Convection Gauge Display Conversion For Selected Gases - Instrutech The Hornet IGM402 User Manual

Instruction Manual

Convection gauge display conversion for selected gases

7.2.1
When using gas species or mixtures of gas other than nitrogen or air, you must use a look-up table to determine
the true pressure of the selected gas as measured by the convection gauge. This holds true for any
manufacturer's convection enhanced pirani type transducer where the principle of measurement is based on
heat-loss from a heated wire contained in the vacuum gauge transducer volume exposed to the inlet gas or gas
mixture.
Refer to the look-up table on the next page and note the following examples:
Example A: If the gas is nitrogen (N
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 true pressure of 760 Torr,
your gauge will be reading about 23.7 Torr. Continuing to backfill your chamber in an attempt to increase the
displayed pressure reading to 760 Torr will over pressurize your chamber which may present a hazard.
Example C: If the gas is helium (He), the gauge will read OP (Overpressure) when pressure reaches about
10 Torr true pressure and opening the chamber to atmosphere prematurely may present other hazards for
both people and product.
CAUTION! What these examples illustrate is that when using gases other than nitrogen (N
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 N
Exercise caution when admitting positive pressures (above local ambient, atmospheric 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 chamber. An O-ring compression fitting type device may
be forcibly released (ejected) from the fitting if internal pressure exceeds the local barometric, ambient
pressure.
Post a warning label on your gauge readout "Do Not Exceed ____ Torr Indicated Pressure" (fill in the blank for
maximum indicated pressure for the gas you use) so that an operator using the gauge will not exceed a safe
pressure.
InstruTech
), when the true total pressure is 500 Torr, the gauge will read 500 Torr.
2
/ air:
2
IGM402 Hornet
) / air, without using
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