Loma Systems: Efficient checkweighers thanks to a digital load cell

The world's most advanced range of checkweighers depend on HBM's FIT (Fast Intelligent Transducer) load cells to handle products at the highest production line rates with very high accuracy and no performance degradation.

The FIT load cell is a key component of the AS range of checkweighers recently launched by Loma Systems of the UK to weigh both rigid and flexible packs of up to 45 kg.

The AS checkweighers from Loma have been awarded the European R51 accreditation for the high accuracy and rapid response demanded by food producers for improved performance and rapid production.

"We needed a high performance load cell for use in the food and pharmaceutical industries, which meant it had to be made of stainless steel and able to handle intensive wash downs. This means that neither water nor chemicals can ingress the load cell." (Andy Alexander, product support manager of Loma Systems)

FIT for dynamic weighing applications

HBM's FIT load cell is specifically designed for dynamic weighing applications because it features high torsion and bending stiffness. Extensive signal processing is integrated into the digital load cell enabling access to all the functions needed for fast and accurate measurement of the weight. With its 20-bit resolution, FIT produces an output rate of up to 600 measurements/sec.

FIT prevents seal failure

Using a digital load cell overcomes problems on earlier models of checkweighers that were fitted with analog load cells. These load cells were viscous damped and experienced a number of problems including seal failure resulting in oil leaks and measurement inaccuracies due to thermal instability.

No temperature compensation required

Unlike analog cells, HBM's FIT does not need temperature compensation and its weighing range can easily be set by the user avoiding any pre-calibration.

One of the key aspects in the design of a checkweigher is its ability to minimize external influences, since these can have a negative effect on the accuracy and performance of the machine. These include things such as floor vibrations in the proximity from other machines or plant. Vibrations induced by the checkweigher conveyor belt can also have a negative effect on the performance and, at small nominal loads, even the effect of air pressure surges caused by the opening and closing of doors and windows can affect measurements adversely.

Digital filters protect from interference effects

The design of the AS range of checkweighers takes these factors into consideration and the FIT load cell gives additional advantages since it is easily calibrated at the start of a production run to ensure accuracy. In some cases external factors may still cause variations in weight to be indicated and the FIT load cell has a nine digital filters that can be applied easily to ensure that all unnecessary background static is removed without degrading the central measurement.

"The built-in programmable filters allow us to maximize the response time for different customers' applications." (Andy Alexander)

FIT provides programming functions

The Loma AS range incorporates the FIT load cell programming functions into its central menu-driven membrane keyboard to ensure integrated access to all aspects of the machine. Loma's research shows that 90 per cent of users do not use the full capabilities of their checkweighers. To overcome this issue, Loma has made the use of its AS range as intuitive as possible and it can be programmed with the parameters for up to 100 different items in a core database.

Password protection for AS series

As part of its security measures the keyboard on the AS range allows each section to be password protected so that operators, for example, cannot alter programmed functions. However, the keyboard will allow operators to change easily the product being weighed for different batch runs without needing to access the product's parameters. The panel also gives access to the FIT load cell to provide an analysis of inconsistent or abnormal readings. The control panel is located at waist height to ease access to the control panel.

There are five models in Loma's AS range including the AS Combo that features a combined metal detector and checkweigher. Four of the models weigh both rigid and flexible packs of up to 5 kg while the AS Heavy Weight checkweigher is designed to weigh sacks and cases of up to 45 kg.

The robust checkweighers are made of stainless steel and are available as stand-alone units or can be supplied with a metal detector head. The range benefits end users since each major component, such as the control unit or the conveyor feeds, are modular and can be located in alternative positions to provide the most suitable and functional layout required and to fully integrate with other equipment on the production line. The system also comes with a wide range of different weighing table and rejection mechanisms to ensure that customers are provided with a bespoke machine.

"It is the load cells that weigh the product and this information is critical to the performance of the checkweighers."

"We have had excellent technical support from HBM throughout this project."
(Andy Alexander)

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