They require low maintenance. 3) In filled-system thermometers there is no need for electric power since they

are self-sufficient. 4) The point of display can be located at a considerable distance from the point

of measurement. 5) They possess satisfactory time response sensitivity and accuracy for most

industrial applications. 6) Their cost is low. 7) They deliver enough power to drive not only a pointer or recording pen but

also a controller mechanism. 8) Three (or more) separate system can be put in a single instrument case. 9) The capillary allows considerable separation between the point of

measurement and the point of temperature indication. Although the system length is limited to 75 m, applications up to 120 m are in successful operation. It is frequently more economical to employ transmitters for single transmission beyond 30 m

Disadvantages: 1) They need a large bulb for the sake of accuracy. 2) The entire system usually has to be replaced in case of failure. 3) Their accuracy, sensitivity, and temperature span is much lower compared to

electrical temperature instruments.


4) Maximum spans are not as narrow as in the bimetallic thermometer or electrical system.

5) They have limited maximum temperature compared to some electrical measuring systems.

6) Thermal system, being under pressure, cannot be broken without destroying the calibration.

7) Separation of the measuring element and bourdon of more than 75 m generally is not recommended in these thermometers. It is frequently more e economical to employ transmitter for single transmission beyond 30 m.

Conclusions: Questions:

1) Write the type of filled system thermometer? 2) Explain liquid filled system and Mercury filled system thermometer? 3) Explain Vapour-pressure thermometers? 4) Write the Sources of Errors in filled-system Thermometers?


LEARNING: 5 Aim: To Study Thermocouple and types.

APPARATUS: Different Ranges Temperature scale, Two Dissimilar metal wire, Voltmeters, Heat Source,

Theory: Thermocouples: The working principle of thermocouple depends on the thermo-electric effect. If two dissimilar metals are joined together so as for a closed circuit, there will be two junctions where they meet each other. If one of these junction is heated, then a current flows in the circuit which can be detected by a galvanometer. The amount of current produced depends on the difference in temperature between the two junctions and on the characteristic of the two metals. This was first observed by Seebeck in 1821 and is known as Seebeck effect. Figure:

Thermocouple Instrument which records the variations in current flow are calibrated in term of temperature and are known as Thermocouple pyrometers. A thermocouple is made from two different kinds of metals. The wires are joined at the end which forms two junction, a measuring junction and a reference junction. Heat the measuring junction produces a voltage greater than the voltages across the reference junction. The difference between two voltages is measured and voltmeter reading id converted to its corresponding temperatures. This conversion table is generally supplied by the thermocouple manufacturers. These various types of thermocouple which are used in industries, viz. copper constant, iron constant, chromel constant, alumel, platinium rhodium and chromel-constantan. A Learning thermocouple used in industries. It consists of a protective well and head across the measuring junction corrosive fluids. These measuring junction of thermocouple is connected to the voltmeter and reference junction with extensions wires. Extension wires are also known as compensating leads. The characteristics of compensation wire must be similar to those of the thermocouple wire it joins, otherwise the voltage generated at the connections will be large enough to affect the instruments accuracy. The voltmeter reads the difference between the


reference and measuring junctions, voltages which can be calibrated to give temperature reading. Figure:

A Learning Thermocouple To protect thermocouple from harmful atmosphere, corrosive fluids, mechanical damage; to support the thermocouples or to permit entry into the pressurized system, protecting tubes or wells are supplied. These tends to reduce the speed of response of the thermocouple, So small thin wall or needle-type installations are supplied where feasible. Disposable-tip thermocouple are supplied in furnace applications. Thermocouple are not limited to single point measurement. They can be connected in parallel to provide the average temperature in a system. They can also be used to measured the different between two temperatures. A single thermocouple can be utilized by two separate measuring instruments, with proper precaution.

Type of thermocouple:


Advantages: 1) They have rugged construction. 2) They are inexpensive. 3) They are simple to use than resistance thermometers. 4) They have extremely wide temperature range from 270 c to 2800c. 5) They possess good accuracy.

Disadvantages: 1) They have limited used in temperature spans of less than about 33c

because of the relatively small change in junction voltage with temperature.

2) They need to hold reference junction temperatures constant or compensation for any deviations.

3) Their temperature-voltage relationship is non-linear. 4) They need expensive accessories for control application. Conclusions: Questions:

1) Explain Working Principle of a Thermocouple? 2) Explain thermocouple in briefly? 3) Write the Advantage and Disadvantage of the thermocouple?


LEARNING: 6

Aim: To study Resistance Temperature Detector.

APPARATUS: Different Ranges Temperature scale, Platinum wires, metal sheath, Alumina powder,

Theory:

Resistance Temperature Detector (RTD):

The resistance of certain of certain metals changes with temperature change. Resistance thermometer utilizes this characteristic. With the increase of temperature, the electrical resistance of certain metals increases in direct proportion to the rise of temperature. Therefore, if the electrical resistence of a wire of known and calibrated material is measured, the temperature of nthe wire can be determined. Platinum, copper and nickel are generally used in resistance thermometer.

