How to Choose the Right Weighbridge

In this guide, Weightron Bilanciai take you through what you need to consider when purchasing a weighbridge. This guide will detail; civil and mechanical considerations, systems, equipment, integration and maintenance.

If you are looking for a weighbridge, or have any questions regarding equipment or software, contact the team at Weightron Bilanciai for more details.

There is evidence that performance, reliability and functionality are being compromised through the emergence of lower priced weighbridge systems with questionable long-term credentials. So, what are the critical design and operational issues which potential purchasers of weighbridge systems should consider from the outset?

 

 

Part 1: Civil and Mechanical Considerations

There are a number of important factors to consider when choosing your weighbridge. These include:

• Design concept and material of construction
• Maximum vehicle sizes in terms of length, width and gross weight
• Available space
• Site accessibility and vehicle manoeuvrability
• On-site health and safety issues
• Required vehicle throughput and weighbridge availability
• Budget and long-term operational costs.

 

Design Concept – Weighbridge Type

Traditionally weighbridges are divided into two main types – pit mounted and surface mounted. However, at Weightron, we expand on these designs to offer four types of weighbridge installation:

1. Traditional Pit with full surround foundations
2. Traditional Surface with full length ramps
3. Compact-build, drive-through, with short ramps
4. Hybrid pit/surface with level approach and exit roads, but no concrete side structure

We believe this increased range of designs offers more versatile installation options and makes choosing the right weighbridge for your application somewhat easier.

In terms of construction, weighbridges are available in three main types:

1. Full steel construction (single and modular deck structure)
2. Concrete pour-on-site with steel subframe
3. Pre-stressed concrete

Full steel construction weighbridges make up most of today’s installations. The two main designs are flat plate deck and side beam drive-through. Beam distribution and sizing are a critical part of the design. Chequer plate decks help prevent vehicles from skidding.

Note: Under the Construction Products Regulations (CPR) 2022, the recognized standard for the steel products used in construction is BS EN1090. This certification places strict controls on the manufacturer, thereby ensuring the highest quality products for the customer.

For steel construction there are two execution levels – BS EN1090-1 and BS EN1090-2. Execution Level 1 refers to the quality of the steel used for construction projects, which must be UKCA certified, whilst Execution Level 2 relates to both the steel and the manufacturing process itself.

Manufactured products under Level 2 are UKCA certified. Weightron are BS EN1090 certified for both execution levels.

For certain applications, concrete weighbridges offer a number of advantages.

Pour-on-site designs can facilitate installation, especially in locations where there is limited access for cranes. The steel subframe is considerably lighter than normal steel decks, making it easier to transport and install. One minor drawback is that the concrete needs time to set and cure, thereby increasing the installation time.

Bespoke Sizes

Although we offer a wide range of standard weighbridge sizes, we can build special sizes to suit your application (metric and imperial). These are ideal for replacing aging pit weighbridges.

We have developed special load cell mounting hardware assemblies that fit in the pits to ensure the new weighbridge deck sits level with the ground. This removes the need for unnecessary civil engineering work to convert the existing pit. We also offer weighbridges up to 6.0 metres in width.

Maximum Vehicle Sizes – Length, Width & Gross Weight

Weighbridges are available in a range of lengths and widths. In the UK, the most common sizes are 15 metre and 18 metre, with a width of 3 metre. These sizes will be suitable for weighing most on-road commercial vehicles. Shorter 7.5 to 9.0 metre decks are suitable for smaller, lower capacity vehicles.

Remember that the length of the weighbridge deck only needs to accommodate the wheelbase of the vehicle, provided there is sufficient space at each end of the installation for the rest of the vehicle. This is particularly important if traffic barriers are installed to control the entry-exit process.

It is also important that there is sufficient entry and exit space for safe maneuverability. Note that 18 metre weighbridges are usually suitable for so-called LSTs (longer semi-trailers) of 14.6 metres and 15.65 metres in length (17.5 and 18.55 metre total vehicle lengths respectively). These were allowed onto our roads in 2012 as part of the Governments trial to reduce carbon emissions. The initial 10-year trial has been extended to 2027.

