CALIBRATION OF A PRESSURE GAUGE

KNS 2591 CIVIL ENGINEERING LABORATORY 3 FACULTY OF ENGINEERING UNIVERSITI MALAYSIA SARAWAK

LAB F1 : CALIBRATION OF A PRESSURE GAUGE

OBJECTIVE :

To determine the accuracy in Bourdon gauge readings and calibration requirements.

APPARATUS :

The Bourdon gauge shown in Figure 1.1 has a transparent dial through which the construction may be viewed. It consists essentially of a thin-walled tube of oval cross section, which is bent to the circular arc encompassing about 270 degrees. It is rigidly held at one end, where the pressure is admitted. The other end is free to move and is sealed. When pressure is applied, the tube tends to straighten, so that the free end moves slightly. This movement operates a mechanism, which drives a pointer round the graduated dial, the movement of the pointer being proportional to the applied pressure. The construction of the dead weight tester is also shown in Figure 1.1. A cylindrical piston, free to move vertically in a closely fitting cylinder, is loaded with known weights. The space below the piston is filled with water, and the pressure is transmitted by the water to the gauge under test through a transparent hose. The pressure generated by the piston is easily found in terms of the total weight supported and the cross-sectional area of the piston.


PROCEDURE :

1. The weight of the piston and its cross-sectional area should be noted. 2. The piston is removed and water is poured into the cylinder until is full to the overflow level. 3. Clear any air trapped in the tube by tilting and gently tapping the apparatus. 4. The piston is then replaced in the cylinder and allowed to settle. 5. A spirit level placed on the platform at the top of the piston may be used to ensure that the cylinder stand quite vertically. 6. Weights are now added in convenient increments, and at each increment the pressure gauge reading

is observed. 7. A similar set of result is then taken with decreasing weights. 8. To guard against the piston sticking in the cylinder, it is advisable to rotate the piston gently while the pressure gauge is being used.


RESULTS / ANALYSIS :

Calibration Of A Pressure Gauge

Weight of piston

=

Cross-sectional area

Total load incl. Piston Weight (kgf) (N)

1.0 1.5 2.0 2.5 3.0 4.0

9.81 14.72 19.62 24.53 29.43 39.24

=

True Pressur e (kN/m2)

31.14 46.73 62.29 77.87 93.43 124.57

9.81

N

3.15 x 10-4

m2

Gauge Reading Increasing Pressure (kN/m2) 30 48 63 80 98 13 0

31 48 63 80 97 12 8

30 48 62 80 94 12 8

Average

30.33 48.00 62.67 80.00 96.33 128.67

Decreasing Pressure (kN/m2) 35 50 64 81 98 13 0

34 49 63 80 97 128

34 49 64 79 95 128

Average

34.33 49.33 63.67 80.00 96.67 128.67

Total load incl. Piston weight (kgf)

1.0 1.5 2.0 2.5 3.0 4.0

Gauge Error ( True Pressure ( True Pressure Increasing Pressure ) Decreasing Pressure) 2 (kN/m ) (kN/m2) 0.81 - 1.29 - 0.38 -2.14 - 2.90 - 4.10

-

3.19 2.62 1.38 2.14 3.24 4.10


a) The graph of gauge reading (kN/m2) versus true pressure (kN/m2) is plotted as shown below.

b) The graph of gauge error (kN/m2) versus true pressure (kN/m2) is plotted as shown below.

KNS 2591 CIVIL ENGINEERING LABORATORY 3

FACULTY OF ENGINEERING UNIVERSITI MALAYSIA SARAWAK

DISCUSSION : The graph plotted shows that the increasing pressure is similar with the decreasing pressure where the slope plotted is almost overlapped to each other. However, the point plotted is not smoothly linear or form a straight line. Furthermore, we can see that the gauge error occurred inconsistently where the line plotted is going upward and downward. There are several factors that may influenced the results of this experiment such as ;

a) There are bubbles or air trapped inside the tube when the experiment is carried out. b) Pressure is exerted on the piston during it is placed into the cylinder where it can affected the reading of gauge pressure taken for entire experiment. c) The piston is not totally in stable condition during the value of gauge pressure is taken. d) Parallax error is occurred where the observer’s eyes are not perpendicular to the scale of the Bourdon gauge during the value of gauge pressure is observed.

CONCLUSION : The objective to determine the accuracy in Bourdon gauge readings and calibration requirements is achieved.

CALIBRATION OF A PRESSURE GAUGE

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