Experiment 3.1 focuses on a calibration of the pressure gauge using dead weight tester. By calibration, it means verification of the working operation of the pressure gauge if it yields accurate results as expected. True pressure readings are obtained and the results compared to gauge pressure readings for both cases of increasing pressure and decreasing pressure.
Experiment 3.2 is aimed at measuring gauge pressure using two devices. These devices are U-tube manometer and Bourdon Gauge. U-tube manometer is available in two forms~ the vertical U-tube manometer and the tilted U-tube Manometer. The pressure in a manometer is due to the level difference of the fluid used. Bourdon gauge uses sensors which detect the displacement caused by the vibration of the diaphragm. Inclined manometer yields more accurate pressure reading than the vertical one.
Finally, the last experiment compares the measurement of vacuum pressure using different measuring instruments. These instruments include~ Inclined Manometer, U-tube Manometer, and Bourdon Gauge and the results compared. All these methods of measurements yield negative results.
Table of Contents
EXPERIMENT - CALIBRATION OF A PRESSURE GAUGE. 4
BACKGROUND THEORY.. 4
Aims and objectives. 5
Importance of the experiment 5
Apparatus. 5
Experimental procedure. 5
Results. 6
Discussion. 8
Conclusion. 8
References. 9
EXPERIMENT - GAUGE PRESSURE MEASUREMENT. 10
Introduction. 10
Objective. 11
Procedure. 11
Results. 12
Discussion. 12
Conclusion. 13
References. 14
EXPERIMENT - VACUUM GAUGE MEASUREMENT. 15
Introduction. 15
Aims and Objectives. 15
Experimental Procedure. 15
Results. 16
Discussion. 17
Possible Sources of Errors. 17
Conclusion. 17
References. 18
EXPERIMENT - CALIBRATION OF A PRESSURE GAUGE
BACKGROUND THEORY
Pressure gauges are typical devices whose role is to measure the pressure of a fluid (gas or liquid). With its name coined from the French inventor Eugene Bourdon, this gauge is among the mostly applied equipment in liquid and gas, such as steam, air, and water up to pressures of 100000 pounds per square inch (Harland, 1985).
The apparatus shown below is a simple arrangement that can be used in measuring pressure. It is made up of a piston, and a cylinder and weight referred to as dead weight test. This combination is used in pressure gauge calibration since it has a transparent dial. It has a tube that has a thin oval cross-section that is bent to a circular arc composed of about 270 degrees (Bodge, 1982). This set of apparatus is rigidly held at one end. Since the movement of pressure is proportional to the applied pressure, the application of pressure makes the tube start straightening. The gauge's sensitivity is dependent on the material and dimension of Bourdon gauge (Venkateshan, 2015).
Figure 1
Aims and objectives
v To demonstrate the operation of a dead weight tester.
v To show how a dead weight tester is used to calibrate a pressure gauge.
Importance of the experiment
This experiment equips the learner with the skills necessary for verifying the accuracy or the working conditions of the pressure gauge. Thus calibration of the pressure gauge means checking on its reliability in taking a reading.
Apparatus
1. The Bourdon Pressure Gauge
2. Dead Weight Tester
Experimental procedure
1. The piston was removed from the unit and the cylinder filled with water. Air trapped in the transparent tube was removed by gently tapping the unit
2. Water was then topped up and the piston inserted into the cylinder. Air and excess water were then allowed to discharge through the top hole of the cylinder, and the piston allowed settling.
3. The cross-sectional area and the mass of the plunger (piston) and the weight platform were then recorded.
4. With the apparatus level, the weights (masses) were then added to the weight platform in small increments up to a maximum of 5.2 kg. The pressure gauge readings were then recorded in Table 1 as each mass is added. To prevent the piston sticking, the piston was gently rotated as each mass was added.
5. The masses were then removed in the reverse order as they were added and each pressure gauge reading recorded.
Results
Table 1: Pressure Measurement and Calibration
GRAPHS
1.Gauge reading against actual pressure (for both increasing and decreasing pressure on the same axis)
2.Gauge error against Actual Pressure (for both increasing and decreasing pressure on the same axis)
Discussion
From the tabulated results, it can be noted that:
v There is a negligible error in the gauge as it shows a reading when no pressure is applied.
v With the zero error neglected, the gauge provided results less than the applied pressure with the magnitude of the deviation between these two sets of readings increasing with increasing pressure.
A plot of gauge reading versus true pressure and gauge error versus true pressure both yielded non-smoothly linear graphs. These plots nearly coincide for both the cases of increasing and decreasing pressure (the lines nearly overlap on each other)
From the graphical plots, gauge pressure is observed to be directly proportional to the true pressure as the graph has a positive slope. This is an implication that this kind of plot may be significant in obtaining the correct pressure of the Bourdon Gauge since every gauge pressure acquired has a corresponding true pressure reading from the graph.
