DOAS measures Cl₂ across an open light path — no sensor, no sampling line, no corrosion.
Electrochemical and extractive chlorine monitors fail in the same way: Cl₂ attacks the sensor or the sampling system. DOAS avoids the problem by keeping all hardware outside the gas.
| Issue | Contact sensor | DOAS open path |
|---|---|---|
| Sensor life in Cl₂ | Typically 3–6 months before drift | No sensor in the gas |
| Sampling line | Corrodes within months | Not required |
| High concentration events | Sensor saturates, data lost | No saturation of the optical path within range |
| Maintenance | Frequent sensor replacement | One to two visits per year |
The first OPSIS chlorine system in China was installed in 2005 at a silica chemical plant for high-concentration process gas, using one analyser for two measurement points. Further systems followed at petrochemical sites and chemical parks, including fenceline installations used to identify the source of chlorine episodes.
| Measurement principle | UV-DOAS, open light path |
| Measured gas | Cl₂, with SO₂ / NOx / NH₃ on the same analyser |
| Path length | Typically 1–5 m in ducts, 100–1000 m for fenceline |
| Response time | Seconds, no sample transport |
| Maintenance | One to two visits per year; xenon lamp every 1–2 years |
Typical data from OPSIS product documentation; specifications depend on the application and are confirmed at quotation stage.
Does chlorine attack the analyser?
No. The emitter and receiver are mounted outside the duct and the light beam crosses the gas. No electronic component, sensor or sampling line is exposed to Cl₂.
How long has this been in service in China?
The first installation dates from 2005 and ran continuously for 18 years before the analyser was replaced; the same plant continues to use OPSIS systems. Systems are also in service at petrochemical sites and chemical parks.
Can one analyser measure other gases as well?
Yes. Additional gases such as SO₂, NOx and NH₃ can be measured simultaneously. For low-level HCl and HF, a second IR-DOAS analyser can be added to the same system.
Send the gases, ranges, duct or path dimensions and required certification — we will respond with a technical proposal.