The UK’s existing domestic gross weight limit for road vehicles with up to 6 axles is 44 tonnes. Therefore a 50 tonne or 60 tonne capacity weighbridge is suitable for normal applications.

For off-road applications, such as quarries, construction sites and steel works, vehicles can have gross weights over 100 tonne and widths up to 6.0 metres. For these applications, special weighbridge designs are available, often with increased over-load capabilities.

Available Space

Site layout and space may dictate the size and type of weighbridge that can be accommodated. Pit weighbridges offer more vehicle freedom of movement, but require more expensive civil works and foundations. Surface weighbridges can be easier to install but require additional space for ramps.

As a rule of thumb, a standard 18 metre surface weighbridge requires at least 26 metres of free space, plus sufficient entry and exit distances for the longest vehicles. However, it is easier to move such weighbridges if required in the future.

When designing the layout for your weighbridge, care must be taken to ensure vehicles can easily and safely manouvre, as they drive on and off the weighbridge. This could cause problems if the weighbridge is close to buildings or has associated traffic barriers and driver terminals. The different types of vehicles using a site must be taken into consideration at the design stage.

Most weighbridges are operated in a drive-through manner. In other words, the vehicles drive on at one end and off at the other. However, in applications where space is at a premium, it is possible to install a single-ended weighbridge, which incorporates a special stop end, complete with barriers if required.

Additional safety measures should be put in place for such applications where vehicles are required to reverse off the weighbridge.

Sloping Terrain

For sites with unlevel, restricted space, our Eurodeck weighbridge can be installed on sloping ground with gradients up to 1:20. Special load cell mounting assemblies ensure the weighbridge deck is securely mounted whilst meeting weights and measures requirements.

This technology reduces civil engineering costs and makes the best use of available space.

Required Vehicle Throughput & Maneuverability

This is a crucial consideration from the outset. In many applications one weighbridge may be sufficient. However, for plants where a large number of vehicles are weighed in and out, the obvious choice is to operate two or more separate weighbridges, specifically designated for IN weighing and OUT weighing.

Although this is clearly a more expensive option, it allows a one-way system to be operated, which not only streamlines traffic flow, but also gives a higher level of site safety. Such configurations also allow sites to continue operations if one weighbridge needs to be taken out of service.

On-Site Health & Safety

Many sites where weighbridges operate are considered high-risk accident areas, especially in areas such as quarries, metal processing works and waste recycling. Therefore, it is important that suitable precautions are taken. If possible, the system should be designed so that drivers do not need to get out of their cabs during the weighing process.

Driver-operated terminals equipped with intercoms allow the driver to initiate the weighing process from the cab and communicate with the gatehouse or control room in case of problems. Traffic barriers and lights help control vehicle movement. Barriers on the sides of weighbridge decks minimise the risk of accidents by ensuring vehicles keep central on the deck.

See more details in this useful resource from HSE: Workplace Transport Safety.

Budget & Long-Term Operational Costs

As weighbridge systems become demanding and operationally complex, the pitfalls of buying on price increase. We understand that cost is an important factor, but the apparent advantages of initial low prices can soon be lost through unreliability and operational limitations.

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

Overall sound mechanical design is crucial for long term reliability. Cutting corners with factors such as steel quality, weld integrity or surface finish may reduce prices, but can have a detrimental effect on overall reliability and longevity. Investing in a weighbridge system with a track- proven pedigree will pay dividends longer term.

 

Part 2: System Components, Instrumentation & Integration

Accurate weight data collection is a vital function within a diverse range of industries. Weighbridges and weighbridge management systems play a pivotal role in providing this information, acting as critical control points for vehicles delivering, collecting and transporting finished goods and raw materials.

