RU61428U1 - PARTIAL OXYGEN PRESSURE SENSOR - Google Patents

Abstract

The utility model relates to the field of analytical instrumentation and can be used as a sensor for measuring the partial pressure of oxygen in the air used for breathing, both at high and low pressure relative to normal atmospheric pressure. The purpose of the utility model is to reduce the warm-up time, increase the time of continuous operation and increase the accuracy of measurements. The proposed oxygen partial pressure sensor contains a heater and a sensing element with electrodes made of a solid zirconia-based electrolyte with an admixture of bivalent or trivalent metal oxide having almost purely oxygen unipolar conductivity. The sensor element is made of two solid electrolyte plates glued together, on which electrodes of porous gas-permeable platinum are applied on both sides, the electrodes in the chamber formed by the plates are in contact and electrically contact each other, and the sensor element is fixed using platinum down conductors extending from the electrodes between two solid electrolyte disks rigidly interconnected by racks of solid electrolyte material, and the heater ene as a wire spanned between the discs and fixed to them by means of platinum wires, wherein the fastening parts of solid electrolyte and platinum wires by using high dielectric adhesive having a thermal expansion coefficient substantially equal to thermal expansion coefficient of the solid electrolyte. A reversible direct current source is connected to the electrodes of one of the solid electrolyte plates, the polarity of which periodically changes depending on the magnitude of the EMF generated on the electrodes of the second solid electrolyte plate, and the partial pressure of oxygen is judged by the length of a single period of operation of the current source.

Description

The utility model relates to the field of analytical instrumentation and can be used as a sensor for measuring the partial pressure of oxygen in the air used for breathing, both at high and low pressure relative to normal atmospheric pressure.

A known sensor for measuring the oxygen content in the gas mixture used in the gas analyzer "Fluorite-C" produced by the company LLC "Angarskoye-OKBA" (gas analyzer "Fluorite-C". Operation manual 5K1.552.045).

The sensor includes a housing in which a heater and a sensing element in the form of a solid electrolyte tube are located. The solid electrolyte tube is installed in the heater, in the working area of which the temperature is maintained with an accuracy of ± 2 ° C. The solid electrolyte is zirconia stabilized with 15% yttrium oxide. A porous platinum electrode is applied to the inner end of the tube, to which the analyzed gas is supplied. A porous platinum electrode, called a comparative electrode, is also deposited on the outer end of the tube, which is washed by atmospheric air due to temperature convection, the oxygen content of which is quite constant.

The analyzed gas enters the solid-state electrolyte tube, and then is discharged into the atmosphere. An EMF meter is connected to the electrodes. EMF is used to judge the oxygen concentration in the analyzed gas.

The main disadvantage of this sensor from the point of view of measuring the partial pressure of oxygen is the need to measure the pressure of the analyzed gas and atmospheric pressure, which significantly complicates the electrical circuit of the sensor.

The closest in technical essence is the oxygen partial pressure sensor (AS USSR No. 1784907 G 01 No. 27/417, Bull. No. 48, 1992). The sensor contains a solid-electrolyte sensing element with a working and comparative electrodes, to which an EMF meter is connected and through a switch-source of direct current.

The analyzed gas is supplied to the working electrode. The reference electrode is located in a sealed reference chamber. Before proceeding with the measurement of the partial pressure of oxygen, a comparative medium with a certain known partial pressure of oxygen is created in the comparative chamber. For this purpose, a direct current source in the plus polarity is connected to the electrodes using a switch - to the working electrode and the voltage is set within 0.5-1.2 V. Under the action of this voltage, oxygen is extracted from the comparative chamber. The almost complete extraction of oxygen is judged by a sharp drop in current and its proximity to zero. After that, the polarity of the voltage applied to the electrodes is changed and a certain amount of electricity is passed, so that a predetermined partial oxygen pressure is set in the comparative chamber. Then, an EMF meter is connected to the electrodes. The measured value of the EMF is used to judge the partial pressure of oxygen in the analyzed gas.

The considered sensor has two significant drawbacks. Firstly, it takes a long time to reach the operating mode, which includes heating the sensor to a sufficiently high temperature, about 650 ° C, and, in addition, pumping and dosing of oxygen. The second disadvantage is the short time of continuous operation of the sensor (not more than 10 hours even with a relative measurement error of 10%), which is associated with the leakage of oxygen into the comparative chamber due to the inherent property of solid electrolyte - the so-called "electrolytic" permeability.

The essence of the utility model is to eliminate these drawbacks.

