36 food & drink processing
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valves automatically, eliminating the need for the constantly, even when the valve is at rest. This can
wasteful venting of control air normally associated with average the equivalent of a 0.75kW (or one-horsepower)
pneumatic tubing between the process valve and its in compressed air for every twenty valves in operation; a
related control solenoid valve. large process site can therefore be using a vast amount of
The control heads integrate electrical and pneumatic energy – unnecessarily.
control components as well as position feedback units Choosing the option of an embedded PID process
and, optionally, fieldbus interfaces for AS-Interface or controller, working in conjunction with the positioner,
DeviceNet. They are mounted directly above the valve provides a fast-acting, decentralised control loop
body, and, because there is little or no distance between in combination with the associated process sensor.
the actuator and the valve that it is piloting, there is no This arrangement also reduces complexity and saves
air bleed: it is sealed. With this system the pressure feed unnecessary components and wiring.
goes directly into the valve head and the control signal is Where the problem is wastage rather than energy
supplied either from a local closed loop control sensor or reduction, this can be improved greatly by accurate
switch; or from a PLC/machine controller via a control monitoring of process fluids, using new, innovative
bus – AS-Interface or DeviceNet – or multipole (parallel) techniques of pH and conductivity measurement, as
directly into the valve. provided by Burkert’s new 8201 and 8221 units. With
Similarly, adopting digital positioners with integral probes made to the highest standards of surface finish,
solenoid valve control heads for regulating modulating and with the use of glass-free, food quality materials, the
process control valves will automatically lead to air opportunity now exists for measuring and controlling
savings, as these will normally ensure zero-air use in their process lines during production and cleaning. p
stable state. The traditional technique of process valve
positioners incorporating pneumatic Burkert Fluid Control Systems is based in Brimscombe, Stroud,
flapper-nozzle systems means that air is being bled Gloucestershire, UK. www.burkert.co.uk
real time process control for food manufacture
r
eal time process control for food leads the research team. “to achieve the mixer’s rotating shaft to monitors
manufacture has come a significant this the sensor has to be pretty special variations in its resonance frequency as
step closer, thanks to pioneering research to detects the changes with sufficient the torsional load varies. an rf (radio
work at university college dublin into sensitivity, yet be robust enough for regular frequency) link is used for wireless
viscosity measurement techniques for wash-downs and general industrial abuse. transmission of signals to an adjacent pick
characterising the flow and mixability of of course it must not compromise hygiene up so that rotation is unhindered.
highly non-newtonian fluids. at the heart standards and regimes either. We tried a pJ cullen and his colleagues have
of the researchers’ experiments is the number of sensors and torqsense stood out simulated food processing techniques
torqsense transducer made by sensor as by far the best at meeting all our needs.” in a number of different laboratory rigs,
technology, which monitors the constantly one of the most used being a helical
changing flow characteristics of materials ribbon mixer similar to those employed
as diverse as tomato ketchup, chocolate, by manufacturers for mixing ingredients
pasta sauce and chicken tikka massala as together. often the key requirement is to
they are mixed. mix sufficiently to achieve a uniform dish,
ireland’s national economy has always but not to waste time and energy by
had a strong agricultural element and over-mixing.
more recently considerable value has been “We do this by monitoring the torque
added to this by becoming one of europe’s on the mixer’s shaft, as it will move to a
foremost manufacturers of processed steady state (within the characteristics of
ingredients and ready meals. the given recipe) once fluid uniformity is
many foods are presented in a sauce or achieved,” says pJ.
as what physicist could describe as a neo- torqsense embraces all the advantages
liquid and can be produced in a process- of saW technology, including no load
type environment. But to date real time torqsense uses surface acoustic imparted to the drive mechanism
control has been virtually impossible due to Waves techniques to provide non-contact under investigation, a broader signal
the non-uniform nature of the food, which monitoring of instantaneous rotary bandwidth than other analogue based
may contain particulates, fibres, vegetables, torque, allowing accurate modelling of technologies and elimination of electronic
meat, nuts, raisins, biscuits etc. the instantaneous load changes. it is in interference. p
“real time process control is vital if effect a frequency dependent strain gauge
food processors are to achieve the ultimate operating at ultrasound frequencies and for more information, visit
in product quality,” says pJ cullen, who consists of a transducer mounted on www.sensors.co.uk
www.scientistlive.com
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