Agilent Technologies 5975T LTM GC/MSD, Troubleshooting And Maintenance Manual

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206 Troubleshooting and Maintenance Guide
13
Analyzer
Entrance lens
The entrance lens ( Figure 31 ) 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)
Entrance lens offset
The entrance lens offset (EntOff) controls the fixed voltage
applied to the entrance lens. It can be varied from 0 to –64 VDC
(–20 V is typical). Increasing the entrance lens offset generally
increases the abundance of ions at low masses without
substantially decreasing the abundance of high mass ions.
Entrance lens gain
Entrance lens gain (EntLens) controls the variable voltage
applied to the entrance lens. It determines how many volts are
applied for each
m/z . It can be varied from 0 to –128 mV/( m/z ).
A typical range is 0 to –40 mV/amu.