Agilent Technologies 7000 Triple Quadrupole GC/MS, Maintenance Manual

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Analyzers and Collision Cell
7
Troubleshooting and Maintenance Manual 155
Ion focus
The voltage on the ion focus lens ( Figure 27 ) can be varied from 0 to
–127 VDC. A typical voltage is between –70 and –90 VDC. In general:
• Increasing the ion focus voltage improves sensitivity at lower masses.
•
Decreasing the ion focus voltage improves sensitivity at higher masses.
• Incorrect ion focus adjustment results in poor high mass response.
Entrance lens
The entrance lens ( Figure 27 ) is at the entrance to the quadrupole mass filter.
This lens minimizes the fringing fields of the quadrupole which discriminate
against high-mass ions. There is a per4.4 volt voltage added to the
entrance lens. The total voltage applied to the entrance lens is the sum of the
entrance lens offset and entrance lens gain and the +4.4 volt permanent offset.
Entrance lens voltage = +4.4 VDC + (gain × mass)