LM 3189 R9PF TLG is designed to allow installations in more challenging locations compared to the original LM 3189 version which is the most cost-effective dust monitor model, equipped with a semiconductor laser. It is excellent for measuring medium to long distances (3 - 10 m) and medium high concentrations. (> 25 mg/m3).

Improved LM 3189 R9PF TLG design

  • Includes laser head protection glass assembly which increases protection against humidity and dust
  • 9-point purge air distributor to eliminate problems caused by pressure variation in stack

These improvements will provide longer, constant operation time as service breaks are needed more seldom than with the standard LM 3189 unit.

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 a small physical size due to the 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 holes, 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 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