JPH09101322A - Flow detection apparatus and method for fluid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flow detector for fluid which is low in pressure loss and power consumption, and has a simple structure. SOLUTION: This flow detector is provided with a thermistor 2 which comes into contact with a fluid to be measured and measures resistance value of the thermistor 2 initially at one detection cycle with a resistance R1, an AD convertor 3 and a MPU 1. The results are converted into temperature. Then, a current is fed to the thermistor 2 to generate heat and the resistance value of the thermistor 2 is measured a specified time after the initial measurement. The results are converted into temperature. When changes in the temperature of the thermistor 2 before and after the heat generation exceed a specified value, no flow is judged to exist and when they are below the specified value, some flow is judged to exist. This procedure is repeated cyclically to detect the presence or absence of the flow continuously. Thus, the presence of the flow of a fluid is detected by one thermistor paying attention to the fact that the changing rate and the time constant change in the temperature of the thermistor depends on the presence or absence of the flow.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and method for detecting a fluid flow, and more particularly, a current for heating or heating is applied to a thermistor arranged in a fluid to be measured, which is caused by the heating. 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 pipes for feeding liquids such as fuel and water, and gas, a device for detecting the presence or absence of the flow of an internal fluid and the flow velocity thereof is used. For example, a paddle type flow switch is known as a device that detects the presence or absence of flow by a mechanical method. In the paddle type flow switch, a movable paddle is installed in a fluid flow path, and movement of the paddle caused by the fluid hitting the paddle is extracted as an electric signal using a microswitch or the like.

As an apparatus for detecting the presence or absence of flow by an electrical method, there is a thermal type 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 supplying a heating current to cause self-heating and measuring the temperature rise of the thermistor accompanying this. 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 temperature difference between the fluid temperature measured by the thermistor A and the temperature of the thermistor B which is self-heated and cooled by the fluid is constant. The presence or absence of fluid flow is determined by whether or not the value is exceeded.

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

[0005]

By the way, in the method using the mechanical flow switch, since a mechanical driving force is obtained by utilizing the flow velocity of the fluid, pressure loss occurs in the fluid. There is. Further, when the flow rate exceeds the predetermined flow rate range, the pressure loss is particularly increased, so that the range of the applicable flow velocity is narrow, and further, the structure itself tends to be large, and it is difficult to secure a mounting space.

On the other hand, the thermal type flow sensor and the thermal type velocity meter are
Although it is easy to secure a space for mounting the sensor, two sets of high-precision thermistors for measuring fluid temperature and for self-heating and a measuring circuit therefor are required, and the device tends to be expensive. Further, since it is difficult to make the temperature characteristics of both thermistors the same, a separate temperature compensation circuit for compensating for the difference in temperature characteristics is required, which complicates the circuit. Furthermore, it is necessary to take a large temperature difference between both thermistors in consideration of differences in characteristics between parts in both measurement circuits and changes over time, so power consumption for heating tends to increase. There is also a drawback.

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 manufacturing cost, and low power consumption for detection. The purpose is to provide.

[0008]

In order to achieve the above object, the flow detecting device of the present invention is configured such that a thermistor arranged in a fluid to be measured and the thermistor are energized periodically or intermittently. An energizing means for heating, a temperature measuring means for measuring the temperature of the thermistor at a predetermined time interval in relation to the energizing timing of the energizing means, and a change in temperature of the thermistor at the predetermined time interval. Flow determining means for determining the presence / absence of a fluid flow based on the flow determining means.

Further, in the flow detecting method of the present invention, a thermistor is arranged in the fluid to be measured, the thermistor is heated periodically or intermittently, and within a predetermined time of the thermistor in relation to the heating timing. Is measured, and the presence or absence of a fluid flow is detected based on the magnitude of the temperature change measurement value.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In one embodiment of the flow detection apparatus and method of the present invention, a thermistor is placed in a fluid, the thermistor is heated by an energizing means, and the thermistor resistance value measuring circuit is used to apply the thermistor. The temperature before warming and the temperature after a lapse of a fixed time from heating are measured. The thermistor
When there is no flow in the fluid, a large temperature change appears, and when there is a flow in the fluid, a small temperature change appears due to the cooling effect of the fluid. Therefore, it can be determined that there is no flow when the temperature difference between the two is greater than or equal to the predetermined value, and it can be determined that there is flow when the temperature difference is less than or equal to the predetermined value. Then, after a period in which the temperature of the thermistor stabilizes, the above procedure is repeated again to detect the presence or absence of the fluid flow 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. Further, R1 is a resistor connected in series with the thermistor 2, TR1 is a p-n-p transistor, TR2 is an n-p-n transistor, and 4 is a DC power supply device. The thermistor 2 is covered with an insulating material such as glass to be protected from a fluid, and is attached to the tip of a holder (plug) 10 having a threaded surface, for example, as shown in FIG. When the plug 10 is screwed into the screw hole (mounting seat) 12 provided in the pipe 11, the thermistor 2
Is a structure that is located in the flow path of the fluid flowing in the pipe 11 and is in contact with the fluid.

