FACULTY OF PETROLEUM AND RENEWABLE ENERGY ENGINEERINGUNIVERSITI TEKNOLOGI MALAYSIA FLUID MECHANICS LABORATORYTITLE OF EXPERIMENT CALIBRATION OF BOURDON TUBE PRESSURE GAUGE (EXPERIMENT 5)

NameMUHAMMAD KHAIRIL IKRAM(A13KP0047) AKMAL FAIZ BIN ABDUL RAHIM (A13KP0008) ABDUL WAHAB (A13KP4006)KSATRIYA ANANTAYUTYA (A13KP4001)

Group / Section1/Section 11

SupervisorAssociate Professor Issham bin Ismail

Date of Experiment24/3/2014

Date of Submission05/4/2014

Marks obtained (%)

Theory

Figure 1. Deadweight Tester for Bourdontube pressure gage

.A dead-weight tester is a device used for balancing a fluid pressure with a known weight. Typically, it is used for static calibration of pressure gages.

As seen in Figure 1, the apparatus is set up for calibration of the pressure gage G. The chamber and cylinder of the tester are filled with clean oil by first moving the plunger to its most forward position and then slowly withdrawing it while the oil is poured in through the opening for the piston. The gage to be tested is installed and piston pressure is now transmitted to the gage when the valve is opened. This pressure may be varied by adding weights to the piston or by using different piston-cylinder combinations of varying areas. The viscous friction between the piston and the cylinder in the axial direction may be substantially reduced by rotating the piston-weight assembly while the measurement is taken. As the pressure is increased, it may be necessary to advance the plunger to account for the compression of the oil and any entrapped gasses in the apertures.

The accuracies of dead-weight tester are limited due to: (1) the friction between the cylinder and the piston, (2) the uncertainty in the area of piston, (3) the buoyancy error and (4) gravity error.

The gravity error due to elevation, z [m], and latitude, [] can be corrected by the dimensionless correction factor as:

egravity = (2.637 *10 3 cos(2 ) + 2.9 *10 8 z + 5 *10 5 )

The changes in pressure reading will be calibrate to give a gauge reading in engineering unit .As the mass is added at the top of the piston ,the pressure produced is measured by:P= F/ AWhere A= and F=gMP=Pressure at the pistonF=Force applied on liquid at pistonM=Total mass including pistong=Gravitational accelerationA=Area of pistonThe unit of pressure is Newton per square meter (N/m) or known as Pascal. To get the pressure in N/m, the M must be in kg, while g in m / s and d in m.As for the liquid used, it must be incompressible fluid such as oil to get a more accurate reading on the gauge reading.

Objective

The objective of this experiment is to perform pressure calibration on a Bourdon tube pressure gage using a dead weight tester.

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 gage. Bourdon-tube pressure gages 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 Fig. 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 indicated is the difference between the system pressure and to the external (ambient) pressure, and is usually referred to as the gauge pressure

Fig. 1: Schematic of a bourdon-tube pressure gage

As the Bourdon tube pressure gage 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 gage readings against a very accurate device. One of the calibration devices that is available in our lab is the so-called Dead Weight Tester

Apparatus

This dead weight pressure gauge calibrator consists of a precision machined piston and cylinder assembly mounted on levelling screws. A Bourdon gauge is supplied for calibration. The weights supplied are added to the upper end of the piston rod which is rotated to minimise friction effects. The gauge is thus subject to known pressures which may be compared with the gauge readings and an error curve drawn.

RAW DATA AND ANALYSIS EXPERIMENTAL DATAMass(kg)True pressure(kN/m2)Calibrated pressure (Bourdon gauge) (kN/m2)Percentage of error

(1)(2)(3)(4)(5)(6)(7)

MassAdded(kg)Total mass (kg)Pressure exerted by total mass

Increasing order of weightDecreasing order of weightIncreasing order of weightDecreasing order of weight

01 (piston)30.92363514.8113.20

0.51.546.3750537.8313.22

1.02.061.8366666.746.74

1.52.577.2981814.804.80

2.03.092.751001007.827.82

2.53.5108.211171158.126.27

3.04.0123.661321346.747.96

3.54.5139.121481506.027.82

4.05.0154.581621664.807.39

4.55.5170.041801805.865.86

RESULTS AND DISCUSSION

The graph of calibrated pressure and true pressure shows the bourdon gauge pressure versus the calibrated pressure. The intersection points of the two lines present are due to parallax error.

The graph show the percentage error versus true pressure for the increasing and decreasing order of weight. As shown in the graph, it show that the error is inconsistently where the line plotted is going upward and downward. The inconsistent reading may be cause by Hooke's Law that happen inside the elastic tube. The tube may be taken a long time recover back to the original state. According to Hooke's Law, all material have their limiting elasticity, when the tube is no longer elastic, the elastic tube will not obey the Hooke's Law.The Hookes Law states that when the pressure imposed is directly proportional to the strain produced but it must be within the elastic limit as all objects have their own elastic limit. The graph of increasing and decreasing order of weight is inconsistent. The inconsistency may be caused by the parallax error during the measurements.

