Accurate weight data collection is a vital function within the recycling, anaerobic digestion and energy from waste industries, with weighbridge management systems playing a pivotal role in providing this essential information.

However, the concept of a stand-alone weighbridge and adjacent weighbridge office, housing a straightforward weight indicator and ticket printer, is becoming a thing of the past in more and more applications. Weighbridge systems are now powerful and versatile management tools, playing a much wider role by acting as critical control points for managing the movement of vehicles and materials arriving at, and leaving from sites, whilst collecting and processing vital weight data.

This is changing the way weighbridge systems are required to operate and how they integrate with peripheral vehicle control equipment, safety equipment and established management software systems.

Choosing the right weighbridge system

There are a number of critical design and operational issues which potential purchasers of weighbridge systems should consider from the outset. As Weightron Bilanciai’s Sales Director Emlyn Roberts explains, there are five distinct areas that need to be considered:

• The number of weighbridges and their location
• The design and build of the weighbridge itself
• The pedigree of key measurement chain components (load cells and instrumentation)
• Required peripheral control equipment such as ANPR cameras, traffic lights and barriers
• Software functionality and software integration.

The number of weighbridges required at a site should take into account anticipated maximum traffic throughput densities and overall site efficiency requirements. Dedicated ‘In’ and ‘Out’ weighbridges are essential for busy sites and it can be prudent to have two incoming bridges and one outgoing bridge to avoid bottle necks. Although the cost implications may seem higher initially, having to install an additional weighbridge at a later stage will cause major site disruption and incur significant civil engineering costs.

Installing bi-directional weighbridges where key instrumentation and control features are mirrored at each end has a number of advantages. This gives flexibility for busy periods and allows weighbridge(s) to be taken out of service for maintenance with minimum impact on site efficiency.

Weighbridge design

There are essentially two main design concepts – pit mounted and surface mounted. The choice for any particular application will depend on a range of factors including: the required site layout, site permanency, vehicle access and cost restraints. Civil engineering costs for surface weighbridges tend be lower, but the access ramps can slow down vehicle throughput. Surface bridges are easier to relocate making them ideal for temporary sites. By comparison pit weighbridges provide a level approach and departure surface.

Weighbridges may seem to be merely pieces of metal or concrete, but sound mechanical design and build procedures are essential both for performance and longevity. In parallel, well-designed foundations and vehicle approach areas also play a vital role. Cutting corners with factors such as steel quality, support beam density, weld integrity or surface finish may reduce prices, but this can have a detrimental effect on overall reliability and longevity.

EN1090

From the 1st July 2014 it has become a legal requirement within the UK that all structural steel work for use within civil engineering works must be CE Marked in accordance with EN1090. This CE requirement, regulated by Trading Standards, is based on the European Construction Product Regulation (CPR). Steel weighbridges and associated structures fall within this regulation and manufacturers must be assessed and certified by a Notified Body. Engineering contractors and insurance companies underwriting works will expect that structural steel arriving at site is CE Marked with the supporting declarations of performance certificate. Meeting this legislation requires strict in-house controls relating to the design, material selection and manufacture of weighbridges.

Unfortunately there is evidence that performance, reliability and functionality are being compromised through the emergence of lower priced weighbridge systems with questionable long term credentials.

Although these may seem initially attractive, the consequences of buying on price alone can be very problematic and expensive.

Weighbridge Measuring Chain

A typical weighbridge measuring chain includes the load cells, junction boxes, driver terminals, weight indicators, large remote displays and software. To ensure optimum system compatibility, there are distinct advantages for the customer if the weighbridge supplier is responsible for the design and manufacture of all these critical components. This provides practical and efficient single source system responsibility. In addition, purchasers should look at the level of after sales support a supplier can offer, together with their quality system accreditation and relevant trade association membership.

Load Cells

The load cells and their associated mounting hardware are considered to be the most crucial part of the weighbridge and are required to work under a range of harsh and challenging environments. Therefore design and application optimisation for these essential components is crucial; not only for performance, but also for long term reliability.

Of all the designs, clear evidence from the field shows that compact stainless steel canister load cells, together with well-designed rocker mounting assemblies, provide the optimum solution for weighbridges.

More cumbersome single-ended bending beam load cells or vulnerable double-ended shear beams with ball bearing mountings are more likely to fail and generally require more ongoing maintenance. It should be remembered that weighbridge decks can be subject to relatively large expansion-contractions, which affect the load introduction angles and this places further importance on the requirement for well designed load cells and mounting assemblies.

