JPH09189586A - Orifice-type flow rate-measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce costs and measure a flow rate highly accurately by using a low flow rate orifice of a small diameter and a high flow rate orifice of a large diameter thereby measuring the flow rate in a wide range. SOLUTION: Normally, a differential pressure transmitter 18 measures a flow rate differential pressure by a low flow rate orifice 12 or a high flow rate orifice 13 via either of orifice switch valves 16 and 17. A valve-switching control means 19 suitably selects and connects the orifice 12, 13 to the transmitter 18 in accordance with an output of the transmitter 18. An optimum differential pressure can thus be taken irrespective of whether the flow rate is large or small. The flow rate can be measured highly accurately with the use of one differential pressure transmitter 18. Particularly, orifices 12, 13 are inexpensive in comparison with the differential pressure transmitter 18, and therefore costs can be remarkably reduced if a count of objects to be measured in increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an orifice type flow rate measuring device for measuring the flow rate of a fluid such as liquid or gas using an orifice.

[0002]

2. Description of the Related Art An orifice type flow rate measuring apparatus introduces a differential pressure gauge or a differential pressure transmitter from both sides of an orifice installed in a pipe through a pressure guiding pipe, and a differential pressure measured by the differential pressure gauge or the differential pressure transmitter. This is a configuration for measuring the flow rate from the pressure.

By the way, when the flow rate of a fluid is measured using an orifice, a turbulent flow occurs because a part of the piping is throttled, and it is said that the measurement accuracy is several percent. As a result, when high-precision measurement is required, it cannot be used, or special correction calculation is performed, or two differential pressure transmitters with different measurement ranges are installed and the flow rate in the pipe is adjusted. It was necessary to switch and measure accordingly.

FIG. 6 is a diagram for explaining a conventional flow rate measuring method using a split range. In this measuring method, when an orifice 2 is installed at a predetermined position of the pipe 1 and the fluid is throttled by the orifice 2, the following differential pressure is generated on both sides of the orifice 2 from Bernoulli's equation.

F = α (ΔP) ^1/2 (1) where F is the flow rate, ΔP is the differential pressure across the orifice, and α is the orifice constant. It is known that the orifice constant is not strictly constant and increases in the constant flow rate region.

However, the differential pressure on both sides of the orifice is set to 1
When measuring with the differential pressure transmitter of the table, the flow rate measurement range becomes very wide, so that the error increases especially when measuring a low flow rate. Therefore, in order to measure the differential pressure on both sides of the orifice 2, as shown in FIG. 6, a high flow differential pressure transmitter 3 and a low flow differential pressure transmitter 4 are installed, and the switching logic 5 is normally set to high. The flow rate state is judged from the output of the differential pressure transmitter for flow rate 3, and when the flow rate is low, it is switched to the low pressure differential pressure transmitter 4 side through the changeover switch 6 for use. Reference numeral 7 is an orifice correction calculation means for correcting the orifice constant α, and 8 is a square root calculation means.

Therefore, in such an orifice type flow rate measuring device, since the high differential pressure transmitter 3 and the low differential pressure transmitter 4 are provided, the flow rate can be accurately measured from the low flow rate region to the high flow rate region.

[0008]

Therefore, in the above-mentioned orifice type flow rate measuring device, since one differential pressure transmitter 4 for low flow rate is newly added, the flow rate can be accurately measured even in the low flow rate region. However, two expensive differential pressure transmitters are required, and the cost becomes very high as the number of measurement targets for the plant increases.

The invention described in claim 1 is to provide an orifice type flow rate measuring device which uses a plurality of orifices to reduce the cost and to measure the flow rate with high accuracy. The invention described in claim 2 is to provide an orifice type flow measuring device for reducing permanent pressure loss that occurs when a plurality of orifices are used. The invention described in claim 3 is to provide an orifice type flow rate measuring device capable of measuring a flow rate with higher accuracy.

[0010]

In order to solve the above problems, the invention according to claim 1 is directed to a low flow rate orifice having a small hole diameter and a high flow rate having a large hole diameter, which are installed in a pipe at a required distance. Orifices, a three-port orifice switching valve provided between the upstream side and the downstream side of the piping with these orifices in between, and an orifice switching valve provided at the remaining port side of each of these orifice switching valves. Differential pressure measuring means for measuring the differential pressure generated by the orifice when the valve is opened, and the flow rate range in the pipe is determined from the measurement output of the differential pressure measuring means, and the plurality of orifice switching valves are determined according to the determination result. And a valve switching control means capable of introducing the differential pressure obtained through the orifice switching valve at the time of opening to the differential pressure measuring means. It is.

