JPH044980Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] The present invention is a liquid level measurement method in which a resistor is immersed in a liquid filled in a container, and the level of the liquid is measured from the resistance value of this resistor. It is related to the device.

[Conventional technology]

The conventional liquid level measuring device using a resistor is the third type.
The configuration is shown in Figure a. In the figure, a container 1 is filled with a liquid 2, which is an object to be measured, up to a liquid level H. A resistor _R1 is immersed in this liquid 2, and a constant current is supplied to it by a constant current source _I1 . The resistor R ₁ is heated by the constant current source I ₁ , and the heat generated from the resistor R ₁ is radiated from the surface of the resistor R ₁ to the surroundings. At this time, the degree of heat radiation is greater in the liquid 2 than in the air. Resistor R ₁ generally has positive temperature characteristics. Therefore, in the portion where the resistor _R1 is immersed in the liquid 2, the temperature rise of the resistor due to heating is low, and the resistance value becomes small. On the other hand, in parts exposed to the air, the temperature rise is large and the resistance value becomes large. Therefore, as the proportion of the portion immersed in the liquid 2 with the resistance value R ₁ increases, the total resistance value of the resistor R ₁ becomes smaller, and since a constant current is supplied to the resistor R ₁ , The terminal voltage V across the resistor R value becomes low. That is, as shown in FIG. 3b, the terminal voltage V becomes a function of the liquid level H. Therefore, by measuring this terminal voltage V, the liquid level H can be detected.

[Problem that the invention attempts to solve]

However, in such a conventional device, in order to increase the measurement sensitivity, it is necessary to increase the liquid level H of the liquid 2.
It is necessary to increase the change in the terminal voltage V of the resistor _R1 with respect to the change in . For this reason, the resistor _R1 is made of a metal with a large resistance temperature coefficient, such as nickel. However, such resistors also become more sensitive to changes in the temperature around which the liquid level is being measured, and the resistance value fluctuates due to these temperature changes, reducing the accuracy of measuring the liquid level. do.

Therefore, in view of the above-mentioned conventional problems, the present invention aims to provide a liquid level measuring device in which the measured value of the liquid level does not fluctuate due to changes in ambient temperature. .

[Means for solving problems]

In order to achieve the above object, the liquid level measuring device according to the present invention has a first resistor for measurement, which increases or decreases the proportion of the part immersed in the liquid depending on the level of the liquid in the container. and a second resistor for temperature compensation, which has the same shape, dimensions, same temperature characteristics, and resistance value as the first resistor, and is arranged so that the entire body is always in the air or in the liquid. and a constant current that causes a constant current to flow through the first resistor from its upper end to the lower end, and a constant current that has the same magnitude as the current that flows through the second resistor. source, a terminal voltage generated across the first resistor, and a terminal voltage generated across the second resistor to a voltage that is always smaller or larger than the terminal voltage of the first resistor. The present invention is characterized by comprising a calculation means that calculates the difference between the converted voltage and outputs a signal that continuously changes depending on the liquid level.

[Effect]

In the above configuration, the first resistor and the second resistor have the same shape and dimensions, the same temperature characteristics, and the same resistance value, and the same constant current is passed through these resistors by the constant current source. Therefore, the terminal voltage of the second resistor for temperature compensation, which is completely disposed in air or liquid at all times, is a resistance that depends on the temperature due to constant current application and the temperature of the surrounding air or liquid. On the other hand, the terminal voltage of the first resistor for measurement, in which the proportion of the part immersed in the liquid increases or decreases depending on the liquid level, depends on the temperature and ambient temperature due to the application of a constant current. In addition to the temperature of the air and liquid, it corresponds to the resistance value that depends on the temperature when heat radiation has progressed by the amount of immersion in the liquid, or the temperature when heat radiation has not progressed by the amount not immersed in the liquid. .

Therefore, the signal that is output by the arithmetic circuit by calculating the difference between the terminal voltage of the first resistor and the voltage obtained by converting the terminal voltage of the second resistor, which corresponds to the level of the liquid, is as follows. It does not include components caused by temperature changes, and changes only according to the liquid level.

