JPS62255822A - Liquid level sensor - Google Patents

Abstract

PURPOSE:To obtain high detection accuracy by a simple amplifier, by utilizing positively a self-heating effect which is generated at the time of allowing a current to flow to a resistance, making a variation of an output voltage large in amplitude at the time a liquid level sensor has come out to the outside of a liquid becomes large. CONSTITUTION:An inner cylinder 2 is installed to the inside of an outer cylinder 1 of a Dewer type cooler. A liquid level sensor 3 is inserted into this inner cylinder 2, and its outside end is connected to an amplifying circuit 4. In the inner cylinder 2, liquid nitrogen 7 being a refrigerant is contained. A liquid level A descends as the nitrogen evaporates, and reaches a liquid level B of a caution level. The liquid level sensor 3 is places so that its lower end comes right above the liquid level B. To a sensor element, an excessive current exceeding a prescribed value of a current which is allowed to flow in case said element is used as a temperature sensor is allowed to flow. That is to way, according to this sensor 3, the self-heating effect which is generated at the time of allowing a current to flow to a resistance thereby is raised. According, when the sensor 3 has come out to the outside of a liquid, a large voltage variation can be fetched.

Description

[Detailed Description of the Invention] L1 Tachidan Aoi (Industrial Application Field) The present invention is suitable for use in infrared detection devices, etc. in which a liquid refrigerant is placed in a dewar-type cooler to cool an infrared detection element. The present invention relates to a liquid level sensor, and in particular to a one-point type liquid level sensor that can detect a liquid level corresponding to a constant remaining amount with a simple configuration and with high accuracy.

(Prior art) In the near-infrared region, for example, If Hg C
Devices using high-sensitivity infrared detection elements such as dTe have been widely used in recent years, and these are usually cooled to 77°K before use.

An infrared detection device that requires cooling of a low-temperature liquid 1, such as liquid nitrogen, is provided with a vacuum insulation space such as a dewar-type cooler to ensure its heat retention. However, the degree of vacuum inevitably decreases over a long period of time, and the retention time of the liquid refrigerant gradually becomes shorter. This ratio is not uniquely determined and can only be predicted. Even if the retention time was checked periodically, it would not necessarily be possible to add a certain amount of liquid refrigerant each time, so conventionally it was customary to pay attention to how much liquid refrigerant was being used.

In these infrared sensing devices that require cooling with a low-temperature liquid, such as liquid nitrogen, if the device continues to operate without realizing that the coolant has run out, the element temperature will naturally rise and the current will exceed the optimum current value. It starts to flow. The excessive current may damage the element or, in the worst case, lead to destruction. In order to prevent such dangers, when the refrigerant reaches a certain level,
If you install a system that detects this with a liquid level sensor and issues an alarm, you can operate the device with peace of mind.

(Problems to be Solved by the Invention) Liquid level sensors for low-temperature liquids have conventionally used (1) 8-volt sensors and resistors (carbon, etc.)
220, etc.), (2) a thermistor with a heater wrapped around it (Japanese Unexamined Patent Publication No. 59-132315, etc.),
and (3) those using optical fibers (Unexamined Japanese Patent Publication No. 5
7-147017 etc.).

The above (1) is an application of a thermometer, but its output signal voltage is generally small and an expensive amplifier is required to obtain accuracy. On the other hand, (2) and (3) are based on a completely different mechanism from (1), and there is no problem in terms of accuracy since the signal is turned on and off at the liquid level, but the former actively generates heat. Since the low temperature liquid is used frequently, there is a large waste of low-temperature liquid, and the latter has problems due to the special nature of the sensor material. Even if the liquid level sensor has these drawbacks, it will not be a big problem when installed in a large η storage container (~50 liters), but if it is installed in a large storage container (~100 cc), such as a small dewar for an infrared detection device, When it comes to attaching it to containers, it becomes a serious problem. Therefore, from a cost perspective, it is desired to develop a new type of liquid level sensor that is both inexpensive and highly accurate.

Therefore, the present invention improves the above-mentioned conventional method (2) and uses the resistor by focusing on the fact that it is both a temperature sensor and a heater. It is an object of the present invention to provide a one-point liquid level sensor that completely overcomes the conventional drawbacks that the consumption of low-temperature liquid due to self-heating is almost negligible in terms of cost.

