During load cell calibration, a device with a standard measurement is attached to the transducer. Its reading is compared to the reading of the load cell; ideally, both the calibrating device and the transducer will have the same measurement. If not, the operator makes the necessary changes and adjustments before measuring again to ensure that the values are identical.
This process of calibration is important because accurate and precise readings from the load cell are important and vital to its proper functioning. An incorrect measurement of the electrical signal may be a safety hazard or could lead to equipment damage. Load cells are generally part of larger systems so other decisions are made based on the reading provided by the transducer which is why they must be checked and calibrated regularly.
Regular calibration also maintains quality standards. Calibration is used not only for load cells but with a wide range of equipment and machines as well as for pressure, speedometers, temperature and torque. Load cells are frequently used for large scale weighing in hoppers, for trucks, tank level, in-line force measuring and weighing research.
Load cells are available in a variety of styles including S-beam, platform and single point, low profile, compression, compression/tension, bending beam and canister. Some are designed to read the force acting on a button while others have larger parts that are bent; all rely on the physical deformation of strain gauges.
As force is applied to the load cell, a strain gauge is bent. The strain is converted into electrical signals, which are amplified; typically one load cell will have at least four strain gauges. The output is then entered into an algorithm to calculate how much force was applied to the transducer. The gauge inside has a spring-like quality that allows it to bounce back after a load is applied. If the loads are changed abruptly, the gauge may vibrate quickly, a consequence called ringing.
During calibration, a certain load with a known exact weight is placed on the load cell. Like other devices that must be periodically calibrated, the load cell is designed to accept calibration by conducting measurements that are within engineering tolerances when used over time in certain environmental conditions. If the load cell has a flawed design then no amount of calibration can correct it.