THEORY OF OPERATION
5-1
5. Theory of Operation
The IAQRAE monitor uses one to five different sensors to
measure a variety of gases. (See Figure 5-1.) A unique
electrodeless discharge UV lamp is used as the high-energy
photon source for the PID sensor. The patented PID sensor
detects a broad range of organic vapors. A miniaturized non-
dispersive infrared (NDIR) sensor measures carbon dioxide
levels. An interchangeable electrochemical (EC) sensor
measures inorganic toxic gases. Humidity is measured with a
polymer-capacitate sensor and temperature with a Thermistor
in a combined by a humidity-temperature (HT) sensor.
Microprocessor
LCD Display
Keypad
Serial
Port
Battery
PID
NDIR
EC
HT
UV Lamp
Pump
Light
Sensor
LED
Buzzer
Charger
Gas Out
Gas In
Figure 5-1
Block Diagram of IAQRAE Monitor
The PID sensor for the IAQRAE monitor is the first plug-and-
play module with a built-in lamp and electrometer. A diaphragm
pump installed in the monitor draws air samples over the PID
sensor and to the NDIR and EC sensors. The HT sensor is
mounted outside the IAQRAE case for fast response.