JP2002071622A - Electrochemical gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep a sensor output constant irrespective of pulsations of a sampling pump. SOLUTION: This electrochemical gas sensor takes a tested gas into an electrolyte 1 via a gas-permeable diaphragm 5 and outputs an electrical signal corresponding to the concentration of the tested gas. A buffer chamber 13 is demarcated/formed by a porous film 12 on the gas inflow side of the diaphragm 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrochemical gas sensor for taking a gas through a gas permeable diaphragm, and more particularly to the structure of a gas inlet.

[0002]

2. Description of the Related Art A constant-potential electrolytic gas sensor or a galvanic cell gas sensor requires that a test gas and an electrolytic solution be brought into contact with an electrode surface through a gas-permeable diaphragm, and that the gas concentration at a remote point is reduced. When measuring, as shown in FIG. 4, a gas inlet C and a gas outlet D are connected to the gas inlet B of the sensor A.
A cap E formed with a hole is attached, and gas is forcibly taken in by a sampling pump F through a sampling flow path G. In addition, the code | symbol H in a figure shows a buffer tank.

Such a sampling pump F uses a diaphragm pump having a simple structure, high reliability, and a large suction pressure and discharge pressure in consideration of taking in a sampling gas through a long sampling flow path G. However, the length of the sampling channel has changed significantly,
Further, if the air supply capacity of the pump changes over time, the flow rate that can be supplied to the sensor A fluctuates, and the detection output, that is, the detection sensitivity also fluctuates. In order to solve such a problem, it is conceivable to control the driving speed of the pump or adjust the supply amount of the sampling gas to the sensor A by providing a flow control valve, but the sampling means becomes complicated. Invites a new problem.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of such a problem, and an object of the present invention is to provide a sampling flow path without complicating the structure of gas sampling means. It is an object of the present invention to provide an electrochemical gas sensor capable of maintaining the detection sensitivity constant regardless of the fluctuation of the fluid resistance and the fluctuation of the air supply capacity of the pump.

[0005]

In order to achieve the above object, according to the present invention, a test gas is introduced into an electrolyte through a gas permeable diaphragm, and an electric signal corresponding to the concentration of the test gas is generated. In the output electrochemical gas sensor,
A buffer chamber is defined by a porous membrane on the gas inflow side of the diaphragm.

[0006]

When the gas to be detected flows, the flow velocity is reduced by the fluid resistance of the membrane and the volume of the buffer chamber, and the gas flows into the sensor substantially by diffusion, so that the detection sensitivity becomes constant regardless of the fluctuation of the flow rate of the sampling gas.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below based on this embodiment. FIG. 1 shows an embodiment of an electrochemical gas sensor according to the present invention, which is configured as a potentiostatic electrolytic gas sensor, in which a cell 2 containing an electrolytic solution 1 has a window 3, 4,
The window 3 serving as a gas inlet for the test is provided with a gas permeable diaphragm 5.
The window 4 is sealed with a material functioning as a working electrode, for example, a working electrode 7 formed with a platinum black layer 6, and the window 4 is sealed with a material functioning as a counter electrode on the permeable diaphragm 8, such as a counter electrode 10 formed with a silver layer 9, Further, a reference electrode 11 made of a silver wire is arranged at a position separated from the working electrode 7 and the counter electrode 10.

A window 3 serving as a gas to be detected is provided with a porous membrane 12 through which a gas to be detected can permeate so as to define a space having a constant width L and a gas permeable diaphragm 5 sealing the window. In this embodiment, a buffer chamber 13 is formed by stretching a membrane (PTFE A, manufactured by Advantech Co., Ltd., J020A) (membrane A) having a pore diameter of 0.2 μm, a porosity of 72, and a thickness of 130 μm. Have been. In the figure, reference numeral 15 denotes a protection frame, and reference numeral 16 denotes a fixed frame.

