Hitachi inverters are the apple of a cider maker's eye
April 1998

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 to 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 inverter supplied and commissioned by HID. Pressure sensors located in the pipeline feed a 4-20mA signal directly to the Hitachi J300 inverter 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 inverter 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 inverter 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 inverter 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 inverter'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 inverters were selected.

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