JP3044791B2 - Container level detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid level detector for a container for detecting the liquid level of a liquid in a container that cannot be seen from the outside such as a metal container.

[0002]

2. Description of the Related Art For example, in a metal hermetic container holding a liquid such as a syrup tank of soft drink or a container of beer, the amount of the liquid inside cannot be seen from the outside. Therefore, if you want to know the amount of liquid in the container easily,
At present, it is inconvenient to pick up a container by hand and obtain a guide from the weight or by shaking the container, or to know that the liquid has run out and then emptied.

There are various liquid level detectors as means for accurately detecting the amount of liquid in such a metal container. However, in the case of a food sealed container which must be frequently replaced, such as the above-described soft drink syrup tank or beer container, the conventional liquid level detector changes the sealed state of the container to replace the sensor. It has to be canceled and cannot be used. Therefore, as a method that can detect the liquid level with the container closed, use a container equipped with a sensor or a communication pipe as a standard, measure the container weight, and predict the liquid level based on the change in weight And other methods.

[0004]

However, the former method is not practical because it is necessary to replace all the metal closed containers which are already widely distributed in the food industry, such as food containers. In the latter, there is a problem that the work of properly placing the container on the weight sensor is required, and the measurement accuracy differs depending on how the operator handles, and thus the accuracy is lacking.

The present invention has been made in view of the above points, and utilizes the difference in specific heat between a gas and a liquid to obtain a boundary surface between a gas and a liquid in an opaque hermetic container such as a metal container (hereinafter referred to as “liquid”). The object of the present invention is to provide a liquid level detector of a container capable of simply and accurately detecting the “surface” from the outside.

[0006]

According to the present invention, there is provided a heating section detachably adhered to a desired position on an outer wall surface of a container holding a liquid therein, and a heating section provided in the heating section. The heating element and the temperature sensing element, and the heating element is controlled to heat the heating unit to a predetermined temperature higher than the temperature of the container detected by the temperature sensing element, and is released from the heating element by the temperature sensing element. And a detection circuit for detecting a temperature change due to a difference in the rate of heat absorption into the container and outputting a signal corresponding to the liquid level.

[0007]

The detection circuit detects the temperature of the container by using a temperature-sensitive element and sets the temperature as a reference temperature. Based on the detected value of the temperature-sensitive element, the heating circuit controls the temperature of the heating section to a predetermined temperature higher than the reference temperature. Control the heating elements of the unit. The rate of absorption of the amount of heat released by the heating element into the container differs depending on the difference in specific heat between liquid and gas, and the detection circuit detects a temperature change due to the difference in the rate of absorption of the amount of heat with a temperature-sensitive element. A signal corresponding to the liquid level in the container is output. Therefore, by activating the alarm etc. by this output signal,
The liquid level in an opaque container such as a metal container can be detected.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail with reference to the accompanying drawings. In FIG. 1, a container 1 is a metal cylindrical container (hereinafter simply referred to as a “metal container”), for example, a beer container, and a liquid level is detected by a belt 2 at a position below the outer wall surface 1 a of the metal container 1. The vessel 3 is attached. The belt 2 has elasticity, for example, a rubber belt 2
a and a buckle 2b fixed to the rubber belt 2a. The liquid level detector 3 is detachably attached to the outer wall surface 1a of the container 1 and is supported by being pressed against the same. In this embodiment, a heating section 5 and a temperature measuring section 6 (FIG. 2) are arranged on the rear surface 4a of the case 4 of the liquid level detector 3 on the left and right sides at the same height and slightly apart. A support pad 7 is provided on the upper part.

As shown in FIGS. 3 and 4, the heating section 5 includes a pad 10, a heat conducting member 11, a heating element 12, and a temperature sensing element 13.
For example, the pad 10 is a heat conductive rubber, the heat conductive member 11 is a heat conductive silicon resin member, the heating element 12 is a heater (hereinafter, referred to as a “heater 12”), and the temperature sensing element 13 is a thermistor (hereinafter, “thermistor”). Thermistor 13 ")
And the like. The surface 10a of the pad 10 which comes into contact with the outer wall surface 1a of the metal container 1 is a curved surface having the same radius as the outer wall surface 1a, and can be in close contact with the outer wall surface 1a. Further, the heater 12 and the thermistor 13 are provided on the substrate 17 and connected to a detection circuit 20 (FIG. 6) described later.

