A loader/shovel loader is a self-propelled earthmoving machine with a boom, linkage mechanism, and loading bucket articulated at the front of a chassis. It performs loading, transporting, unloading, and leveling operations while in motion. With appropriate attachments, it can also bulldoze, lift, and load/unload timber and steel, making it a very versatile piece of construction machinery. Introduction I. Characteristics and Weighing Measurement of Loaders Loaders are heavy, have short wheelbases, and are constantly in a mobile operating state, making it difficult to weigh their loads using fixed-position scales, as this would affect work efficiency. Therefore, finding a method to weigh the loads during operation is crucial to solving this problem. Generally, the higher the accuracy of the weighing, the better; a weighing error of approximately 0.1% to 0.5% is generally required. When loading bulk cargo with a loader, the initial method of estimating the weight by measuring specific gravity and drawing lines is used. However, this method suffers from large errors, high randomness, and inconvenience in management. Overloading results in direct economic losses and over-load transportation; underloading reduces transportation efficiency and harms customer interests. Furthermore, because loaders lack weighing devices, material loading and unloading still rely on truck transfers and weighbridges, leading to low efficiency and high costs. With the development of logistics loading and unloading industries such as railways, automobiles, ports, and docks, the requirements for loading efficiency, safety, and accuracy are increasingly stringent. An advanced loader weighing system is needed to achieve automatic and accurate measurement of goods during loading, significantly improving loading operation management, preventing overloading and underloading, increasing loading and unloading efficiency and benefits, and ensuring vehicle transportation safety. II. Introduction to the Weighing System Working Principle: A loader weighing system generally consists of two parts: a signal acquisition section and a signal processing and display section. The signal acquisition section typically uses sensors or transmitters, and the accuracy of the signal acquisition is crucial to the accuracy of the loader's weighing. 1. Static weighing systems are commonly used for retrofitting existing loaders or forklifts. When suitable weighing equipment is unavailable on-site, but the user needs to measure weight for trade settlement, static weighing is typically chosen due to cost constraints. Static weighing equipment consists of: a pressure sensor (one or two, depending on accuracy requirements) + a standard weighing display instrument (a printer can be added if necessary) + installation accessories (pressure pipes or process interfaces, etc.). General characteristics of static weighing: 1) The weighing hopper must be positioned consistently for each weighing to ensure accuracy, thus affecting weighing efficiency; 2) The equipment has fewer functions, requiring manual assistance for many tasks, such as recording and calculation; 3) Suitable for short-term operations where extensive data processing is not required; 4) Low cost, suitable for individual businesses or small units; 5) Fewer parameters involved, making installation and commissioning relatively convenient. 2. Dynamic weighing systems are recommended for loading and weighing in large units such as railway stations and ports to meet the needs of rapid, continuous weighing and large-scale data management. The dynamic weighing equipment mainly includes: pressure sensors (2 units) + dynamic control instrument (with printing function) + installation accessories. The main features of the dynamic weighing equipment are: 1) Cumulative loading, weight setting, display, and overload alarm functions; 2) Single bucket weight weighing and cumulative display functions; 3) Truck model selection or input function, truck number input function; 4) Operator, loader number, and loading station code input functions; 5) Operation time (year, month, day, hour, minute) recording function; 6) Basic operation data storage, printing, and query functions; 7) Employs dynamic sampling and fuzzy algorithms to achieve dynamic calibration and dynamic weighing, automatic weighing during lifting without stopping the bucket; 8) Powered by the loader's power supply; 9) Employs dual hydraulic sensors and a high-precision A/D converter for higher accuracy; 10) Can be set to automatic or manual zeroing. III. Scope of Application Applicable to automatic weighing and metering, overload protection, and workload management of loaders (including forklifts). It can weigh coal or coke, non-ferrous ore, earthwork, granite or marble, sand, crushed stone bricks, industrial and domestic waste, excavated materials, and building additives, etc. Applications: Wheel loaders in mines, stations, ports, docks, factories, freight yards, etc. IV. Sensor Selection Based on the operating characteristics of loaders, the signal acquisition section generally includes three types: load cells, pressure (hydraulic) sensors, and pressure (hydraulic) transmitters. It is important to emphasize that the sensors should have good overload resistance, vibration resistance, insulation, and anti-interference performance. A> Load cells generally use sensors to replace pins to achieve the weighing purpose. This solution requires high precision in sensor structural design and installation dimensions, so in actual operation, it often results in low accuracy, inconvenient installation and replacement, and even safety accidents, therefore it has not been widely adopted. B> Pressure (hydraulic) sensors convert liquid