Report 7

SKF 1711 2010/2011 [FLUID MECHANICS LAB]

Title: Calibration of Bourdon Tube Pressure Gauge Apparatus: The equipments that we used are Bourdon gauge and dead weight tester, as shown in Figure 1.

Figure 1: Bourdon gauge and dead weight tester

Abstract:

This experiment was conducted to perform pressure calibration on a bourdon tube pressure gage using a dead weight tester. Weights are loaded on the piston and the indicated Bourdon tube pressure was read. . In this experiment, the error and percentage of error that occur inside the Bourdon tube will be calculated and compared to the true pressure that exerted by the total mass. According to the experimental results, the error that occurs in the Bourdon tube is inconsistent.

EXPERIMENT: Calibration of Bourdon Tube Pressure| 2-SKB (SECTION 01)

1


1.0 Objective: The objective of this experiment is to determine the accuracy in Bourdon Gauge and calibration requirement.

2.0 Introduction Bourdon Tube Pressure is widely used to measure pressure differences. The pressure sensing element is a tube of oval cross-section bent to a circular shape. One end of the tube is fixed to the gauge case and is connected to the fluid to be measured. The other end is closed and is free to move as it is connected via mechanical linkage and gear sector to a pointer. As measured fluid pressure increased above that of surrounding, the tube cross-sectional tends to straighten out and causes the tube deflects at this second end. This motion is transmitted via linkage to the pointer, which directly indicate on the calibrated scale or dial the gauge pressure. Calibration means checking the pressure gauge reading against a very accurate device. One of the calibration device that is available in our lab is called “Dead Weight Tester”. The Dead Weight Tester which is the device that supply highly accurate pressure for calibrating other compare to some other calibrating devices such as transducer, bottom-hole, and bourdon tube gauge. A tester may be used as a Dead Weight Gauge to determine unknown pressure by connecting the gas pressure to the gauge connector through suitable tubing and a valve exact regulation of the supply pressure to the tester is obtained by balancing the force exerted by the fluid pressure on a piston of know area against weight of known mass. A tester’s weight and a piston are calibrated in sets to give an accuracy of 0.1% which is 1 pound in 1000 pounds.

The most accurate instrument available for measurement of pressure above the range where monometers may be used is the Dead weight Tester. This type of terter operates on the principle balancing a known mass against the forced exerted by an exact balance is achieved, the unknown pressure P is equal to mass, M of the weight divided by the area, A of the piston, according to the formula:


2


3.0 Theory By using know pressure, variation in pressure sensor reading may be calibrated to give a gauge reading in engineering units. By applying mass to a column of fluid, the pressure produced is: P= Where F= gM

and

A=

P

= the pressure at the bottom of the piston

F

= force applied to the liquid in the calibrator cylinder

M

= the total mass including the piston

g

= the acceleration due to gravity

A

= the area of the piston

Using SI units, the units of pressure are Newtons per square meter (N/m², also known as Pascals). To obtain the pressure in N/m², M must be in kg, g in m / s² and d in m.

4.0 Procedure Firstly, the weight of the piston and its cross-sectional area should be noted. While measuring the weight and the cross-section area water is poured into the cylinder until is full to the overflow level. Meanwhile, make sure that there is no air trapped in the tube by tilting and gently tapping the apparatus. Next, the piston is then replaced in the cylinder and allowed to settle. Next, a spirit level placed on the platform at the top of the piston may be used to ensure that the cylinder stand quite vertically.

After all the instrument had settled, weights are now added in convenient increments, and at each increment the pressure gauge reading is observed. To guard against the piston gently while the pressure gauge is being used. This procedure is repeated by increasing the weights. After that, this procedure is repeated again by decreasing the weights.


