Agilent Technologies 5975C TAD VL MSD, Troubleshooting And Maintenance Manual

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Analyzer
7
5975 Series MSD Troubleshooting and Maintenance Manual 207
Entrance lens
The entrance lens ( Figure 46 ) 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 + offset + (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.