64 tinb29e1-c (2019-10) VGC083A_B.om
Do not assume this data applies to other convection gauges which may or may not
be the same. See Table 1 below and note the following examples:
Example A: If the gas is nitrogen (N2), when the true total pressure is 500 Torr, the
gauge will read 500 Torr.
Example B: If the gas is argon (Ar), when the true pressure is 100 Torr, the gauge
will read about 9 Torr.
If you are backfilling your vacuum system with Ar, when your system reaches a
pressure of 760 Torr true pressure your gauge will be reading about 23 Torr. Con-
tinuing to backfill your system, attempting to increase the reading up to 760 Torr,
you will over pressurize your chamber which may present a hazard.
Example C: If the gas is helium (He), the gauge will read 1.10E+03 (overpressure
indication) Torr when pressure reaches about 10 Torr true pressure and opening
the chamber to atmosphere prematurely may present other hazards for both peo-
ple and product. You probably will not cause damage to your vacuum system, but
opening the chamber to atmosphere with the internal chamber pressure at only
10 Torr true pressure, may present other hazards for both personnel in the
proximity and product that may be inside the chamber/vessel.
What these examples illustrate is that using gases other than nitrogen (N
2
) without
using accurate gas conversion data and other proper precautions could result in
injury to personnel and/or damage to equipment.
Suggested precautions when using gases other than N2:
• Install a pressure relief valve or burst disk on your chamber to provide pro-
tection from the dangers associated with over pressurizing the chamber.
• Post a warning label on your gauge readout such as "Do Not Exceed
_______ Torr Indicated Pressure" (fill in the blank for the gas type you are
using) so that an operator using the vacuum chamber system and connected
gauge will not exceed a safe operating pressure.
Do not assume this data applies to other convection gauges, which may or
may not be the same.
Risk of over pressurizing a gas containment vessel and attached apparatus
exists when using pressure measurement devices that are calibrated for a specific
gas type. Use a pressure relief device to safely limit the internal pressure of a
containment vessel to less than the maximum allowable working pressure rating for
the vacuum/pressure system and all devices attached to the system.
Using a thermal conductivity gauge with gases other than that for which it is
calibrated could result in death or serious injury. Be sure to use gas correction data
in this manual when measuring pressures of gases other than N
2
/ air.
Exercise caution when admitting positive pressures (above local ambient, atmos-
pheric pressure) of gas into any enclosed volume. Install pressure relief devices on
your vacuum / pressure vessel or chamber to limit the maximum allowable working
pressure inside the devices and vessel internal volume to less than the lowest
rated device - in some cases, the maximum allowable working pressure may be
dictated by the type of connections or fittings used to attach devices to your cham-
ber. An O-ring compression fitting type device may be forcibly released (ejected)
from the fitting if internal pressure exceeds the local barometric, ambient pressure.
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