JPH02179433A - Device for measuring pressure - Google Patents

Abstract

PURPOSE:To reduce an error in pressure measurement due to non-uniformity of a tube by providing a tube pressing element which presses parts in the axial direction in front and the rear of a position of the tube pressed by a pressure detecting element, with a slightly smaller pressure than the pressure of the pressure detecting element. CONSTITUTION:When the internal pressure of a tube 8, i.e. an object of measurement, is zero, the tube 8 is set in a tube insertion part formed in a housing 6 of a pressure detecting unit 2. On the occasion, the tube 8 is positioned at the center of a pressure sensing element 4. Then, a cover body 7 is fixed in a closed. The sensing element 4 is subjected to a slight force when the cover body 7 is closed, and therefore the sensing element 4 generates a slight offset voltage. In the output of a pressure sensor, a positive voltage is generated from the offset voltage when a positive pressure is applied inside the tube 8, and a negative voltage is generated from the offset voltage when a negative pressure is applied. By subtracting the offset voltage from a voltage generated under some pressure P, in this constitution, an output voltage for this pressure is obtained. Based on this output voltage, a measured pressure is displayed in a measured pressure value display unit 3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pressure measuring device used for detecting pressure in an extracorporeal circulation blood circuit such as a plasma separator, an artificial dialysis machine, an artificial lung, or a blood purification device.

Specifically, the present invention relates to a pressure measuring device that indirectly detects the pressure inside a soft blood circuit tube used in an extracorporeal circulation blood circuit.

[Prior Art] Conventionally, when detecting the pressure in an extracorporeal circulation blood circuit such as a plasma separation device, an artificial dialysis machine, an artificial lung, or a blood purification device,
As shown in FIG. 12, blood 32 is stored in a drip tube in a blood circuit 31, and the pressure inside the drip tube 30 is guided to a pressure transducer 35 through a pressure tube 33 attached to the drip tube and detected. Note that a filter 34 that does not allow blood to pass is attached to the pressure tube 33 so that the blood does not reach the pressure transducer when the blood level rises.

[Problems to be Solved by the Invention] However, the above pressure measuring device has the following problems.

(1) Since the drip tube 30 is used, the amount of blood filled in the drip tube 30 portion increases, and the so-called priming volume increases.

(2) It is necessary to attach a blood-impermeable GL filter 34 to the pressure tube 33 for pressure detection, and to connect a pressure transducer 35 thereon, which is troublesome in operation.

Furthermore, there are usually multiple pressure detection points, especially in blood circuits for plasma separation devices, where there are several pressure detection points.
The above-mentioned increase in priming volume and operational complexity have become bigger problems.

Therefore, an object of the present invention is to solve the problems of the conventional pressure measuring device, without increasing the originally required priming volume of the blood circuit, and which is easy to install and operate. The present invention provides a pressure measuring device that improves pressure measurement errors caused by variations in tubes used in blood circuits.

[Means for Solving the Problems] What achieves the above object is a pressure measuring device that measures the internal pressure of a tube, which includes a pressure detection section that detects the pressure while pressing the tube to be measured, and a pressure detection section that detects the pressure while pressing the tube to be measured. This pressure measuring device has a tube pressing section that presses the front and rear portions of the tube position to be pressed, when viewed in the axial direction of the tube, with a force equal to or slightly less than that of the pressure detection section.

Furthermore, the pressure detection section presses the tube so that the outer diameter of the tube becomes 82 to 90% of the pressure before the tube is pressed. It is preferable that the pressure is 90 to 95% of that before pressing. Furthermore, it is preferable that the pressure on the tube by the tube pressing section is 0.85 to 0.96 times the pressure on the tube by the pressure detection section.

Therefore, the pressure measuring device of the present invention will be specifically explained with reference to embodiments shown in the drawings.

The pressure measuring device 1 of the present invention is a pressure measuring device for measuring tube internal pressure, and includes a pressure detecting section 4 that detects pressure while pressing a tube 8 to be measured, and a pressure detecting section 4 at a position of the tube pressed by the pressure detecting section 4. It has a tube pressing section 5 that presses the front and rear portions of the tube with a pressure equal to or slightly less than that of the pressure detection section 4 when viewed in the axial direction of the tube.

