RU2256884C2 - Capacitance fluid amount sensor for urofluometer - Google Patents

Abstract

FIELD: medical equipment.

SUBSTANCE: sensor can be used for measuring amount of urine during urination. Amount capacitance sensor has metal mug with bottom made of dielectric material. The mug has two plates, each plate is provided with electric output. Side wall of the mug has to be one plate of capacitor and surface of fluid to be measured has to be its second plate. Electric output of the plate is brought into contact with surface of fluid. DC capacitor is mounted between electric outputs of both plates of mentioned capacitor.

EFFECT: improved conditions of operation; better hygiene of process of measurement.

1 dwg

Description

The proposed capacitive liquid volume sensor for uroflowmeter is intended for use in measuring technique for measuring the volume of ion-conducting fluid, in particular in medical equipment in uroflowmetry, when it is necessary to measure urine volume changing in time during urination.

Known weight sensor fluid volume for uroflowmetry, converting the mass of fluid into volume [1]. However, such a sensor cannot be used to measure the volume of an ion-conducting liquid, since it does not take into account the fact that all ion-conducting liquids are solutions of various chemical compounds and their densities differ significantly from unity (by 20-30% or more). In 100 ml of water it is possible, for example, to dissolve up to 35.7 g of sodium chloride, while the density of such a solution is 1.18. Therefore, when measuring the volume of an ion-conducting liquid, such sensors give a large measurement error.

Known capacitive sensor volume of ion-conducting liquid, converting the volume of liquid into an electric capacitance, followed by converting the electric capacitance into a volume in digital form [2]. Such a capacitive sensor converts the volume of ion-conducting fluid that has entered it into an electric capacitance, the magnitude of which is directly proportional to the volume of the fluid, and not its mass, and therefore not sensitive to the density of the ion-conducting fluid. It contains a mug made of a dielectric with a double-sided board made of foil-coated fiberglass with electric leads from both layers of the foil having a dielectric coating in contact with the ion-conducting liquid entering the mug, and the two layers of foil are two plates of the capacitor of the electric capacitance formed upon the arrival of the ion-conducting liquid in a mug. With an increase in the liquid level in the circle, the foil area on the board of foil-coated fiberglass coated with ion-conducting liquid increases, therefore, the electric capacitance of such a sensor also increases proportionally. This capacitive sensor in its physical essence is the closest to the offer.

However, such a capacitive sensor for the volume of an ion-conducting liquid is not very convenient in operation for the following reasons:

- does not have an indication of the reliability of the connection of its electrical terminals to the liquid volume indication circuit;

- requires before starting the measurement of the preliminary filling in a mug of 75-100 ml of tap water so that the lower end of the board made of foil fiberglass is immersed in an ion-conducting liquid;

- requires after the end of the process of measuring the volume of the liquid before pouring the liquid from the mug preliminary removing the board from the foil-coated fiberglass from it, while the remaining urine is dripped from the board, which is inconvenient and unhygienic during operation.

The aim of the present invention is to improve the operating conditions of a capacitive liquid volume sensor for uroflowmeter.

This goal is achieved due to the fact that in the well-known capacitive liquid volume sensor for the uroflow meter, containing a mug with a bottom made of a dielectric, two plates of a capacitor of electric capacity, each with an electrical output, and one of the plates is metal and has a dielectric coating in contact with the liquid, the metal lining of the capacitor of the electric capacitance entering the mug during the measurement process is the side wall of the mug, and the surface of the measured liquid is the second lining of the condenser torus electrical capacitance, electrical terminal which is in contact with the measured fluid, wherein the electrical connections between the capacitor capacitance fluid volume sensor capacitance set for the capacitor Uroflowmeter constant capacitance.

