Silo weighing for inventory control

In a move to improve efficiency, BP Performance Films has recently installed six new silos fitted with weighing systems for inventory control supplied by Vishay Nobel

The silos receive raw material in the form of polyethylene pellets or resin of various grades.

The pellets are extruded into film, which is then further processed on site.

Following this, the film is printed to customer requirements and converted to finished products.

These include bread bags, diaper bags and carrier bags.

The Vishay Nobel weighing systems have been incorporated into the BP inventory management system and have proved to be a cost effective investment.

The BP Performance Films group is using one weight output to display the silo contents level and the weight on an HMI type display, configured to display vessel graphics.

The other output, connected to a modem, is use by suppliers for access to the raw material status.

This enables the product level weight values of each silo to be integrated remotely and the new deliveries arranged without the intervention of BP employees.

Previously, this would have meant checking stock levels on a regular basis, checking availability of the product, raising orders and organising delivery schedules.

Each outdoor raw material storage silo is supported on four double-ended N3500 series load cells.

These have been supplied in an all stainless steel construction, making them ideal for outdoor installation.

The double-ended load cell design allows the load cell beam to be supported at each end by the base plate assembly.

The beam is fitted into the support frame/base plate assembly and held in position by loading pins, which are in turn held in place by keep plates.

The beam is loaded in the centre by a load bar to form part of the top plate.

This arrangement is designed to accommodate some installation mis-alignment, which simplifies the installation and saves both time and cost.

The load cell design also incorporates a self-jacking feature, which, when engaged, permits vessel installation with the beam removed.

This can save on the potentially costly replacement of load cells, where welding or mis-handling of the silo can cause shock or fatal overloads.

The four load cells are wired to summation terminals and are fitted inside a locally mounted enclosure, which also includes the AST-3P weight transmitter.

The AST-3P is a DIN rail mounting module, providing both 4-20 mA and RS485 MODBUS outputs.

The transmitter can be set-up locally via the multi-function push buttons and integral display, or remotely on a laptop using the Vishay Nobel Delta Com software package.

The AST-3P is a high performance instrument with over eight million internal counts.

Should a unit ever require changing, the existing calibration values can be re-entered (or down loaded).

Since the calibration values are set up so precisely, the system does not require re-calibration.

This effectively means that production down time is kept to an absolute minimum.

The task can be carried out easily by a plant technician, ensuring a speedy return to production.

The module is design to operate from 24V DC, but, in this case, a mains power unit was included to suit the local voltage supply.

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