Therefore, the pressure measuring device of the present invention will be explained using the embodiments shown in FIGS. 1 to 5.

FIG. 1 is a schematic diagram showing the basic configuration of an embodiment of the pressure measurement device of the present invention, and FIG. 2 is a front view of the pressure detection section of the pressure measurement device of the embodiment shown in FIG. 3 to 5 are cross-sectional views of the pressure detection section shown in FIG. 2.

The pressure measuring device 1 of this embodiment, as shown in FIG.
It is composed of a pressure detection section 2 and a pressure measurement value display section 3 that displays a pressure measurement value based on an electrical signal output from the pressure detection section 2.

As shown in FIG. 2, the pressure detecting section 2 includes a pressure detecting section 4 that presses the tube 8 to be measured, and a tube pressing section 5 that presses the tube 8 at the front and rear positions. The tube pressing section 5 is housed in a housing, and the pressure sensing section 4 is inserted into the housing from one end. The housing is provided with a lid 7, and the tube 8 to be measured is pressed between the lid 7, the pressure detection section 4, and the tube pressing section 5, and the pressed portion is pressed. The cross-sectional area of the tube is reduced.

The structure of the pressure detection section 2 will be explained using FIGS. 2 to 5. FIG. 2 is a front view of the pressure detection unit 2 attached to the tube 8 to be measured, viewed from the lid 7 side, and FIG. 3 is a sectional view taken along line II in FIG. 2. Moreover, FIG. 4 is a sectional view taken along the line ■--■ in FIG. 2. FIG. 5 is a sectional view of the pressure detection section 2 before being attached to the tube to be measured.

As shown in FIG. 2, the lid body 7 has a square plane,
This lid body 7 is attached to the housing 6 as shown in FIG.
It is attached by a member 10 so as to be openable and closable. Further, the lid body 7 is fixed to the housing 6 by a stopper 12 so as to be openable and closable. Then, as shown in FIG. 5, by releasing the engagement of the stops 12a and 12b, the lid body 7 is placed in an open state with respect to the housing 6. Further, like the lid body 7, the housing 6 also has a substantially square cross section. As shown in FIGS. 2, 4, and 5, the nozzle housing 6 has two tube insertion portions 6a, 6a at opposing positions. These insertion parts 6a, 6a
Position the tube 8 so that it is approximately at the center of the pressure sensing section 4. The pressure sensing part 4 is inserted into the inside of the housing 6 so as to protrude from the center of the bottom of the housing 6, and is fixed therein. A tube pressing section 5 is provided within the housing 6 so as to surround the pressure sensing section 4 .

This tube pressing portion 5 may be formed integrally with the housing 6. It is preferable that the tip of the tube pressing section 5 is formed at approximately the same position as the tip of the pressure sensing section 4, or so that the pressure sensing section 4 protrudes slightly as shown in FIG. The distance between the pressure detection unit 4 and the lid 7 (the distance when the lid 7 is closed) is set to be smaller than the outer diameter of the tube 8 to be measured. Similarly, the distance between the tube pressing part 5 and the lid 7 is also set smaller than the outer diameter of the tube 8. Therefore, as shown in FIGS. 3 and 4, the tube 8 to be measured is pressed by the pressure detection part 4, and furthermore, the front and rear parts (the front and rear parts when viewed in the axial direction of the tube) are pressed by the tube pressing part. 5, and the internal cross-sectional area is reduced. By doing so, it is possible to reduce variations in measurement values due to the tube. More preferably, as shown in FIG. 2, the pressure on the tube 8 is such that the pressure on the pressure detection section 4 is strong and the pressure on the tube pressing section 5 is slightly weaker. This makes it possible to further reduce variations in measured values due to tubes. The pressure on the tube 8 by the pressure detection unit 4 is 82 to 82 before the outer diameter of the tube 8 is pressed.
The pressure by the tube pressing part 5 is such that the outer diameter of the tube 8 is 90% before being pressed.
It is preferable that the pressure be applied to 0 to 95%. More preferably, the pressure by the tube pressing part 5 is within the above range and the pressure by the pressure detection part 4 is 0,
It is 85% to 0.96%.

