A pressure measuring instrument based on the standard atmospheric pressure differential method

Abstract

This invention discloses an instrument device for measuring pressure based on the standard atmospheric pressure differential pressure method, comprising a glass funnel, ball valve I, a high-pressure end flange of a pressure transmitter, a pressure transmitter, a constant-pressure glass tube, a constant-pressure flange, a balance nut I, a low-pressure end flange of the pressure transmitter, ball valve II, an inverted L-shaped glass tube, a base, a balance nut II, a leveling device, and a scale. This invention uses a constant pressure generated by a mercury column of a certain height to replace the local atmospheric pressure, serving as the low-pressure input pressure of the pressure transmitter. P (L), P The value of (L) is one standard atmosphere, i.e., 101.325 kPa; the pressure inside the device under test is used as the input pressure at the high-pressure end of the pressure transmitter. P (H); then the gauge pressure Δ of the equipment P = P (H)- P (L). This invention effectively eliminates the problem of inaccurate gauge pressure readings from pressure transmitters caused by changes in local environmental factors such as temperature, humidity, altitude, and weather.

Description

Technical Field

[0001] This utility model belongs to the field of chemical instrumentation and measurement technology, and in particular relates to an instrument device for measuring pressure based on the standard atmospheric pressure differential pressure method. Background Technology

[0002] In the instrumentation, thermal automation, and control industry, the pressure measured by pressure transmitters is called gauge pressure. Gauge pressure is the pressure value after deducting one standard atmosphere, i.e., gauge pressure = absolute pressure - standard atmosphere. Gauge pressure is greatly affected by external environmental factors, such as the altitude of the measuring device, local temperature and humidity, and weather conditions, resulting in varying atmospheric pressure values. Previous technologies typically placed the low-pressure end of the pressure transmitter directly in the atmosphere as the low-pressure input value. Since atmospheric pressure can change constantly, the low-pressure input value also changes accordingly. Therefore, the pressure value measured by the pressure transmitter in actual use cannot accurately reflect the true pressure of the measured equipment. However, in many actual production and experimental processes in pharmaceuticals and chemical reactions, accurate pressure values ​​in equipment containers and reaction devices, unaffected by external geographical environment and weather factors, are required. Utility Model Content

[0003] To effectively solve the existing problems, this utility model provides an instrument device for measuring pressure based on the standard atmospheric pressure differential pressure method.

[0004] The purpose of this utility model is achieved through the following technical solution: an instrument device for measuring pressure based on the standard atmospheric pressure differential pressure method, comprising a glass funnel, ball valve I, a high-pressure end flange of a pressure transmitter, a pressure transmitter, a constant-pressure glass tube, a constant-pressure flange, a balance nut I, a low-pressure end flange of the pressure transmitter, ball valve II, an inverted L-shaped glass tube, a base, a balance nut II, a leveling device, and a scale; the glass funnel, ball valve I, and constant-pressure glass tube are connected in sequence; the constant-pressure flange and the low-pressure end flange of the pressure transmitter are fixed to the base by bolts; the lower end of the constant-pressure glass tube is connected to the constant-pressure flange; a graphite gasket is provided between the constant-pressure flange and the low-pressure end flange of the pressure transmitter; a through hole is provided on the side of the constant-pressure flange; the inverted L-shaped glass tube... The upper end of the glass tube communicates with the through hole, and a ball valve II is installed at the lower end of the inverted L-shaped glass tube; the high-pressure flange of the pressure transmitter is connected to the device under test, and pressure sensors are respectively installed inside the low-pressure flange and the high-pressure flange of the pressure transmitter. The low-pressure flange and the high-pressure flange of the pressure transmitter are respectively connected to the pressure transmitter through wires; the zero point of the scale is horizontally aligned with the upper end of the low-pressure flange of the pressure transmitter; the 760mm position of the scale is horizontally tangential to the position of the constant pressure glass tube and must be lower than the position of ball valve I; the zero point of the scale is vertically fixed to the base; balance nuts I and II are installed on both sides of the base; the leveling device is fixed on the base.

[0005] Furthermore, the leveling device adopts one of a bubble level or a cone level.