In this type of thermometer, a temperature sensitive resistance element is fabricated in a suitable from to insert in the medium whose temperature is to be measured, and is connected by leads to a whetstone bridge as a shown in fig.

Figure:

Resistance Thermometer Bridge Circuit


the bridge consists of sensing element resistance x heving high temperature. LR1 and LR2 are the lead wire resistanices of the sensing element. The principle of wheatstone bridge states that in balanced condition ( when on current flows through galvanometer ) the ratio of resistances is given by:

Now when resistances X changes, the wheatstone bridge becomes unbalanced and thus galvanometer will give deflection which can be calibrated to give suitable temperature scale.

Resistance elements are generally long, spring like wires enclosed in a metal sheath. The construction prectical resistance thermometer is shown in fig.

Figure:

A Resistance Thermometer

The resistance element is surrounded by a porcelain insulator which prevents short circuit between wire and the metal sheath. Two lead are attached to each side of the platinum wire. When this instrument is place in a liquid or gas mediam whos temperature is to be measured the sheath quickly reaches the temperature of the medium. This change in temperature causes the platinum wire inside the sheath to heat or cool, resulting in a proportional change in the wire’s resistance. This change in resistance can be directly calibrated to indicate the temperature.


The conductors used for resistances thermometer are platinum, nickel of various purities, 70 per cent nickel/ 30 per cent iron and copper, listed in order of decreasing temperature range capability. These conductors are all available as fine wire for sensor winding. Platinum is also available as a deposited film sensor, and nickel and balco are available in foil- type sensors. A comparison chart of various resistance temperature detectors (RTD) or sensors, is given in table

Advantages: following are the advantages of resistance thermometer:

(i) they possess high accuracy of measurement. (ii) They have a wind temperature range from -200 to 650 c (iii) They are small in size. (iv) They are fast in response. (v) They have good reproducibility. (vi) Temp. Compensation is not required.

Disadvantages: following are the disadvantages of resistance thermometer:

(i) Their cost is high. (ii) They good a bridge circuit power supply. (iii) They so inaccuracy resolution from the current following the bridge

circuit and their by heating resistance and element. (iv) They produce mechanical abuse of vibration. (v) They have larger bulb size than thermocouple.

Conclusions:

Questions:

1) Explain RTD in detail? 2) Write the advantage and disadvantage of the RTD? 3) Write the Comparison between the RTD and Thermocouple?


LEARNING: 7 Aim: To study Thermistors. Apparatus: Different Ranges Temperature scale, Bridge circuits, Battery. Theory: Thermistors:

Thermistors are semiconductor, made from a specific mixture of pure oxides of nickel, manganese, copper, cobalt, iron, magnesium, titanium, and other metals sintered at temperatures above 982 c. Their distinguishing characteristics are a high temperature coefficient, usually negative, although it can be positive as well, and the fact that their resistance is a function of absolute temperature. Thermistors were recognize in the early 1800, but their use was first introduced by Bell laboratories in about 1940, naming them from the term “thermally sensitive resistors” Only in recent years have they found general industry-wide acceptance.

Figure:

Various Configurations of thermistors:

Thermistor are available in number of configuration most familiar is the bead type usually glass coated as show in figure.(a) they can also be meat into washers, discs or road, as show figure(b),(c)and(d) ,and can also be encapsulated in plastic cemented soldered in blots, encased in glass tube,


needles or a variety of other forms these assemblies serve to support the sensor, protect against damage to the wires, direct flow across the unit uniformly, permits sealing of conduits or flow lines, and provide for easier handling.

To measure temperature with a thermistor, it is placed in the environment whose temperature is to be measured. As the temperature of the substance or environment increases, the resistance of the thermistor decreases and vice versa. This change in thermistor resistance can be detected which will be the measure of the temperature of the substance. Generally, the thermistor is placed is one leg of a Wheatstone bridge circuit shown in fig.

Figure:

Wheatstone bridge:

At balanced condition, when there is no change in a temperature the galvanometer indicates zero. As the temperature increases or decrease, the resistance of the thermistor also decreases or increases due to which the Wheatstone bridge circuit becomes unbalanced. Thus electric current flows through the galvanometer which indicates on the calibrated scale The deflection of the galvanometer can be calibrated as a temperature scale. For very accurate temperature measurements, a differential bridge circuit is used in which two thermistors are connected as two legs of the Wheatstone bridge. In this case the unbalance is determined by resistance difference caused by temperature difference of the two thermistors.


Advantages:

1) They have small sizes and fast response. 2) They are suitable for narrow span. 3) Their cost is low. 4) Resistance is a function of absolute temperature, so cold junction compensation is not necessary.

Disadvantages:

1) Temperature versus resistance curve is very non linear.

2) They are unsuitable for wide temperature spans.

3) They are limited for process application.

4) Stability is doubtful at higher temperature. (over 316c)

Conclusion:

Questions:

1) Explain types of thermistors? 2) Explain thermistor in briefly? 3) Explain advantage and disadvantage of thermistor? 4) Write the comparison between thermistor and RTD?


LEARNING: 8

AIM: To Study Radiation Pyrometer and Optical Pyrometer.

