Laser diffraction analysis of various metered dose inhalers, pump and propellant gas sprays with droplets or solid particles from 0.25 µm to 1,750 µm in flexible measurement arrangement, especially with large spray cone angles

The laser diffraction sensor HELOS/KR-Vario in combination with the flexible actuator SMACTOR is designed for particle size analysis of a wide variety of sprays. Droplets or solid particles from MDI, pump or propellant gas bottles are analysed reliably and reproducibly in the range from 0.25 µm to 1,750 µm. The open, width-variable measuring zone, together with a versatile universal rack, supports adaptation of the optical measuring system to customer-specific requirements.

In order to achieve reproducible measurement conditions, a wide range of parameters must be taken into account that play a role in the formation of a manually actuated spray. These include, for example, the force and acceleration conditions during the application of the atomizer as well as the distance and orientation of the spray in relation to the measuring zone. In the HELOS & SMACTOR system, the key measurement and actuation parameters can be documented, controlled and stored as retrievable measurement methods (Standard Operating Procedures (SOPs)) with the software.

The intelligent force and trajectory actuator SMACTOR simulates individual thumb and actuation processes. The force mode ensures the spray is actuated with a definable, constant maximum force and its rise time by pushing the actuator piston onto the actuation mechanism. In the trajectory mode, the atomizer can be actuated with a motion path for the actuator piston that is defined by the travel (stroke), acceleration and maximum velocity. A profile mode allows more complex travel/time profiles to be stored. The predefined profile is run during the next spray stroke. The use of controlled actuation processes by the actuator not only supports the establishment of reproducible measurement methods, but also enables the investigation of any undesirable user influences.

Together with a universal rack, SMACTOR can be used in free experimental set-ups. The rack with spring-loaded holding mechanism adapts flexibly to manually operated sprays and enables a variety of different spray applications. Aerosol generators or atomizer nozzles with their spray cone can be directly positioned in the measuring zone of the standard profile, which offers a working depth of up to 1,400 mm. With the separable housing components of the HELOS/KR-Vario, it is also possible to integrate special structures such as spray chambers in a measurement setup. Here, the light source and detector are mounted on their own profiles, positioned and adjusted – if necessary even over larger distances. Optional purge air nozzles ensure low contamination of the optical components and thus support the high availability of the overall system.

For the investigation of dynamic changes in the particle size distribution of an aerosol cloud or of a spray cone, a time-resolved data acquisition (pulsed measurement) is recommended. With a frequency of up to 2,000 measurements per second and a measuring duration of up to 1,000 seconds, the dynamic behaviour in continuous spray processes can also be tracked. If, by contrast, an averaged droplet size distribution over a longer period of time is of interest, then it is possible to start an individual measurement that integrates the measurement data over the defined period of time.

With time-segmented measurements, a subsequent investigation, selection and summary of time segments within a measurement are possible. This allows both temporal changes in droplet size distribution during the measurement to be investigated as well as location-dependent distributions of droplets recorded at different positions of the spray cone during a measurement. Multiple separate measurements are not required. Reports and diagrams document and visualise not only the droplet size distribution but also the temporal course of all data of the measurement as well as the segment selection on which the result is based.

The modular concept of the HELOS laser diffraction series allows this configuration to be systematically expanded with numerous dispersion units and dosing options to open up many more product-appropriate measuring applications.

  • Particle and droplet size distribution
  • For aerosols and sprays from MDI, pump or propellant gas bottles
  • For analyses in laboratories and pilot plants
  • Time-resolved, time-segmented and time-integrated measurements
  • 5 high-resolution measuring ranges from 0.5 µm to 1.750 µm | R2 to R6
  • Variable measuring zone from 123 mm to 1,400 mm with the standard profile
  • Measuring zones in excess of 1,400 mm are possible in a free arrangement