FA18-BME-030
COMSATS University Islamabad,
Wah Campus
Department of Mechanical Engineering
NAME: - MUHAMMAD AMMAR NASIR
REG NO: - FA18-BME-030
SECTION: - 6A
SUBJECT: - INSTRUMENTATON AND
MEASUREMENT LAB
LAB REPORT: - 1st
SUBMITTED TO: - SIR ENGG NADEEM IQBAL
FA18-BME-030
Experiment no 01: To find out pressure with a Dead weight tester and compare
it with theoretical results?
Objective: The objective of this experiment is to find out the pressure using a Dead weight
tester and compare it with theoretical results.
Apparatus: • Dead weight tester apparatus.
• Calibrated dead weights.
Theory: Dead Weight Tester uses known traceable weights to apply pressure to a fluid for
checking the accuracy of readings from a pressure gauge. A dead weight tester is a
calibration standard method that uses a piston cylinder on which a load is placed
to make an equilibrium with an applied pressure underneath the piston.
Deadweight tester are so called primary standards which means that the pressure
measured by a deadweight tester is defined through other quantities: length, mass,
and time. Typically, deadweight testers are used in calibration laboratories to
calibrate pressure transfer standards like electronic pressure measuring devices.
The mechanism of the gauge is shown in the figure below. A tube, having a thin
wall of oval cross section, is bent to a circular arc encompassing about 270 degrees.
It is rigidly held at one end, where the pressure is admitted to the tube, and is free
to move at the other end, which is sealed. When pressure is admitted, the tube
tends to straighten, and the movement at the free end operates a mechanical
system which moves a pointer round the graduated scale - the movement of the
pointer being proportional to the pressure applied. The sensitivity of the gauge
depends on the material and dimensions of the Bourdon tube; gauges with a very
wide selection of pressure ranges are commercially available.
FA18-BME-030
Formula: The formula on which the design of the apparatus is based basically is expressed as
follows:
F=mg [N]
P=F/A [Pa]
So here.
F= force applied on piston [N]
m= mass [kg]
g=acceleration due to gravity = 9.8
P=reference pressure
A= effective area
Procedure: 1.
2.
3.
4.
5.
6.
7.
8.
Open cylinder cap bolt.
Fill cylinder with oil.
Open cylinder oil valve.
Close cylinder cap bolt.
Close cylinder oil valve.
Hydraulic oil will move to piston cylinder.
Insert piston.
Apply weight and note down reading.
FA18-BME-030
To check the zero point of the manometer, proceed as follows:
1.
2.
3.
4.
Press the piston out of the cylinder.
Remove the piston and weight support.
Adjust the oil level in the open cylinder until the cylinder is filled up.
The manometer being tested should now indicate zero, as it is only subject
to ambient pressure.
5. Assemble Bourdon's pressure gauge with dead weight tester.
6. Apply pressure in terms of weights on table and measure the value of it on
pressure gauge.
7. Repeat the procedure for ascending and descending weights on table and
corresponding.
Result: Sr.#
Applied load (Kg)
Applied
(N)
1
2
3
4
5
0.5
1
2.5
3.5
4.5
4.905
9.8
24.5
34.3
44.145
load Area (m2)
3.46185*10-4
3.46185*10-4
3.46185*10-4
3.46185*10-4
3.46185*10-4
Theoretical
pressure
(N/m2)
14168.72
28308.5
70771.4
99079.9
127518.52
Practical
pressure
(N/m2)
14375
28538
70881
99088
131018
Discussion: Two different kinds of error may normally expect in a gauge of this type. Firstly,
there is a possibility of hysteresis, friction and backlash which will yield smaller
gauge readings when the pressure is increasing than when it is decreasing.
Secondly, there is error due to the scale being marked off incorrectly. It will be
found that this error increases to a maximum of around 2.5% of the full-scale
reading. This is acceptably small for many engineering purposes, although gauges
with an error of only 0.5% of the full-scale reading are commercially obtainable.
Conclusions: To ensure proper calibration, measurement tools must have a reliable system setup
that does not introduce sources of error to the device. The pressure gauge could
not be accurately calibrated with the apparatus used in this experiment due to
several sources of error. These sources include, but are not limited to leakage, poor
FA18-BME-030
lubrication, trapped air, mechanical fatigue, poor weight calibration, differential
dead weight masses, and general user error. Upon repeating this experiment, a
thoroughly sealed piston-cylinder device should be used along with a uniform set
of dead-weights. In addition to this, a high-lubricity fluid should be used instead of
water to prevent any restricted motion. With these adjustments, the experiment
may be repeated and re-evaluated as a reliable calibration method.
Reference: https://www.sika.net/en/products/sensors-and-measuring-instruments/mechanical-pressuregauges/bourdon-tube-pressure-gauges.html
https://www.wika.us/landingpage_bourdon_tube_pressure_gauge_en_us.WIKA
https://www.wika.com/en-en/lp_bourdon_tube_pressure_gauge.WIKA