[0006] Furthermore, the cone leveling device includes a top plate, a suspension line, cone I, cone II, a bottom plate, and a side plate; the upper and lower ends of the side plate are perpendicularly connected to the top plate and the bottom plate, respectively; cone I is suspended and fixed on the top plate by the suspension line, and cone II is fixed on the bottom plate; when the bottom plate is in a horizontal state, cone I and cone II are coaxial.

[0007] Furthermore, a discharge port is provided at the lower end of the ball valve II.

[0008] Furthermore, the discharge port is a glass tube, one end of which is connected to the lower end of ball valve II.

[0009] Furthermore, the constant pressure flange is used in conjunction with the low-pressure end flange of the pressure transmitter, and the size of the graphite gasket matches the inner diameter of both the constant pressure flange and the low-pressure end flange of the pressure transmitter.

[0010] Compared with the prior art, the advantages of this utility model are: (1) The constant pressure generated by a mercury column of a certain height replaces the local atmospheric pressure. The input pressure of the low-pressure end of the pressure transmitter is a standard atmospheric pressure of 101.325 kPa and the value is constant and is not affected by external factors; (2) Mercury has stable chemical properties and constant density. The pressure value generated by the mercury column is accurate and can be used as a standard substance; (3) The device has a simple structure, is easy to operate, and can be widely used in various pressure measurement fields. Attached Figure Description

[0011] The accompanying drawings are provided to further understand the present invention and form part of the specification. They are used together with the embodiments of the present invention to explain the present invention and do not constitute a limitation thereof.

[0012] Figure 1 This is a schematic diagram of the device structure of Embodiment 1 of this utility model.

[0013] Figure 2 This is a schematic diagram of the structure of the cone leveling instrument of Embodiment 2 of this utility model.

[0014] Figure 1 In the diagram, 1 is a glass funnel, 2 is ball valve I, 3 is the high-pressure end flange of the pressure transmitter, 4 is the pressure transmitter, 5 is a constant-pressure glass tube, 6 is a constant-pressure flange, 7 is a balance nut I, 8 is the low-pressure end flange of the pressure transmitter, 9 is ball valve II, 10 is an inverted L-shaped glass tube, 11 is a base, 12 is a balance nut II, 13 is a bubble level, 14 is a scale, 15 is the 760mm position of the scale, and 16 is the zero point position of the scale.

[0015] Figure 2 In the diagram, 17 is the top plate, 18 is the suspension line, 19 is cone I, 20 is cone II, 21 is the bottom plate, and 22 is the side plate. Detailed Implementation

[0016] The following will provide a more detailed description of the operation method of this utility model in conjunction with specific embodiments. It should be understood that the preferred embodiments described herein are only for illustration and explanation of this utility model and are not intended to limit this utility model. Example 1

[0017] See attached document Figure 1 This embodiment provides an instrument device for measuring pressure based on the standard atmospheric pressure differential pressure method. Taking a carbon monoxide gas holder as an example, the device includes a glass funnel 1, a ball valve I 2, a high-pressure end flange of a pressure transmitter 3, a pressure transmitter 4, a constant-pressure glass tube 5, a constant-pressure flange 6, a balance nut I 7, a low-pressure end flange of a pressure transmitter 8, a ball valve II 9, an inverted L-shaped glass tube 10, a base 11, a balance nut II 12, a bubble level 13, and a scale 14. The glass funnel 1, ball valve I 2, and constant-pressure glass tube 5 are connected in sequence. The outer diameter of the lower end of the glass funnel 1 is 15mm. The ball valve I 2 is made of polypropylene plastic with an inner diameter of 15mm. The constant-pressure glass tube 5 is a thick-walled glass tube with an outer diameter of 15mm, an inner diameter of 5mm, and a length of 1000mm.

