Ultimate guide on how to install a farm weighbridge

Jul 06, 2023

There are many reasons a farm business would want to weigh product moving in and out of the yard, from simply recording crop yields of individual fields to getting the accurate weight of a trailer load of silage sold to a neighbour.

For bigger arable units with a significant volume of shared grain storage, having vehicle weighing facilities is essential in ensuring every last kernel from each enterprise is accounted for.

See also: 14t and 16t silage trailer buyers guide

A quick online search for weighbridges throws up a very wide range of options in both hardware and suppliers.

Each system has its merits, so we asked industry veteran Colin Kempthorne of Milton Keynes-based manufacturer and supplier New City Scales to outline the most important things to consider before parting with any cash.

Strong ramps are essential for easy access

Much of the decision will depend on the purpose of weighing and the type and volume of traffic moving across the weighbridge from year to year.

For a farm simply looking to record grain yield or forage going into a feedstock clamp, traffic will be largely tractors and trailers, rather than trucks.

In these situations, it is also likely that no "trade" will be taking place, so the choice of weighbridge is not limited by the Weights and Measures Act 1985.

The Act requires those trading goods to have a full-size system with a certificate of calibration provided by an approved verifier. This ensures it is working within the accuracy tolerance stipulated in the regulations.

So, for predominately tractor and trailer traffic with no trade, farm businesses can opt for several more cost-effective options for weighing vehicles.

These options include fixed-installation, multi-axle scales, which measure and combine each axle's weight to give a gross weight, or portable axle scales that work in a similar way, but offer the flexibility to shift them from site to site.

Where a farm bridge is likely to have a combination of truck and tractor/trailer traffic year-round, and grain is being stored for others or traded by weight, a trade-approved unit is required.

It might be the case that this is permanently installed at a main store, with portable units used at satellite stores.

This portable set of Griffith Elder 18m ramps are surface-mounted and quick to set up

Location is where some farm weighbridge buyers have come unstuck.

There have been instances where it has been installed and blocked off shortcuts to adjacent buildings or land for large vehicles such as combines and forage harvesters.

Space around the system is a critical part of getting the location correct, especially where a drive-through type is installed.

With the bridge platform typically 15m and concrete or steel ramps about 5m long, enough room for a 16.5m-long articulated lorry to drive on and off in a straight line should be planned in.

In yards where space is at a premium, a pit design – where the hardware is dropped into a hole so the platform is flush to the ground – is more appropriate, as long vehicles can screw on and off without causing damage.

Pit bridges are more expensive to install but finish level with the ground

The space available in a yard and turning circle for vehicles will dictate if a surface-mounted weighbridge or pit version is most suitable, but there are other factors to mull over.

One is whether the chosen location is level. Full-size or multi-axle pit bridges have to be installed on perfectly level ground, so are unsuitable for sloping yards or roadways.

Portable-axle scales and many full-size, drive-through setups can be installed on existing roadways or concrete, but, in many cases, the ground must also be dead level.

However, some designs, like those offered by New City Scales, allow a drive-through to accurately weigh on a 1:30 gradient due to the type of load cell used. This offers a degree of flexibility on location.

The other major deciding factor between a pit and drive-through design is cost. The hardware, load cells and electronics are largely the same, but with more groundworks required to install a pit bridge, costs can escalate.

New City Scales HD bridge going in by crane

There is plenty of choice in both specification and price, but, as with any farm kit purchase, you tend to get what you pay for.

At the upper end of the price range are full-size weighbridges that are manufactured and delivered in one piece.

There are several UK firms that offer this type, including New City Scales and two Yorkshire businesses, John Maguire and Sons and Scales, Spares and Service (SS&S).

These designs are suited to heavy-duty use in quarries or waste transfer sites, but where a farm has plenty of weighbridge traffic throughout the year, they are also a good, durable option.

New City Scales’ setup is designed and made in Sheffield using British steel, where possible, and consists of two heavy section universal steel beams, usually 15m long.

The location of the weighbridge will affect how long it lasts

These are held together by 203mm heavy beam cross-members, like the rungs of a ladder, and covered with 10mm or 12mm durbar deck plate. The cross-members are spaced on 500mm centres, which is narrower than some designs on 700mm centres.

With wider spacing between the cross-members, the weight on each vehicle axle is only supported by the deck plate. Over time, the bowing of the plate can twist each cross-member back and forth, eventually leading to cracking or complete breakage.

The heavy section beams used in New City Scales’ drive-through design are 686mm tall and on its deep pit weighbridges, a hefty 762mm.

This is in contrast to some low-profile arrangements that use 300mm beams and are considerably weaker. This should be factored in when deciding which option to buy.

