Bourdon Tube

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ITEMAcknowledgements Importance of pressure measurement Introduction to bourdon tube Classifications of bourdon tube Types of bourdon tubes C-type Bourdon Tube Spiral & helical type Bourdon Tubes Differential Gauge Advantages of Bourdon tubes Limitations of Bourdon tubes













ACKNOWLEDGEMENT:Before I delver into the deeper aspects of this project I would like to acknowledge the contribution of the internet & the central library of this institute for providing the relevant information about this project. The report has been written with the active support and assistance of my friends. I would also express my sincere thanks to our Head of the Dept. Prof. DEBADUTTA GHOSH for his assistance in writing this report. Last but not the least I would like to thank my beloved teachers of our dept. who has provided me the opportunity to do this project. .


IMPORTANCE OF PRESSURE MEASUREMENTNearly all industrial processes (e.g. metal, chemical, etc) use liquids, GASSES or both. Controlling these processes requires the measurement and control of liquid and gas pressure. So, pressure measurement is one of the most important of all process measurement. UNDERSTANDING OF PRESSURE: Pressure is defined as the amount of force applied to a surface or distributed over it.

PRESSURE=FORCE/AREA. METHODS OF PRESSURE MEASUREMENT:Most pressure instruments measures a difference between two pressures, one usually being that of the atmospheric. The different methods of pressure measurements are: 1. Manometer method. 2. Elastic pressure transducers. 3. Pressure measurement by measuring vacuum. 4. Electrical pressure transducer


INTRODUCTION TO BOURDON TUBE:Bourdon tube is one type of elastic primary sensing element which is used in elastic pressure transducer. The principle of inferring the pressure from the measured deformation of an elastic material is used here. It may be emphasized that any material will be deformed or distorted when any force, no matter how small or great, is applied to it. If all material react in this manner, the amount of deformation or movement of distortion can be used as the measure of the force, and consequently of the pressure which created the force. The pressure range, the no. of operating cycles, formability and the medium which exerts the pressure on the inside of the tube will dictate the material to be used in tube constructions. Phosphorbronze, beryllium copper, steel chrome-alloy steels and stainless steels are generally used. For the low pressure ranges (upto 2000 psi) Phosphorbronze is generally preferred; where corrosion is a problem, stainless steel may be employed. Stainless steel is used for high pressure ranges (above 2000psi). It is most frequently used pressure gauge because of its simplicity and rugged construction. It covers the range from vacuum to very high pressure. It measures the pressure of liquids and gases of all kinds, including steam, water, and air up to pressures of 100,000 pounds per square inch.


The majority of pressure gauges in use have a Bourdon-tube as a measuring element. (The gauge is named for its inventor, Eugene Bourdon, a French engineer.) The Bourdon tube is a device that senses pressure and converts the pressure to displacement. Since the Bourdon-tube displacement is a function of the pressure applied, it may be mechanically amplified and indicated by a pointer.


Depending upon the no. of tappings the bourdon tube pressure gauges are classified as: Simplex type Duplex type A simplex gauge has only one bourdon tube and measures only one pressure. When two bourdon tubes are mounted in a single case with each mechanism acting independently but with two pointers mounted on a common dial, the assembly is called a duplex gauge.


TYPES OF BOURDON TUBESThe Bourdon tubes are designed in various forms. These are1. C-type Bourdon tube 2. Spiral type Bourdon tube 3. Helical type Bourdon tube


C-TYPE BOURDON TUBECONSTRUCTION:The bourdon tube pressure instrument is one of the oldest pressure sensing instruments in use today. The bourdon tube (refer to Figure A-1) consists of a thinwalled tube that is flattened diametrically on opposite sides to produce a crosssectional area elliptical in shape, having two long flat sides and two short round

sides. The tube is bent lengthwise into an arc of a circle of 270 to 300 degrees. The main parts of this instrument are as follows: An elastic transducer that is bourdon tube which is fixed and open at one end to receive the pressure which is to be measured. The other end of the bourdon tube is free and closed. The cross-section of the bourdon tube is elliptical. The bourdon tube is in a bent form to look like a circular arc. To the free end of the bourdon tube is attached an adjustable link, which is in turn connected to a sector and pinion as shown in diagram. To the shaft of the pinion is connected a pointer which sweeps over a pressure calibrated scale. MECHANICAL DETAILS: JOYSRI DATTA (09/EI/59) 7

