JP3173272B2 - Pressure transmitter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure transmitter for measuring the absolute pressure or the difference between the pressures of two media and transmitting a detection signal, and more particularly to a structure for reducing hydrogen permeation to a pressure measuring section. .

[0002]

2. Description of the Related Art A pressure transmitter detects a pressure received by a diaphragm with a sensor and transmits an electric signal detected by the sensor to the outside.
Some measure the pressure difference between two media, that is, the differential pressure, the former and the latter being called a pressure transmitter and a differential pressure transmitter, respectively.

The pressure transmitter comprises a pressure receiving section and an amplifier for transmitting the measurement result of the pressure received by the pressure receiving section to the outside.

[0004] The structure of the pressure receiving portion is described in, for example, Japanese Patent Laid-Open No.
No. 073 discloses a configuration in which a pressure receiving chamber and an isolation chamber partitioned by a diaphragm are connected by a pressure guiding path, and a sensor is provided in the pressure guiding path.

[0005] Such a pressure transmitter is used in a chemical plant, a food plant, and the like. From the viewpoint of ensuring the safety of the plant and the quality of the product, an accuracy of ± 0.1% is desired.

Further, as a method for reducing hydrogen permeation of a diaphragm in a pressure transmitter, Japanese Patent Application Laid-Open No. 4-348243 discloses a method.
There is disclosed a pressure transmitter having a structure in which a non-conductive film is coated directly on the surface of the diaphragm on the measurement fluid side or through another non-conductive film or a hydrogen permeation blocking film having good adhesion to the diaphragm.

[0007]

Since the pressure transmitter is used in various plants such as a chemical plant and a food plant, a measurement accuracy of ± 0.2% is desired from the viewpoint of ensuring plant safety and product accuracy. It is rare. However, there are the following problems based on hydrogen permeation of the diaphragm,
It has been difficult to maintain that accuracy for a long time.

That is, a part of the hydrogen atoms or hydrogen ions contained in the measurement fluid permeates the diaphragm and accumulates as hydrogen gas in the silicon oil filled in the pressure introducing path, so that the pressure applied to the diaphragm is reduced. The change cannot be sufficiently transmitted to the sensor, and the accuracy decreases. Also,
In the worst case, the measurement may not be possible at all with the hydrogen gas accumulated in the silicon oil.

Such a phenomenon occurs remarkably when the hydrogen concentration in the pressure receiving chamber is high or when the amount of hydrogen adsorbed on the diaphragm surface is large. Generally, the diaphragm is made of a material having high corrosion resistance (for example, stainless steel or Ni-Cr-Mo steel), but the pressure receiving portion except the diaphragm is often made of a material having low corrosion resistance.

In a pressure transmitter made of a combination of such a high corrosion resistant material and a low corrosion resistant material, corrosion occurs in the pressure receiving portion and piping due to galvanic action, and electrons are emitted from the diaphragm surface in proportion to the amount of corrosion. It gives electrons to hydrogen ions in the fluid. As a result, the amount of hydrogen adsorbed on the diaphragm surface increases, and the amount of hydrogen permeated through the diaphragm also increases. Further, such a phenomenon also occurs due to local battery action on the surface of the diaphragm, for example, corrosion due to battery action between a foreign matter attached to the surface and a material forming a surface around the foreign matter-attached portion.

In particular, if the measurement fluid is a conductive fluid and the measurement temperature is relatively high, regular and irregular inspection and maintenance must be performed, and there is a drawback that the operating efficiency of the equipment is reduced. Furthermore, in the conventional hydrogen permeation prevention technology, since the surface of the diaphragm is coated with a multilayer film, the rigidity of the diaphragm is increased, and thus the performance of the pressure transmitter may be reduced.

An object of the present invention is to provide a long-term reliable pressure transmitter which prevents or reduces hydrogen permeation through a diaphragm.

[0013]

SUMMARY OF THE INVENTION An object of the present invention is to provide a pair of pressure receiving chambers each having a diaphragm into which a measuring fluid flows and deformed by the pressure of the measuring fluid, and a pressure measuring pressure of the measuring fluid flowing into the pair of pressure receiving chambers. In a pressure transmitter including a sensor for detecting a difference, the pressure transmitter is achieved by providing a film made of any one of chromium oxide, titanium nitride, and boron nitride on the surface of the diaphragm.

