By Larry Behrens
Electronic scales are available in many different configurations to meet diverse application requirements. Though they come in many forms, electronic scale systems deliver dependable accuracy in a rugged, convenient package. From material collection to processing, storage and sale, users will find a suitable scale for each stage of aggregate production.
The heart of an electronic scale is the load cell weight sensor, which converts force measurements into an electrical signal read by a connected weight indication system. The most common style of load cell is based on the cantilever principle, where one side of the cylindrical device is fixed and the other suspended. A load – in this case, either a vehicle carrying aggregate materials or the aggregate alone – is placed on the suspended end, which absorbs the force of the applied load. This force measurement is translated as the load’s weight.
One particularly effective style of load cell operates using two pairs of electronic sensors, also called strain gauges, placed on the outside of the load cell structure – one on top and one on the bottom. The advantage of two sensor pairs is demonstrated when load placement varies in position atop the load cell, or when various types of loading errors occur such as end loading, side loading and torsion effect. The sensor arrangement ensures uniform compressive strain throughout the full load cell structure, delivering consistent readings despite these variances.
This load cell may be incorporated into many types of scales, including a truck scale. An electronic load cell may also be integrated into aggregate processing and handling equipment, such as conveyors and front-end loaders, to deliver accurate material weighing and tracking from aggregate collection to sale.
Tracking Raw Material
Typically, an aggregate producer will weigh company trucks and program the connected digital weight indicator to store the weight, as well as any pertinent data such as truck number or driver ID, for each vehicle. This arrangement facilitates one-time weighing: A driver returns from the quarry with the aggregate load and, once prompted, enters a driver ID via the indicator’s keypad.
This ID is associated with the empty truck weight taken earlier, which now serves as a tare weight. The truck is then weighed full, and the indicator generates the net weight of the load. The indicator is often accompanied by a printer as well, allowing drivers to print a receipt immediately after the transaction. An alternative, simpler solution utilizes the weight indicator as basically a local display: The indicator will merely gather and convey the truck’s weight so that it can be manually documented.
To measure the amount produced of each grade, a belt scale can be used to obtain the weight of the aggregate materials during the transport process. In this arrangement, load cells replace the idlers in the traditional conveyor design. As aggregate travels down the conveyor belt, the belt scale obtains the weight of all material crossing the load sensors.
This weight data is gathered by the belt scale’s indicator, which also tabulates the aggregate produced to determine a total. Users can document the total weight by hand, or the indicator can communicate the weight data directly to the aggregate producer’s inventory system. Since each belt scale is used for a different grade of aggregate, the weight information collected can be easily categorized by grade to simplify inventory monitoring.
Another way to improve aggregate inventory records involves installing a scale system onto a front-end loader. Load cells can be installed beneath the scoop of the front-end loader, so that the aggregate materials are weighed as they are lifted and transported into stock. These load cells send electronic signals in response to the strain experienced by the load to an in-cab instrument, which replaces the traditional weight indicator in this scale arrangement. More sophisticated in-cab instruments can be programmed to store each load’s weight by the grade, allowing users to closely monitor gravel inventory with every delivery.
Selling Aggregates with High Accuracy
When aggregates are sold to trucking and construction companies, truck scales are obviously used to gather the weight of materials by the truckload. This scale may be paired with a simple weight indicator used to display and print weight designations, as with raw materials. However, when selling materials, several factors may need to be tracked:
- Purchasing company’s name.
- Amount of aggregate to be purchased (by weight).
- Grade of aggregate to be purchased.
- Driver ID.
- Truck number.
Here, a sophisticated weight indicator can also prove advantageous. The display on the indicator can provide operator messages and images to enhance the operator HMI. This operating routine of the indicator can be tuned to meet the application. It can facilitate one-time weighing by storing the empty weights of trucks from multiple customers – plus information such as truck number, driver ID and company name – in the indicator to serve as tare options.
Then, when picking up a purchased load, a driver from one of these companies merely enters an ID number into the indicator to set the tare weight, as well as the grade and amount of aggregate to be purchased. The indicator then generates the legal-for-trade net weight of the load in a single step. The driver can then select to print a receipt of the transaction, or for invoicing, the weight indicator may be programmed to communicate this data to the aggregate producer’s main computer database.
In addition, if the indicator software is linked to the aggregate producer’s inventory system, the benefit is twofold. First, users can verify that current inventory levels can support their customer’s order. Second, once the aggregate is loaded and weighed, this amount can be subtracted from inventory immediately, updating records in real time. These advantages ensure aggregate producers not only remain compliant with legal-for-trade requirements, but also improve inventory records – all by tracking aggregate production from start to finish.
By utilizing advanced weighing technology to enhance aggregate applications, weighing inaccuracies and humor error is minimized and uptime is maximized, allowing operators to improve productivity and profitability.
Larry Behrens is global product manager, Truck and Rail Scale, Avery Weigh-Tronix, www.averyweigh-tronix.com.