JPH06123648A - Flow rate measuring apparatus - Google Patents

Abstract

PURPOSE:To provide a flow rate measuring apparatus which can maintain a wide measuring range of the flow rate and the accuracy in the measuring range. CONSTITUTION:The apparatus is provided with a throttle mechanism 1 having at least two or more different apertures 1a, 1b to be inserted into a conduit 2 where a fluid is flowing, a differential pressure sensor 3 for measuring the differential pressure before and after the apertures are opened, and means 6 for calculating the flow rate of the fluid basing on the measuring value of the differential sensor 3. Moreover, the apertures of the throttle mechanism 1 are formed separately from each other, and the distance between opening ends of the apertures being adjacent to each other is set smaller than the inner diameter of the conduit. A switching means 4 is provided for selecting the optimum diameter for the apertures of the throttle mechanism 1 to be inserted into the conduit corresponding to the size of the flow rate of the fluid. Since the suitable diameter of the apertures of the throttle mechanism is automatically selected corresponding to the flow rate of the fluid, the flow rate can be measured with high accuracy in the wide range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow rate measuring device, and more particularly to a flow rate measuring device suitable for improving measurement accuracy in a wide measuring range by a diaphragm mechanism.

[0002]

2. Description of the Related Art The prior art is shown in FIG. As shown in FIG. 5, when the throttle mechanism (orifice or the like) 1 defined in “Method of measuring flow rate by JISZ8762 throttle mechanism” is installed in the middle of the pipeline 2 through which the fluid flows, upstream of the throttle mechanism 1 Since the difference in static pressure between the downstream side and the downstream side has a unique relationship with the flow rate in the conduit 2, the difference in static pressure was measured by the differential pressure gauge 3 to determine the flow rate in the conduit 2. However, the proper measurement range with one diaphragm mechanism is limited, and no consideration has been given to the wide measurement range and the measurement accuracy in that range.

[0003]

In order to maintain the accuracy of flow rate measurement, the above-mentioned prior art requires the ratio of the maximum value and the minimum value of the flow rate measurement range to be about 4 to 1 or less, and a wide range of flow rate measurement is possible. Has not been taken into consideration, and there was a problem that the accuracy in wide flow rate measurement was poor. It is an object of the present invention to provide a wide flow rate measurement range and a flow rate measurement device capable of maintaining accuracy in the measurement range.

[0004]

In order to achieve the above object, a first invention of the present application is to provide a throttle mechanism having an opening provided in a pipe in which a fluid is flowing, and a differential mechanism for measuring a differential pressure before and after the opening. In a flow rate measuring device comprising a pressure gauge and a means for determining a fluid flow rate based on a measurement value of a differential pressure gauge, the throttle mechanism is provided with at least two openings having different diameters, and the opening end distances of the respective openings approaching each other. Is set to be smaller than the inner diameter of the fluid conduit, and a means for selecting and switching the opening of the throttle mechanism provided in the conduit to an appropriate diameter according to the magnitude of the fluid flow rate is provided. .

A second aspect of the present invention is a throttle mechanism having an opening provided in a conduit through which a fluid is flowing, a differential pressure gauge for measuring a differential pressure before and after the opening, and a fluid flow rate is calculated based on a measured value of the differential pressure gauge. And a means for displaying the calculated flow rate on an indicator, the throttle mechanism is provided with at least two openings having different diameters at a predetermined distance to increase or decrease the fluid flow rate. According to the operation of the aperture switching means, a means for switching the flow rate range used by the flow rate calculating means, a means for switching the aperture and the flow rate. The present invention relates to a flow rate measuring device, which is provided with a signal holding switcher for temporarily holding a flow rate signal sent to the indicator at the time of range switching.

[0006]

[Function] It is possible to secure the measurement accuracy in each flow rate range by preparing a plurality of throttle mechanisms for measuring the flow rate in advance and having a function of automatically selecting the optimum one for the measured flow rate. That is, when measuring a certain flow rate with a certain throttling mechanism, if the measured flow rate increases or decreases and exceeds the preset measurement flow rate range from the measurement accuracy,
This is a flow rate measurement device that has the function of automatically selecting the next throttle mechanism and ensuring the measurement accuracy.

