JPH01311250A - Method and device for measuring fluid viscosity - Google Patents

Abstract

PURPOSE:To measure the viscosity of fluid continuously by inserting a crystal vibrator into the pipe where the fluid flows and measuring its loss resistance. CONSTITUTION:The AT cut crystal vibrator 1 is fixed on the internal wall surface of the pipe 2 in parallel to the flowing direction 7 of the fluid so that only one surface is brought into contact with the fluid. Then when the fluid flows in the pipe 2, the vibrator 1 receives mechanical resistance based upon the shearing stress between the fluid and the surface of the vibrator 1 and its resistance coefficient is equal to electric resistance, so variation in the viscosity is measured by measuring the loss resistance of the resonance frequency of the vibrator 1 continuously. Further, variation in the resonance frequency reflects upon the variation in the viscosity. Then while the viscosity is varied by varying the temperature, the fluid is made to flow and an impedance measuring instrument 3 is connected to the vibrator 1 to measure the impedance almost at the resonance frequency of the vibrator 1; and a computer 4 computes the loss resistance value and resonance frequency to measure the viscosity of the fluid.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1] The present invention relates to a method and apparatus for measuring the viscosity of a liquid in a fluid state in chemistry, physics, physical chemistry, biochemistry, medicine, and the chemical industry.

[Summary of the Invention] The fluid viscosity measuring method and device of the present invention are characterized in that the viscosity can be measured even when the liquid is not in a static state but in a flowing state. A piezoelectric element is used as the detector, and the viscosity of the fluid is measured by bringing one or both sides of the piezoelectric element into contact with the liquid and determining the resonance frequency or loss resistance of the piezoelectric element.

Further, in the present invention, the fluid viscosity measuring device is constituted by at least a piezoelectric element and either a device for measuring the resonance frequency of the piezoelectric element or a device for measuring loss resistance.

[Prior Art] Conventionally, the capillary method, rotation method, falling ball method, etc. have been mainly used for viscosity measurement. The capillary method determines the viscosity from the rate at which the sample liquid falls through a capillary tube, and the falling ball method involves placing a metal ball in the sample liquid and determining the viscosity from the rate at which it falls. In addition, the rotation method rotates a cylindrical metal rod in a sample liquid and determines the viscosity by determining the shear stress. In addition, a viscosity measurement method using a torsional oscillator has also been developed.

[Problems to be Solved by the Invention] Conventional viscosity measurement methods involve extracting and measuring a sample, and it is difficult to continuously measure the viscosity of a liquid in a flowing state. Therefore, for example, it is difficult to accurately measure the viscosity of a sample in a fluid state, such as a substance (non-Newtonian fluid) whose viscosity differs between a static state and a fluid state. Furthermore, since the amount required as a sample is not small, it is unsuitable for systems that handle trace amounts, such as analytical devices. Furthermore, these measurement methods require a certain amount of time for measurement, and it is also difficult to automate the measurement.

[Means for Solving the Problems] The fluid viscosity measuring method and measuring device of the present invention, for example, AT
The viscosity of the fluid is measured by using a cut crystal resonator as a detector and measuring the loss resistance or resonance frequency of the crystal resonator. Therefore, viscosity can be measured simply by bringing the crystal oscillator into contact with the object to be measured. Therefore, for example, by inserting a crystal resonator into a pipe through which liquid is flowing, it is possible to measure the viscosity of the liquid while it is flowing. Furthermore, since the output is obtained as an electrical signal, it is very easy to automatically measure and record measurement data.

[Function] A crystal resonator is a device that utilizes the piezoelectric effect, and it causes mechanical vibrations by applying a voltage with a frequency near the resonant frequency. Although this vibration is extremely small, when it comes in contact with a liquid, it produces mechanical vibrations. is subjected to resistance due to shear stress between the liquid and the surface of the crystal oscillator. The resistance coefficient of this mechanical resistance can be considered to be equivalent to the electrical resistance when considering the correspondence between the mechanical vibration and the electrical vibration of the crystal resonator. Therefore, the loss resistance at the resonance frequency is considered to be a value reflecting the friction coefficient of the surface of the vibrator, and by continuously measuring this loss resistance, changes in the viscosity of the liquid can be measured. Furthermore, since the shear stress of the crystal oscillator balances the force of the quartz crystal oscillator to vibrate as an elastic body, the resonance frequency also takes on a value that reflects changes in the viscosity of the fluid.

Therefore, it is also possible to measure the viscosity of a fluid by measuring changes in the resonance frequency. Furthermore, even if another piezoelectric element, such as a SAW device or a piezoelectric ceramic oscillator, is used in place of the crystal resonator, the above two measurements can be performed in the same manner.

