JPH0334823B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrochemical gas sensor that detects the concentration of gas by oxidizing or reducing the gas that has passed through a gas permeable membrane with a working electrode placed in an electrolytic solution.

BACKGROUND ART Conventionally, as an electrochemical gas sensor as described above, the one described in, for example, Japanese Utility Model Application Publication No. 56144351 is known. This device stores an electrolytic solution in a plastic body, and installs first and second electrodes (working and counter electrodes) in the electrolytic solution, and adjusts the concentration of the gas, such as oxygen, that has passed through the gas permeable membrane. Corresponding signals are detected between the first and second electrodes. however,
Since the body of this sensor is made of plastic and the impedance of the gas sensor is high, the electrodes that generate electrical signals and the lead wires that transmit this signal are susceptible to external electrical noise. , there is a problem that an error occurs in the output signal of the sensor.

The present invention was made in view of the above-mentioned problems, and an object of the present invention is to provide an electrochemical gas sensor that is not affected by external electrical noise.

This purpose is achieved by covering the sensor body with a metal case in an electrochemical gas sensor that detects the concentration of gas by oxidizing or reducing the gas that has passed through a gas permeable membrane with a working electrode placed in an electrolyte. This can also be achieved by connecting the metal case to either one of the electrodes of the sensor body to shield the sensor body from external noise.

Hereinafter, the configuration of an embodiment of the present invention will be described based on the drawings.

The drawings show an example in which the present invention is applied to an oxygen sensor. In FIG.
is stored. There is a window 4 in the center of the end wall 3 of the container 1.
is formed, and this window 4 is closed by a gas permeable membrane 5. This permeable membrane 5 is connected to the end wall 3
The periphery is attached to the ring 6 housed in the ring 6 and is stretched around the ring 6. A dome-shaped working electrode 7 as one electrode is inserted into the window 4, and this working electrode 7
is in contact with the inner surface of the permeable membrane 5 via two extremely thin electrolyte layers. As a result, the working electrode 7 is placed in the electrolyte 2. A holding plate 9 is attached to the end wall 3 with a plurality of screws 8, and the holding plate 9 has a recess 10 and a passage 11 formed therein. 12 is a rubber ring housed in the recess 10, and this rubber ring 12 presses the permeable membrane 5 against the working electrode 7. A lead wire 13 has one end connected to the working electrode 7 , and this lead wire 13 extends through the electrolytic solution 2 and is drawn out from the end wall 14 . 15
is a counter electrode as the other electrode which is paired with the working electrode 7 and immersed in the electrolytic solution 2, and one end of a lead wire 16 is connected to this counter electrode 15. A thermistor 17 and a resistor 18 for temperature compensation are interposed in parallel between this lead wire 16 and the lead wire 13. An injection port 19 for the electrolytic solution 2 is formed in the end wall 14, and this injection port 19 is connected to a packing 20.
It is closed by screwing the plug 21 through. The container 1 has a cylindrical portion 23 with a slit 22 formed in the end wall 14 side, and a holder 24 made of plastic is inserted into the tip of the cylindrical portion 23 and fixed with machine screws 25.
An insulating plate 26 is inserted and fixed into the opening at the tip of this holder 24, and this insulating plate 26 has a lug 27 and a contact 2.
8 is installed. Then, the contact point 28
The other end of the lead wire 13 is connected to. The aforementioned container 1, electrolyte 2, working electrode 7, counter electrode 15, permeable membrane 5, ring 6, holding plate 9, rubber ring 12,
Lead wires 13, 16, thermistor 17, resistor 1
8, the plug 21, the holder 24, the insulating plate 26, and the contacts 28 constitute a sensor body 29 as a whole, and this sensor body 29 has a complete function as an oxygen sensor, but the working electrode 7 and the lead wire 13 are Easily affected by external electrical noise. Reference numeral 30 denotes a generally cylindrical body with a bottom, and this body 30 is made of conductive metal. This body 30
A hole 32 through which the tip of the holder 24 passes is formed in the bottom wall 31 of the holder 24 . The sensor main body 29 is located inside the body 30 on the distal end side, that is, the holder 24
It is inserted from the side. Reference numeral 33 denotes a metal spring piece interposed between the bottom wall 31 of the body 30 and the front end surface of the sensor main body 29, that is, the step surface 34 of the holder 24, and this metal spring piece 33 is shown in detail in FIG. It has a wavy ring shape and is manufactured so that it can be elastically deformed in the axial direction by press working. This metal spring piece 33 has the lead wire 16
The other end of the body 30 is connected to the counter electrode 15 of the sensor body 29 via the metal spring piece 33.
It is connected to the opposite electrode 15 and has the same potential as the counter electrode 15. Reference numeral 35 denotes a threaded ring made of plastic with a threaded tip protruding from the bottom wall 31 of the holder 24. By screwing this threaded ring 35,
The metal spring piece 33 is reliably electrically connected to the body 30 which is clamped between the bottom wall 31 and the stepped surface 34. 36 is a set screw screwed into the screw ring 35, and 37 is a pin attached to the body 30 as an output terminal. Furthermore, 38 is an O-ring for positioning the sensor main body 29 interposed between the body 30 and the container 1. The proximal opening of the body 30 is closed by a cap 39 made of conductive metal, and each cap 39 is fixed to the body 30 so as to be electrically connected to the body 30. A hole 4 through which gas passes is provided in the center of the cap 39 facing the passage 11.
0 is formed. The aforementioned body 30 and cap 39 collectively constitute a metal case 41 that covers the sensor body 29, and since this metal case 41 is connected to the counter electrode 15 as described above, the signal generating portion of the sensor body 29 That is, the working electrode 7 and the lead wire 13 are shielded from external electrical noise, and the metal case 41 can be used as one of the output terminals.

