From the first DKD calibration laboratory to present-day DAkkS accreditation

Heartfelt congratulations to the DKD (German Calibration Service) on 40 years of successful collaboration with accredited calibration laboratories. Since its foundation in 1977, the DKD has demonstrated staying power through a history of ups and downs, including its transition to the DAkkS (German Accreditation Body) and refoundation in 2011.

The road to the DKD's first calibrating center

Back in 1967, 10 years before the DKD (German Calibration Service) was founded, HBM launched a project for three direct load test machines. Direct load test machines function on the basis of force generated by weights in the Earth's gravitational field. These very precisely defined weights ensure the optimum measurement uncertainty for achieving the measured quantity 'force'.

As part of this project, the weights were defined at the PTB (German National Metrology Institute). The result was a test certificate specifying the weight and its respective "uncertainty" (how this uncertainty was defined is unknown; it differs from the measurement uncertainty commonly in use today). As the weights were supposedly the determining factor of the machine, their uncertainty was equated directly with the machine's accuracy.

Load test machine from 1967
Test certificate of weights for the direct load test machine
Direct load test machine at HBM

When it became known in 1977 that industrial calibration laboratories could obtain certification from the PTB, HBM became extremely interested in taking this route. The motivation was "measuring better" and the traceability of the entire machine, not just the weights. In order for force test machines to be certified as standard test machines, extensive measurements had to be conducted. To this aim, measurements were performed once at PTB using transfer devices, and then at HBM. The results were compared and discrepancies determined. This procedure was extremely time-consuming. Two PTB employees (including Dr. Sawla, Force Laboratory Manager at PTB for many years) conducted the initial measurements at HBM over three to four weeks. It turned out that the mechanical installation, in particular, was influencing the measurement result. HBM benefited greatly from this technical collaboration and was able to build up a wealth of expertise.

From these extensive measurements, the PTB drew up a test certificate for the force test machine. This included a detailed report of the measurements, the results, and diagrams lovingly drawn on graph paper.

The 20 kN system was certified as the first force test machine, but only for a range of 1 kN to 10 kN. The reason for this restriction was the forthcoming Hanover Fair, where the calibration laboratory was to be presented as an example of quality.

As well as satisfying the technical prerequisites, official requirements also had to be met. A contract was concluded between the PTB and HBM for this purpose. The footnote of the contract stated that Paragraph 11 was still to be amended. This Paragraph 11 concerned liability. Today, it is quite inconceivable that a contract could be signed without clarification of this vital point! But this is where HBM had an advantage over the larger corporations, and was certified as the DKD's first calibration center on 04.07.1977. The certificate bore the number 0101.

There was as yet no accreditation certificate at that time; the first official document bore the title Confirmation, and neither the German eagle nor the DKD logo are anywhere to be seen. The DKD logo can be found in HBM documents for the first time on a Confirmation from the year 1989, and the first "real" certificate is dated 1992.

Test certificate of the force test machine with diagram
Signatures under the first contract between the PTB and HBM
First certification as the first calibration laboratory in the DKD

From force to torque - further measured quantities followed

Then, in 1979 all three force test machines from the 1967 project were certified as standard test machines. The years that followed were the scene of continuous further development. In 1980, the measured quantity 'pressure' was included in accreditation with three deadweight testers of 60 bar, 600 bar and 3500 bar.

This was followed in 1986 by the voltage ratio "mV/V", 0 mV/V to 10 mV/V at 5 V and 10 V bridge excitation voltage and 225 Hz carrier frequency. Further carrier frequencies subsequently followed. Acceleration was added as a measured quantity in 1987, but was abandoned again in 1993, as only one calibration was performed over this period. The necessity of calibration was not yet standard in industry. The addition of torque in 1990 is also of interest, because the PTB did not yet have a standard test machine for torque at this time. So up until 1992/1993, the 20 kN·m torque test machine was pretty much the German standard.

Greater accuracy, higher forces – requirements become more stringent

By now, various applications required sensors with ever greater accuracy. To satisfy these demands, the new direct load test machines were built in accordance with the state of the art, with improved measurement uncertainty (2.5 kN and 25 kN in 2000; 200 N in 2003; 1 kN·m and 25 kN·m in 2005).

The next goal was expansion to cover higher forces and torques. These machines function using the reference principle and work with reference transducers, as weights would be too large and unwieldy. A force test machine for calibration in the tensile and compressive direction up to 5 MN went into operation in 2009, and a torque test machine up to 400 kN·m in 2015.

Standard torque test machine 25 kN·m
Standard torque test machine 400 kN·m
List of standard force and torque test machines at HBM in 2017

Accreditation establishes global acceptance and encourages innovation

HBM was first accredited by the DAkkS (German Accreditation Body) in 2012, which meant that accreditation number DKD-0101 was then lost. Since the safety test laboratory was already accredited by the DAkkS, its number 12029 was used instead. The advantage is that now joint system inspections could be performed.
In all, the accreditation of the calibration laboratory and the ILAC MRA Mark are of major importance to a global company, as this is the only way to guarantee international acceptance and so gain access to the markets. HBM was the first company in Germany to be certified to ISO 9001 back in 1986. HBM's environmental management system has been certified to ISO 14001 since 1996.

As a company, HBM benefits from the accredited calibration laboratory, as the requirements for precision applications are therefore known, and this know-how drives innovation for product developments. The standard test machines of the accredited laboratory are used for development projects. And the calibration laboratory, in turn, makes use of the company's precision test and measuring equipment.

The "New DKD" is an important expert forum, particularly during meetings of the DKD expert committee, for exchanging information between the calibration laboratories and the PTB. The joint compilation of DKD guidelines, which are freely available, is another important aspect. Moreover, the company benefits from the DKD's support with interlaboratory comparisons and numerous seminars.

We would like to wish the DKD every success for the future! Here's to the continued successful collaboration of the DKD with the accredited calibration laboratories.

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