Realization, maintenance and dissemination of the measurand “AC voltage ratio in mV/V ” for strain gauge measurements

Strain gauges allow the measurands force, pressure, torque or strain to be converted into voltage ratios and to be indicated by measuring amplifiers. Precision measurements are preferably carried out at 225 Hz and at voltage ratios of up to 2 mV/V. Bridge standards, which have to be traced back to national standards, are used for the electrical calibration of these measuring amplifiers. More than 15 years ago, in PTB the first measuring arrangement for this purpose has been developed and installed. The present contribution explains the traceability principle of bridge standards, shows the long-term stability of selected bridge standards on the basis of measurement results and brings first investigations into the interchangeability of measuring amplifiers up for discussion. Traceability of bridge standards Strain gauge transducer and measuring amplifier form a measuring chain. For the calibration of the measuring amplifiers, the transducer is replaced by a so-called bridge standard which allows defined voltage ratios to be realized with high precision and to be applied as calibration signals to the measuring amplifier. Bridge standards contain resistance divider