Weigh to integrate

In today's manufacturing industries, many applications need reliable weight data to manage the bulk materials handling process - whether bag filling, belt weighing, vessel, tank or silo monitoring or measuring throughput rates.

Trade approved or non-trade, weighing is a tried and tested form of process measurement. It is simple to implement, easy to operate and highly accurate.

Aside from the necessary function of recording weight for sale or supply, there is a growing trend to reduce costs, increase operational efficiency and comply with legislation that determines the quality and safety of product. Increasingly, companies are seeking to accomplish this by integrating of the data from weighing equipment into the plant management systems.

Installing the right load cell assembly is the key to a successful vessel weighing system.

Before choosing a system, operators should work with the supplier to implement the ideal design for the application, matched with rigorous load cell manufacturing and test routines for total reliability.

Some manufacturers offer fast-fit assemblies that require no additional restraint for wind forces and climate conditions, making them ideally suited to harsher environments exposed to the elements.

The load cells mountings should also be engineered to allow for any misalignments in steelwork and vessel expansion and contraction.

One manufacturer chose an Avery Weigh-Tronix vessel weighing system to monitor the mortar levels in remotely-located 50tonne silos. The installed load cells send data to programmable indicators at each site, which in turn relay the information to Head Office via a GSM link. This enabled the company to determine which silos were running low and plan delivery routes to restock.

Most manufacturers will be able to offer a range of industry-standard interfaces, including Ethernet, Fieldbus, Modbus and Profibus, plus serial communications and modem link, to suit existing networks. This can save processors valuable time and expense on costly system modifications and is ideal for retrofit applications.

HTTP protocol via a web browser is another choice and can provide monitoring and data acquisition and SMTP email alerts can give operational updates and error reporting.

<b>Belt weighing systems</b>

Continuous weighing systems are common in sectors such as extraction, quarrying, food processing, cargo weighing and grain handling applications. Each of these applications has its own requirements, making it important to choose a belt weigher that provides the ideal functionality to accurately monitor product throughput.

Operational factors will determine whether a new system is required, or whether a belt weigher can be retrofitted to the existing conveyor. These will also affect the choice of mild steel or stainless steel equipment and the maximum capacity required for the application.

A correctly specified system can contribute to effective process management by providing information to manage costs, waste and efficiency in the weighing processes. Systems can be connected to PCs, printers and other devices for greater management information and control, providing real-time information on batch totals and feed rates to very high accuracies.

A power station chose an Avery Weigh-Tronix solution when it began a programme to reduce fossil fuel consumption and harness the energy from pine kernels. In implementing the belt weighing system, it was able to reduce paperwork, save process time and increase plant efficiency.

Its existing conveyors were converted with new digital instrumentation and a new belt weigher was installed. All the belt weighers communicate back to an industrial IP65-rated programmable terminal.

<b>Bag and sack weighers</b>

The system is monitoring the rate of flow, which allows the plant control station to control feed levels to the furnace. The system was simple to install thanks to the terminal's PLC flexibility and extensive networking capabilities, which could be matched to the plant's existing methods. The plant has now fully automated this part of its process and is also assured of reliable, meaningful data.

Bag weighers range from single mechanical units through faster electronic machines up to high speed automated systems at the top end of the market. Equipment can be categorised into three types, depending on whether it has a gravity, screw or belt feeder. The choice of feeder depends on the particle size of the material being filled. Free flowing materials such as sugar, plastic pelts, barley and lentils require a gravity feeder. A belt feeder is suitable for coarse ration or 'meal' type products such as animal feed pellets.

It can often cover a wide variety of materials to be bagged by the same machine. Powdery products such as flour or limestone-based carriers need a screw feeder.

A supplier should carry out a survey of the site to ensure the system meets all requirements. This will take into account factors such as the bulk density of the product when it is loosely packed, the maximum and minimum weights to be filled, and the throughput required.

Digital indicators and dedicated weighing software offer significant benefits for many bag and sack filling processes. The information they provide can help plant managers monitor quality control, reduce wastage, manage processes remotely and maximise throughput. Bag weighing software is designed to help analyse applications such as average weight monitoring.

Packages range from simple data capture programmes to an integrated management system for an entire process. By integrating these packages into existing systems, management can enhance control across production and, with local or remote access; can easily keep up-to-date with the entire operation; even when it is spread over a number of sites.

Many processors have a more specialised requirement for weighing equipment for use in hazardous areas. Recent legislation specifies new safety regulations for equipment used in explosive atmospheres to ensure their absolute safety, from the design and test procedures put in place by the manufacturer, to the health and welfare of operatives working.

Approximately 75% of dusts are explosive and therefore represent a potential safety hazard. The ATEX directives also include specific requirements for the use of equipment in dusty environments, including many areas handling airborne particles, such as a grain store or a flour mill, which may not have previously been classed as hazardous.

Avery Weigh-Tronix recently specified a number of ATEX-approved throughput weighing systems to breweries handling grain. In these environments, airborne dust is ever present and the company was able to gain Zone 21 & 22 type approval quickly for its weighing system, enabling safe operation within the hazardous area.

<b>Service and support</b>

Proper maintenance and servicing of the process weighing equipment is essential to maintain business efficiency. When choosing a supplier, operators need to consider how critical service support is to the operation and whether occasional support or round-the-clock service, 52 weeks a year is required.

A proper assessment of whether the level of service and expertise offered matches the business requirements will ensure that the weighing equipment, like every other part of the production process, can perform at optimum level to avoid downtime.PE

Stephen Cox is Process Weighing Marketing Manager for Avery Weigh-Tronix.