4 Operation
25
Series 275 Convectron Gauge Bridge Amp PC Board
Instruction Manual - 275331
4.5.1 Examples
Example 1 –
Maximum safe indicated pressure.
Assume a given vacuum 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 the backfilling process.
Assume you wish to measure the pressure of Freon 22. On Figure 4-4, 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). 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 label on the system stating “DO NOT EXCEED 11
TORR FOR FREON 22" for this example.
Example 2 –
Indicated to true pressure conversion.
Assume you wish to determine the true pressure of helium in a system when the Convectron is
indicating 10 Torr. On Figure 4-3, follow the vertical graph line up from the 10 Torr (N
2
equivalent)
indicated pressure to the Helium curve and then move horizontally to the left to reveal a true
pressure of 4.5 Torr. Thus 4.5 Torr Helium pressure produces an indication of 10 Torr (N
2
equivalent).
Example 3 –
True to indicated pressure conversion.
Assume you wish to set a process control setpoint at a true pressure of 20 Torr of C0
2
. On Figure
4-3, locate 20 Torr on the true pressure scale, travel horizontally to the right to the C0
2
curve and
then down to an indicated pressure of 6.4 Torr (N
2
equivalent). The correct process control setting
for 20 Torr of C0
2
is 6.4 Torr (N
2
equivalent).
Example 4 –
True to indicated pressure conversion.
Assume you wish to obtain a helium pressure of 100 Torr in the system. On Figure 4-3, locate 100
Torr on the left hand scale, travel horizontally to the right to attempt to intersect the He curve.
Because the intersection is off scale, it is apparent that this true pressure measurement requirement
for helium exceeds the capability of the instrument.
NOTE: For gases other than those listed, the user must provide accurate conversion data for safe
operation. The Convectron Gauge is not intended for use above approximately 1000 Torr true
pressure.