SUBMITTED BY
SAMAKSH MODI 2022TT12132
SANIDHYA GARG 2022TT12142
AMAN GUPTA 2022TT12151
OM MISHRA 2022TT12146
ARJUN SHARMA 2022TT12137
GROUP-1
EXPERIMENT 9
• OBJECTIVES
A. To study the working of Bourdon pressure gauge and to calibrate it using
a dead-weight pressure gauge calibrator.
B. To calibrate piezo-resistive transducer using a ‘U’ tube manometer
• THEORY
A)
The Bourdon gauge contains as its key transduction element a hollow
elliptical cross-section tube enclosed at one end and bent in the form of a
‘question mark’. The other end of the tube is connected to the pressure
source. The high pressure in the tube tends to straighten the hollow bent
tube. This motion of the tube, dependent on the magnitude of the pressure,
is further amplified and converted to rotary motion by a set of gears.
Finally, the rotary motion is read on a circular readout on the outside face
of the gauge. The schematic sketch is shown in figure (a).
The dead weight pressure tester is schematically shown in figure (b). It
operates on the principle of equalization of pressure in a liquid at the same
horizontal level. The motive fluid is oil, which supports known weights at
end ‘A’. The piston/plunger arrangement acting over a known sectional area
at end ‘A’ generates a standard pressure in the system equal to
weight/piston-area. This serves as the input or the reference pressure
measurement. The pressure gauge to be calibrated is put at end ‘B’, care
being taken (in the manufacture of the apparatus itself) that there is a
negligible elevation difference between point of application at ‘A’ and point
of measurement at ‘B’. The system is pressurized by means of a
piston/plunger arrangement connected to a lead screw. The plunger is
moved inwards by turning the lead screw, till the supporting dead weight
at ‘A’ just floats. Then, the pressure shown by the test gauge is noted and
checked against the reference pressure.
B)
In this part of the experiment a MEMS based piezo-resistive pressure
transducer is to be calibrated using a U tube manometer with water as the
manometric fluid. The device in question is MPX5700AP made by Freescale
Semiconductors. Figure (c) shows a schematic of the experimental set-up.
Since the sensor measures absolute pressure (one side of the transducer
membrane is evacuated) it can be used for both positive and negative gauge
pressures.
• APPARATUS
➢ Bourdon Gauge
➢ Deadweight calibrator
➢ Calibration weights
➢ Pressure transducer with signal conditioner
➢ U tube manometer
➢ A collapsible cylinder used to generate the required gauge pressure
• PROCEDURE
A)
1. Study the pressure gauge that has been dis-assembled and draw a
detailed sketch of the inner mechanism.
2. Record the least count of the dead-weight system and the pressure
gauge to be calibrated.
3. Place the first weight and turn the lead screw till it just floats and record
the pressure gauge reading. 4. Repeat step 4 for the full range of weights
till the maximum weight is reached.
5. Decrease the weight in steps and again note the pressure gauge reading
as in step 4. Take care each time that the chamber is de-pressurized before
removing the weight so that oil does not flow out.
B)
1. Record the least count of the manometer and the display unit.
2. Ensure that the two limbs of the manometer are at the same level and
note down the reading of the display unit for gauge pressure equal to zero.
3. Increase the pressure from 0 to approximately 50cm of water in 5 steps
and note down the reading on the display unit.
4. Bring the pressure down to zero again and repeat step 3 for negative
gauge pressures (final value approximately -50cm of water).
5. Bring the system back to atmospheric pressure (zero gauge pressure)
at the end of the experiment.
• OBSERVATION
1. Least count of manometer = 0.1 cm
2. Least count of display unit = 0.0001 V
At PGAUGE = 0, the reading of the display unit is 0.48653 V.
Change in Height Voltage
+50 0.50515
+40 0.50179
+30 0.49767
+20 0.49416
+10 0.49065
0 0.48653
-10 0.48225
-20 0.47874
-30 0.47569
-40 0.47126
-50 0.46760
Increasing
0.51
0.505
0.5
0.495
0.49
0.485
0.48
0.475
50 40 30 20 10 0
Decreasing
0.49
0.485
0.48
0.475
0.47
0.465
0.46
0.455
0 10 20 30 40 50
Decreasing y = -x(0.000428) + 0.48653
Increasing y = x(0.000412) + 0.48653
Change in Height Voltage
0 0.49004
509.912 0.49187
990.406 0.49370
1421.87 0.49538
2029.842 0.49767
2618.202 0.49996
-598.166 0.48775
-1000.212 0.48622
-1598.378 0.48393
-1980.812 0.48241
-2775.098 0.47935
1. y = x(0.00000378) + 0.4901
2. y = x(0.00000385) + 0.49005
• DISCUSSION QUESTIONS
1) The graph obtained and also the straight line fit, shows that the
voltage output varies almost linearly with the gauge pressure.
Also, sine the points on the graph are very close to the straight
line, the gauge is highly accurate.
2) In Part A, we first increase the weights and then decrease them.
After this we can compare the initial and final readings, both
displaying that of the same weight. Comparing these values can
detect the hysteretic behaviour in the gauge.