Theory: PYROMETERS

There are two types of pyrometers generally use in industries.

1) Radiation pyrometers. 2) Optical pyrometers.

1) Radiation Pyrometers: Figure:

A typical radiation Pyrometer

Operation of radiation pyrometer is based upon the measurement of radiant energy emitted by the hot body. Show in fig. It consist of a lens to focus radiated energy from the body, whose temperature is required, on to a detector or receiving element. This receiving element have a , or variety of forms such as resistance thermometer, or a thermocouple or thermopile. A thermopile consists of several thermocouples connected in series. A temperature indicators recorder or controller is attached with the receiving elements to indicate the temperature.

When the total energy radiated by a hot body, whose temperature is to be measured. Enters the pyrometers it is focussed by the lens on the detector. The detector is a thermopile whose measuring junctions are attached to a blackened disk. The disk absorbs energy when the pyrometer is focussed on a hot body, and its temperature rises. The reference junction of thermopile is attached to the pyrometer case. The difference in temperature between the measuring junction attached to the disk and the reference junction attached to the case generate a voltage that is directly related to the temperature of the blackened disk, which is indicates by the recording instrument.


Sources of Errors:

1) They are quite sensitive to any obstruction in the line of sight between the pyrometer and the hot body. They should not be used when infrared-absorbing water vapour, dust, or other particles are in the air.

2) They are also sensitive to emittance errors. To compensate for such errors, the device should be calibrated using an optical pyrometer which is less sensitive to emittance errors.

The radiation pyrometers measure temperature without direct physical contact with the object whose temperature is being measured. They are also capable of measuring lower temperature than optical pyrometers.

Advantages:

1) They are able to measure high temperatures. 2) In radiation pyrometers , there is no need for contact with target of

measurement. 3) They possess fast response speed. 4) They have high output and moderate cost.

Disadvantage:

1) Their scale is non linear. 2) Errors due to presence of intervening gases or vapours that absorb

radiating frequencies is possible in these pyrometers. 3) Emissivity of target material affect measurement .

Applications: 1) They are used for the temperatures above the Learning operating range

of thermocouples. 2) They can be used in the environments which contaminate or limit the

life of thermocouples. 3) They are used for moving targets. 4) They are used for the targets not easily accessible, such as funave

interiors. 5) There are used for the targets which would be damaged by contact

with primary elements like thermocouples and resistance thermometers.

6) They are used for the measurement of average temperatures of large surface areas.


3) Optical Pyrometers:

Optical pyrometers provide an accurate method of measuring temperatures between 600 to 3000c and are very useful for checking and calibrating radiations pyrometers. But they are not suitable for recording or controlling temperatures.

The method of operating of optical pyrometers is based on the comparison of the intensity of the visual radiation emitted by the hot body with the radiation emitted by the source of known intensity. The brightness of radiation emitted by the hot body whose temperature is to be measured, is matched with brightness of a calibrated reference whose temperature is known. A typical industrial optical Pyrometer is for the temperature range from 700 to 3000c.show in fig. The schematic arrangements of an optical pyrometer.

Figure:

Optical pyrometer Schematic Diagram

An optical pyrometer consists of an incandescent lamp filament which is used as the as reference source of radiations. This is arranged in the field of vision of a telescope through which both it (the filament) and the hot body, are viewed simultaneously. The filament is heated by a 2 volt battery in series with a rheostat by which the temperature of the filament is adjusted. This filament is


connected in one arm of wheat-stone bridge circuit across which is connected a moving coil galvanometer. The electrical resistance of the lamp filament varies in accordance with its temperature, while the resistance in other arms of the bridge are of material, the ohmic value of which does not alter with a change of a temperature. As the temperature of he filament is increased the bridge is progressively thrown out of balance. The degree of unbalanced is shown by the magnitude of the galvanometer deflection which is calibrated in term of temperature.

In operation the object is viewed through the telescope when the filament first appears as a dark line against the glowing background. Show in fig ‘A’ . On rotating the rheostat the temperature of the filament is progressively increased until the visible radiation matches that of the hot object, when the tip of the filament becomes invisible against the background. Show at fig. B.

Figure:

The Disappearing filament

When this stage is reached, the temperature may be read off from the galvanometer provided that the rheostat is not moved after the temperature matched is obtained. An absorption screen is used between the object and the filament so that the filament may be matched to a hot mass which is at a considerably higher temperature than the filament itself. A monochromatic red screen is fitted to the eye piece so that it may be brought into the field of vision at will. Its function is to eliminate colours difference between the filament and the hot body of facilitate matching and also to prevent dazzle at a higher filament temperatures.

Advantages:


1) It is light in weight. 2) It has a good accuracy. 3) It possess flexibility, portability and is convenient for use. 4) It is useful for high temperature.

Disadvantages:

1) It is relatively expensive. 2) It is subject to emissivity errors. 3) It is not useful for measuring the temperatures of clean burning gases

that do not radiate visible energy. Conclusion: Questions:

1) Write the type of Pyrometers? 2) Explain Radiation Pyrometers in detail? 3) Explain optical Pyrometer with schematic diagram?


