JP2503288Y2 - Liquid level detector - Google Patents

Description

[Detailed Description of the Invention] (Industrial field of application) The present invention relates to a liquid level detection device for detecting the liquid level of a drain pan of an air conditioner by utilizing the resistance change of a temperature detection element, and particularly to the liquid level detection. Concerning measures to control the deterioration of accuracy.

(Prior Art) Conventionally, as a liquid level detection device for detecting the liquid level position,
For example, as disclosed in Japanese Patent Application Laid-Open No. 60-194319, a thermistor as a temperature detecting element and a measuring means for measuring the electric resistance value of the thermistor are provided, and it is used that the electric resistance value of the thermistor changes with temperature. Then, there is known a liquid level detection device which detects whether the temperature detection element is in liquid or gas based on the resistance value of the temperature detection element.

As an application of this type of liquid level detection device, for example, as disclosed in JP-A-60-14125, a temperature detection element attached to a train pan of an air conditioner and application of a pulse voltage having a constant width. And a heating means for heating the temperature detecting element by means of the heating means, and measuring the temperature deviation between the temperature detecting element temperature at the start of heating and the temperature detecting element temperature at the end of heating with respect to the temperature detecting element by the heating means. There is a method in which the position of the liquid surface with respect to the temperature detecting element is detected by comparing with a predetermined threshold value for gas-liquid determination, and the liquid surface position of the drain pan is held at an appropriate position.

(Problems to be solved by the invention) By the way, when the temperature dependency of the resistance value of the temperature sensing element is used for liquid level sensing, the temperature sensing element temperature changes depending on the temperature of the environment itself in which the temperature sensing element is installed. Therefore, according to the former publication, the usable environmental temperature range is limited.

On the other hand, in the latter publication, a constant pulse voltage is used by utilizing the fact that the heat dissipation amount of the temperature detecting element is different depending on the environment around the temperature detecting element, that is, whether it is in liquid or gas. It is intended to measure the change in temperature of the temperature sensing element with respect to time when a voltage is applied.In this case, since it does not depend so much on the difference in the absolute value of the ambient temperature, it can be measured over a wide range of environmental temperatures. It can be used.

However, depending on the place where the temperature detecting element is installed, the amount of heat radiation may change in a certain time even in the same fluid due to the forced flow of liquid or gas. For example, when a strong wind is directly exposed outdoors as in the latter publication, the amount of heat radiation increases due to the increase in heat transfer coefficient, and the temperature sensing element shows a smaller temperature deviation than in the standard condition. In particular, when the wind is extremely strong, the temperature deviation in the air may be equal to or less than the threshold value for determining the liquid surface position, which may cause erroneous detection of the liquid surface position.
Also, when the liquid flow is vigorous, the temperature changes in a direction that decreases, so the temperature deviation in the liquid does not exceed the threshold value, but on the other hand, the liquid surface position is wavy and the accurate liquid surface The problem may be that the position cannot be detected. Moreover, since the flow of such a fluid as air is not always constant, correction is usually difficult. Therefore, the above-mentioned conventional device has a problem that the liquid surface position cannot be accurately detected when there is such a change in the flow of liquid or gas.

The present invention has been made in view of such a point, and an object thereof is to suppress a decrease in liquid level detection accuracy by providing an appropriate means for blocking a flow other than convection based on a fluid temperature difference. To do.

(Means for Solving the Problems) In order to achieve the above object, the solution means of the present invention has a characteristic that the electric resistance value changes with temperature, as shown in FIG. A self-heating type temperature detecting element (4) to be heated, and the temperature detecting element (4)
A heating means (20) for intermittently heating
The liquid level detection device is adapted to detect the liquid level of the drain pan of the air conditioner based on the temperature change of the temperature detection element (4).

The temperature detecting element (4) is arranged in the tubular cap (2) that blocks the forced flow of liquid and gas from the surroundings and near the lower end of the tubular cap (2). To do.

