WB-X400P Steel-Reinforced Pit Type Truck Scale

Code and position: what does the P stand for?

The P in the model name refers to pit installation. X400 indicates a concrete deck and places the scale in the standard segment of the range. The same deck is used in the surface-mounted WB-X400F; the one essential difference between the two is the height at which each scale is set. For a business considering WB-X400P, the real question therefore comes before “concrete or steel”: it is “ramps or a pit”.

In a pit installation the platform surface ends at the same level as the surrounding paving. Vehicles neither climb nor descend; the driver approaches the scale as if entering an ordinary stretch of road. As a result there is no needless braking on the platform, horizontal force during weighing drops, and the indicator settles on a stable value more easily.

WB-X400P is chosen most often by businesses whose scale will sit on the main entrance road of the site. The gate of a factory receiving raw materials usually opens onto a public road, leaving no spare distance between gate and building for the length of a ramp. At haulage and cargo yards, vehicles have to pull up both at the scale and at the loading docks; a scale at road level simplifies that manoeuvre. Where forklifts, loaders or pedestrians cross the same point as the lorries, a flat crossing surface improves both safety and flow.

Why a concrete deck works well in a pit

The platform is derived from the pre-stressed construction used in road bridges. Tensioned reinforcement is placed in a casing formed by the steel frame, and the void is filled with high-strength C50 concrete. The steel frame protects the edges and gives the deck its shape; the concrete adds mass and compressive strength.

In a pit, this construction brings two separate benefits. First, the heavy deck sits steadily in the pit, and the oscillation set up by a lorry crossing the scale dies away quickly. Second, a concrete surface in contact with rainwater, mud and salt does not wear as fast as bare steel plate; only the frame edges and connection points need watching for corrosion. Where the scale sits on a main internal road also crossed by forklifts and loaders, that durability matters even more.

The load-bearing deck stands on compression load cells of 30 t each. The cells are made of stainless steel, sealed to IP68 against water and dust, and belong to accuracy class OIML R60 C4. As the pit is the installation type where moisture is felt most, this protection is particularly valuable here. Standard mounting hardware restricts sideways movement of the platform so that the push of an entering vehicle does not upset the reading.

Designing the pit

The success of a pit-type scale depends largely on a well-designed pit. For WB-X400P, pit dimensions are worked out from the chosen platform length, the capacity and the ground survey. These are the main points to settle at the design stage:

• Drainage: the base of the pit slopes towards a sump, emptied by gravity or by pump
• Edge protection: the pit mouth is framed with steel sections so that tyres do not break the concrete edge
• Movement gap: the space between deck and pit wall must be cleanable; stones or ice jammed in it make the scale under-read
• Maintenance access: the route to the load cells and the junction box is planned before installation
• Cable route: cables run from the pit to the weighbridge office through a protected, watertight duct

Removing ramp construction reduces the total site area needed, but it does not remove civil work; excavation, pit concrete and a drainage line mean more building than a surface installation. That difference should be weighed against the space gained and the smoother traffic flow.

Dimensions and load cell layout

WB-X400P is 3 m wide, with a choice of five lengths: 8, 12, 14, 16 or 20 m. The number of cells carrying the platform rises with length: 6 at 8 m, 8 at 12 m, 10 at 14 and 16 m, and 12 at 20 m. Capacity is in the 60–80 t range for every size, and the scale interval works in two ranges of 20/50 kg.

In practice, dual-range division means the indicator reads in 20 kg steps while the load is in the lower range and in 50 kg steps once it passes into the upper range. For example, the tare weighing of an empty tractor unit is taken in fine steps, while a loaded articulated lorry is weighed in coarser steps that suit the capacity. A single scale thus gives meaningful results on both empty returns and loaded arrivals.

When choosing length, remember that extending a pit installation later in practice means building a new pit. If a plant that works with rigid trucks today plans to receive articulated lorries within a few years, choosing 16 m or more from the start is the more economical route.

Measurement, records and automation

The weighing indicator works with a 24-bit sigma-delta converter and has an internal resolution of 1/30000. Its vibration filter suppresses the fluctuation produced by a lorry waiting with its engine running. The 26 mm digits on the backlit LCD are easy to read from the weighbridge office, and the dual-range function delivers finer results in the lower range for legal-for-trade weighing.

The weighbridge software keeps weighings in a database and can export them to XML, PDF, HTML, TXT and spreadsheet files. Traffic lights and a plate recognition camera can be connected to the software, and an optional web database gives access to records from outside the site. Considering that a pit-type scale usually sits at the plant entrance in the middle of heavy traffic, a light-controlled flow that recognises plates on its own shortens queues noticeably.