LEARNING: 9

AIM: To study Direct methods of level measurement.

Apparatus: measurement scale, sight glass, f loat, displacer

Theory: Methods of liquid level measurement

Generally ,there are two methods used in industries for measuring liquid level .

These are:

(i) Direct methods (ii) Indirect methods

DIRECT METHODS:

This is the simplest method of measuring liquid level .In this method , the level of liquid is measured directly by means of the following level indicators;

1) Sight glass

2) Float type

3) Displacer type

1) SIGHT GLASS

A sight glass is another method of liquid level measurement. It is used for the continuous indication of liquid level within a tank or vessel .

Figure: Sight glass for an open tank:


Construction and working:

A sight glass instrument consist of a graduated tube of toughened glass which is connected to the interior of the tank at the bottom in which the water level is required .figure shows a simple sight glass for an open tank in which the liquid level in the sight glass matches the level of liquid in the tank . as the level of liquid in the tank rises and falls ,the level in the sight glass also rises and falls accordingly. Thus, by measuring the leveling the sight glass, the level of liquid in the tank is measured. In sight glass, it is not necessary to use the same liquid as in the tank. any other desired liquid also can be used .

Figure:

High pressure sight glass

When it is desired to measure a liquid level with the liquid under pressure or vacuum , the sight glass must be connected to the tank at the top as well as at the bottom , otherwise the pressure difference between the tank and the sight glass would cause false reading. In this case, the glass tube is enclosed in a protective hosing , and two valves are provided for isolating the gauge from the tank incase of breakage of the sight glass . the smaller valve at the bottom is provided for blowing out the gauge for cleaning purposes .figure shows a high pressure sight glass in which measurement is made by reading the position of the liquid level on the calibrated scale . this type of sight glass in high pressure tanks is used with appropriate safety precautions . the glass tube must have a small inside diameter and a thick wall.


Ranges:

The standard practice is not to go in for a glass tube of more than 900mm , to or more sight glass level gauges are provided at different level . this type of gauge is made to with stand pressures of 350psi of stem pressure at 252oc , or 1000psi liquid pressure.

Advantages:

1) Direct reading is possible.

2) Special designs are available for use up to 316oc and 10000 psi.

3) Glassless designs are available in numerous material for corrosion resistance.

Disadvantages:

(1) it is read only where the tank is located , which is not always convenient.

(2) since sight glasses are located on the out side of the tank ,the liquid in the sight glass may freeze in cold weather even through the liquid in side the tank does not, and thus, it may cause error in the reading.

(3) heavy , viscous liquids or liquids containing material which fall out of the solution and clog the tube cannot be measure satisfactorily by a sight glass .

(4) overlapping gauges are needed for long level spans

(5) accuracy and readability depends on the cleanliness of glass and fluid

2) FLOAT-TYPE:

Float operated level indicator is used to measure liquid level in a tank in which float rests on the surface of liquid and follows the changing level of liquids. the movement of the float is transmitted to a pointer through a suitable mechanism which indicates the level on a calibrated scale. Various type of floats are used such as hollow metal spheres . cylindrical shaped floats and disc shaped floats.


Figure in show the simplest from of float operated mechanism for the construction liquid level measurement. in this case, the movement of the float is transmitted to the pointer by stainless still or phosphorus-bronze flexible cable wound around a pulley , and the pointer indicates liquid level in the tank .


Figure:

Float-operated liquid level indicator:

The float is made of corrosion resisting material and rests of liquid level surface between two grids to avoid error due to turbulence. With this type of instrument, liquid level from 1/2ft to 60,ft. can be easily measured.

With float operated type of mechanism, the liquid level can be transmitted to a distant place using a hydraulic transmission system, as shown in fig.below. . it consist of four bellows elements, two in the transmitter side and two in the receiver side that are fixed at the outer ends. Bellows B,C and A,D are hydraulically connected through pipes filled with an oil. When the float moves up or down according to change in level, its position is transmitted by a lower arm to the bellows assembly A-B. when the level rises, B is compressed and expands, thus causing oil in the pipe to flow from B to C , and from D to A. the bellows are balanced so that the movement at the transmitter end is reproduced in reverse mode at the receiving end, i.e. C expands and D is compressed as the liquid level rises the two bellows C and D act on the compensating link pivoted on the pointer in the same directions and will rotate the pointer in proportion to the level value. Any change in ambient temperature affects both the bellows,


I. e. both expand or contract. Therefore level transmission at the pointer is not affected. With this type of instruments, level transmission up to 250 ft can be achieved.

Figure:

Hydraulic transmission system for level indication

Advantages:

(i) It is possible to read the liquid levels in a tank from the ground level even if the tank is kept bellow the ground level.

(ii) Its cost is low and has reliable designs. (iii) It operates over a large temperature range. (iv) There is a choice of corrosion resistant materials to make these.

Disadvantages:

(i) They are normally limited to moderate pressures. (ii) They are tailored to tank geometry.