Further, the upper end of the cylindrical cap (2) is closed so as to prevent the inflow of liquid from above, and the lower end thereof is opened so as to allow the propagation of natural convection based on the temperature difference between the liquid and the gas. The inside of the cylindrical cap (2) is ventilated so that the liquid level can be moved into the cylindrical cap (2) on the side wall of a predetermined height above the position where the temperature detecting element (4) of the cylindrical cap (2) is arranged. The ventilation hole (2e) is provided.

(Operation) With the above configuration, in the present invention, the temperature detecting element (4) is, for example, intermittently heated by the heating means (20),
Based on the temperature change, it is determined whether the temperature detecting element (4) is in liquid or in gas, and the liquid surface position of the drain pan of the air conditioner is detected.

In that case, the temperature sensing element (4) is replaced by the tubular cap (2).
Since it is installed inside and the forced flow of gas is shut off, the amount of heat released from the temperature detecting element (4) into the gas for a certain period of time is almost constant. In addition, since the forced flow of liquid from the surroundings is also blocked, the liquid surface is kept substantially horizontal without being disturbed. Further, since the lower end of the cylindrical cap (2) is opened and the propagation of convection caused by the temperature difference of the fluid is allowed, the heat is smoothly radiated from the temperature detecting element (4) to the surroundings. Therefore, there is a clear difference depending on whether the temperature change of the temperature detecting element (4) is in liquid or gas.

On the other hand, since the upper end of the tubular cap (2) is closed, even if the liquid is installed in a place where the liquid drops and flows down from above, such as the drain pan of the air conditioner, the liquid remains at the temperature detecting element (4). ), There is no erroneous detection such as determining that the liquid level has risen. Further, since the ventilation hole (2e) is provided at a predetermined height above the position where the temperature detecting element (4) of the tubular cap (2) is disposed, the liquid level in the tubular cap (2) is increased. Is not obstructed, the liquid level position according to the change in the surrounding liquid amount is maintained, and the detection accuracy of the liquid level position is not adversely affected.

Therefore, the temperature sensing element (4) is used to perform accurate liquid level sensing.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows the overall structure of a liquid level detecting device according to an embodiment of the present invention. (1) is a liquid level detecting device for controlling a liquid level attached to a drain pan (not shown) of an air conditioner. The liquid level sensor (1) includes a cylindrical casing (1a) made of stainless steel and a flange portion (1b) expanded in a flange shape. The inside of the tip of the casing (1a) of the liquid level sensor (1) is a self-heating type thermistor made of a semiconductor as a temperature detecting element having a characteristic that an electric resistance value changes with temperature, as shown in enlarged detail in FIG. (4), glass beads (5) obtained by hardening the thermistor (4) inside, and an adhesive portion (7) made of epoxy resin or urethane resin for fixing the entire glass bead (5) to the bottom of the casing (1a). ) And is composed of. Lead wires (8) and (8) are connected to the two terminals of the thermistor (4), respectively, and these two lead wires (8) and (8) extend upward and are located above the casing (1a). Is connected to the main body of the device through an upper surface of a windshield cap (2) described later, and a current signal for detecting voltage application from the main body of the device to the thermistor (4) and temperature of the thermistor (4) can be transmitted.

Next, (2) is a windshield cap that is a cylindrical cap for surrounding and holding the liquid level sensor (1), and the windshield cap (2) is the same as the liquid level sensor (1). Formed by a cylindrical tube main body (2a) having an inner diameter substantially equal to the outer diameter of the flange portion (1b), and a flat plate-shaped mounting portion (2b) protruding from the upper half of the cylindrical main body (2a). It is mounted vertically in the drain pan. The upper portion of the windshield cap (2) is closed by an upper lid (2f) so that the forced flow of air cannot be propagated except the portion where the lead wire (8) penetrates, and the upper lid (2f). And tube body (2
Due to a), the forced flow of liquid or air to the liquid level sensor (1) is blocked.

