JP3264609B2 - Apparatus and method for detecting fluid flow - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for detecting a flow of a fluid, and more particularly, to applying a current for heat generation or heating to a thermistor disposed in a fluid to be measured. The present invention relates to a fluid flow detection device and method capable of detecting the presence or absence of a flow based on the magnitude of a temperature change within a predetermined time.

[0002]

2. Description of the Related Art In a pipe for sending a liquid or gas such as fuel or water, a device for detecting the presence or absence of a flow of an internal fluid and a flow velocity is used. For example, a paddle type flow switch is known as an apparatus for detecting the presence or absence of a flow by a mechanical method. In the paddle type flow switch, a paddle serving as a movable obstacle is installed in a fluid flow path, and movement of the paddle generated when the fluid hits the paddle is extracted as an electric signal using a microswitch or the like.

[0003] As a device for detecting the presence or absence of a flow by an electric method, there is a thermal flow sensor using two thermistors as sensors as shown in FIG. One thermistor A is for measuring the temperature of the fluid itself, and the other thermistor B is for applying a heating current to cause self-heating and for measuring the temperature rise of the thermistor accompanying the self-heating. These thermistors A and B are arranged in a fluid such that the thermistor A is located on the upstream side of the pipe, and the difference between the fluid temperature measured by the thermistor A and the temperature of the thermistor B self-generated and cooled by the fluid is constant. The presence or absence of the fluid flow is determined based on whether the value exceeds or does not exceed the value.

Further, there is an apparatus which detects the flow velocity of a fluid by using a device similar to the above. For example, a method of converting the temperature difference between the thermistor A and the thermistor B into a flow rate at a preset ratio, or controlling a current value flowing through the thermistor B so that the temperature difference between the thermistor A and the thermistor B is always constant. And a method of calculating the flow velocity from the current value.

[0005]

The above-mentioned method using a mechanical flow switch has a problem that a pressure loss occurs in a fluid because a mechanical driving force is obtained by utilizing the flow velocity of the fluid. There is. Further, when the flow rate exceeds the predetermined flow rate range, the pressure loss particularly increases, so that the range of flow velocity that can be handled is narrow, and the structure itself tends to be large, so that there is a problem that it is difficult to secure a mounting space.

On the other hand, a thermal flow sensor and a thermal anemometer are:
Although it is easy to secure the mounting space for the sensor, two sets of high-precision thermistors for measuring the fluid temperature and self-heating and a measuring circuit for the same are required, and the apparatus tends to be expensive. Further, since it is difficult to make the temperature characteristics of both thermistors the same, a temperature compensating circuit for compensating for the difference in temperature characteristics is required separately, and the circuit becomes complicated. Furthermore, it is necessary to increase the temperature difference between the two thermistors in consideration of the difference in characteristics between the components in the two measurement circuits and changes over time, so that power consumption for heating tends to increase. There is also a disadvantage.

SUMMARY OF THE INVENTION In view of the above, the present invention provides a fluid flow detection device which has a small pressure loss, a wide detection range, a simple structure, low production cost, and low power consumption for detection. The purpose is to provide.

[0008]

In order to achieve the above object, a fluid flow detecting device according to the present invention comprises a thermistor disposed in a fluid to be measured, and a periodic or intermittent current supply to the thermistor. An energizing means for heating this, and a resistance value measuring means for measuring the resistance value of the thermistor, wherein a first resistance value measurement is performed at a predetermined time immediately before the energization by the energization means or at a predetermined time after the energization start, Next, a resistance value measuring means for performing a second resistance value measurement at a predetermined time interval from the first resistance value measurement, and the first time resistance value obtained from the measurement by the resistance value measurement means. It is characterized by comprising flow determining means for determining the presence or absence of fluid flow based on the temperature change of the thermistor from the time when the resistance value is measured to the time when the second resistance value is measured.

