The demand for economical drive concepts for vehicles that meet environmental guidelines is always accompanied by an increase in requirements for the test equipment. Highly dynamic, high-resolution torque measurements in the shaft train are essential for designing and optimizing engine-transmission combinations. Reproducibility is very good with modern torque transducers with strain gages. The overall accuracy of the torque measuring system is basically determined by the mechanical disturbance variables and by thermal and humidity effects that have not been compensated. The resolution limit, as the total of errors resulting from the measuring body and the strain gage application that cannot be compensated, exceeds the metrological possibilities of the electronics currently used in rotating transducers, with a DC amplifier, analog signal conditioning and frequency analog signal transmission. The analysis of the measurement chain shows that because of temperature gradients and non-linear temperature coefficients, the thermoelectric voltages produce considerable measurement signal errors that are induced by disturbance quantities and which up to now, have not been compensated. Additional wrong measurement values result from overloading or damage to the transducer. The subject of the paper is the development of a contactless torque measuring system with a carrier-frequency amplifier. Optimization of the temperature effect on the measurement signal by the high level of symmetry of the measuring bridge is supplemented by digital compensation of the residual temperature effects. Digital signal conditioning and transmission make it possible to achieve the current high accuracy of non-rotational torque transducers in a rotating shaft train as well. Measurements with the carrier-frequency amplifier have shown that non-compensatable random errors could be greatly reduced. This is the only way that the T12 torque transducer can be specified for an accuracy class of 0.03. The measurement results displayed below were recorded with a 3 kNm transducer of the smarttorque series. The temperature curve of the zero signal for three temperature cycles between 10 deg C and 60 deg C, shows that the random content of the temperature effect is below 0.003 %. The reproducibility of the static characteristic curve is also in the order of magnitude 0.002 % with a hysteresis of around 0.008 %. The specified uncertainty of the calibration machine is achieved here, as far as reproducibility is concerned. The linearity error of the transducer being examined is less than the hysteresis. This high-precision torque functionality was supplement in the smarttorque series by speed and angle of rotation sensor technology. The result is a measurement system that provides the user with the most important parameters of the shaft train: torque, speed, angle of rotation, rotational power and temperature. The validity of the measured values is ensured by the rotor's self-monitoring function. The system monitors the operating state of the measuring bridge and the most important functions of the carrier-frequency amplifier, so that if there is a defect, a warning signal is output or the measured values are identified as invalid. The maximum transducer loadings are also recorded, so that overload damage can be detected. The measurement signals are output at a bandwidth of up to 6 kHz at a scalable frequency output and an analog output. At the same time, it is possible to achieve sampling rates of up to 4.8 kS/s on two channels with CAN and Profibus. A software assistant is used to parameterize the extensive functions of the T12 torque transducer via CAN, making it possible to access all the settings and to perform standard measurement and analysis tasks. The user management allows to hide and to lock critical parameters in normal user mode.


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    Title :

    High precision torque measurement system


    Additional title:

    Hochgenaue Drehmomentmessung


    Contributors:
    Kuhn, Sven (author)


    Publication date :

    2007


    Size :

    6 Seiten, 5 Bilder, 3 Quellen



    Type of media :

    Conference paper


    Type of material :

    Print


    Language :

    English




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