According to the invention corresponding to claim 1, by taking the above means, when the flow rate in the pipe from the measurement output of the differential pressure measuring means is in the low flow rate range, the valve switching control means is low. When the flow rate is in the high flow rate range, the valve switching control means opens the orifice changeover valve connected to the high flow rate orifice side so that the flow rate of the flow rate is increased. It is possible to properly use the low flow rate orifice and the high flow rate orifice depending on the size of, and it is possible to significantly reduce the cost as compared with the conventional one using two differential pressure transmitters. The flow rate can be measured with high accuracy.

Next, the invention according to claim 2 is to install a low flow rate orifice having a small hole diameter and a high flow rate orifice having a large hole diameter at a required distance in the pipe, depending on the flow rate range in the pipe. Thus, one orifice is rotated in a direction against the flow of fluid, and the other orifice is rotated in the direction of fluid flow.

In the invention corresponding to claim 2, since the unused orifices are set to rotate in the fluid flow direction by taking the above-mentioned means, even if two orifices are installed in series. The permanent pressure loss is the same as in the case of one orifice, and the permanent pressure loss can be significantly reduced.

Further, in the invention according to claim 3, an orifice having a hole diameter reducing mechanism is installed in the pipe, and the orifice of the hole diameter reducing mechanism is controlled according to the flow rate range in the pipe, and the orifice is provided. It is an orifice type flow rate measuring device that can change the hole diameter.

By taking such means, even if one orifice is provided in the pipe, the hole diameter of the orifice can be appropriately changed according to the flow rate state, and a wide flow rate range from a low flow rate range to a high flow rate range can be obtained. The flow rate can be measured with high accuracy.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a block diagram showing an embodiment of an orifice type flow rate measuring device according to the present invention. This embodiment is to measure the flow rate accurately by using a plurality of orifices.

In this measuring apparatus, specifically, an orifice 12 having a small hole diameter and an orifice 13 having a large hole diameter are installed in series in a pipe 11 at a required distance. Generally, the hole diameter of an orifice is determined by the fluid conditions, but since it has a correlation with the magnitude of the flow rate, two orifices 12 and 13 with different hole diameters are installed, and in the case of a low flow rate range The orifice 12 is used, and in the case of a high flow rate region, the high flow rate orifice 13 is used.

The low flow rate orifice 12 and the high flow rate orifice 13 are individually provided with pressure guiding pipes 14,
Orifice switching valves 16 and 17 are attached via 15. A differential pressure transmitter 18 is provided in common for these two orifice switching valves 16 and 17. Reference numeral 19 is a valve switching control means, which compares the output of the differential pressure transmitter 18 with a measured flow rate range defined in advance in the memory 20,
When the output of the differential pressure transmitter 18 is in the low flow rate range, the low flow rate orifice 12 is connected to the differential pressure transmitter 18, and when the output is in the high flow rate range, the high flow rate orifice 13 is connected to the differential pressure transmitter 18. It has a function to do. Reference numeral 21 is a square root calculating means for square root calculating the output of the differential pressure transmitter 18.

Next, the operation of the first embodiment configured as described above will be described. Normally, the differential pressure transmitter 18
Measures the flow rate differential pressure by the orifice 12 or 13 via any of the orifice switching valves 16 or 17. At this time, if the valve switching control means 19 determines from the output of the differential pressure transmitter 18 that the flow rate is in the low flow rate region, and the high flow rate orifice 13 is currently connected to the differential pressure transmitter 18, the low flow rate control device 19 is used. The differential pressure transmitter 18 is provided with an orifice switching valve 16 installed in a pressure guiding pipe 14 connecting both sides of the orifice 12.
And measure the flow rate of the fluid at low flow rates.

On the other hand, when it is judged from the output of the differential pressure transmitter 18 that the valve switching control means 19 is in the high flow rate region, and the low flow rate orifice 12 is currently connected to the differential pressure transmitter 18, it is high. Pressure guiding pipe 15 connecting both sides of the flow rate orifice 13
Orifice switching valve 17 installed in the differential pressure transmitter 1
8 and measure the flow rate of the fluid at high flow rate.

Therefore, according to the above embodiment,
The valve switching control means 19 appropriately selects the orifices 12 and 13 according to the output of the differential pressure transmitter 18 and connects to the differential pressure transmitter 18 to measure the flow rate, so that the optimum difference is obtained regardless of the magnitude of the flow rate. The pressure can be taken in, and the flow rate can be measured with high accuracy using one differential pressure transmitter 18. In particular, the orifice 1
Since the prices of 2 and 13 are cheaper than the differential pressure transmitter,
When the number of measurement targets increases, the cost can be significantly reduced compared to the conventional method. (Second Embodiment) FIG. 2 is a view for explaining another embodiment of the orifice type flow rate measuring device according to the present invention.

