exp5

SKKK 2721 2012/2013 [FLUID MECHANICS LABORATORY]

FINAL REPORT SKKK 2721FLUID MECHANICS LABORATORY

2012/2013-SEM 2

EXPERIMENT 5CALIBRATION OF BOURDON TUBE PRESSURE GAUGE

DATE OF EXPERIMENT11th MARCH 2013

LAB INSTRUCTORDR LAI JAU CHOY

SECTION 09GROUP 3

NO.

TEAM MEMBERS NRIC

1. HOW CHEE YANG 911123-14-53712. 921001-01-73033. MUHAMMAD ZA'IM BIN MOHD ZIN 921128-03-61654. NUZUL ARDZAN BIN MOKHTAR

EXPERIMENT 5: CALIBRATION OF BOURDON TUBE PRESSURE GAUGE | 2-SKKK (SECTION 09) 1

Faculty of Chemical Engineering(FChE)


Date of submission: 18th MARCH 2013

MARKING FORM: Criteria Maximum Percentage Score Comment

Technical Aspects 5%

Abstract 5%

Introduction 5%

Literature Review/Theory 5%

Methodology 5%

Results 5%

Discussion 5%

Conclusion 5%

References 5%

OVERALL TOTAL 45%

TABLE OF CONTENTS



Section Page

Abstract 4

Introduction 4

Literature Review 5

Methodology 6

Results and Discussion 8

Conclusion 11

References 11

Appendix 12

1.0 ABSTRACT



The objective of this experiment is to perform pressure calibration on a Bourdon tube

pressure gauge using a dead weight tester. Calibration is very important both in laboratory

and industry for both safety and economic reasons. In this experiment, different amount of

weights were used to produce different readings of the gauge. It was found that calibrated

pressure correlated linearly with true pressure. The linear calibration curve meant that given

any reading on the gauge, we can determine the true pressure from the calibration curve with

high accuracy. In conclusion, pressure calibration was performed successfully on the Bourdon

tube pressure gauge.

2.0 INTRODUCTION

The pressure intensity at any point in static or moving fluid can be measured using various

types of pressure measuring instrument. One of these devices is the bourdon tube pressure

gauge. Bourdon tube pressure gauges are most widely used now-a-days because of their

reliability, compactness, low cost and ease of use. It consists of a curved tube of elliptical

cross section bent into a circular arc as shown in Figure 1. When pressure is applied to the

tube, it tends to straighten out, and the deflection of the end of the tube is communicated

through a system of levers to a recording pointer. This gauge is widely used for steam and

compressed gases. The pressure indicted is the difference between the system pressure and to

the external (ambient) pressure, and is usually referred to as the gauge pressure.

Figure 1 Schematic of a Bourdon-tube Pressure Gauge

As the bourdon tube pressure gauge is used extensively, the stiffness of the internal

components change from factory setup and therefore calibration is necessary to give correct

pressure readings. Calibration means checking the pressure gauge readings against a very

accurate device. One of the calibration devices that is available in our lab is the so-called

“Dead Weight Tester”.



2.1 OBJECTIVE

The objective of this experiment is to perform pressure calibration on a Bourdon tube

pressure gauge using a dead weight tester.

2.2 SIGNIFICANCE OF STUDY

Calibration is the process of checking devices and making sure that their readings are as

accurate as possible or within engineering tolerances. Thus, through this experiment, the

findings of the experiment (e.g. calibration curve) are very important to recalibrate the

Bourdon tube pressure gauge in order to have a higher accuracy. Besides that, we usually

need to know the pressure in a high pressure boiler industrially. If a pressure gauge shows a

lower pressure than actual, explosion may occur despite the pressure gauge indicating a safe

pressure level. With routine calibration, we can ensure the safety of personnel and equipment

with measuring device.

3.0 LITERATURE REVIEW

Bourdon tube is a mechanical pressure measurement device, named after the French engineer

and inventor Eugene Bourdon according to Cengel and Cimbala (2010). According to

www.ehow.com bourdon tube pressure gauges are usually used for a number of applications

such as oil drilling, ocean liner operations and manufacturing plants. These gauges inform the

operator concerning the amount of pressure in tanks or running through pipe work. This

pressure can involve air, steam, water, oil or other materials. The machinery operator should

calibrate the pressure gauge to ensure the readings are accurate.

In this experiment, a piston of known area, A was loaded with a known weight,

therefore the actual pressure in the cylinder was

P=FA

=mgA

……………………………………3.1

where m is total mass of load and g is gravitational acceleration. From equation 3.1 the actual

pressure can be calculated.

The basic principle of bourdon tube pressure gauge is when an elastic transducer is

subjected to a pressure, it deflects. This deflection is proportional to the applied pressure



when calibrated according to yourinstrumentation.blogspot.com. These bourdon tube pressure

gauges can give accurate results as long as it calibrated.

The only significant source of error is due to static friction along the interface between

the piston and cylinder, but even this error is usually negligibly small. The reference pressure

port is connected to either an unknown pressure that is to be measured or to a pressure sensor

that is to be calibrated.

4.0 METHODOLOGY

4.1 APPARATUS

Dead Weight Tester apparatus, Bourdon gauge, piston, 0.5 kg weights, oil.

4.2 PROCEDURE

1. A cylinder and connecting hose were filled up with oil.

2. The piston was inserted into the cylinder and air bubble was removed as much as

possible from cylinder and hose.

Figure 2 Inserting Piston

3. Weights were loaded on the piston in an increment of 0.5 kg so as to cover pressure

reading of the Bourdon-tube pressure ranging from zero to maximum pressure on the scale.



