Vehicle scale
Vehicle scales determine the total or partial weight of vehicles and their load. The scale is not integrated in the vehicle. There are vehicle scales for road and rail vehicles . Depending on the system, the weighings are carried out dynamically while driving or statically at a standstill.
history
With the beginning of industrialization and the associated larger flows of goods , more and more heavy transport goods had to be weighed. Until well into the 18th century, the goods, which were allowed to weigh a maximum of 500 kg due to the manual procedure, were loaded onto the scales by hand. This corresponded to the weight of the barrels customary at the time.
In 1726 , Jacob Leupold , who came from Leipzig , described the so-called “ Leipzig Council Heuwaage ” in his work “Theatrum staticum ”, which represents a significant simplification of the weighing of heavy loads. With the help of these scales, the weight of entire freight wagons could be determined according to the principle of the running weight scale. The scales were attached to a beam with a trolley and the carriage to be weighed was hooked into the structure with chains. The car could be lifted and weighed by means of a gear train .
In order to shorten the time-consuming weighing process, attempts were made with the aim of replacing the previous principle of the hay scales with a system based on the table scales . In 1740 the master carpenter John Wyatt created the first weighbridge. The bridge, which was accessible at ground level after a modification by James Edgell, worked on the substitution principle and consisted of a weighing surface and a weight tray. There were weights in the shell, the amount of which reflects the maximum load of the vehicle. After driving on the weighing surface, the weights were removed from the pan until the scales were in equilibrium. In the 19th century, the principle of the decimal balance prevailed, as the use of levers meant that fewer weights were required. In 1822 the Benedictine monk Quintenz developed the “Strasbourg scales”. The weight tray and the use of the weights were later replaced by barrel weight levers.
Heavy loads caused heavy wear and tear on the levers and joints installed on the scale. For this reason, a relief device was developed that separates the bridge from the lever system in the unloaded state. After this relief was initially done manually, this process was soon taken over by electric motors and hydraulic power machines. As a result of this development, the first 100-ton scale was put into operation in 1888.
The restrictive calibration law required an improvement of this measuring method, as no new weighing techniques could be introduced. In 1924 the first inclination scale was approved for general trade. With the inclination scale , the weight to be measured is compensated by the deflection of a mass on a lever, which enables reading on a scale . Although this technology initially only achieved measurements with high inaccuracies, this scale was able to spread quickly. In 1930 , the Physikalisch-Technische Reichsanstalt approved the first unloaded vehicle scale. The weighing process could be accelerated again by installing shock absorbers and pendulum hangers, which were later replaced by ball supports.
Since the 1950s, electronic scales have been increasingly used in the construction of scales, displacing mechanical scales. Existing lever work scales were partially converted into hybrid scales by replacing the lever system with load cells , which now take the load. The basis for the load cell was laid in 1843 by the English physicist Sir Charles Wheatstone , who developed a bridge circuit for the precise measurement of electrical resistance . These Wheatstone bridges have been used since the 1940s to measure changes in resistance in strain gauges (DMS), a central component of the load cell.
Since the mid-1990s, new vehicle scales have only been built with load cells.
Types
Vehicle scales are divided into three different types:
- Mechanical lever scale
- Electromechanical scales
- Hybrid versions
In addition, a distinction is made between above-ground and under-floor scales, which are offered in reinforced concrete and steel. Vehicle scales with multi-part bridge combinations enable individual scale sizes to be provided.
Electromechanical scales and hybrid scales can be equipped with strain gauges, a weighing terminal with digital weight display and operator guidance, as well as various interfaces for printers , switching contacts, EDP connections, secondary displays and other additional equipment that enables a largely automated weighing process.
Types of weighing
A distinction is made between non-automatic and automatic weighing. A vehicle scale is usually a non-automatic scale because it is operated manually. The automatic scales automatically carry out the weighing process, including adding and removing the load. This type of balance requires special approval.
Self-weighing system
The vehicle to be weighed is positioned on the scale. The vehicle driver independently triggers the weighing process at the switch cabinet at the beginning of the scale. In order to avoid manipulation of the measurement, camera and / or sensor-supported position detection is installed. In addition, the license plate is recorded and the weighing is assigned to a stored order.
