JP2002005872A - Sensor housing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sensor housing in which a process fluid does not enter a sensor even when a pressure / temperature change that may cause electrolyte contamination occurs. A sensor containing at least one electrode (9, 11) capable of electrochemical contact with a process fluid.
In the housing 1, the sensor housing 1 can be sealed with a porous seal 8, whereby the inner surface of the sensor housing 1, the outer surface of the at least one electrode 9, 11, and the porous seal 8 can be sealed. Seal 8
An inner chamber is formed between the first electrolyte and the inner surface, and the inner chamber can be filled with the first electrolyte. The sensor housing 1 further comprises a deformable part such that the volume of the inner chamber is variable. Electrochemical sensor 15 comprises sensor housing 1 and is resistant to temperature and pressure over a wide range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a sensor housing containing at least one electrode capable of electrochemically contacting a process fluid through a porous opening, wherein the porous opening defines the electrode housing. An interior chamber is formed between an interior surface of the sensor housing and an exterior surface of the at least one electrode, wherein the interior chamber is configured to be filled with a first electrolyte.

[0002]

2. Description of the Prior Art A sensor housing of this type is disclosed in U.S. Pat. No. 4,128,468, which describes an ion-sensitive electrode structure which can be used, for example, for measuring the pH of process fluids.

[0003] This structure is composed of a tubular housing composed of a glass electrode and a reference electrode. One end of the housing is sealed with a sealing ring, and a signal conductor of an electrode communicates with the outside via the sealing ring.
The other end of the housing can be in contact with the process fluid to be measured.

[0004] This end is sealed with a plug made of a porous material such as, for example, porous polytetrafluoroethylene (PTFE). The reference electrode is in electrochemical contact with the process fluid via the porous plug. Inside the plug is a passage into which the glass electrode can be inserted, whereby the detection side of the glass electrode protrudes to the process side of the housing.

[0005] In the process industry, it is common to use concentrated electrolytes for pH sensors. This is to prevent the electrolyte from being excessively consumed, especially when a relatively porous material is used for the plug serving as the liquid junction. The porous material of the plug, porous polytetrafluoroethylene (PTFE), has relatively large pores (about 10 microns) and may be excessively consumed if the electrolyte is not sufficiently viscous.

As a result, the life of the pH sensor is significantly shortened. On the other hand, concentrated electrolytes have the disadvantage that the volume increases relatively significantly with increasing temperature.
The volume increase can be about 5-10%. If the wall of the housing holding the concentrated electrolyte is hard and the temperature coefficient of the housing material is such that the volume increment of the housing is less than the volume increment of the electrolyte, a considerable pressure will develop inside the sensor.

As a result, the sensor housing may be broken, the plug may be disconnected, or the electrolyte may be consumed.
In the first two of these cases, the sensor becomes unusable because the electrolyte flows out of the sensor. In the third case, as the temperature drops, the process fluid penetrates and replaces the lost electrolyte, contaminating the electrolyte. As a result, the pH sensor operates without calibration and the readings become unreliable.

Accordingly, it is an object of the present invention to provide a sensor housing having excellent temperature and pressure resistance, for example, for a pH sensor, that is, even if a change in pressure and temperature that may cause electrolyte contamination occurs, To provide a sensor housing in which process fluid does not penetrate into the sensor over the full pressure and temperature range specified.

The object is achieved by a sensor housing according to the preamble of claim 1, characterized in that it comprises a deformable part such that the volume of the inner chamber is variable. One advantage of such a sensor housing is that expansion caused by hot process fluids and concentrated electrolytes is absorbed by the deformable portion of the sensor housing. No pressure builds up in the housing as the inner volume of the sensor increases as a result of the deformable part deforming outward.

Thus, there is no leakage of the electrolyte and subsequent contamination of the electrolyte when the sensor is cooled.

US Pat. No. 4,659,451 discloses a reference electrode for measuring fluids under high pressure. A part of the pH measurement circuit can be configured using such a reference electrode.

The reference electrode has a liquid storage therein, and the liquid storage has a liquid storage space and a liquid junction therein, and one end of the liquid junction contacts the process fluid to be measured and the other end thereof. Is in contact with the liquid in the liquid storage space. A flexible bellows is provided between these spaces and is in contact with the internal liquid storage portion, so as to correct the pressure of the high-pressure liquid applied to the internal liquid via the liquid junction. All of these are housed in a rugged sensor housing itself.