3) DISPLACER LEVER DETECTORS:

The displacer type level detectors work on the Archimedes principle which states that a body, wholly or partially immersed in fluid, is buoyed up by a force


which is equal to the weight of the fluid displaced. If the cross sectional area of the displacer and the density of the liquid are constant, then a unit change in level will result in a reproducible unit change in the displacer weight. By detecting apparent weight of the immersed displacer the level of the fluid is measured.

The simplest level measuring device of this type consists of a displacer that is heavier than the process liquid and is suspended from a spring scale. When the liquid level is below the displacer, the scale shows the full weight of the displacer. As the level rises the apparent weight of the displacer decrease, thereby yielding a linear and proportional relationship between the spring tension and level. The spring scale can be calibrated 0 to 100 per cent, or in other level units. But this is simple device is limited to the application in open tank. In actual industrial liquid level measurement, the basic problem is to seal the process from the spring scale for other force detecting mechanism. This seal has to be frictionless and used full over a wide range of pressure, temperatures, and corrosion condition.

The various types displacer level detectors are defined, based on the variations in the design of the seal which are listed below.

(i) Magnetically coupled switch type. (ii) Torque tube type. (iii) Diaphragm and force bar type. (iv) Spring balanced type (v) Flexible dice type . (vi) Flexible shaft type

All the above types operate on Archimedes principle, but are different as far as their scale are concerned. All of them can detect liquid vapor interface liquid, liquid interface and if level is constant, they can be used to detect density changes.

A torque tube type displacer for liquid level measurement is shown in fig.. it constant cylindrical displacer which can be furnished in a wide length of plastic and alloy materials. Although any length displacer up to 3m can be obtained , the most common lengths used are 0.3, 0.8, 1.2 and 1.5m. the volume of the standard displacer 1638 cc and consequently the diameter is reduced as of the length increase. A hollow torsion tube is used to both support the displacer ,


which is always heavier then process fluid, and to provide frictionless pressure seal. This make it possible to transfer the changes in the apparent weight of the displacer or through the wall of the pressure vessel in to suitable measuring device. The displacer is connected to the torque tube by the help of the torque arm which absorbs lateral forces. Fabrication is minimized by use of knife edge bearing support as shown in fig..below.

Figure:

Torque tube displacer type liquid level detector

A limit stop attached with the torque are to prevent accidental for stressing of the torque tube by limiting the downward motion of the torque are. As torque rod as placed in the torque tube which is attached with flapper nozzle assembly. Angular displacement of the torque tube arm are the some at the knife edge end of the tube. At the flange end, the tube does not rotate it all because it is solidly held, but the torque rod is free to rotate the some amount as it did at the knife edge. The angular displacement, which is about 5 to 6 degrees is linearly proportional to apparent weight of the displacer and thus liquid level.

Torque tube displacer type liquid level measuring device can be amounted internally or externally to the vessel or tank. Internal displacer are used on application where the tank can be drained when the level detector requires maintains. For installation where the vessel or tank cannot be depressurized and drained in order to perform maintains displacer, the displacer should installed in


an external chamber mounted outside the tank isolated from the process, by means of isolating valves.

Advantages:

1) They have high accuracy.

2) They are in the reliable in clean liquids.

3) They can be amounted externally or internally.

4) Externally amounted units can be disconnected from the process for maintains.

5) They are adaptable to liquid interface measurement

Disadvantages:

1) This instrument have limited ranges device exceeding 1.2m in length are bulky difficult to handle.

2) The cost of these device increase appreciably for externally mounted units as pressure rating increase.

3) Externally units may require heating to avoid freezing.

4) External units may be error because of temperature difference between the vessel fluid and the level chamber fluid .

5) Internal units may require stilling chambers.

Conclusions:

Questions:

1) Write the type of direct methods? 2) Explain sight glass level measurement? 3) Explain Float type level indicator? 4) Explain Torque tube displacer type liquid level detector?


LEARNING:10 Aim: To Study Bubbler method. Theory: Bubbler Method:

Air purge (also known as bubbler tube) system is one of the most popular hydrostatic pressure types of liquid level measuring system which is suitable for any liquid as shown in figure.

Figure:

Air Purge System

Construction:-

An air purge system consists of a hollow tube (known as bubbler tube ) inserted in liquid of the tank. Two connection are made with the bubbler tube , one to the regulated air supply and the other to a pressure gauge , calibrated in terms of liquid level. A bubbler is connected in the air supply line which serves simply as a visual check to the flow of the supply air. A level recorder may be connected may be connected with the pressure gauge to keep the continues record of liquid level as shown in figure.

Working:-

When there is no liquid in the tank is the below the bottom end of the bubble tube, the air flows out of the bottom of the bubble tube and the


pressure gauge indicates zero. In other words, there is no back pressure because the air escapes to the atmosphere. As the liquid level in the tank increases, the air flow is restricted by the depth of liquid and the air pressure acting against liquid head appears as back pressure to the pressure gauge. This back pressure causes the pointer to move on a scale, calibrated in terms of liquid level the full range of head pressure can be registered as level by keeping the air pressure fed to the tube, slightly above the maximum head pressure in the tank. The range of the device is determined by the length of the tube. Because air is continuously bubbling from the bottom of the tube, the tank liquid does not enter the bubbler tube and hence, the tube is said to be purge. The common purging fluid is air, but , if air reacts with the tank fluid or is absorbed, different gases (like carbon & nitrogen ) are chosen depending on liquid properties.

