JPH09170942A - Method and apparatus for detecting liquid level - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correctly detect a liquid level by comparing a preset value with the changing amount which is an enlarged changing amount of a temperature output of a liquid level detection sensor and conducting a predetermined level detection. SOLUTION: In order to detect a liquid level, a steady-state temperature Td then a temperature detection part 5 is set at a liquid phase part 14 and a steady-state temperature Tu when the temperature detection part 5 is set at a gas phase part 12 are measured beforehand. And, a minimum supply power of a heater 6 and a level detection sensitivity Ts of a level control circuit part 9 are set at optional points between the temperatures Td and Tu. For example, when a liquid level 13 is raised subsequent to the supply of a liquid to a liquid container 1 and starts to be in touch with a liquid phase of the temperature detection part 5, a heat conduction path for an output of the heater 6 from an outer surface of a sheath 4 of a level detection sensor 2 is changed from a gas phase to the liquid phase, and consequently a temperature indicated by the temperature detection part 5 is suddenly changed to the steady-state temperature Td. When the temperature reaches the level detection temperature Ts, the supply of the liquid is stopped by the level control circuit part 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid level detecting method and device, and more particularly to a liquid suitable for controlling the liquid level of a low temperature fluid used in a coolant supply device for cooling a sample stage of a semiconductor manufacturing apparatus. The present invention relates to a surface detection method and device.

[0002]

2. Description of the Related Art As a conventional liquid level detecting device, for example,
As disclosed in Japanese Unexamined Patent Publication No. 5-288591, there is a method in which a temperature difference between a gas phase portion and a liquid phase portion in a liquid tank is taken out as a sensor output to perform liquid level detection.

[0003]

In the above-mentioned prior art, the liquid level is detected by taking out the temperature difference between the gas phase portion and the liquid phase portion in the liquid tank as a sensor output. That is, the steady-state temperature Td of the sensor when the sensor is installed in the liquid phase is compared with the steady-state temperature Tu of the sensor when the sensor is exposed to the gas phase due to the decrease in the liquid level due to the consumption of liquid. The liquid level detection temperature is set at an arbitrary point between Td and Tu, and is taken into the liquid level control circuit section as a sensor output to supply / deliver the liquid.
The liquid level is kept within a certain range by repeating the stop.

In the above prior art, since the liquid level detection by the sensor is carried out by utilizing the temperature difference between the gas phase portion and the liquid phase portion in the liquid tank, the liquid tank itself has a structure insulated from the surroundings, or If heat conduction from the outside to the sensor body cannot be expected due to the sensor mounting method that inserts the sensor into the liquid from the bottom of the liquid tank, the difference in the sensor output temperature between the gas phase and the liquid phase will be extremely reduced, and the sensor liquid There is a drawback that the surface detection setting range is narrow and accurate liquid surface detection cannot be performed. Further, in the above-mentioned structure, when heat is input to the liquid tank from the outside, the temperature of the gas phase portion changes due to fluctuations in the heat input, so it is necessary to determine the liquid level detection temperature setting for each heat input condition from the outside. However, there is a drawback that the control liquid surface position fluctuates.

An object of the present invention is to accurately detect the liquid level in a liquid container in which the difference in sensor temperature output between the gas phase portion and the liquid phase portion is extremely small in order to eliminate the above-mentioned drawbacks of the prior art. An object of the present invention is to provide a liquid level detection method and device capable of stably detecting the liquid level with respect to the temperature change of the gas phase portion due to external heat input into the liquid sensor.

[0006]

In order to solve the above-mentioned problems, a hollow metal sheath which is inserted into the liquid container from the outside of the liquid container and comes into contact with a liquid, and at least one or more places which are installed in the hollow metal sheath and have a temperature A liquid level detection sensor in which a detection thermocouple and a heater that locally generates heat near the thermocouple contact are electrically isolated from each other by an insulating material and housed therein, a power supply unit that supplies a predetermined electric power to the heater, and a liquid container. A liquid level controller for detecting the output of the thermocouple due to the fluctuation of the liquid level of the liquid inside and supplying / stopping the liquid according to the liquid level of the liquid to keep the liquid level within a certain range. It is composed of.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG. A liquid level detection sensor 2 is installed in the liquid from the lower part of the liquid container 1 via a seal portion 3. The liquid level detection sensor 2 is housed in a hollow metal sheath 4 and is composed of a thermoelectric material 16 electrically isolated from each other by an insulating material 7 and a heater 6 having a local heat generating portion 15 in a temperature measuring portion 5. To be done. The heater 6 is provided with a power source section 8 for supplying a relatively weak electric power, and the temperature measuring section 5 is provided with a liquid level control circuit section 9. The liquid container 1 is composed of a liquid supply unit 10 and a liquid supply valve 11.

The liquid level detecting device constructed as described above is
It works as follows. As the liquid is supplied to the liquid container 1 and the liquid level 13 rises, the temperature of the temperature detection unit 5 of the liquid level detection sensor 2 approaches the temperature of the liquid. In performing the liquid level detection, the steady temperature Td when the temperature detecting unit 5 is installed in the liquid phase unit 14 and the steady temperature Tu when the temperature detecting unit 5 is installed in the gas phase unit 12 are measured in advance. Every time, the minimum supply power of the heater 6 and the liquid level detection sensitivity Ts of the liquid level control circuit unit 9 are
It is set at an arbitrary point between Td and Tu.