[0007]

1 shows a flow rate measuring apparatus according to an embodiment of the present invention, FIG. 1 (a) is a sectional view, and FIG. 1 (b) is a front view of a diaphragm mechanism thereof. The basic configuration and the measurement principle of the flow rate measurement by the differential pressure are the same as those of the conventional technique, and the throttling mechanism 1 is installed in the middle of the pipeline 2 through which the fluid flows. The diaphragm mechanism 1 is provided with an opening having two types of measuring ranges, a large range orifice 1a and a small range orifice 1b.
The throttle mechanism 1 is provided with an actuator 4 for switching between large and small ranges, the static pressure difference generated between the upstream side and the downstream side of the throttle mechanism 1 is measured by the differential pressure gauge 3, and the measured differential pressure is transmitted to the control device 6. The transmitter 5 is installed.

FIG. 2 shows a control system of the control device 6. The differential pressure signal from the transmitter 5 is converted into a flow rate signal by the square root calculator 7 and displayed on the indicator 9. The flow rate signal is also input to the monitor switch 8, and the actuator 4 is operated by the operation of the monitor switch 8 to switch between the large and small ranges of the diaphragm mechanism 1. At this time, the multiplier 1 is connected to the flow rate signal line for range matching between the indicator 9 and the throttle mechanism 1 used.
0, a switch 11, and signal generators 12 and 13 are installed, and a signal holding switch 15 and a bumpless switch 14 are installed to ensure continuity of signals at the time of switching.

In FIG. 1, if the flow rate is within the small range of the throttle mechanism 1, the throttle mechanism 1 on the small range side is selected. Where the flow rate increases and exceeds the small range,
The monitor switch 8 shown in FIG. 2 operates to select the large range, and the actuator 4 for switching the diaphragm mechanism 1 shown in FIG. 1 operates to select the large range diaphragm mechanism 1 and at the same time.
The switching device 11 shown in FIG. 2 operates to perform range matching with the indicator 9.

The relationship between the signal of the transmitter 5 and the indicated value of the indicator 9 at this time is shown in FIG. The large / small range switch 11 and the hold switch 15 are simultaneously switched at the timing of switching from the small range orifice opening to the large range orifice opening (operation timing of the monitor switch 8). The hold switch 15 holds the signal immediately before the monitor switch 8 operates and continues to output the signal.

The hold release timing is the limit switch operation timing for detecting that the actuator 4 has operated and the orifice has been switched. In order to prevent the disturbance due to the deviation between the signal during the hold and the signal after the orifice switching at the time of this release, the bumpless switching device 14 is used so that the signal after the switching gradually approaches and smooth switching is performed. Although the flow is interrupted for a short time during the switching of the throttle mechanism 1, the dimension of the distance A between the large and small openings shown in the front view of the throttle mechanism 1 in FIG. 1B should be smaller than the inner diameter of the conduit 2. This allows the flow rate when switching between the large and small ranges to be flown by using part of the small range opening holes and part of the large range opening holes so that the process side is not affected even during movement of the large and small ranges. Secure a hole, and
The flow signal holding switch 15 shown in FIG. 2 is switched at the same time as the range matching switch 11 is switched, and the flow signal is held during the switching of the diaphragm mechanism 1.

The minimum distance between the large-range orifice opening 1a and the small-range orifice opening 1b is, for example, when the small-range orifice opening 1b is located at the center of the flow path of the conduit 2. Pipe 2 at the end
It is necessary to take it whenever it does not enter the flow path. After switching the throttling mechanism 1, the hold is reset and the flow rate measurement is started. In order to prevent disturbance due to switching deviation at that time,
The bumpless switch 14 is used to switch to bumpless. The operation timing at this time is shown in FIG. When the flow rate decreases again, the operation is the reverse of the above.