Next, the operation of one embodiment of the invention will be explained.

First, the gas or liquid whose oxygen concentration is to be measured is poured into the hole 4.
When oxygen is led to the permeable membrane 5 through the passage 11 and the recess 10, it permeates through the permeable membrane 5, is supplied to the two electrolyte layers between the permeable membrane 5 and the working electrode 7, and diffuses.
Then, when the oxygen reaches the working electrode 7, the oxygen is reduced at the working electrode 7, and the working electrode 7 and the counter electrode 1
A galvanic current flows between 5 and 5. At this time, as described above, the signal generating portion of the sensor body 29, that is, the working electrode 7 and the lead wire 13, are connected to the counter electrode 15.
Since the external electrical noise is covered by a metal case 41 connected to the metal case 4,
1 and cannot reach the signal generating part, and as a result, the galvanic current value accurately corresponds to the oxygen concentration, which is not affected by external electrical noise. When this galvanic current flows through the thermistor 17 and resistor 18, an output voltage proportional to the oxygen concentration is generated, and this output voltage is
8 and pin 37.

If the above-mentioned measurements are carried out over a long period of time,
The vapor of the electrolytic solution 2 escapes to the outside through the permeable membrane 5 and the amount of the electrolytic solution 2 decreases, or the electrolytic solution 2 changes over time and deteriorates. In this case, it is necessary to replenish or replace the electrolyte 2, so in this embodiment, the metal case 41 and the sensor body 29 are separate bodies, and the sensor body 29 is provided inside the metal case 41, especially the body 30. is inserted so that it can be taken out and taken out.
However, when the sensor main body 29 and the metal case 41 are separated in this way, a problem arises as to how to connect the ground. One idea is to attach a grounded metal tongue piece to the outer periphery of the sensor body 29 so that when the sensor body 29 is inserted into the metal case 41, particularly the body 30, this metal tongue piece comes into pressure contact with the body 30. It is possible, but
If this is done, there is a problem that the body 30 is worn out due to the sliding contact between the metal tongue piece and the body 30, and abrasion powder is generated. Therefore, in this embodiment, a metal spring piece 33 connected to the counter electrode 15 is interposed between the bottom wall 31 of the body 30 and the front end surface of the sensor main body 29. As a result, the body 30 is not worn and wear particles are not generated, and furthermore, even if the sensor main body 29 is not inserted sufficiently, or more specifically, the threaded ring 35 is not screwed in enough, the body 30 is securely attached to the body 30. A metal spring piece 33 can be brought into contact.

In the above-described embodiments, the present invention was applied to a galvanic cell type gas sensor, but the present invention can also be applied to gas sensors using a constant potential electrolysis type, a polarographic type, a coulometric type, a solution conductivity type, etc. In this case,
The gas may also be oxidized at the working electrode. Moreover, although the metal case 41 was connected to the counter electrode 15 in the embodiment described above, it may be connected to the working electrode 7 in the present invention.

As explained above, according to the present invention, there is no influence from external electrical noise, so
Gas concentration can be measured accurately, and
It can withstand shocks such as drops.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, and FIG. 2 is an exploded perspective view of the vicinity of a metal spring piece. 2... Electrolyte, 5... Gas permeable membrane, 7... Working electrode, 29... Sensor main body, 41... Metal case.

Claims (1)

[Claims] 1. In an electrochemical gas sensor that detects the concentration of gas by oxidizing or reducing the gas that has passed through a gas permeable membrane with a working electrode placed in an electrolyte,
An electrochemical gas sensor characterized in that the periphery of the sensor body is covered with a metal case, and the metal case is connected to one of the electrodes of the sensor body to shield the sensor body from external noise.