In this embodiment, when a sample gas is attached to the cap E as shown in FIG. The test gas flows at a flow rate corresponding to the fluid resistance of the pump F and the sampling flow path.

The flow of the test gas which has flowed into the buffer chamber 13 is reduced by the small and numerous pores formed in the film 12 and flows into the buffer chamber 13, and is diffused by the gas in a state where the gas flow is impeded. It flows into the gas permeable diaphragm 5. As a result, the sensor output, that is, the electrolytic current flowing through the working electrode 7 and the counter electrode 10 depends on the gas concentration without being affected by the change of the sampling flow rate caused by the fluctuation of the capacity of the sampling pump F or the fluid resistance of the sampling flow path. It will be the corresponding value.

FIG. 2 shows the flow rate of the gas to be detected as a parameter (note that A is 100 ml / min, B is 500 ml).
/ min, and the symbol C indicates 1000 ml / min), and shows the relationship between the width L of the buffer chamber 13 and the sensor output when the width L is 1.0 mm or more, that is, in practice,
If the porous membrane is arranged at a distance such that it does not adhere to the gas permeable diaphragm 5 constituting the working electrode 7, the detection output can be kept constant even with a flow rate change of about 10 times.

For comparison, filter paper (membrane B), ethylene tetrafluoride polymer membrane (membrane C) of different specifications (pore size 0.1 μm, porosity 76, thickness 90 μm), and ventilation forming the working electrode When a comparative experiment was performed using the same membrane (membrane D) as the permeable membrane 5, the membrane B received the fluctuation of the sampling flow rate, and the membrane C could slightly reduce the fluctuation of the flow rate, but the detection accuracy was guaranteed. Is impossible, and the membrane D is
Although there is no fluctuation in the flow rate, the amount of gas permeation is extremely small, so that the detection output is extremely reduced, making it impossible to use the gas sensor. That is, the detection characteristics of the films A to D are summarized in Table 1.

[0013]

[Table 1]

In the above-described embodiment, the porous membrane is attached to the gas inlet of the sensor. However, as shown in FIG. The same effect can be obtained even if the porous film 12 is stretched over the cap E so as to be located therebetween.

Further, in the above-described embodiment, an example has been described in which a constant potential electrolytic sensor is used. However, the same applies to a gas sensor of another type in which a test gas is introduced into an electrolyte through a diaphragm. It is clear that the action of

Further, in the above-described embodiment, the test gas is sucked into the cap, but it has been confirmed that the same effect can be obtained even if the test gas sucked by the pump is supplied.

[0017]

As described above, in the present invention,
In an electrochemical gas sensor that takes a test gas into an electrolytic solution through a gas permeable diaphragm and outputs an electric signal corresponding to the concentration of the test gas, a buffer chamber is defined by a porous film on the gas inflow side of the gas permeable diaphragm. Since it is formed, the flow velocity is greatly reduced by the fluid resistance of the membrane and the volume of the buffer chamber, and the gas in the buffer chamber flows into the sensor by diffusion, eliminating fluctuations in the flow rate due to the sampling pump and sampling flow path. Gas can be detected with a specified sensitivity.

[Brief description of the drawings]

FIG. 1 is a sectional view showing one embodiment of an electrochemical gas sensor of the present invention.

FIG. 2 is a diagram showing output characteristics of the gas sensor.

FIG. 3 is a sectional view showing another embodiment of the present invention.

FIG. 4 is a diagram showing an example of a gas measuring device using a conventional electrochemical gas sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrolyte solution 2 Cell 3, 4 Window 5, 8 Air-permeable diaphragm 7 Working electrode 10 Counter electrode 12 Porous membrane 13 Buffer chamber

Claims (1)

[Claims] 1. An electrochemical gas sensor for taking a test gas into an electrolyte through a gas permeable diaphragm and outputting an electric signal corresponding to the concentration of the test gas, wherein a porous film is provided on a gas inflow side of the diaphragm. An electrochemical gas sensor in which a buffer chamber is defined by the