Experimental 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.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.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.5.After the maximum pressure reading was obtained, the weight was unloaded from the piston by the same increment and step 4 was repeated.

Laboratory report

1. Show sample calculations2. Plot a graph of bourdon pressure (calibrated ) for increasing and decreasing orders of weight versus true pressure. Extend the graphs and check if they intercept a point of origin. Comment on the difference in the graph profiles and explain the possible reason for the graphs (if so) not intercepting the origin point. 3. Plot a graph of percentage of error versus true pressure. Compare and comment on the difference in the percentage of error with respect to true pressure and briefly discuss factors contributing to such error.4. Propose recommendation to improve the results5. Briefly discuss safety measures taken during the experiment 6. Conclusions7. References

Report Summary:The Objective of this experiment is to perform pressure calibration on a Bourdon tube pressure gage. A dead weight tester is used to carry out this experiment. The dead weight tester is a device that supplies a high accurate pressure for calibration as compared to other calibration devices which could be used. Weights are loaded on the piston and noted down. The reading in the bourdon tube pressure was recorded for further processes with different weights.One of the major results achieved from this experiment is amount of percentage error for our experiment. These errors could be calculated as the pressure by the bourdon tube is compared with the weight exerted by the masses.As from our results, the errors that occur due to bourdon tube are inconsistent.

References1.http://www.thefreedictionary.com/Hooke's+law2. R.V Giles, Fluid Mechanics and Hydraulics (Third Edition), McGrawHill Inc; 1994.3. Lab Manual University Teknologi Malaysia.4.Robert A. Granger. Experiments in Fluid Mechanics.Holt, Rinehart and Winston, Inc. NewYork. 1988.5. http://www.ehow.com/how_12082003_calibrate-bourdon-tube-pressure-gauge.html6. http://yourinstrumentation.blogspot.com/2011/10/bourdons-tube-pressure-gauge-principle.html7. http://www.me.uprm.edu/laboratories/inme4031/pdf_Documents/Classes/Microsoft%20 Word%20-%20Class%204_Pressure%20Measurements.pdf

AppendixSample of calculation:Mass of piston: 1 kgCross sectional area of the piston: 3.173x10 m

Example:

Conclusion

The Bourdon tube pressure gauge was calibrated using a dead weight tester since its calibration data showed good correlation with a linear curve. There is a slight error exist that occurs during the reading, which is the air bubble trapped inside the tube while conducting the experiment, the piston is not stable during the value is taken and parallax error that occur at the observer eyes while taking the reading. When calibrating Bourdon tube type or any other type of analogue dial pressure gauge you should adjust the pressure calibrator so that the applied pressure is set to the cardinal point on the pressure gauge. The error can then be read to a much higher precision from the calibrator The hysteresis in the mechanism cause the barometer to read low on a rising atmospheric pressure. So, if the barometer is tapped gently with a finger or perhaps better still by using umbrella handle, the reading will be seen to be increased slightly by the vibration. Conversely, if the reading is seen to fall, the barometric pressure will be declining. The tapping therefore gives not only a better indication of atmospheric pressure but also an indication of whether it is rising or falling

There are several factors may influence the result of this experiment, such as1. Pressure is exerted on the piston during it is press into the cylinder where it can affect the reading of gauge pressure taken for entire experiment. 2. There is air bubbles trapped inside the pipe when the experiment is carried out3. Parallax error is occurring when the observer eyes are not perpendicular to the scale of the bourdon gauge during the value of the gauge pressure is observed. 4. There is minor losses occur inside the pipe that connecting the bourdon tube and cylinder, such as friction force and sudden contraction. 5. During the calculation, round-off error may happen when the intermediate answer is round-off earlier. 6. Moreover, during the experiment, water was observed to be leaked out from the cylinder while loading the weight. That is also one of the reasons for the fluctuation because water leaked out will reduce the fluid pressure in the cylinder.There are other several factors that influencing the results. The gauge can be read when there are forces applied to its elastic structure. But, in the tube of the gauge, there are air bubbles that can affect the accuracies of the experiment. We use the bourdon gauge that has a very little sensitivity so that it is harder for us to read the actual force exerted to it. We have to estimate the real value, and during the estimation of the reading, parallax error occur. The friction and small contraction inside the tube might cause minor losses in the tube. To minimkelreduce the error and inaccuracy in the experiment, the following solutions can be considered:1. When taking reading from the Bourdon tube, the eyes level must be perpendicular to the device until no shadow of pointer is seem. 2. The scale of reading should be improved by dividing the measure device into smaller scale. 3. Only final answer can be round-off to 2 decimal point to Increase the accuracy of the answer