Electrochemical vs. HMOS Ozone Sensing Technology
Two inexpensive technologies exist to detect
ozone. They are electrochemical and heated metal oxide semiconductor
(HMOS).
Electrochemical Sensor:
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 |
| rapid response - around 1-sec |
| excellent repeatability and accuracy |
Disadvantages
|
limited temperature range and
sensitive to changes in temperature |
|
humidity extremes can
destabilize the sensor |
|
sensitive to EMF/RFI |
|
limited storage life |
|
not accurate below 0.01-PPM |
|
affected by chlorine gas |
|
slow start-up if depolarized |
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for our best electrochemical ozone detector.
HMOS
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
| very linear |
| can detect PPB ozone levels |
| good repeatability and accuracy |
Disadvantages
|
slow start-up - requires 8-24
hour minimum warm-up time to heat element |
|
not an instantaneous response
- around 1-2 min |
| cannot tolerate any
smoke from cigarettes - smoke requires a minimum of 24-hours to burn off |
| cannot handle any VOCs
[volatile organic compounds] as VOC sensors utilize the same technology |
| affected by Chlorine gas |
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for our best HMOS ozone detector.
|