[0018] The constant pressure flange 6 is used in conjunction with the low-pressure end flange 8 of the pressure transmitter. Both the constant pressure flange 6 and the low-pressure end flange 8 are made of stainless steel and have a size of DN15. The constant pressure flange 6 and the low-pressure end flange 8 are bolted to the base 11. The lower end of the constant pressure glass tube 5 is connected to the constant pressure flange 6. A graphite gasket is used for sealing between the constant pressure flange 6 and the low-pressure end flange 8. The size of the graphite gasket matches the inner diameter of both the constant pressure flange 6 and the low-pressure end flange 8, and the graphite gasket size is DN15. A small through hole with a diameter of 5mm is provided on the side of the constant pressure flange 6. The upper end of the inverted L-shaped glass tube 10 communicates with the through hole, and the outer diameter of the inverted L-shaped glass tube 10 is 5mm. A ball valve II 9 is installed at the lower end of the inverted L-shaped glass tube 10. The ball valve II 9 is made of polypropylene plastic and has an inner diameter of 5mm. A discharge port is provided at the lower end of ball valve II9. The discharge port is a glass tube, and the upper end of the glass tube is connected to the lower end of ball valve II9. The high-pressure flange 3 of the pressure transmitter is connected to the device under test. Pressure sensors are installed inside the low-pressure flange 8 and the high-pressure flange 3 of the pressure transmitter, respectively. The low-pressure flange 8 and the high-pressure flange 3 of the pressure transmitter are connected to the pressure transmitter 4 through wires.

[0019] The zero point of the scale 14 is vertically fixed to the base 11, and the zero point 16 of the scale is horizontally aligned with the upper end of the low-pressure flange 8 of the pressure transmitter; the 760mm position 15 of the scale is horizontally tangential to the position of the constant pressure glass tube 5 and is 100mm lower than the position of the ball valve I2.

[0020] In this embodiment, a bubble level 13 is used as a leveling device for leveling the base. The bubble level has a bubble located inside the top curved surface, and when the base is in a horizontal state, the bubble is located at the center of the curved surface.

[0021] The design principle and operation method of this embodiment are as follows.

[0022] Local air temperature measured using a thermometer t To calculate the actual height of a mercury column equivalent to one standard atmosphere at that temperature. H Based on the definition of the volume expansion coefficient, we can derive:

[0023] ;

[0024] In the formula: Δ V —Change in mercury column volume with temperature, in mm 3 ;

[0025] α—— The coefficient of volume expansion of mercury, ℃ -1 ;

[0026] V 0 — Initial volume of mercury column, mm 3 ;

[0027] t —The temperature at that time, in °C;

[0028] t 0 — Temperature under standard conditions, with a value of 0℃.

[0029] Due to the base area of ​​the mercury column S It is a constant, and has V 0 = SH 0, Δ V = SΔH Therefore, the above formula can be simplified to:

[0030] ;

[0031] In the formula: Δ H —The change in mercury column height with temperature, in mm;

[0032] α—— The coefficient of volume expansion of mercury, ℃ -1 ;

[0033] H 0 — The initial height of the mercury column, i.e., the height under standard conditions, with a value of 760 mm;

[0034] t —The temperature at that time, in °C.

[0035] The volume expansion coefficient of mercury is known. α 1.82×10 -4 ℃ -1 Under standard conditions (i.e., temperature) t 0 = 0℃, atmospheric pressure P 0 = 101.325 kPa) One standard atmosphere P 0 corresponds to the actual height of the mercury column. H 0 is 760 mm, so at that temperature, one standard atmosphere was equivalent to the actual height of the mercury column. H for:

[0036]

[0037] Calculations show that one standard atmosphere at different temperatures corresponds to the actual height of a mercury column. H As shown in Table 1:

[0038] Table 1. The actual height of a mercury column equivalent to one standard atmosphere at different temperatures.

[0039] Temperature / °C Mercury column height / mm Temperature / °C Mercury column height / mm Temperature / °C Mercury column height / mm -30 756 -5 759 20 763 -25 757 0 760 25 763 -20 757 5 761 30 764 -15 758 10 761 35 765 -10 759 15 762 40 766

[0040] The actual temperature was measured to be 26℃. According to Table 1, the actual height of a mercury column equivalent to one standard atmosphere at this temperature is 763mm (select a value closer to the temperature). The device will now be operated as follows.