Additionally, it is observed that there is an inconsistent occurrence of the error only where the line slopes upwards or downwards.
Conclusion
In a nutshell, connections were made as therein procedure and values of various parameters obtained and recorded as tabulated in results. From the results, connected graphs were plotted and analyzed as under discussion. These plots conformed to the expected theoretical profile. In this respect, the lab session was instrumental in imparting in us necessary practical skills as well as verifying the functionality of the dead weight tester. The accuracy of the concerned device was verified hence the experimental objectives were justified.
References
Bodge, K. R. (1982). The design, development, and evaluation of a differential pressure gauge directional wave monitor.
Harland, P. W. (1985). Pressure gauge handbook (3rd ed.). New York, M. Dekker.
Venkateshan, S. (2015). Measurement of Pressure. Mechanical Measurements, 243-279.
EXPERIMENT - GAUGE PRESSURE MEASUREMENT
Introduction
Pressure is the force acting normally per unit area. Different methods of pressure measurement exist. The most suitable method of pressure measurement depends on the reason why the pressure is being measured as well as the applications (Bayer, 2018). Gauge pressure uses the atmospheric pressure as its reference value. Gauge pressure is not definite due to the fluctuations in the atmospheric pressure.
Gauge pressure is commonly signified by a ‘g' after the standard pressure unit, e.g. 20psig. This particular type of pressure is measured relative to the ambient atmospheric pressure. A fluctuation in the conditions of the atmosphere due to altitude or climatic conditions affects the output of the gauge pressure. In case the measured pressure falls below the standard atmospheric pressure, under such circumstance this pressure is known as vacuum pressure. If it is greater than atmospheric pressure, then it is known as positive pressure (Amritanandamayi Devi, Udupa, " Sreedharan, 2017).
Gauge pressure sensors always have a single port. The atmospheric air pressure is conveyed to the back of the sensor through a vent tube/hole. A gauge pressure transmitter with a vent permits the air pressure to impinge on diaphragm's negative side to make sure that the measured pressure is relative to ambient barometric pressure
A sealed gauge is always adopted in high-pressure applications including the hydraulic pressure.
Gauge pressure uses the atmospheric pressure as its reference value. Gauge pressure is not definite due to the fluctuations in the atmospheric pressure. A fluctuation in the conditions of the atmosphere due to altitude or climatic conditions affects the output of the gauge pressure. In case the measured pressure falls below the standard atmospheric pressure (Leck, 1989). A fluctuation in the conditions of the atmosphere due to altitude or climatic conditions affects the output of the gauge pressure (Bayer, 2018).
Objective
To measure gauge pressure using Bourdon Gauge and manometer and compare the readings.
Procedure
1. Connections were made as per figure 1 " 2 (on this page).
2. The vertical and inclined manometers were then filled using water.
Figure 1.
Pressure Measurement Bench
Figure 2.
Layout of Manometer
3. The syringe was then connected firmly and slowly moved stepwise and the resulting measurements recorded as in results.
4. The syringe was then connected firmly and slowly moved stepwise and the resulting measurements recorded under results in the tables below.
Results
Discussion
Comparison of Pressure Measurement between Vertical U-tube manometer and Inclined U-tube Manometer
The adjusted pressure readings (ΔmmH2O) of the inclined manometer were computed using the relation below:
Adjusted ΔmmH2O = P2Sin θ – P1, where θ = 540 is the angle of inclination of tube 2
while those of the vertical U-tube manometer were calculated using the relation:
Adjusted ΔmmH2O = P1– P2
It was noted that the inclined manometer yields relatively a higher rate of deflection in the tube for similar pressure changes compared to vertical U-tube manometer. This enhances measurement smaller pressure changes with greater accuracy.
Comparison between the manometer Pressure readings and the Bourdon Gauge Pressure Readings
Notable discrepancies were observed to exist between the manometer gauge pressure readings and the Bourdon Gauge Pressure readings. These differences can be attributed to the following sources of experimental errors:
i). Calibration errors in the Bourdon gauge
ii). Possible pressure leakages in the manometer system
iii). Exclusion of the effect of the atmospheric pressure by the Bourdon gauge as opposed to the manometers which take into account the atmospheric pressure effects.
iv). Presence of air bubbles in the manometer compromise the accuracy of the obtained results.
v). Parallax errors are resulting from poor positioning of the eye when taking the readings.
Conclusion
In conclusion, the experimental set-up was configured on the Pressure Measurement Bench and the gauge pressure readings taken in accordance with the given procedure. The yielded data of the gauge pressure read from the manometer were then compared to those of the Bourdon gauge, and the discrepancies noted. It was learned the Bourdon gauge finds applications in the blood pressure measurement and tyre pressure control while the manometers are used to sustain the relative pressure of the two vessels such as feed line and compressor tank. Due to the achievement of the set objectives, the experiment was thus successful.