As the pressure detection section 4, a pressure sensor, a load cell, etc. can be suitably used. A load cell is an element that directly converts a load or force into an electrical signal, and includes strain gauge type, magnetostrictive type, differential transformer type, capacitance type, tuning fork type, body resistance variable type, etc., and particularly preferably strain gauge It is a gauge type. Further, the strain gauge type includes a beam type, a compression type, and a tension type, and the beam type is preferable.

Further, as the pressure sensor, a diffusion type semiconductor pressure sensor is preferable. Diffusion-type semiconductor sensors utilize the piezoresistance effect of semiconductors whose resistance changes when subjected to pressure, and impurities are thermally diffused in four locations on a silicon single crystal.

This acts as a strain resistor that changes resistance when pressure is applied.
These four strain resistors are connected as a Wheatstone bridge circuit, and an electric signal corresponding to the measured pressure is output by increasing or decreasing the four resistors. Furthermore, among the diffusion type semiconductor pressure sensors, those called stainless steel pressure sensors or diaphragm pressure sensors can be more preferably used.

As shown in FIG. 7, this diaphragm pressure sensor has a diffusion type semiconductor pressure sensor chip 11 inside, the upper part of this sensor chip 11 is filled with a fluid such as silicone oil 12, and a stainless steel diaphragm 13 is installed. It has a closed structure.

The pressure applied to the diaphragm 13 is configured to be transmitted to the sensor chip 13 via the silicone oil 12.

[Function] Next, the function of the pressure measuring device 1 of the present invention will be explained using the embodiment shown in FIGS. 1 to 5.

First, when the internal pressure of the tube 8 to be measured is zero, the tube 8 is set in the tube insertion portions 6a, 6a formed in the housing 6 of the pressure detection section 2. At this time, the tube 8 is located at the center of the pressure sensing section 4. Then, the lid 7 is closed, the stops 12a and 12b are engaged, and the lid 7 is fixed in the closed state. Since the pressure detection section 4 receives a slight force when the lid body 7 is closed, the pressure detection section 4 generates a slight offset voltage. and,
When positive pressure is applied within the tube 8, the output of the pressure sensor generates a voltage (+) from the offset voltage, and when negative pressure is applied, a voltage (-) from the offset voltage is generated. If we subtract the offset voltage from the voltage at a certain pressure P, we get
An output voltage for this pressure is obtained.

Output voltage-(measured voltage>p-<offset voltage) Based on this output voltage, the measured pressure is displayed on the pressure measurement value display section 3.

[Example] Next, an example of the pressure measuring device of the present invention will be described.

(Example) As a pressure detection unit, the housing has a shape as shown in Figs. 2 to 5, and has a width of 10zR and a length of 701
! A piece with a shoulder thickness of 50 cm and a depth of 23 tpm was used.

Then, it was fixed so that the pressure sensing part protruded from the center of the bottom. Fixing was performed by fixing the annular projection at the rear end of the pressure sensor to the bottom surface of the housing using a fixing blanket.

As the pressure detection part, a diaphragm pressure sensor (manufactured by Copal Electronics Co., Ltd., P-
8100102G) was used. The outer diameter of the tip of the pressure sensor was approximately 18xx. Further, a tube pressing portion was provided in the housing so as to surround the pressure sensor. The housing and the lid have a hinge member and a claw for fixing the lid at the tip facing the hinge member, the middle part is rotatably fixed by a shaft fixing blanket, and the rear end has a compression spring. It was fixed so that it could be opened and closed using a fixing member attached to it. This fixing member has a protrusion slightly on the rear end side of the fixing claw, and by pressing this protrusion,
The fixing member rotates to release the engagement between the fixing claw and the lid. Furthermore, the pressure measurement value display used was one composed of a DC amplifier that amplified the output of the pressure sensor and a digital volt meter that read the output voltage of this amplifier.