The latest digital designs offer a range of benefits including more efficient commissioning, remote diagnostics, easier calibration and quicker replacement if load cells are damaged.

Environmental sealing is a vital factor for load cells especially in pit mount designs where occasional flooding can occur. The latest design of fully weld-sealed load cells meets the onerous IP69K classification, introduced for the hot wash-down testing of off-road vehicles. This demonstrates that the load cells can withstand high-pressure steam cleaning in line with the stringent test specification outlined in the German DIN 40 050-9 standard.

Instrumentation

Traditional weighbridge instrumentation has developed significantly over the past five years. Intuitive touch-screen terminals adjacent to the weighbridges have replaced standard weight indicators housed in the weighbridge office. These terminals provide a wealth of operational and management features. For optimum site efficiency dual height terminals allow easy access for drivers in a range of different height vehicles including lorries and vans. The terminals can also act as a vehicle control point even if the vehicle in question is not required to be weighed. Single or multi-use cards allow controlled access to different parts of a site.

End users should explore the future proof capabilities of software and instrumentation. It is important to check how easy it is to set up or re-configure fundamental features such as databases and libraries. Driver terminals must be capable of operating with the wide array of recognition technologies such as RFID, magnetic and voice activation.

Software

Today’s weighbridge systems are expected to integrate seamlessly with an array of management software systems including SAP, Sage, Microsoft Navision and J D Edwards. However, although system functionality for a specific project may appear to be well defined at the outset, functional design specifications invariably change throughout a project. As a result it is therefore beneficial for the weighbridge supplier to take responsibility not just for the weighbridge software, but also for the all-important interface between the weighbridge system and the overall plant management system.

The use of third party software suppliers, who have little or no knowledge of weighing, can turn out to be more complicated and expensive in the long run. In parallel the weighbridge software must be fully compatible with the growing range of peripheral equipment including automatic number plate cameras, overhead cameras, control barriers, traffic lights, card readers and radiation detection systems.

Storage Software

Versatile storage software, linked in with the weighbridge system, provides invaluable inventory control for sites where different materials are delivered to and collected from sites by a wide range of contractors. These products may be processed straightaway or stored on site. Such software also manages processed materials being collected from site. A range of data analysis reports effectively controls stock movement in and out of the site, providing information for invoicing, reprocessing and recycling efficiencies together with other important site parameters.

Peripheral Control Equipment

Radiation Detection Systems

The recycling chain is becoming more and more complex with materials now coming from a range of sources and countries. As a result, the need to be able to detect loads that may be contaminated with radioactive waste is vitally important. If radioactive waste does enter the recycling process, whether the material is shredded, composted, burned, or otherwise processed, the contamination becomes more wide spread and the costs associated with any clean up escalate.

Radiation detection systems located at the approach to the weighbridges are effective in identifying contaminated loads as the vehicles drive through the detector plates. The detection software links directly
with the weighbridge system and warns operators of any potential problems so that suspected loads can be quarantined before they are offloaded.

Control Barriers and Traffic Lights

Barriers and lights at each end of a weighbridge are effective at controlling the vehicle access to and from the weighbridge. The system is designed so that the weighing process can only take place when the correct
sequence of these control features is in place.

Vehicle Recognition Systems

A range of options are available to identify vehicles entering and leaving the weighbridges. Automatic number plate (ANPR) cameras are very effective at identifying vehicles whose data is entered into the system database. Details relating to vehicle, contractor, product and even tare weight can be stored. The vehicle is identified as it approaches the bridge and is only allowed access if the stored information is correct.

Service and Support

Weighbridges are expected to work reliably and accurately: day-in and day-out in all types of environments. It is easy to forget that underneath the deck structure are precision measuring sensors that can provide weight data to one part in 3000! Effective rapid-response support is essential for weighbridges to minimise downtime. This is far easier if the original supplier has supplied and installed the complete system and also has readily available trained engineers.

Therefore it is prudent for operators to invest in a comprehensive service and support agreement. This ensures ongoing maintenance and calibration is carried out within manufacturer’s specifications and legal for trade legislation. In addition, it makes sense for operators to carry out regular preventative maintenance procedures. These can involve regular cleaning of the weighbridge deck, visual inspections of peripheral equipment and simple testing of the weighbridge by standing on the deck.

Conclusion

As weighbridge systems become demanding and operationally complex, the pitfalls of buying on price increase. It is recognised that cost is an important factor, but the apparent advantages of initial low prices can soon be lost through operational limitations and unreliability. Changing designs once systems have been installed can be very expensive in terms of additional civil work, cabling and software changes. Single source responsibility for key hardware components and software offers distinct advantages.