As described above, disturbance during switching of the diaphragm mechanism 1 can be prevented, continuity of measurement can be ensured, and accurate measurement can be performed over a wider measurement range than in the case of the prior art. The signal from the multiplier 10 in FIG. 2 is switched to the large range orifice before the proper measurement range of the small range orifice is shaken off, and conversely, when the flow rate measurement signal is decreased, it is switched to the small range orifice. To prevent hunting when switching between large and small ranges, a cutting difference is provided as shown in FIG. This function is also given to the monitor switch 8.

The above will be specifically described with reference to the mantissa value. In FIG. 6, when the flow rate increases during measurement with the small range orifice, the signal from the multiplier 10 in FIG. 2 increases. When this signal reaches 98% of the maximum flow rate measured by the small range orifice, the monitor switch 8 operates to operate the solenoid valve 16 shown in FIG. 7, so that a → b communicates with each other and the actuator 4 connects the large range orifice. Operates to set in channel 2 and a large range orifice is used.

On the contrary, when the flow rate decreases to 2% of the maximum flow rate while using the large range orifice, the monitor switch 8
Operates to operate the solenoid valve 16 of FIG. 7 to communicate a → c, the actuator operates, and the small range orifice is used. The switch 11 switches a coefficient for performing range matching of large and small ranges. If the small range orifice is 0-
10t / h, 0-100t / h for large range orifice
Then, the signal generator 12 has a coefficient of 1.0, and the signal generator 1
3 has a coefficient of 10 and is switched to 1.0 when using a small range orifice and to 10 when using a large range orifice.
The signal from the square root calculator 7 is multiplied to perform range matching. The timing of switching is the same as the timing of switching the large and small range orifices.

In the present embodiment, two types of diaphragm mechanism, large and small, have been described.
A wide measurement range can be achieved. Further, the aperture provided in the diaphragm mechanism is not limited to the orifice and may be an aperture such as a bell mouth.

[0017]

According to the present invention, a wide range of flow rate measurement is possible and measurement accuracy can be maintained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

FIG. 2 is a control system diagram in the embodiment of FIG.

3 is a diagram showing the relationship between the transmitter measurement signal and the indicator value shown in FIG.

FIG. 4 is a diagram showing operation timing when switching the aperture mechanism.

FIG. 5 is an explanatory diagram of a conventional technique.

FIG. 6 is an explanatory diagram of range switching.

FIG. 7 is an explanatory diagram of an actuator operation at the time of range switching.

[Explanation of symbols]

1 ... Throttling mechanism, 1a, 1b ... Orifice, 2 ... Pipe line, 3
... differential pressure gauge, 4 ... actuator, 5 ... transmitter, 6 ... control device, 7 ... square root calculator, 8 ... monitor switch, 9 ... indicator, 10 ... multiplier, 11 ... switcher, 12, 13 ... signal generation Bowl, 14 ... bumpless switch, 15 ... switch, 16 ...
solenoid valve.

Claims (2)

[Claims] 1. A throttle mechanism having an opening provided in a conduit through which a fluid flows, a differential pressure gauge for measuring a differential pressure before and after the opening, and means for determining a fluid flow rate based on a measurement value of the differential pressure gauge. In the flow rate measuring device, the throttle mechanism is provided with at least two openings having different diameters separated from each other, and the opening end distance of each opening approaching each other is set to be smaller than the fluid pipe inner diameter, and according to the magnitude of the fluid flow rate. And a means for selecting and switching the aperture of the throttle mechanism provided in the pipe line to an appropriate diameter, and providing a means for switching. 2. A throttle mechanism having an opening provided in a conduit through which a fluid flows, a differential pressure gauge for measuring a differential pressure before and after the opening, and means for calculating a fluid flow rate based on a measurement value of the differential pressure gauge. In a flow rate measuring device having means for displaying the calculated flow rate with an indicator, at least two openings having different diameters are provided at a predetermined distance in the throttle mechanism, and a pipe line is provided according to an increase or decrease in the fluid flow rate. Means for switching the aperture of the throttle mechanism provided therein to one having an appropriate diameter, means for switching the flow rate range used by the flow rate calculating means in accordance with the operation of the aperture switching means, and the means for switching the aperture and the flow rate range. A flow rate measuring device comprising a signal holding switch for temporarily holding a flow rate signal sent to an indicator.