Fluid Mechanics LAB:
PRESSURE MEASUREMENT AND GAGE
CALIBRATION
ENTC - 303
ENTC-303
Dr. ALVARADO
1
Objective
• To learn about the different pressure
measuring devices frequently used to
measure pressure difference in fluid flow.
• To calibrate a pressure gage.
Pressure Measurement
Pressure measurement is important for many
reasons. It can provide information needed to
determine a system’s flow rate.
Pressure measuring devices can also allow
operating pressures to be monitored, so that
any necessary adjustments can be made. Since
the pressure in any fluid is not constant from
one point to the next, it is important to measure
the pressure at different points in the system.
Pressure Measuring Devices
• Bourdon tube gages
- can measure both pneumatic and
hydraulic pressure.
- cannot measure low pressure in the range
of 0-5 psi
• Diaphragm-type dial gages
Pressure Measuring Devices
• Manometer
A manometer employs a column of liquid, which is forced upward
to a height where it balances the pressure being measured. The
pressure exerted by the liquid column depends on it height and the
density of the liquid.
-
U-tube manometer
 The reading is taken as the difference in height of the two
columns.
- Well-type manometer

The column height can be read directly.
Pressure Gage Calibration
• Calibration refers to the process of comparing
the reading of an instrument or device that is
used to measure a desired variable, with a
primary reference standard.
• The primary reference standard is a device,
which measures the desired variable in basic
units such as mass, length, time which is
reproducible and accurate.
Pressure Gage Calibration
Steps:
1. Make sure that the pressure gauge tester is filled with oil and that
it has no air bubbles inside.
2. Note down the mass of the platform and piston of the gage tester.
Also record the area of the piston.
3. Record the gage reading without any additional weight. In order to
ensure that the piston is not stuck inside due to friction, always
make sure to spin the platform before noting the reading of the
pressure gage.
4. Place weights in the following increments (0.5, 1.0. 2.0, 3.0, 4.0, 5.0
kg.), noting down the gage reading at each step.
5. Remove the weights one at a time, and note the readings on the
gage at each step. This is done to check for gage hysteresis.
6. Perform a total of five trials.
Pressure Gage Calibration
Steps:
7. The apparent pressure is the average of all the gauge readings per
weight increment.
8. Calculate the true pressure by dividing the sum of the weights on
the platform and the weight of the platform with no load by the
cross sectional area of the piston. Use the following equation:
Pture
(Weights + Plarform)
å
=
Cross _ Sectional _ Area
Data Analysis:
Plot the following:
– Actual pressure (gage readings) as a function of true pressure
(from equation above).
– Gage correction (True Pressure – Actual Pressure) as a function of
true pressure.
Mass Total
added mass
True
to
on pressure
piston piston
(kg)
0.0
0.5
1.0
2.0
3.0
4.0
5.0
(kg)
(kPa)
Increasing Pressure
Gage Reading(kPa)
Average
(kPa)
Gage
Gage
Correction error
(kPa)
(%)
Mass Total
added mass
True
to
on pressure
piston piston
(kg)
5.0
4.0
3.0
2.0
1.0
0.5
0.0
(kg)
(kPa)
Decreasing Pressure
Gage Reading(kPa)
Gage
Gage
Average
Correction error
(kPa)
(kPa)
(%)