The drawing shows a possible design of the proposed capacitive liquid volume sensor for uroflowmeter, when the side wall of the cup 1 is made of metal and has a dielectric coating applied to the entire inner surface 2. A bottom made of dielectric 4 is inserted into the cup. A contact made from the bottom of the insulated circle 4 stainless steel 6 so that one end of the contact 6 is inside the cup and has electrical contact with the ion-conducting fluid entering the cup, and the other end of the contact 6 comes out of the bottom of the circle and outwards so that the cup can be installed on the pad. The lower edge of the circle 3 is the electrical terminal of the metal plate of the capacitor of the electric capacitance of the capacitive liquid volume sensor, and the end of the contact 6, extending outward from the bottom of the circle, is the electric terminal of the second plate of the capacitor of the electric capacitance formed by the surface of the ion-conducting liquid 5 in contact with the dielectric coating 2 of the inner surface the side wall of the mug 1. Between the side wall of the mug 1 and the contact 4 is installed a capacitor of constant electric capacity 7, providing The possibility of indicating the reliability of the contact of the capacitive liquid volume sensor for the uroflowmeter with the liquid volume indication circuit connected to the capacitive sensor. As a simple scheme for indicating the volume of a liquid, a standard electric capacitance meter can be used, the scale of which is calibrated in units of volume.

The work of the proposed capacitive liquid volume sensor for uroflowmeter on the example of the design shown in the drawing, is as follows. When the ion-conducting liquid 5 enters the cup 1, an electric capacitor is formed in it, the capacitor plates being the side wall of the cup 1 with a dielectric coating 2 and the surface of the ion-conducting liquid 5 entering the cup 1 and in contact with the dielectric coating 2.

The electric capacitance of such a capacitor in pF is determined by the well-known formula of a flat capacitor:

where ε is the absolute dielectric constant of the dielectric deposited on the surface of the metal plate of the capacitor, in pF / SM;

π = 3.14;

S is the surface area of the ion-conducting fluid in contact with the dielectric coating deposited on the metal plate of the capacitor of the electric capacity, in cm;

d is the thickness of the dielectric deposited on the metal plate of the capacitor, in cm

Given that the diameter of the cup 1 is hundreds of times greater than the thickness of the dielectric coating 2 deposited on its inner surface, it is possible to use formula (1) to calculate the electric capacitance of the proposed capacitive liquid volume sensor. The area of the inner surface of the circle 1, covered with liquid 5, is determined as follows:

where D is the inner diameter of the circle 1, in cm;

h is the height of the liquid level 5 received in the mug, in cm

Substituting S from formula (2) into formula (1), we obtain:

From the description of the operation of the capacitive liquid volume sensor of the uroflowmeter and formula (3), it follows that the electric capacitance of the capacitor formed by the ion-conducting liquid entering the cup with a constant diameter of the cup D and a constant thickness of the dielectric coating d deposited on the inner side surface of the cup linearly depends only on the height of the liquid level h, i.e., from the volume of the ion-conducting liquid poured into the mug.

For subsequent measurements, the cup is removed from the contact pad, and the liquid is poured out, while ensuring the convenience of operating the capacitive liquid volume sensor for the uroflow meter by medical staff from the point of view of sanitation and hygiene due to the absence of elements that can be removed or inserted into the cup.

From the above it follows that the proposed capacitive liquid volume sensor for the uroflowmeter significantly improves the convenience and sanitary conditions of the uroflowmeter as a medical device.

Sources of information

1. Prospectus “Urocap Uroflowmeter Laborie Urodynamic Systems. Laborie Medical Technologies Corp., 1960.

2. Single Channel Uroflow Service / User Information Manual /, Lectromed UK Lim., Unit 23, 1991.

Claims (1)

A capacitive liquid volume sensor for a uroflowmeter, containing a mug with a dielectric bottom, two capacitor plates with an electric output each, and one of the plates is metal and has a dielectric coating in contact with the liquid entering the cup during measurement, characterized in that the metal lining of the capacitor of electric capacity is the side wall of the circle, and the surface of the measured liquid is the second lining of the capacitor of electric capacity, the output terminal of which is in contact with the liquid being measured, and a capacitor of constant electric capacity is installed between the electrical terminals of the capacitor of the electric capacitance.