Rank Brothers Ltd

PDA3000 Particle and Flocculation Monitor

PDA3000 Particle and Flocculation Monitor

The PDA3000 is a simple, rugged, but very sensitive monitor for flowing suspensions and emulsions, especially for assessing their state of aggregation. The method is based on the Turbidity Fluctuation principle and was originally developed at University College London. The unit is very compact and lightweight.

Applications include:

Some advantages of the PDA3000 over other techniques are:

Principle of Operation

The flowing suspension is illuminated by a narrow beam of light perpendicular to the direction of flow. For the PDA3000, a novel flow cell has been developed; transparent flexible tubing fits in a detachable block that houses a light source (miniature light-emitting diode) and a sensitive photodetector. The LED has a wavelength in the near infrared and the detector response is closely matched to this. The sample flows through transparent plastic tubing located in a slot between the light source and detector. A narrow light beam passes through the flowing sample by means of two aligned pinholes about 1mm in diameter. The standard cell is designed for tubing of 3mm bore, but other cells, for 1mm bore and 5mm bore tubing can be supplied.

The output from the photodiode is converted to a voltage, which consists of a large average (DC) component, together with a small, fluctuating (AC) component. The DC component is simply a measure of the average transmitted light intensity and is dependent on the turbidity of the suspension. The AC component arises from random variations in the number and size of particles in the sample volume (i.e. the volume illuminated by the light beam, typically of the order of 1mm3 with a 3mm bore tube). Because the suspension flows through the cell, the actual sample in the light beam is continually being renewed and local variations in particle number and size give fluctuations in the transmitted light intensity. These fluctuations cease when the flow is stopped.

The root mean square (RMS) value of the fluctuating signal is related to the average number concentration and size of the suspended particles. For fairly uniform suspensions, estimates of particle size and number concentration can be made, but the main use of the PDA3000 is in the monitoring of flocculation and dispersion processes.

The RMS value of the fluctuating signal increases when aggregation of particles occurs. Measurable changes in the RMS value occur long before any visible signs of aggregation are apparent. Conversely, when aggregates are broken, the RMS value decreases, reaching a minimum when disaggregation (or dispersion) is complete. The DC value (related to the turbidity) is much less sensitive to changes in the state of aggregation, but can still give useful information. In many cases, the Ratio value (RMS/DC) is the chosen parameter, since this is not affected by drift in the opto-electronic components or by fouling of the tube wall by adhering particles. The Ratio is often referred to as the Flocculation Index.


The supplied software (Rank Brothers Logger) provides simple operation of the PDA3000, and only a few settings need to be made. The light intensity and sampling interval can be set, and two of the parameters, DC, RMS and RMS/DC can be chosen to be displayed graphically. The software allows numerical values to be saved to a file or exported to a spreadsheet.

Rank Brothers Logger Information


W: 200mm H: 40mm L: 750mm
Cell type 1:
suitable for 1mm bore tubing
Cell type 2:
suitable for 3mm bore tubing
Cell type 3:
suitable for 5mm bore tubing

Operating Manual

The manuals on this website are provided as PDF files, please see the Downloads page for links to reader software.

PDA3000 Particle and Flocculation Monitor Manual

Ordering Information

Order Code Description
PDA020A PDA3000 Particle and Flocculation Monitor with 3mm Cell
PDA021A PDA3000 Particle and Flocculation Monitor with 1mm Cell
PDA022A PDA3000 Particle and Flocculation Monitor with 5mm Cell
PDA133A PDA3000 Cell for 3mm Bore Tubing
PDA134A PDA3000 Cell for 1mm Bore Tubing
PDA135A PDA3000 Cell for 5mm Bore Tubing
PDA300A 1mm tube
PDA301A 3mm tube
PDA302A 5mm tube

Rank Brothers Ltd reserve the right to change specifications in the light of continuing developments.

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