Detector; Detector Ion Focus; High Energy Dynode; Em Horn - Agilent Technologies 5975C TAD VL MSD Troubleshooting And Maintenance Manual

Detector

The detector
dynode (HED) coupled to an electron multiplier (EM). The detector is located
at the exit end of the quadrupole mass filter. It receives the ions that have
passed through the mass filter. The detector generates an electronic signal
proportional to the number of ions striking it. The detector has three main
components: the detector ion focus, the HED and the EM horn.

Detector ion focus

The detector ion focus directs the ion beam into the HED, which is located off
axis. The voltage on the detector focus lens is fixed at –600 V.

High energy dynode

The HED operates at –10,000 volts for EI and PCI, and +10,000 volts for NCI. It
is located off-axis from the center of the quadrupole mass filter to minimize
signals due to photons, hot neutrals, and electrons coming from the ion
source. When the ion beam hits the HED, electrons are emitted. These
electrons are attracted to the more positive EM horn. Do not touch the
insulator.

EM horn

The EM horn carries a voltage of up to –3000 volts at its opening and 0 volts at
the other end. The electrons emitted by the HED strike the EM horn and
cascade through the horn, liberating more electrons as they go. At the far end
of the horn, the current generated by the electrons is carried through a
shielded cable outside the analyzer to the signal amplifier board.
The voltage applied to the EM horn determines the gain. The voltage is
adjustable from 0 to –3000 VDC. Use the EM voltage found in autotune as a
baseline for the EM voltage setting.
• To increase signal gain, increase the EM voltage.
• For concentrated samples where less signal gain is needed, decrease the EM
5975 Series MSD Troubleshooting and Maintenance Manual
(Figure 48) in the MSD analyzer is a high energy conversion
voltage.
7
Analyzer
211