[0013] The flexible bellows is adapted to transmit the pressure of the process fluid into the reference electrode. For that purpose, it is necessary to transmit the pressure of the process fluid to the flexible bellows via the capillary. The capillaries are easily contaminated with the process fluid, so that pressure cannot be transmitted or transmitted poorly. Further, inside the sensor, there are various joints where various components are fixed to each other. For example,
The flexible bellows is fixed to the glass reference electrode by fixing means. These anchors essentially constitute the weak points of the sensor.

US Pat. No. 4,406,766 discloses a pH sensor for measuring the pH of a process fluid under high temperature and pressure. In this case, the detection part of the measurement electrode is not exposed to high temperature, and even if the pressure of the process fluid changes, contamination of the internal electrolyte does not occur. This is achieved by arranging the detector of the measurement sensor at a distance from the end of the pH sensor that contacts the process fluid.

Attachment of the pH sensor to the piping containing the process fluid or a similar part is performed by using various heat insulating materials so that the detection part of the pH sensor is maintained at almost the ambient temperature. A deformable wall included in the inner chamber is attached to the end of the glass electrode and the end of the reference electrode that are remote from the end of the pH sensor that contacts the process fluid.

The pressure of the process fluid can be transmitted to the inner chamber via the capillary and at the same time to the electrolyte in the glass electrode and the reference electrode via the deformable wall. As a result, the internal pressure of the glass electrode and the reference electrode becomes equal to the pressure of the process fluid.

[0017]

However, such a conventional pH sensor has several disadvantages. First, because the deformable wall is made of a different material than the glass and reference electrodes, its joints are inherently fragile.

Further, a capillary for transmitting pressure is provided in the pH sensor. However, this capillary is easily clogged, so that pressure compensation is not (partially) performed, and the pH sensor may be damaged or electrolyte may leak. Might be.

In a preferred embodiment of the sensor housing according to the invention, said sensor housing is made of the same material, including the deformable part. Therefore, fabrication is simple. Also, since there is no joint between different materials, there is no breakage or liquid leakage.

In another embodiment of the sensor housing according to the invention, a second material is added to the material of the sensor housing, except for the deformable part. This second material may be a reinforced material, whereby the sensor
While the housing is stiffer and more robust, the deformable portion still maintains sufficient flexibility to allow for variable internal volume.

In one embodiment of the sensor housing according to the present invention, the sensor housing has a unitary structure including a deformable portion. That is, since there are no joints between the components of the sensor housing, there are essentially no fragile parts and excellent resistance to external influences.

In another embodiment of the sensor housing according to the present invention, the deformable portion is located at a location that contacts the process fluid during operation. As a result, the pressure of the process fluid is transmitted to the internal volume of the sensor housing via the deformable portion, so that there is no pressure difference between the inner chamber of the sensor housing and the process fluid. Since this method does not require a capillary, the sensor according to the present invention
Sensors using a housing do not clog.

In the embodiment of the sensor housing according to the present invention, it is preferable that the sensor housing has a reinforcing rib in a deformable portion. This makes the sensor housing more robust and can be easily mounted, for example, without risk of damage in the process piping. This is further the case, for example, for glass electrodes and reference electrodes, usually made of rigid glass parts.
It also enhances the protection of the electrodes located within the sensor housing.

In one preferred embodiment of the present invention, the sensor
The material constituting the housing has chemical resistance. The sensor housing is preferably made of a plastic, such as PVDF, which withstands a pH of 12 or more, depending on the temperature.

In another embodiment, the deformable portion is formed by locally thinning the wall of the sensor housing. The thickness of the deformable portion is desirably 0.50 mm or less, for example, 0.25 mm. This allows the sensor housing to have sufficient deformability to absorb volume changes in the inner chamber. Further, the sensor housing having such a thickness can be manufactured using a standard manufacturing method.

A second aspect of the present invention relates to a sensor provided with the sensor housing according to the present invention. A first embodiment relates to a pH sensor comprising a reference electrode located in the interior of the sensor housing.

In a second embodiment, the sensor comprises a glass electrode for measuring the pH of the process fluid.
For this purpose, the porous seal can be provided with a passage in which the glass electrode fits closely.

The third embodiment relates to a sensor having a separate temperature detector disposed in the sensor housing.

The sensor of the fourth embodiment further comprises an ORP electrode or a so-called liquid ground electrode disposed in the sensor housing, the contact of the electrode protruding through a porous seal, and a process fluid. Contact is possible. The liquid ground electrode can also be used for diagnosing the behavior of a sensor during operation.

