Entwicklung von Druckwächtern für die Ventilüberwachung aus Polyvinylidenfluorid
Within this work novel pressure sensors for the control of pneumatic and hydraulic valves were developed. Valve control is achieved by detecting, whether the pressure drop over the valve changes after a signal for valve switching has been sent. This is achieved by detecting whether the pressure falls below or exceeds a specified threshold. Besides this, the price of the pressure sensor needs to be much less than the price of the valve. Different concepts were considered to design a low-cost pressure sensor. Comparison of these concepts resulted in the conclusion that the best solution would be to design a pressure sensor from the polymer Polyvinylidenefluoride (PVDF). In this concept the sensor element of the pressure sensor is made of a piezoelectric PVDF film and the housing is made of not piezoelectric PVDF. Equations for the calculation of the characteristic curve and the influence of external factors on the output signal of the pressure sensor are derived and presented in this work. Anisotropic properties of PVDF films could be included only approximately in these equations. That is why the equations have a limited accuracy, but they correctly describe the qualitative influence of different external factors on the characteristic curve of the sensor. PVDF pressure sensors are distinguished by the ability to measure very fast and also very slow pressure changes. Measurements show that they achieve a response time of less than 0.1 ms. According to literature, the response time can be as small as several nanoseconds. The longest time interval, in which slow pressure changes can be measured with appropriate accuracy, is temperature dependent. Slow pressure changes can be measured for several minutes at room temperature. In these pressure sensors the applied pressure stretches the piezoelectric PVDF film. This stretching produces an electrical charge at the surface of the PVDF film. The electric charge and the corresponding electric voltage, which are proportional to the applied pressure, are measured by an electronic circuit. Several PVDF pressure sensors were produced and their properties were measured. The following properties of the pressure sensors were measured amongst others: characteristic curve, linearity, hysteresis, repeatability, resolution, cracking pressure, working pressure range, working temperature and humidity ranges, temperature and humidity dependence, aging at constant and cycling pressure loads, chemical resistance to strong acids and solvents. Advantages and disadvantages of the pressure sensor are presented and discussed. Pressure sensors from PVDF can be used not only for valve control, but also in a number of other applications where low price, long service life, good resistance to chemicals, fast response time, broad working temperature and humidity ranges, small size and weight are required.
info:eu-repo/classification/ddc/620, Ingenieurwissenschaften, Polyvinylidenfluorid, Ventil, Piezoelektrischer Drucksensor, Polyvinylidenefluoride, valve, piezoelectric pressure sensor
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