JPH0336889Y2 - - Google Patents

Description

[Detailed description of the invention] (Industrial field of application) The invention is a hot wire flow rate measuring device.
The present invention relates to the above-mentioned device that compensates for temperature changes and enables accurate flow velocity measurement when measuring the flow velocity of a fluid whose temperature changes moment by moment, such as with a hot-wire respirocurrent meter.

(Prior art) A hot wire flow velocity measuring device places a hot wire in the flow path of the fluid to be measured, detects changes in the electrical resistance of the hot wire radiated by the fluid, and calculates the flow velocity using the well-known King equation. It is something. That is, the relationship between the output voltage V of the hot wire and the flow velocity v is V ² /R=(A+B√)(θ−θa) − However, θ...hot wire temperature, θa...fluid temperature, R...operating resistance of the hot wire, A, B...Constant determined by the properties of the fluid In the above equation, if the output voltage when v = ₀ (m/s) is V ₀ ; V ₀ ² /R = A (θ - θa) - (2) From the formula, V ² = V ₀ ² + R・B (θ−θa)・√ √=V ² −V ₀ ² /R・B (θ−θa) − ∴v={V ² −V ₀ ² /R・B (θ−θa)} ² − From formula (3), there is a linear relationship between √ and V ² , and B
Since and R and θ are considered constants, from Eq.
If V ₀ , V and θa are known, the flow velocity v can be calculated.

(Problem to be solved by the invention) However, in the above equation, in the case of a fluid where θa changes from moment to moment, the following problem occurs. For example, in the case of measuring the flow rate of respiratory flow, there is a considerable temperature difference between exhaled air and inhaled air, and this temperature difference causes a corresponding measurement error in the measured flow rate value. Therefore, in order to eliminate errors, it is necessary to measure the temperature of the fluid every moment and correct the flow velocity value. One way to do this is to insert a temperature sensor into the flow path, but this method not only disrupts the flow and prevents accurate fluid movement, but also disrupts the thermal equilibrium of the temperature sensor due to the airflow, making it difficult to read instructions. It won't be accurate. Focusing on this point, a method was proposed to correct the heat rays and the low drag rays at the same time (Japanese Patent Laid-Open No. 56-51618).
Even with this proposal, there still remain problems such as obstruction of fluid flow and the need for complicated circuit configurations and calculations.

The present invention was developed in view of the above, and in correcting the influence of fluid temperature on hot wire output,
The purpose of this invention is to provide a device that can measure flow velocity in real time, is non-invasive, and does not disturb the flow.

(Means for Solving the Problems) The configuration for achieving the above object will be explained using diagrams corresponding to embodiments. Figures 2A and B are block diagrams showing two embodiments of the ultrasonic temperature measurement section, Figure 3 is an explanatory diagram of an example in which ultrasonic receiving sensors are arranged in a facing relationship, and Figure 4 is a constant temperature type hot wire flow velocity. Figure 5 is a block diagram of the measuring section, and is a block diagram explaining the operation of the arithmetic unit.As shown in the figure, the present invention consists of an ultrasonic temperature measuring section, a constant temperature type hot wire flow velocity measuring section, and an arithmetic device. The ultrasonic temperature measuring section includes ultrasonic transmitting/receiving sensors 1 and 2, an ultrasonic pulse transmitting circuit 3,
The constant temperature type hot wire flow velocity measuring section includes an ultrasonic pulse receiving circuit 4 and an ultrasonic pulse propagation time counting means 5, a hot wire 6 for flow velocity measurement, a bridge circuit 7, a control circuit 8 for keeping the hot wire temperature constant, and a current −
The hot wire includes a voltage converter 9, and the arithmetic unit takes in the fluid temperature outputted from the measuring section and the output voltage of the hot wire outputted from the measuring section, respectively, and calculates the flow velocity at that temperature. Related to type flow rate measuring device.

In the above configuration, the ultrasonic temperature measuring section measures the temperature of the fluid to determine θa in the equation, and the constant temperature hot wire flow velocity measuring section measures the output voltage V of the hot wire corresponding to the ever-changing temperature of the fluid. The calculation device inputs the above θa and V and calculates v according to the formula, which is essentially a computer.
It is a CPU device.

Each will be explained in more detail below with reference to figures.
The principle of measuring the fluid temperature θa by the ultrasonic temperature measuring section is as follows. The speed of sound C in air is a function of temperature θa (°C): C20.067√273+331.6+0.61θa (m/s) ∴θa=C-331.6/0.61 - θa can be found by measuring C from the formula. In the present invention, the sound velocity C is determined by measuring the propagation time of an ultrasonic pulse. That is, let L be the distance between transmitting and receiving ultrasonic pulses,
Let the distance of the ultrasonic pulse be the propagation time between L and t
Then, C=L/t(m/s) −. Therefore, by measuring the propagation time t, the speed of sound C can be determined by the formula.

