Products - Aerosol Spectrometers - PROMO® Overview

PROMO® Aerosol Spectrometers for Process Monitoring

White Light scattering at 90°90 Degree Light Scatter

The PROMO® aerosol spectrometers are an innovative range of products which use white light scattering at 90° to analyse particle size distributions in gases and liquids designed for use in process industries.

With a wide range of sensing heads, an interchangeable cuvette design for the fluid sample flow chamber, digital signal analysis and a unique design of measuring volume giving coincidence—free measurement, the PROMO® range offers the largest selection of different sensor options for measurements in the 200nm - 105µm particle size range. A built in touch screen PC allows stand alone continuous monitoring and control with industry standard control system interfacing capability.

The product range is made up of 2 models with interchangeable welas® sensors:

PROMO® 2000 - single remote sensor aerosol spectrometer using fibre optic cable technology to locate sensor array and source in the control unit, enabling sensor placement upto 50 meters from the control unit. Size range 0.2 µm - 105 µm at concentrations to 106 particles / cm3.

PROMO® 3000 - unique twin remote sensor aerosol spectrometer using fibre optic cable technology to locate single sensor array and source in the control unit, enabling quasi simultaneous measurements at two points in a process. Sensor placement upto 50 meters from the control unit. Size range 0.2 µm - 105 µm at concentrations to 106 particles / cm3

Well defined 2-stage T Sensing Zone

The welas sensors use a detector array to detect the intensity of light scattered by particles moving through a sensing zone. White light from a Xenon source is focused onto a sensing zone volume in the sample flow.

The intensity of white light across the full illuminated area of the measurement zone is relatively uniform, in comparison with the intensity distribution generated by a monochromatic source such as a laser. The scattered white light intensity at 90° for particles in the region 0.1 µm to 5 µm (‘Mie’ scattering region) is also a relatively smooth relationship (compared with monochromatic laser light intensity), allowing excellent resolution of particle sizes in this size range and allowing a simple method for calibration.

Intensity v Particle diameter @ White light at 90deg
Intensity v Particle Size Laser at 90 deg

A major patented development in the sensor design is in the definition of a T shaped sensing zone. The volume of this zone is varied to enable the measurement of individual particles passing through it at high and low concentrations. The T shape allows the instrument to correct for both border zone error, (occurs when only a portion of a particle passes through the measurement zone, it is measured as smaller than it actually is, so distorting the distribution smaller) and coincidence, (occurs when two particles or more pass through the measurement zone simultaneously and are measured as a single particle, so larger than the individual particles distorting the distribution larger).

Coincidence error increases with concentration and therefore for higher concentration measurement it is important to reduce the measurement volume. The easily interchangeable welas® sensors allow the selection of the correct measurement volume for the aerosol characteristics being measured.

T Aperture SchematicThe T shape of the measurement zone allows particles which would be measured in the border zone to be eliminated from the measurement analysis, but then statistically assessed for true size and added for a better resolution of the aerosol distribution.

Particles passing throught the top of the T section but partially or not throught the leg of the T can be identified as either not counted or as a border zone particle. The signal might look like the following for 4 particles passing through each area of the T and so border zone error particles can be identified making the instrument very powerful and accurate in assessing particle sizes passing through the measurement area.

4 Particle Tracks through the T zone Scattered Intensity for 4 particles