Further, according to the flow detecting method of the present invention, a thermistor is arranged in a fluid to be measured, and the thermistor is periodically or intermittently heated, and the resistance value of the thermistor is immediately before or after the start of the heating. Then, at predetermined time intervals from the measurement of the resistance value, the resistance value of the thermistor is measured again, and the resistance obtained after the previous resistance value measurement time obtained from the measured resistance value is measured. It is characterized in that the presence or absence of a fluid flow is detected based on the magnitude of the temperature change of the thermistor up to the time of the value measurement.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In one embodiment of the flow detecting device and method of the present invention, a thermistor is placed in a fluid, the thermistor is heated by a current supply means, and the thermistor resistance is measured by a thermistor resistance measurement circuit. The pre-warming temperature and the temperature after a certain period of time from the heating are measured respectively. The thermistor
When there is no flow in the fluid, a large change in temperature appears. When there is a flow in the fluid, a small change in temperature appears due to the cooling effect of the fluid. Therefore, when the temperature difference between the two is equal to or more than the predetermined value, it is determined that there is no flow, and when it is equal to or less than the predetermined value, it can be determined that there is flow. Thereafter, after a period in which the temperature of the thermistor is stabilized, the above procedure is repeated again, and the presence or absence of fluid flow is detected periodically or intermittently.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1A is a circuit diagram showing a configuration of a fluid flow detecting device according to a first embodiment of the present invention. In the figure, 1 is a microcomputer (MPU), 2 is a thermistor, and 3 is an AD converter. R1 is a resistor connected in series with the thermistor 2, TR1 is a pnp transistor, TR2 is an npn transistor, and 4 is a DC power supply. The thermistor 2 is covered with an insulator such as glass to be protected from fluid, and is attached to the tip of a holder (plug) 10 whose surface is threaded, for example, as shown in FIG. When the plug 10 is screwed into a screw hole (mounting seat) 12 provided in the pipe 11, the thermistor 2
Is a structure located in the flow path of the fluid flowing through the pipe 11 and in contact with the fluid.

The detection of the presence or absence of the flow of the fluid is performed by a series of procedures that appear at a constant cycle. Each detection cycle includes a temperature measurement step of the fluid to be measured, a thermistor heating step, a thermistor calming step, a temperature measurement step after the calming step, and a thermistor cooling step. The temperature measurement value obtained after the sedation step is compared with the temperature measurement value of the fluid to be measured first, and if the temperature difference between the two falls below a predetermined value, there is a fluid flow, and this is determined. If it exceeds, it is determined that there is no fluid flow.

The operation of the flow detecting device according to the present embodiment will be described in detail with reference to the time chart of FIG.
In the step of measuring the temperature of the fluid to be measured, the transistor TR1 is turned off.
At N, the transistor TR2 is turned off. The current passing through the transistor TR1 passes through the thermistor 2 and the resistor R1
To the ground via the resistor R1, and a voltage drop corresponding to the resistance value of the thermistor 2 is generated at both ends of the resistor R1. This voltage drop is converted into a digital signal by the AD converter 3 and input to the MPU 1, which then converts the temperature in the MPU 1 and stores it. As described above, first, the resistance value of the thermistor 2 is measured, and this is converted into a temperature, which is used as the measured temperature of the fluid to be measured.

The step of heating the thermistor 2 is performed with the transistor TR2 turned on. The current that has passed through the transistor TR1 flows to the ground via the thermistor 2 and the transistor TR2, and the thermistor 2 self-heats by the supplied current. The thermistor 2 is cooled by the fluid and raises the fluid temperature. This heating step
For example, for a few seconds.

Next, as a calming step, the transistor T
R1 and TR2 are turned off and thermistor 2 is heated
The time at which the heat in the central portion of the substrate spreads over the insulating material such as glass and the surrounding fluid to be measured is averaged. This period is, for example, about 1 second. Next, the transistor TR1 is turned on for a short time, and the temperature of the thermistor 2 after heating is measured. This measured temperature is compared with the previously measured temperature before heating, that is, the temperature of the fluid to be measured.If the temperature rise exceeds a preset reference value, the fluid is in a stationary state, and Is determined to be flowing. This is based on the principle that the temperature rise of the thermistor 2 is small when the fluid flows, and the temperature drop is large when the fluid flows.

In the cooling step, the thermal energy applied in the heating step is diffused into the fluid to be measured, so that the thermistor approaches the temperature before the heating.
Are turned off. This period is, for example, several seconds.
It is. One flow detection cycle T is constituted by a series of steps from the pre-heating temperature measurement step to the cooling step.

FIG. 3 shows the relationship between the temperature of the thermistor 2 and time in each of the above steps. This graph was obtained in an experiment using water as the fluid, and is a diagram when the water temperature is 25 ° C., when there is a flow of 1 liter per minute, and when there is no flow. As shown in the figure, the temperature of the thermistor 2 is about 1 second from the start of heating when there is a flow in the fluid.
Saturates at 3 °, and when there is no flow, 3se after starting heating
Continue to rise after c. For example, if a heating step of about 3 seconds is performed, and then a sedation step of about 1 second is provided, a discernible difference between the two descending curves can be obtained as shown in the figure.

Here, comparing the temperature at the temperature measurement point A of the fluid to be measured and the temperature at the sedation completion point B, there is almost no difference when there is a flow, and when there is no flow, the difference is equal to or more than a certain value. There is a difference. The presence or absence of a flow is determined by comparing the temperature difference between the time points A and B with a preset reference value.

