Testing facilities, development labs, and materials research organizations face a number of difficulties: The form and origin of particles can vary greatly; they can be pigment, sand, liquid, powder, tablets, or microplastics. To analyze this variability, labs must learn to strike a balance between accuracy, productivity, and pragmatic needs.
Accuracy and reproducibility are particularly important, as even the smallest deviations in particle size distribution – often in the micro- or nanometre range – can have a significant impact on material properties. At the same time, the high throughput in production environments requires numerous samples to be analysed quickly without compromising on measurement quality.
Innovative technology for dynamic image analysis
This is where dynamic image analysis (DIA) comes in. This innovative technology makes it possible to record a large number of parameters for determining particle size and shape in real time. “Dynamic image analysis has proven itself as a viable R&D and quality control method in various industries. Particles are recorded as they flow through a measuring cell using high-speed cameras or other imaging sensors and then analysed using software,” explains Dr Christian Moitzi, Research & Development at Anton Paar GmbH. The Austrian company specialises in particle characterisation. The devices developed by the company for this purpose are designed to capture high-speed images of moving particles. One of the most important components in their successful dynamic image analysers is a uEye Warp10 high-speed camera from IDS Imaging Development Systems GmbH in addition to the sample chamber and lighting system.
“With the Litesizer DIA series, the size and shape of particles can be characterised easily and reliably by directly analysing the particle images. The most powerful device in the series, the Litesizer DIA 700, can measure particle sizes from 0.5 micrometres to 16 millimetres,” emphasises Dr Moitzi. Thousands or even millions of particles can be visualised in a matter of seconds during a measurement. Thanks to the high frame rate and fast data transmission, it is possible to image an unrivalled number of particles within a short measuring time and analyse them in real time.
One million particles for errors of less than one per cent
“It starts with the preparation of a representative sample. This sample can consist of various materials, e.g. powders, granulates, suspensions or even biological preparations such as cells. As a rule, more than one million particles are required to achieve a maximum error of less than one per cent. Samples are fed in using one of three interchangeable dispersion units, which enables both dry powders and dispersions to be measured,” says Dr Moitzi.
The sample is placed in a chamber in which it is continuously moved or dispersed. Various mechanisms such as vibration, air flow or fluid circulation can be used to keep the particles in motion. The particles, which move through the image field at a speed of up to 30 m/s, are illuminated like stroboscopes. To avoid motion blur, the illumination pulse is shorter than 100 nanoseconds. The magnification can be adjusted by automatically changing three lenses.
The challenge of high-speed processing
“Large amounts of data have to be processed in real time,” says Christian Moitzi, citing an important requirement for the system. The 10GigE Vision high-speed camera integrated with the help of the IDS peak SDK records an image sequence at the required high frame rate and thus enables the observation of fast particle movements.
In addition to the speed, the interface and sensor are decisive for the selection of the camera model. The uEye Warp10 with integrated Sony IMX255 global shutter CMOS sensor delivers everything the demanding task requires: high resolution, high frame rates and noise-free image reproduction. Readout noise and dark current are among the lowest values in the entire sensor market. With its resolution of 5.10 MP (2472 x 2064 px) at 220 fps, the camera is particularly suitable for applications where high speeds are required. The high resolution ensures that even the smallest details are captured.
“Compared to 1GigE cameras, the uEye Warp10 achieves up to 10 times the transmission bandwidth. Together with the combination of high resolution and high dynamic range, the GV-7090WP presents itself as an ultra-fast, powerful all-rounder,” says Marcus Rembold, Product Owner 2D Cameras at IDS, describing the camera model used. The robust, GenICam-compliant uEye Warp10 camera can forward image information in the Gigabit Ethernet-based network with virtually no delay. It therefore shows its strengths precisely in inspection tasks such as this, where objects need to be recorded and analysed in full detail and without motion blur.
Sophisticated image analysis algorithms
“The camera images are transferred to the PC, where they are segmented and various size and shape parameters of each individual particle are calculated,” says Christian Moitzi, explaining the next steps in image processing. “The heart of DIA lies in analysing the captured images. Sophisticated image analysis algorithms and software are used to process the images and extract relevant information about the particles. The user receives, practically in real time, averaged size distribution functions as a result. However, it also has the option of analysing individual particles and filtering images of particles with special properties from the whole.“
Example building materials industry
The analysed parameters provide detailed insights into the properties and behaviour of a material sample. These can be bulk material properties such as density, flowability, ballistics and others. Useful information for sectors such as the building materials industry. “The quality of cement depends heavily on the size and shape of its particles, which affect its surface, compressive strength and curing time,” says Christian Moitzi. Particles that are too fine cause the end product to set exothermically, while particles that are too large do not hydrate completely. The flowability and water requirement of cement can vary drastically between regular (spherical) and irregular particles. These factors can lead to cracking, shrinkage or porosity and thus severely impair the quality, durability and mechanical properties of the cement.
Investing in a dynamic image analyser such as the Litesizer DIA 700, which is equipped with an ultra-fast, extremely high-resolution 10 GigE industrial camera, pays off in the long term. Thanks to fast image processing and precise analysis in real time, process sequences are optimised and production decisions are made on the basis of better data. More precise particle characterisation enables better process control and optimised material usage – for example through more precise dosing and the reduction of faulty batches. The availability of this high-speed camera technology and fast image processing makes dynamic image analysis a particularly attractive, future-proof alternative to traditional methods such as laser diffraction.