On the other hand, at the lower end of the windshield cap (2), the cylinder body (2
A circular lower opening (2g) is formed by cutting a) horizontally and the lower opening (2g) allows the thermistor (4) of the liquid level detection sensor (1) and the liquid (mainly in the drain pan) Propagation of convection based on the temperature difference between water) or gas (mainly air) is allowed.

Further, the flange portion (1b) of the liquid level sensor (1)
Is fixed to the inner peripheral surface of the cylinder body (2a) of the windshield cap (2) by the upper and lower resin adhesive portions (9a) and (9b), and the portion directly below the lower resin adhesive portion (9b), that is, the thermistor. Above the predetermined height of (4), two ventilation holes (2e), (2e) formed by opening a part of the cylinder body (2a) in a rectangular shape are provided at positions of 180 degrees with respect to each other. The two ventilation holes (2e), (2e)
Thus, the inside of the cylindrical cap (2) is vented so as not to hinder the movement of the liquid level in the cylindrical cap (2) when the liquid level in the drain pan moves upward or downward.

In addition, (2c) is a mounting hole provided in the mounting portion (2b) of the windshield cap (2), and (2d) is provided directly above the upper resin bonding portion (9a) to discharge the drain leaked from above. It is a drain port for.

Next, FIG. 3 shows a schematic configuration of the main body of the apparatus, (10) is a constant voltage power supply for supplying a constant voltage power to the entire apparatus
(12) is a timer circuit that outputs a synchronization time signal according to the output of the built-in timer, and (11) is the timer circuit (1
A switching circuit for outputting a constant voltage from the constant voltage power supply device (10) as a pulse signal having a predetermined width in accordance with the synchronization time signal of 2), the constant voltage power supply (10),
The timer circuit (12), the switching circuit (11) and the thermistor (4) themselves constitute a heating means (20) for intermittently heating the thermistor (4).

Next, (13) is an A / D converter that receives the analog current signal from the thermistor (4) and converts it into a digital signal,
(14) receives the signal from the A / D converter (13), and in accordance with the synchronization time signal from the timer circuit (12), a CPU for calculating the thermistor temperature at every predetermined time, (15) The C
It is a RAM that stores intermediate data and the like according to the calculation of the PU (14).

Further, (16) is a ROM that stores basic data and the like necessary for determining the liquid surface position, and the ROM (16) has a standard temperature when a constant voltage is applied to the thermistor (4). Based on the change characteristics, the threshold value for judging whether or not it is in the liquid, which is obtained from the temperature deviation between the thermistor temperature at the heating start time and the thermistor temperature at the heating end time in water and in air, is used as basic data in advance. It is stored for each temperature condition.

Further, (17) compares the threshold value stored in the ROM (16) with the temperature deviation calculated by the CPU (14) to determine whether the liquid surface position is above or below the thermistor (4). It is a comparator for judging.

That is, when an intermittent pulse signal is output from the switching circuit (11) to the thermistor (4), the thermistor (4) generates heat due to its self-heating action, depending on its own heat capacity and cooling by surrounding substances. Change in temperature
After that, when the application of the voltage ends, a temperature drop occurs in accordance with the heat capacity of itself and the cooling by the surrounding material from the temperature rise value corresponding to the heating amount until then, and when the application of the next voltage is started, The basic cycle of temperature change is repeated to return the temperature to almost the same value as the initial temperature. The temperature change signal of the thermistor (4) is the A / D converter (13).
Is converted to a digital signal by the CPU (14),
Based on the synchronization time signal from the timer circuit (12), the thermistor temperature at the pulse voltage application start time is captured and temporarily stored in RAM (15), and then the thermistor temperature at the pulse voltage application end time is captured. Then, the temperature deviation between the thermistor temperatures at both times is calculated. Further, the comparator (17) compares the temperature deviation with a threshold value stored in the ROM (16) in advance as a criterion for judging which of liquid and liquid exists, and the position of the liquid surface is detected. Will be. A pump (not shown) for discharging the water in the drain pan when the liquid surface position is above the thermistor (4) according to the output of the comparator (17).
Is activated and the liquid level is below the thermistor (4), the pump is controlled to stop, and the liquid level is held at an appropriate position.