As can be understood from FIG. 3, the presence or absence of the flow can also be determined from the temperature difference between the time point C, for example, about 1 second after the start of the heating, and the time point D immediately before the end of the heating for 3 seconds. By doing so, the time required for one measurement is reduced. Further, in this case, since the temperature at the measurement time point C may be high, the time of the cooling step after the measurement time point D can be reduced. Here, the detection based on the temperature difference between the time points A and B and the detection based on the temperature difference between the time points C and D can be used in combination.

By continuously repeating the above flow detection procedure, continuous flow detection is performed. Also,
Instead of such periodic detection, when it is necessary to detect the presence / absence of a flow, intermittent detection of performing the above detection procedure may be performed each time.

From the experimental results shown in FIG. 3, it can be understood that the equivalent time constant of the temperature change of the thermistor during or after the heating differs depending on whether or not the fluid flows. That is, when there is a flow, the time constant is small, and when there is no flow, the time constant is large. By utilizing this, the time required for flow detection can be further reduced from the example described above. This is shown in FIG.
This will be described with reference to FIG. In a state where there is a flow, the temperature of the thermistor saturates about 1 second after the start of heating. Therefore, it is also possible to determine the presence or absence of the flow by reducing the heating time to 1 second and measuring the temperature difference between the heating start time A and the heating end time or the sedation end time B. When performing periodic detection, if it is determined that there is a flow in a certain detection cycle, the cooling period of that cycle is set to 1 second,
If it is determined that there is no flow, the cooling period of the cycle is 3se
c. Thereby, the detection cycle T can be reduced.

According to the first embodiment, the temperature measurement before and after the heating and the temperature measurement at a predetermined time interval related to the heating time are performed by the common thermistor. The cause of the error is smaller than that of the detection device. That is, since there is no need to consider variations such as temperature characteristics and changes over time, the temperature difference between before and after heating can be effectively measured even with a small amount of heating, and power for heating can be reduced. For example, when measuring the presence / absence of water flow using two thermistors, considering the variation in characteristics,
It is necessary to set the temperature of the fluid to be measured at 25 ° C. and the heating temperature to about 5 ° C. In this case, the power consumption is required to be about 50 mW. On the other hand, in the present invention, since the variation does not need to be considered, the heating temperature may be a minimum of about 2.5 ° C., and in this case, the power consumption may be about 25 mW. In addition, the number of components is reduced, and adjustment for absorbing variations and errors of the components is not required.
Manufacturing costs can be reduced.

Next, referring to FIGS. 5A and 5B,
A description will be given of a fluid flow detecting device according to a second embodiment of the present invention. Elements that are the same as or correspond to the elements described in the first embodiment are given the same reference numerals, and descriptions thereof are omitted. This embodiment is the same as the previous embodiment in that one thermistor 2 is used as a sensor. The difference lies in the circuit configuration. As shown in FIG. 5A, the point is that a capacitor C is provided instead of the resistor R1 in series with the thermistor 2, the AD converter is omitted, and the MPU 1 includes a Schmitt circuit.

Each detection cycle in the second embodiment is shown in FIG.
As shown in (b), the configuration is similar to that of the first embodiment. First, the transistor TR1 is turned on and the transistor TR2 is turned off, and the temperature of the fluid to be measured is measured. The current passing through the transistor TR1 passes through the thermistor 2 and charges the capacitor C. The terminal voltage of the capacitor C depends on the resistance value of the thermistor 2, and the value is MPU
1 to the Schmitt circuit. The time from the start of charging the capacitor C to when the voltage reaches the H level voltage of the Schmitt circuit is measured and converted into a temperature. Here, when the transistor TR2 is turned on, the electric charge of the capacitor C is instantaneously discharged, and the terminal voltage of the capacitor C returns to zero. At the same time, the thermistor 2 is heated and starts self-heating.

After the elapse of the heating period of 3 seconds, as a calming step, both the transistors TR1 and TR2 are turned off, and a time for averaging the temperatures is secured as in the previous embodiment. This period is, for example, 0.5 sec. When the temperatures are averaged, the transistor TR1 is turned on. The terminal voltage of the capacitor C is input to the Schmitt circuit of the MPU 1 and the time until the Schmitt circuit reaches the H level is measured and converted to temperature. The above temperature is compared with this temperature, and the presence or absence of a flow is determined from the temperature difference.

The cooling step is provided for the same purpose as in the previous embodiment, and is obtained by turning off both the transistors TR1 and TR2. This period is, for example, 3.5.
as sec. The above procedure is repeated periodically or intermittently to detect a continuous flow.

Next, a third embodiment of the present invention will be described with reference to FIG. In the present embodiment, the underwater electrodes 21 and 22 of the electric conductivity measuring device for measuring the electric conductivity of pure water sent from the ion-exchange type pure water producing device, and the thermistor 2 of the flow detecting device of the embodiment described above. Are arranged on one plug 20 as shown in FIG.

