THEORY OF OPERATION
6 - 2
The ionization chamber for this ToxiRAE 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 pass in front of the UV window. The
ions collected on the electrode are measured by an
electrometer. A centrifugal pump is installed inside the
sensor module to draw an air sample into the sensor
chamber for faster instrument response.
A single chip microcomputer is used to control the
operation of the lamp, alarm buzzer, LED, power supply
and the electrometer. It measures the electrometer
readings and calculates the gas concentrations based on
calibration to a known standard gas. The data is stored in
non-volatile memory so that it can be sent to a PC for
record keeping. A pair of infrared transceivers provides a
wireless interface between the unit and the serial port of a
PC. An 8-digit LCD display is used to show the readings.
The user interacts with the unit through three keys on the
front panel.
A rechargeable Ni-CD or alkaline battery pack powers the
unit.