Advantages:-

Following are the advantages of air purge system :

A. In this system, the pressure gauge can be placed above or below the tank level and can be kept as far away as 500 ft (12.7 m) from the tank with the help of piping.

B. This type of devices is as well- suited for measuring the level of corrosive or abrasive liquid.

Conclusion:

Questions:

1) Write the construction and working of the Air Purge system? 2) Write the Advantages of the Bubbler method?


LEARNING: 11

Aim: To Study Capacitance Type level Measurement method.

Apparatus: Capacitance measuring instrument, insulated capacitance prob, Electric wire, metal tank.

Theory:

CAPACITANCE LEVEL INDICATOR:

The principle of operation of capacitance level indicator is based upon the familiar capacitance equation of a parallel plate capacitor given by:

C = K *A/D

WHERE, C = capacitance, in farad

K = dielectric constant

A = area of plate, in m2

D = distance between two plate, in m

Therefore, it is seen from the above equation that if A & B are constant, then the capacitance of a capacitor is directly proportional to the dielectric constant, and this principle is utilized in the capacitance level indicator.

Construction & Working :-

Fig. shown a capacitance type liquid level indicator. It consists of an insulated capacitance probe ( which is metal elytroid) firmly fixed near and parallel to the motel wall of the tank. If liquid in the tank is non-inductive, the capacitance probe and and the tank wall from the plates of the parallel plate capacitor and liquid in between them acts as the dielectric. If liquid is conductive, the capacitance probe and liquid plates of the capacitor and the insulation of the probe acts as dielectric. A capacitance measuring device is connected with the probe and the tank wall, which is calibrated in terms of level of liquid in the tank.

When the level of liquid in the tank rises, the capacitance increases. When liquid level in tank decreases. This increase and decreases in the capacitance is measured and is displayed on the indicator calibrated in terms of liquid level.


Figure:

Capacitance level indicator

Advantages:

Following are the advantages of capacitance level indicator:

1. it is very useful in small system. 2. it is very sensitive. 3. there are no moving parts exposed to fluid. 4. it is suitable for continuous indicating and/or control. 5. remote adjustment of span and zero is possible in this type of level

indicator. 6. it is good for use with slurries. 7. prob materials for must corrosive are available.

Disadvantages:

Following are the disadvantages of a capacitance level indicator:

1. the performance of capacitance level indicator is severely affected by dist and other contaminants, because they change the dielectric constant.

2. it is sensitivity is adversely affected by change in temperature. 3. measured fluid must have proper dielectric qualities. 4. they usually require recalibration if measured material changes in

composition or moisture content.

5. prob length and mounting must suit the tank.


Conclusion:

Questions:

1) Explain construction and working of the Capacitance level indicator? 2) Explain advantage and disadvantage of the Capacitance level indicator?


LEARNING: 12

Aim: To Study Radiation type level measurement method.

Apparatus: Source holder, Electric wire, gamma detector, indicating instrument.

Theory:

RADITRUTION LEVEL DETECTOR :

Radiation level detectors are used where other electrical methods would not survive. Also, the most common reason for using a radiation level detector is that is does not need to come in contact with the liquid being measured.


Fig. shown a radiation level detector. It consist of gamma rays source holder on one side of the tank and gamma detector on the other side of the tank. The gamma rays from the source are directed towards the detected towards the detector in a thin band of radiation. When the gamma rays penetrate the thick wall of the tank, its energy level afterwards is greatly reduced. The radiation received at the gamma detector is inversely proportional to the thickness of the tank walls and the medium between the radiation source and detector, that is, the thicker the medium between source and detector, less radiation received by the detector and vice versa.

Figure:

Radiation type level indicator


When the tank is empty, the gamma rays pass only through the two tank walls and the air or vapour in the empty tank. When liquid enter the tank and its level rises, the radiation beam passes through a path in the liquid, as well as the tank walls. The liquid in the tank reduces the radiation received by the detector. The amount of radiation received is inversely proportional to the amount of liquid between the radiation source and detector. The difference in the amount of radiation received by the detector, corresponds to the liquid level in the tank. Thus, when liquid level rises, the amount of radiation received is reduced and visa versa. The radiation loss received by the tank walls is constant whether the tank is full or empty.

Advantages :

Following are the advantages of radiation level indicators

1) There is no physical constant with the liquid. 2) They are suitable for molten metal’s as well as liquid of all types

(corrosive, abrasive, highly viscous, adherent). 3) They are useful at very high temperature pressures. 4) They behave good accuracy and response. 5) They have no moving points. Disadvantages:

Following are the disadvantages of radiation level indicators:

1) The reading is affected by density change of liquid. 2) Radiation source holders may be heavy. Their cost is relatively high

Conclusion:

Questions:

1) Write the construction and working of the Radiation level detector? 2) Write the advantage and disadvantage of the radiation level detector?


LEARNING: 13

Aim: To Study Ultrasonic level Detector.

