JPH0239356Y2 - - Google Patents

Description

[Detailed explanation of the idea]

Technical Field of the Invention The present invention relates to a ceramic heater sensor for detecting the level of a liquid. Prior Art and Problems As a sensor for detecting the velocity of a liquid, a sensor using a thin platinum wire, a sensor using a thermistor, or a mechanical sensor such as a torque meter is known. Level sensors that detect liquids such as water, oil, and freon include sensors that use electrical discharge,
Sensors using a thermistor, sensors using a float relay, etc. are known. However, mechanically operated sensors such as torque meters and float relays are difficult to operate stably for long periods of time, and are also difficult to miniaturize. In addition, sensors using thin platinum wires have the disadvantage that they cannot be used in water, etc., and sensors that use electrical discharge have the disadvantage that they have electrode wear and cannot be used with flammable liquids such as oil. There is. On the other hand, sensors using thermistors are easy to downsize and can be used semi-permanently, but self-heating thermistors have a large temperature coefficient, so they start at a constant voltage depending on the temperature conditions when energizing. Indirectly heated thermistors have the advantage of being less affected by the operating temperature, but have the disadvantage of being expensive. Purpose of the invention The object of the invention is to provide a sensor that has a simple configuration and is inexpensive and can detect a liquid level. Examples will be described in detail below. Embodiment of the invention FIG. 1 is a sectional view of an example of a conventional ceramic heater/sensor, in which 1 is a cylindrical or cylindrical ceramic body, 2 is an annular heater part, and 3 is a heater part 2 that is heated by electrical current and heated. A lead part 4 is connected to the heater part 2 so that resistance can be measured; 4 is a soldering part; 5
is the lead wire. A method for forming the heater section 2 and the lead section 3 will be briefly described. Tungsten,
A conductive paste containing metal powder such as molybdenum is used to create widths, lengths, and
Heater part 2 and lead part 3 of thick heating pattern
The printed material is wrapped around a separately extruded raw ceramic pipe or ceramic rod and fired. At this time, both ends of the lead part 3 are exposed or through holes are formed.
It is fired in a reducing atmosphere at 1300° C. to 1600° C., nickel plating is applied to the exposed portion of the lead portion, and the lead wire 5 is connected by the brazing portion 4. Connect this lead wire 5 to a detection circuit (not shown),
It is used to heat the heater section 2 and detect changes in resistance. FIG. 2 is a sectional view of another example of a conventional ceramic heater sensor, in which the same reference numerals as in FIG. 1 indicate the same parts, and 6 is a metal nipple. This metal nipple 6 is provided to facilitate installation, and is installed by brazing or the like. FIG. 3 shows a sectional view of an embodiment of the present invention, in which heater parts 2-1, 2-2 and lead parts 3-1, 3-
2 is provided within the ceramic body 1. The two heater parts 2-1 and 2-2 are arranged with their positions shifted in the axial direction. In this embodiment, the heater section 2-1,
A case is shown in which one of the lead portions 3-1 and 3-2 of 2-2 is shared. Therefore, there are two lead wires 5-1, but only one lead wire 5-2. Of course, it is possible to provide two lead wires for each of the lead portions 3-1 and 3-2 without making the lead wires 5-2 common. In this embodiment, the liquid level can be detected by a bridge connection. FIG. 4 shows the circuit configuration of a conventional ceramic heater/sensor, and R represents the resistance of the heater section 2 of the ceramic heater/sensor shown in FIG. 1 or 2. In FIG.
Further, r1 is a compensation resistor, r2 is a detection resistor, OUT is an output terminal, and V is a constant voltage. This constant voltage V is added to the compensation resistor r1, the resistor R serving as the heater section 2, and the detection resistor r2, and the change in the resistance R due to contact with the liquid surface is detected by the voltage drop across the detection resistor r2. For example, in the configuration shown in Figure 1, the outer diameter is 4.5 mm,
An example of the characteristics of a sensor in which the length of the heater section 2 is 10 mm and the total length is 40 mm is shown below. Temperature characteristics are R = R0 (1 + αT) However, R0 is the resistance at 0℃, 154Ω, temperature coefficient α is 0.00425/℃, time constant (in air) is 25~
30sec, time constant (underwater) is 2-3sec, heat dissipation coefficient (in air) is 9.67mW/℃, heat dissipation coefficient (underwater) is
It is 199.5mW/℃. Therefore, the resistance of the heater section 2 changes greatly depending on whether it comes into contact with a liquid such as water, and the liquid level can be detected. Also, in Fig. 4, r1=0, r
2 = 2Ω, and the heater temperature is in still air at 25℃.
Table 1 shows the changes in heater temperature with respect to air temperature TA and water temperature TW when a constant voltage of V=13.5 volts is applied so that the temperature becomes 100°C. According to this, the heater temperature when the air temperature is 0°C is 79.8°C, and the water temperature corresponding to this heater temperature is 76°C. Therefore, under the above setting conditions, when the air temperature is 0°C or higher, the water temperature is 76°C. It becomes possible to detect the water surface level up to ℃. In this case, the output is
Since the voltage is about 100mV, it is necessary to connect an amplifier to the output terminal.