The heat conducting member 11 has one end surface adhered and fixed to the back surface of the pad 10 so as to conduct heat, and the other end surface is fixed to the substrate 17 so as to enclose the heater 12 and the thermistor 13 provided on the substrate 17. The heat generated by the heater 12 is transmitted to the outer wall surface 1a of the container 1 via the pad 10.
That is, the heater 12 indirectly heats the metal container 1 by heating the heat conductive member 11 and the pad 10. Further, the thermistor 13 detects a temperature change of the metal container 1. The heating unit 5 includes a heater 12 and a thermistor 13.
Thus, the predetermined temperature is maintained. The heat conduction member 11
May be formed integrally with the pad 10 to form the pad 10.

The temperature measuring section 6 includes a pad 1 similar to the heating section 5.
4, the heat conduction member 15 and the thermistor 16. The thermistor 16 is sealed in the heat conduction member 15 like the thermistor 13. The temperature measuring section 6 measures the reference temperature of the metal container 1 by the thermistor 16. still,
The heat conducting member 15 may be formed integrally with the pad 14 to form the pad 14. Further, the heating unit 5, the pads 10 and 14 of the temperature measuring unit 6, and the heat conducting members 11 and 15 are formed in the same shape and have the same heat conditions. And the heating unit 5,
The pads 10 and 14 of the temperature measuring section 6 are slightly separated from each other to eliminate thermal interference as described above, and have the same height so that the same conditions are satisfied with respect to the metal container 1. It is arranged side by side in the position. The heater 12 and the thermistor 13 of the heating unit 5 and the thermistor 16 of the temperature measurement unit 6
Are connected to the detection circuit 20 (FIG. 6) provided on the substrate 17. As shown in FIG. 5, the heating unit 5 includes a portion (range) 1a ′ where the pad 10 of the outer wall surface 1a contacts.
Is heated, and the temperature measuring unit 6 detects the temperature of the portion (range) 1b ′ of the outer wall surface 1a where the pad 14 contacts.

As shown in FIG. 6, the detection circuit 20 includes, for example, a bridge circuit 21, a differential amplifier 22, a power transistor Tr, and the like.
Is connected to one adjacent two sides of the bridge circuit 21, the Zener diode ZD is connected to the thermistor 13 in series, and the resistors R1 and R2 are connected to the other adjacent two sides. The zener diode ZD is for heating the heating unit 5 to a temperature higher by a predetermined temperature than the reference temperature of the metal container 1 detected by the thermistor 16. That is, under certain conditions, the surface temperature of the metal container 1 is constant, and the temperature is set to the reference temperature Ts.
In this case, the thermistor 16 of the temperature measuring unit 6 determines that the reference temperature T
s, and the Zener diode ZD detects the set temperature Te.
Is set, for example, to a temperature higher than the reference temperature Ts by + 10 ° C. (hereinafter referred to as “set temperature”).

Thermistor 16 and Zener diode ZD
And a connection point b between the resistors R1 and R2 are connected to respective input terminals of the differential amplifier 22, and an output terminal of the differential amplifier 22 is connected to the base of the power transistor Tr via the resistor R3. And to the output terminal 23. The collector of the power transistor Tr is connected to the power supply Vcc, and the emitter is grounded via the heater 12. Then, the detection circuit 20 detects the temperature (reference temperature) Ts of the metal container 1 by the thermistor 16 and
, The thermistor 13 and the Zener diode ZD always keep the temperature of the heating unit 5 at a set temperature Te (= Ts + 10).
Hold every time.

The liquid level detector 3 is provided with an alarm (not shown), to which an output voltage V of the detection circuit 20 is inputted.
When the voltage V falls below a predetermined level, an alarm is issued. The liquid level detector 3 has a built-in battery (not shown). The support pad 7 is a metal container 1
Each pad 10 of the heating unit 5 and the temperature measuring unit 6 on the outer wall surface 1a of
14 is made laterally long by a dummy pad provided to make good contact, the front surface 7a is a curved surface having substantially the same radius as the outer wall surface 1a, the back surface is fixed to the back surface 4a of the case 4, and Is set to the same height as each of the pads 10 and 14. The support pad 7 is formed of, for example, a normal rubber member. As shown in FIG. 1, the liquid level detector 3 is configured such that the outer surfaces 1a, 14a and 7a of the pads 10, 14 and the support pad 7 are brought into contact with the outer wall 1a at predetermined lower positions of the metal container 1. It is fixed by the belt 2.