[0041] First, observe the bubble level to determine if the base 11 of the device is level. If the bubble in the bubble level is not centered on the top curved surface, it indicates that the base 11 is not level, meaning the constant pressure glass tube 5 is not vertical, which may cause the measurement result to be too low. Adjust the balance nut I7 and balance nut II12 under the base of the device until the bubble in the bubble level is centered on the top curved surface. At this time, the base 11 is level. Close ball valve II9 and open ball valve I2 to inject mercury from the top of the glass funnel 1 into the constant pressure glass tube 5 and the constant pressure flange 6. When the constant pressure glass tube 5 is completely filled with mercury and... When there is excess mercury in glass funnel 1, open ball valve II 9. Mercury flows downwards under gravity until it completely fills the constant pressure flange 6 and the inverted L-shaped glass tube 10, expelling all air from them. Mercury continues to drain from the constant pressure glass tube 5. When the mercury level in the constant pressure glass tube 5 is 1-2 cm above ball valve I 2, close ball valve I 2. Mercury flows out of the inverted L-shaped glass tube 10, and the mercury level in the constant pressure glass tube 5 continues to drop, creating a vacuum above the mercury level. When the mercury level in the constant pressure glass tube 5 drops to the horizontal tangential scale 13... When the mercury column in the constant pressure glass tube 5 is at the 763mm position, ball valve II9 is ​​closed. At this time, the height of the mercury column in the constant pressure glass tube 5 is 763mm, and the area between the liquid surface and ball valve I2 is a vacuum. The pressure acting on the low-pressure flange 8 of the pressure transmitter is the pressure generated by 763mm of mercury, which is one standard atmosphere, 101.325kPa. Connect the high-pressure flange 3 of the pressure transmitter to the pressure measuring port of the device under test. According to the working principle of the dual-flange differential pressure transmitter, the pressure measured at the high-pressure end of the pressure transmitter... P (H) Subtract the pressure measured at the low-pressure end of the pressure transmitter P (L), the pressure Δ inside the device under test is calculated. P This is the output value Δ of the dual-flange differential pressure transmitter. P=P (H)- P (L), because P (L) = 101.325 kPa, therefore the pressure Δ inside the container of the tested equipment is... P = P (H)-101.325kPa; thus Δ P The pressure value measured under standard atmospheric pressure is called gauge pressure; the pressure transmitter 4 is connected to the AI ​​card of DCS or PLC and can calculate the gauge pressure of the device under test through simulation calculation and display it on the terminal.

[0042] In this embodiment, the device to be tested is a carbon monoxide gas holder with a gauge pressure range of 3 kPa to 6 kPa. The device is now used to measure the gauge pressure value inside the carbon monoxide gas holder.

[0043] The operation steps are as follows:

[0044] Step 1: Measure the local temperature with a thermometer to be 26℃. By referring to Table 1, we can find that one standard atmosphere at this temperature is equivalent to an actual height of 763mm of mercury column.

[0045] Step 2: Observe whether the bubble in the bubble level is in the center of the top curved surface. If it is not in the center of the top curved surface, adjust the balance nut I7 and balance nut II12 under the device platform until the bubble is in the center of the top curved surface. If the bubble is already in the center of the top curved surface, proceed directly to the next step.

[0046] Step 2: Close ball valve II9 and open ball valve I2. Inject mercury from the top of glass funnel 1 into constant pressure glass tube 5 and constant pressure flange 6. When the constant pressure glass tube 5 is completely filled with mercury and there is excess mercury in glass funnel 1, open ball valve II9. Under the action of gravity, the mercury flows down until it completely fills the constant pressure flange 6 and inverted L-shaped glass tube 10. All the air in constant pressure flange 6 and inverted L-shaped glass tube 10 is discharged.

[0047] Step 3: Continuously drain the mercury from the constant pressure glass tube 5. When the mercury level in the constant pressure glass tube 5 is 1-2 cm above the ball valve I2, close the ball valve I2. The mercury flows out from the inverted L-shaped glass tube 10. The mercury level in the constant pressure glass tube 5 continues to drop and forms a vacuum state inside the constant pressure glass tube 5 above the mercury level. When the mercury level in the constant pressure glass tube 5 drops to the position of 763 mm on the horizontal tangential scale (18), close the ball valve II9.

[0048] Step 4: Connect the high-pressure end flange 3 of the pressure transmitter to the pressure test port of the carbon monoxide gas holder, and read the pressure value displayed on the terminal. This value is the standard gauge pressure value of the carbon monoxide gas holder.