A third aspect of the invention relates to a method for manufacturing a sensor housing according to the invention. For example, the sensor housing can be manufactured by an injection molding method. Further, the sensor housing can be manufactured by a vacuum forming method. The deformable part of the sensor housing may be manufactured by integral molding or may be manufactured by partially removing the material.

As another manufacturing method, the deformable portion may be manufactured by applying another process using a welding technique. As a result, an integrated sensor housing is obtained, and its internal volume can be made variable by partially deforming it. In addition, a separate process using glue bonding is applied to the deformable portion, so that a sensor housing having a variable internal volume can be obtained.

[0032]

FIG. 1 is a sectional view of a sensor housing 1 according to a preferred embodiment of the present invention. The sensor housing 1 has a process side 2 and a connection side 3 and is preferably tubular. The sensor housing can be fixed, for example, in an opening of a process pipe (not shown) by means of a parallel thread 4.

The sensor housing 1 is further provided with a groove 5, and the connection between the sensor housing 1 and the process pipe can be made liquid-tight by mounting an O-ring in this groove. The process side end 2 of the sensor housing 1 is provided with a protective collar 6, which serves to protect the electrode projecting from the sensor housing.

A deformable portion 7 is provided between the screw portion 4 of the sensor housing 1 and the protective collar 6, so that the internal volume of the sensor housing 1 can be increased or decreased.

FIG. 2 is a cross-sectional view of an element which can be mounted in the sensor housing to form, for example, the pH sensor 15. The porous seal 8 can form a liquid bond between the process fluid and the electrolyte inside the sensor housing 1 by, for example, being mounted inside the protective collar 6.

The porous seal 8 has an O-ring groove, and a liquid-tight seal is formed by mounting an O-ring in this groove. In one embodiment of the sensor housing 1 according to the invention, a rim 12 is provided inside the protective collar 6 and can be fitted, for example, in a groove 13 above the porous seal 8. Thereby, the porous seal 8 can be easily fixed to the sensor housing 1, and a good seal can be obtained.

Further, a glass electrode 9 can be provided, and the membrane glass of the glass electrode 9 projects from the opening of the porous seal and comes into contact with the process fluid. The glass electrode 9 can be, for example, a glass electrode with silver / silver chloride collector pins in a pH buffered KCl solution, as is well known to those skilled in the art.

To construct the composite pH electrode 15, as is well known to those skilled in the art, the sensor housing 1 may further comprise at least one reference electrode 10 or at least one KCl solution in the sensor housing 1. Eg silver /
Must have silver chloride reference collector pins.

The reference electrode 10 of the illustrated embodiment need not be in direct contact with the process fluid. The reference electrode 10 in the figure is arranged in a so-called salt bridge formed by the sensor housing 1.

In this case, the electrochemical bonding is performed by starting from the process fluid with the liquid junction 8, the electrolyte in the sensor housing 1, the second liquid junction in the reference electrode 10, and the electrolyte in the reference electrode. Via the collector of the reference electrode
(Pin).

The pH sensor 15 can further include a temperature sensor 11 combined with a liquid ground. The latter can be brought into contact with the process fluid through the opening of the porous seal 8, just like the glass electrode 9.

The temperature sensor 11 measures the temperature of the process fluid, and the liquid grounding is for forming a clear grounding to obtain a stable pH measuring circuit. This liquid grounding can also be used for the purpose of online diagnosis of the operation of the pH sensor 15 as a whole.

These electrodes 9, 10 and 11 are fixed in the sensor housing 1 by a sealing plug 16. A sealing plug 16 can be mounted on the connection side 3 of the sensor housing 1 and seals the sensor housing 1.

Thus, the porous seal 8 has at least one opening, and the sensor housing 1
The inner electrodes 9 and 11 can come into contact with the process fluid by protruding outward through the openings.

The openings of the porous sealing 8 are adapted to the electrodes 9, 11 so that a sufficient liquid-tight seal can be formed at the contact surface. Alternatively, the electrodes 9, 10, 11 and the porous seal 8 may be
May be sealed.

As a result, there is no danger of the process fluid penetrating into the inner chamber and contaminating the electrolyte unless it diffuses.
Therefore, inaccurate measurements or pH sensor 15
There is no breakdown. Also, sensor housing 1
This will prevent the electrolyte inside from leaking from around the contact surface.