Generally, in an ion-exchange type pure water producing apparatus,
In order to ensure the purity of pure water, end point detection is performed to detect that the performance of the ion exchange resin has decreased. In this case, the electric conductivity of pure water at the outlet of the apparatus is measured, and when it is detected that the electric conductivity has risen to a predetermined value or more, the end point of the ion exchange resin is detected as degraded. By the way, it is known that the electric conductivity of pure water obtained by a pure water producing apparatus of this type is high at the start of operation of the apparatus, and that the value stabilizes after about 30 seconds from the start of operation. . That is, in order to detect the end point, it is necessary to measure the electric conductivity after a lapse of 30 seconds or more from the start of the operation of the device. Therefore, in this type of pure water producing apparatus, generally, the start of pure water flowing at the outlet of the apparatus is detected by a flow switch or the like, and the electric conductivity is measured 30 seconds after the detection.

The electric conductivity of pure water is measured by applying an AC voltage between a pair of electrodes in contact with the pure water to be measured, and measuring a current value flowing between the electrodes. By the way, even with pure water of the same purity, the electric conductivity greatly differs depending on the water temperature at the time of the measurement. For this reason, JI
Also in S, the electric conductivity of water is specified to use a value at a water temperature of 25 ° C., so it is necessary to convert the value to 25 ° C. That is, in the measurement of the electric conductivity of water, the measurement of the water temperature at the time of the measurement is indispensable.

Therefore, in this embodiment, as described above, the thermistor 2 of the flow detecting device and the underwater electrodes 21 and 22 of the electric conductivity measuring device are combined as one component, and these are attached to the tip of the plug 20. . By screwing this plug into the mounting seat of the outlet pipe of pure water, this one part can be used for detection of pure water flow, water temperature measurement for water temperature conversion, and electric conductivity measurement. . In this way, in the present embodiment, the number of parts and the space in the pure water production apparatus are reduced.

[0031]

According to the flow detecting apparatus and method of the present invention, 1
The present invention uses two thermistors to measure the temperature change of the fluid before and after its heating, and to detect the presence or absence of flow according to the magnitude of the temperature change. Therefore, the present invention reduces the manufacturing cost by reducing the number of parts. In addition, a flow detection device with a low pressure loss and a wide detection range that has reduced the factors of error due to variations in the characteristics of elements and components and reduced power for heating has been provided. It works.

[Brief description of the drawings]

FIG. 1A is a circuit diagram of a fluid flow detecting device according to a first embodiment of the present invention, and FIG. 1B is a timing chart showing the operation of the circuit.

FIG. 2 is a sectional view showing a structure of a flow detection unit in FIG. 1;

FIG. 3 is a graph showing a temperature change of the thermistor of the embodiment of FIG.

FIG. 4 is a graph showing a temperature change of a thermistor according to a modification of the embodiment of FIG. 1;

FIG. 5A is a circuit diagram of a fluid flow detecting device according to a second embodiment of the present invention, and FIG. 5B is a timing chart showing the operation of the circuit.

FIG. 6 is a perspective view showing the structure of a sensor part of an electric conductivity measuring device according to a third embodiment of the present invention.

FIG. 7 is a schematic side view of a conventional fluid flow detection device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Microcomputer (MPU) 2 Thermistor 3 A / D converter 4 DC power supply R1 Resistor TR1, TR2 Transistor 10, 20 Holder (Plug) 11 Piping 12 Screw hole (Mounting seat) 21, 22 Underwater electrode

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01P 5/12 G01P 13/00

Claims (3)

(57) [Claims] 1. A thermistor disposed in a fluid to be measured, energizing means for energizing and heating the thermistor periodically or intermittently, and resistance value measuring means for measuring a resistance value of the thermistor. The first resistance value measurement is performed immediately before the energization by the energization means or at a predetermined time after the energization is started.
Resistance measurement means for performing a second resistance measurement at a predetermined time interval from the resistance measurement, and from the first resistance measurement time obtained from the measurement by the resistance measurement means A fluid flow detection device, comprising: flow determination means for determining the presence or absence of fluid flow based on the magnitude of temperature change of the thermistor up to the second resistance value measurement. 2. The fluid flow detection according to claim 1, wherein the first and second resistance measurements or the second resistance measurement is performed after the power supply is stopped by the power supply unit. apparatus. 3. A thermistor is arranged in a fluid to be measured, the thermistor is heated periodically or intermittently, and a resistance value of the thermistor is measured immediately before or after the start of the heating.
Next, the resistance value of the thermistor is measured again at a predetermined time interval from the measurement of the resistance value, and the resistance value obtained from the measured resistance value is measured from the previous resistance value measurement time to the subsequent resistance value measurement time. A method for detecting the presence or absence of fluid flow based on the magnitude of temperature change of the thermistor.