# فلويدdocx

```In the Name of Allah
College of Engineering and Technology
Department of Mechanical Engineering
Fluid mechanics and thermal lab
Experiment No. 2: Calibration of a Pressure
Gauge
Date: 22/2/2019
Student name:
Instructor name:
Abstract:
In bourdon gauge pressure calibration, we are required to compare experimental results
with the actual ones. We are also required to find the error in order to calibrate the
gauge pressure.
Objective:
To calibrate a Bourdon tube pressure gauge using Dead weights.
Introduction:
To calibrate a measurement system, you have to compare its output with a standard
known input. Consider, for example, a pressure gauge. This device could be calibrated
by mounting the transducer in a closed vessel with a piston at one end. (Such a vessel
is called a dead-weight tester). Placing a weight on the piston produces a known
pressure in the vessel equal to the weight divided by the piston area. After applying a
series of weights and measuring the corresponding output voltages of the pressure
gauge you can plot the relationship between the gauge reading and added weights. Now,
if you want to measure the pressure in a pipe you can use the gauge and the calibration
curve to convert mass weights into pressures at the pipe. Having a repeatable and
accurate calibration is obviously a prerequisite for an accurate measurement. Therefore,
repeating a calibration at regular intervals is a good idea since it may drift with time or
ambient conditions.
Apparatus:
1- Accurate Weights.
2- Pressure gauge (Bourdon Tube)
Theory:
Bourdon pressure gauge is a thin-walled tube that is
bent into a quarter-circular arc. The tube is rigidly
fixed at the end where the pressure is applied, and
free to move at the end. The exterior of the tube is
usually open to the atmosphere. When the fixed end
is subjected to a pressure, the arc tends to straighten,
thus causing the tube end to move upward (or
downward for vacuum measurements). The
deflection of the end is transmitted mechanically to rotate the pressure gauge needle.
The magnitude of the deflection is proportional to the applied pressure.
The Bourdon tube pressure gauge is loaded with known
pressures using a Dead weight tester. This Known pressure
will be used for calibration. A diagram of Bourdon pressure
gauge with a dead weight tester is shown in the figure.
Figure: Dead Weight tester for calibration of pressure gauge.
• A piston of known area (A) is loaded by a known Weights, therefore the
actual pressure in the cylinder is
P
W mg

*10 3
A
A
( KN / m 2 )
p  m * k,
Where K= a constant found from g/A (calibration constant)
• For the piston with
Area  315 mm 2
K
the calibration constant can be calculated
g 9.81m /( s ) 2

2
A
315(mm)
 31143
• For each mass, calculate the actual pressure, P and record the gauge reading.
Procedure:
1- Observe the Pressure gauge unit setup. Be sure all hoses are attached securely
to the Bourdon gauge.
2
2- Record the gauge reading ( KN / m ) for the unloaded piston, which
corresponds to a total mass of 1 Kg.
3- Place the given dead weight one by one and record the reading of the
gauge.
4- To prevent the piston from sticking, rotate the piston gently as each mass is
added, so that the friction in the piston can be reduced.
(under static conditions the friction is significant, therefore its better to change
the static friction to sliding friction which is considerably less)
5- Remove mass from the piston in the same order added, recording the gauge
6. Plot the Gauge Reading Hysteresis curve and determine the best fit, and the bias
error.
Result:
Total
Mass
(Kg)
Force
W
(N)
F=m*g
Applied
Pressure
1
Gauge
Gauge
( KN / m )
( KN / m )
( KN / m )
( KN / m )
Pa =m*k
(increasing)
(decreasing)
Pg
Average
Error
Pa  Pg
9.81
31.142
33
34
33.5
2.3572
1.1786
2
19.6
62.285
60
65
62.5
0.2143
0.10715
3
29.4
93.428
92
95
93.5
0.072
0.036
4
39.2
124.57
123
126
124.5
-0.07
0.035
5
49
155.714
154
155
154.5
-1.214
0.607
5.5
53.9
171.285
174
170
172
0.715
0.3575
6
58.8
186.857
185
186
185.5
-1.357
0.6785
6.2
60.76
193.085
190.5
190.5
190.5
-2.585
1.2925
2
2
Average
2
2
Note: first reading is due to weight of the piston m  1 kg .
Error
(% of full
scale)
Ряд1
y = 0,9803x + 2,2723
250
200
172
154,5
150
124,5
93,5
100
62,5
33,5
Pressure gauge
190,5
185,5
50
0
250
200
150
100
50
0
Applied Pressure
3
2,585
2,3572
2,5
1,357
1,5
1,214
1
0,715
0,07
0,072
0,5
0,2143
0
250
200
150
100
50
0
-0,5
Error
2
Discussion:
Possible sources of error in this experiment:
1- Wear and backlash in the gauge linkage can increase or decrease
the
pressure.
2- Air bubbles inside the tester unit may result in inaccurate reading.
3- Static friction between the piston and cylinder, yield smaller gauge
4- Human error.
Conclusion:
In this experiment, our task was to calibrate a Bourdon tube gauge. The
result obtained shows the calibration curve of the measurement system.
The curve represent relation between a known input (mass) and a
measuring instrument (pressure). The relation between the applied
pressure and the gauge pressure is determined using linear regression.
The fitted curve is linear. The sensitivity of the pressure gauge is the
slope of the calibration curve and equal to (0.98).
References:
For Figure:
Mmpx2XLLhk?usp=sharing
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