Two-stage weighing: net weight without subtracting by hand

Two-stage weighing means weighing a vehicle twice, on entry and on exit, with the weight of the goods being the difference between the two. For a delivery the vehicle comes in full and leaves empty, for a collection the other way round, and in both cases the system calculates the net weight, meaning the weight of the load alone, by itself. The arithmetic is simple provided the two weighings are linked to each other automatically, and most weighing errors come from that link being missing. In TraxSystem both weighings belong to the same entry, so nobody subtracts on a piece of paper or has to remember what the vehicle weighed three hours earlier.

Where errors arise in two-stage weighing

The weighbridge itself measures correctly; the errors arise between the weighings.

The link gets lost when the first weighing goes into a notebook, the second comes three hours later and the operator changes in between. Which entry belongs to which exit is then decided by memory.

The weight read from the indicator is also sometimes copied into the document by hand. One digit missing is enough to make the weighbridge ticket untrue, and the discrepancy only comes to light at the customer’s end.

The most important case, and the one most often overlooked, is a vehicle that leaves in a different state from the one it arrived in: with a different trailer, with a load added somewhere else on site, after refuelling. The difference then no longer describes the weight of the goods, and nobody notices, because the system does the subtraction mechanically. Two-stage weighing assumes that only the load has changed between the weighings, and once that assumption stops being true, the result is formally correct and factually wrong.

Automatic two-stage weighing in TraxSystem

In TraxSystem two-stage weighing runs in four steps:

1. On entry, the vehicle stops on the weighbridge, and the system reads the weight directly from the indicator and links it to the entry registration, meaning to a specific vehicle, driver and transport document.
2. During the visit, loading or unloading takes place, and the record waits, open.
3. On exit, the second weighing goes into the same record, and the net weight is calculated from the difference.
4. The weighbridge ticket is produced automatically, with both weights, the times and the vehicle details.

Both weighings belong to the same entry, so nobody has to match up two independent weighing events.

Two-stage weighing is part of the Weighing module, together with automatic and manual weighing and the weighbridge ticket, and all of them use the entry log. The module is priced by the number of weighbridges, and the limit grows with the size of the base package. The pricing configurator will work out what the module costs with your base.

When single-stage weighing is enough

Single-stage weighing is enough when the tare, meaning the weight of the empty vehicle, is known and constant. The vehicle is then weighed once and the tare is subtracted. This method is quicker and less accurate, because the tare from the registration document does not account for fuel, the driver or equipment, and the difference can reach several hundred kilograms.

TraxSystem supports both modes, plus manual entry for when the indicator is unavailable.

What TraxSystem does not do in weighing

TraxSystem does not replace legal verification of the weighbridge. The weighbridge has to be verified in accordance with metrology regulations regardless of the software that runs it. The system reads the indicator and records the reading, but it is not a measuring instrument itself.

Nor will it detect that a vehicle left in a different technical state from the one it arrived in. It calculates the difference between two weighings, and interpreting that difference is the operator’s job.

It does not do stock management: it records the weight and the weighbridge ticket, but it does not update stock levels and does not replace a WMS.

Questions and answers

See also: Weighbridge tickets: what they must contain and how to issue them automatically · Controlling vehicle dwell time on site