At present we can see that both International Recommendation R76-1 and product standards and calibration procedures provide strict and comprehensive regulations for automotive weighing products.
1.The relevant provisions
(1) The scales shall have a calibration division equal to the actual division , i.e. e=d.
Type of scale Calibration division value
division ed scales without auxiliary indicating device e = d
Scales for direct sale to the public shall not be equipped with auxiliary indicating devices and extended display devices.
(2) Provisions concerning nLC ≥ n
For each load cell, the maximum number of divisions of the load cell, nLC, shall be not less than the scale’s certified divisions n.
nLC≥n
This provision essentially limits the number of divisions of the scale. In other words, if a load cell of class C3 (3000v) is used for a vehicle scale, the maximum number of divisions that it can be certified to is 3000e. 2.
2.Reasons for specifying e = d
(1) Initial inherent error
This is a term that is closely related to the basic components of the scale.
The “initial inherent error” is the error of the scale as determined prior to the performance and range stability tests.
It is clear from the definition of “inherent error” that the fate of any scale has been determined since the design and manufacture of the scale was completed. Why do we say this? Because a scale is made up of four main components: the load cell, the load cell, the weighing instrument and the foundation. During the design process, the rigidity and strength of the load cell are determined by the design, the technical specifications of the load cell are also selected during design, the parameters of the weighing instrument are also selected during design, and the quality of the foundation is determined during construction and manufacture. The quality of the foundation is determined during construction and manufacture. With these raw data determined, the inherent error of the scale is naturally determined.
If a truck scale with a maximum capacity of 150t is calibrated to a 50kg division value, when the actual division value is 20kg, it is unlikely that the actual weighing value in use will reflect the true load weight, because when calibrated to a 50kg division value, it will reflect the 50kg initial inherent error. If the scale is simply set to 20kg, the value displayed during weighing is not representative of the actual weight of the load being weighed. Only a scale designed, manufactured and installed in accordance with the 20kg division value will reflect the actual weight value of the 20kg division value. The curve of the initial inherent error of a vehicle scale of the same weighing capacity in different error bands can be clearly seen from the graph below.
(2) Environmental impact issues
Inherent error: the error of a scale as determined under standard conditions.
The definition of inherent error shows that it is possible to change a certain measurement performance after careful commissioning (e.g. by linear correction) when the site is relatively stable in terms of certain environmental climates, supply voltages and electromagnetic field disturbances, but not fundamentally change its measurement division.
This is why the international recommendation R76-1 recommends that n = 3000 for general scales, and that n can only be greater than 3000 if very special methods are used.
