Two “standard” measurement methods
If you want to calibrate any type of testing machine, either for quality purposes or to obtain an official calibration certificate, then choose a transfer reference force transducer. There are two methods which can be used to measure a force with accuracy:
- ‘dead-weight machines’, and
- testing machines equipped with a transfer force transducer.
The first solution is quite expensive and difficult to operate, but the second one is cost-effective and gives you added flexibility.
These also meet the requirements dictated by quality control requirements in the context of Quality Assurance (ISO 9000) and certifications of calibration laboratories according to ISO 17025.
We have also developed standard reference force transducers with a digital output and dedicated ISO 376 software to connect them to your computer, thus greatly improving the value for money of the measurement chain.
The ISO 376 standard covers the calibration of force-measurement instruments used for the static verification of uniaxial testing machines, such as tension/compression testing machines, and describes a procedure for classifying these instruments.
As a result, this rubric offers a full description of various SENSY products designed for calibrating all testing machines (force or torque) used for quality control. Below, the heads of testing laboratories will find useful information to guide their work.
Force and torque transducer calibration
When the ratio of force applied to a dynamometer or a torque meter cannot be accurately determined by a calculation, it is necessary to perform a calibration procedure. This involves establishing the exact ratio between the force (or torque) applied to a dynamometer (torque transducer) – input – and the electrical signal it releases – output. In essence, the operation comprises applying forces to a dynamometer that can be accurately measured then registering the values provided by the electronic equipment connected to the transducer. This operation is generally performed by applying the protocol established by international standard ISO 376 which provides for classification of the dynamometer according to precision criteria. The results of the dynamometer calibration will determine the mathematical polynomial to the 2nd or 3rd degree, which enables calculation the value of the force applied to the dynamometer as indicated by the electronic equipment. The formula allowing the level of uncertainty of this value to be calculated is also part of the calibration.
Preferably, the calibration procedures used are those acknowledged as accredited by calibration laboratories, according to ISO 17025 (SMB, COFRAC, DKD, UKAS, etc.).
Another application of dynamometers concerns the testing machines used to describe the resistance of materials or products. This field is largely covered by standards such as ISO 7500-1 which includes uniaxial static tests for metallic materials, or the European standard EN 12390 section 4, which deals with hardened concrete.
Unlike the dynamometer, there is currently no unified standard that can serve as a guideline for the calibration of torque meters. However, a calibration guide has been issued by EURAMET, the European Association of National Metrology Institutes, under reference cg-14 / V.01 dated July 2007, available at: www.euramet.org.
ISO 6789 establishes a calibration procedure for dynamometric wrenches.
Two documents drafted by the International Bureau of Weights and Measures (BIPM) are available on its website and constitute the reference on metrology:
- The "International vocabulary of metrology – Basic and General Concepts and Associated Terms (VIM)" is available at : www.bipm.org/fr/publications/guides/vim.html
This document is also available from ISO under reference ISO/CEI Guide 99:2007.
- The "Guide to the Expression of Uncertainty in Measurement (GUM)" is available at: www.bipm.org/fr/publications/guides/gum.html