Rae MiniRAE Plus PGM-76, Operation And Maintenance Manual, Page: 142 / 168

SECTION 7 THEORY OF OPERATION
7 - 2
A sampling pump continuously draws air sample into the
ionization chamber. The ionization chamber for the MiniRAE
Plus Professional PID unit is constructed as a small cavity in
front of the UV lamp. The electrode is made of wired mesh so
that the high energy UV light can shine through the mesh and
excite the gas molecules when they across the face of the UV
window. The ions collected on the electrode are measured by
an electrometer.
A single chip microcomputer is used to control the operation of
the lamp, alarm buzzer, LED, sampling pump, power supply
and the electrometer. It measures the electrometer readings
and calculates the gas concentrations based on calibration to a
known reference gas. A 7-digit LCD display is used to show
the readings. The user interacts with the unit through 5 keys on
the front panel.
The unit is powered by a rechargeable lead acid batteries. A
built-in charging circuit allows the batteries to be charged
directly from a 12 VDC source.