In the above, there are the following modes.

The thickness of the coating is 5 nm, and when the thickness of the diaphragm is t and the thickness of the coating is d, d / t is 0.0
The range should not exceed 5.

A coating is provided on the side of the diaphragm that contacts the fluid.

[0017] Coatings are provided on both sides of the diaphragm.

Particles having a small surface free energy are arranged on the surface of the coating.

The particles having a small surface free energy are coarsely arranged so that the surface on which the particles are arranged has conductivity.

The particles having a small surface free energy are polytetrafluoroethylene.

The purpose of the filter is to detect the difference between the pressure of the measurement fluid flowing into the pair of pressure receiving chambers having a diaphragm into which the measurement fluid flows and deformed by the pressure of the measurement fluid. A pressure transmitter comprising a sensor made of any one of chromium oxide, titanium nitride, and boron nitride on the surface of the diaphragm, wherein the coating has a hydrogen permeation of 0.02 mm ³ / cm ² · year or less. This is achieved by using

The object of the present invention is to detect a difference between the pressure of the measurement fluid flowing into the pair of pressure receiving chambers and a pair of pressure receiving chambers each having a diaphragm which is deformed by the pressure of the measurement fluid. In a pressure transmitter including a sensor, the pressure is achieved by disposing platinum on a surface in a pressure receiving chamber.

In the above, the material constituting the pressure receiving chamber is stainless steel.

The object of the present invention is to detect a difference between the pressure of the measurement fluid flowing into the pair of pressure receiving chambers and the pair of pressure receiving chambers provided with a diaphragm which is deformed by the pressure of the measurement fluid. In a pressure transmitter including a sensor, a coating made of chromium oxide, titanium nitride, or boron nitride is provided on the surface of the diaphragm, and platinum is disposed on the surface in the pressure receiving chamber.

[0025]

[0026]

[0027]

[0028]

[0029]

[Function] The diaphragm has a hydrogen permeation amount of 0.02 mm ³ /
By providing a membrane of less than cm ² · year, the amount of hydrogen permeation into the isolation chamber is very small compared to the amount of sealed liquid in the isolation chamber even within the useful life of the transmitter (for example, 15 years). Has no effect. The material of this film is selected from the group consisting of chromium oxide, titanium nitride, boron nitride and gold, and has a high hydrogen permeation preventing effect. The film thickness is at least 5 nm, and the thickness t of the diaphragm and the thickness d of the film are different. By using a film whose ratio (d / t) does not exceed 0.05, high-performance measurement can be performed without greatly changing the rigidity of the diaphragm. The effect of preventing hydrogen permeation is almost the same whether this film is used on one side of the diaphragm or provided on both sides so that the total thickness becomes a predetermined thickness.

Further, by coating the surface of the diaphragm in contact with the measurement fluid with a hydrogen permeation reducing film containing particles having a small surface free energy, the adsorption of hydrogen on the surface of the diaphragm is prevented, and the amount of permeated hydrogen is significantly reduced. Can be.

Further, by making the material constituting the measurement fluid pressure receiving chamber stainless steel and providing a platinum electrode in the pressure receiving chamber, the rate of progress of corrosion can be significantly reduced. The mechanism is that platinum is an anode and stainless steel is a cathode, and stainless steel is corroded due to the difference in galvanic potential of the materials. However, due to the potential characteristics of the two metals, the stainless steel is covered with the immobile body coating after a certain period of time and does not corrode.

Therefore, since no electrons are emitted from the surface of the diaphragm, the amount of hydrogen adsorbed on the surface of the diaphragm does not increase, and the amount of permeated hydrogen can be reduced.

When the pressure transmitter or the differential pressure transmitter of the present invention is used in a plant that handles fluid, the operation of the plant can be stably performed without a decrease in measurement accuracy due to hydrogen permeation from the diaphragm surface.

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing embodiments of the present invention, a schematic structure of a pressure transmitter or a differential pressure transmitter will be described with reference to FIGS. The major difference in the structure of the pressure transmitter and the differential pressure transmitter lies in the structure of the detecting section for detecting the pressure difference, and the other structures are almost the same. Therefore, the following description will be made using the differential pressure transmitter.