In particular, since the first resistor and the second resistor have the same shape and dimensions, the same temperature characteristics, and the same resistance value, and the same constant current is passed through them, the terminals of both resistors are Compensation for ambient temperature fluctuations can be easily performed on the basis of voltage.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, a resistor _R1 for measuring the liquid level is immersed in a liquid 2, and a constant current _I1 is supplied from a terminal a. Further, a temperature compensating resistor R ₂ having the same shape and dimensions as the resistor R ₁ is arranged at a position symmetrical to the resistor R ₁ with respect to a plane perpendicular to the level of the liquid 2 .
This resistor _R2 has the same positive temperature characteristics and resistance value as the resistor _R1 , and a constant current having the same current value as the constant current source _I1 is supplied from the constant current source _I2 through the terminal b. ing. Further, the resistor R ₂ is not immersed in the liquid 2 but is constantly exposed to the air. In the configuration shown in FIG. 1, resistors R ₁ and R ₂ are loaded into the protective tube 3,
A hole is provided in the lower surface of the protective tube 3 of the resistor R ₁ to introduce the liquid 2, and the lower surface of the protective tube 3 of the resistor R ₂ is sealed to prevent the liquid 2 from being introduced. Note that the other terminals c and d of each resistor R ₁ and R ₂ are grounded, respectively. a of resistor _R1
The terminal voltage V ₁ obtained at point B is supplied to the positive phase input of the differential amplifier (arithmetic circuit) OP, and the terminal voltage V ₂₀ obtained at point b of resistor R ₂ is divided by resistors R ₃ and R ₄ . , the divided voltage V ₂₁ is supplied to the negative phase input of the differential amplifier OP.

In such a configuration, the terminal voltages of the measuring resistor R ₁ to which a constant current is supplied for each liquid level H ₁ and H ₂ are as shown in the liquid level characteristics and ambient temperature characteristics shown in FIG. In other words, the ambient temperature T is T ₁
As the voltage increases from T ₂ to T 2 , the terminal voltage V ₁ increases. This is because the resistance value of the resistor R ₁ has a positive temperature characteristic and changes depending on the temperature of the air in the exposed portion and the temperature of the liquid 2 .

On the other hand, the compensating resistor _R2 , which is always placed in the air, is also supplied with a constant current of the same current value as the resistor _R1 , and since both resistors have the same shape and dimensions, The change in the terminal voltage _V20 with respect to the ambient temperature is the liquid level H of the measuring resistor _R1 .
= 0, that is, the temperature change is the same as the terminal voltage V ₁ when the resistor R ₁ is not immersed in the liquid 2.
In other words, if the ambient temperatures at the resistors R ₁ and R ₂ are the same, the terminal voltages will be the same.

Therefore, the terminal voltage V ₂₀ of the compensation resistor R ₂ is
The voltage V ₂₁ divided by R ₃ and R ₄ is always applied to the measurement resistor.
If it is set to a value lower than the terminal voltage V ₁ of R ₁ , the voltage V ₂₁ has a characteristic that depends only on the ambient temperature, so the terminal voltage will be reduced by the differential amplifier OP.
If we take the difference between V ₁ and voltage V ₂₁ , the output voltage V ₀ is independent of the ambient temperature, as shown in Figure 2.
It becomes a function only for the liquid level H, and temperature compensation can be achieved. Therefore, if the liquid level H is constant,
Differential amplifier OP output voltage even when ambient temperature changes
Since V ₀ does not change, it is possible to accurately measure the liquid level.

In the above embodiment, the resistor R ₂ for temperature compensation was constructed so as to be exposed in the air at all times, but it was constructed so that the entire resistor R 2 was always immersed in the liquid 2 to obtain the voltage for temperature compensation. You can.

Further, although the voltage V ₂₁ is set to always have a value lower than the voltage V ₁ , it may be set to always have a value higher than the voltage V ₁ .

Furthermore, as an arithmetic circuit, the terminal voltage V ₁ of the measuring resistor R ₁ is inverted at a predetermined reference level, and the compensation voltage V ₂₁ obtained from this inverted voltage and the terminal voltage V ₂₀ of the compensation resistor R ₂ is calculated. It may be configured to add .

[Effect of idea]

As described above, according to the present invention, when measuring the liquid level of a liquid to be measured, it is possible to improve the accuracy of measuring the liquid level without being affected by changes in ambient temperature.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the liquid level measuring device according to the present invention, FIG. 2 is a diagram showing the liquid level characteristics and temperature characteristics of the detection voltage and terminal voltage of the resistor in the device shown in FIG. FIGS. 3a and 3b are diagrams showing a conventional liquid level measuring device and the liquid level characteristics of its detection voltage, respectively. _R1 ...Resistor for liquid level measurement, _R2 ...Resistor for temperature compensation, _I1 , _I2 ...Constant current source, OP...Differential amplifier, 2...Liquid.

Claims (1)

[Claims for Utility Model Registration] A first resistor for measurement whose proportion of the portion immersed in the liquid increases or decreases depending on the level of the liquid in the container, and a shape identical to the first resistor. - A second resistor for temperature compensation, which has the same dimensions, the same temperature characteristics, and the same resistance value, and is arranged so that the entire body is always in the air or in the liquid, and its upper end is connected to the first resistor. a constant current source that flows a constant current from the to the lower end toward the lower end, and that flows a constant current that is the same magnitude as the current that flows through the first resistor through the second resistor, and both ends of the first resistor. and a voltage obtained by converting the terminal voltage generated across the second resistor to a voltage that is always smaller or larger than the terminal voltage of the first resistor, 1. A liquid level measuring device comprising: arithmetic means for outputting a signal that continuously changes according to the liquid level.