Whatever your requirement, a range of factors need to be considered in the decision process. These include:

• Type of load cell and mounting hardware
• Instrumentation
• Vehicle recognition and management systems
• Software and system integration
• Specialist safety systems (example: radiation detection systems)

 

Load Cell & Mounting Hardware

Load cells and their associated mounting hardware are arguably the most crucial parts of the weighbridge and are required to work in a range of harsh and challenging environments. Therefore, their design and application optimisation is crucial; not only for performance, but also for long term reliability.

Design

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 temperature related expansion-contractions, which affect the load introduction angles and this places further importance on the requirement for well-designed load cells and mounting assemblies.

Today’s weighbridge load cells are available in both analogue and digital versions, in a range of accuracy levels. The latest digital load cells offer distinct advantages, especially in terms of:

• Weighing precision
• Reduction in weighbridge commissioning times
• Remote preventative monitoring

Multi-range versions are also available for use under specified operating conditions. Multi-range weighbridges usually have two distinct measuring ranges with different approved scale increments. The display range is decided automatically by the applied load.

For example, a 50,000 kg weighbridge may display in 10 kg increments up to 10000 kg and then in 20 kg increments above this. This allows smaller vehicles to be weighed on a normal weighbridge with improved accuracy.

Capacity

Standard length weighbridges (15 and 18 metres) typically have six or eight load cells. For approved, legal for trade weighbridges, the capacity of these individual load cells is controlled by their approved utilisation specification.

The lower this value, the better the load cell, which in turn means lower strain levels and more overload capability. At Weightron, our 18 metre, 60 tonne weighbridges feature eight off 35 tonne load cells, giving a combined capacity of 280 tonnes.

Environmental Protection

Optimised sealing integrity for weighbridge load cells is of a major importance, especially for those operating in harsh environments. Fully weld-sealed stainless steel load cells, with glass to metal cable entry, can provide sealing to the stringent IP69K level.

When combined with rodent proof cables and built-in lightning protection, this design collectively provides the best protection against the elements. This ensures your weighbridge will continue to do what it is designed for – accurate weighing – day in, day out, whatever the weather.

Instrumentation

Traditional weighbridge instrumentation has developed significantly over the past five years. In a growing number of applications, intuitive touch-screen terminals have replaced standard weight indicators and provide a wealth of operational and management features without compromising on durability.

Driver Operated Terminals

These versatile instruments bring significant benefits, speeding up the weighing process, extending weighbridge operating hours; whilst improving site security and safety. The screen, pre-programmed with easy-to-use graphics, guides drivers through the weighing process without them having to leave their cabs. Dual height installations accommodate vehicles with different cab heights and terminals at each end of a weighbridge allow bi-directional weighbridge use.

Note: If drivers of left-hand drive vehicles will use your weighbridge, additional terminals should be considered at the design stage.

It is important to note that so-called automated weighbridges legally require physical intervention by the driver to ensure they are still classified as legal for trade NAWIs (non-automatic weighing machines).

Vehicle Recognition & Traffic Management Systems

Weighbridges are ideally suited to act as critical control points for vehicles entering and leaving sites. It makes sense to integrate broader vehicle management capabilities with the weighing process, with one entity responsible for the overall design and installation. This provides a more seamless and smooth-running system. Equipment includes:

1. Traffic lights and barriers
2. Vehicle recognition systems
3. Large Message Boards

The integration of these elements brings:

• Increased site security
• Improved vehicle throughput
• Comprehensive data capture

The management of vehicles can start when vehicles arrive on site, with large message boards controlling and directing vehicles to the correct area prior to weighing.

Vehicle Recognition Systems (VRS)

This plays a vital role in the overall weighing and vehicle management process. The system’s database can be programmed to store key information relating to the vehicle, its type of load and the haulier. The two main recognition technologies are:

• ANPR (Automatic Numberplate Recognition)
• RFID (Radio Frequency Identification)

The choice of ANPR camera is important. The technology has advanced significantly over the past decade and the latest cameras are easy to install and can provide up to 97% reading efficiency, even under poor operating conditions. (Earlier cameras relied on outdated FTP technology to analyse data from the camera).