References
Amritanandamayi Devi, M., Udupa, G., " Sreedharan, P. (2017). Anti-Bourdon tube pressure gauge. Measurement, 101, 190-199.
Bayer, R. (2018). Using a Strain Gauge for Pressure Measurement and Pressure Distribution Mapping within a Flow Measurement and Mapping Chamber. ECS Transactions, 87(1), 291-294.
Leck, J. H. (1989). Gauge calibration. Total and Partial Pressure Measurement in Vacuum Systems, 125-137.
EXPERIMENT - VACUUM GAUGE MEASUREMENT
Introduction
Vacuum Gauge Measurement is differential pressure measurements, that is the pressure in relative to the atmospheric pressure. The measured pressure can either be negative or positive concerning the atmospheric pressure (Heeley, 2005). When the measured pressure is negative, then it is referred to as a vacuum. This vacuum pressure can either be measured using a manometer or any other pressure measuring set-up (De Araujo Duarte, 2011). In the measurement of vacuum pressure, mechanical manometers provide a relatively quicker response compared to liquid column manometers. For the elastic sensing element, type, there is a time lag as a result of the time required to equalize pressure to measured and that at sensing media (Vries " Damstra, 2015). Bourdon gauge refers to a metallic device that converts pressure to distance irrespective of the position at which they are held. By reading this distance, vacuum pressure can be evaluated (Heeley, 2005).
In this experiment, vacuum pressure is measured using manometer after which the obtained result is measured using Bourdon gauge.
Aims and Objectives
To measure vacuum gauge readings using a manometer.
To compare vacuum measurements using a manometer and a Bourdon gauge.
The experiment compares the measurement of vacuum pressure using different measuring instruments. These instruments include~ Inclined Manometer, U-tube Manometer, and Bourdon Gauge. It also shows that vacuum pressure values are always negative.
Experimental Procedure
A pressure measurement bench (Figure 1) while Figure 2 shows a vertical schematic of the inclined and vertical and inclined manometer
The vertical and horizontal manometers were then filled by inserting a funnel into the open of the tube and water poured. The suitable color was added to improve clarity. Pipe clamps were then employed in clamping short pipes at the back of the apparatus to avoid water from leaking out of the pressure socket. Manometer tubes were tapped as they were being filled.
A blank table similar to table 3 in the Lab manual was created. The number of rows created depending on the number of readings during the experiment.
Care was taken never to apply the pressure to the vacuum gauge to avoid damaging it.
The syringe piston pressed in full before connecting it to the apparatus pressure sockets.
For accurate comparison and to save time, we used ‘Tee’ pieces and spare pipes (supplied) to connect a vacuum gauge and a manometer at the same time.
Care was taken to ensure that the nozzle of the syringe was firmly connected.
The syringe was then Slowly moved outwards in steps to create a vacuum gauge changes of 20 mm of H2O. At each step, the change in both the vacuum gauge reading and the two manometer levels were recorded at the same time. The manometer levels were then monitored so that water did not spill.
Results
Discussion
Account for the Negative sign of the Results
From the obtained results, the values of the vacuum pressure measured using both the manometers and the Bourdon gauge were found to be negative. This is because vacuum levels fall below the value of the atmospheric pressure. Hence, the Bourdon gauge's calibration is done with an absolute zero pressure corresponding to perfect vacuum and increasing vacuum represented by numerically increasing negative values.
Mathematically,
Vacuum Pressure = Absolute Pressure – Atmospheric Pressure
But Atmospheric Pressure ˃ Absolute Pressure, thus always negative results of vacuum pressure.
Possible Sources of Errors
The accuracy of the obtained values is however questionable. These deviations in the values obtained via use of manometer and use of the measurement gauge could be attributed to possible sources of experimental errors including:
Calibration errors in the Bourdon gauge
Possible pressure leakages in the manometer system
Exclusion of the effect of the atmospheric pressure by the Bourdon gauge as opposed to the manometers which take into account the atmospheric pressure effects.
Presence of air bubbles in the manometer compromise the accuracy of the obtained results.
Parallax errors are resulting from poor positioning of the eye when taking the readings.
Conclusion
In conclusion, the experimental set up was implemented as in procedure. The yielded data of the gauge pressure read from the manometer were then compared to those of the Bourdon gauge, and the discrepancies noted. It was evident that the vacuum pressure yielded negative results due to the reasons accounted for under discussion. This lab session imparted in us necessary practical skills. Due to the achievement of the set objectives, the experiment was thus successful.
References
De Araujo Duarte, C. (2011). A thermocouple vacuum gauge for low vacuum measurement. Vacuum, 85(10), 972-974.
Heeley, D. (2005). Understanding Pressure and Pressure Measurement. Freescale Semiconductor.
Vries, L., " Damstra, G. (2015). A vacuum measurement system with penning gauge for high voltage application. Vacuum, 38(3), 171-173.
