Hfig Smart Overpressure Protection; Setting The Auto-On Pressure Level - Varian XGS-600 Instruction Manual

HFIG Smart Overpressure Protection

Hot filament ion gauges all exhibit non-linearity at high pressure such that they give
readings lower than the actual pressure. For gauges that are rated up to 10 mTorr or higher,
operating the BA gauge at low emission current can minimize this measurement error.
Unfortunately, many applications require operating the gauge at emission currents that
would result in poor measurement accuracy at high pressure, thereby compromising the
ability to provide effective overpressure protection.
XGS-600 adjusts the overpressure limit based upon the emission current. When the
emission current is 0.7ma or less, the gauge's full high pressure range can be used. If,
however, the emission current is set to higher values, XGS-600 protects the gauge by turning
off the filament at 1 mTorr. Overpressure Protection uses the same fast pressure signal that is
used for fast set points, and is displayed by the P>MAX error message.

Setting the Auto-ON pressure level

When enabling the Auto-ON feature, the XGS-600 defaults the threshold pressure to
5 mTorr. If the convection gauge is installed so that it is measuring the same high vacuum
chamber as the ion gauge, this is a good value to use. However, in many applications users
may want to monitor the high vacuum pump's fore-line pressure instead. In this application,
the foreline may never get down as low as 5 mTorr, especially if a large volume of gas is
being pumped. The XGS-600 allows you to program a threshold pressure as high as 1 Torr.
When Auto-ON is being used, the gauge overprotection feature is still active to protect the
high vacuum gauge.
XGS-600 Gauge Controller
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