VRS Operation

Although the layout of weighbridge systems using VR technology varies from one installation to another, there are four common types of operation:

ANPR Only

Induction loops in front of the weighbridge can be used to detect the presence of the vehicle as it drives onto the weighbridge. The loops may control traffic lights and/or barriers if they are installed.

To initiate the weighing process the driver must press a button on the driver terminal. If the captured registration of the vehicle is stored in the database, the weighing can then take place. If not, the driver either has to fill out the relevant information on the screen or is prompted to contact the weighbridge office via the integral intercom.

The vehicle is not usually allowed to leave the weighbridge until the weighing has been completed successfully.

ANPR & RFID Short Range

In this case, the ANPR is used to identify the vehicle, whilst the RFID tag usually identifies the driver. This may include details of any required site induction training or other relevant information together with the validity.

RFID Only – Short Range

The RFID tag is typically used to identify the vehicle but can also identify the driver as well.

RFID Only – Long Range

In this application the driver uses a button on a long-range key fob to identify the vehicle as it approaches the weighbridge. Once on the weighbridge, the driver presses a second button to initiate the weighing. Typically, traffic lights control entry-exit to the weighbridge. Such systems are ideal for off-road vehicles where their design makes it difficult for the driver to interact with a weighing terminal without getting out of the vehicle.

In parallel, recognition systems can control access for security gates and any bypass lanes used for non-weighed vehicles.

Software & System Integration 

Powerful and versatile weighbridge software can now manage the ‘local’ weighing and vehicle management processes, whilst integrating directly with bespoke and proprietary software platforms including SAP, Sage, Microsoft D365, Microsoft Dynamics 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, radiation detection systems, control barriers, traffic lights and card readers.

Radiation Detection Systems

As more and more materials are recycled or incinerated, there is a growing need to monitor the waste material for traces of radioactivity before it enters the process. If any traces of radiation-contaminated material go undetected, the environmental and financial consequences can be very grave.

Weighbridges are usually critical control points at reprocessing operations and therefore, the ideal location for installing radiation detection systems as an integral part of the weighbridge management system. As the loaded vehicle passes through the portal detector plates, (positioned each side of the weighbridge,) it is scanned for traces of radioactivity.

The system can be programmed for specific radiation thresholds and if it determines that a radioactive source is present, either in the load or the vehicle, the system actuates an alarm to immediately notify site security. The radiation portal system should be linked to the VRS to capture vehicle identification to provide a 360-degree traceability of the vehicle identification.

 

Part 3: Maintenance Considerations

As with any critical operational system, this means implementing a structured preventative and regular maintenance programme. We strongly advise operators to take out an annual Service Plan which can provide support and regular servicing.

Preventative Maintenance

A regular preventative maintenance regime is very straightforward to carry out and can prevent a number of unnecessary problems. Such a planned programme should consist of:

• Checks on the weight reading
• Visual checks of the weighbridge decks and entry-exit areas, including gaps between deck and foundations or ramps
• Visual checks of any equipment such as traffic barriers, driver terminals, end sensors and ANPR cameras
• Visual checks on cabling, junction boxes and cable pits
• Cleaning of the weighbridge deck and approach areas
• Cleaning of Driver Terminals, traffic lights and ANPR cameras
• Checks on load cells
• Checks on drainage

Note: Weighbridges should not be operated if there is damage to any peripheral equipment.

Health & Safety Considerations

Before any preventative maintenance checks or work are carried out, the weighbridge area must be cordoned off to prevent vehicles or unauthorised personnel entering. Site protocol for PPE must be followed, together with requirements for working in confined spaces and working at height.

Frequency

The recommended frequency of checks will depend on several factors including:

• The operating environment
• Seasonal weather patterns
• Vehicle throughput

Weighbridges operating in areas such as quarries and construction sites will typically require more regular cleaning than those in cleaner environments. More regular checks and cleaning should be carried out during and after periods of heavy rain or snow. Visual checks should be carried out daily and any damage or issues reported immediately. Operators should draw up a simple chart showing the frequency of checks for their installation.

