E1001A-171107
25
V
m
= Corrected volume increase at the center of the ΔV volume increase
ΔP =Corrected pressure increase in the linear zone of the pressure-volume
curve between V
1
and V
2
ΔV =Corrected volume increase in the linear zone of the pressure-volume curve
between V
1
and V
2
Pressure and volume are corrected as follows:
P = P
r
+ P
l
- P
c
Where:
P = Corrected pressure.
P
r
= Pressure reading on the control unit.
P
l
= Hydrostatic pressure between control unit and the probe.
P
c
= Pressure correction for the stiffness of the instrument at corresponding
volume; determined with the pressure calibration.
V = V
r
- V
c
Where:
V = Corrected volume.
V
r
= Volume reading on the control unit.
V
c
= Volume correction for the volume expansion of the instrument during the
test; determined with the volume calibration.
V
c
is obtained with a volume correction factor "c" given by the following
equation:
c = a - b
The correction factor "a" is calculated from the linear part of the curve of the
calibration in the steel tube.
The "b" parameter takes into account the expansion of the steel tube during the
calibration and is calculated with following equation:
b = (2V * (r + e * (1 + m))) / E
m
* e
Where:
V = Volume of the probe when in contact with the metallic calibration tube
r = Internal radius of the calibration tube
e = Wall thickness of calibration tube
m = Poisson's ratio of calibration tube material
E
m
= Modulus of elasticity of calibration tube material
The deflated volume of the probe
Vo
is a value necessary for determining the modulus and
the limit pressure. Theoretical values of
Vo
are given below.
PROBE DIAMETER
(mm)
PROBE ASSEMBLY
VULCOLAN RINGS
METALLIC RINGS
Distance
L
(cm)
Volume
Vo
(cc)
Distance
L
(cm)
Volume
Vo
(cc)
44 (A)
54
820
58
880
70 L (N)
46
1770
n.a.
n.a.
For more representative results,
Vo
must be estimated with the following formula:
Vo = (pi D
2
/4) L - Vi