Energy Balance

Abstract

Bourdon tubes are categorizes as elastic-elements methods for pressure-measurement device this experiment was done to measure the error difference between the theoretical and experimental measurement of pressure and how to eliminate the experimental error

Table of content

1. Objective

To determine the accuracy in Bourdon gauge readings and calibration

1. Introduction

        The pressure at any point in static or moving can be measured using pressure measuring instrument. Bourdon-tube pressure gages are one of the common methods used. This device is used to measure fluid pressure from nearly perfect vacuums to about 7000 atm. Bourdon tubes are categorizes as elastic-elements methods for pressure-measurement device. Bourdon tube pressure gauge is a thin walled tube with an oval cross-section, bent into an arc. One end of the tube is held rigidly which admits pressure. The other end of the tube, connected to a dial and pointer mechanism, is free to move. The tube tends to straighten when pressure increase, causing pointer attached to the tube to rotate. The position of the pointer on the calibrated dial gives the gauge pressure of the fluid. This gage pressure means relative to ambient atmospheric pressure, as opposed to absolute pressure; vacuum is sensed as a reverse motion.

        Pressure gauges are either direct- or indirect-reading. Hydrostatic and elastic gauges measure pressure is directly influenced by force exerted on the surface by incident particle flux, and are called direct reading gauges. As the Bourdon tube categorizes elastic so it gives direct reading. So to check if the device gives the susceptible and error reading due to influence, we need to do calibration which can be checked using “Dead weight tester”. Calibration defined as the process of comparison of specific values of input and output of instrument with the corresponding reference standards. Calibration must be performed periodically to test the validity of performance of device or system.

[pic 1][pic 2]

Figure 1: Bourdon tube pressure gage

1. Theory

        Bourdon tube pressure gauge is calibrated by means of dead weight tester. To calibrate the gauge, add weights to a platform on a dead weight tester. The weights put a known force on to a piston and area of piston can be calculated. A flexible tube containing water transfers the pressure on the piston to the Bourdon tube. Add the weights in increments, recording pressure readings from the gauge at each increment until at maximum pressure. Then remove the weights and record gauge readings. When the pressure in the tube increases, it tries to straighten and so moves the pointer by an amount proportional to the pressure increase. The gauge pressure reading should give a reading corresponding to the amount scribed on the weight if it is operating correctly. If not, the dial is rotated so that the needle points to be correct pressure.

1. Experimental Procedure

1. The piston was inserted into the cylinder and air bubble was removed as much as possible from    cylinder and hose.
2. 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.
3. The indicated Bourdon-tube pressure gauge reading was read. Prior to take a reading for each weight rotates the piston to minimize friction effect on reading.
4. After the maximum pressure reading is obtained, weights were unloaded from the piston by the same increment and step 3 was repeated.

1. Experimental data and analysis

Mass of the piston: 1 kg

Cross sectional area of the piston: ᴨr2 = ᴨ (0.00365m) 2

                                           = 4.1853x10-5

True pressure exerted by piston:  kN/m2[pic 3]

= 234.39 kN/m2

True pressure exerted by total mass:  kN/m2[pic 4]

= 351.59 kN/m2

Percentage of error % = [pic 5]

                = 84.5%

Table and graph :