The inner wall of the sensor housing 1 and the electrodes 9,
The inner compartments bounded by the outer surfaces of 10, 11, the sealing plug 16 and the porous sealing 8 are filled with electrolyte.

In order to prevent this electrolyte from leaking rapidly through the porous sealing 8, a concentrated supersaturated KCl
It is customary to use a concentrated electrolyte, such as a solution.

The thickening agent used for this includes hydroxyethyl cellulose (HEC), polyethylene glycol (PEG), polyvinyl alcohol (PVA), polyacrylamide (PAA) and the like.

FIG. 3 is a sectional view of a pH sensor 15 having a sensor housing according to the present invention. The pH sensor 15 includes the electrodes 9, 10, and 11 described above. Of these electrodes, electrode 10 is glass electrode 9 and temperature /
Since it is arranged behind the liquid ground sensor 11, it cannot be seen in this sectional view.

In FIG. 3, since the concentrated electrolyte is used for the pH sensor 15 as described above, the number of times of replenishment of the reference electrolyte can be reduced, and the number of times of maintenance is also reduced. If the electrolyte is not concentrated, the electrolyte leaks out quickly and the life of the pH sensor 15 is shortened.

As the temperature of the process fluid increases, the volume of the electrolyte increases. If the temperature coefficient of the sensor housing material is such that the increase in housing volume is less than the increase in electrolyte volume, a significant pressure builds up inside the sensor housing.

As a result, the sensor housing 1 may be damaged or the housing may be cracked, causing the pH sensor 15 to fail immediately or soon.

When the pressure is high, the porous sealing 8 comes off the housing 1 and the electrolyte disappears. Even a small amount of lost electrolyte will create a negative pressure in the sensor housing 1 when the temperature drops later. This leads to the ingress of process fluids, contaminating the electrolyte and significantly shortening the life of the pH sensor 15.

On the other hand, the effect of the sensor housing 1 having the deformable wall portion 7 can absorb an increase in volume due to a rise in temperature. Preferably, this deformable wall is located between the thread 4 and the protective collar 6 and is in contact with the process fluid during operation.

The deformable wall 7 transmits the pressure of the process fluid to the electrolyte, so that the pressure on both sides of the porous seal 8 is equal. That is, the pH sensor 15 including the sensor housing 1 according to the present invention is resistant to changes in both temperature and pressure.

FIG. 4 is a partial side view of an embodiment of the sensor housing according to the present invention. Where the deformable part 7 of the sensor housing 1 is provided, a reinforcing rib 14 is arranged in the longitudinal direction.

As a result, the strength of the sensor housing 1 is increased, while the effect of the deformable portion 7 increases the sensor housing 1.
The volume inside the housing 1 can be expanded and compressed.
As a result of the increased strength of the sensor housing 1, the electrodes 9, 1 in the housing can be used when handling and installing
The risk of damaging 0,11 is reduced.

FIG. 5 is a partial side view of another embodiment of the sensor housing according to the present invention. In this embodiment, the deformable part 7 is surrounded by cross-shaped reinforcing ribs 14.

It is clear that the amount of expansion and compression of the sensor housing of this embodiment is more limited than in the previous embodiment, but it is sufficient if the dimensions and thickness of the material of the deformable part are properly selected. The effect is obtained.

From this, it is obvious to those skilled in the art that other embodiments of the deformable part 7 and the reinforcing rib 14 are possible. The protective collar 6 in FIG. 5 has a shape with some protruding teeth. This shape has an effect that the process fluid around the electrode is easily flown and the electrode is sufficiently protected.

FIG. 6 is a cross-sectional view of the sensor housing shown in FIG. 4 taken along the line VI-VI. As is apparent from this figure, the deformable portion 7 is formed of a corrugated thin material, and the reinforcing rib 14 is formed of a thick material.

The waveform of such a waveform deformable portion 7 is
The sensor housing can be formed by an injection molding method using a mold so that the sensor housing can be easily manufactured. It is clear to a person skilled in the art that the deformable part 7 can be formed in other ways. For example, the waveform portions may be arranged vertically in the longitudinal direction of the sensor housing 1.

It is desirable that the sensor housing 1 is made of the same material, and that it can be easily manufactured without forming a fragile joint between different materials. It is desirable that the sensor housing 1 has an integral structure and has no joint.