FIG. 1 is a perspective view of a differential pressure transmitter. The differential pressure transmitter includes a pressure receiving unit 1 for measuring the pressures of two measurement fluids, and an amplifying unit 3 for processing the pressure measured by the pressure receiving unit and sending the processed signal to the outside. Two fluid inlets 2 for externally applying a pressure to a pressure or differential pressure sensor built in the pressure receiving unit 1 are attached to the two fluid measurement pressure receiving chambers 7 and 7 ′, respectively, in a connecting cavity amount. An amplifying unit 3 for transmitting a signal detected by a pressure or differential pressure sensor to the outside is coupled to the pressure receiving unit 1. A connector or the like to which a lead wire for transmitting a sensor signal is connected is attached to the joint.

The amplification unit 3 has a built-in amplifier unit for performing signal processing of the main body of the detector and a terminal plate for sending power supplied from the outside to the amplifier unit. The amplifier unit houses an electronic circuit unit that incorporates electronic components for exciting a sensor, arithmetically amplifying a sensor signal, and converting the sensor signal into a generalized analog signal or digital signal. The indicator for displaying the output signal has a cover 12 with a glass.
Is attached. FIG. 2 shows a cross section of the pressure receiving portion.
FIG. 2 is a cross-sectional view taken along the line AA ′ of FIG. 1 and shows a cross section of the differential pressure transmitter. As is apparent from the figure, the two measurement fluid pressure receiving chambers 7 and 7 ′ are opposed to each other with the pressure guiding path 26 interposed therebetween, and are separated from the pressure guiding path 26 by the seal diaphragms 8 and 8 ′. Further, stoppers 25 and 25 'which are sealed by the seal metals 21 and 21' and have a thickness which are not deformed are attached to the opposite sides of the seal diaphragms 8 and 8 '.

An overload protection diaphragm 8 "is provided on the side opposite to the mounting section of the amplification section 3, and a sensor section 23 is provided on the amplification section 3 side of the diaphragm 8".
The overload protection diaphragm 8 ″ is provided with a plug 25 ″ by a seal metal 21 ″ on the opposite side of the sensor from the overload protection diaphragm 8 ″ to form an isolation chamber 28.

The sensor side of the seal diaphragms 8, 8 ', the sensor side of the overload protection diaphragm 8 "and the sensor section 23 are connected by a conduction path.

With the pressure receiving portion having such a configuration, the pressure applied to the measurement fluid pressure receiving chamber can deform only the seal diaphragms 8 and 8 '.

Further, when there is a pressure difference in the fluid to be measured, the pressure receiving section detects a pressure guiding path 26 for transmitting a volume change caused by the pressure change, an isolation chamber 28 storing the change, and a change in the isolation chamber 28. The sensor unit 23 is provided. Impulse line 26
Is filled with a filling liquid 29 (for example, silicone oil).

With the above-described configuration, the differential pressure transmitter uses two measurement fluid receiving pressures of the differential pressure transmitter to respectively control the pressures on the inflow side and the outflow side of the orifice or other squeezing mechanism provided in the pipe through which the measurement fluid flows. In addition to the chamber, a diaphragm that forms part of the measuring fluid pressure receiving chamber transmits the pressure to the isolation chamber. The isolation chamber that receives the pressure of the two measurement fluid pressure receiving chambers measures the pressure difference by applying the pressure of the two measurement fluid pressure receiving chambers to both sides of the sensor, and applies the pressure to both sides of the overload protection diaphragm in the same manner. A mechanism is provided to prevent the sensor from being damaged even when a large pressure difference outside the allowable range is applied. A major difference between the differential pressure transmitter and the pressure transmitter is that the differential pressure transmitter is provided with a diaphragm for overload protection.

Next, a structure for preventing hydrogen permeation of the pressure transmitter according to the embodiment of the present invention will be described below. FIG.
FIG. 3 is a cross-sectional view schematically showing a pressure receiving portion of the pressure transmitter.

The pressure transmitter shown in FIG.
8 ′, two concave pressure receiving chambers 92, 92 ′ covered by diaphragms 96, 96 ′ provided in the pressure receiving section 91 and a pressure sensor 94 installed substantially in the center of the pressure receiving section 91 change the volume of the other pressure receiving chamber. Are provided. Further, the pressure receiving chambers 92, 92 ′ and the pressure guiding passage 93 are filled with a filling liquid (for example, silicone oil), and the pressure receiving cover 98 is provided.
Is connected to a pressure receiving portion 91 via an O-ring 99.