The reference temperature may be measured by the thermistor 13 of the heating unit 5. In this case, a circuit for storing the reference temperature may be incorporated. The operation will be described below. Now, the amount of beer in the metal container 1 is large, and the liquid level is the height Ha of the upper ends of the pads 10 and 14 of the liquid level detector 3 in FIG.
And higher. As described above, under the constant temperature condition, the surface temperature of the metal container 1 is constant, and this temperature is set as the reference temperature Ts. Metal container 1
Is transmitted to the thermistor 16 via the pad 14 of the temperature measuring section 6 and the heat conducting member 15, and the thermistor 1
6 changes its resistance value to a value corresponding to the surface temperature Ts. This resistance value is thereafter maintained at a value corresponding to the surface temperature Ts.

In this initial state, the thermistor 13 of the heating unit 5 has the surface temperature Ts similarly to the thermistor 14, and its resistance value is a value corresponding to the temperature Ts. The resistance value of the thermistor 13 gradually changes thereafter. The bridge circuit 21 of the detector 20 (FIG. 6) is 10 degrees C. lower than the respective resistance values of these thermistors 16 and 13 and the surface temperature Ts by the Zener diode ZD.
Difference voltage Δ corresponding to the Zener voltage corresponding to the higher temperature
Generate V. The difference voltage Δ of the bridge circuit 21 at this time
V becomes maximum, and the output voltage V of the differential amplifier 22 becomes maximum. The differential amplifier 22 amplifies the difference voltage ΔV input from the bridge circuit 21, makes the power transistor Tr conductive, and energizes the heater 12. At this time, the heater 12 is supplied with the maximum current required to heat the heating unit 5 to the set temperature Te. As a result, the heater 12 generates heat and heats the heat conductive member 11, the thermistor 13, and the pad 10 to the set temperature Te. The resistance value of the thermistor 13 gradually decreases as the temperature of the outer wall surface 1a 'increases, and becomes a value corresponding to the set temperature Te.

Since the thermal conductivity of the liquid is higher than the thermal conductivity of the gas, if the inside of the metal container 1 corresponding to the outer wall surface 1a 'is liquid, the outer wall surface of the metal container 1
The heat radiation from a 'to the liquid is large. Therefore, in this state, the difference voltage ΔV of the bridge circuit 21 becomes maximum,
The heater current is kept at a maximum, and as a result, the heating unit 5
As shown in FIG. 7, the set temperature Te is maintained at 10 ° C. higher than the reference temperature Ts. Further, the detection circuit 20 outputs the maximum voltage Va as shown in FIG. The detection circuit 20 outputs the maximum voltage Va until the liquid level of the liquid in the metal container 1 decreases to the height Ha at the upper end of the pad 14 as shown in FIG.

When the remaining amount of the liquid (beer) in the metal container 1 decreases and the height H of the liquid surface becomes equal to or less than the height Ha of the pad 10 of the heating unit 5 (FIG. 5), the difference (Ha-H) is obtained. ) The heat radiation from the outer wall surface 1a 'to the inside of the container decreases according to the minute,
Accordingly, the output voltage V of the detection circuit 20 decreases as shown in FIG. 7, and the current supplied to the heater 12 decreases. Therefore, the liquid level in the metal container 1 can be detected by the change of the output voltage V of the detection circuit 20.

Then, the height H of the liquid level in the metal container 1 is
When the height of the lower end of the pad 10 of the heating unit 5 becomes equal to or less than Hb,
Only gas is present in the vicinity of the pad 10 and heat conduction of the gas occurs, so that there is no difference in the rate of absorption of the amount of heat radiated by the heater 12 into the metal container 1. As a result, the output voltage of the detection circuit 20 no longer changes. It becomes constant voltage Vb (FIG. 8). Then, a range ΔH (Ha−Hb) between the height Ha of the upper end of the pad 10 and the height Hb of the lower end of the pad 10 is a measurable range. Note that the case where the liquid level height H changes stepwise is described. This is a change when the liquid in the metal container 1 is intermittently withdrawn.