[Example] Hereinafter, an example of the present invention will be described based on the drawings. FIG. 1 shows a schematic diagram of the fluid viscosity measuring device of the present invention. In FIG. 1, an AT-cut crystal oscillator 1 is fixed to the inner wall surface of a pipe 2 in parallel to the flow direction 7 of the liquid so that only one side is in contact with the liquid. Further, the AT-cut crystal resonator 1 is connected to an impedance measuring device 3 whose measurement frequency can be set arbitrarily, and the impedance measuring device 3 is
connected to a computer 4 for calculation and control;
A printer 5 and a display 6 are connected to the computer 4.

Impedance was measured near the resonance frequency of the crystal resonator while flowing a liquid into the pipe and changing the viscosity of the liquid. Viscosity was varied by varying the temperature of the liquid. When the temperature changes, the density of the liquid changes at the same time, affecting the resonance frequency and loss resistance value, but the change in density due to temperature of the liquid is small compared to the change in viscosity, so it can be ignored.

Specifically, in impedance measurement, since there is a resonance frequency between the frequencies that give the maximum and minimum values of susceptance, which is the imaginary part of admittance, the maximum and minimum values of susceptance are found by frequency sweeping and Conductance and susceptance were measured at equal intervals with respect to frequency. As for the measured values, conductance and susceptance data were processed by the circular least squares method to obtain the diameter of the circle, and the reciprocal of this was taken as the value of the loss resistance. In addition, a frequency on the circle having the same value as the susceptance value at the center point of the circle was found from a polynomial approximation of the susceptance and the measurement frequency, and this was taken as the resonant frequency.

Similarly, the resonance frequency of the crystal resonator when not in contact with the liquid was also determined, and the difference between the two was defined as ΔF.

Such measurement and calculation processing can be automatically performed by a computer, and in the device of the present invention, 1
It is possible to perform multiple measurements within 3 seconds.

Next, an example in which the viscosity of a fluid was measured using this apparatus will be described.

(Example of flowing water into a pipe) Water is flowed into a pipe at a constant flow rate, and the temperature of the water is 20°C.
The viscosity of water was changed by changing the temperature from 70°C to 70°C, and the resonance frequency and loss resistance value of the AT-cut crystal resonator I were measured. Figure 2 shows the resonant frequency of the crystal resonator with respect to the viscosity of water, and Figure 3 shows the loss resistance value with respect to the viscosity of water.The resonant frequency and loss resistance value of the crystal resonator reflect the viscosity of water well. It has become.

Although this example shows the case where an AT-cut crystal resonator is used as a detector, it has been confirmed that measurements can be made in the same way when a GT-cut crystal resonator is used.

(Example using SAW device) SAW using Rochelle salt with two comb-shaped electrodes
When we measured hexane using the device as a detector, a similar response corresponding to viscosity was obtained.

[Effect of the Invention 1] The fluid viscosity measuring method and measuring device of the present invention make it possible to continuously measure the viscosity of a liquid in a flowing state. This also made it possible to measure the viscosity in the fluid state of substances whose viscosity differs between the static state and the fluid state.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the fluid viscosity measuring device of the present invention, Figure 2 is a diagram showing the relationship between the viscosity of water and the resonance frequency of a crystal resonator when water is passed through a pipe, and Figure 3 is a diagram showing the relationship between the viscosity of water and the resonance frequency of the crystal resonator when water is passed through a pipe. FIG. 3 is a diagram showing the relationship between the viscosity of water and the loss resistance value of a crystal resonator in the case of FIG. l... AT-cut crystal oscillator 3... Impedance measuring device 4... Computer and above Applicant Seiko Electronics Co., Ltd. agent Patent attorney Takayuki Hayashi Sukekiyo Body Viscosity 1st edition; F
l Apparatus ρ term 8 Figure 1 Tool 4 & Surrounding liquid number [Hz

Claims (1)

[Claims] (1) At least one side of the piezoelectric element is brought into contact with a liquid in a flowing state, and the resonant frequency of the piezoelectric element is measured, or the loss resistance value of the piezoelectric element is measured. A fluid viscosity measurement method characterized by measuring the viscosity of a liquid. (2) The fluid viscosity measuring method according to claim 1, wherein the piezoelectric element is a crystal oscillator. (3) The fluid viscosity measuring method according to claim 2, wherein the crystal resonator is an AT cut or GT cut crystal resonator. (4) At least one side of the piezoelectric element is brought into contact with a liquid in a flowing state, and the piezoelectric element is configured to include at least a circuit that measures the resonant frequency of the piezoelectric element or a circuit that measures the loss resistance value of the piezoelectric element, and is in a flowing state. A fluid viscosity measuring device characterized by measuring the viscosity of a liquid. (5) The fluid viscosity measuring device according to claim 4, wherein the piezoelectric element is a crystal oscillator. (6) The fluid viscosity measuring device according to claim 5, wherein the crystal resonator is an AT cut or GT cut crystal resonator.