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

The operation of the flow detection apparatus of this embodiment will be described in detail with further reference to the time chart of FIG. 1 (b).
In the process of measuring the temperature of the fluid to be measured, the transistor TR1 is turned on.
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 across the resistor R1. This voltage drop is converted into a digital signal by the AD converter 3 and input to the MPU 1, and further converted into temperature in the MPU 1 and stored. As described above, first, the resistance value of the thermistor 2 is measured, and the resistance value is converted into the temperature to obtain the measured temperature of the fluid to be measured.

The heating process of the thermistor 2 is continued by turning on the transistor TR2. The current passing through the transistor TR1 flows to the ground via the thermistor 2 and the transistor TR2, and the thermistor 2 self-heats due to this energized current. The thermistor 2 is cooled by the fluid and raises the fluid temperature. This heating process is
For example, a few seconds.

Next, as a soothing step, the transistor T
Thermistor 2 heated by turning off R1 and TR2
The time at which the heat of the central part of the diffuses to the insulating material such as glass and the surrounding fluid to be measured and is averaged is secured. This period is, for example, about 1 sec. Then, the transistor TR1 is turned on for a short time, and the temperature after heating the thermistor 2 is measured. If this measured temperature is compared with the previously measured pre-heating temperature, that is, the temperature of the fluid to be measured, and if the temperature rise exceeds a preset reference value, the fluid is in a stationary state and falls below the reference value. Is judged to be flowing. This is based on the principle that the temperature rise of the thermistor 2 is small when there is a fluid flow, and the temperature drop is large when there is a fluid flow.

In the cooling step, the thermal energy applied in the heating step is diffused into the fluid to be measured so that the thermistor becomes close to the pre-heating temperature, and the transistors TR1 and TR2 are used.
Turn off both. Note that this period is, for example, several seconds.
It is. One flow detection cycle T is constituted by a series of processes from the pre-heating temperature measurement process to the cooling process.

FIG. 3 shows the relationship between the temperature of the thermistor 2 and time in each of the above steps. This graph was obtained by an experiment using water as a fluid, and is a diagram at a water temperature of 25 ° C., with a flow of 1 liter / min and without flow. As shown in the figure, the temperature of the thermistor 2 is about 1 second from the start of heating when the fluid has a flow.
It becomes saturated at, and when there is no flow, after heating starts 3se
Continues 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 as shown in the figure can be made between the two descending curves.

Here, comparing the temperature at the temperature measurement point A of the fluid to be measured with the temperature at the sedation completion point B, there is almost no difference when there is a flow, and a certain level or more when there is no flow. There is a difference. Whether or not there is a flow is determined by comparing the temperature difference between time A and time B with a preset reference value.

As can be understood from FIG. 3, the presence or absence of the flow can be discriminated also from the temperature difference between the time point C about 1 second after the start of heating and the time point D just before the end of heating for 3 seconds. By doing so, the time required for one measurement is shortened. 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 shortened. 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 together.

Continuous flow detection is performed by periodically repeating the above flow detection procedure. Also,
Instead of such periodic detection, it is also possible to perform intermittent detection in which the detection procedure is performed each time it is necessary to detect the presence or absence of flow.

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 heating or after heating differs depending on the presence or absence of fluid flow. 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 shortened from the example described above. This is shown in FIG.
This will be described with reference to FIG. When there is a flow, the temperature of the thermistor becomes saturated about 1 second after the start of heating. Therefore, the presence / absence of the flow can be determined by shortening the heating time to 1 second and measuring the temperature difference between the heating start time point A and the heating end time point or the sedation end time point 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 sec,
If it is determined that there is no flow, set the cooling period for that cycle to 3se
set to c. Thereby, the detection cycle T can be shortened.

According to the first embodiment described above, the temperature measurement before and after heating and the temperature measurement at the predetermined time interval related to the heating time are performed by the common thermistor. As compared with the detection device, the factors of error are reduced. That is, since it is not necessary to consider variations such as temperature characteristics and changes with time, it is possible to effectively measure a temperature difference before and after heating even with a slight heating, and it is possible to reduce electric power for heating. For example, when measuring the presence or absence of water flow using two thermistors, considering variations in characteristics,
It is necessary to set the temperature of the fluid to be measured to 25 ° C. and the heating temperature to about 5 ° C. In this case, power consumption is required to be about 50 mW. On the other hand, in the present invention, since it is not necessary to consider the variation, the minimum heating temperature may be about 2.5 ° C., and in this case, the power consumption may be about 25 mW. In addition, the number of parts is small, and adjustments to absorb variations and errors in components are unnecessary, so
Manufacturing costs can be reduced.

Next, referring to FIGS. 5A and 5B,
A fluid flow detecting device according to a second embodiment of the present invention will be described. The same or corresponding elements as those described in the first embodiment are designated by the same reference numerals and the description thereof will be 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, a capacitor C is provided instead of the resistor R1 in series with the thermistor 2, an AD converter is omitted, and a Schmitt circuit is included in the MPU1.