The surfaces of the diaphragms 96 and 96 ′ are coated with chromium oxide as a surface coating 100. In the pressure transmitter of this embodiment having such a configuration, the atmospheric pressure is applied to the measurement fluid pressure receiving chamber 95 constituted by the diaphragm 96 and the pressure receiving cover 98,
The pressure of the measuring fluid is applied to the measuring fluid pressure receiving chamber 95 'constituted by the pressure receiving chamber 6' and the pressure receiving cover 98 ', and the pressure is measured by detecting the resistance value of the sensor 94 corresponding to the pressure of the measuring fluid. In a conventional pressure transmitter that does not employ a hydrogen permeation prevention structure, hydrogen permeates through the diaphragms 96 and 96 'depending on the type of the measurement fluid and the measurement time, and remains as a gas in the sealed liquid in the pressure introducing path. Therefore, when the transmission amount increases, the measurement accuracy may decrease or measurement may not be possible.

For example, as shown in FIG. 4, the indicated change in the zero point indicating the difference between the output value in the atmospheric pressure state and the output value when the measurement fluid pressure receiving chamber is depressurized, and the permeation amount of hydrogen permeating the diaphragm. Shows the relationship. From the figure, it can be seen that the indicated change amount of the zero point increases as the hydrogen permeation amount increases.

However, in the pressure transmitter of this embodiment, the chromium oxide coated on the surface of the diaphragm 96 is a membrane having a hydrogen permeation amount of 0.02 mm ³ / cm ² · year or less. This permeation amount is, for example, when the diameter of the diaphragm is 30 mm and the service life is 15 years, the amount of hydrogen gas permeating through the diaphragm is very small compared to the amount of the sealed liquid in the pressure guiding path, and the zero point is Stable measurement is possible for a long time with little shift.

Hereinafter, the hydrogen permeation amount is 0.02 mm ³ / cm ²
The effect of chromium oxide, which is a film of less than one year (hereinafter referred to as a hydrogen permeation blocking film), will be described in detail. In general,
On the surface of stainless steel, there is an oxide film of about 2 nm as a natural oxide film. In this example, a 0.1 mm thick, 50 mm square stainless steel (SUS316L) having such a natural oxide film was used as a measurement sample, and the surface of the measurement sample was coated with chromium oxide in a vacuum vessel.

After the measurement sample is placed in a vacuum vessel, the inside of the vacuum vessel is evacuated to 10 to ⁸ Torr by a vacuum pump, and then a mixed gas of argon and oxygen is supplied so that the pressure in the vacuum vessel becomes 10 to ⁵ Torr. Is introduced. Further, the measurement sample was heated at 470 ° C.
And then hold for 1-2 hours and then cool in a vacuum vessel. A chromium oxide film of about 10 nm was formed on the surface of the measurement sample manufactured by such a procedure.

The hydrogen permeation amount of the thus prepared measurement sample and that of the sample not subjected to the treatment were evaluated using an evaluation apparatus shown in FIG. The evaluation device includes a vacuum chamber 111 provided with a quartz window 114, a vacuum pump 112, a gas analyzer 113, an infrared heating device 115, and a thermometer 116. After the measurement sample 117 coated with chromium oxide or the measurement sample 118 made of untreated stainless steel is set in the vacuum chamber 111, the infrared heating device 11 is set through the window 114 of the vacuum chamber 111.
5, only the test piece was heated, and the hydrogen gas released from the measurement sample was measured.

This measuring method is to release hydrogen by heating the hydrogen stored inside the stainless steel, and to reduce the amount of release when there is a film that prevents permeation on the surface. is there. FIG. 6 shows a measurement sample 117 coated with chromium oxide (a in the figure) and a measurement sample 118 made of untreated stainless steel (b in the figure).
4 shows the results of comparing the relationship between the temperature and the amount of hydrogen released per unit time. The evaluated temperature was in the range from room temperature to 400 ° C. in consideration of the environment in which the pressure device was used.

