3B SCIENTIFIC PHYSICS U104001 Instructions D'utilisation page 19

= + + ⋅ −
s s s C p C
ϑ
e 0 p
By substituting in equation 4, we get:
(
⋅ + + β ⋅ − β
p s s p
ϑ
e 0 p
ϑ + ϑ
0
If we take several readings at various temperatures
and pressures, we can calculate the term:
(
⋅ + + β
⎛
p s s
n
∑ ⎜ ⎜
= i i 0 p
Q
ϑ +
⎝
=
i 1
, β
The free parameters s
0
priately selected so that the value of Q is reduced to a
minimum.
Additionally required (see also chapter 8):
1 Compressor or
bicycle pump and valve
1 Bath/circulating thermostat
1 Dig. quick-response pocket thermometer U11853
1 Type K NiCr-Ni immersion sensor,
-65°C-550°C
2 Silicone tubes, 1 m
1 l Anti-freeze fluid with corrosion-inhibiting additive
for aluminium engines (e.g., Glysantin® G30 ma-
nufactured by BASF)
Conducting the calibration:
•
Connect the circulation thermostat as described
in chapter 8 and fill it with the water/anti-freeze
mixture.
•
Connect the plastic tube (3-mm internal diameter)
to the 1/8" gas connection fittings.
•
Open the regulating valve.
•
Wind the handwheel outwards, making the piston
move till it reaches say the 46.0 mm position.
•
Use a compressor or a bicycle pump to create an
excess air pressure of approx. 3-8 bar in the
measuring cell.
•
Shut the regulating valve.
•
To record measurements, vary the volume in the
measuring cell or the temperature of the thermo-
stat and wait till a stationary equilibrium has
been attained. Then take a pressure reading.
•
Use appropriate adjustment software to set the s
β , β
and n parameters so that the quadratic
ϑ
P
equation for the errors Q is reduced to a mini-
mum (see equation 11).
•
If you like, you can adjust the vernier scale
around s so that this correction is not necessary.
0
With the set parameters, it is possible to calculate the
"effective" piston displacement s from the measured
displacement s using Equation 9 and then to calcu-
e
late the calibrated measuring cell volume using Equa-
ϑ ⋅
)
ϑ ⋅ ⋅
A
− ⋅ =
n R 0
)
2
⋅ − β ϑ ⋅ ⋅
⎞
p A
ϑ
⎟ ⎟
i i − ⋅
n R
ϑ
⎠
0
, β
and n should be appro-
ϑ
P
U14400
U11854
U10146
tion 8.
(9)
Sample measurements:
Table 1: Measured values for calibration
(10)
i
1
2
(11)
3
4
5
6
7
8
9
10
The following parameter values are obtained:
s = 0.19 mm,
0
n = 0.00288 mol.
7.1 Handling of sulphur hexafluoride:
Sulphur hexafluoride (SF
absolutely safe for humans. The MAC value for danger
of suffocation on account of oxygen deprivation is
1000 ppm. That is equivalent to 6 filled measuring
3
cells per 1 m of air.
However, SF is extremely harmful to the environment
6
and can give rise to a greenhouse effect 24,000 times
stronger than CO
tities to be released into the environment.
7.2 Gas connection via fixed pipes:
Additionally required:
1 SF gas cylinder with manufacturer's/supplier's rec-
6
ommended gas fittings/valves, e.g. SH ILB gas cylinder
and Y11 L215DLB180 regulating valve from Airgas
(www.airgas.com).
,
0
1 Pipes with outer diameter of 1/8" and, if necessary,
adapters, e.g. from Swagelok (www.swagelok.com).
1 open-end spanner (13 mm), 1 open-end spanner
(11 mm)
According to the principles of "good laboratory prac-
tice", it is recommended to utilise a gas supply via
fixed pipes, especially if the equipment is regularly in
operation.
5
ϑ
s / mm
e
40.0 20.0°C
20.0 20.0°C
10.0 20.0°C
5.0 20.0°C
3.5 20.0°C
5.0 20.0°C
5.0 10.0°C
5.0 30.0°C
5.0 40.0°C
5.0 50.0°C
mm
β = β =
0 . 023 , 0.
ϑ
P
bar
7. Filling with test gas
) is a non-toxic gas and is
6
. Therefore, do not allow large quan-
2
p / bar
6.6
12.4
23.3
41.8
53.9
41.8
38.9
45.3
49.0
53.5
mm
034 and
grd