THEORY OF OPERATION6-16. THEORY OF OPERATIONThe MiniRAE 2000 monitor uses a newly developedelectrodeless discharge UV lamp as the high-energyphoton source for the PID. As organic vapors pass by thelamp, they are photo-ionized and the ejected electrons aredetected as a current. The PID sensor with a standard 10.6eV lamp detects a broad range of organic vapors. A lampwith high photon energy (e.g. 11.7 eV) will measure themore kinds of compounds, whereas low photon energies(e.g. 9.8 eV) are selective for easily ionizable compoundssuch as aromatics. In principle, any compound with anionization energy lower than that of the lamp photons canbe measured.The PID sensor for the MiniRAE 2000 monitor isconstructed as a small cavity in front of the UV lamp. Adiaphragm pump draws the gas sample into the sensor andthen pumps it out through the side of the instrument.Figure 6-1 MiniRAE 2000 Block DiagramMicro-processorLCD DisplayKeypadSerialPortBatteryPID SensorUV lampPumpLightsensorLEDBuzzerChargerSample GasInlet ProbeSample GasOutlet