In order to measure this propagation time t, the present invention employs ultrasonic propagation time counting means 5. One of the means 5 is a clock pulse counting method, and the other is a repeating frequency counting method of ultrasonic pulses. The previous method will be explained with reference to FIG. 2A. The figure shows an example of a pulse reflection type, and an ultrasonic transmission signal is transmitted from the pulse transmission circuit 3 triggered by the pulse repetition frequency transmission circuit 30. The ultrasonic pulses sent to the sensor 1 and emitted from the sensor 1 cross the fluid f in the fluid pipe 10, collide with the other pipe wall, and are reflected by the ultrasonic receiving sensor 2, where they are caught and then converted into ultrasonic waves. It is received by the pulse receiving circuit 4, and further amplified and
Detected. The clock pulse is sent from the clock pulse oscillator 31 to the gate 32 of the counter 33 and also to the pulse repetition frequency oscillator 30.
A start pulse is sent in synchronization with the trigger pulse, and the gate 32 is opened by this start pulse, allowing gate-in of the above-mentioned clock pulse. When the ultrasonic pulse is received (amplified and detected) by the pulse receiving circuit 4, this received pulse is inputted to the gate 32 as a stop pulse to close the gate. Therefore, the time period from emission to arrival (reception) of the ultrasonic pulse, that is, the propagation time t, is calculated by the count value of the clock pulse taken into the counter 33 during the time period from opening to closing of the gate 32. In the latter method, as shown in Fig. 2B, ultrasonic pulses are emitted from the transmitter sensor 1 in response to a signal from the pulse oscillation circuit 3, are caught by the receiver sensor 2 as in the previous example, and are received (amplified and detected) by the pulse receiver circuit 4. ), which passes through the shaping circuit 34 to be shaped into a waveform, passes through the pulse oscillation circuit 3 again, and circulates through the closed loop circuit to form a pulse repetition frequency. Therefore, the propagation time t of the ultrasonic pulse can be calculated using the pulse repetition frequency counter 35.

In this manner, the ultrasonic temperature measuring section determines the temperature θa of the fluid from the propagation time t of the ultrasonic pulse. Next, the constant temperature type hot wire flow velocity measuring section is used in a hot wire flow velocity device to maintain the temperature of the hot wire at a constant value when the heat radiation amount of the hot wire changes depending on the fluid. The current flowing through changes. This current is detected as a flow velocity signal. Specifically, as shown in Figure 4, the hot wire 6
A resistor bridge circuit 7 is connected to the hot wire 6, the current of the hot wire 6 is taken out by a current amplifier 60, and a current corresponding to the detection amplification current is sent to the hot wire 6 from a control circuit 8 to maintain a constant heat generation temperature. On the other hand, the detected amplified current is taken out as a voltage V by the current-voltage converter 9, and is input to an arithmetic unit to perform calculations according to the formula.

An example of the operation of the arithmetic unit is shown in the block diagram of FIG. 5, and when compared with the system block diagram of FIG. 1, the operation principle can be easily understood. When taking in V from the flow rate measuring section, V and v have a 4th power functional relationship according to the equation, so in signal processing, V must first be input through a linearizer (not shown) or converted into a straight line after being input. It is better to adopt one of the following. A filter (not shown) for removing noise in the V signal is also preferably employed, as is often done. The use of a storage device and a display device in conjunction with an arithmetic unit is similar to that of ordinary microcomputer technology.

(Function) As described above, the device of the present invention determines the temperature θa of the fluid f from the propagation time t of the ultrasonic pulse between the tube walls of the fluid conduit 10 in the ultrasonic temperature measurement section.
At the same time, find the output voltage V of the hot wire under the above temperature θa in the constant temperature hot wire flow velocity measuring section,
By inputting the temperature θa and the output voltage V into an arithmetic unit and determining the current flow velocity v from time to time using King's formula, it is possible to compensate for errors in the flow velocity v due to temperature fluctuations in real time.

(Embodiment) The transmission and reception of ultrasonic pulses in the ultrasonic temperature measurement unit can be of a facing type instead of the emission type described in the description. FIG. 3 shows an example of the facing type, in which the transmitting sensor 1 and the receiving sensor 2 are placed opposite each other in a straight line. Ultrasonic pulse propagation time counting means 5
When considering the responsiveness, it is desirable that the pulse propagation time t be long, so a reflective type is preferable in this respect, but if the responsiveness is fast, a facing type can also be used.
In the latter type, it is desirable to make the ultrasonic pulse orthogonal to the fluid f in order to reduce the influence of the flow velocity of the pulse, and to make the fluid a laminar flow, it is desirable to make the ultrasonic pulse orthogonal to the fluid f. It is preferable to provide the wire mesh 11 vertically. Furthermore, both the former reflective type and the latter opposing type can transmit and receive ultrasonic pulses with a single sensor (not shown). A well-known one-piece sensor may be used for this purpose. Furthermore, instead of providing the linearizer and filter on the arithmetic unit side as described above, it is also possible to connect them later to the current-voltage converter 9 shown in FIG.