This makes the sensor housing 1 inherently more robust and allows for leaks, breakage,
The risk of cracking is reduced. The sensor housing 1
It is desirable to be formed of a material that is resistant to the action of the most common process fluids.

As an example of a material having such characteristics,
There is PVDF plastic. PVDF is drug resistant and also belongs to the drug resistant fluoropolymer.
Also, for applications that do not require a particularly large range, the sensor housing can be made of a common plastic material such as, for example, polypropylene.

In another embodiment of the sensor housing 1, a reinforcing material such as glass is added to the material of the sensor housing except for the deformable portion. sensor·
By combining a glass filling material for the housing 1 and a single composition material (virgin material) for the deformable portion 7, a strong and robust sensor housing 1 having a feature that the inner volume is variable by the deformable portion 7. Can be realized.

The sensor housing 1 is desirably manufactured by an injection molding method. As a result, the sensor housing 1 has an integral structure, and the deformable portion 7 having a thickness of 0.50 mm or less, for example, a thickness of 0.25 mm can be simultaneously formed.

The sensor housing 1 may be manufactured by a vacuum forming method. As described above, the deformable portion 7 may be formed at the same time as the sensor housing 1 or may be formed by partially removing the material in a separate step.

[Brief description of the drawings]

FIG. 1 is a sectional view of an embodiment of a sensor housing according to the present invention.

[Fig. 2] By mounting inside the sensor housing, p
It is sectional drawing of the element which can comprise an H sensor.

FIG. 3 shows a p with a sensor housing according to the invention.
It is sectional drawing of an H sensor.

FIG. 4 is a partial side view of an embodiment of the sensor housing according to the present invention.

FIG. 5 is a partial side view of another embodiment of the sensor housing according to the present invention.

FIG. 6 is a sectional view of the sensor housing of the embodiment shown in FIG. 4 as seen from line VI-VI.

Claims (19)

[Claims] 1. A sensor housing containing at least one electrode capable of electrochemically contacting a process fluid through a porous opening, wherein said porous opening defines an inner surface of said sensor housing. An inner chamber is formed between an outer surface of the at least one electrode and the inner chamber can be filled with a first electrolyte, and the sensor housing (1) has a volume of the inner chamber. A sensor housing comprising a variable deformable part (7). 2. The sensor housing according to claim 1, wherein the sensor housing including the deformable portion is made of the same material. 3. The sensor housing according to claim 2, wherein the material of the sensor housing (1) except for the deformable part (7) has an additional reinforcing material. 4. The sensor housing according to claim 1, wherein the sensor housing (1) including the deformable part (7) is of one-piece construction. 5. The sensor according to claim 1, wherein the deformable part is arranged at a position which comes into contact with a process fluid during operation of the sensor housing. ·housing. 6. The sensor housing according to claim 1, wherein the sensor housing has a reinforcing rib provided on the deformable portion. 7. The sensor according to claim 1, wherein the deformable portion is formed by locally thinning a wall of the sensor housing. housing. 8. The sensor housing according to claim 1, wherein the material constituting the sensor housing is resistant to chemicals. 9. The sensor housing according to claim 8, wherein said material is plastic. 10. The deformable portion (7) has a thickness of 0.5.
The sensor housing according to any one of claims 1 to 9, wherein the sensor housing has a thickness of 0 mm or less, and preferably has a thickness of 0.25 mm. 11. A sensor provided with a sensor housing according to claim 1, further comprising a reference electrode (10) disposed in an inner chamber of said sensor housing (1). sensor. 12. The sensor according to claim 11, further comprising a glass electrode (9) for directly contacting the process fluid and measuring the pH of the process fluid. 13. A temperature sensor (1) disposed within said sensor housing (1).
The sensor according to claim 11, further comprising (1). 14. The sensor according to claim 11, further comprising a liquid ground electrode disposed on the sensor housing and directly contacting the process fluid. Item 14. The sensor according to Item 13. 15. The method according to claim 1, wherein the sensor housing is manufactured by an injection molding method. 16. The method according to claim 1, wherein the sensor housing is manufactured by a vacuum forming method. 17. The sensor according to claim 1, wherein the deformable portion of the sensor housing is manufactured by partially removing material.
The described method for manufacturing the sensor housing. 18. The sensor housing as claimed in claim 1, wherein the deformable portion of the sensor housing has a different process using a welding method. Method. 19. The sensor housing as claimed in claim 1, wherein the deformable portion of the sensor housing has an additional process using an adhesive method. Method.