MKS Stabil-Ion 370 Series, Инструкция по эксплуатации, Страница: 78 / 122

4 Preparing the Stabil-Ion System for Operation
4-20
Series 370 Stabil-Ion Instruction Manual - 370119
Note that 1 mbar = 100 Pa, so the mbar charts may be used for Pascal units by multiplying the
values on the axes by 100.
A useful interpretation of these curves is, for example, that at a true pressure of 2 x 10
-2
Torr of CH
4
the heat loss from the sensor is the same as at a true pressure of 3 x 10
-2
of N
2
(see Figure 4-10 on
page 4-23). The curves at higher pressure vary widely from gas to gas because the thermal losses at
higher pressures are greatly different for different gases.
If you must measure the pressure of gases other than N
2
or air, use Figures 4-9 through 4-14 to
determine the maximum safe indicated pressure for the other gas as explained below.
4.7.2 Examples
Example 1 –
Maximum safe indicated pressure.
Assume a certain system will withstand an internal pressure of 2000 Torr or 38.7 psia. For
safety, you wish to limit the maximum internal pressure to 760 Torr during backfilling. Assume
you wish to measure the pressure of Freon 22. On Figure 4-11 on page 4-24, locate 760 Torr
on the left hand scale, travel to the right to the intersection with the Freon 22 curve, and then
down to an indicated pressure of 11 Torr (N
2
equivalent). Thus, in this hypothetical situation,
the maximum safe indicated pressure for Freon 22 is 11 Torr.
For the sake of safety, it is prudent to place a warning label on the instrument face which under
the assumed conditions would read “DO NOT EXCEED 11 TORR FOR FREON 22".
If the Convectron Gauge calibration is for a gas type other than air, N
2
or Air, we
suggest placing a label, supplied with the installation hardware, to the right of the
second and third lines of the display indicating the gas type or types used for calibration
to prevent mix-ups.
Table 4-5
Pressure vs. Indicated N
2
Pressure Curve
Fig. No. Pressure Range and Units Gases
4-9 10
-4
to 10
-1
Torr All
4-10 10
-1
to 1000 Torr Ar, CO
2
, CH
4
, Freon 12, He
4-11 10
-1
to 1000 Torr D
2
, Freon 22, Kr, Ne, O
2
4-12 10
-4
to 10
-1
mbar All
4-13 10
-1
to 1000 mbar Ar, CO
2
, CH
4
, Freon 12, He
4-14 10
-1
to 1000 mbar D
2
, Freon 22, Kr, He, O
2