It can be seen from the figure that the amount of released hydrogen gas increases as the temperature rises. Further, it can be seen that there is a difference in the release amount depending on the presence or absence of the chromium oxide coating. In other words, it can be seen that the amount of released hydrogen can be reduced to 1/5 or less when coated with chromium oxide as compared with when not coated.

Next, FIG. 7 shows the relationship between the film thickness of chromium oxide and the amount of released hydrogen gas. The figure shows the ratio of the amount of release when the coating thickness was increased, with the amount of release at 400 ° C. being 1 without coating. According to FIG.
The emission amount gradually decreases to nm and becomes constant at 5 nm or more. Therefore, the thickness of the hydrogen permeation blocking film may be 5 nm or more.

Next, titanium nitride is used as a hydrogen permeation preventing film,
The examination result in the case of using TiN will be described.

A surface of stainless steel (SUS316) having a thickness of 0.1 mm and a square of 50 mm was coated with titanium nitride having a thickness of 1 μm by a reactive vapor deposition method, and a test similar to that of chromium oxide was performed to evaluate a hydrogen permeation amount. . As a result, it was confirmed that the amount of hydrogen permeation was reduced to about 1/5 of that of the conventional stainless steel as in the case of chromium oxide.

It has been confirmed that a boron nitride film has a similar effect.

Next, the thickness of the hydrogen permeation preventing film and the performance of the pressure transmitter will be described.

In the pressure transmitter, as described above, ± 0.1%
Measurement accuracy is desired. In order to maintain the measurement accuracy in the range of ± 0.1%, the hydrogen permeation amount is suppressed to a certain value or less, and the rigidity of the diaphragm is related.

FIG. 8 shows the relationship between the rate of change of the diaphragm thickness and the measurement accuracy. As can be seen from the figure, ± 0.1%
In order to satisfy the accuracy of (1), the change in the rigidity of the diaphragm must be suppressed within a range of ± 15%. Further, the rigidity of the diaphragm is proportional to the thickness of the diaphragm to the power of 2.5. Therefore, the thickness t of the diaphragm and the thickness d of the hydrogen permeation blocking film are defined as shown in FIGS. 9 and 10, and the measurement accuracy of the pressure transmitter is ± 0.1%, that is, the rigidity accuracy is ± 15%. In order to fall within the range, the thickness t of the diaphragm and the thickness d of the hydrogen permeation blocking film must satisfy the relationship of the following equation (1).

[0059]

(Equation 1)

Calculating d / t from equation 1 gives 0.05. Therefore, the rate of change of the diaphragm thickness is set to 0.0.
By setting it to 5 or less, the performance (measurement accuracy, measured pressure) of the pressure transmitter is not reduced. Although the relationship between the rigidity of the diaphragm and the thickness of the diaphragm is slightly different depending on the material of the hydrogen permeation preventing film, there is no difference in the hydrogen permeation preventing film of this embodiment, and the rigidity of the diaphragm is 2.5 times the thickness of the diaphragm. We confirm that it is proportional to the power.

Next, the effect when the hydrogen permeation preventing film is coated on one or both surfaces of the diaphragm will be described. FIGS. 11 and 12 schematically show the gradient of the hydrogen concentration in the cross section of the diaphragm. Both figures show models in which hydrogen is dissociated and dissolved in the hydrogen permeation preventing film and the diaphragm, respectively, and the ratio of the hydrogen concentration is assumed to be equal to the ratio of the hydrogen solubility of each material. As can be seen from the figure, when one surface of the diaphragm 121 is coated with the hydrogen permeable element blocking film 122, the hydrogen concentration is a1, a2, a3, a4.
It becomes the distribution shown by. However, when both surfaces of the diaphragm 121 are coated with the hydrogen permeable element blocking film 122, the hydrogen concentration becomes like a1, a2, a3, a4, a5, a6. Therefore, by coating the both surfaces of the diaphragm 121 with the hydrogen permeation preventing films, the hydrogen permeation amount can be remarkably reduced. In addition, when the hydrogen permeation preventing films are formed on both sides of the diaphragm as shown in FIG. 12, the diaphragm is not deformed by the coating and the manufacture becomes easy.

As another embodiment of the present invention, a method for producing a hydrogen permeation preventing film containing polytetrafluoroethylene particles and its effect will be described. The hydrogen permeation blocking film formed in this embodiment is used by covering the surface of the diaphragm as in the above embodiment.

