JPS5952718A - Method and device for liquid level detection - Google Patents

Abstract

PURPOSE:To employ an external detection type and to improve reliability, by detecting a temperature difference generated at one side of a metallic level tube between a high and a low liquid level when a specific heating area at the other end of the metallic level tube is heated, and confirming the presence of liquid level in the heating area. CONSTITUTION:The temperature difference is generated between the wall position of the metallic level tube 6 at a vapor part O and the wall position of the metallic level tube 6 at a liquid part L. Therefore, thermocouples 9 and 10 are connected at the same polarity to a detection terminal A on the wall surface of the vapor part O and the detection terminal B on the wall surface of the liquid part L, and then electromotive force is generated between one-side terminals C and D of the thermocouples 9 and 10. When the liquid part L is a freon refrigerant, the vapor part O is saturated vapor and the liquid part L is saturated liquid. Consequently, the heating value of an electric heater 8 from the metallic level tube 6 to the saturated vapor (freon) is observed as it is. The heating value of the electric heater 8 from the wall of the metallic level tube 6 to the saturated liquid is observed as latent heat.

Description

[Detailed Description of the Invention] The present invention detects whether or not there is a liquid level that fluctuates up and down within a predetermined level range of metal level pipes, particularly metal level pipes drawn from each ψ liquid storage tank, etc. in parallel. This invention relates to a liquid level detection method used for the purpose of and a device directly used for its implementation.

Conventional liquid level detection devices installed in various types of liquid storage tanks are internal detection types with a detection part built into the tank, and are not adversely affected by the pressure inside the tank, the pH of the stored liquid, or external temperature changes. It is difficult to perform maintenance and maintenance, requiring double checks inside and outside, and those that use ultrasonic waves as a detection means can cause major damage to the equipment, have high equipment costs, are low in reliability, and are vulnerable to changes in external conditions. Furthermore, if the liquid storage tank is installed in a device that is subjected to vibrations or shocks during operation, it is not applicable at all.

In view of the above conventional drawbacks, the present invention aims to provide a liquid level detection method and device that can be of an external detection type, is resistant to changes in internal and external conditions, is highly reliable, has a compact design, and has a low equipment cost. It is something to do.

An embodiment of the device of the present invention will be described with reference to FIG.

Metal level pipes with good thermal conductivity, such as copper, are drawn out in parallel on one side, and the upper and lower outlet and inlet sides are branched and connected to the liquid supply pipe and drain pipe through the throttle valve and the upper and lower outlet and inlet sides, respectively. An electric heater ♂, which is connected to the separately provided detector 7, is glued to one side of the upright part of the metal level tube O, and a pair of thermocouples are connected to the inside of the storage tank 3. .

10 is connected to the detector 7 at one end, and the other ends are connected with opposite polarity to form each detection end A.

A metal level tube B corresponding to the electric heater g is attached above and below the other side of the metal level tube B in the predetermined area at intervals, and a power source E for operating the detector 7 is connected to the metal level tube B. Note that when the power source E is AC, it may be converted to DC via a rectifier (not shown).

As shown in FIGS. 2 and 3, the detector 7 includes a pair of thermocouples, an input terminal T+ for inputting/outputting a temperature difference detection signal SI from 10, an input section/T2, and an on/off switch SW. /, a reference potential setting section /2 which is configured by a constant power source E1 and a variable resistor VR that separately sets a reference potential, e.g., oy~5■, and generates a reference potential signal s2; A comparator/3 that simultaneously inputs and compares the difference detection signal 81 and the reference potential signal S2 and outputs the potential difference detection signal S3 only when the temperature difference detection signal 81 has a higher potential than the reference potential signal S2, and the potential difference detection signal S3. Transistors Tr+ and Tr2 and resistors R1 and R2 respectively amplify the input
and power supplies E2 and Ex, each of which has a two-stage width amplification part /lA of, for example, about 6 mm, and an amplified potential difference detection signal S4 from the said widening part /ll-. Output terminals Ts, T+ that issue operation command signals S5 to various output devices (not shown) such as lighting lamps, buzzers, meters, etc.
and an output section /j.

G in the figure is ground.

An embodiment of the method of the invention will now be described with reference to FIGS. 1 and 4.

The tank liquid level L1 appears in the metal level tube A as the same horizontal level liquid level L2.

As shown in Figure 4, since the thermal conductivity of the steam section 0 is smaller than that of the liquid section (generally about 2 degrees), the amount of heat from the electric heater is The metal level pipe in the steam part O is easily stored in the wall part, and the metal level pipe in the liquid part is difficult to be stored in the wall part O.

In this way, a temperature difference occurs between the second wall of the metal level pipe in the steam section 0 and the second wall of the metal level pipe in the liquid section.

Therefore, if the thermocouple 10 is connected with the polarity as shown in FIG. , p generates an electromotive force.

Here, when the liquid part is a fluorocarbon refrigerant, the vapor part 0 is saturated vapor, and the liquid part is saturated liquid. For this reason, the amount of heat given to the saturated steam (Freon) by the metal level tube B by the electric heater is observed as heat-sensitive. The amount of heat given by the electric heater to the saturated liquid from the wall of the metal level tube is observed as latent heat. Thus, in the case of fluorocarbon refrigerant, the thermal conductivity is poor in the vapor part 0, and since the change is heat-sensitive, the rate of temperature change (rate of rise) on the wall of the metal level tube is large, and the temperature easily approaches the temperature of the electric heater g. The thermal conductivity in the liquid part is about 10 times higher than that in the steam part 0, and since it is a change in latent heat, the rate of temperature change (rate of rise) of the metal level pipe O wall in contact with the liquid part is higher than that in the steam part 0. The temperature change rate is negligible compared to the temperature change rate of the metal level pipe A wall surface that is in contact with the metal level pipe. In this way, the temperature difference between the metal level tube A wall surface in contact with the refrigerant vapor and the metal level tube A wall surface in contact with the refrigerant liquid is rapidly provided by the electric heater ♂. As a result, it is possible to determine whether or not the refrigerant liquid level L2 exists between the detection ends A and B in a short time and with high sensitivity.

