CN111504172A - Calibration device for thin liquid film sensor of conductive ring - Google Patents

Abstract

The invention relates to a calibration device for a conductive ring thin liquid film sensor, comprising two flat strip electrodes, a stepping motor, a controller, a lead screw, an inner thread sleeve, a water tank, an excitation and acquisition module and a host computer. The length and spacing of the two planar strip electrodes are the same as the circumference and spacing of the two conductance rings of the conductance ring thin liquid film sensor to be calibrated. The inner thread of the sleeve matches the outer thread of the lead screw. The controller drives the lead screw to move up and down by controlling the stepper motor to change the distance between the two flat strip electrodes and the bottom of the water tank, thereby changing the surface liquid of the two flat strip electrodes. The thickness of the film; the excitation and acquisition module is used to apply a voltage signal to the two flat strip electrodes, measure the current signal passing between the two electrodes, and send the liquid film thickness information represented by the current signal to the host computer.

Description

A conductivity ring thin liquid film sensor calibration device

technical field

The invention belongs to the field of ring mist flow liquid film measurement, and relates to a thin liquid film calibration technology, which can be used for the calibration of the thin liquid film thickness of a conductivity ring sensor.

Background technique

Wet gas is a two-phase flow pattern with the gas (vapor) phase as the continuous phase and the liquid phase as the discrete phase. Due to heat loss and temperature reduction, it enters a saturated or supersaturated state, often forming an annular mist flow.

In annular mist flow, the liquid phase exists in the form of discrete droplets and a liquid film on the wall. The liquid film is attached to the inner wall of the pipe in a ring shape [1][2] and is usually very thin. The thickness of the liquid film on the wall is usually measured online with a conductance sensor, such as a conductance probe, a conductance ring, a plane electrode and other electrode shapes. The conductance ring is widely used in the measurement of the liquid film because its structure is not affected by the unevenness of the circumferential direction of the pipeline. . Because the liquid film in the annular mist flow is very thin, basically below 1mm, the calibration of the conductivity ring liquid film sensor is difficult. How to accurately calibrate the conductivity ring liquid film sensor is the key to the normal application of the sensor.

references

[1] Li Weidong, Li Rongxian, Wang Yueshe, et al. Theoretical Model for Predicting Circumferential Liquid Film Thickness Distribution of Gas-Liquid Annular Flow in Horizontal Pipes [J]. Chinese Journal of Chemical Engineering, 2001(03):18-22.

[2] Setyawan A, Indarto, Deendarlianto. Experimental investigations of the circumferential liquid film distribution of air-water annular two-phaseflow a horizontal pipe[J]. Experimental Thermal & Fluid Science, 217, 85(Complete): 95-118.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the calibration problem of the traditional pipeline conductance ring thin liquid film sensor, and to provide an equivalent calibration device to realize the rapid and accurate calibration of the liquid film sensor. The technical scheme of the present invention is as follows:

A conductive ring thin liquid film sensor calibration device, comprising two flat strip electrodes, a stepping motor, a controller, a lead screw, an internal thread sleeve, a water tank, an excitation and acquisition module and a host computer, the two The length and spacing of the flat strip electrodes are the same as the circumference and spacing of the two conductance rings of the conductance ring thin liquid film sensor to be calibrated. The internal thread matches the external thread of the lead screw. The controller drives the lead screw to move up and down by controlling the stepper motor to change the distance between the two flat strip electrodes and the bottom of the water tank, thereby changing the thickness of the liquid film on the surface of the two flat strip electrodes. ; The excitation and acquisition module is used to apply a voltage signal to the two flat strip electrodes, measure the current signal passing between the two electrodes, and send the liquid film thickness information represented by the current signal to the host computer.

The invention designs a calibration device for the thin liquid film conductance ring sensor. The conductance ring is equivalent to a flat strip electrode, and COMSOL is used to simulate and verify the feasibility. The stepper motor is used to drive the planar electrode to move to change the electrode surface. The device can calibrate the liquid film thickness of the conductivity ring sensor below 1mm.

Description of drawings

Figure 1 shows the conductance ring thin liquid film sensor that needs to be calibrated

Accompanying drawing 2 is that the conductance ring is equivalent to the COMSOL simulation model of the long planar electrode

Accompanying drawing 3 is the simulation result comparison diagram of conductance ring and long strip plane electrode

Accompanying drawing 4 is the structure diagram of the calibration device

Accompanying drawing 5 is the block diagram of excitation and acquisition module

In the attached drawings: 1-metal conductance ring 2-insulated circular measuring pipe 3-wall surface liquid film 4-excitation and acquisition module 5-host computer 6-plane strip electrode 7-insulation plate 8-PIC single-chip microcomputer 9-stepper motor 10-reduction box 11-lead screw 12-internal thread sleeve 13-water tank

Detailed ways

The invention designs a calibration device and a method for measuring a sensor of thin liquid film thickness of a pipeline. The device uses an equivalent method to calibrate a flat strip electrode, and applies the calibration result to a conductance ring sensor. In order to further understand the features, technical means, and specific objectives and functions of the present invention, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