In this embodiment, two orifices 12,
When installing 13 in series, these orifices 12, 1
Since the permanent pressure loss of No. 3 is added to increase the permanent pressure loss of the entire pipe, the permanent pressure loss is to be reduced.

In this permanent loss reduction method, as shown in FIG. 2, two orifices 12 and 13 are provided with rotating mechanisms,
Of these two orifices 12, 13, the orifice on the unused side, for example 13, is rotated and set in the direction of fluid flow so that the permanent loss is zero, and the permanent loss is the same as that of one orifice. Reduce.

Constitutionally, for example, as shown in FIG. 3, rotary shafts 31 and 32 for allowing rotation to the respective orifices 12 and 13 are provided so as to penetrate the pipe 11 so as to project therefrom. Disc-shaped rotating bodies 33, 34
Is attached. Further, the protrusions 35, 36 are fixed at predetermined positions by being displaced from the center positions of the side surfaces of the rotating bodies 33, 34 opposite to the rotation shaft side.
One ends of arms 37 and 38 are movably engaged with each other.

Reference numeral 39 denotes a rotary drive source that repeats forward / reverse operation by a predetermined angle in accordance with a switching instruction from the valve switching control means 19. A rotary cam of the rotary drive source 39 is provided with a deformable cam 40. The other ends of the arms 37 and 38 are engaged with mutually opposite portions of the deformable cam 40.

Therefore, according to the embodiment having such a configuration, when the valve switching control means 19 determines from the output of the differential pressure transmitter 18 in the positional relationship shown in FIG. 3, the valve switching control is performed. The means 19 outputs an instruction for setting the low flow rate orifice 12 at the flow rate measurement position. Upon receiving this instruction, when the deforming cam 40 is rotated by 90 degrees, the rotary drive source 39 causes the arms 37 and 38 to move back and forth along the surface of the deforming cam 40, thereby rotating the rotating bodies 33 and 34 by 90 degrees. , The low flow rate orifice 12 is set to oppose the flow of fluid, while the high flow rate orifice 13
Is set in the direction of fluid flow, and high flow rate orifice 1
The permanent loss due to 3 can be almost zero. Therefore, even if the two orifices 12 and 13 are used, they can be handled substantially as in the case of one orifice as in the conventional case, and the permanent pressure loss can be greatly reduced. (Third Embodiment) In the third embodiment, by installing one orifice and arbitrarily changing the hole diameter of the orifice, the flow rate can be varied over a wide flow range from a low flow range to a high flow range. It is to measure accurately.

The reason for changing the hole diameter of the orifice in this way is that the measurable range of the orifice, that is, the rangeability is usually about 1: 3, while the rangeability of the differential pressure transmitter is the latest. One-to-one with technological progress
It is expanding to 0 or 1:50. Therefore,
Considering the rangeability of these devices, the orifice becomes a bottleneck and the flow rate measuring range is greatly limited. Therefore, the flow rate measuring range is flexibly expanded by changing the hole diameter of the orifice.

FIG. 4 is a view showing the structure of the orifice installed in the pipe 11. That is, in this orifice, edge support members 41, ... With a predetermined length are arranged from the three directions at substantially equal intervals on the outside of the pipe 11 toward the center of the inside of the pipe. A plurality of ring-shaped orifice edge portions 42 having different diameters,
... is attached. And the orifice edge portion 4
A hole diameter reducing mechanism 43 is provided in the pipe 11 on the side opposite to 2 ,.

As shown in FIG. 5, the hole diameter reducing mechanism 43 has a cam 46 and a throttle portion 47 on the central axis of the fluid flow pipe 11.
And the fixed base 48 is arranged. The cam 46 has an annular shape as a whole, an opening 461 is formed in the central portion, and a plurality of holes 462 are radially formed around the opening 461. The throttle portion 47 is composed of a plurality of diaphragm plates 471, ... As shown in the drawing, and has an engaging piece 472 inserted into each hole 462 of the cam 46 at one end of each of the diaphragm plates 471 ,. On the surface of the end of the fixed base 48 side, the fixed base 48
Shaft 47 rotatably inserted into holes 481, ...
3 (refer to the same figure b) are provided. The plurality of diaphragm plates 471, ... Are combined so that one surface of each diaphragm plate 471 is superposed on the other surface of the adjacent diaphragm plate 471. An opening 482 is formed in the center of the fixed base 48, and a hole 481 into which the corresponding shaft 472 of the plurality of diaphragm plates 471, ... Is rotatably inserted is formed around the opening 482.

