A novel temperature chamber in combination with a deadweight force standard machine (FSM) allows the testing and certification of load cells with nominal loads up to 200 t by the Physikalisch-Technische Bundesanstalt (PTB). This facility is unique in Europe; for the first time, it offers manufacturers and customers the possibility of certifying load cells with very high nominal loads as used in the heavy industry for instance.

With an annual export of 500 million Euro (in 2004), the industry of measuring instruments represents one of the most important industrial sectors in Germany. Nowadays, the weighing technology reaches from "micro weighing instruments" with a maximal load of only 5 g and a digital resolution of 0.001 mg to huge crane weighers as used in the heavy industry with maximal loads of 500 t and typical resolutions of 200 kg. Numerous applications of weighing instruments, whether for business trade with goods or for the determination of mass for the billing of fees, are subject to verification in conformity with national or European legal prescriptions. The legally prescribed precondition for the national or European verification is the certification of weighing instruments for which the PTB department "Mass" is responsible in Germany. Since it is not always useful or feasible to test the whole weighing instrument, it is possible to test individual weighing modules.

The most important weighing module is the load cell as the core of modern electromechanical weighing instruments. In a load cell, the weight force applied usually causes an electrically evaluable resistance change in so-called strain gauges. Further measuring principles, such as the electromagnetic force compensation, are limited to applications in special-accuracy and high-accuracy weighing instruments. The metrological tests for the certification of load cells must take climatic influence factors into account and are documented in the internationally accepted OIML-Recommendation R60. The most important assessment criteria laid down in the OIML-Recommendation R60 are reproducibility, linearity and hysteresis as well as creeping and zero returning of load cells at temperatures of 20 °C, 40 °C and -10 °C.

The equipment available so far at PTB allows the testing of load cells with nominal loads of a few grams up to 100 t. But to meet the legal requirements also for the certification of load cells with very high nominal loads, it is necessary to extend the existing test range. By providing the 2-MN-FSM, which was put into operation in 2004, subsquently with an adapted temperature chamber, PTB keeps pace with ongoing developments in the field of weighing technology. In this way, the testing of load cells with nominal loads of up to 200 t, which had been required for a long time by the industry, becomes possible. Until now, such possibilities have not been available in Europe.

A photomontage and a schematic representation of the 2-MN-FSM and the fitted temperature chamber as well as the cooling unit installed on the crosshead are shown in figure 1.