pressure into the weight of the loading bucket to complete the weighing operation. It is easy and quick to modify, and the measurement accuracy of the equipment is greatly improved compared to using load cells, while ensuring safety performance. C> Pressure (hydraulic pressure) transmitter sensors output mV signals. These small signals are easily interfered with during transmission and processing, leading to errors in the calculated weight and placing high demands on the display section. This makes them difficult to use in systems requiring high weighing accuracy. Transmitters effectively solve these problems. They have strong anti-interference capabilities and a large output signal (typically 4-20mA or 0-10VDC, 0-5VDC), significantly reducing the requirements for signal processing and display sections, and correspondingly enhancing the accuracy of the weighing system. Below are two pressure sensors and transmitters suitable for loader or forklift weighing devices: A1. Sputtered Thin Film Pressure Sensor (PPM-216A) This product uses sputtered thin film technology and is designed to meet the characteristics of loader weighing systems. It primarily measures the loader's hydraulic pressure and converts it into a weight signal. 1) Main features of this product: a) Small size and light weight, suitable for direct process installation; b) High precision and good long-term stability; c) Good resistance to vibration, impact, and overload; d) Corrosion resistant, high temperature resistant, and low temperature drift. 2) Main technical parameters of this product: Item Specification Item Specification Range 25MPa; 40 MPa; 60 MPa; 100 MPa; Safe overload 150%FS Output: 1.5～2.2mV/V Sensitivity temperature drift ±0.015%FS/℃ Power supply 5-10VDC Zero point temperature drift ±0.015%FS/℃ Accuracy ±0.1%; ±0.2% Ambient temperature -40～+125℃ Pressure interface M10x1 (double O-ring seal) Bridge arm resistance ≤2KΩ±0.5KΩ M14x1.5; M16x1.5; M20x1.5 Insulation resistance ≥2000MΩ (50V DC) A2, Sputtered Thin Film Pressure (Hydraulic) Transmitter (PPM-241A) The PPM-241A also acquires weight signals by measuring hydraulic pressure. Digital circuitry is used to process the sensor signal according to specific customer requirements. 1. Features of this product: a. Large signal strength, easy to convert. b. High accuracy and good stability. c. Good resistance to vibration, shock, and overload. d. Strong anti-interference capability. e. Corrosion resistant, high temperature resistant, and low temperature drift. 2. Main technical parameters of this product: Item Specification Item Specification Range 25MPa; 40 MPa; 60 MPa; 100 MPa; Safe overload 150%FS Output 4-20mA, 0-10VDC, 0-5VDC Sensitivity temperature drift ±0.01%FS/℃ Power supply 9-32VDC Zero point temperature drift ±0.01%FS/℃ Accuracy ±0.1%; ±0.2%; ±0.5% Ambient temperature -40～+125℃ Pressure interface M10x1 (double O-ring seal) Bridge arm resistance M14x1.5; M16x1.5; M20x1.5 Insulation resistance ≥2000MΩ (50V DC) B1. Resistance strain gauge pressure sensor (commonly known as patch sensor PPM-242L) When a loader weighs cargo, the oil pump connected to the bucket is constantly moving. The oil (the medium being measured) inside the pump experiences repeated high-pressure cycles, causing its temperature to rise. The PPM-242L sensor takes temperature factors into full consideration in its strain gauge selection, employing a high-temperature strain gauge. During manufacturing, appropriate measures are taken to minimize the sensor's temperature drift (<±0.03%FS). Installation is typically via a pressure-sensing pipe. This mitigates the temperature and impact on the sensor, thereby increasing the equipment's operational stability. 1) Main features of the PPM-242L: a) High accuracy and good long-term stability. b) Good sealing and corrosion resistance. c) Low cost and high cost-effectiveness. 2) Main Technical Parameters: | Item | Specification | Item | Specification Range | 0-100MPa selectable | |---|---|---|---|---| | Safe Overload | 150%FS | | Sensitivity | 1.5-2.0mV/V | | Sensitivity Temperature Drift | ±0.03%FS/℃ | | Power Supply | 10～12V DC (Recommended) | | Zero Point Temperature Drift | ±0.03%FS/℃ | | 15V DC (Maximum) | | Ambient Temperature | -30～+90℃ | | Accuracy | ±0.1%; ±0.2%; ±0.5% | | Bridge Arm Resistance | 350Ω | | Pressure Interface | M20x1.5; G3/8; Customized | | Insulation Resistance | ≥5000MΩ (50V DC) | | Wire | Φ5.5x5m | | Protection Rating | IP68 Based on the above and our experience accumulated during production, as well as customer feedback, we do not recommend using weighing sensors. Among hydraulic sensors, the PPM-242L is an economical option. The PPM-216A sensor and PPM-241A transmitter are both excellent sensors in terms of performance and ease of installation. The PPM-241A transmitter, in particular, has very low requirements for subsequent signal processing and instrument display, making it easier to use. V. Installation Precautions 1. Installation Location: On the hydraulic circuit of the left and right support arm cylinders. One on each side, as shown in the left diagram. Installation Method: 1. Install via an oil circuit adapter block. 2. Alternatively, connect via a pressure tap. 2. Installation Precautions: 1) Ensure a tight seal during threaded installation. Use sealant or Teflon tape as an auxiliary tool during installation. 2) Strictly follow the product manual for wiring to prevent product damage due to misoperation. 3) During calibration, perform multi-parameter tests for different orientations and angles to ensure consistent weighing accuracy under various conditions. 4) If space constraints prevent normal installation, consider using a pressure tube for installation. Secure the tube after debugging.