Drives are the
apple of a cider makers eye
Making cider relies on a constant supply of water and at Inch's Cider,
part of the Bulmers group, the maker has its own water supply and
a novel way of maintaining accurate pressure in the system. Inch's
Cider found that mains water pressure varied according to the time
of year and yet needed too maintain a steady 6 bar pressure irrespective
of demand within its system. Nick Forrester, Inch's Cider's engineer,
devised a system whereby the standard PID control features of an
Hitachi J300 inverter could be deployed to control the high delivery
pump.
Two
stainless steel pumps with 37kW 2-pole motors are fitted within
the system to enable dual redundancy. The pumps, which are switched
periodically to share the duty, are controlled by a fan and pump
rated 30kW Hitachi J300 drive supplied and commissioned by HID.
Pressure sensors located in the pipeline feed a 4-20mA signal directly
to the Hitachi J300 which ramps up the motor as soon as the pressure
starts to fall. To maintain a pressure above the PID control's set
point when demand is low, a simple "donkey" pump is employed - the
pumps do not need to switch in every time a toilet is flushed! Throughout
the commissioning stage, Nick Forrester had a high level of support
from HID's engineering team.
Another Hitachi drive is employed to maintain the pressure from
Inch's two bore holes. These holes - one of which is 200 feet deep,
the other 180 feet - were sited thanks to the help of a water diviner
and supply water for the cider makers' critical cooling system.
The cider must be maintained at a constant temperature for the fermentation
process to be successful. The water is pumped through a heat exchanger
and a line pressure of 2 bar is required. Again, a 30kW Hitachi
J300 is used with PID control.
A further Hitachi inverter is used in the recipe mixing process
to govern the level in a reservoir tank where the cider recipes
are mixed. This complicated application demands that the reservoir
level is maintained even though fill rates vary. Hence, the drive
must control the rate of emptying to keep a constant level in the
tank. The application makes use of PID control but with a useful
feature of the drive's programming to enable the 4-20mA signal to
be scaled. Using the Hitachi inverter's EXS command for the start
point (0 or 1Hz) and the EXE command to set the end point, the 4-20mA
signal can be reversed to expand the band width. The signal is received
from an ultrasonic level probe mounted in the reservoir tank.
The cider process at Inch's Cider, Winkleigh, Devon, site starts
with the apple crushing, before fermenting and then storing the
resultant cider. The cider is then blended to a recipe before the
finished product is transferred by tanker to the bottling plant.
Like any high volume manufacturing process, plant reliability is
critical - another reason the Hitachi drives were selected.
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