In short, the method of the present invention, when heating a predetermined heating area on one side of the metal level tube B where the liquid level L2 fluctuates internally due to the difference in thermal conductivity between gas and liquid, the metal level tube B above and below the liquid level L2 is heated. The temperature difference occurring on the other side is detected, and the liquid level L is placed in the heating area.
2.Therefore, the difference in electromotive force between detection ends A and B is input to the detector 7 as a temperature difference detection signal S1, and the amplification part/4L
The potential difference detection signal S3 is amplified at the output section /j
It can be extracted as the operation command signal S5. Therefore, when the temperatures of detection ends A and B are equal, the temperature difference detection signal 81 is not emitted, and the liquid level L2 does not exist in the heating region. is the liquid level L
It becomes possible to determine that there are 2.

In the embodiment of the present invention, an electric heater r is used as the heating means.
Although resistance heating is used, the present invention is not limited to this, and other heating methods such as electronic heating and induction heating may also be used.

As described above, in the present invention, the temperature of the wall surface of the metal level tube 6 is set to a value near the r section of the electric heater that heats the liquid level L2 through the metal level tube B wall, because the area near the r section is absorbed by the liquid part as latent heat. It does not rise further. Conversely, heating to the steam section ○ is
It is absorbed as heat sensitive, and the heat transfer resistance is large, so the steam part O
The temperature of the wall surface of the metal level pipe O which is in contact with continues to rise until the temperature of the electric heater ♂. For this purpose, thermocouples are installed on the wall of the metal level tube A part in contact with the liquid part and the metal level pipe A part in contact with the steam part O, and 10 are connected to each other with opposite polarity to detect the detection ends A and B. When attached, a potential difference is created. By directly extracting and amplifying this change in potential difference, the liquid level L2
It can be determined whether or not it is within the monitoring level.

And since the present invention can be detected from the outside, the liquid storage tank 3
It is unaffected by the internal pressure, the pH of the liquid, etc., and detects temperature differences, so it is not affected by the external temperature, and the sensitivity can be adjusted.When the liquid level Ll in the liquid storage tank 3 has large ripples. Since fluctuations in the liquid level L1 can be integrated by adjusting the throttle valve ≠ and j, the ripples of the liquid level L2 in the metal level tube O can be made small, making it less susceptible to external disturbances, and all electrical components are made of semiconductors. It has a long lifespan and can be used for monitoring from a distance of up to 500 m in general use.

As a result, the present invention exhibits excellent effects such as being conveniently applicable to various liquid storage tanks such as liquid receiving tanks of refrigerators, hydraulic tanks of hydraulic machines, and fuel tanks of bulldozers and the like.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram showing an embodiment of the apparatus of the present invention, FIGS. 2 and 3 are block diagrams and wiring circuit diagrams showing the configuration of a detector, and FIG. 4 is an explanatory diagram of the method of the present invention. X...Liquid level detection device A, B...Detection end L+
, L2...Liquid level /...Liquid supply pipe No...Drainage pipe 3...Liquid storage tank ≠,! ...Shibori 9 valves...
・Metal level tube 7...Detector and...Electric heater, 10...Thermocouple //...Input section /2
...Reference potential setting section/3...Comparison section/l...Width increasing section /j...Output section S1...Temperature difference detection signal S
2...Reference potential signal S8...Potential difference detection signal S4
... Increased potential difference detection signal S5 ... Operation command signal

Claims (1)

[Claims] 1. When a predetermined heating area on one side of a metal level tube whose liquid level fluctuates internally due to the difference in thermal conductivity between gas and liquid is heated, the other side of the metal level tube above and below the liquid level A liquid level detection method 2 comprising detecting a temperature difference occurring in the heating area and confirming the presence of the liquid level in the heating area, wherein the metal level tube is made of copper having good thermal conductivity, as set forth in claim 1. The liquid level detection method 3 according to claim 1 or 2, wherein the heating is any one of resistance heating, induction heating, and electronic heating. An electric heater is attached to one side of a metal level tube that communicates the top and bottom of the drawer with the inside of the liquid storage tank, and one end of a pair of thermocouples is connected to a detector on the other side, and the other ends are connected in opposite directions to each other. The liquid level detecting device 5 is connected with the polarity of , and has detecting ends installed at intervals above and below corresponding to the electric heater, and the metal level tube has throttle valves interposed on the inlet side and the outlet side, respectively. The liquid level detection device 6 according to claim 4, which consists of a detector, includes an input section for inputting a temperature difference detection signal from a pair of thermocouples, and a reference voltage for setting a reference potential and emitting a reference potential signal. At the same time, the temperature difference detection signal and the reference potential signal from the input section are input and compared with the attached foot, and only when the temperature difference detection signal has a higher potential than the reference potential signal, the potential difference is detected and one word is output. A patent consisting of a comparison section that outputs an output, an amplification section that inputs and amplifies the potential difference detection signal, and an output section that inputs the amplified potential difference detection signal from the amplification section and issues an operation command signal to various output devices. Claim 4 or 5
Liquid level detection device described in section