Although the above embodiment has been described with reference to the case where the set temperature Te is kept constant, heating and cooling may be repeated intermittently after heating to the set temperature Te. The output of the detection circuit 20 is supplied to the alarm contained in the case 4. This alarm indicates that the input voltage V is, for example,
When the liquid level H becomes equal to or lower than a predetermined voltage between the maximum voltage Va and the minimum voltage Vb (FIG. 8) (the liquid level H becomes a predetermined height between the heights Ha and Hb), the operation is performed and an alarm is issued.

By this alarm, the worker can use the metal container 1
The user can know that the liquid (beer) in the tank has become low or empty, remove the belt 2, remove the liquid level detector 3 from the metal container 1, replace the metal container 1 with a new metal container, and then again The liquid level detector 3 is attached to the metal container 1 in the same manner as described above, and is fixed with the belt 2. Thus, the worker can attach and detach the liquid level detector 3 to and from the metal container 1 very easily.

By the way, according to the present invention, the temperature change due to the difference in the rate of absorption of the amount of heat released from the heating element 12 of the sensor 5 into the metal container 1 by utilizing the difference in the specific heat between the gas and the liquid is electrically measured. By evaluating and detecting the liquid level inside,
It detects whether the inside of the metal container 1 near the heating unit 5 and the temperature measuring unit 6 is liquid or gas. Therefore, it is also possible to detect the liquid level in other high-pressure gas cylinders such as IPG and various special gases without being limited to syrup tanks of soft drinks and containers of beer.

In this embodiment, the case where the present invention is applied to a metal container having good heat conductivity as a container has been described.
The invention is not limited to a metal container as long as it is formed of a member having thermal conductivity, and can be applied to, for example, a container formed of an opaque resin member having thermal conductivity.

[0024]

As described above, according to the present invention, a heating section detachably adhered to a desired position on an outer wall surface of a container holding a liquid therein, a heating element provided in the heating section, and a temperature sensing element An element and controlling the heating element to heat the heating unit to a predetermined temperature higher than the temperature of the container detected by the temperature sensing element, and into the container of the amount of heat released from the heating element by the temperature sensing element. And a detection circuit that detects a temperature change due to a difference in absorption rate of the liquid and outputs a signal corresponding to the liquid level. There is an excellent effect that the height can be easily and accurately detected, and the detector can be easily replaced with a new container when replacing the container.

[Brief description of the drawings]

FIG. 1 is a perspective view of a metal container equipped with a liquid level detector according to the present invention.

FIG. 2 is a rear view of the liquid level detector shown in FIG.

FIG. 3 is a cutaway side view of a main part of FIG. 1;

FIG. 4 is a sectional view taken along the line IV-IV in FIG. 3;

5 is a diagram showing a relationship between a liquid level and a heating unit and a temperature measuring unit in FIG. 3;

FIG. 6 is a circuit diagram showing one embodiment of a detection circuit of the liquid level detector of FIG. 1;

FIG. 7 is a diagram showing a temperature change in the vicinity of a heating section on the outer wall surface of the metal container of FIG. 3;

FIG. 8 is a diagram showing a change in an output voltage of a detection circuit according to a change in the liquid level in FIG. 5;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal container 2 Belt 3 Liquid level detector 4 Case 5 Heating part 6 Temperature measuring part 10, 14 Pad 11, 15 Heat conduction member 12 Heating element (heater) 13, 16 Temperature sensing element (thermistor) 20 Detection circuit

Claims (1)

(57) [Claims] 1. A heating section detachably attached to a desired position on an outer wall surface of a container holding a liquid therein, a heating element and a temperature sensing element provided in the heating section, and a container detected by the temperature sensing element. Controlling the heating element to heat the heating section to a predetermined temperature higher than the temperature, and detecting a temperature change due to a difference in absorption rate of the amount of heat released from the heating element into the inside of the container by a temperature-sensitive element. And a detection circuit for outputting a signal corresponding to the liquid level.