An electrochemical ozone sensor uses a porous membrane that allows ozone to diffuse into a cell containing liquid or gel electrolyte and the electrodes. When the gas comes into contact with the electrolyte, a change in electrochemical potential between the electrodes is produced. Associated electronic circuitry will amplify, and control the signal. The signal is proportional to the ozone concentration (partial pressure) and is displayed in PPM or PPB.

Advantages

•	Very Linear
•	Very quick response time - 1-2 Seconds
•	Good repeatability and accuracy

Disadvantages

•	limited temperature range and sensitive to changes in temperature
•	humidity extremes can destabilize the sensor
•	sensitive to EMF/RFI
•	limited sensor life (18-24 months)
•	not accurate below 0.01-PPM

HMOS Ozone Sensor

A heated metal oxide semiconductor (HMOS) sensor works by heating a small platinum substrate to a 300-deg F temperature. At this temperature, the substrate is very sensitive to ozone. A proportional signal is sent to the electronics and displayed in PPM or PPB.

Advantages

•	more accurate than electrochemical sensors
•	more linear vs. electrochemical
•	can detect PPB ozone levels - will go below 0.01 PPM
•	Excellent repeatability and accuracy

Disadvantages

•	slow start-up - can require 8-24 hour minimum warm-up time to heat element & burn off contaminants
•	not an instantaneous response - around 1-2 minutes
•	cannot tolerate any smoke from cigarettes - smoke requires a minimum of 24-hours to burn off - other airborne particulates must be eliminated
•	cannot handle any VOCs [volatile organic compounds] as VOC sensors utilize the same technology