LM 3189 is the most cost-effective dust monitor model, equipped with a semiconductor laser. It is excellent for measuring at the medium to long distances (3 - 10 m) and medium high concentrations. (> 25 mg/m3).

The system setup

  • The transmitter unit L 318
  • The receiver unit R 318
  • The monitor unit M 318
  • Purge air unit or the external instrument air source
  • Optional data logging software available


  • Direct continuous measurement of opacity or optical density
  • Small, lightweight and easy installation
  • No moving parts and simple optics for long life operation
  • Light source is a semiconductor laser
  • Adjustable alarm values and alarm relay
  • Linear voltage output 0 - 1 V and current output 4 - 20mA
  • Digital LCD-display and analogue display for D-value
  • 4 operation ranges (0 - 0.03 D, 0 - 0.1 D, 0 - 0.3 D, 0 - 1.0 D)
  • Low maintenance requirements and small physical size due to simple optics

Advantages of a semiconductor laser

  • A very compact and intense light beam, the diameter is only a few millimetres. This means that only small hole, about 20mm, are needed in the stack simplifying the installation and requiring less purge air for the transmitter.
  • Good stability and long life. In contrast to designs that use more traditional light bulbs, needing constant compensation, the laser source is relatively immune to the aging effect. The typical life span of a semiconductor laser is up to 10 years.
  • Due to the high intensity of the laser the device can easily penetrate also higher dust densities
  • Operation with known, clearly defined wave lengths. This makes the theoretical calculations and their results more predictable as opposed to conventional sources that operate over a broad range of wave lengths and whose spectrum changes with age.

Typical applications

  • Continuous particle emission control in applications, where the measuring path is max 40 meters
  • Max. dust content 2 g/m3
  • This model is most commonly used in power plants burning oil, coal or bio-fuel, in cement plants or in steel or iron furnaces