In addition, the distance A between the pressure sensor and the lid and the distance B between the tube pressing part and the lid were combined as shown in Tables 1 and 2 below.

Table 1, in parentheses, shows the ratio to the outer diameter expressed as a percentage, assuming that the outer diameter of the tube is 6 cm.

A/B indicates the degree of pressure by the tube pressing section when the pressure by the pressure sensor is set to 1.

The values in parentheses in Table 2 indicate the outer diameter of the tube. The ratio to the outer diameter is expressed as a percentage when li+x.

A/B indicates the degree of pressure by the tube pressing section when the pressure by the pressure sensor is set to 1.

(Comparative Example) As shown in FIG. 6, the same as the example was used except that the tube pressing part provided in the housing did not press the tube.

In addition, the distance A between the pressure sensor and the lid was shown in Table 3 below.

Table 3 [Experiments] (Experiment 1) Pressure measurement experiments were conducted using the pressure measurement devices of Examples 1 to 4 and Comparative Examples 1 to 6.

The tube to be measured has an outer diameter of 6. Omy, with an inner diameter of 5.0xx (wall thickness 0.5 mm), was used for three different tubes, and one tube was measured three times each to check for variations in installation. went. Then, the pressure measurement error due to the difference in tubes was calculated from the measured values. The error pressure ΔP was determined as follows.

The output voltage of the pressure sensor when the pressure is 300 x z g is
300, and if the output voltage at pressure P is V out, then the reading of the pressure sensor at this pressure is P out
is PouL=V out/V 300x 300
(xxHg), and the error ΔP is ΔP = P out −P (itiHg).

The pressure measurement errors by the pressure measurement devices of Comparative Examples 1 to 4 were as shown in FIG.

As shown in FIG. 8, the error ΔP is minimum when the distance A is 5.33131. However, although the error due to tube attachment was not so large, the error between different tubes was large.

The pressure measurement errors in Examples 1 to 4 of the pressure measurement device of the present invention were as shown in FIG.

As shown in FIG. 9, the error between different tubes is smaller than that shown in FIG. 8, and the distance A is 5.3.
The minimum value was mm. Also, when the pressure from the pressure sensor and the pressure from the tube pressing section are the same, the internal pressure of the tube is difficult to transmit to the diaphragm, so the coefficient of output voltage/pressure is small, and in this respect, the pressure from the pressure sensor is slightly stronger. It turns out that this is preferable.

In this experiment, a tube with a wall thickness of 0.5 mm was used as described above, and positive pressure was mainly detected.

The pressure could be detected up to about +300 to -100xxHg. Also, the thinner the tube, the more output voltage/
The pressure coefficient becomes thicker, but due to limitations in tube manufacturing,
Problems arise with the strength and pressure resistance of the tube. Therefore, when the main purpose is to detect positive pressure, the wall thickness of the tube to be measured is desirably 0.4 to 0.61. In addition, positive pressure (300
m1g), the tube wall thickness should be set to 0.
This is achieved by setting it to 7 to 0.9x*.

(Experiment 2) Using the pressure measuring devices of Examples 5 to 10 and Comparative Examples 4 to 7, the tube to be measured had an outer diameter of 5.1 mm and an inner diameter of 3.5 ytx (wall thickness 0.8 R1). As in Experiment 1, the pressure was measured for three different tubes using the same method as in Experiment 1, and the pressure measurement error was calculated.

The pressure error caused by the pressure measuring device of the comparative example was as shown in FIG. Further, the pressure error according to the embodiment of the pressure measuring device of the present invention was as shown in FIG.

