JPH0419479Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention is a thermal liquid level detection system that detects whether one of two liquids with different properties, such as water and oil, is present at a predetermined position. It is related to vessels.

[Prior art] Thermal liquid level detectors are a method that has been attracting attention in recent years because they can be used for a wider range of liquids than float or electrode types, and they are also easier to convert into electrical signals and take out to the outside. It is.

FIG. 4 is a configuration diagram of a conventionally known thermal liquid level detector, in which an indirect heating type temperature sensor 2 and a correction temperature sensor 3 are installed on a mounting screw 1 facing downward. As shown in the cross-sectional view of FIG. 5, the indirect heating type temperature sensor 2 is equipped with a heater 5 in the wall of the distal end of a protective tube 4 made of ceramic or the like whose distal end is sealed, and a thermistor 6 inside the tube. 5 receives current from a control section (not shown) through a heater lead wire 7 to generate heat, and the output of the thermistor 6 is transferred to the control section through a thermistor lead wire 8 . At this time, the control section controls the amount of current supplied to the heater 5 so that, for example, the output value from the thermistor 6 is always constant, that is, the temperature at the tip is constant. Therefore, in order to keep the output of the thermistor 6 constant regardless of changes in the amount of heat radiated from the heater 5 to the outside, the amount of current supplied to the heater 5 must be adjusted. It can be detected as a change in the amount of current supplied to the In this case, there is also a method in which the current supplied to the heater 5 is kept constant and changes in the output of the thermistor 6 are taken out.

By the way, the amount of heat radiated from the heater 5 is generally different for liquids and gases, so if this is used to know the change in the amount of current supplied to the heater 5, it is possible to detect whether or not a liquid is present. . However, in reality, the amount of heat radiated from the heater 5 changes depending on the temperature of the liquid or gas, so the correction temperature sensor 3 detects these temperatures and corrects the amount of heat radiated. The correction temperature sensor 3 has a temperature measuring element such as a thermistor inserted into a protective tube whose tip is sealed.

The heat radiation coefficient obtained based on the outputs of these two temperature sensors 2 and 3 will draw an output curve as shown in the graph of Figure 6 in the relationship between liquid and gas. It can be seen that the heat radiation coefficient changes significantly near the gas interface. Therefore,
When actually detecting the liquid level relative to gas,
The reference output point L is set at the midpoint between the output levels for liquid and gas, and if the heat radiation coefficient is higher than the reference output point L, a signal indicating that liquid is present up to a predetermined level is emitted, and if it is low, a signal is issued. is adapted to emit a signal indicating that the liquid has not reached a predetermined level.

[Problem that the invention aims to solve] However, when detecting the interface between liquids, there is no large difference in their heat dissipation coefficients, so
Changes in the output curve are minute. Therefore, it becomes difficult to determine the reference output point L of the intermediate value of the heat radiation coefficients of the two liquids, and it is difficult to perform stable and accurate liquid level detection.

[Object of the invention] An object of the invention is to provide a thermal liquid level detector that can stably detect, for example, whether one of two types of liquid is at a predetermined level.

[Summary of the invention] The gist of the invention to achieve the above objectives is as follows:
A tubular heated temperature sensor that dissipates heat and detects temperature changes caused by changes in the amount of heat, and a tubular correction temperature sensor that is placed near the heated temperature sensor to detect ambient temperature. A thermal liquid level detector comprising: a convection plate for causing liquid convection from the heating type temperature sensor side to the correction temperature sensor in the tube body of the heating type temperature sensor. It is a thermal liquid level detector.

[Embodiments of the invention] The invention will be explained in detail based on the embodiments shown in FIGS. 1 to 3.

1a and 1b show the configuration of a thermal liquid level detector according to the present invention, where a is a side view and b is a sectional view taken along line B-B of a. A convection plate 10 is installed obliquely near the tip of the conventional indirectly heated temperature sensor 2 shown in FIG. This convection plate 10 is provided above the heater 5 in the indirectly heated temperature sensor 2, and is preferably made of a thin plate-like material having heat insulating properties.

