Instruction Manual CVM211 Stinger
InstruTech Page 17
Gas Correction Chart
The Y- axis of the above chart is actual pressure as measured by a capacitance manometer, a diaphragm gauge
that measures true total pressure independent of gas composition. The X-axis is the pressure reading indicated
by the convection gauge under test. This chart shows readings for an InstruTech convection gauge (CVG) and
Granville-Phillips®
Convectron® gauge to illustrate that the difference in the response for both of these types of
gauges is virtually indistinguishable.
CAUTION! Do not assume this data applies to other convection gauges, which may or may not be the same.
Refer to the table in section 6 and note the following examples:
Ex A: If the gas is nitrogen (N
2
), when the true total pressure is 533 mbar, the gauge will read 533 mbar.
Ex B: If the gas is argon (Ar), when the true pressure is 133 mbar, the gauge will read about 11.7 mbar.
If you are backfilling your vacuum system with Ar, when your system reaches a pressure of 1.01 bar
true pressure, your gauge will be reading about 31.5 mbar. Continuing to backfill your system, attempting to
increase the reading up to 1.01 bar, you will over pressurize your chamber which may present a hazard.
Ex C: If the gas is helium (He), the gauge will read 1.33 bar when pressure reaches about 13.3 mbar 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 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 nitrogen (N
2
):
Install a pressure relief valve or burst disk on your chamber, to protect it from overpressure. Post a warning
label on your gauge readout that states "Do Not Exceed ____ mbar 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
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