Abstract: A density measurement instrument measures the density of a fluid by determining the frequency of oscillation of a vibrating tube filled with the fluid. An electronic excilation system vibrates the tube and the frequency of oscillation is representative of the density and the temperature. The frequency is accurately measured. A temperature control system controls the temperature of the fluid during oscillation by comparing a single temperature set point with the measured temperature of the sample. Based on this comparison, current in a first direction or in a second direction is applied to a Peltier element for heating or cooling the sample. Substantially continuous temperature readings and adjustments of the current are thus provided. The temperature information may be applied to an external data link or to a display.