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Load Cell in Accuracy Class C3 Approved to OIML R60
At the heart of modern scales is the load cell. Depending on the scale type and model, it might feature several such cells. For smaller platforms catering for relatively nominal loads, it is normally sufficient to use just a single load cell (single-point scales). Larger platform, floor and pallet scales and many other weighing systems tend to be equipped with 4 or more of an shear beam load cell. The accuracy of the instrument and the reproducibility of the measured values are determined by the quality of the load cell. That is why force transducers from BOSCHE come with an accuracy of minimum 0.03. Most BOSCHE transducers meet the requirements of OIML accuracy class C3. Our products thus conform to the stringent requirements that apply to verified scales. All BOSCHE load cells are designed as strain gauges with full bridge circuits. The output / full bridge signals of the load cell are in mV / V. BOSCHE load cells are based on four-wire technology and can be upgraded on request for six wires. Read more...
At the heart of modern scales is the load cell . Depending on the scale type and model, it might feature several such cells. For smaller platforms catering for relatively nominal loads, it is...
read more »
Load Cell in Accuracy Class C3 Approved to OIML R60
At the heart of modern scales is the load cell. Depending on the scale type and model, it might feature several such cells. For smaller platforms catering for relatively nominal loads, it is normally sufficient to use just a single load cell (single-point scales). Larger platform, floor and pallet scales and many other weighing systems tend to be equipped with 4 or more of an shear beam load cell. The accuracy of the instrument and the reproducibility of the measured values are determined by the quality of the load cell. That is why force transducers from BOSCHE come with an accuracy of minimum 0.03. Most BOSCHE transducers meet the requirements of OIML accuracy class C3. Our products thus conform to the stringent requirements that apply to verified scales. All BOSCHE load cells are designed as strain gauges with full bridge circuits. The output / full bridge signals of the load cell are in mV / V. BOSCHE load cells are based on four-wire technology and can be upgraded on request for six wires. Read more...
The quality of the installed load cells is crucial for high weighing accuracy and reproducible values. For this reason, the force sensors belonging to the weight sensors by Bosche Weighing Technology, have a minimum accuracy of 0.03, but most of them are certified according to the OIML accuracy class C3. This allows our load cells to meet the high requirements set for calibrated scales. All BOSCHE load cells are based on the STRAIN GAUGE measuring principle with full-bridge circuitry. The output signal / bridge signal of the load cells is mV / V. By default, all measuring cells use 4-wire technology. Connection in 6-wire technology is available upon request. Optional models with an extended compensated temperature range or ATEX certified load cells for use in hazardous areas can also be offered.
Please note: Load cells are only one part of the components required for weight determination. In addition, you need evaluation electronics such as weighing transmitters or a scale display.
Depending on the application, a targeted question leads to the right load cell. For example, in crane scales and similar applications, tension force sensors are used, and wherever tension force needs to be determined, an S-shaped load cell is used. For vertical force application, shear beams are suitable. The rated load is also crucial in choosing the right load cell. While single point load cells with rated loads of up to 2000 kg are mainly used for low loads with high resolution in the g or mg range, compression load cells offer a weighing range of up to 500 t, optionally more.
Load cells are needed to build weighing devices (scales). The most important part of a load cell is the so-called load-bearing body. This is a metal part that deforms under weight. This deformation is detected by a strain gauge and converted into an electrical signal.
In the case of a bending beam, the most commonly used load-bearing body, the applied weight causes a deformation of the load-bearing body. The operation of a multi-bending beam is similar, with multiple bending beams coupled so that simultaneous deformation occurs in all beams when force is applied. Coupling multiple bending beams is used in platform scales. For weighing devices with higher rated loads, shear beam load cells are used. The operation is similar to that of bending beams. Shear beams are suitable for measuring with a vertical force application. S-shaped load cells are used when measuring tension force. The load-bearing body is deformed by tension. Column-like compression load cells or hollow cylinder load cells are deformed by compression. Membrane load cells also react to pressure, but they are smaller and have higher rigidity.
The different load cells have different mechanical properties that are required for various applications. Load cells with high dynamics are used where many weighing processes must be performed in the shortest possible time, such as on automatic sorting systems. For static applications, such as a weighing platform, dynamics are less important. Here, the load cells are selected based on size or mounting direction.
Technical Terms and Definitions for Load Cells
Load-Bearing Body – A load-bearing body is the main component of a load cell. It is a piece of metal that deforms slightly under the influence of force or weight. The load-bearing body must be designed so that the deformation process is reproducible and linear. The deformation stretches the surface of the load-bearing body. This stretching is measured by a strain gauge attached to the load-bearing body.
Strain Gauge (DMS) – The strain gauge is attached to the load-bearing body. It consists of a measuring grid applied to a carrier. When the load-bearing body deforms due to the application of force, the deformation is detected by the measuring grid and converted into an electrical pulse. To compensate for measurement errors, usually four strain gauges are connected to form a Wheatstone bridge circuit. The strain gauges on the load-bearing body are placed in such a way that two strain gauges are always compressed and two are stretched.
Electrical Pulse – An electrical pulse occurs when electrons (negatively charged particles) move toward a positively charged pole. In weighing technology, the electrical pulse is the voltage output by the strain gauge when the measuring grid in the strain gauge detects deformation. This electrical pulse is then transmitted to a control unit, which calculates a change in weight from this electrical signal.
Control Unit – The control unit converts the electrical pulses forwarded by the strain gauges into the actual weight. This means that the control unit calculates the weight from the electrical pulses and displays it on a display.
Resolution – In weighing technology, resolution refers to the precision with which weighing can be done. The resolution of a scale is calculated from the minimum division value of the load cell and the number of load cells used.
Tare Weight – Tare weight refers to the packaging weight or the weight of the empty container.
Tensile Force – Tensile force refers to a force that acts from the attachment point of an object to the point of force application, i.e., the force with which an object is pulled. Tensile force is measured in Newtons (N).
Measurement Parameters of Load Cells
In addition to mechanical properties, load cells also have specific measurement properties that are relevant for their use. Of course, the rated load is very important. This is given in grams, kilograms, or tons. Another value is the maximum load, at which the load-bearing body is permanently deformed or damaged. Another important value is the sensitivity, which describes the output signal at rated load. The common value here is 2mV/V. The designer of a scale also needs the minimum division value of the load cell. From these parameters, technical data of the scale can then be calculated, such as the measurement accuracy, the rated load of the scale, or the maximum allowable tare weight.
Other important parameters include the output resistance (especially when multiple load cells are connected in parallel) or the load creep (variations in output value with longer load application).
Since scales are often used in the food industry, where scales are subject to legal calibration requirements, the load cells used there must also be suitable for calibration. The special requirements for a legally calibrated scale or load cell in this regard are regulated by law.
Applications of Load Cells
Load cells in various designs are mounted wherever tensile or compressive forces or deformations of solid components need to be measured. In addition to the load cells, evaluation is also required. In the evaluation units for load cells section, we offer a comprehensive range of weighing electronics and transmitters. There is a suitable solution for every area, whether you only want to read a value, need an output signal for further processing in an SPS, or want to switch relays with potential-free contacts. Individual solutions with our weighing systems are also possible. In addition to the existing standardized software packages, adaptations can be made to your existing system.
We are happy to provide our expertise for your planning.
