JPH029702B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pressure transmitter used to measure fluid pressure, liquid level, etc.

Conventionally, as this type of pressure transmitter, one shown in FIG. 1 is known. To explain the diagram,
Reference numeral 1 is the main body. This main body 1 consists of a body part 2 formed in a cylindrical shape with a bottom, and a flange part 3 fitted into an opening on one side of the body part 2. Inside this main body 1, a pair of insulating members 4a, 4b are provided.
A range spring 6 is held between them via support rings 5a and 5b. The insulating member 4
a and 4b are fixed inside the main body 1 by the wall 2a of the body 2 and the flange 3.

Further, a recess 3 is provided on the outer surface side of the flange portion 3.
a is formed, and a circular through hole 3b is bored in the center of this recess 3a. One end of a bellows 7 as a pressure receiving element is fixed to this flange portion 3 so as to close the through hole 3b. The other end of the bellows 7 and the center of the range spring 6 are connected by a round rod-shaped connecting shaft 8, and the pressure applied to the bellows 7 is applied to the range spring 6 through the connecting shaft 8. It is now being transmitted to

Further, movable electrodes 10a and 10 are disposed on the connecting shaft 8 so as to face each other with the range spring 6 in between.
b is fixed. These moving electrodes 10a,
10b constitutes a capacitive conversion mechanism 12 for converting the displacement amount of the range spring 6 into an output signal, together with fixed electrodes 11a and 11b provided on the opposing surfaces of the insulating members 4a and 4b. There is.

In addition, a through hole 2 is provided in the center of the wall 2a of the main body 1.
A temperature compensating diaphragm 13 is provided on the outer surface side of the wall portion 2a, and a temperature compensating diaphragm 13 is provided on the outer surface side of the wall portion 2a.
is fixed. The space closed by the bellows 7 and the temperature compensating diaphragm 13 of the main body 1 is filled with a sealed fluid.

The above pressure transmitter uses a bellows 7 when measuring.
When a pressure to be measured is applied to the bellows 7, a force is applied to the connecting shaft 8 according to the effective pressure receiving area of the bellows 7, and the range spring 6 is accordingly displaced according to the force transmitted through the connecting shaft 8. occurs. The amount of displacement of this range spring 6 is determined by the fixed electrodes 11a, 1
1b and the moving electrodes 10a, 10b, it is possible to obtain a signal corresponding to the pressure to be measured.

By the way, in this type of conventional pressure transmitter, when expansion (or contraction) occurs in each component due to a temperature change, the rigidity ratio of the bellows 7 as a pressure receiving element and the range spring 6 is affected. The movable electrodes 10a, 10b and the fixed electrode 1 of the conversion mechanism 12
There was a problem in that a temperature-dependent displacement occurred in the relative position with respect to 1a and 11b, causing a zero point fluctuation of the output. This is due to the temperature characteristics of the thermal expansion coefficient of the connecting shaft 8 that connects the tip 7a of the bellows 7 and the moving electrodes 10a, 10b that constitute the conversion mechanism 12, and the temperature characteristics of the bellows 7 and the conversion mechanism 12. This is due to the fact that there is a difference between the temperature characteristics of the effective coefficient of thermal expansion of the assembly of members such as the main body 1 and the insulating member 4a interposed between the fixed electrodes 11a and 11b. Conventionally, as a measure to solve this problem, temperature compensation for zero point fluctuations has been performed by electrical processing. However, each member as mentioned above is made of different materials (for example, the main body 1 is made of SUS430,
When the bellows 7 is constructed using SUS316, etc., the effective thermal expansion characteristics of the assembly do not change linearly with temperature changes and have complex characteristics, so this can be accommodated. A new problem has arisen in that electrical temperature compensation means are expensive.

The present invention was made in view of the above circumstances, and
It is an object of the present invention to provide a pressure transmitter that can prevent zero point fluctuations due to temperature changes without requiring electrical temperature compensation means.

In order to achieve this object, the present invention includes a pressure receiving element on one side of a transmitter main body, and a displacement conversion mechanism for converting the amount of displacement of the pressure receiving element into an output signal inside the main body. In a pressure transmitter in which at least the pressure receiving element and the displacement conversion mechanism are connected by a connecting shaft, the connecting shaft is configured by a combination of two or more types of materials, and the thermal expansion coefficient of the connecting shaft is The temperature characteristics of the effective thermal expansion coefficients of the plurality of members interposed between the portion supported by the main body of the displacement conversion mechanism and the pressure receiving element can be matched. .

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 1 to 3.

