UNIVERSITY OF BAHRAIN
COLLEGE OF ENGINEERING
DEPARTMENT OF MECHANICAL ENGINEERING
MEG 381 Instrumentation
Calibration of a pressure gauge (dead weight test)
Introduction:
DEAD WEIGHT TESTERS
The operation of dead weight testers is based on the principle of balancing known weights
against the force produced by an unknown pressure action on a hydraulic piston of a known
area. When these forces reach equilibrium, the unknown pressure equals the dead weight and
piston. Dead weight testers incorporate a built-in pump for generating pressure and can be
used for checking spring gauges, calibrating bourdon gauges, recorders, transmitters or other
instruments, pressure testing small vessels, and measuring gas pressure with high accuracy.



Brass weights (optional stainless steel weights)
Measuring units psi, bar, kPa or kg/cm2
Supplied with metal carrying case(s)
Portable version with an accuracy of +/- 0.1 % of rated pressure: Pressure ranges from 500 psi
up to and including 15,000 psi.
Laboratory version with an accuracy of +/- 0.05 % (optional +/- 0.03 %) of rated pressure:
Pressure ranges from 500 psi up to and including 20,000 psi, electric motor drive 220 V
(optional 110 V).
High pressure laboratory dead weight tester with an accuracy of +/- 0.1 % for very high
pressures: 25,000 psi, 35,000 psi and 40,000 psi
Objective:
Getting to know the concept of calibration by calibrating a Burdon tube pressure gauge using
Deal weights.
Apparatus:
As shown in the figure below.
The
ory:
The
applie
d
pressu
re on
the
piston
p
Wher
e,
F= force.
= mg
A= area.
m= mass.
g= acceleration due to gravity ( g=9.81 m/s2 ).
It is given that the piston has a diameter of 20mm. Therefore the area,
F
A
A

4

 20  10  3

2
 314.16  10 6 m 2
For a mass of 1kg:
F  1Kg  9.81m / s 2  9.81N
P
9.81
314.16 106
 0.0312  10 6 N / m 2
 0.31  105 N / m 2
= 0.31 bar
Sensitivity: 0.3 bar per 1kg.
Procedure:
1) Placed the pressure gauge unit on a table and see that it is properly installed according
to the manufacturer’s manual.
2) Pressure Gauge Nullification: At atmospheric conditions you will find that the pointer
below zero. An adjustment is necessary to eliminate the reading due to piston’s
weight. On adjust the knob on the backside of the gauge until the pointer reaches zero.
3) Placed the given dead weights one by one. Read the pointer of the gauge
precalculation: place the weights gently on the piston . The pressure creating piston is
not entirely free from friction to its motion in the cylinder. Under static conditions the
friction is of considerable amount. In order to eliminate the error due to friction. The
piston together with the weights should be in rotational motion. Then static friction
change to sliding friction which is considerably less. Make sure that the piston is
rotated in the same direction.
Result:
Piston
Mass
(kg)
Area of
piston
(m2)
Pressure in
cylinder
Pc(KN/m2)
Gauge (1)
Reading Pg
( KN/m2)
Gauge (2)
Reading Pg
( KN/m2)
Average
PR
( KN/m2)
Absolute
Gauge Error
PC-PR
%Error
(PCPR)/PC
*100
0
0
5
2.5
-2.5
___
1
31.2
20
30
25
6.23
19.93884
2
62.5
45
60
52.5
9.95
15.93578
93.7
75
90
82.5
11.2
11.93272
125
105
125
115
9.9
7.929664
156
135
155
145
11.1
7.129052
6
187
165
185
175
12.4
6.595311
7
219
195
195
195
23.6
10.78899
3
4
5
314.16*10^-6 m2
0
By using mat lab program, we can get precision error and bise error.