There are different options for operating truck scales. Firstly, the vehicle is driven onto the scale. The driver can then initiate weighing him/herself via the operator terminal or control cabinet. Various identification methods are available (e.g. a mobile device or barcode) for pairing the weighing operation with an order and preventing unauthorized manipulation. Furthermore, the vehicle number plate is recorded and paired with an order using camera and/or sensor-based position monitoring.
These days, it is also possible to remotely control scales from an office building, for example, using large displays that are actuated by encrypted data communication, for instance.
Methods of measurement
In modern truck scales, weight is measured with the aid of load cells such as RTN or C16i from HBK. For legal-for-trade use, these analogue or digital load cells must satisfy certain basic conditions and be installed in conformity with the applicable guidelines for Europe (WELMEC 2.4). Strain gauge load cells are commonly used. When a load is applied, the load cell – which acts as a spring element – deforms, causing an electronically measurable change in resistance on the load cell's strain gauge. This is transmitted to an electronics such as a weighing terminal, processed and shown on the display as a weight figure.
Nowadays, use is frequently made of digital load cells that enable conversion to a digital signal in the actual cell. To achieve this, a small amplifier board is integrated into the load cell, which is then hermetically sealed. The amplifier then converts the analogue strain gauge signal into a digital and therefore considerably less noise-sensitive signal in the load cell itself. This eliminates interference due to influences acting on measurement channels, and also largely prevents manipulation of the sensor signal.
As commercial, medium accuracy weighing machines, truck scales must conform to accuracy Class III, as set out in the German Measures and Verification Ordinance. Accuracy is based on relative resolution, i.e. the quotient of maximum load (max) and the smallest resolved weight value, the verification scale interval e (=d).