FIGS. 13 to 15 show the steps of producing a gold film containing polytetrafluoroethylene particles. In this embodiment, a diaphragm having a diameter of 75 mm and a thickness of 70 μm was used. First, as shown in FIG. 13, a 0.5 μm gold coating 128 was formed on the surface of the diaphragm 121 by plating.
Next, as shown in FIG. 14, gold tetrafluoroethylene particles 123 having an average particle size of 0.2 μm were dipped in a binder-dispersed method, that is, dipped in a uniformly dispersed solution and then pulled up. The coating was applied so that the particles did not adhere to the plating surface so as not to adhere to each other, and then dried. Incidentally, the polytetrafluoroethylene particles have an average particle size of 0.1.
Although a particle having a size of 2 μm is used, the particle size is not limited thereto, and a particle having a particle size of up to several tens μm can be used as long as the particles can be distributed to such an extent that the particles do not adhere to each other.

Next, the polytetrafluoroethylene particles 1 were placed in a furnace.
The polytetrafluoroethylene particles 123 were heated to about 325 ° C., which is higher than the temperature at which 23 melts (about 320 ° C.), to be in a molten state and adhered to the gold film. As shown in FIG. 15, in order to maintain the conductivity of the diaphragm surface in this state, the distribution of the polytetrafluoroethylene particles 123 is set so that the molten polytetrafluoroethylene particles 123 do not completely cover the gold coating surface. Control the density.

Using the pressure transmitter coated with the hydrogen permeation preventing film manufactured in such a process, the zero point drift amount of the detected value was measured in a weak corrosion solution. As a result, compared to the conventional pressure transmitter, the pressure transmitter of the present embodiment did not show any drift even after two months or more, and obtained a good result. In other words, the effect of gold as a hydrogen permeation preventing film and the fact that polytetrafluoroethylene particles are exposed on the surface of the diaphragm are superimposed on the effect of difficulty in adsorbing hydrogen, and the amount of hydrogen permeation is remarkably reduced. It is.

When the diaphragm is gold-plated through chrome or titanium, the adhesion strength of the gold plating can be increased.

Further, in this embodiment, a gold film is used. However, the same effect can be obtained by attaching polytetrafluoroethylene particles as in this embodiment using chromium oxide, titanium nitride, boron nitride or the like. Can be

Next, as another embodiment of the present invention, an example in which a platinum electrode is provided in a pressure receiving chamber will be described. In conventional pressure transmitters, high-corrosion-resistant materials are used for the diaphragm and general materials are used for the pressure-receiving cover. Release occurs. Therefore, the permeation of hydrogen through the diaphragm is promoted. Therefore, if corrosion of the pressure receiving cover is prevented, the amount of hydrogen permeation can be significantly reduced. In general, there is a method of contacting dissimilar metals as a metal corrosion prevention technique. This method utilizes the fact that the potential of a noble metal becomes low when a metal of different material comes into contact, and the potential of a noble metal becomes noble. The cathodic reaction is accelerated by a noble metal and suppressed by a noble metal. An example of using this method is to use Zn as an anode for anticorrosion of a marine structure made of Fe.

The material of the pressure transmitter targeted in the present embodiment is often stainless steel, and when a platinum electrode is arranged in the pressure receiving chamber, the platinum electrode becomes an anode and the stainless steel becomes a cathode. Accordingly, stainless steel is corroded, but due to the potential characteristics of both metals, the stainless steel can enter the passivation region after a certain period of time and reduce the corrosion rate. That is, when two kinds of metals having different natural potentials are brought into contact with each other, the potential of the noble metal becomes noble and the potential of the noble metal becomes noble corresponding to the area ratio of the two metals, and is electrically stable. There is a point. This point is the corrosion potential when metals having different natural potentials are brought into contact. FIG. 16 is a schematic diagram of the polarization characteristics of stainless steel. By controlling both areas of platinum and stainless steel, the corrosion potential can be stabilized as shown in FIG.