Apparatus: Ultrasonic pulse source, Echo receiver, tank, level indicator, liquid.

Theory:

Ultrasonic Level Detectors

Working & construction:

Ultrasonic level detectors operate either by the absorption of acoustic energy as it travels from source to receiver or by the attenuation of a vibrating diaphragm face, oscillating at 35 to 40 KHz. It operates by generating an ultrasonic pulse and measuring the time it takes for the echo to return. When an ultrasonic transmitter is mounted at the top of the tank. The pulse travels in air at a speed of 331 meter/second at 0 C. the ti9me of travels is an indication of the depth of the vapour space above the liquid in the tank. If an ultrasonic transmitter is mounted on the bottom of the tank, the time of travel reflects of liquid in the tank and the speed of travel is a function of what that liquid is. In case of water at 25 C, an ultrasonic pulse travels at the speed of 1,496 meters/second. Figure illustrates the working of an ultrasonic level detector.

Figure:

Ultrasonic level detector

Temperature compensation is essential in ultrasonic level measurement because the velocity of sound is proportional to the square root of temperature &, in case of air; it changes by about 0.6 meter/second for per C change in


temperature. The speed of travel rises with temperature, & it amount to about 0.18% per C.

In order to measure the time of travel of the echo of an ultrasonic pulse, it is essential that some of the sonic energy be reflected. Liquids & solids with large & hard particles are good reflected. Loose dirt have poor reflecting characteristics as they tend to absorb the sonic pluse. Since the angle of reflected is equal to the angle of incidence, it is important that the reflecting surface be flat. If the sonic pulse is reflected from a sloping surface, its echo will not be directed back to the source & the round –trip travel time will not accurately where only small portion of the total vertically back to the source.

Ultrasonic level measuring devices can be used for both continuous & point measurement. The point measuring ultrasonic detectors are used for measurement. The point measuring ultrasonic detectors are used for measurement of gas/liquid, liquid,/liquid , or gas/solid interfaces.

Advantages:

1) Ultrasonic level detectors are non – contact type measurement techniques. They have are ability to measure level without making physical contact with the process material.

2) They have no moving parts. 3) The reliability of the reading is unaffected by changes in the

composition, density, moisture content, electrical conductivity, or dielectric constant of the process fluid.

Disadvantages:

1) An ultrasonic transmitter is subject to many interferences, which affect the strength of the echo it receives. The echo can be weak due to dispersion (which in dry air reduces its energy level).

2) Temperature compensation is essential in ultrasonic level measurement.

3) The dirt, irregular and slope surface affect the accuracy of the measurement.


Conclusion:

Questions:

1) Explain construction and working of Ultrasonic level detector? 2) Write the advantage and disadvantage of the Ultrasonic level detector?


LEARNING: 14

Aim: To study about the mass, spring, seismic sensor and piezo-electronic sensor

Theory:

Vibration measurement:

Vibration is general characteristics by the frequency in Hz or the amplitude of the measured parameter which may be displacement velocity for accretion.

Vibration sensor Mass spring seismic sensor Piezo-electric sensor

Mass-spring seismic sensor:

Figure:

Mass-spring seismic sensor


The displacement of a mass, resulting from an applied forced is measured and to the acceleration.

The schematic a common spring-mass damper accomplishes this task. The mass is supported by a spring and damper is connected to the housing fame.

The acceleration imported by the machine to the frame, the mass move to the frame is sensed.

The spring-mass system is the acceleration represent equation neatens second law.

Md2x2/dt2 + c dxa/dt + kx3 = cdx1/dt + k.

The proportional to the velocity the vibratory motion applied to the housing frame.

Piezo-electric sensor:

Figure:

Piezo- electric acceleration


The unit is the simplest and most commonly used transducer for measuring acceleration. The piezo-electric crystal between two electrode and mass on it.

The base acts as a spring and the mass against the crystal mass a force on the crystal and a certain output voltage is generated.

Newton’s second low.

Force = mass X acceleration.

The decrease in force in proportion to the acceleration.

The direction increases the force on the crystal in proportional to the acceleration.

Advantages & limitations:

Inexpensive device. High output impedance. High frequency response from 10 Hz to 50Hz. High sensitivity. Sensitivity to change in temp. Ragged device.

Conclusion:

Questions:

1) Explain to the Mass-spring seismic sensor? 2) Explain to the pizeo-electric sensor?


LEARNING:15

Aim: To study about force & torque measurement.

Theory:

Definition of force:-

Force represent the mdraniced which change to changes the relative motion of a body to which is applied Newton’s second low of motion states that force is proportional to the rate of change of momentum

F X d/dt (mv)

Figure:

Proving Ring

Scales and balances:

Force is weight is indicated by making a comparison between the force to gravity acting on a standard mass and the force to gravity acting the mass.Equal arm beam balance consists of a beam pivoted knife-edge at the centre. The


condition exists when the clock wise rotating moment equals the anticlock. The two arms of the beam are equal they would be equabarium.

M1 =M2

The equal-arm balance require a set at weight the heaviest load to the measured these unefoul arms are called load the power arm the balance specified in two ways.