Therefore, in the above embodiment, since the thermistor (4) is heated and the liquid surface position is detected from the temperature change at the predetermined time difference, the influence of the change in the resistance value of the thermistor (4) due to the difference in the liquid temperature is affected. Can be almost ignored, and the function can be exerted over a wide temperature range of the liquid.

In that case, in the above-described embodiment, since the forced flow of air to the thermistor (4) is blocked by the windshield cap (2), even if a strong flow is generated in the surrounding gas, a constant flow is maintained. A change in the amount of heat radiation from the thermistor (4) to the air with respect to time is suppressed. In addition, since the forced flow of liquid from the surroundings is also blocked, the liquid level in the cylinder body (2a) of the windshield cap (2) is kept substantially horizontal without being disturbed. Further, since the lower opening (2g) is provided below the windshield cap (2) to allow the propagation of convection caused by the temperature difference of the fluid, the thermistor (4) can smoothly dissipate heat to the surroundings. Done.

On the other hand, since the upper end of the windshield cap (2) is closed, even if it is installed in a place where liquid drips and flows down from above, such as the drain pan of the air conditioner of the above embodiment,
There is no erroneous detection such that the liquid flows to the temperature detecting element (4) and the liquid level rises. Further, since the ventilation hole (2e) is provided at a predetermined height above the position where the temperature detecting element (4) of the windshield cap (2) is arranged,
The movement of the liquid surface in the windshield cap (2) is not obstructed, the liquid surface position is maintained according to the change of the surrounding liquid amount, and the detection accuracy of the liquid surface position is not adversely affected.

Therefore, the temperature deviation of the thermistor (4) in the air increases and becomes larger than the threshold value due to the increase in the heat radiation amount in the air, as in the conventional thermistor (4) which is exposed to the wind of the outdoors and the like. Since the value that is clearly distinguished from that in the liquid is maintained without causing erroneous detection of the liquid surface position,
The deterioration of the liquid level detection accuracy is suppressed as much as possible.

In order to quantitatively explain the above, as shown in the experimental data of the drain pan of FIG. 4, the one according to the present invention having the windshield cap (2) (the curve of the broken line in the figure) and the conventional windshield cap (2) are shown. In this case, the liquid is usually stationary, so the temperature changes in the liquid are shown by the curves −1 and 1, respectively.
-2, and the difference between the two is slight. On the other hand, when the wind speed is 0.1 m / sec., The temperature changes in the air are as shown by curves -1 and -2 in the figure, respectively, and the conventional one shows a considerable decrease in temperature. And wind speed 3m
/ sec., as shown by curve-2 in the figure,
In the case of the conventional type, a large temperature drop occurs and the value becomes less than the threshold value (ΔC _{D in the} figure), so that the liquid level position is erroneously detected. That is, the amount of heat released by the thermistor (4) changes due to the influence of wind in the air. On the other hand, in the case of the present invention, as shown by the curve -1 in the figure,
The temperature does not drop so much, and the value is maintained well above the threshold. That is, since the forced airflow of the windshield cap (2) is blocked, the change in the amount of heat radiation is suppressed, and the decrease in temperature detection accuracy can be prevented as much as possible.

Further, the application of the present invention is not limited to the detection device for intermittently heating the thermistor (4) as in the above embodiment. FIG. 5 shows another example of the present invention in which the thermistor (4) is continuously heated and the liquid level position is detected from the value of the temperature deviation between the thermistor (4) and the ambient temperature. In case of / sec., the characteristic curve in the figure is
2 ', the temperature deviation of the windshield cap (2) is almost the same as -1' in the figure. When the wind speed is 3 m / sec., The temperature deviation is drastically reduced as shown by -2 'in the figure in the conventional case, and the difference from the temperature deviation in water (-2' in the figure) is extremely small. There is a possibility that it becomes smaller than the threshold (ΔC _{D in the} figure) or less, but with the windshield cap (2) of the present invention, the decrease in temperature deviation is suppressed as in -1 'in the figure. Therefore, there is a sufficient difference from the temperature deviation in water (-1 'in the figure), and the difference is maintained above the threshold value. That is, it is possible to obtain the same effect as that of the above embodiment.

