What Is a Dynamometer? A Guide to Force Testing for Packaging
Updated: 2 days ago
A dynamometer is a measuring instrument designed to evaluate the mechanical strength of materials, containers and products. It applies compressive or tensile forces and quantifies the resistance the material offers before it deforms or fails. Dynamometers are essential tools in quality control laboratories, in particular in the packaging, beverage and manufacturing industries.
How does a dynamometer work?
A dynamometer works with a load cell, a transducer that converts mechanical forces into measurable electrical signals. Compression and tensile test equipment combines a dynamometer and a motor: the motor applies the tensile or compressive force to the container, and the dynamometer measures this force, which reveals the deformation it produces.
Compression: measures the force a material can withstand before it deforms or crushes (for example, crushing a bottle).
Tension: measures the resistance to the separation of components (for example, removing a cap from a bottle).
The load cell is the key component. Its mechanical deformation is converted into a voltage or an electrical current, and an electronic controller processes this signal to display both the complete force curve and the maximum (peak) force the material withstood.
Main applications
Beverage industry: compression resistance tests on glass and plastic (PET) bottles.
Caps and corks: measurement of the force required to remove caps or corks from bottles.
Tubes: evaluation of tube welds and laminate strength.
Cables and cords: tensile tests to determine the strength of solid or braided materials.
Metal containers: aluminum cans for soft drinks or metal cans for preserved food.
Key concepts: precision, accuracy and resolution
These terms are often confused:
Precision (repeatability): the ability of an instrument to give the same value when it measures several times under the same conditions.
Accuracy: how close the measurement is to the true value. It is often given as a percentage of full scale (for example ±0.5% F.S.).
Resolution: the smallest difference the instrument can display between two close values.
In general, the larger the measuring range, the coarser the resolution. For example, the AT2E BTLT-2, which measures up to 20 kN, has a resolution of 0.01 kN (10 N), while the TCT-2, which measures up to 1500 N, has a resolution of 0.01 N. In the same way, a 30 cm ruler cannot easily measure below one millimeter.
The elastic phase of materials
All materials have an elastic phase: the range in which they deform and return to their original shape when the force is removed. Beyond this elastic limit, the material deforms permanently or breaks.
For example, a rubber band stretches and returns to its shape, but breaks if it is stretched too far. Concrete has an almost imperceptible elastic phase, while plastic has a more pronounced one. The dynamometer measures the force required to go beyond the elastic phase and cause rupture.
Dynamometer calibration
A dynamometer is calibrated against another dynamometer used as a reference standard. This process, called calibration by direct comparison, consists of:
Placing a reference load cell (of known value) in contact with the load cell of the equipment to be calibrated.
Applying progressive forces and comparing the measurements of the two cells.
Recording the errors and uncertainties to issue a calibration certificate.
When a dynamometer shows an error above the acceptable limit, the cell is not replaced immediately: the conversion factor is first adjusted in the control software. If the error still exceeds the limits after adjustment, the cell must be replaced.
AT2E dynamometers
On AT2E force testers, the operator installs the sample and starts the test; the machine applies the force and records the deformation or the breaking force.
DYNA-4000: top load tests on containers in different materials, with a measuring range of 0-3000, 0-4000 or 0-5000 N.
TCT-2: traction and compression tester, 0-1500 N in compression and 0-500 N in traction, with fixtures for many other tests.
BTLT-2: top load tests on glass bottles up to 20 kN, in line with ISO 8113:2004.
POT-1: two-step opening force of pull-off caps.
Conclusion
The dynamometer is an essential tool for ensuring the quality and safety of packaged products. Understanding how it works, the difference between precision, accuracy and resolution, and the importance of regular calibration helps choose the right equipment and obtain reliable results.
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