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Development and investigation of force transducers with thin-film strain gauges


Within the scope of a DFG research project at PTB, metal thin-film strain gauges were sputtered on force transducers, and their behaviour was investigated. In some fields of force measurement, the use of thin-film strain gauges promises advantages compared to the usually used foil strain gauges.

In cooperation with the PTB Department 5.5 ”Scientific Instrumentation”, a procedure was developed which allows microstructured thin-film strain gauges to be manufactured on curved surfaces [1]. By combining sputter techniques with laser lithography and wet chemical etching processes, strain gauge structures with linewidths of a few 10 µm could be realized on cylindrical, metallic surfaces. These thin-film strain gauges are applied to elastic bodies and tested with respect to their suitability for force transducer construction. The omission of an adhesive layer and of the polymer carrier – as used in the case of conventional foil strain gauges – promises advantages in particular in the fields ”long-term stability”, ”endurance strength”, ”dynamic force measurement” and for the measurement of small forces.

For systematic investigations of the metrological properties in Department 1.2 ”Solid Mechanics”, prototypes (force up to 10 kN) were fitted with foil strain gauges and thin-film strain gauges and compared (see Fig. 1). The investigations were focussed on the temperature behaviour and time response of sensitivity and zero point as well as on the endurance strength and transfer function at frequencies up to 1 kHz.

After approx. 2·106 cycles, the strain gauges showed no measurable damage or aging phenomena. The sensitivity of the thin-film strain gauges was slightly above that of foil strain gauges. In static measurements, a creeping fraction, which decays with a time constant of 70 seconds, was observed during loading and unloading in the case of bonded strain gauges. This does not occur in the case of sputtered strain gauges and must be attributed to viscoelastic processes inside the foil and adhesive layer. Constant optimizations of the manufacturing process and the strain gauge geometry as well as further investigations will allow thin-film strain gauges in a future to be used in the field of high-precision force measurement of small and dynamic forces.

Elastic body with thin-film strain gauge (see enlarged detail)

Figure 1: Elastic body with thin-film strain gauge (see enlarged detail)

[1] A. Buß; J. Illemann; R. Kumme; D. Hagedorn; R. Meeß; F. Löffler: "Development and investigations of force transducers for high-precision measurement of static and dynamic forces", VDI Reports 2011, Düsseldorf (2008), pp. 107-116. (In German)

Contact person:

Andre Buß, Department 1.2, WG 1.21, E-mail: andre.buss@ptb.de