Veeco MS40 Operation And Maintenance Manual page 50

Auto Zero
The "Auto-Zero" or "Zero" feature, activated from the User Panel, allows
the operator to test with the presence of residual helium. Pressing
the ZERO button will cancel out the measurement of any helium present
in the vacuum system or test object (the unit will display the amount of
helium above the "zeroed out" amount).
The Zero function works in all test modes (Gross, Reverse and Direct,
and also when using the Sniffer probe). When activated, helium
present and being measured in the vacuum system is "zeroed" out on the
leak test bar graph and therefore is not counted as part of the test.
When the Zero function has been activated, leak test measurement is
automatically restricted to two ranges below the current range. When
auto-ranging, the unit will automatically stop two decades below
the point when the Zero button was pressed. When manually ranging,
the unit will emit a short beep whenever the user attempts to range
more than one decade below the point when the Zero button was pressed.
Note that when the Zero function is activated, it does not inhibit ranging
upward during testing. The Zero function is canceled at the end of a test
cycle (i.e., when the VENT button is pushed); it can also be cancelled by
halting the test cycle (pushing the START button a second time).
Peak Scan
Peak Scan is a function the operator of the MS-40 can use to quickly
verify that the unit is operating correctly. By using this function while in
Standard Mode, the user will be able to ascertain whether the leak rate
indication is due to helium or is the result of a poorly tuned spectrometer.
By changing the function on the Service Panel to Anode Voltage while
still in Standard Mode, and by then pressing either the left or right SET
buttons, the user will temporarily alter the spectrometer peak tuning
voltages either -30 or +30 volts from its prior setting (releasing either
button will return the voltages to its normal condition). If this is done
to an optimally tuned spectrometer, the displayed leak rate will decrease
to zero indicating that the measurement is actually due to the presence of
helium. Both SET buttons should be used for this test. If the displayed leak
rate does not decrease to zero after either SET button is pressed, the
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spectrometer is not tuned and the TUNE function (see below) must be initiated
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to retune the mass spectrometer.
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