Instrutech VGC301 User Manual page 18

Instruction Manual
1000
100
10
0.1
0.01
0.001
0.0001
0.0001
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 on the next page and note the following examples:
Ex A: If the gas is nitrogen (N
Ex 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. Continuing to backfill your system, attempting to
increase the reading up to 760 Torr, you will over pressurize your chamber which may present a hazard.
Ex C: If the gas is helium (He), the gauge will read 999 Torr 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 using gases other than nitrogen (N
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
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 ____ 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, Inc.
Indicated vs. True Total Pressure
1
0.001 0.01
CVG N2 Convectron N2
), when the true total pressure is 500 Torr, the gauge will read 500 Torr.
2
Convection Vacuum Gauge
Test Gases - N2, Ar, He
0.1 1
Indicated Pressure (Torr)
(convection gauge)
CVG Ar Convectron Ar
):
2
VGC301 Controller
Ar
N2
He
10 100 1000
Convectron He CVG He
) without using accurate
2
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