Pressure Measurement and Calibration

TABLE OF CONTENTS

Title ............................................................................................................ Page 1. Experiment Title ..........................................................................................................2

1.1. Experiment objectives .................................................................................2

2. Introduction ..................................................................................................................2

3. Theoretical background ...............................................................................................2

4. Apparatus and procedure ......................................................................................... 3-4

4.1. Apparatus ....................................................................................................3

4.2. Procedure/s ..................................................................................................3

5. Results ...........................................................................................................................5

6. Discussion .....................................................................................................................5

7. Conclusion ....................................................................................................................6

8. Recommendation ..........................................................................................................6

9. References .....................................................................................................................7

1. EXPERIMENT TITLE: PRESSURE MEASUREMENT AND CALIBRATION

1.1. -

Experiment objective:

Calibrate the pressure gauge using a “dead weight tester”.

2. INTRODUCTION: In engineering, properties of materials such as pressure, density, ductility, toughness, and hardness are important to be studied as these affect the performance of many industrial applications. To determine these properties, different types of apparatus are used. One of the most commonly used apparatus to determine such properties (in this case the pressure) is the pressure gauge. Many instruments have been invented to measure pressure, with different advantages and disadvantages. Pressure range, sensitivity, dynamic response and cost all vary by several orders of magnitude from one instrument design to the next. The oldest type is the liquid column (a vertical tube filled with mercury) manometer invented by Evangelista Torricelli in 1643. The U-Tube was invented by Christian Huygens in 1661. [1]. For a mechanical pressure gauge, accuracy is defined as a percentage of the full-scale range [2]. To make sure that the apparatus (pressure gauge) is accurate, a calibration method called dead weight tester (DWT) is used, using a dead weight tester apparatus.

3. THEORETICAL BACKGROUND: Pascal’s principle – (definition of pressure):

Used to determine-calculate the actual pressure that is needed in the testing of the pressure gauge. Page 2

4. Apparatus and Procedure: 4.1. Apparatus: Deadweight tester (figure 1): apparatus uses known traceable weights to apply pressure to a fluid for checking the accuracy of readings from a pressure gauge [3].

(Figure 1): Deadweight tester apparatus- readings from a supplied pressure gauge

4.2.

PROCEDURE:

1- Bleeding the apparatus - using water as the fluid (figure 2) to apply pressure (load) on it.

2- Placing weights (figure 3) on the table (figure 4) and reading off the pressure for each weight (increasing pressure).

3- Removing the weights from the table and reading off the pressure readings on the gauge again (decreasing pressure).

Page 3

(Figure 2): The operating fluid. – Type: water

(Figure 3): Different weight up to 5.2 kg. to be placed on the table above the piston.

(Figure 4): The piston which holds the weights on its surface

Page 4

5. RESULTS:

Mass added to piston

Total mass on piston

Actual Pressure

Increasing pressure

Gauge (kg)

(kg)

(kN/m2)

reading (kN/m2)

Gauge error %

Decreasing

Gauge reading (kN/m2)

pressure

Gauge error %

1

1

31.15

30

3.69

30

3.69

0.5

1.5

46.70

44

5.78

45

3.64

0.5

2

62.28

60

3.66

60

3.66

0.5

2.5

77.85

72

7.51

74

4.94

0.5

3

93.42

89

4.73

85

9.01

1

4

124.57

120

3.66

115

7.67

1

5

155.71

148

4.95

143

8.16

1

6

186.85

175

6.34

175

6.34

6. DISCUSSION: As results shown, different types of weight were placed on the piston starting with 1 kg. of the piston weight itself, after this a 0.5 kg. and 1 kg. weights were added gradually. For the increasing pressure the error between the pressure gauge reading and the actual pressure is start to be 3.69% for the first amount of weight, this shows that there could be some friction, or due to lack of accuracy when reading the gauge pressure, or it need more time to adjust itself as a first load on the piston. The error decrease and increase with small amount, 5.78% for 1.5 kg. and 3.66% for 2 kg, but after the third load were placed on the piston which equal 2.5 kg, the error increased up to 7.51%, on this point an inaccurate reading for the pressure gauge could be the main reason. After adding the next load the error decreased and almost being stable at 3.66% comparing to the first load.

Page 5

As the last weight added which equal 6 kg, the error increased again up to 6.34%, for this level a 6 kg weight could be considered as an over max weight for the apparatus, as the recommended max weight is 5.2 kg for the apparatus used in the test. For the decreasing pressure the error between the pressure gauge reading and the actual pressure is said to be almost same to the increasing pressure, as weight are removed gradually, the error should not reach a very high or very low amount as it is a reverse action by removing the same loads which were added respectively (same sequence). It started with 6.34% and ended up with 3.69%, in between there were small amounts of decreases and increases but for the load 2.5 kg the error was 4.94% as it had a high error at the increasing pressure comparing to other errors during the test.

7. CONCLUSION: To conclude, using a dead weight tester method and its apparatus to calibrate the pressure gauge would give an overall good result but there are many effects that could change or decrease the accuracy of the gauge.

8. RECOMMENDATIONS: - Using oil or air (gas) as an operation fluid, as they should give better or more accurate results than water depending on the job site-manufacturer. - Using a bigger or portable modified dimension for the deadweight tester to increase the ability of taking or placing more loads (weights).

Page 6

9. REFERENCES: [1]- “Pressure measurement,” http://en.wikipedia.org/wiki/Pressure_gauge accessed October 7, 2013. [2]- “Seven steps to select a pressure gauge,” http://www.ashcroft.com/tech/upload/AshBulG_7.pdf accessed October 7, 2013. [3]- “Deadweight tester,” http://en.wikipedia.org/wiki/Deadweight_tester accessed October 7, 2013.

Page 7