FIG. 2 is a sectional view showing the configuration of the connecting shaft 18 when the present invention is applied to the pressure transmitter shown in FIG. 1. The connecting shaft 18 shown in this figure is a cylindrical first
The shaft member 19 and the cylindrical second shaft member 20 are made of different materials, these two shaft members 19 and 20 are coaxially fitted, and their end faces are welded.
It is made by combining.

In this case, the first shaft member 19 is made of SuS316 with a coefficient of thermal expansion of 16×10 ^-6 /°C (hereinafter referred to as material A), while the second shaft member 20 is made of Ni
-SPAN C: Formed using a thermal expansion coefficient of 8×10 ⁻⁶ /° C. (hereinafter referred to as material B). In addition, the main body 1 is made of SuS316 (thermal expansion coefficient: 16×10 ^-6 /℃), and the fixed electrode parts 4a and 4b are made of ceramic (8×10 ^-6 /℃),
Support rings 5a, 5b, moving electrodes 10a, 10b
is formed of Ni-SPAN C (8×10 ⁻⁶ /° C.).

A connecting shaft 1 constructed by joining shaft members 19 and 20 made of two or more different materials as described above.
8, its thermal expansion characteristics are determined by the coefficient of linear expansion and elastic constant of each shaft member 19, 20, and how initial residual stress is applied upon connection. The above elastic constant can be set in consideration of the material and dimensions of each shaft member 19, 20, and the initial residual stress can be set arbitrarily when joining the two shaft members 19, 20 (by welding, etc.). can give.

Now, assume that the length of the connecting shaft 8 at the reference temperature is l (therefore, at the reference temperature, the bellows tip 7a
The distance between the moving electrode 10a and the moving electrode 10a is also l. ). When the temperature increases by Δt, the main body 1 and the bellows parts 7, 7
a, fixed electrode 4b, support ring 5b, and moving electrode 1
Due to the thermal expansion of 0a, the distance between the bellows tip 7a and the moving electrode 10a becomes l'. One connection shaft 8
has a length of (1+αΔt)l, where α is the coefficient of thermal expansion.

Therefore, the difference is Δl=l'-(1+αΔt)l, and the movable electrode moves by a length of δ=K ₁ /K ₁ +K ₂ Δl (1), which appears as an output error. Here, K ₁ : Spring constant of bellows 7,
K ₂ : Spring constant of range spring.

To set the output error to 0 with δ=0, Δl=0
In other words, it is necessary to select a material for the connecting shaft that has a coefficient of thermal expansion of α=l'-l/lΔt (2).

Next, a specific example will be described. The distance l' between the bellows tip 7a and the moving electrode 10a after the temperature change depends on the dimensions and coefficient of thermal expansion of the main body and each component, but if l = 20 mm and l' = 20.013 mm. Assuming that, in order to make the output temperature fluctuation zero in this state, from equation (2), α=l'-l/lΔt=20.013-20/20×50=13×10 ^-6 m
m/mm℃ (However, when temperature change Δt=50℃) Therefore, if l cannot be changed due to design, in this example it is necessary to select a material with a coefficient of thermal expansion of 13×10 ^-6 mm/mm℃. becomes.

However, considering workability, strength, and corrosivity,
If it is not possible to select a material having the above coefficient of thermal expansion, the present invention can be utilized in the following manner.

The first shaft member 19 of the connecting shaft 18 according to the present invention is SuS316 (coefficient of thermal expansion 16×10 ^-6 mm/mm°C), and the second shaft member 20 is Ni-SPAN C (coefficient of thermal expansion 8
×10 ^-6 mm/mm℃). Each shaft member 1
If the lengths of 9 and 20 at the reference temperature are both 20 mm, then the length l ₁ of the first shaft member 19 and the length l of the second shaft member 20 when the temperature changes by Δt=50°C. ₂
should be as follows: l ₁ = 20 × (1 + 16 × 10 ^-6 × 50) = 20.016 l ₂ = 20 × (1 + 6 × 10 ^-6 × 50) = 20.006, but currently both are welded etc. Therefore, the length l' of the shaft member 19 after the temperature change (50° C.) is l'=l ₂ +K ₂₀ /K ₁₉ +K ₂₀ (l ₁ −l ₂ ). Here, K ₁₉ : Spring constant of the first member,
K ₂₀ : Spring constant of the second member.

At this time, the coefficient of thermal expansion α ₁₈ for the connecting shaft 18 is expressed as α ₁₈ = l′−l/lΔt, and in order to obtain α ₁₈ = 13×16 ⁻⁶ mm/mm°C, it is 13×10 ⁻⁶ From =l'-20/20x50, it is necessary to determine _K19 and _K20 that satisfy l'= _l20 + _K20 / _K19 + _K20 ( _l1 - _l2 )=20.013.

