Method for controlling piezoelectric drives in filling level measuring devices

Abstract

A method for controlling piezoelectric drives in filling level measuring devices, in the case of which a piezoelectric device ( 7 ) is coupled to a fork resonator, and this piezoelectric device ( 7 ) is used to excite and detect vibrations. The excitation signal (B) is an at least approximately trapezoidal signal, as a result of which the generation of undesired harmonic resonances in the fork resonator can be effectively avoided. The excitation signal preferably comprises two phases with approximately constant maximum and minimum levels, respectively, which are interrupted in each case by a phase of defined period and defined limited rate of signal change.

1 . Method for controlling piezoelectric drives in filling level measuring devices, in which a piezoelectric device ( 7 ) is coupled to a fork resonator and, firstly, an excitation signal (B) is applied to this piezoelectric device ( 7 ) for the purpose of exciting vibrations and, secondly, this piezoelectric device ( 7 ) is used to detect vibrations, characterized in that the excitation signal (B) is a signal having at least an approximately trapezoidal profile.  
     
     
         2 . Method according to  claim 1 , characterized in that the maximum level (Emax) and the minimum level (Emin) of the trapezoidal excitation signal (B) correspond to the maximum and minimum levels (U + , U − ) of an operating voltage supplying the piezoelectric drive.  
     
     
         3 . Method according to  claim 1  or  2 , characterized in that the falling and rising edges (F 1 , F 2 ) of the trapezoidal excitation signal (B) have at least approximately equal gradient in terms of absolute value.  
     
     
         4 . Method according to one of  claims 1  to  3 , characterized in that the falling and rising edges (F 1 , F 2 ) correspond to approximately 0.15 to 0.30, preferably approximately 0.25, of a half-period (T/2) of the trapezoidal excitation signal (B).  
     
     
         5 . Method according to one of  claims 1  to  4 , characterized in that the trapezoidal excitation signal (B) is tapped at the output of an integrator device ( 4 ,  5 ,  6 ) whose input is fed a rectangular signal (A).  
     
     
         6 . Method according to  claim 5 , characterized in that the integrator device ( 4 ,  5 ,  6 ) is a rail-to-rail integrator.  
     
     
         7 . Method according to  claim 5  or  6 , characterized in that the rectangular signal (A) has maximum and minimum levels (Rmax, Rmin) of at least approximately equal length.  
     
     
         8 . Method according to one of  claims 1  to  7 , characterized in that the trapezoidal excitation signal (B) and/or the rectangular signal (A) are/is symmetrical.  
     
     
         9 . Method according to one of  claims 1  to  8 , characterized in that the trapezoidal excitation signal (B) is fed to a single piezoelectric element of the piezoelectric device ( 7 ) and this piezoelectric element is used both to excite vibrations and to detect vibrations.