Force sensors, load cells and their amplifiers are the fundamental components of every force measuring system in industry, testing, weighing and process control. They convert a mechanical quantity (force, weight, pressure) into a measurable electrical signal (mV/V, V, mA, digital) by means of transducers based on various physical principles. The availability of load cells in many geometries, capacities and accuracy classes makes it possible to build custom solutions for tailor-made test stands, integration into industrial machinery, structural monitoring systems and industrial weighing.
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Transduction technologies
The most widespread technology is the strain gauge load cell, in which wire or thin-film resistive strain gauges are bonded to an elastic transduction element (S, button, pancake, pin, beam or canister geometry); elastic deformation under load changes the resistance of the gauges, producing an imbalance signal from the Wheatstone bridge. Piezoelectric cells use quartz crystals or piezoelectric ceramics that generate an electrical charge under deformation: they are ideal for high-frequency dynamic forces but not for prolonged static measurement. Capacitive cells measure changes in the capacitance of a moving electrical transducer and are used for high-precision, low-force applications.
Types of strain gauge cell
The most widespread load cell geometries are: S-type (for tension and compression up to a few kN, test stand applications); pancake (low profile, high load capacity, up to hundreds of kN); button (small, for integration into machines, up to kN); bending beam (for industrial weighing, up to a few tonnes); shear beam (for medium to high capacity applications); canister (for weighing tanks, silos and weighbridges, up to hundreds of tonnes); and pin (for measuring tension in ropes and tie rods). Each geometry is optimized for a specific load direction.
Amplifiers and indicators
Strain gauge cells produce low-level output signals (typically 2 mV/V at full scale) that require amplification and conditioning before they can be read. Dedicated amplifiers provide a stabilized supply to the Wheatstone bridge, signal amplification with offset and shunt calibration, and conversion to an analog output (4-20 mA, 0-10 V) or a digital one (RS-485, Modbus RTU, CAN, Profibus, Profinet). Industrial indicators combine the amplifier with a digital display, calibration functions, alarm thresholds and data output. They are the typical front end of weighing and testing systems.
Applications
Load cells and force sensors are used in: universal materials testing machines (UTM); custom test stands (tensile, compression and fatigue testing, in line with the product); industrial weighing (bench and floor scales, weighbridges, silos, closed containers); dynamic weighing systems (filling machines, dosing units, in-line weight control); structural maintenance (monitoring forces on columns, tie rods and trusses); safety systems (force-sensing doors, intrusion detection); robotics (control of gripping force and working pressure); and sports engineering and biomechanics applications.
Characteristics and standards
The main characteristics of a load cell are: rated capacity, accuracy class (C3, C4, C6 for legal weighing; classes 0.02 / 0.05 / 0.1 / 0.5% F.S. for industrial applications), linearity error, hysteresis, repeatability, thermal drift (the effect of temperature on the output), rated sensitivity (mV/V), bridge resistance (Ω), maximum supply voltage and safe overload. The reference standards are OIML R60 (cells for weighing instruments) and ISO 376 (calibration of cells for testing machines). ISO 17025 calibration is required for applications with certified accuracy.
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