(Means for solving the problem) In order to achieve the above object, the liquid level sensor according to the present invention includes an infrared sensing element that requires cooling attached to the inner cylinder of a dewar-type cooler, It is equipped with an infrared transmission window in a predetermined part of the outer cylinder on the front side, and is suitable for use in infrared detection devices etc. that cool the element by putting liquid refrigerant in the cooler, and has a temperature coefficient of resistance. Consists of a small, high-resistance element with high
It is placed in a position where it comes out of the liquid when the liquid level drops below a predetermined level, and a current higher than the specified current value normally applied when used as a temperature sensor is passed, so that when the level of the liquid refrigerant drops and it comes out of the liquid. It is characterized by a large voltage change.

That is, in the liquid level sensor of the present invention, the self-heating effect that occurs when a current is passed through a resistor is actively incorporated into a small, high-resistance element with a high temperature coefficient of resistance, thereby increasing the change in output voltage when the element exits the liquid.

The small high-resistance element used for this purpose is preferably made of thin film platinum (or ultra-small platinum) or carbon. In addition, a water level sensor is installed in a circuit that amplifies the voltage change when a small high-resistance element comes out of the liquid and activates an alarm device such as an alarm lamp, and replenishes the liquid refrigerant when it reaches a certain level. Preferably, it is used to automatically notify that a is required.

(Example) Examples of the present invention will be described below with reference to the drawings. still,
Although a case where the present invention is applied to an infrared detection device will be exemplified, the application of the water level sensor is of course not limited to this.

First, FIG. 1 shows a cross-sectional view of the main part of a dewar-type infrared detection device to which the liquid level sensor of the present invention is applied. 1 is an outer cylinder of a dewar-type cooler; is housed in both cylinders 1 and 2, through the refrigerant inlet 6 on the top.
A sealed pipe type one-point liquid level sensor 3 according to the present invention is inserted into the inner tube 2 from the outside, and its outer end is connected to an amplification circuit section 4 equipped with a warning lamp, which will be described later.

5 indicates a 5VDC input terminal and an external output signal terminal.

Liquid nitrogen 7, which is a refrigerant, is introduced into the inner cylinder 2 through an injection port 6, and A is its liquid level. The liquid level A decreases over time as the liquid nitrogen evaporates, and eventually reaches the mid-tooth point! The liquid level reaches a predetermined caution level indicated by jlB. The liquid level sensor 3 is arranged so that its lower end is just above the caution level B, and therefore the liquid nitrogen 7
When the liquid level drops to B, the liquid level sensor 3 comes out of the liquid. An infrared detection element 9 is attached to one side of the lower end of the inner cylinder 2 via a heat block, and a part of the outer cylinder 1 corresponding to the infrared detection element 9 is infrared! A lam window 8 is provided. In the figure, 10 is 1/4 seal-off pulp, 11 is a terminal guard, and 12 is a terminal.

FIG. 2 shows an example of the sensor element 13 used in the liquid level sensor 3 of the present invention. That is, the sensor element 13 is a square ceramic substrate 1 of 1.2 x 2.3 mm.
A small resistor 15 having a high temperature coefficient of resistance, for example, to
A platinum thin film resistor with a resistance of 3750 ppm/00Ω is provided by vapor deposition as shown in the figure.The small resistor 15 may be one having a high temperature coefficient of resistance, and a platinum external resistor may be used. good.

Such a sensor element 13 is packaged 13° in a ceramic or metal protection tube, etc., and attached to the lower end of the liquid level sensor 3, and its detection end 16 is connected to the amplification circuit section 4 as shown in FIG. ing. The amplification circuit section 4 may have a well-known simple configuration, in which 5V DC power is supplied to the sensor element 13 via a resistor, and the voltage level at the detection end 16 is conducted to one terminal of the amplifier 17. It will be destroyed. On the other hand, the partial voltage level between DC5V and ground is led to the middle terminal of the amplifier 17, and the difference between the two voltage levels is detected and amplified by the amplifier 17. For example, a light emitting diode 18 constituting an alarm device is connected to the output of the amplifier 17, and when the output from the amplifier 17 exceeds a set value, the light emitting diode 18 emits light and issues an alarm.