1) Mechanical advantage that the ratio of load to power.

2) Multiple in detained.

M=power arm/load arm

Unequal arm beam balance:

The force beam applied to test specimen. The lower the vertically from of loading gripped and attached to the beam.

Palette knife edge the right hand size beam calibrated in force units.

Where content R = ac/bh is called the multiplication ratio of the scale are available ratio whighenas 10,000 to 1. The knife edges pivot beaming of such scale is to be maintained good condition. \

Electrical force meter:

The force measuring units measure the force applying to electrical element than measuring the electric deformation the electric range at the materials of the force. The relations for the electric OC are outlined below the material deflection content derived.

K= f/x are also given.

Simple bar:-

X=F1/AE K=AE/2

Simply supplied beam:-

X=1/48 F13/E1 K› 48E1/L3


Coutiever:-

X =1/3 F13/E1 K= 3E1/L3

Spring:-

X= 8FDM3N/ED104 K = ER, DW/8DM3W

‘Where’ DM = Meam coil diameter. N = number of term the wits.

DW = unit diameter. Ea = shear modules.

Thin ring

X = 1/16 ( /2 - /4 ) . FD3 /E1

K= 16/ ( /2 - 9/ ) . E1/Da

The materials used for contracting the electric force meter.

1) A large & proportional elastic range. 2) Force dam foam hydectrsis.

Application:- force increases the liquid pressure.

The force magnitude divided by the effective area of the diaphragm.

The pressure is transmitted to and caadion accurate pressure gauge calibrated dridty in force units.

Conclusion:

Questions:

1) Write the definition of force? 2) Explain Scales and balances of force measurement?


LEARNING:16

Aim: To study about load cell

Theory:

The load cell:

There are three types of they load cell.

1. Mechanical load cell. 2. Hydraulic load cell. 3. Pneumatic load cell.

1) Mechanical load cell:

A term load cell is used to describe a variety of force transducer which may utilize the deflection or entrain of electric member or than the increase in pressure of enclosed fluids.

The resulting fluid pressure is transducer to some form of pressure sensing device such as a manometer or a Burdon tube pressure gauge the gauge reading is identified and calibrated in unit of force.

2) Hydraulic load cell:

A force variable is impressed upon a diaphragm which deflates and there by transmits the force to a liquid.

The liquid medium contained in a confide space has a preload pressure at the order of 2 kg/cm2.

Application:

When the force increase the force magnitude divided by the effective area of the diaphragm.

Construction:

A hydraulic force meter consists of metal diaphragm. The metal diaphragm is attached to a fluid chamber.

Which is connected to a spiral type Burdon type a pointer is attached to the Burdon tube which moves on a scale?


Figure:

Hydraulic force meter

Working:

When force is a applied on the diaphragm than fluid pressure is in the chamber.

This pressure is indicated by the pointer on the calibrated scales and gives the value of the applied force.

Disadvantage:-

Linkage case measurement errors.

High cost.

Difficult to calibrate the instruments.

3) Pneumatic load cell:

The pneumatic load cell operates on the force balance principle.

Construction:

A pneumatic force meter is consists of diaphragm and this is attached to the rod and flapper.


Nozzle is flaked near the flapper which is connected to the air supply and p[ressure measuring device such as manometer and Bourdon tube etc.

Working:

When force is applied on the diaphragm Rod. The diaphragm is down word so the flapper and nozzle back pressure generate.

The flapper and nozzle are shut off so the nozzle back pressure acting on the diaphragm and diaphragm is return to the mean position.

Advantages:

They are suitable for use in. The temperature related error free. Transmitting system is not required.

Disadvantages:

Water vapors freezing at temp below 32®F. They are responding slowly.


1) Write the type of load cell? 2) Explain to the Mechanical load cell? 3) Explain to the Hydraulic load cell with application?


LEARNING:17

Aim: To study about electronic torsion meter and mechanical torsion meter

Theory:

Electrical Torsion meter:

The property of material to pass electromagnetic flux through it is called the permeability.

Variation in the permeability can be used to measure the torque.

The permeability increase under the tension stress and decreases under the compression stress.

Figure:

Electrical torsion meter


Construction & working:

The electrical torsion meter consists of primary and secondary winding mounted on the rotating shaft as shown in figure.

When there is no loading on the shaft the permeability of the shaft is uniform and equal.

When the shaft is under the torsion thus the permeability is increase is the direction of the tension and permeability is decrease in direction at compression.

The voltage is included in the secondary winding which is proportional to the torque.

The primary winding and secondary winding are arranged so the detect the deflection of the magnetically shown in what stone bridge.

When these are no loading on the shaft the bridge circuit is balanced connection and the output voltage is zero.

Mechanical torsion meter:

Shown the schematic diagram of electric torsion meter. Rotating shaft is used to measure the torque.

The calibrated scale is attached to the rotating shaft.

This system is given varying angle between the driving engine and the when loan as the torque changes.

Application:

There are simple constructions. There cost is low. There sensitivity is high.


1) Explain Electrical Torsion meter with construction and working?

urvish soni government polytechnic ahmedabad · the vapour-pressure thermometer is also a...

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