METHOD FOR ON-LINE RAPID MEASUREMENT OF FLUID DENSITY USING PIEZORESISTIVE MICROCANTILEVER

摘要

A method for on-line rapid measurement of fluid density using a piezoresistive microcantilever, comprising the steps of: (1) immersing a piezoresistive microcantilever in a standard fluid with a density of ρ₁, connecting a Wheatstone bridge to a constant current power supply, then applying a sinusoidal alternating current to an excitation coil (9) of the piezoresistive microcantilever, wherein the frequency of the sinusoidal alternating current is f, and the amplitude thereof is U₁, so as to obtain an output V₁ of the Wheatstone bridge; (2) changing the amplitude of the alternating current applied to the excitation coil (9) of the piezoresistive microcantilever to U₂ to obtain an output V₂ of the Wheatstone bridge; (3) changing the density of the standard fluid to ρ₂, repeating steps (1) to (2) to obtain outputs V₃ and V₄ of the Wheatstone bridge respectively; (4) solving simultaneous equations ρ₁ = ak₁ + b and ρ₂ = ak₂ + b to obtain parameters a and b, where k₁ = (V₁ - V₂)/(U₁ - U₂), and k₂ = (V₃ - V₄)/(U₁ - U₂); and (5) immersing the piezoresistive microcantilever in a to-be-detected fluid, repeating steps (1) to (2) to obtain outputs V₅ and V₆ of the Wheatstone bridge respectively, and then according to a formula ρ = ak + b, obtaining the density of the to-be-detected fluid, where k = (V₅ - V₆)/(U₁ - U₂). The present application can realize on-line measurement without changing the existing devices; more importantly, there is no need to acquire the resonant frequency of the cantilever in a to-be-detected fluid, thus greatly saving measurement time and providing a guarantee for a truly on-line and rapid measurement. Using the method provided in the present application, the measurement of the density of a to-be-detected fluid can be realized within several seconds or an even shorter time by means of a calibrated piezoresistive microcantilever.