Product category:
Loadcells, Force Sensors and Torque Sensors
News Release from: Weightron Bilanciai | Subject: Solar weighing system
Edited by the Engineeringtalk Editorial
Team on 28 February 2003
Rail-weighing system appeals to railways
A new concept in high-accuracy in-motion rail-weighing technology from Pfister Waagen Bilanciai is set to provide the user with distinct advantages over existing systems.
A new concept in high-accuracy in-motion rail-weighing technology from Pfister Waagen Bilanciai is set to provide the user with distinct advantages over existing systems Their new Solar weighing system has already proven itself in Australia and mainland Europe, across a broad spectrum of industries
This article was originally published on Engineeringtalk on 9 Apr 2001 at 8.00am (UK)
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Pfister has extensive experience in rail weighing and is part of the successful Bilanciai Group whose UK operation, Weightron Bilanciai, is based in Chesterfield.
Current systems for weighing rolling stock fall into two main categories, relatively low accuracy portable or retrofit systems and higher accuracy, designated fixed installations.
The latter are expensive and require significant disruption to the existing track during installation.
The Solar dynamic rail weighing system offers the high accuracy of traditional rail weighbridges without the track disruption and need for comprehensive foundations.
The system offers exceptional performance of Class 0.5 (calibration error 0,25 %) as laid down by the internationally recognised OIML R106 requirements for approved (legal for trade) in motion, rail-weighing systems.
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Although optimum accuracy is achieved at speeds of around 5-15km/h, the Solar has been used for weighing at speeds of up to 60km/h when it still returns accuracies of around 2% (non approved).
The performance of the Solar is such that it can also act in static mode as the reference scale for weighing the railcars used for dynamic calibration of weighing systems.
This removes the necessity for a separate, external static scale.
As the movement of freight by rail increases, the accurate monitoring of the weight of trains is becoming increasingly important for both commercial and safety considerations.
The recent crash at Hatfield was directly attributed to damage to the track and subsequent checks highlighted extensive wear throughout the UK rail network.
It can clearly be shown that most track damage is done by freight trains, especially if the rolling stock is over loaded or has poor load distribution.
Even 1% overloading significantly increases track wear and damage.
An important feature of the Solar is that it can check both overloading and asymmetric loading of railcars during the weighing process.
Rail network operators are now looking to obtain revenue from freight companies to help pay for upkeep of the tracks.
Freight operators are already being charged for rail usage on a weight basis in mainland Europe and it is only a matter of time before this is instigated in the UK.
So called 'freight corridors' across Europe have designated check areas where the weights of passing trains can be recorded in order to charge the operators.
Nick Catt, Sales Director for Weightron Bilanciai is very upbeat about the new system: "The Solar meets the growing demands in the UK for accurate rail weighing that can be installed with the minimum of fuss.
This new technology is based on an innovative blend of sound mechanical principles, modern electronics and versatile software.
Special weighing sleepers, whose size and weight exactly match standard concrete sleepers, are at the heart of this new concept.
These are used to replace the existing sleepers over a designated length of track, thus converting the section into an accurate weighing scale.
There is no need to cut the track and a typical system can be installed and calibrated in less than two days, compared with conventional fixed installations which can take several weeks to fit".
The sleepers are made from steel plate and house two special fully sealed load cells mounted directly underneath the rail supports.
The load cells have a pretensioning assembly to ensure consistent loading and are interconnected by means of an I beam which maintains track gauge stability.
By using load cells specifically designed for the application, Pfister ensures optimum load introduction and high accuracy.
By comparison, retrofit systems rely on fitting sensors directly to the rail itself and therefore are subject not only to errors arising from the anomalies of the track dimension and material but also low signal levels The Solar system does not rely solely on the weighing sleepers to provide accurate weight information.
Lateral forces in the rail have a small yet significant affect on weighing performance and the errors introduced are dependent on factors such as speed and track settlement.
To compensate for these errors, the Solar system uses lateral force sensors fitted directly in the track before and after the designated weighing section.
These sensors measure the shearing strain between the measuring sleepers and the adjacent, not sensored rail section.
The results from these sensors are combined with the weight readings from the sleepers to compensate for lateral forces.
Fitting the special weighing sleepers is very straightforward and requires the minimum of disturbance of the track ballast.
Once the sleepers are fitted and the track bolted down, the ballast consolidating equipment re-tamps the ballast around the sleepers.
The weighing accuracy is proportional to the number of sleepers replaced and for an approved system, the weighing part must be at least 4.2m, equating to seven sleepers.
The system monitors the ongoing condition of the track bed below the sleepers for resilience and local settling which will affect weighing performance.
Any settlement will increase the lateral forces in the rails and variations in signal distribution over time are statistically analysed.
Results outside acceptable tolerances are then flagged up so that remedial action can be taken.
If any of the sleepers become loose, the ballast can be re-tamped without affecting calibration.
Signals from the sleepers and lateral sensors are transmitted via an optical fibre bus system to the master control unit.
The optical fibres provide a robust communication and prevent interference from electrical noise.
Both the load cells and control unit are protected against electrical surges caused by lightning or electric locomotives Pfister has invested considerable time and effort into developing the powerful software and data collection system.
This provides extensive data from any weighing that takes place.
The system can differentiate between different rolling stock, for instance whether it has single, double or triple axles and whether these are close coupled.
It can also tell whether the rolling stock is being pulled or pushed and whether the train is accelerating or braking.
Predetermined train profiles can be entered into the unit, which can be then called up as required.
If an 'unknown train' is keyed in, the system will learn the characteristics of this for future reference.
The system can calculate net weights of goods or materials either using tare weight data or weighing results for the full and empty train.
If it is registered that the train comes back over the weighing section in reverse after unloading, the system will automatically reverse the train profile to ensure correct results.
It will also automatically subtract the weight of the locomotive from the rest of the train.
All the accumulated data is stored in the archives, building up extensive historic records of train weights and characteristics.
As Nick Catt concludes: " We are confident that the Solar system will be attractive to both rail operators and industries including mining, nuclear, petrochemical and minerals.
It is designed to meet commercial and legislative requirements and is already ahead of its time.
Not only can the system be installed very quickly but it can also be easily moved to a new location if required".
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