FIG. 17 shows a sectional structure of a pressure receiving chamber of a pressure transmitter with a platinum electrode. The platinum electrode 131 is used for the pressure receiving cover 13.
2 is fixed by screws 133 of the same material as the pressure receiving cover 132. Using such a pressure transmitter, the amount of hydrogen permeation and the state of corrosion in the pressure receiving part were evaluated from the drift amount of the detected value in a strong corrosion solution. As a result, the amount of hydrogen permeation was significantly reduced as compared with the conventional pressure transmitter, and the pressure receiving cover 132 was not corroded at all.
As a result of comparing the amount of hydrogen permeation with a pressure transmitter coated with chromium oxide in a highly corrosive environment, it was confirmed that the pressure transmitter with a platinum electrode of the present example could significantly reduce the amount of hydrogen permeation. When the pressure receiving chamber of this embodiment is made of stainless steel, the effect of reducing the hydrogen permeation amount is large.

Further, if a platinum electrode is attached to a structure having a coating film on the surface of the diaphragm as described in the other embodiments described above, the effect is further enhanced.

The pressure transmitter shown in each of the above-mentioned embodiments is effective when the pressure transmitter is attached to a pipe used in a plant for handling a liquid and the pressure of the liquid is measured. Even if ions and the like are easily absorbed on the surface of the diaphragm by electrons generated by corrosion due to galvanic action caused by a combination of materials in the pressure receiving chamber, permeation into the diaphragm can be reduced. In addition, polytetrafluoroethylene particles disposed on the film on the surface of the diaphragm further suppress the adsorption of hydrogen, thereby further increasing the effect.

[0073]

According to the present invention, when the thickness d of the hydrogen permeation preventing film is at least 5 nm on the surface of the diaphragm, the ratio (d / d / d) of the thickness t of the diaphragm to the thickness d of the hydrogen blocking film is obtained.
t) By coating in a range not exceeding 0.05, the amount of hydrogen permeating the diaphragm can be significantly reduced without deteriorating the performance of the pressure transmitter. further,
By providing a platinum electrode in the pressure receiving chamber, corrosion of the pressure receiving chamber is prevented, and as a result, the amount of hydrogen permeating the diaphragm can be significantly reduced, the reliability of the pressure transmitter can be improved, and the life can be extended. .

[Brief description of the drawings]

FIG. 1 is a perspective view of a differential pressure transmitter according to the present invention.

FIG. 2 is a sectional view of a differential pressure transmitter according to the present invention.

FIG. 3 is a sectional view of the pressure transmitter of the present invention.

FIG. 4 is a diagram showing a relationship between a hydrogen permeation amount of a diaphragm and a shift amount of a zero point.

FIG. 5 is a cross-sectional view of an evaluation device for measuring a hydrogen permeation amount.

FIG. 6 is a diagram showing the relationship between the temperature of a test piece and the amount of permeated and released hydrogen.

FIG. 7 is a diagram showing the relationship between the thickness of the hydrogen permeation blocking film and the hydrogen permeation blocking effect.

FIG. 8 is a diagram showing a relationship between diaphragm rigidity and measurement accuracy.

FIG. 9 is a diagram illustrating the definition of the thickness of the hydrogen permeation blocking film and the thickness of the diaphragm.

FIG. 10 is a diagram illustrating the definition of the thickness of a hydrogen permeation blocking film and the thickness of a diaphragm.

FIG. 11 is a diagram illustrating the hydrogen concentration of a diaphragm.

FIG. 12 is a diagram illustrating the hydrogen concentration of a diaphragm.

FIG. 13 is an explanatory view of a step of coating the surface of the diaphragm of the present invention with a gold film containing polytetrafluoroethylene particles.

FIG. 14 is an explanatory view of a step of coating the surface of the diaphragm of the present invention with a gold film containing polytetrafluoroethylene particles.

FIG. 15 is an explanatory view of a step of coating the surface of the diaphragm of the present invention with a gold film containing polytetrafluoroethylene particles.

FIG. 16 is a schematic diagram illustrating polarization characteristics of stainless steel.