Checking Weight Readings

A simple way to regularly check your weighbridge’s performance is to use a loaded vehicle, ideally with an all-up weight of 50% or more of the weighbridge capacity. This can be driven onto the weighbridge and the weight readings taken for three positions along the weighbridge (the shorter the vehicle the better).

These end-middle-end readings should agree within one scale division (typically 20 kg for a 50/60 tonne weighbridge) and the reading should return to zero when the vehicle drives off. However, this ‘repeatability’ check does not guarantee that the weight reading is correct, just repeatable.

Regular Calibration

The only way to ensure the actual weight reading is correct, is to have your weighbridge calibration checked regularly by a certified company using weights traceable to National Standards. Ideally, this should be carried out every 12 months. Owners of trade weighbridges have a legal responsibility to ensure their weighbridges continue to weigh within the prescribed legal tolerances as laid down in BS 45501.

Failure to do this can lead to prosecution and fines; Trading Standards have the power to close down weighbridges that do not comply. In parallel, inaccurate weighbridges can result in the overloading of vehicles, loss of profits or the short-changing of customers.

Pit Mounted Weighbridges

These can be more prone to problems caused by blocked or inadequate drainage, which can lead to build-up of debris around load cells. Although fully sealed IP69K load cells can withstand some periods of flooding, it is always advisable to minimise the risk of this if possible.

Build-up of material around load cells can affect weighing and affect any integral lightning protection capabilities. The weighbridge decks are designed to move by controlled amounts and debris between the deck and the pit walls will cause problems. T-section rubber fitted in the gap around the deck will minimise problems.

Surface Mounted Weighbridges

These are usually easier to keep free of debris, but if rocks and stones become wedged between the deck structure and the ground weighing results can be affected. The fitting of T-section rubber between the deck ends and the ramp is advisable.

Speed Control

A serious problem, especially for pit weighbridges, can be caused by drivers driving too fast onto the weighbridge and then applying their brakes too harshly. This introduces high end forces, which can cause the deck to act like a battering ram against the foundation walls. High exit speeds can also be damaging.

Speed limit signage can help reduce the problem, but traffic barriers and/or traffic lights ensure vehicles have to stop before driving onto and off the weighbridge. Surface weighbridges with ramps can be less prone to these problems, but precautions should still be taken.

Cleaning

This must be carried out with due care and attention to avoid damage to weighbridge components. High power pressure washers should be used with caution. The jets can dislodge surface coatings and cause damage to load cells and their mounting assemblies. Normal pressure hosing can be a less damaging alternative.

Winter Ice & Snow

Ice and snow on weighbridges can cause a number of problems. Weighing results can be adversely affected and vehicles can lose traction or skid. Large deposits can cause the weighbridge to go outside its zero-tracking range. The use of rock salt to remove snow and ice should be avoided. Alternative non-salt-based products are available. Salt deposits from vehicles should be removed as soon as practical.

Load Cells

Care should be taken when cleaning build-up of debris around load cells and cabling. Sharp tools must not be used. Any damage to cables should be reported immediately. Rodents can be problematic and the use of steel braided cable is advisable for a wide range of applications.

Note: Instrumentation, computers and printers in the weighbridge office or gatehouse should not be neglected and should be regularly checked and cleaned.

Welding

Under no circumstances should electric welding be carried out on the weighbridge deck. High electrical currents can cause damage to load cells and electronics. The operator should seek advice from us if work is needed.

Flooding

Although stainless steel load cells sealed to IP69K can withstand periods of flooding, where possible steps should be taken to minimise the risk. If a weighbridge is flooded for more than a few days, it is advisable to contact us so that our engineers can carry out thorough checks before the weighbridge is used again.

If you are looking for a weighbridge and need advice, contact the team at Weightron Bilanciai, or find your local sales manager on our areas covered page.