ELECTRONIC-CIRCUIT FOR SUSTAINING THE OSCILLATIONS OF A VIBRATING ELEMENT - APPLICATION TO DENSITY-MEASUREMENTS

An electronic circuit has been designed to sustain the oscillations of a vibrating element. It has been applied to density measurements of f luids with a vibrating tube densimeter. The electronic part of the app aratus has been designed to avoid the presence of elements attached to the tube (such as wires or magnets), since the tube itself performs t he excitation and the detection, making possible an easy manufacture. The mechanical part permits the best temperature control and a fast th ermal response, since it can be totally immersed in a thermostat. The precision has been tested by calibration with pure substances and appl ied to density measurements of a colloidal solution (sodium decanoate in water). Relative measurements are obtained with a precision of bett er than 1 x 10(-6) g cm(-3), in the temperature range studied (between 293 and 313 K). (C) 1997 American Institute of Physics.