Model 979 Series Helium Mass Spectrometer Leak Detector
DRAFT 9/15/03
2-3
The ZERO button is only active while the leak detector is in the test state. Press
the ZERO button to cause the 979 to read the background leak rate signal plus
electronic noise signal for the current flow rate (for example, mid-stage), store
the reading in memory, and then reset the zero reference point on the leak rate
display. The ZERO indicator LED lights while zeroing is taking place.
Subsequent test measurements include both helium from the real leak and
helium from background conditions. The 979 automatically subtracts the
recorded background signal from the measurement and displays the real leak
rate only.
NOTE
Pressing the ZERO button while you are introducing helium
tracer gas to the test object could result in the suppression of a
real leak. Only use the ZERO button after the helium tracer gas
source has been removed.
When used correctly, the ZERO capability of the 979 is very powerful. It allows
for testing to sensitivity levels that are below the system background. This feature
also reduces test cycle times by reducing the amount of time required for
background levels to naturally clean up or by allowing for testing to begin at
relatively high test pressures.
The READ STANDARD LEAK button is only functional while the leak detector is
in a test state. The READ STANDARD LEAK button activates the optional internal
calibrated leak, allowing verification of the system calibration. When the system
is in READ STANDARD LEAK mode, its LED indicator lights.
Press the READ STANDARD LEAK button to isolate the test port from the system,
evacuate the calibrated leak manifold, and expose the leak to the spectrometer
tube. Compare the
displayed
leak rate value to the
calibrated
leak value.
Because the test port is isolated from the forepump and rough pump in this
mode, a slight increase in test port pressure may be indicated on the test port
pressure bar graph display.
The CALIBRATE button is used to perform an automated calibration based upon
the parameters set on the Calibrated Leak Set-Up screen (Section 2.6.1
“Calibrated Leak Set-Up” on page 2-14). CALIBRATE causes the 979 to rough
out and expose the internal standard leak to the system or, if EXTERNAL LEAK is
set during configuration, verifies that the test port is roughed out and exposed to
the system. The variable focus is scanned, then the ion voltage is scanned to find
the peak signal. The system notes the leak rate reading, then the leak is turned
off and the system is zeroed. Finally, a gain is calculated from the leak rate
reading to make the signal match the value of the calibrated leak and the system
is returned to TEST mode. The CALIBRATE indicator LED lights while calibration
is taking place.
Summary of Contents for 979 Series
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