(Effects of the invention) As is clear from the above explanation, the invention has the following effects:
Without introducing an invasive object such as a temperature sensor into the fluid pipe, the ultrasonic temperature measuring unit emits ultrasonic pulses from the wall of the fluid pipe, and determines the fluid temperature θa from the propagation speed. At the same time, the output voltage V of the hot wire at the temperature θa is determined by a constant temperature type hot wire flow velocity measurement unit, and these are input to a calculation device to calculate the flow velocity v corresponding to each temperature of the fluid. Therefore, in compensating for the influence of fluid temperature on the thermal output, it has the advantage of being able to measure the flow velocity in real time and non-invasively without disturbing the flow. This is particularly useful for measuring flow velocity when the flow rate changes from moment to moment.

[Brief explanation of the drawing]

Fig. 1 is a system block diagram showing the relationship of the entire device of the present invention, Fig. 2 A and B are block diagrams showing two embodiments of the ultrasonic temperature measuring section, and Fig. 3 shows the ultrasonic receiving sensor in a facing relationship. FIG. 4 is a block diagram of a constant-temperature type hot wire flow velocity measurement section, and FIG. 5 is a block diagram illustrating the operation of the arithmetic unit. Explanation of symbols, ... Ultrasonic temperature measurement section, ...
Constant temperature type hot wire flow velocity measurement unit, ... calculation device, 1,
2... is an ultrasonic transmitting/receiving sensor, 3... is an ultrasonic pulse transmitting circuit, 4... is an ultrasonic pulse receiving circuit, 5... is
...Ultrasonic pulse propagation counting means, 6... Hot wire for measuring flow velocity, 7... Bridge circuit, 8... Control circuit, 9... Current-voltage converter.

Claims (1)

[Scope of Claim for Utility Model Registration] 1. Consists of an ultrasonic temperature measurement section, a constant temperature type hot wire current velocity measurement section, and an arithmetic device, and the ultrasonic temperature measurement section includes ultrasonic transmission/reception sensors 1 and 2, and an ultrasonic pulse transmission circuit 3. , ultrasonic pulse receiving circuit 4
and an ultrasonic pulse propagation time counting means 5, and the constant temperature type hot wire flow velocity measuring section includes a hot wire 6 for measuring flow velocity, a bridge circuit 7, a control circuit 8 for keeping the hot wire temperature constant, and a current-voltage converter 9. A hot wire flow velocity measuring device, wherein the arithmetic unit takes in the temperature of the fluid output from the measuring section and the output voltage of the hot wire output from the measuring section, respectively, and calculates the flow velocity under the temperature. 2 Ultrasonic transmitting/receiving sensors 1 and 2 are spaced apart on one side wall of the fluid pipe 10, and the ultrasonic pulse emitted from the transmitting sensor 1 crosses the fluid f and is reflected from the other pipe wall and reaches the receiving sensor 2. 2. The apparatus according to claim 1, wherein the ultrasonic pulse is transmitted and received, and the time limit between emission and reception is the propagation time of the ultrasonic pulse. 3 Ultrasonic transmitting/receiving sensors 1 and 2 are attached to mutually opposing pipe walls of the fluid conduit 10, and ultrasonic pulses emitted from the transmitting sensor 1 cross the fluid f at approximately right angles and are received by the receiving sensor 2. , the device according to claim 1, wherein the time limit between emission and reception is the propagation time of the ultrasonic pulse. 4. The ultrasonic pulse propagation time counting means 5 includes a clock oscillator 31 and a counter 33, and the gate 32 of the counter 33 is within the time limit in which the ultrasonic pulse emitted from the ultrasonic transmitting circuit 3 arrives at the ultrasonic receiving circuit 4. The propagation time of the ultrasonic pulse is determined by determining the number of clock pulses input into the gate 32 from the clock oscillator 31 during this period when the clock pulse is opened. Apparatus described in section. 5. The ultrasonic pulse propagation time counting means 5 includes a shaping circuit 34 installed in series between the ultrasonic pulse transmitting circuit 3 and the ultrasonic receiving circuit 4, and a pulse frequency counter 35 installed in parallel with the receiving circuit 4.
The apparatus according to claim 2 or 3, wherein the pulse repetition frequency from the receiving circuit 4 is counted by the counter 35 and the propagation time of the ultrasonic pulse is determined from the pulse repetition frequency. 6. The device according to claim 1, wherein the ultrasonic transmitting/receiving sensors 1 and 2 perform transmission and reception with one sensor.