The figure shows a drawing of the proposed sensor. The sensor element 4 consists of two plates 5 and 6 of solid electrolyte glued with dielectric adhesive 8. Electrodes 7, 10 and 11 of porous platinum are applied to the plates on both sides, and the electrodes 7 are electrically in contact with each other. To the electrodes 7, 10 and 11 are connected, respectively, down conductors 13, 12 and 14, made of platinum wire and rigidly fixed to the disks 1 and 18 using dielectric glue. A reversible stabilized current source 15 is connected to the electrodes 7 and 10, and an EMF meter is connected to the electrodes 7 and 11, by a signal from

which changes the polarity of the current source 15. The sensor is heated using a heating wire 9 fixed by platinum pins 19. The pins 19, in turn, are secured by dielectric glue on the disks 1 and 18. To give structural rigidity, the disks 1 and 18 are connected by posts 2 of solid electrolyte material fixed with dielectric glue. For sealing the sensitive element, a shell 20 is used, which is also a heat-insulating screen. The analyzed gas enters through the nozzle 3, washes the sensing element 4 and exits through the nozzle 17.

Consider the physical nature of the processes occurring in the sensing element 4 in the process of measurement. The sensor uses two properties of solid electrolyte cells, which allow them to be used in analytical practice. The first property is as follows. If on different sides of the solid electrolyte there are gas mixtures with different partial pressures of oxygen, then on its electrodes there is an EMF associated with the partial pressures of oxygen by the Nernst formula:

where E is the EMF;

R is the universal gas constant;

T is the temperature of the working area (electrodes);

n = 4 is the number of charges in the ionized oxygen molecule;

F is the Faraday number;

and - partial pressure of oxygen.

The second property is as follows. If an electric current flows through a solid electrolyte, then practically only oxygen ions participate in its transfer, and the amount of oxygen transferred is calculated in accordance with the Faraday law.

In the process of measurement using the proposed sensor through the electrodes 7 and 10 flows constant in value, but with a changing

polarity is the current that carries oxygen, and in the plus polarity on the electrodes 7, oxygen enters the chamber in which the electrodes 7 are located, and in the opposite polarity, oxygen is extracted from this chamber. The current is set in the range from 50 to 300 μA. Switching the polarity of the current is carried out when the EMF on the electrodes reaches some values. Oxygen pumping starts at a constant EMF value in the range from 40 to 50 mV, and oxygen dosing - at a constant EMF value in the range from 70 to 80 mV. The analytic signal of the sensor is the total time of dosing and pumping oxygen for one period, which increases with increasing partial pressure of oxygen in the analyzed gas. An experimental check showed that there is a linear relationship between the partial pressure of oxygen in the analyzed gas and the time of oxygen dosing and evacuation, that is, the static characteristic of the sensor has the form:

where P is the partial pressure of oxygen in the analyzed gas;

k is the coefficient of proportionality;

Tests of the proposed sensor showed that it has the following basic metrological characteristics:

- t is the total time of dosing and pumping oxygen for one period.

- the range of measurements of the partial pressure of oxygen from 5 to 300 kPa;

- the main relative measurement error of not more than 5%;

- testimony establishment time no more than 5 s .;

- warm-up time no more than 100 s.

In terms of measurement accuracy, the sensor is significantly superior to analogues. In addition, the sensor warm-up time is three times less than that of the analogue, and its continuous operation time is almost unlimited. The sensor also has significantly less weight and overall dimensions.

Claims (1)

An oxygen partial pressure sensor containing a heater, a sensing element with electrodes made of a solid zirconia-based electrolyte mixed with bivalent or trivalent metal oxide having practically purely oxygen-ionic unipolar conductivity, characterized in that, in order to reduce the heating time, increase the time continuous operation and improve measurement accuracy, the sensitive element is made of two solid electrolyte plates glued together, on which both Oron, electrodes made of porous gas-permeable platinum are deposited, and the electrodes in the chamber formed by the plates are in contact and electrically contact each other, and the sensing element is fixed using platinum down conductors extending from the electrodes between two solid electrolyte disks rigidly connected to each other by racks of solid electrolyte material, and the heater is made in the form of a wire stretched between the disks and fixed to them using platinum wires, and the fastening of all t of electrodelectrolyte parts and platinum wires is carried out using a high-temperature dielectric glue having a coefficient of thermal expansion almost equal to the coefficient of thermal expansion of solid electrolyte, and a reversible direct current source is connected to the electrodes of one of the solid electrolyte plates, the polarity of which periodically changes depending on the magnitude of the emf generated on electrodes of the second solid electrolyte plate, moreover, on the partial pressure of oxygen, the court T duration of a single period of the current source.