Measurement method
In modern vehicle scales, weight is recorded electromechanically with the help of load cells. In order for them to be used for legal-for-trade purposes, they must be installed in accordance with the relevant WELMEC directive. Usually, analog load cells with integrated elastic force transducers and strain gauges on them are used for this purpose, which convert the loads into electrical signals. Supports made of special steel are built into the measuring cells, which deform under load and cause an electronically measurable change in resistance in the integrated strain gauges. This is forwarded to a weighing terminal for conversion into a digital signal and displayed as weight information.
In the meantime, digital load cells are often used, in which the conversion into a digital signal takes place in the measuring cell.
Measurement accuracy
The accuracy of the measurement depends on the qualitative design, the site conditions, and the proper use and operation of the scales. The legal requirements for the accuracy of vehicle scales are defined in the Measurement and Verification Ordinance by the accuracy class III, whereby the basis for this is the relative resolution and the quotient of the maximum load Max and the smallest resolved weight value, the calibration value. Vehicle scales can be found in accuracy class III.
| class | Calibration values | Minimum load (min) | Number of calibration values | |
| minimum | minimum | maximum | ||
| I. | 0.001g <e | 100 e | 50000 | - |
| II | 0.001 g <e <0.05 g | 20 e | 100 | 100,000 |
| 0.1g <e | 50 e | 5000 | 100,000 | |
| III | 0.1g <e <2g | 20 e | 100 | 10,000 |
| 5g <e | 20 e | 500 | 10,000 | |
| IIII | 5g <e | 10 e | 100 | 1000 |
The error tolerances of a calibrated scale are specified by the International Organization for Legal Metrology ( OIML R76) and have been adopted in Directive 2014/31 / EU.
Verification of vehicle scales
When weighing in business transactions, the calibration of the scales is necessary to guarantee the accuracy of the measurement result and to protect consumer protection. Some industries are not subject to national calibration obligations. In these cases, globally applicable guidelines, such as the SOLAS agreement for freight forwarders, apply.
Thus, a balance from the Bureau of Standards can be calibrated, it must advance by the scale manufacturer conformity assessment (formerly erstgeeicht) are. Scales that have been commissioned must be registered by the operator within the first six weeks after commissioning. The conformity assessment loses its validity 3 years after it has been issued and the scales must be recalibrated by the regional calibration office. It is the responsibility of the operator to have the balance reevaluated by the Weights and Measures Office in due time.
Web links
- http://www.waagenmuseum-balingen.de/ Waagenmuseum Balingen with original hay scales
Individual evidence
- ↑ Manfred Kochsiek: Handbook of weighing: with 24 tables . 2., arr. u. exp. Edition. Vieweg, Braunschweig a. a. 1989, ISBN 3-528-18572-4 , pp. 6 .
- ↑ Manfred Kochsiek: Handbook of weighing: with 24 tables . 2., arr. u. exp. Edition. Vieweg, Braunschweig a. a. 1989, ISBN 3-528-18572-4 , pp. 7 .
- ^ Official Journal of the Royal Prussian Government in Bromberg: 1830 . Government Official Gazette, 1830, p. 97 ( google.de [accessed on May 23, 2018]).
- ↑ Manfred Kochsiek: Handbook of weighing: with 24 tables . 2., arr. u. exp. Edition. Vieweg, Braunschweig a. a. 1989, ISBN 3-528-18572-4 , pp. 12 .
- ↑ Inclination balance . S. 14 ( hennef.de [PDF; accessed on May 23, 2018]).
- ↑ load cells. Retrieved May 23, 2018 .
- ↑ Directive 2014/31 / EU of the European Parliament and of the Council of February 26, 2014 on the approximation of the laws of the member states relating to the making available on the market of non-automatic weighing instruments Text with EEA relevance . OJ L, 32014L0031, March 29, 2014 ( europa.eu [accessed May 23, 2018]).
- ↑ Signature pad and IP intercom self-service terminals. Retrieved May 23, 2018 .
- ↑ History of the Libra. (PDF) Retrieved May 23, 2018 .
- ↑ load cells. Retrieved May 23, 2018 .
- ↑ Error limits Eichamt NRW. (PDF) Retrieved May 23, 2018 .
- ↑ Measurement and calibration ordinance. (PDF) Retrieved May 23, 2018 .