[0049] The next time the device is used to measure gauge pressure, after step one, check whether the height of the mercury column in the constant pressure glass tube 5 is consistent with the height of the mercury column obtained by referring to Table 1. If so, skip steps two and three and start directly from step four. If not, open ball valve I2 and ball valve II9 to drain all the mercury from the constant pressure glass tube 5 and the constant pressure flange 6 before starting from step two. Example 2

[0050] In another embodiment, the difference from Embodiment 1 is that a conical level is used as a leveling device for leveling the base 11. (Refer to...) Figure 2The cone leveling device includes a top plate 17, a suspension line 18, cone I 19, cone II 20, a base plate 21, and a side plate 22, which is fixed to the base 11 via the base plate 21. The upper and lower ends of the side plate 22 are perpendicularly connected to the top plate 17 and the base plate 21, respectively. Cone I 19 is suspended and fixed on the top plate 17 via the suspension line 18, and cone II 20 is fixed on the base plate 21. When the base plate 21 is in a horizontal state, cone I 19 and cone II 20 are coaxial, and both cone I 19 and cone II 20 are made of stainless steel.

[0051] In another embodiment, the difference from embodiment 1 is that the leveling process of the base is as follows: first, the base 11 of the device is judged to be horizontal by observing whether cone I 19 and cone II 20 are coaxial. If cone I 19 and cone II 20 are not coaxial, it indicates that the base 11 is not horizontal. The balance nut I 7 and balance nut II 12 under the base of the device can be adjusted until cone I 19 and cone II 20 are coaxial. At this time, the base 11 is in a horizontal state.

Claims

1. An instrument device for measuring pressure based on the standard atmospheric pressure differential pressure method, characterized in that: Includes a glass funnel, ball valve I, high-pressure end flange of pressure transmitter, pressure transmitter, constant pressure glass tube, constant pressure flange, balance nut I, low-pressure end flange of pressure transmitter, ball valve II, inverted L-shaped glass tube, base, balance nut II, leveling device, and scale. The glass funnel, ball valve I, and constant pressure glass tube are connected in sequence. The constant pressure flange and the low-pressure flange of the pressure transmitter are fixed to the base with bolts. The lower end of the constant pressure glass tube is connected to the constant pressure flange. A graphite gasket is placed between the constant pressure flange and the low-pressure flange of the pressure transmitter. A through hole is provided on the side of the constant pressure flange, and the upper end of the inverted L-shaped glass tube communicates with the through hole. Ball valve II is installed at the lower end of the inverted L-shaped glass tube. The high-pressure flange of the pressure transmitter is connected to the device under test, and the low-pressure flange of the pressure transmitter is connected to... Pressure sensors are installed inside the high-pressure flange of the pressure transmitter. The low-pressure flange and the high-pressure flange of the pressure transmitter are connected to the pressure transmitter by wires. The zero point of the scale is horizontally aligned with the upper end of the low-pressure flange of the pressure transmitter. The 760mm position of the scale, tangentially to the position of the constant pressure glass tube, must be lower than the position of ball valve I. The zero point of the scale is vertically fixed to the base. Balance nuts I and II are installed on both sides of the base. The leveling device is fixed on the base.

2. The instrument device for measuring pressure based on the standard atmospheric pressure differential pressure method according to claim 1, characterized in that: The leveling device is either a bubble level or a cone level.

3. The pressure measuring instrument based on the standard atmospheric pressure differential pressure method according to claim 2, characterized in that: The cone leveling device includes a top plate, a suspension line, cone I, cone II, a bottom plate, and side plates; the upper and lower ends of the side plates are perpendicularly connected to the top plate and the bottom plate, respectively; cone I is suspended and fixed on the top plate by the suspension line, and cone II is fixed on the bottom plate; when the bottom plate is in a horizontal state, cone I and cone II are coaxial.

4. The instrument device for measuring pressure based on the standard atmospheric pressure differential pressure method according to claim 1, characterized in that: The lower end of the ball valve II is provided with a discharge port.

5. The pressure measuring instrument based on the standard atmospheric pressure differential pressure method according to claim 4, characterized in that: The discharge port is a glass tube, one end of which is connected to the lower end of ball valve II.

6. The instrument device for measuring pressure based on the standard atmospheric pressure differential pressure method according to claim 1, characterized in that: The constant pressure flange is used in conjunction with the low-pressure end flange of the pressure transmitter, and the size of the graphite gasket matches the inner diameter of both the constant pressure flange and the low-pressure end flange of the pressure transmitter.

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