Functional Description
MS Detector
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@'JOOJHBO-52
5IFSNP
&-&$530/$03103"5*0/
2-38
______________________ Finnigan LTQ Hardware Manual _______________________
Ion Detection System Electronic Assemblies
The ion detection system electronic assemblies provide high voltage to the
two electron multipliers and conversion dynodes of the ion detection system.
They also receive the electron multiplier output current signal, convert it to a
voltage (by the electrometer circuit), and pass it to the data system. A
functional block diagram of the ion detection system electronic assemblies is
shown in Figure 2-19.
The ion detection system electronic assemblies include the following:
•
Electron multiplier/conversion dynode power supply
•
Electrometer circuit
The electron multiplier/conversion dynode power supply supplies the -0.8
kV to -2.5 kV dc high voltage to the cathodes of the electron multipliers. The
high voltage set control signal for the electron multiplier power supply comes
from the Analog PCB. This signal controls a feedback control circuit and is
proportional to the final high voltage to be applied to the electron multiplier
cathode. The electron multiplier voltage is lowered by the Analog during
sample ionization to prolong the life of the electron multiplier.
The electron multiplier/conversion dynode power supply also supplies
+15 kV and -15 kV dc high voltage to the conversion dynode. The polarity of
the voltage applied to the conversion dynode is determined by a control signal
from the Analog PCB.
The electrometer circuit, located in a shielded enclosure on the Electrometer
PCB, receives the amplified ion current from the anodes of the electron
multipliers, converts the current into a voltage, and then integrates the voltage
over time. The integrated voltage is then passed to the Signal/Power
Distribution PCB where it is processed and sent to the data system.
