T he p re ss ur e i nt en si ty a t a n y p oi nt i n s ta ti c o r m ov in g f lu id c an b e m e a s u r e d u s i n g various types of pressure measuring instrument. One of these devices is the Bourdon tube pressure gage. Bourdontube pressure gages are most widely used nowadays because of their reliability! compactness! low cost and ease of use. "t consists of a curved tube of e l l i pt i c a l c r o s s s e c t io n b e n t i n t o a c i r c u l a r a r c a s s h o w n i n f i g . # . $ h e n p r e s s u r e i s a pp li ed t o t he t ub e! i t t e nd s t o s tr ai gh te n o ut! a nd the deflection of the end o f the tube is communicated through a system of levers to a recording pointer. This gauge is widely used for steam and compressed gases. The pre ss ure in di cate d is th e dif fe ren ce bet we en th e sys te m pre ss ure an d to th e e%t ern al &amb ient' press ure! and is u suall y ref erred to as the gauge pressure
(ig. #) schematic of a bourdontube pressure gage
*s the Bourdon tube pressure gauge is used e%tensively! the stiff ness of the internal components change from factory setup and therefore calibration is necessary to give correct pressure readings.
To calibrate the gauge! weights are added to a platform on a dead weight tester. The weights put a known force on to a piston. The piston has a known area! so the pressure can be calculated. * fle%ible tube containing water transfers the pressure on the piston to the Bourdon tube. $eights are added in increments! recording pressure readings from the gauge at each increment. The weights are then removed and gauge readings are recoded. By working out theoretical results gauge error and be found.
PROCEDURE
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The weight of the +iston! and its cross sectional area should be noted. The piston should be removed! and water is poured into the cylinder until it is full to the overflow level. *ny air trapped in the tube may be c leared by tilting and gently tapping the apparatus. * small amount of air left in the system will not affect the e%periment! however! a large amount of air would cause the piston to bottom on the base of the
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cylinder. The piston is then replaced in the cylinder and allowed to settle. * spirit level placed on the platform at the top of the piston may be used to ensure that that the cylinder is
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vertically upright. $eights are now added in convenient increments! and at each increment! the pressure gauge reading is observed. * similar set of results is then taken with decreasing weights. To guard against the piston sticking in the cylinder! it is advisable to rotate the piston gently while the pressure gauged is being read.
THE GRAPHS
Error 2 1.5 1 0.5
Error
0 30.66 -0.5
46
61.31
91.97
122.63
153.28
183.94
-1 -1.5 -2 -2.5 -3
True pressure Increasing pressure
Decreasing pressure
Gauge Reading 200 180 160 140 Increasing ressure
120
True pressure
100
Decreasing ressure
80 60 40 20 0 30.66
46
61.31 91.97 122.63153.28183.94
Gauge Reading
CONCLUTIONS
Through the lab we were able to study and sketch the construction of a typical Bourdon Gauge and describe how it works. *nd were able to establish the calibration curve of the Bourdon Gauge. Steps should be taken to minimi,e the error and continue the e%periment to achieve the final results
REFERANCES
ra,,a! t.! #-/. scribd. 0Online1 *vailable at) http)22www.scribd.com2doc234/5/-#26*L"B7*T"O8O(*+79SS:79 G*:G9;scribd (luid
rd 9dition by ?.(. @ouglas A 7.@.
