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Industrial inverter drives from Mitsubishi Electric are helping bring cold-stored fresh produce gently back to ambient temperature to ensure perfect condition for sale to discerning consumers.

Crop Systems, based in rural North Walsham, Norfolk, designs and installs potato and crop-storage controllers and equipment for farmers, growers and produce suppliers.

‘If you take, say, potatoes out of cold storage and let their temperature rise in an uncontrolled manner, you risk impairing flavour, texture and appearance,’ said Crop Systems’ Ray Andrews.

‘You can also make them more prone to shattering and other handling-related damage,’ he said.

‘In the past this was acceptable, but the constant march of quality standards means we have to reduce this problem and thus give our customers an edge over their competitors,’ Andrews added.

The basic concept Crop Systems has developed is a 14-bay batch-warming facility.

Potatoes are transferred from storage to a bay, where a controller is set to provide gradual warming to a set point temperature over a specified period of time.

The target temperature varies between 4 and 10.5C, and the time is typically 3-5 days.

This isn’t a simple open-loop linear warming; parameters such as humidity and carbon dioxide concentration are monitored and controlled throughout the process.

Looking at storage, newly harvested potatoes have a high moisture content that needs to be reduced over the first few weeks.

The Evolution is designed with an automatic load cure program, this keep the fans running at an economical speed until the stock has settled down.

The potatoes also emit heat, which, if left to build up, would compromise storage; the fans adapt their speed to compensate for different conditions.

‘We have also developed an automatic fogging program so that we can better address the distribution of ‘cleaning in place’ fog within the storage area and we have proven that ‘stirring’ and re-circulating the air at reduced air speeds helps give far better efficacy and extends the fogging intervals dramatically – this speeds the payback period to less than 18 months in some cases,’ said Andrews.

Central to the storage processes above is the use of an F740 variable speed drive from Mitsubishi.

The F740 is the fan-rated version of the F700 range of drives and offers improved motor efficiency during constant speed operation and acceleration periods, and optimum torque patterns that accurately match the power delivered to that required at any instant.

The speed of optimisation is effectively instant, so the drive is always giving maximum performance and efficiency to the load.

Mitsubishi Electric Automation Systems

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