When the convection plate 10 is installed in this way, convection is generated in the liquid by heating from the heater 5 in the indirectly heated temperature sensor 2, as shown in FIG. Heat is transferred to. FIG. 3 is a graph showing how the change in the heat radiation coefficient at that time is detected as an output.

For example, in FIG. 2a, the boundary surface between liquids A and B is below the convection plate 10, and liquid A heated by the indirectly heated temperature sensor 2 rises as it is to the temperature detected by the correction temperature sensor 3. is almost not affected by the heater 5, so it is the temperature of the liquid A itself. Therefore, in the region a of FIG. 3, the heat radiation coefficient specific to the liquid A is obtained as an output, as in the conventional example.

Next, in FIG. 2b, the boundary surface between liquids A and B is in contact with the convection plate 10, and the heated liquid B is transferred to the correction temperature sensor 2 side by the convection plate 10 as shown by the arrow. Since the direction is changed and the liquid B flows along the boundary surface, the temperature detected by the correction temperature sensor 3 is influenced by the heater 5 and becomes higher than the actual temperature of the liquid B. Therefore, as the corrected heat radiation amount increases, the apparent heat radiation coefficient increases and a large peak is formed as shown in b in FIG. 3.

In FIG. 2c, the boundary surface is located considerably above the convection plate 10, and the liquid B flows upward as shown by the arrow, so the temperature detected by the correction temperature sensor 3 is influenced by the heater 5. I hardly received it,
The temperature of liquid B itself is detected. In the region c of FIG. 3, the heat radiation coefficient specific to the liquid B is obtained as an output, as in the conventional example. In this way, the change in the heat dissipation coefficient near the interface appears to be large, so
It becomes easy to determine a reference output point for liquid level detection, and stable liquid level detection becomes possible.

In the embodiment, an indirect heating type temperature sensor is used as the heating type temperature sensor, but a self heating type temperature sensor may also be used, which does not have a separate sensor and uses a measuring element as a heating element.

[Effects of the invention] As explained above, in the thermal liquid level detector according to the invention, by attaching a convection plate to the heating type temperature sensor, it is possible to enlarge the difference in the apparent heat radiation coefficient, It is now possible to detect boundaries between liquids with almost no difference in heat radiation coefficient, which was difficult in the past.

[Brief explanation of drawings]

Figures 1 to 3 show an embodiment of the thermal liquid level detector according to the present invention, where Figure 1a is a side view and Figure 1b is a side view.
Figure 2 a, b, and c are explanatory diagrams of convection due to heat, Figure 3 is a graph of heat radiation coefficient characteristics, and Figure 4 is a conventional thermal liquid level detector. FIG. 5 is a cross-sectional view of the indirectly heated temperature sensor 2, and FIG. 6 is a graph of heat radiation characteristics between liquid and gas. Reference numeral 2 is an indirect heating type temperature sensor, 3 is a correction temperature sensor, 4 is a protection tube, 5 is a heater, 6 is a thermistor, and 10 is a convection plate.

Claims (1)

[Claims for Utility Model Registration] 1. A tubular heated temperature sensor that radiates heat and detects temperature changes caused by changes in the amount of heat radiated, and a tubular heated temperature sensor that is placed near the heated temperature sensor to detect ambient temperature. In a thermal liquid level detector comprising a tubular correction temperature sensor, the convection causes liquid convection in the tubular portion of the heating temperature sensor from the heating temperature sensor side to the correction temperature sensor. A thermal liquid level detector characterized by being equipped with a plate. 2. The thermal liquid level detector according to claim 1, wherein the convection plate is provided slightly above the tip of the heating type temperature sensor. 3. The thermal liquid level detector according to claim 1, wherein the convection plate is provided so as to rise obliquely toward the correction temperature sensor at a predetermined angle with respect to the boundary surface of the liquid. . 4. The thermal liquid level detector according to claim 1, wherein the convection plate is a plate-like member having heat insulation properties.