Strona 2_redak - Instytut Agrofizyki im. Bohdana Dobrzańskiego ...

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efficient flow control using optical methods. Harvill et al. [60] described one of
such devices, based on laser diffraction of light and used in a large range of
laboratory and industrial applications. Measuring unit consists of an optical head,
interface, pc and software. Stream of particles flows through the cylindrical
channel across the laser light beam. Velocity of the stream does not influence the
result of the measurement. Scattered light passes through the receiver lens and is
focused on the log-scaled annular ring detector. The detector is scanned by the
interface with high speed and levels of signal on the separate rings are recorded.
Each ring of the detector measures the total signal intensity. Each particle scatters
light on all rings of the detector, therefore the measured signal is the summation
of all the light scattered from all particles. After acquiring a significant number of
scans, relative particle concentration is calculated by the software. The instrument
allows for efficient determination of both particle size distribution and particle
concentration directly and in real time. It has been successfully used in production
of pharmaceuticals for optimization of the mill. The instrument provides
continuous feedback control to compensate for mill-setting drift, wear, operator
errors, variations in raw material etc.
Like in pharmaceutical industry, in-line process control may increase
efficiency of food industry. The basic factor in food product quality is its structure.
Bijnen et al. [18] analysed current trends in development of process sensors in food
industry. Market requirements enforce precise process control. The development of
these new process regimes requires better understanding of the structure-processequipment
relationships. Precise in-line measurements become necessary. Basic
attributes of product microstructure are: overall product composition, properties and
state of all phases, distribution properties of dispersed phases and spatial organization
of dispersed entities. The authors reviewed methods that might be applied for
in-line measurements and pointed out their limitations.
ƒ Sensors for the determination of product composition (the content of: water,
fat/oil, carbohydrates, and proteins) currently achieve a relative accuracy of
0.1 to 1%. These are often sufficient, but the calibration procedures (if any)
in a rapid changing product portfolio should be minimal.
ƒ Sensors for monitoring the state of phase will be mainly applied for
understanding the basic phenomena underlying the process, for development
of new processes and process control. The use of laser-based
acoustic pulse sensors and detectors seems promising for monitoring the
properties of phase state because of the flexibility due to remote sensing.
In-line quality assessment will remain often difficult because in many food
products the final state of phase (rate of crystallization or gelation) is
formed after the filling operation and during storage.