Figure 3 Loading Weights

4. The indicated Bourdon-tube pressure gauge reading was taken. The piston was rotated

prior to taking a reading for each weight to minimize friction effect on the reading.

Figure 4 Loading More Weights

5. After the maximum pressure reading was obtained, the weight was unloaded from the

piston by the same increment and step 4 was repeated.

Figure 5 Unloading Weights



5.0 RESULTS AND DISCUSSION


Figure 6 Graph of Bourdon Pressure (Calibrated) versus True Pressure



Figure 7 Graph of Percentage of Error versus True Pressure


Based on the data obtained, the true pressure exerted by total mass and the percentage error of

the data was calculated. According to the Figure 6, the R2 value for increasing and decreasing

pressure was 0.9994 and 0.9993 respectively where R2 stands for coefficient of determination.

According to Chapra (2012), coefficient of determination is an indicator indicates how well

your data fits the model we are testing. The closer the R2 value is to 1 the more likely the data

points are solution to the equation that defines the curve. Hence based on the R 2 value

obtained, we can conclude that the line was a good fit to the data obtained throughout the

experiment. The graph also showed that the lines nearly intercept the origin.

Besides that, based on the Figure 6, the slope of the increasing and decreasing graph

was 1.0492 and 1.0378 respectively. According to University of Puerto Rico (2010) the slope

of the calibration curve shows the sensitivity of the pressure gauge. Sensitivity is a measure

of its ability in established that such differences are significant. Ideally, the line should have a

slope of 1. The reason that might affect both values of slope above was the large scale

division of the Bourdon tube pressure gauge (i.e. in scale of 10 kN/m2) compared to the true

pressure correct to 2 decimal places. Non-zero intercepts of both lines suggested that positive

zero error of about 3 kN/m2 existed.

According to Figure 7 it can be calculated that the average percentage error for

increasing and decreasing was 8.32 percent and 8.80 percent respectively. Based on the

percentage error calculated, the rather low percentage error meant that calibrated pressure did

not deviate much from true pressure. Based on Figure 7, it can also be observed that the

percentage errors of the first and second readings were quite high compared to the other

readings. This was due to the rather small value of true pressure used as denominator in the

calculation of the percentage error.

In addition to that, others factors that might contribute to errors or inaccuracies in

experimental data were:

1. Presence of microscopic bubbles of air trapped inside the tube when the experiment

was carried out.

2. Wear and backlash in the gauge linkage can affect the pressure.

3. Parallax error when observer’s eyes were not perpendicular to the scale of the

Bourdon gauge during the value of gauge pressure was recorded.



4. Friction between piston and cylinder.

Some ways that can be practiced in order to improve the result were to:

1. Carry out a few replicate measurements to reduce random errors.

2. Increase the division of the scale of the Bourdon tube pressure gauge so more accurate

data can be taken.

3. Make sure the eyes were perpendicular to the scale when taking the reading to avoid

parallax error.

4. Make sure no air bubbles inside the tube when conducting the experiment.

5. Make sure to rotate the piston after adding each weight to minimize frictional effect

on the reading.

All in all, it can be said that when we already minimize all the errors, it can be

concluded that the Bourdon tube pressure gauge need to be recalibrated and maintained well

to increase its accuracy.

6.0 CONCLUSION

The Bourdon tube pressure gauge was calibrated using a dead weight tester since its

calibration data showed good correlation with a linear curve.

7.0 REFERENCES

1. Cengel, Y. A. and Cimbala, J. M. (2010). Fluid Mechanics Fundamentals and Applications,

2nd ed. New York, N. Y.: McGraw-Hill. 87.

2. Chapra, S. C. (2012). Applied Numerical Methods with MATLAB for Engineers and

Scientists, 3rd ed. New York, N. Y.: McGraw-Hill. 342.

3. http://www.ehow.com/how_12082003_calibrate-bourdon-tube-pressure-gauge.html

4. http://yourinstrumentation.blogspot.com/2011/10/bourdons-tube-pressure-gauge-

principle.html

5. http://www.me.uprm.edu/laboratories/inme4031/pdf_Documents/Classes/Microsoft%20

Word%20-%20Class%204_Pressure%20Measurements.pdf



8.0 APPENDIX

SAMPLE CALCULATION

Mass of the piston: 1 kg

Cross sectional area of the piston: 3.1731 x 10-4 m2

Table 1 Sample Data

Mass (kg) True

pressure

(kN/m2)

Calibrated pressure

(Bourdon gauge)

(kN/m2)

Percentage of error

Mass

added (kg)

Total mass

(kg)

Pressure

exerted by

total mass

Increasing

order of

weight

Decreasing

order of

weight

Increasing

order of

weight

Decreasing

order of

weight

0 1 (piston) 30.92 35 37 13.20 19.66

0.5 1.5 46.37 52 53 12.14 14.30

True Pressure Value:

True Pressure exerted by piston=Mass of the piston×(9.81×10−3)Cross sectional area of piston

kN /m2

True Pressure exerted by piston=1kg× (9.81×10−3 )kN /kg

3.1731×10−4m2 =30.92kN /m2

True Pressure exerted by totalmass=Totalmass (weight+ piston)×(9.81×10−3)

Cross sectional area of pistonkN /m2

True Pressure exerted by totalmass=1.5kg× ( 9.81×10−3 )kN /kg

3.1731×10−4m2 =46.37 kN /m2

Percentage of Error:



Percentage of error= Increasing∨decreasing pressure−Tru e pressureTrue Pressure

×100 %

Percentageerror of increasing pressure=35−30.9230.92

×100 %=13.20 %

Percentageerror of decreasing pressure=37−30.9230.92

×100 %=19.66 %