FIG. 17 is a sectional view of a pressure receiving chamber with a platinum electrode of the pressure transmitter of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Pressure receiving part, 2 ... Fluid introduction port, 3 ... Amplifier part, 4 ... Terminal plate, 5 ... Display part, 6 ... Electronic circuit part, 7, 7 '... Measurement fluid pressure receiving chamber, 8, 8' ... Seal diaphragm, 8 ": Overload protection diaphragm, 12: Cover, 21, 21 ': Seal metal, 22, 22,', 22": Weld, 23: Sensor, 25, 25 ', 25 ": Plug, 26: Conductor Pressure path, 2
7: Fixing bracket, 28: Isolation chamber, 29: Filled liquid, 94: Pressure sensor, 95: Measurement fluid pressure receiving chamber, 96, 96 ': Diaphragm, 98, 98': Pressure receiving cover, 99: O-ring, 100: Oxidation Chrome film, 111: vacuum chamber, 112: vacuum pump, 113: gas analyzer, 114
... window, 115 ... infrared heating device, 116 ... thermometer, 11
7. Measurement sample coated with chromium oxide, 118
… Measurement sample without coating treatment, 121… diaphragm, 122… hydrogen permeation prevention film, 123… polytetrafluoroethylene particles, 129… gold plating film, 131… platinum electrode,
132 ... pressure receiving cover, 133 ... fixing screw.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yoshimi Yamamoto 882 Ma, Katsuta-shi, Ibaraki Hitachi, Ltd.Measurement Equipment Division (72) Inventor Akira Nagasu 882 Ma-Ma, Katsuta-shi, Ibaraki Hitachi, Ltd. In the Measurement Equipment Division (72) Inventor Toshihiro Onose 882 Ma, Katsuta-shi, Ibaraki Hitachi, Ltd. Measurement Equipment Division (56) References JP-A-5-60633 (JP, A) JP-A-62-86528 ( JP, A) JP-A 3-93757 (JP, U) JP-A 58-47141 (JP, U) JP-A 59-3338 (JP, U) (58) Fields surveyed (Int. Cl. ⁷ , (DB name) G01L 9/00-13/06

Claims (11)

(57) [Claims] 1. A pair of pressure receiving chambers having a diaphragm into which a measuring fluid flows and which is deformed by the pressure of the measuring fluid,
A pressure transmitter including a sensor for detecting a difference in pressure of the measurement fluid flowing into the pair of pressure receiving chambers, wherein a coating made of any one of chromium oxide, titanium nitride, and boron nitride is provided on the surface of the diaphragm. Features pressure transmitter. 2. The method according to claim 1, wherein said coating has a thickness of 5n.
A pressure transmitter, wherein d / t is within a range not exceeding 0.05, where m is the thickness of the diaphragm and d is the thickness of the coating, from m. 3. The pressure transmitter according to claim 1, wherein the coating is provided on a side of the diaphragm that contacts the fluid. 4. The pressure transmitter according to claim 1, wherein the coating is provided on both sides of the diaphragm. 5. The method according to claim 1, wherein
A pressure transmitter, wherein particles having small surface free energy are arranged on the surface of the coating. 6. The pressure transmitter according to claim 5, wherein the particles are coarsely arranged so that the surface on which the particles are arranged has conductivity. 7. A pressure transmitter according to claim 5, wherein said particles are polytetrafluoroethylene. 8. A pair of pressure receiving chambers having a diaphragm into which a measurement fluid flows and which is deformed by the pressure of the measurement fluid,
A pressure transmitter including a sensor for detecting a difference in pressure of the measurement fluid flowing into the pair of pressure receiving chambers, wherein the surface of the diaphragm is a coating made of any one of chromium oxide, titanium nitride, and boron nitride, A pressure transmitter wherein the coating has a hydrogen permeation of not more than 0.02 mm ³ / cm ² · year. 9. A pair of pressure receiving chambers having a diaphragm into which a measurement fluid flows and which is deformed by the pressure of the measurement fluid,
A pressure transmitter, comprising: a sensor for detecting a difference in pressure of a measurement fluid flowing into the pair of pressure receiving chambers, wherein platinum is disposed on a surface in the pressure receiving chamber. 10. The pressure transmitter according to claim 9, wherein the pressure receiving chamber is made of stainless steel. 11. A pair of pressure receiving chambers having a diaphragm into which a measuring fluid flows and deformed by the pressure of the measuring fluid, and a sensor for detecting a difference in pressure of the measuring fluid flowing into the pair of pressure receiving chambers. A pressure transmitter comprising: a coating made of any one of chromium oxide, titanium nitride, and boron nitride provided on a surface of the diaphragm; and platinum disposed on a surface in the pressure receiving chamber.