Stationary parts:

A: Receiver block. This joins the inlet pipe to the fixed end of the Bourdon tube (1) and secures the chassis plate (B). The two holes receive screws that secure the case. B: Chassis plate. The face card is attached to this. It contains bearing holes for the axles.

C: Secondary chassis plate. It supports the outer ends of the axles. D: Posts to join and space the two chassis plates.

Moving Parts: 1. Stationary end of Bourdon tube. This communicates with the inlet pipe through the receiver block. 2. Moving end of Bourdon tube. This end is sealed. 3. Pivot and pivot pin. JOYSRI DATTA (09/EI/59) 8

4. Link joining pivot pin to lever (5) with pins to allow joint rotation. 5. Lever. This is an extension of the sector gear (7). 6. Sector gear axle pin. 7. Sector gear. 8. Indicator needle axle. This has a spur gear that engages the sector gear (7) and extends through the face to drive the indicator needle. Due to the short distance between the lever arm link boss and the pivot pin and the difference between the effective radius of the sector gear and that of the spur gear, any motion of the Bourdon tube is greatly amplified. A small motion of the tube results in a large motion of the indicator needle.9.

Hair spring to preload the gear train to eliminate gear lash and hysteresis.

OPERATING PRINCIPLE:The pressure to be measured is connected to the fixed open end of the bourdon tube. The applied pressure acts on the inner walls of the bourdon tube. Due to the applied pressure, the bourdon tube tends to change in cross section from elliptical to circular. This tends to straighten the bourdon tube causing a displacement of the free end of the bourdon tube. This displacement of the free closed end of the bourdon tube is proportional to the applied pressure. The resulting movement of the free end of the tube causes the pointer to move over the scale. The displacement of this end is amplified and is calibrated in terms of pressure. The movement of the tube at the free end is called tip travel. Connecting link connects the tip of the bourdon tube of the linear rotary motion unit for transmitting the motion of the tip to the linear rotary motion unit.


The movement of the tube at the free end is called tip travel. Connecting link connects the tip of the bourdon tube of the linear rotary motion unit for transmitting the motion of the tip to the linear rotary motion unit. Since, the resulting tip motions non-linear because less motion results from each increment of additional pressure. It has to be converted into linear rotational pointer response. This is done mechanically by means of a geared sector and pinion movement In practice, a flattened thin-wall, closed-end tube is connected at the hollow end to a fixed pipe containing the fluid pressure to be measured. As the pressure increases, the closed end moves in an arc, and this motion is converted into the rotation of a (segment of a) gear by a connecting link which is usually adjustable. A small diameter pinion gear is on the pointer shaft, so the motion is magnified further by the gear ratio. The positioning of the indicator card behind the pointer, the initial pointer shaft position, the linkage length and initial position all

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provide means to calibrate the pointer to indicate the desired range of pressure for variations in the behavior of the Bourdon tube itself. The angle between the connecting link and the sector tail is called the traveling angel. This angle changes with tip movement compensating for the nonlinearity of the tip movement itself. Differential pressure can be measured by gauges containing two different Bourdon tubes, with connecting linkages. Bourdon tubes measure gauge pressure, relative to ambient atmospheric pressure, as opposed to absolute pressure; vacuum is sensed as a reverse motion. Some aneroid barometers use Bourdon tubes closed at both ends (but most use diaphragms or capsules, see below). When the measured pressure is rapidly pulsing, such as when the gauge is near a reprocating pump, an orfice restriction in the connecting pipe is frequently used to avoid unnecessary wear on the gears