By increasing the wall thickness of the tube, the output voltage/pressure coefficient has become smaller, but it has a range of -300xxHg to 1300x
A range of xHg was measurable. It was found that the pressure error was the smallest when the distance l1lIA between the pressure sensor and the lid was 4.3H. Furthermore, when the combination of the distance A between the pressure sensor and the lid and the distance B between the tube pressing part and the lid is A = 4.31113I and B = 4.7xi (Example 6), the pressure error is the highest. It was found that the pressure error was smaller than that of Comparative Example 7 (distance A was 4.3 mm). However, it was also found that if the tube wall thickness is increased, the drift of the sensor's output voltage (zero point of pressure measurement) after the cover is closed becomes about four times thicker.

From Experiments 1 and 2, it was found that the pressure on the tube by the pressure sensor was 78 to 92% of the outer diameter of the tube, preferably 82 to 9%.
0%, and the tube in the front and rear parts in contact with this pressure sensor is 88 to 96% of the tube outer diameter, preferably 90
It has been found that by providing a tube pressing section that presses the tube to ~96%, it is possible to improve pressure measurement errors due to variations in the circuit tube.

Moreover, it was found that the pressure by the tube pressing part is 0.85 to 0.96 of the pressure by the pressure sensor, and more preferably 0.89 to 0.96.

[Effects of the Invention] The pressure measuring device of the present invention is a pressure measuring device that measures the internal pressure of a tube, and includes a pressure detecting section that detects pressure while pressing the tube to be measured, and a pressure detecting section that detects pressure while pressing the tube to be measured, and a pressure detecting section that detects pressure while pressing the tube to be measured, and a pressure detecting section that detects pressure while pressing the tube to be measured. , since it has a tube pressing part that presses the front and rear parts of the tube as viewed in the axial direction, equal to or slightly less than the pressure of the pressure detection part, so there is no need for pressure measurement of a drip tube or the like in the circuit to be measured. Since there is no need to provide another liquid chamber, there is no need to increase the priming volume of the circuit. Furthermore, since it is only necessary to attach it from the outside of the circuit, it is easy to attach and operate. Furthermore, by having the tube pressing section, pressure measurement errors due to variations in tubes used in the circuit to be measured are reduced.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the basic configuration of an embodiment of the pressure measuring device of the present invention, and FIG. 2 is a front view of the pressure detecting section of the pressure measuring device of the present invention attached to a tube to be measured. , FIG. 3 is a sectional view taken along the line 1-1 in FIG. 2, and FIG.
5 is a sectional view of the pressure detection section of the pressure measurement device of the present invention before being attached to the tube to be measured, and FIG. 6 is a pressure detection section of the pressure measurement device of the comparative example. 7 is a partially cutaway sectional view showing an example of a pressure sensor used in the pressure measuring device of the present invention, and FIGS. 8 and 10 are pressure measuring devices using a pressure measuring device of a comparative example. 9 and 11 are diagrams showing pressure measurement errors in pressure measurement experiments using the pressure measurement device of the embodiment of the present invention, and FIG. It is a figure showing a measuring device. Fig. 1 1...Pressure measuring device 2...Pressure detection section 3...
Pressure measurement value display section 4...Pressure detection section 5...Tube pressing section 6.
...Housing 6a...Tube insertion part 7...
・Lid body 8...Tube Fig. 6 Fig. 7 Fig. 4 Fig. 5 (arrow example 1) Fig. 9 Fig. 11

Claims (3)

[Claims] (1) In a pressure measuring device that measures tube internal pressure,
A pressure sensing section detects pressure while pressing the tube to be measured, and the front and rear portions of the tube position pressed by the pressure sensing section when viewed in the axial direction of the tube are equal to or slightly less than the pressure of the pressure sensing section. 1. A pressure measuring device comprising: a tube pressing section that presses a tube. (2) The pressure on the tube by the pressure detection section is such that the outer diameter of the tube is 82 to 90% of that before the pressure is applied, and the pressure by the tube pressing section is such that the outer diameter of the tube is 2. The pressure measuring device according to claim 1, wherein the pressure is 90 to 95% of the pressure before pressing. (3) The pressure measuring device according to claim 1 or 2, wherein the pressure on the tube by the tube pressing section is 0.85 to 0.96 times the pressure on the tube by the pressure detection section.