When the liquid level 13 rises and the temperature detector 5 starts to contact the liquid phase, the heat transfer path from the outer surface of the sheath 4 of the liquid level detection sensor 2 of the heater 6 changes from the gas phase to the liquid phase. Therefore, the instruction temperature of the temperature measuring unit 5 rapidly goes to the steady temperature Td. The temperature indicated by the temperature measuring unit 5 is the liquid level detection temperature T.
When s is reached, a liquid level control circuit unit 9 causes a timer (not shown) for preventing chattering of the liquid level 13, and after a lapse of a predetermined time, the liquid supply valve 11 is closed and the liquid supply is stopped.

Next, when the liquid is consumed, the liquid surface 13 is lowered, and the temperature measuring portion 5 starts to be exposed from the liquid surface, the heat transfer path from the outer surface of the sheath 4 of the liquid surface detecting sensor 2 of the heater output is formed. Since the liquid phase 14 changes to the gas phase 12, the temperature indicated by the temperature measuring unit 5 suddenly moves toward the steady temperature Tu. When the temperature instructed by the temperature measuring unit 5 reaches the liquid level detection temperature Ts, the liquid level control circuit unit opens the liquid supply valve 11 to supply the liquid again into the container. During this time, the heater heating section 15
Emits a relatively weak amount of heat at all times by the electric power supplied from the heater power supply unit 8. By repeating the above operation, the liquid surface is maintained within a certain range with respect to the liquid surface level corresponding to the liquid surface detection temperature Ts.

As described above, according to the present embodiment, with the configuration described above, the tip of the sensor is heated by the heater which locally generates heat in the vicinity of the thermocouple contact for temperature detection. The steady temperature of the temperature detector is determined by the heat conduction component transmitted to the heater body through the sensor body and the heat transmission component radiated from the sensor surface. Of these, the heat transfer component largely depends on the state of the heat transfer surface. It is generally known that when the heat transfer surface is in contact with the liquid phase, the heat transfer coefficient is several hundred times larger than when the heat transfer surface is in contact with the gas phase. For this reason, it is possible to make a large difference in the detected temperature between the liquid phase detection part in the liquid phase and the liquid level detection part in the gas phase with a small heater output setting. When detecting the liquid level in the liquid container with an extremely small difference, the liquid level detection temperature setting range of the liquid level detection sensor can be widened, and accurate liquid level detection can be performed. Further, when there is heat input to the liquid container from the outside, by setting a heater output that is sufficiently large with respect to the expected heat input, stable liquid level control is possible even with variations in heat input.

In this embodiment, the liquid level detection sensor 2 is set to 1
Although described in two cases, for example, liquid nitrogen is supplied as a liquid refrigerant to the liquid storage space inside the sample table, and the sample table temperature is controlled at two different temperatures such as −50 ° C. and −100 ° C., for example. If necessary, two types of fins with different lengths are provided in the liquid storage space inside the sample table so that the number of fins that come into contact with liquid nitrogen differs depending on the storage level of liquid nitrogen. Control the face level.
At this time, by providing the liquid level detection sensor 2 at two locations according to the liquid level of liquid nitrogen, the liquid level can be accurately controlled according to each level. As a result, the materials to be etched having different laminated structures and different kinds of samples can be etched in the same apparatus while changing the sample temperature, and the shape of the etching can be easily controlled.

[0013]

According to the present invention, when detecting the liquid level in a liquid container in which the temperature difference between the liquid phase portion and the gas phase portion is extremely small, the liquid level detection temperature setting range of the liquid level detection sensor can be widened. It becomes possible and accurate liquid level detection becomes possible. Further, when the liquid container has heat input from the outside, setting a heater output that is sufficiently large with respect to the expected heat input has the effect of enabling stable liquid level detection even with variations in heat input. is there.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a liquid level detection device according to an embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Liquid container, 2 ... Liquid level detection sensor, 4 ... Hollow metal sheath, 5 ... Temperature measuring part, 6 ... Heater, 7 ... Insulating material, 8 ... Power supply part, 9 ... Liquid level control circuit part, 10 ... Liquid supply Department, 12 ...
Gas phase part, 13 ... Liquid surface, 14 ... Liquid phase part, 15 ... Exothermic part.

Claims (2)

[Claims] 1. A liquid level detecting sensor comprising a temperature detecting thermocouple and a heater which locally generates heat near a thermocouple contact, electrically isolated from each other by an insulating material, and a liquid level detecting sensor inside the liquid container from outside the liquid container. At least one or more locations are provided in one hollow metal sheath inserted into the liquid container to increase the amount of change in the temperature output of the liquid level detection sensor due to the change in the liquid level position of the liquid in the liquid container. A liquid level detecting method, characterized in that a predetermined liquid level is detected by comparing the expanded change amount with a preset setting value. 2. A hollow metal sheath which is inserted into the liquid container from the outside of the liquid container and comes into contact with the liquid, and at least one or more locations inside the hollow metal sheath which are locally located near a temperature detecting thermocouple and a thermocouple contact. Liquid level detection sensor in which heaters that generate heat are electrically isolated from each other by an insulating material are housed, power supply means for supplying a predetermined electric power to the heater, and liquid level position variation of the liquid in the liquid container. A liquid level controller for detecting the output of the thermocouple, supplying / stopping the liquid according to the liquid level of the liquid, and maintaining the liquid level of the liquid within a certain range. Liquid level detection device.