Checking the tension applied to wires, yarns, tapes, drive belts, wire ropes and bolts is a key technological parameter in many production and operating processes. In textile and wire-drawing processes, the tension of the material determines the geometrical and mechanical quality of the product. In belt drives, correct tension is essential for service life, efficiency and quiet running. In critical bolted connections, monitoring the elastic elongation of the bolt by ultrasound provides more reliable control than torque tightening alone.
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Principles of tension measurement
Mechanical three-roller tension meters exploit the deflection of the material between two guide rollers and a movable central one held by a calibrated spring: the force needed to keep the central roller aligned is proportional to the tension of the material. Electronic tension meters use high-sensitivity strain gauge load cells with a digital display, memory and data output. For drive belts, static methods (deflection under load) and dynamic methods (vibration frequency) are used, measured with optical or contact tension meters. Ultrasonic bolt tension monitoring measures the flight time of a UT pulse in the shank before and after tightening: the elastic elongation is derived from the difference, with accuracies better than 5 % on the axial force.
Categories of instrument
This section comprises portable mechanical tension meters (single-head or three-head) for measuring tension on wires, yarns and fibres in classes from cN to kN, electronic tension meters with memory and data output, stationary single-roller and three-roller tension meters for integration into production lines, tension meters for V-belts, timing belts and mechanical drive belts, specific tension meters for steel ropes, tie rods and structural cables, sensors, indicators and tension amplifiers for custom applications, and ultrasonic bolt tension monitors for critical mechanical constructions.
Fields of application
The main applications are in the textile and knitwear industry (checking yarn tension at every stage of processing), in the drawing of metal wires and electrical cables, in the production of plastic tapes and films, in the maintenance of industrial belt drives, in checking the tie rods of structures (bridges, roofs, antennas, cranes), in monitoring stay cables and ropes in infrastructure, and in tightening critical bolts in turbines, pumps, generators, and petrochemical and nuclear plants. Ultrasonic measurement of bolt tension is today regarded as best practice in sectors where failure through fatigue or loss of preload has catastrophic consequences.
Standards
For drive belts, DIN 7753 (narrow belts) and ISO 1081 for terminology apply. Ropes and structural cables are governed by EN 12385 (terminology and classification) and by EN 1993-1-11 for structural calculation. Ultrasonic bolt monitoring follows ASTM E1924 and sector-specific standards (for example PMI – Power Industry, ASME PCC-1). Periodic calibration of tension meters is carried out with calibrated masses or master transducers calibrated to ISO 17025.
Selection criteria
Choosing the right tension meter depends on the material (yarn, tape, rope, belt, bolt), on the tension range (cN, N, kN, tens of kN), on the dynamics of the process (static or high speed), on the accuracy required, on portability or integration, and on the output interfaces. Ultrasonic bolt tension meters require preparation of the surfaces and a preliminary check of the acoustic coefficient of the bolt material. The child pages illustrate each type in detail, with performance parameters and fields of application.
Integrating stationary tension meters with line control systems allows automatic adjustment of the process tension, reducing scrap and improving the consistency of the product. In recent years, wireless transmission of measurements from portable tension meters to mobile platforms has also become widespread, for immediate archiving and reporting.
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