Small bridges like this can provide a helpful record of grain movements during the year

New City Scales also offers slightly lighter-weight options to compete in the budget market, including a 533mm-tall beam drive-through and a shallow pit bridge built around 356mm heavy section beams.

The main disadvantage of a heavy-duty one-piece weighbridge is that it requires a crane to lift it off a lorry and into position, which adds to the cost.

A New City Scales four load cell, heavy-duty, fully welded, surface-mounted weighbridge, including installation and cranage, costs about £18,000. Groundworks, including a concrete pad/ramps, is an additional £11,000-£12,000.

For a four load cell heavy-duty deep-pit version, the hardware costs about £19,000 installed. Groundworks (including muck away) cost about £23,000, depending on the location of site, taking the total cost to about £42,000.

Where farms are looking for a more cost-effective solution, there are also some well-established firms offering lighter, modular weighbridges.

Norfolk-based firm Griffith Elder has trade-approved, full-size units that come in four sections, each weighing no more than 2t.

Once in place, all the sections are fixed together with a specially designed lockup mechanism, which simply requires a 30mm socket to operate.

One of the reasons for offering this modular system is that it can be containerised and shipped to export markets, which account for about 40% of the company's sales.

It also means sections can be delivered to farm and moved around with a telehandler, simplifying installation. Once fitted, a quarter section can also be lifted out to clean underneath.

This advantage can also be seen as a weakness, though, with the joins between modules serving as potential weak points that can break under stress when subjected to heavy lorry traffic over a long period of time.

Griffith Elder's full-size bridge is available in 15.3m and 18.3m lengths, which cost £18,900 and £22,100, respectively. Steel ramps are an additional £4,950 and allows the system to be moved if desired.

For buyers not requiring trade approval, its 4.4m long multi-axle pit weighbridge is the most cost-effective fixed option for about £9,100 ex-works. This can weigh tractors/trailers and trucks in two weighings within a 0.5% error.

The firm also offers 2.8m and 4.4m plug-and-play portable weigh beams for tractor and trailers, weighing to within +/- 1% accuracy and adequate for monitoring crop yields across multiple sites.

These can handle artic trucks, but as the front axle, drive axles and tri-axle trailer have to be weighed in three sittings, and the fifth wheel coupling is more ridged than a tractor hitch, accuracy is compromised.

All products come with a load indicator with USB output for data processing, a tally roll printer and large weight/traffic light display as standard. In-cab controls are an additional £1,200.

Another farm weighing specialist, Parker Farm Weighing Systems, offers a similar product range out of its Chesterfield factory.

Prices range from £9,000 to £25,000 depending on the type and size of the weighbridge, with all prices including delivery, installation, calibration and trade certificate, where appropriate.

Groundworks cost extra and the company recommends that the installation is carried out by its own skilled technicians.

Parker Farm also sell its Portable Axle Scale, which comes in 3m and 4.4m options, depending on the size of the vehicle needing to be weighed. The 4.4m PAS costs about £8,000.

A load cell is a transducer that converts tension, compression or pressure into an electronic or digital signal, which can be measured to give a weight reading.

There are several types of load cell, but the main ones used in weighbridges are shear beam, compression or S-type load cells.

Mr Kempthorne says there is little difference in terms of accuracy between the different types, or between digital and analogue, but there are slight variations in longevity and serviceability.

Although load cells are fairly robust in harsh conditions, installation within the bridge structure can have a bearing on their longevity.

A double-ended bar loadcell

Some designs place them directly on the foundation, which can leave them consistently exposed to moisture and debris, and lead to reliability problems, to the point of failure.

Access to the load cells or buffer system can also make servicing and repairs awkward and time-consuming.

It should be noted that the buffer system or restraint mechanism that prevents the weighbridge from oscillating or moving too far when under load is one of the most important components of any setup. If not up to the task or set up correctly, load cells and their mounts can be damaged.

To avoid these issues, New City Scale's drive-through and heavy-duty pit-mounted weighbridges use a double-ended shear beam load cell.

These are located on the side of the structure and is sat high on a pedestal, supporting the platform load via two heavy-duty load links and M39 EN8 load pins or bobbins.

This keeps the load cells out of harsh conditions, and to facilitate access, a cover panel is simply lifted off at the side if any repair or replacement is needed.

Farm businesses should also be aware of a weighbridge myth before purchase – as a sales pitch, some firms will claim that more load cells mean greater accuracy.

There should be enough room at either end of the bridge for vehicles to enter and exit easily

This is not the case, because all trade-certified weighbridges have to perform to the same high accuracy under the Weights and Measures Act, so will weigh exactly the same, whether there are four, six, eight or even 10 load cells.