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 is charged in the capacitor C. The terminal voltage of the capacitor C depends on the resistance value of the thermistor 2, and its value is MPU.
1 is input to the Schmitt circuit. The time from the start of charging the capacitor C until reaching the H level voltage of the Schmitt circuit is measured and converted into temperature. Here, when the transistor TR2 is turned on, the electric charge of the capacitor C is instantaneously discharged, the terminal voltage of the capacitor C returns to zero, and at the same time, the thermistor 2 is heated and starts to generate heat by itself.

After the lapse of the heating period of 3 seconds, both transistors TR1 and TR2 are turned off in the sedative step to secure the time for averaging the temperature as in the previous embodiment. This period is 0.5 sec, for example. 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 required to reach the H level of the Schmitt circuit is measured and converted into temperature. The previous temperature and this temperature are compared, and the presence or absence of flow is determined from the temperature difference.

The cooling step is provided for the same purpose as in the previous embodiment, and can be obtained by turning off both the transistors TR1 and TR2. Note that this period is, for example, 3.5
It is as sec. The above procedure is repeated periodically or intermittently to continuously detect the flow.

Next, with reference to FIG. 6, an electric conductivity measuring apparatus for water such as pure water according to a third embodiment of the present invention will be described. 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. As shown in FIG. 6, they are arranged on one plug 20 to be integrated into one component.

Generally, in the ion exchange type pure water producing apparatus,
In order to ensure the purity of pure water, the end point detection is performed to detect that the performance of the ion exchange resin has deteriorated. 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 is detected as the performance of the ion exchange resin is lowered. By the way, it is known that the electric conductivity of pure water obtained by this type of pure water producing apparatus is high at the time of starting the operation of the apparatus, and that the value stabilizes after about 30 seconds have elapsed from the start of the operation. . That is, in order to detect the end point, it is necessary to measure the electrical conductivity after 30 seconds or more have passed from the start of operation of the device. For this reason, in this type of pure water producing apparatus, it is generally detected that pure water has started to flow at the outlet of the apparatus with a flow switch or the like, and the electrical 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 pure water to be measured and measuring the value of the current flowing between them. By the way, even with pure water of the same purity, the electric conductivity varies greatly depending on the water temperature at the time of measurement. Therefore, JI
Also in S, the electric conductivity of water is specified to use the value at a water temperature of 25 ° C., so it is necessary to convert it to 25 ° C. That is, in measuring the electric conductivity of water, it is essential to measure the water temperature at the time of the measurement.

Therefore, in the present 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 integrated as one component, and these are attached to the tip of the plug 20. . By screwing this plug into the mounting seat of the pure water outlet pipe, this one part can be used for all the detection of the flow of pure water, the water temperature measurement for water temperature conversion, and the electric conductivity measurement. . In this way, the present embodiment aims to reduce the number of parts and space in the pure water producing apparatus.

[0031]

According to the flow detecting apparatus and method of the present invention,
Since the temperature change of the fluid before and after the heating is measured using two thermistors and the presence or absence of the flow is detected according to the magnitude of the temperature change, the present invention reduces the manufacturing cost by reducing the number of parts. In addition to providing a flow detection device with a low pressure loss and a wide detection range, it is possible to reduce the power source for heating by reducing the factors of error caused by variations in the characteristics of elements and parts Produce an effect.

[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 cross-sectional view showing the structure of the flow detection unit of FIG.

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

FIG. 4 is a graph showing a temperature change of a thermistor of a modified example of the embodiment of 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 a structure of a sensor portion of an electric conductivity measuring apparatus 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]

 1 Microcomputer (MPU) 2 Thermistor 3 AD converter 4 DC power supply device R1 Resistor TR1, TR2 Transistor 10, 20 Holding tool (plug) 11 Piping 12 Screw hole (mounting seat) 21, 22 Underwater electrode

Claims (3)

[Claims] 1. A thermistor arranged in a fluid to be measured, an energizing means for energizing the thermistor to heat the thermistor periodically or intermittently, and a thermistor of the thermistor in relation to the energizing timing of the energizing means. A temperature measuring means for measuring the temperature at predetermined time intervals, and a flow determining means for determining the presence or absence of a fluid flow based on the magnitude of the temperature change of the thermistor at the predetermined time intervals. Fluid flow detector. 2. A fluid electrical conductivity measuring device comprising the fluid flow detecting device according to claim 1, wherein the thermistor is used for water temperature measurement during electrical conductivity measurement, and
The thermistor and the underwater electrode of the electric conductivity measuring device
An electric conductivity measuring device characterized by being arranged on one plug. 3. A thermistor is arranged in a fluid to be measured, the thermistor is heated periodically or intermittently, and a temperature change within a predetermined time of the thermistor is measured in relation to the timing of the heating. A method for detecting a fluid flow, which comprises detecting the presence or absence of a fluid flow based on the magnitude of a temperature change measurement value.