PerkinElmer Photovac 2020, Manual

Page: 159 / 190

Technical Description
157
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Lamp Power
Supply
Lamp Driver
Circuit
Microprocessor
Light Sensor
Electrometer
+125 Volts
Sample In
Detector Cell
UV Lamp
Lampholder
High Voltage
Plates
Sample Out
UV Lamp
UV Light
Sample
Ionized Molecule
Collector Electrode
Repeller Electrode
Figure 30 Photoionization Detector
The ionized molecules in the detector cell are subjected to a
continuous electric field between the repeller electrode and the
collector electrode. The ions move in the electric field, generating a
current which is proportional to the concentration of the ionized
molecules in the detector cell. An electrometer circuit converts the
current to a voltage which is then fed to the microprocessor.
The UV lamp is operated by a high voltage lamp driver circuit which
delivers high voltage energy to the lamp through plates in the
lampholder. The lamp driver power supply is controlled by the
microprocessor based on a feedback signal from a light sensor on
the driver circuit board.