In the above embodiment, the lower opening (2g) of the windshield cap (2) allows convection based on the temperature difference between the water in the tubular cap (2) and the surrounding water, that is, the water in the drain pan. As shown in FIG. 5, the temperature deviation in water does not deviate from an appropriate value by attaching the windshield cap (2).

The position above the thermistor (4) to which the vent hole (2e) of the windshield cap (2) is attached is a predetermined height.
The thermistor (4) is set to such a degree that it is submerged deep enough in the water to make a difference from the temperature deviation in the air.

Furthermore, the position of the lower resin adhesive part (9b) that attaches the flange part (1b) of the liquid level sensor (1) to the windshield cap (2) is inside due to wetting with the inner peripheral surface of the windshield cap (2), that is, capillary action. Is set above the position where the liquid level rises, and the thermistor (4) does not remain submerged in the windshield cap (2) despite the water level of the drain pan dropping.

The temperature detecting element used in the present invention is not limited to the self-heating type thermistor (4) as in the above embodiment, but may be a self-heating type diode, a metal resistor such as platinum, or a heating element. It goes without saying that a so-called indirectly heated thermistor provided with the means (20) separately can be used.

In addition, in the above-mentioned embodiment, in order to prevent the entry of drain or the like into the windshield cap (2) from above, the lead wires (8), (8) above the windshield cap (2) are provided with penetrating portions. May be attached with a cover, and the lead wires (8), (8) may be penetrated at the side surface of the windshield cap (2).

(Effects of the Invention) As described above, according to the liquid level detection device of the present invention, while the forced flow of liquid and gas from the surroundings to the temperature detection element is blocked, the fluid based on the temperature difference is blocked. Since natural propagation of natural convection is allowed, it suppresses the change in the amount of heat released from the temperature sensing element due to the forced flow of liquid and gas, and suppresses the deterioration of the liquid level detection accuracy of the drain pan of the air conditioner. can do.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention, FIG. 1 is a vertical cross-sectional view showing the structure of a liquid level sensor, FIG. 2 is an enlarged vertical cross-sectional view showing a mounting state of a thermistor, and FIG. 3 is a control of a liquid level detection device. FIG. 4 is a circuit configuration diagram of the apparatus, and is experimental data of temperature change due to intermittent heating of the thermistor in gas and liquid.
FIG. 5 shows another example, which is experimental data showing the temperature deviation between the thermistor continuously heated in gas and liquid and the ambient temperature. (2) ... Windshield cap (cylindrical cap), (2e) ... Vent hole, (2g) ... Lower opening, (4) ... Thermistor (temperature detection element), (20) ... Heating means.

Claims (2)

(57) [Scope of utility model registration request] 1. A temperature detecting element (4) having a characteristic that an electric resistance value changes with temperature, and the temperature detecting element (4).
And a heating means (20) for heating the temperature detecting element (4) for detecting the liquid level position of the drain pan of the air conditioner based on the temperature change of the temperature detecting element (4). 4) is disposed in the cylindrical cap (2) that blocks the propagation of the forced flow of liquid and gas from the surroundings, and near the lower end of the cylindrical cap (2). The upper end of the cap (2) is closed so as to prevent the inflow of liquid from above, while the lower end thereof is open to allow the propagation of natural convection due to the temperature difference between the liquid and the gas. The cylindrical cap (2) is provided on the side wall at a predetermined height above the position where the temperature detecting element (4) is arranged.
A liquid level detecting device, characterized in that a vent hole (2e) is provided to allow the liquid level to move inward so as to ventilate the inside of the cylindrical cap (2). 2. The utility model registration claim (1) wherein the temperature detecting element (4) is heated by its own heat generation.
The liquid level detection device according to item.