The reason for having more load cells is usually because the design is structurally weaker and requires more points of support, whereas the heavy-duty bridges tend to have less.

A further advantage of having a more robust weighbridge with fewer load cells is that there are less parts to go wrong and potentially require replacement.

Beware the provenance of load cells, as some sellers make their own or have a tie-up with a certain load cell manufacturer, so customers will be restricted when it comes to replacement and price.

Mr Kempthorne says in his 35 years’ experience a customer has never questioned where the load cells are manufactured and the replacement cost, something he encourages farmers to do when getting quotes for a new system.

New City Scales steel ramps

For surface-mounted and pit weighbridges, groundworks will vary significantly, depending on the conditions and infrastructure on site and the brand being installed.

Most full-size designs only need level hardstanding to function accurately and, where steel ramps are specified, additional concrete may not be necessary.

However, on sites where construction starts from scratch and a four-load-cell drive-through is being installed, New City Scales’ groundworks team typically lay a 200mm-thick concrete pad the length of the bridge.

The concrete is thickened to 300mm underneath the four feet and load cells to provide more ground clearance. This eases access for cleaning and servicing of load cells when the bridge is in use.

Where opting for concrete ramps over heavy-duty steel equivalents, two steel-reinforced ramps are formed at either end, which are typically 5m long and no more than a 1:10 gradient.

For a heavy-duty deep pit system, a typical process would be to dig the pit and lay a 300mm-thick concrete base. Formwork would then be used to construct 300mm-thick reinforced concrete sidewalls.

For shallower installations, using hollow concrete blocks to build the sidewalls is a more cost-effective option, and these can be reinforced with rebar and concrete in the cavity where necessary.

Before groundworks begin on a pit weighbridge, the water table and drainage at the site must be assessed to ensure water can be prevented from filling the pit and potentially damaging load cells in the long term.

Where existing drainage is deep enough, water can be diverted straight into the system, otherwise a pump (circa £150) may need to be fitted to push water out and away from the pit.

Once a bridge is up and running, an analogue or digital signal will be sent from the load cells to the weight indicator via a summing board (a device that combines the signal from multiple load cells into one).

A simple weight indicator on a digital display for manual recording is the cheapest option for data handling and these can be picked up for as little as £250.

For about £1,000, the next level up is a more flexible weight indicator and printer added into the system, which will allow the customer to print out date, time, registration, product, first weight, second weight, gross and net weights, on a three-ply ticket.

The ticket can then be split and given to relevant parties, such as the weighbridge office, customer and driver.

These can also be linked to a computer running suitable software, where the weight data can be stored or automatically exported to a cloud-based system.

The most advanced setups integrate indicator readings into PC software programmes as described above, which, for a large grain-storage facility, can assign loads to fields, record separate varieties and assign loads to specific stores.

Quality characteristics can also be added, such as linking the weighbridge system to the moisture analysers and grain samplers. All information can then be integrated into a database and exported to accounting and invoicing systems such as Sage.

Further sophistication sees automatic number plate recognition (ANPR), traffic management systems such as traffic lights and road barriers, and driver control panels integrated into the weighing operation.

It should be noted that driver controls are not suitable when tractor and trailers make up a significant portion of traffic, as the operator cannot reach the panel – this is aimed at trucks.

If driver operation is required, firms such as Griffith Elder offer a key fob that can be activated when the vehicle is stationary on the weighbridge and the indicator records the data.

The most complex and sophisticated systems are only likely to be needed on busy industrial sites or large grain storage operations, especially as the cost can be as much as £25,000.

Maintenance demands tend to be relatively low. However, weighbridges are typically installed and operated in harsh environments, so dirt and debris can build up underneath the platform – especially in pit installations – and start to restrict the free movement required for accurate weighing.

Regular cleaning underneath the platform should be carried out and certain weighbridge designs can be advantageous in easing this process. For example, deeper pit bridges and higher ground clearance for drive-through versions allow better access.

Shallow pit or low-profile modular bridges need to be taken apart or lifted out of the way for thorough cleaning.

Once trade certified, there is no legal requirement to regularly have a weighbridge weight tested – a process that checks it is weighing evenly and accurately across the platform – or professionally serviced.

However, the industry standard is one service visit and one calibration check or weight test a year, which should include a certificate of test or calibration for the farm's records and to approve accuracy.

A full weight test with a certified unit costs about £650. Weighbridge providers will typically offer an annual service visit, which will include a load cell inspection, mounting and buffer system check and a look over cabling for damage.

Buyers should be very wary when purchasing a second-hand weighbridge, as they may have had a lot of use and be in worse condition than initial appearances would suggest.

In addition, prices are often inflated relative to the cost of a brand-new one.

Mr Kempthorne says there are six golden rules:

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