In such a hole diameter reducing mechanism 43, the cam 4
When 6 is rotated, the diaphragm plates 471, ... Of the diaphragm portion 47 rotate in the rotation direction of the cam 46 with the adjacent diaphragm plates 471 overlapping each other around the shaft 472, and a plurality of diaphragm plates 47 are formed.
The opening diameter formed by the inner peripheral edges of 1, ... Can be changed.

This means that if the data corresponding to the measured flow rate region and the rotation angle of the cam 46 are set in the memory 20 in advance, the valve switching control means 19 will be installed in the pipe from the output of the differential pressure transmitter 18. By reading the rotation angle according to the flow rate and rotating the cam 46, it is possible to measure the flow rate by changing the hole diameter according to the flow rate state.

Therefore, according to the embodiment having such a configuration, if the hole diameter of the orifice is changed according to the flow rate in the pipe 11, a stable differential pressure can be secured from the low flow rate range to the high flow rate range. The rangeability of the pressure transmitter 18 can be expanded. Moreover, the orifice edge portions 42, ... Are prepared with several diameters according to the hole diameter, and by narrowing the hole diameter reduction mechanism 43, the hole diameter of the orifice can be changed in stages, and the orifice flow rate can be changed according to the flow rate. Therefore, the optimum differential pressure can be taken out, and thus the rangeability of flow rate measurement can be increased more than that of the differential pressure transmitter, and the flow rate measurement accuracy can be further improved.
In addition, although the differential pressure transmitter is used in the above-described embodiment, it is not necessary to have a transmission function as long as the device measures the differential pressure.

[0033]

As described above, according to the present invention, the following various effects are exhibited. In the invention of claim 1, by using a plurality of orifices, the flow rate can be measured over a wide range from a low flow rate range to a high flow rate range,
Moreover, the cost can be significantly reduced, and the differential pressure that matches the flow rate of the pipe can be taken out, so that the flow rate can be measured with high accuracy.

According to the second aspect of the present invention, even when a plurality of orifices are used, it is possible to reduce the permanent pressure loss to the same level as when one orifice is used. According to the third aspect of the invention, the hole diameter of the orifice can be continuously changed according to the flow rate range, and the flow rate can be measured with higher accuracy.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of an orifice type flow rate measuring device according to the present invention.

FIG. 2 is a view for explaining the measurement principle of a second embodiment of the orifice type flow rate measuring device according to the present invention.

FIG. 3 is a configuration diagram showing an example of a second embodiment,

FIG. 4 is a piping cross-sectional view illustrating a third embodiment of the orifice type flow rate measuring device according to the present invention.

FIG. 5 is a configuration diagram showing an example in a third embodiment,

FIG. 6 is a diagram illustrating a conventional flow measurement method using a split range.

[Explanation of symbols]

11 ... Piping, 12 ... Low flow rate orifice, 13 ... High flow rate orifice, 16, 17 ... Orifice switching valve, 18 ...
Differential pressure transmitter, 19 ... Valve switching control means, 39 ... Rotational drive source, 40 ... Deformation cam, 43 ... Hole diameter reduction mechanism.

Claims (3)

[Claims] 1. A low flow rate orifice having a small hole diameter and a high flow rate orifice having a large hole diameter, which are installed in a pipe at a required distance, and between the upstream side and the downstream side of the pipe with these orifices sandwiched therebetween. Three-port orifice switching valves provided respectively, and differential pressure measuring means provided on the remaining port side of each of these orifice switching valves for measuring the differential pressure generated by the orifice when the orifice switching valve is opened, The flow rate range in the pipe is determined from the measurement output of the pressure measuring means, the plurality of orifice switching valves are selectively opened based on the determination result, and the differential pressure obtained via the orifice switching valve at the time of opening. An orifice type flow rate measuring device comprising: a valve switching control means capable of introducing the differential pressure measuring means into the differential pressure measuring means. 2. A low flow rate orifice having a small hole diameter and a high flow rate orifice having a large hole diameter are installed in a pipe at a required distance, and one of the orifices is used for the fluid flow depending on the flow rate range in the pipe. An orifice type flow rate measuring device characterized by rotating in the opposite direction and rotating the other orifice in the direction of fluid flow. 3. An orifice having a hole diameter reduction mechanism is installed in the pipe, and the throttle of the hole diameter reduction mechanism is controlled according to the flow rate range in the pipe to change the hole diameter of the orifice. Orifice type flow rate measuring device.