Fig. 1 shows the thin liquid film sensor of the conductance ring that needs to be calibrated for the thickness of the liquid film. It consists of two metal conductance rings 1, which are embedded in the insulating pipe 2. The excitation and acquisition module 4 applies a voltage signal to the two electrodes to measure the passing The current size is measured, and the measurement results are sent to the host computer 5 through the serial port, and the host computer calculates and displays the thickness of the liquid film 3 between the two electrodes, which is defined by the conductance formula:

Among them, G is the conductance of the conductor under test, σ is the conductivity of the conductor under test, S is the cross-sectional area of the conductor, and L is the length of the conductor. Since the liquid film in the pipe is attached to the pipe wall, it can be considered that the liquid film between the two electrodes is an annular cylinder. When h<<D, its conductance is:

Among them, D is the diameter of the pipe, d is the distance between the two conductivity rings, σ _l is the conductivity of the liquid, and h is the thickness of the liquid film. Therefore, it can be considered that the thickness of the liquid film is proportional to the conductance between the two metal rings. However, since the liquid film is inside the circular pipe and the thickness is less than 1 mm, it is difficult to precisely control the change of the liquid film thickness, and static calibration cannot be performed directly.

It can be seen that if there are two long strip electrodes, the distance is also d, and the length is l=πD, then the conductance of the liquid film between them is:

It can be seen that when measuring thin liquid films and satisfying h<<D, the ring electrode can be equivalent to a flat strip electrode for the calibration experiment of thickness measurement, and the calibration results of the flat strip electrode can be applied to the measurement of the conductance ring. .

Using COMSOL software to simulate the two shapes of electrodes, Figure 2 is the simulation model diagram, the left side is the conductance ring structure, the right side is the planar strip electrode structure, the length of the strip electrode is equal to the circumference of the conductance ring, and the distance between the two strip electrodes The distance between the two conductive rings is 5mm, and the electrode width is 1mm. Set the metal electrode material property to copper, the insulating material to plastic, and the liquid film to tap water. A sinusoidal signal of 5V500kHz was applied between the two electrodes respectively, and the change of the current passing through the electrodes with the thickness of the liquid film was detected. Figure 3 shows the simulation results. It can be seen that when the liquid film thickness is low, especially when the liquid film thickness is less than 1 mm, the measurement curves of the two shapes of electrodes basically overlap. The measurement results of , begin to be small, so when the thickness is less than 1mm, the flat strip electrode can be used instead of the conductance ring to calibrate the thickness of the liquid film.

Fig. 4 is a structural diagram of the calibration device. The stepper motor 9 is controlled by the PIC microcontroller 8 as the controller. The stepper motor drives the lead screw 11 to rotate after passing through the reduction box 10, and the lead screw drives the female threaded sleeve 12 to move up and down. The flat strip electrodes (6, 7) are installed at the bottom of the sleeve and go deep into the water tank 13 filled with water. By moving up and down, the distance between the electrode and the bottom of the water tank is changed, thereby changing the thickness of the liquid film on the electrode surface.

The pitch of the lead screw and the threaded sleeve are both 0.5mm, the step angle of the stepper motor is 1.8°, and the gear ratio of the gearbox is 1:5, so the motor needs 200 pulses to rotate once, because the subsequent 1:5 deceleration Therefore, the motor rotates 5 times and the lead screw rotates once and the electrode moves 0.5mm. To achieve 0.1mm step, the motor rotates exactly once, that is, 200 pulses control the lead screw to move 0.1mm, and the single-chip microcomputer is used to control the given 200 pulses. The signal can realize the step of 0.1mm, and the thickness of the liquid film on the electrode surface can be controlled to be adjusted from 0 to 2mm in steps of 0.1mm.

In the case of known liquid film thickness, use FPGA to excite and collect electrodes, as shown in Figure 5, first use the DDSIP core to output a 5V, 500kHz sine signal through high-speed DA, and apply it on the low-pass filter and amplitude modulation circuit. between the two electrodes. Then measure the current signal passing between the two electrodes, amplify the current signal into a voltage signal through the current amplification circuit, and then convert the AC signal into a DC signal through the peak detection circuit and collect it into the FPGA through the AD module, and the FPGA converts the voltage signal into a liquid film The thickness information is sent to the host computer through the serial port, the measured liquid film thickness is displayed on the host computer and the data is saved, so as to realize the online measurement of the liquid film thickness.

Using the above device and method, the calibration of the thin liquid film thickness measurement by the conductance ring sensor can be realized.

Claims (1)

1. A conductivity ring thin liquid film sensor calibration device, comprising two flat strip electrodes, a stepper motor, a controller, a lead screw, an internal thread sleeve, a water tank, an excitation and acquisition module and a host computer, the The length and spacing of the two flat strip electrodes are the same as the circumference and spacing of the two conductance rings of the conductance ring thin liquid film sensor to be calibrated. The inner thread of the cylinder matches the outer thread of the lead screw. The controller drives the lead screw to move up and down by controlling the stepper motor, changing the distance between the two flat strip electrodes and the bottom of the water tank, thereby changing the liquid film on the surface of the two flat strip electrodes. The excitation and acquisition module is used to apply a voltage signal to the two flat strip electrodes, measure the current signal passing between the two electrodes, and send the liquid film thickness information represented by the current signal to the host computer.

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