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168 Erol Murad et al.
harvest of products which require drying; for this reason it is necessary a high
level of energy independence and high reliability. [ 5] - [7], [9], [10].
For optimizing the drying process is still necessary to measure the mass of
water extracted during the drying process. In order to reduce production costs of
the dryer, the measurement is performed for a sample represented by one or
more boxes of dry suspended on a force transducer.
To simplify design, transducer should be arranged in the drying chamber at
high temperatures and high humidity. In papers [5], [6], [9] have been examined
these issues and therefore was developed a pneumatic force transducer,
unconventional, which is adapted to operating conditions of convective dryers
and requires only 63mW electrical power and 5mW power air power. [12] - [14]
Optimal management of drying processes requires online measurement of
the variation of water extracted from the dried bodies during a drying.
Constructive solution for measuring the change in weight of a column of tray is
technically complicated and expensive. Hence, it is used a weight measurement
of the change in middle column boxes, specifying that the drying process has a
similar evolution throughout the column height. It should be noted that the
temperature in the drying is in the range 50...80°C, therefore, was decided to
use pneumatic sensors for measuring forces, because measured size, pressure, is
not influenced by changes of temperature. [4] - [6]
Convective dryers consume more thermal power and about 8% electrical
power, required for operating the fan and automation system. [8], [10]
This paper presents and analyzes the operation and performance of a
scheme for measuring on-line weight of boxes loaded with dried material using
a pneumatic force transducer working under sampled. The solution presented is
remarkable due to very low energy consumption and a reduced price. The
measurement system is coupled to dedicated leadership PLC automatic dryers.
They use basic concepts of low cost automation, minimize energy
consumption and not least are extremely efficient economically.
2. Pneumatic Force Transducer
Applying concepts of minimizing energy consumption, energy
independence and low cost automation system was designed an unconventional
pneumatic transducer which does not require special source of compressed air
consumption is very low, which simplifies construction, and hence the cost
transducer, and the total energy consumed is very small.
It was chosen a pneumatic system because of the pressure signal, that is
proportional to the measured weight, which is not influenced by environment
temperature of measurement, and accuracy is high.
The main element of the force transducer is pneumatic load cell, which
converts measured force Fmas in a force proportional pressure pmas.