3


5.0 Data and results

Mass Added(kg)

Mass (kg) Total mass(kg)

0 0.5 1.0 1.0 1.0 0.5

1.0 1.5 2.5 3.5 4.5 5.0

Mass (kg) Mass added(kg) 0 0.5 1.0 1.0 1.0 0.5

Total Mass(kg) 1.0 1.5 2.5 3.5 4.5 5.0

Calibrated Pressure (Bourdon Gauge) (kN/m2) Increasing order of weight Decreasing order of weight 1 2 3 Mean 1 2 3 Mean 35 36 40 37 40 38 41 39.7 43 43 43 43 60 60 60 60 68 68 65 67 98 95 90 94.3 98 98 100 98.7 128 125 124 125.7 133 132 130 131.7 143 142 143 142.7 143 144 143 143.3 143 144 143 143.3 Table 1: Experiment data

True Pressure (kN/m2) Pressure exerted by total mass 30.92 46.37 77.29 108.21 139.12 154.58

Percentage of error (%) Increasing Decreasing order of weight order of weight 19.66 28.40 7.27 29.39 13.31 22.00 8.78 16.16 5.33 2.57 7.29 7.29

Table 2: Calculated data (True Pressure and Percentage error)


4


6.0 Analysis and Discussion: 160

Calibrated Pressure (kN/m2)

y = -0.0052x2 + 1.8241x - 12.911 140 120 100

Increasing order of weight

y = 0.002x2 + 0.5203x + 16.711

80

Decreasing order of weight

60

Extend line for increasing order of weight

40 20

Extend line for decreasing order of weight

0 -50

-20 -40

0

50

100

150

200

True Pressure (kN/m2)

Figure 2: Calibrated pressure at different true pressure (kN/m2) i.)Figure 2 shows that Bourdon pressure (calibrated) versus true pressure for increasing and decreasing orders of weight. When the graph is extended, it is not intercept at the origin. This is might be cause by the parallax error when the readings are taken. 35

Percentage error(%)

30 25 20 Increasing order of weight

15

Decreasing order of weight 10 5 0 0

50

100

150

200

True Pressure(kN/m2)

Figure 3: Percentage error(%) against true pressure (kN/m2) EXPERIMENT: Calibration of Bourdon Tube Pressure| 2-SKB (SECTION 01)

5


ii.) Figure 3 shows the percentage of error versus true pressure for the increasing and decreasing orders 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 to 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.

iii.) There are several factors may influence the result of this experiment, such as:

1.

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 out.

3.

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. This is also one of the reasons for the fluctuation because water leaked out will reduce the fluid pressure in the cylinder.

To minimise/reduce 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.


6


4.

Replacing the water with hydraulic fluid which has better hydrostatic property so that the consistency of the pressure can be improved.

7.0 Conclusion: The objective of the experiment is to perform pressure calibration on a Bourdon tube pressure gauge using a dead weight tester. In the graph of percentage error versus true pressure, it shows the percentage error decreases when the pressure increases. The bourdon gauge gives more accurate reading when measuring high pressure compared to that of low pressure. Furthermore, the error occurred in the experiment was inconsistent. 8.0 References: i.)Irfan A. Khan (1987); Fluid Mechanics; Holt, Rinehart and Winston, The Dryen Press, Saunders College Publishing. ii.)Victor L. Streeter, E. Benjamin Wylie (1975); Fluid Mechanics (Sixth Edition); McGraw-Hill Book Company. iii.)J. W. Ireland (1971); Mechanic of Fluids; Butterworth & Co (Publishers) Ltd. 10.0 Job distribution No

Job

People incharge

1

Loading weights

Chan Kian Hwa

2

Record data for increasing weight

3

Unloading weight

4

Record data for decreasing weight

5

Report-abstract-theory

6

Report-procedure

7

Report-data and discussion

8

Report-references and appendix

Chan Kian Hwa


7


11.0 Appendix Sample of calculation: Mass of the piston: 1 kg

Cross sectional area of the piston:

True Pressure exerted by piston ⁄

Example of calculation 1: True Pressure exerted by piston ⁄ ⁄

True Pressure exerted by total mass ⁄

Example of calculation 2: True Pressure exerted by total mass (Taking extra weight of 0.5 kg) ⁄ ⁄

Percentage of error |

calibrated pressure true pressure | true pressure


8


Example of calculation 3: Percentage of error |

|


9

Report 7

Recommend Documents