Open Pad


LaserGasTM II Open Path Monitor


The Open Path monitor from NEO Monitors AS is designed for long distance monitoring in ambient air, monitoring of production halls, gas fencing or leak detection of gases such as HF, CH4, H2S (see ‘Table of Gases’ below). Measurement lengths of up to 500 m are possible. Based on the well-proven tuneable diode laser (TDLAS) technology the instrument has a number of unique features.


  • Up to 500 m measurement path
  • Response time down to one second
  • No cross interference from other gases
  • Very low detection limits (ppb and low ppm)
  • Unaffected by fog or rain down to <1% transmission
  • Low cost of ownership
  • Ethernet connection (optional)
  • Portable, battery powered version available

The monitor consists of a transceiver and retro-reflector unit, which are both suitable for outdoor use. As option a portable, battery-powered version of the LaserGas II OP is available containing a control keypad and a flash memory for data logging. Different path lengths between 1 and 500 m are easily measured by entering the selected distance (automatic phase correction included in HW).

Measuring principle

LaserGas II monitors employ the measurement principle known as ''single line spectroscopy'', which eliminates cross interference from other gases. A single gas absorption line with no interference is chosen in the near IR spectral range and scanned by a single-mode diode laser. A retro-reflector located opposite to the laser reflects the light back to the transceiver. A detector collects the returned light for further analysis and calculation of the gas concentration.

Installation and Operation

The LaserGas II OP monitor is easy to install using a special x/y alignment platform or tripod for the transceiver and rigid platform or tripod for the retro-reflector. A visible aiming laser and sighting optics simplify alignment even over long distances. For installation in hazardous areas an ATEX approved EEx P solution is available. The instrument contains no moving parts, thereby limiting preventive maintenance to visual inspection and cleaning of optical windows. A fan is advisable in rough industrial environments to prevent dust from fouling the optical windows. Calibration checks are recommended every 6 - 12 months.

Table of Gases



Detection limit

Min meas. range



0.008 ppm

0.006 mg/m3

0 - 0.6 mg/m3



0.003 ppm

0.004 mg/m3

0 - 0.4 mg/m3



0.001 ppm

0.001 mg/m3

0 - 0.1 mg/m3



0.15 ppm

0.23 mg/m3

0 - 20 mg/m3



0.002 ppm

0.001 mg/m3

0 - 0.1 mg/m3



1.5 ppm

1.9 mg/m3

0 - 200 mg/m3


CO (low conc)

0.015 ppm

0.019 mg/m3

0 - 2 mg/m3



0.75 ppm

1 mg/m3

0 - 100 mg/m3



0.25 ppm

0.5 mg/m3

0 - 50 mg/m3



0.01 ppm

0.007 mg/m3

0 - 0.7 mg/m3


NH3 + H2O

0.01 ppm

0.008 mg/m3 / 0.003 %

0-1 mg/m3 / 0-0.3%


HF + H2O

0.001 ppm

0.001 mg/m3 / 0.001 %

0-0.1 mg/m3 / 0-0.1 %


NOTE: Detection limits are specified as two standard deviations for 100 m optical path length and gas temperature / pressure = 25 °C / 1 bar abs. Other gases are available on request.

 Main applications

The LaserGas II OP monitors play an important role in continuous monitoring across a wide range of industrial applications. The following are some of the most typical applications:

·        Monitoring of production halls (e.g. Aluminium smelters)

·        Leak detection

·        Gas fencing in the proximity of industries

·        Fire protection

·        Monitoring of traffic exhaust

Ankersmid M&C bvba,  (32) - 3/820 80 01