Silo-Weigh™ solves challenging high capacity weighing application at Castle Hill Quarry
A high capacity Silo-Weigh™ system, installed by AV Technology Ltd (AVT) on two large limestone silos, is playing a vital operational role at Castle Hill Quarry in Cannington, Somerset.
The two outdoor silos, with a combined capacity of 400 tonnes, are mounted on a common structure supported by six steel legs. It is notoriously difficult to achieve accurate contents measurement on such silos. Modern level control systems may be able to achieve reasonable average level measurement results, but changes in bulk density and surface topography during filling and emptying prevent them from providing sufficiently accurate weight related contents. Retro-fitting traditional load cells is not only very disruptive but also prohibitively expensive, with structural cross-talk further complicating matters.
The cost effective Silo-Weigh solution brings a fresh approach to high capacity silo weighing and is the result of extensive development over more than a decade. It has an excellent track record on large steel and concrete silos in applications where established measurement systems do not give reliable results. Unlike traditional weighing companies, AVT have a detailed understanding of the behaviour of structures based on over 25 years’ experience and their approach takes into account application problems such as low signal levels, temperature effects and cross-talk. While most current retrofit sensors are based on electrical resistance strain gauges, which struggle to provide sufficient stability and accuracy, the Silo-Weigh system uses specially developed ‘low strain’ sensors. These devices are insensitive to moisture, long cable runs and low signal levels.
Castle Hill set a number of difficult challenges for the AVT system: not only did they want to measure the individual and combined contents of each silo, but also be able to weigh out known amounts into waiting vehicles, whilst the silo filling process continued. The latter enables optimum vehicle loading, prior to final check weighing on the weighbridge.
The raw compressive strain levels in the legs are measured using six spot weldable strain sensors, mounted so that any bending components of strain are cancelled out. Data from these, together with information from the adjacent temperature sensors, is fed back to a powerful Campbell Scientific CR1000 data logger. Engineers applied protective coatings to the sensors and UPVC thermal shielding wrapped around the legs minimizes the temperature effects on the strain gauges.
There are four individual weight displays in the central control and readout unit. The first three show the combined weight contents of the two silos and the calculated individual content weights. The fourth display normally indicates the average fill rate in tonnes per hour, but is also used during load outs to show the amount taken out of the silos. This is calibrated from 0- 50 tonnes and is zeroed just prior to vehicle loading by pressing a button adjacent to the display. This action also increases the system measurement update rate to improve accuracy. To compensate for the material entering the silos as product is simultaneously discharged, the calculated weight taken out is automatically adjusted using an historic ten minute fill rate measured just prior to vehicle loading.
The Silo-weigh system, which is totally non-intrusive, can be fitted without having to stop the process or empty the silos. Calibration at the Castle Hill Quarry site was achieved using theoretical values and known physical load additions. During the commissioning phase, data from the system was transmitted via modem to AVT’s offices in Cheshire. This remote access to data allowed AVT engineers to fine tune the system over a period of several weeks, without the need for unnecessary site visits.
Castle Hill’s Operations Manager Stephen Ford is delighted with the Silo-Weigh system and as he concludes: “At first we were a little sceptical about the system, but AVT were confident they could achieve what we wanted. Our initial concerns were unfounded and we can now reliably measure combined silo capacity better than 1.5%. Being able to measure and control how much material is loaded into vehicles is extremely useful and results are better than expected. Prior to the Silo-Weigh installation, over-loaded vehicles had to return from the weighbridge and discharge part of their load before departure from site. AVT’s attention to detail has been excellent and they spent time remotely fine tuning the system based on actual results.”
The Silo-Weigh™ System
Silo-Weigh™ solves challenging high capacity weighing application at Castle Hill Quarry
A high capacity Silo-Weigh™ system, installed by AV Technology Ltd (AVT) on two large limestone silos, is playing a vital operational role at Castle Hill Quarry in Cannington, Somerset.
The two outdoor silos, with a combined capacity of 400 tonnes, are mounted on a common structure supported by six steel legs. It is notoriously difficult to achieve accurate contents measurement on such silos. Modern level control systems may be able to achieve reasonable average level measurement results, but changes in bulk density and surface topography during filling and emptying prevent them from providing sufficiently accurate weight related contents. Retro-fitting traditional load cells is not only very disruptive but also prohibitively expensive, with structural cross-talk further complicating matters.
The cost effective Silo-Weigh solution brings a fresh approach to high capacity silo weighing and is the result of extensive development over more than a decade. It has an excellent track record on large steel and concrete silos in applications where established measurement systems do not give reliable results. Unlike traditional weighing companies, AVT have a detailed understanding of the behaviour of structures based on over 25 years’ experience and their approach takes into account application problems such as low signal levels, temperature effects and cross-talk. While most current retrofit sensors are based on electrical resistance strain gauges, which struggle to provide sufficient stability and accuracy, the Silo-Weigh system uses specially developed ‘low strain’ sensors. These devices are insensitive to moisture, long cable runs and low signal levels.
Castle Hill set a number of difficult challenges for the AVT system: not only did they want to measure the individual and combined contents of each silo, but also be able to weigh out known amounts into waiting vehicles, whilst the silo filling process continued. The latter enables optimum vehicle loading, prior to final check weighing on the weighbridge.
The raw compressive strain levels in the legs are measured using six spot weldable strain sensors, mounted so that any bending components of strain are cancelled out. Data from these, together with information from the adjacent temperature sensors, is fed back to a powerful Campbell Scientific CR1000 data logger. Engineers applied protective coatings to the sensors and UPVC thermal shielding wrapped around the legs minimizes the temperature effects on the strain gauges.
There are four individual weight displays in the central control and readout unit. The first three show the combined weight contents of the two silos and the calculated individual content weights. The fourth display normally indicates the average fill rate in tonnes per hour, but is also used during load outs to show the amount taken out of the silos. This is calibrated from 0- 50 tonnes and is zeroed just prior to vehicle loading by pressing a button adjacent to the display. This action also increases the system measurement update rate to improve accuracy. To compensate for the material entering the silos as product is simultaneously discharged, the calculated weight taken out is automatically adjusted using an historic ten minute fill rate measured just prior to vehicle loading.
The Silo-weigh system, which is totally non-intrusive, can be fitted without having to stop the process or empty the silos. Calibration at the Castle Hill Quarry site was achieved using theoretical values and known physical load additions. During the commissioning phase, data from the system was transmitted via modem to AVT’s offices in Cheshire. This remote access to data allowed AVT engineers to fine tune the system over a period of several weeks, without the need for unnecessary site visits.
Castle Hill’s Operations Manager Stephen Ford is delighted with the Silo-Weigh system and as he concludes: “At first we were a little sceptical about the system, but AVT were confident they could achieve what we wanted. Our initial concerns were unfounded and we can now reliably measure combined silo capacity better than 1.5%. Being able to measure and control how much material is loaded into vehicles is extremely useful and results are better than expected. Prior to the Silo-Weigh installation, over-loaded vehicles had to return from the weighbridge and discharge part of their load before departure from site. AVT’s attention to detail has been excellent and they spent time remotely fine tuning the system based on actual results.”
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