That is, K ₂₀ /K ₁₉ +K ₂₀ = 0.7 (3) Here, assuming that the Young's moduli of the first and second shaft members 19 and 20 are equal, K ₁₉ and K ₂₀ are respectively K ₁₉ = A ₁₉ /lE, K ₂₀ = A ₂₀ /lE ......(4) (Here, A ₁₉ and A ₂₀ are the cross-sectional areas of the first and second shaft members, respectively.) Substitute (4) into (3) Then, A ₂₀ /A ₁₉ +A ₂₀ = 0.7 (5) If A ₁₉ + A ₂₀ = 100 mm ² due to design, A ₂₀ = 70 mm ² A ₁₉ = 30 mm ² . In other words, under the above conditions (length l = 20 mm at reference temperature, Young's modulus is equal, first shaft member is
SuS316, the second shaft member is Ni-SPAN C) In order to make the shaft member 18 with a thermal expansion coefficient of 13 × 10 ^-6 mm/mm°C, the cross-sectional area of the first shaft member 19 and the second shaft member The ratio to the cross-sectional area of 20 may be 3:7.

FIG. 3 is a graph showing the results of measuring the thermal expansion characteristics of the connecting shaft 18 and materials A and B, in which the horizontal axis represents the temperature change and the vertical axis represents the amount of expansion. In this figure, the thermal expansion characteristics of the connecting shaft 18 are shown by a solid line, the thermal expansion characteristics of material A are shown by a dashed line, and the thermal expansion characteristics of material B are shown by a broken line. Although not shown, an insulating member 4a that supports the fixed electrode 11a
- As a result of measuring the thermal expansion characteristics of the system consisting of the main body 1 and the bellows 7, characteristics approximately equal to those of the connecting shaft 18 were obtained. As can be seen from this figure, the connecting shaft 18 has a coefficient of thermal expansion intermediate between that of material A and material B, and exhibits nonlinear thermal expansion characteristics when the amount of temperature change is large. As mentioned above, this thermal expansion characteristic can be set arbitrarily by selecting materials, setting dimensions, and applying initial residual stress. It is possible to match the thermal expansion properties of the part.

According to the pressure transmitter in which the thermal expansion characteristics of the connecting shaft 18 are appropriately set as described above, the bellows 7 as a pressure receiving element, the movable electrode 10a of the displacement conversion mechanism 12,
Thermal expansion characteristics of the connecting shaft 18 that connects the center part of the bellows 7 and the fixed electrodes 11a, 11b (main body 1, insulating member 4a, etc.) Since the range spring 6 can be made to match the thermal expansion characteristics, even if temperature fluctuation occurs, the range spring 6 will not undergo unnecessary displacement, and therefore zero point fluctuation will not occur.

Note that the present invention is not limited to the configuration of the connecting shaft shown in the above embodiment, and as shown in FIG. The connecting shaft 25 may be constructed by combining them as appropriate, and the material, dimensions, etc. of each shaft member can be appropriately selected depending on the purpose. Further, the mechanism for converting the displacement amount of the range spring into an output signal is not limited to the above-mentioned capacitance type, but a variable inductance type, a strain gauge type, etc. can also be applied.

As is clear from the above description, the present invention has a connecting shaft that connects a pressure receiving element of a pressure transmitter and a range spring by combining two or more types of materials,
By appropriately setting the thermal expansion characteristics of this connecting shaft, zero point fluctuations caused by temperature fluctuations in the pressure transmitter are eliminated, so there is no need for expensive electrical temperature compensation means as in the past. This has the effect of providing a pressure transmitter with excellent temperature characteristics at a low price.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing an example of a pressure transmitter to which the present invention is applied, Fig. 2 is a sectional view of a connecting shaft as an embodiment of the present invention, and Fig. 3 is a sectional view of the connecting shaft shown in Fig. 2. FIG. 4 is a cross-sectional view of a connecting shaft showing a modification of the present invention. 1... Body, 6... Range spring, 7...
Bellows (pressure receiving element), 12...displacement conversion mechanism,
18, 25... Connection shaft, 19... First shaft member,
20... Second shaft member, 22, 23, 24... Shaft member.

Claims (1)

[Claims] 1. A pressure receiving element is provided on one side of the transmitter main body, and a displacement conversion mechanism for converting the amount of displacement of the pressure receiving element into an output signal is provided inside the main body, and the pressure receiving element and the displacement conversion mechanism are In a pressure transmitter that is connected by a connecting shaft,
The connecting shaft is made of at least two different materials.
A pressure transmitter characterized in that it is constructed by laminating different types of shaft members and integrally connecting both longitudinal ends of these shaft members.