Patent ID: 8220313
Filing Date: 2012-07-17
Classification: G01F,G01N

Abstract:
1. An apparatus for determining or monitoring at least one process variable, of a medium, comprising: at least one mechanically oscillatable unit; at least one exciting/receiving unit, which excites said at least one mechanically oscillatable unit to execute mechanical oscillations and which receives the mechanical oscillations of said at least one mechanically oscillatable unit; an evaluating unit embodied in such a manner that it ascertains density of the medium essentially according to the following formula: wherein: K is a coefficient for pressure sensitivity of said at least one mechanically oscillatable unit; F C is a coefficient for temperature sensitivity of said at least one mechanically oscillatable unit; T is a temperature value for the medium; F D is a coefficient for pressure sensitivity of said at least one mechanically oscillatable unit; and P is a pressure value for the medium at least one electronics unit, which applies an electrical, exciter signal to said at least one exciting/receiving unit, and which obtains from said at least one exciting/receiving unit an electrical, received signal, wherein: said at least one electronics unit is embodied in such a manner that it produces the exciter signal in such a manner, that, between the received signal and the exciter signal, a phase difference results, which is essentially equal to a predeterminable, desired value of phase difference; the desired value of this phase difference is predetermined in such a manner the, at the desired value of the phase difference, effects of changes of viscosity of the medium on mechanical oscillations of said at least one mechanically oscillatable unit are essentially negligible; the desired value of phase difference is predetermined at least as a function of ratio of impedance of said at least one exciting/receiving unit to input impedance of said at least one electronics unit; and the input impedance is with respect to that input, via which said at least one electronics unit receives the received signal.