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Laser gas monitors

Key features

Conventional industrial gas analyzers for continuous measurement of high dust-concentration inflammable/exhaust gases require pre-treatment/sampling devices that absorb the gas for dust collection and processiing of the dust and moisture content. Because of the time for pre-treatment/sampling and then response of the analyzer, conventional analyses can take 5 to 10 minutes, depending on the type of gas.

Meanwhile, laser gas monitors, which are high-speed with a minimal response time of about 2 seconds and are directly mountable at measurement points with no need for a sampling device, enable the real-time measurement of gas concentrations. In addition, with no need for regular maintenance, the monitors have become increasingly popular for the continuous measurement/process control of various gases in Japan.

  • The real-time monitoring function (with a minimal response time of approx. 2 seconds) can be applied to control various types of gases.
    – No need for gas pre-treatment/sampling devices

  • The laser gas monitors can be directly mounted to measurement points for continuous measurements, even at high temperature and/or high dust concentrations.
    – Can be installed easily with flange JIS10K 50A, and also easy to handle.
    – No need for test solutions/standard gases or regular maintenance besically.

  • No interference from background gases. Highly sensitive and effective.


The laser gas monitors operate on the principle of “infrared absorption line spectroscopy,” which is based on the fact that most gas molecules absorb light at a specific wavelength. The monitor conducts measurements using the correlation between the amount of laser light absorbed by the molecules of the object gas and the concentration of the gas.

A technique called “laser wavelength modulation” is used in the monitor in order to increase the detection sensitivity of the receiver unit.


The laser gas monitors consist of a transmitter embedded with a semiconductor laser unit and an optical receiver unit that incorporates a photodetector. The transmitter and the optical receiver both have purge unit/optical-axis alignment functions. In addition, the LC display panel of the light sensor displays the gas concentration, laser transmission rate, and error messages (at the time of error).


O2 Process control at the outlets of incinerators, waste incinerators, gasification melting furnaces, converters, and blast furnaces. Monitoring of vinyl chloride/coal gasification, chemicals/iron/steel, and aluminum melting plants. HCl Process control at the outlets/inlets of bag filters (BF) for waste incinerators and incinerators. Monitoring of waste incinerators, incinerators, and at fertilizer/paper/pulp/cement plants.
NH3 Control of leakage NH3 at the outlet of SCR/SNCR NOx removal equipment. Control of leakage NH3 at the explosion proof (EP) outlets in power generation plants. Monitoring at power generation/fertilizer plants. HF Efficiency maximization control of the desalination systems of aluminum melting furnaces. Monitoring at aluminum melting furnaces, waste incinerators, brick/tile furnaces, and fertilizer plants.
H2S Monitoring at paper/petrochemical plants. HCN Monitoring at various types of plants.
CO Process control at the outlets of incinerators, waste incinerators, gasification melting furnaces, converters, and blast furnaces. Monitoring at aluminum melting/chemical waste plants. CO2 Monitoring at waste incinerators.
H2O Monitoring at waste incinerators. CH4 Monitoring at various types of plants.

Gas type Lower detection limit Maximum gas
Maximum gas
pressure (kPa・abs.)
O2 0.01 % 1,500 2,000
NH3 0.15ppm 600 200
HCl 0.05ppm 500 200
HF 0.015ppm 400 200
H2S 3 ppm 300 200
HCN 0.3 ppm 300 200
CO(standard concentration) 30ppm(0.1%) 800(1,500) 200
CO(low concentration) 0.3ppm 1,500 200
CO2(standard concentration) 30ppm(0.1%) 800(1,500) 200
CO2(low concentration) 0.2ppm 300 200
NO 10ppm 300 200
N2O 3ppm 200 200
CH4 0.2 ppm 300 200
C2H2 0.1ppm 200 200
C3H6 0.01% 200 300
CH3I 3ppm 200 200
CH3OH 0.05% 200 200
H2O(standard concentration) 0.005% 1,500 200
H2O(low concentration) 0.03ppm 400 200

(The lower detection limits above apply to a duct diameter of 1 m, a pressure of 1 bar, and a temperature of 25 ℃)


Standard specifications Measurable range
(Optical path length)
Maximum 6 m (optional: maximum 15 m)
Response time about 2 seconds
Average time Rolling average from 2 seconds – 24 hours (variable)
Span drift Less than 4% of the measurement range during maintenance intervals.
Zero drift Insignificant error of less than 2% of the measurement range during maintenance intervals.
Maintenance interval Although annual maintenance is recommended, because no consumables are used, parts replacement is not necessary.
Calibration A separate cell is used for calibration.
Signal input/output Analogue output Current signal: 4 – 20 mA Isolated signal: Max. 500 Ω
Digital output RS-232 format, Optional fiber optic (ASCII format)
Relay output High gas relays (normally closed-circuit relays)
Warning relays (normally closed-circuit relays)
Fault relays (normally closed-circuit relays)
Analogue input Optional 4–20 mA process temperature and automatic calibration by pressure reading
Operating environment Ambient temperature (-)20℃~(+)55℃
Protection classification Transmitter/Optical receiver unit IP66
Junction box IP55
Output power supply unit AC100/200V、50/60Hz
Power consumption Less than 20W
Installation Standard installation ANSI 150LB 2″(equivalent to flange JIS10K 50 A)(parallel)
Alignment tolerances Flanges parallel within 1 °
Purging of windows Dry and oil-free pressured air or N2 gas
Dimension and weight Transmitter 428×226×166mm 7Kg
Receiver unit 418×126×128mm 4Kg
Junction box 500×500×200mm 25Kg
Cable length Transmitter - Receiver unit standard length: 5m (max. 150m)
Transmitter - Junction box standard length: 15m (max. 100m)

* The above specifications are subject to change without prior notice.

Enviromental Preservation