Furthermore, as an important feature of the present invention, an excess current is passed through the sensor element 13, which exceeds the specified current value normally passed when the sensor element 13 is used as a temperature sensor. In other words, in the liquid level sensor of the present invention, the self-heating effect that occurs when current is passed through the resistor is further enhanced by passing an excessive current.

Therefore, when the level of the liquid refrigerant decreases and the liquid level sensor 3, that is, the small resistor 15 comes out of the liquid, it is possible to extract a large voltage change that could not be obtained with the conventional method using a resistor element.

Next, install the above liquid level sensor to the liquid nitrogen capacity of 100cc.
An experimental example in which the sample was inserted and fixed in a metal dewar-type infrared detection device as shown in FIG. 1 with a retention time of about 6 hours will be described.

Figure 4 records the signal output characteristics just before entering the amplifier 17, and the horizontal axis is time (chart speed 1mm/m1
n), the vertical axis is the voltage (full scale 0.5V).When the liquid level sensor is in the liquid, it shows an almost constant voltage C, but the liquid volume decreases due to natural evaporation and the level B requires attention. When it reaches the voltage level, it leaves the liquid surface, and as soon as it comes out of the liquid, it jumps to an extremely high voltage value D in just 1 minute, as shown in the figure. The amount of change is about 110 mV, and the alarm lamp lights up during the change.

Compared to the time it takes for conventional detectors to detect when the level of liquid refrigerant drops below the detection point, the liquid level sensor of the present invention, which operates by applying excessive current, can issue a detection signal in a short time, resulting in faster detection speed. It becomes a liquid level sensor.

It is obvious to those in the same industry that when using conventional thermocouple thermometers and platinum resistance thermometers, it is not possible to obtain such a large voltage change in such a short period of time near the liquid surface, and there is no comparison. Dew.

Even if the liquid level sensor of the present invention is inserted and an excessive current is applied to the liquid nitrogen retention time, there is almost no effect and there is no practical problem.

(Effects of the Invention) As described above, according to the liquid level sensor of the present invention, the self-heating effect that occurs when a current is passed through the resistor is actively used, and the output voltage change when the liquid goes out of the liquid becomes large. As a result, high detection accuracy can be obtained with a simple amplifier, a one-point liquid level sensor can be obtained at low cost, and consumption of low temperature liquid due to self-heating can be almost ignored.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing the configuration of an infrared detection device to which the liquid level sensor of the present invention is applied, Fig. 2 is a view showing a sensor element used in the liquid level sensor, Fig. 3 is an amplified circuit diagram, and Fig. 4 is a chart showing changes in the output voltage from the sensor. 10. , outer cylinder of dewar type cooler, 203. Same inner tube, 3
91. Liquid level sensor, 401. Width amplification circuit section, 710. Liquid nitrogen, 815. Infrared vj, transmission window, 911. Infrared detection element, 13. ,,sensor element,14. ,,ceramic substrate,15. . , small resistor, 17. ,,amplifier,18. , , Alarm devices such as light emitting diodes, A10. Liquid nitrogen level, B...
, a cautionary level of liquid nitrogen.

Claims (3)

[Claims] (1) An infrared detecting element that requires cooling is attached to the inner cylinder of a Dewar type cooler, an infrared transmitting window is provided in a predetermined part of the outer cylinder in front of the element, and a liquid refrigerant is put into the cooler to detect the element. It is a liquid level sensor used in infrared detection equipment etc. that cools the liquid.It is made of a small high resistance element with a high temperature coefficient of resistance. A liquid level sensor that causes a large voltage change when the liquid refrigerant level drops and comes out of the liquid by passing a current higher than the specified current value when used as a sensor. (2) The liquid level sensor according to claim 1, wherein the small high-resistance element is made of a thin film of platinum (or ultra-small platinum) or carbon. (3) Claim 1, characterized in that the small high-resistance element is provided in a circuit that amplifies the voltage change when it comes out of the liquid and activates an alarm device such as an alarm lamp. Liquid level sensor listed.