STANDARD REFERENCE FORCE TRANSDUCERS (VERY HIGH CAPACITIES)

The verification of uniaxial testing machines, such as tension and/or compression testing machines, is carried out with force-measuring instruments previously calibrated according to ISO 376, and referred to as standard reference force transducers.

Calibration of a load cell involves accurately applying a known force within a given interval and recording the signal provided by the sensor.

ISO 376 defines the calibration procedure, the criteria and the maximum permissible value for classifying the force-measuring instruments in one of four accuracy classes corresponding to the accuracy classes of the machines to be calibrated, according to EN 7500:

• Class 00 (very high accuracy class for intercomparisons)
• Class 0.5 (for calibration of testing machines according to classes 0.5, 1 and 2)
• Class 1 (for calibration of testing machines according to classes 1 and 2)
• Class 2 (for calibration of testing machines according to class 2)

On request, we are also able to provide a calibrated sensor according to ISO 376 (certificate valid for two years according to the standard). In this context, SENSY offers you its expertise for:

1. choice of the appropriate official laboratory to calibrate the sensor to the requested capacity.
2. choice of electronics: display, output cable, USB ports, etc.
3. design, manufacturing and logistics of tools/accessories: In general, we develop accessories for calibration tests according to the requirements of ISO376. For standard reference transducers to be tested in tension, the accessories can be complex since we must take into account the interfaces of the selected laboratory and their size, which sometimes requires finding innovative solutions.

   

   The use of sensors in a horizontal machine requires special precautions, in the case of long connecting rods, to cope with the effect of bending on the measurement and mechanical resistance. In addition, the assembly devices are designed to take into account the specificities of the customer's installation.

   The first example is a device developed to ensure the centring of the standard reference transducer and the mounting accessory in the assembly.

   

   The second example is related to the technique of split-coupling to limit the mass of the set and, in particular, to meet the space constraints. Logistical constraints are also important and SENSY proposes to manage this aspect as well.

   

4. Performing a pretest for tension tests if the laboratory in charge of the calibration requires it.
5. The analysis of the certificate and its validity for your organisation after calibration by the laboratory.

THE CASE OF VERY-HIGH-CAPACITY TRANSDUCERS

Above 16.5 MN, there is no testing machine available with an uncertainty equal to or better than 0.02% or even 0.05%, which enables qualification of standard force transducers for ISO 376 classes, such as "00"; "0.5" or even "1".

Nevertheless, SENSY is privileged to have manufactured several sensors in compression and/or tension of 20, 25 and 30 MN. Furthermore, the market in very-high-capacity sensors is developing in parallel with the important growth of industrial installations worldwide.

Faced with this difficulty for many years, SENSY has participated in various intercomparison projects aiming to qualify its standard reference sensors by calibrating them in different test laboratories. Some tests are carried out at full load but with some uncertainty which does not allow for their qualification, while other tests have been performed at the PTB laboratory on its 16.5 MN testing machine by means of specially developed accessories at a lower load with an uncertainty of 0.01%.

By means of a series of comparisons and extrapolations, our very-high-capacity standard reference transducers become a new reference, not only for their use at the customer's premises but also for their participation in other international intercomparison campaigns for which they are sometimes rented.