A Comprehensive System For Measuring Physical Parameters Of The Liquids

Surface tension, viscosity and density are the important physical parametersof liquids. The physical properties of liquids are important criteria of evaluatingthe liquid quality, and they are also very important in the chemical, metallurgy,medical and food industries. So, it has important practical significances for theproduction and every-life to develop the comprehensive system of measuringphysical parameters of liquids.A comprehensive system for measuring the physical parameters of liquidshad been designed in this paper. In this system, the single parametermeasurement was replaced by multi-parameters test. After improving themeasuring method of physical parameters, surface tension and density wasmeasured by the two-time descent method derived from the maximum bubblepressure method. Namely, the capillary was vertically dipped into the liquids attwo different heights, and the maximum bubble pressure at different height wasmeasured. The surface tension and density of liquids could be calculatedaccording to the maximum pressures. The viscosity of liquids was measured byusing rotatary cylinder method.The comprehensive measuring system wass mainly composed of mechanicalmechanism and computer. The mechanical mechanism mainly comprised themultifunctional probe, the lifting movement unit, the constant temperature unitand so on. The multifunctional probe embedded in temperature sensor, pressuresensor and torque sensor was used for monitoring the temperature, the bubblepressure and the torque of rotor. The lifting movement unit was used for drivingthe probe and thermostatic bath by the electric mode. The constant temperatureunit was used to control the temperature of liquids. The system had the merits ofsmall volume, compact structure, rational layout, and the simultaneousmeasurement for multiple parameters. According to the required functions of the comprehensive system, thehardware and software were designedg, respectively. The hardware included thepressure sensor, temperature sensor, torque sensor, the control circuit ofmovement units, the signal amplification circuit, data acquisition card, andcomputer and so on. Under the monitoring of the software, the signals oftemperature, maximum bubble pressure and torque could be acquired through thedata acquisition and processing programs; through the conversion and processingof these signals, theviscosity, density, surface tension and temperature could begot, and also the measuring results could be displayed and stored. Theexperimental results showed that the range and error of measuring the surfacetension, viscosity, density and temperature were as follows:The measurement range of surface tension is10-300mN/m, and the error is±1.0mN/m; The range of viscosity is20-3000mPa·s, and the error is±1.5mPa·s;The range of density is0-1.5×10~3kg/m~3, and the error is±0.01×10~3kg/m~3; Therange of temperature is0-40℃, and the error is±0.1℃.