【table】

[Table] FIG. 5 shows a circuit configuration when two sensors of FIG. 1 or 2 or the sensor of the embodiment shown in FIG. 3 are used. In the figure, V is a constant voltage, OUT
is the output terminal, R1 and R2 are the heater section 2 or 2-
1, 2-2, and r1 is a compensation resistor.
Similarly to the above, a constant voltage V of 27 volts is applied so that the heater temperature becomes 100°C in still air at 25°C.
was applied to the series resistors r1, R1, and R2 to detect the water surface level. In that case, air temperature 25
℃, a voltage of 0.01 volt appears at the output terminal, but when resistor R2 is immersed in water at 25℃, an output voltage of 3.65 volts appears. This is due to 70.6°C when TA and TW = 25°C in Table 1, and when the air temperature changes to 0°C, the water temperature is 76°C.
This indicates that it is possible to detect water surfaces at temperatures up to In this embodiment, the output voltage is large so that the switching transistor can be directly driven. FIG. 6 shows an embodiment of the bridge connection;
The same reference numerals as in the figure indicate the same parts. Resistors r3, r are connected to the sides of the bridge connection resistors r1, R1, R2.
4 is connected. In this embodiment, since the output voltage is large, it is possible to directly drive relays and the like. Fig. 7 shows an example in which two heater parts are electrically separated, and the resistance R1 of one heater part is heated by a constant voltage V, and the resistance change of the resistance R2 of the other heater part is heated. is configured to be detected at the output terminal OUT. This embodiment is suitable for connecting a semiconductor integrated circuit or the like to the output terminal OUT because the power supply for heating the heater section and the output terminal can be electrically separated. In the embodiment shown in Fig. 3, the outer diameter is 4.5 mm, the lengths of heater parts 2-1 and 2-2 are each 10 mm, the interval between heater parts 2-1 and 2-2 is 10 mm, and the total length is 60 mm. In this case, the characteristics were approximately the same as those of the sensor of the embodiment shown in FIG. However, in the embodiment shown in FIG. 3, since the heater parts are arranged at intervals in the axial direction, the change in resistance of the heater part 2-2 due to heat conduction of the ceramic body 1 is small, although slight. but,
There is an advantage that the circuit shown in FIG. 6 or 7 can be constructed with a single sensor, and manufacturing is easy. Effects of the Invention As explained above, the present invention uses a ceramic heater in which the heater parts 2, 2-1, and 2-2 are embedded in the ceramic body 1, and has a simple structure and is therefore inexpensive. This has the advantage that the liquid level of liquids such as water and oil can be easily detected. Furthermore, in the above-mentioned sensor, detection sensitivity can be increased by covering or shielding a portion of the sensor or one of the two sensors. Note that there is an advantage that one ceramic heater/sensor of the present invention can perform the operations of two conventional sensors.

[Brief explanation of drawings]

Figures 1 and 2 are sectional views of a conventional ceramic heater/sensor, Figure 3 is a sectional view of an embodiment of the present invention, Figure 4 is a circuit diagram of a conventional ceramic heater/sensor, and Figure 5 is a sectional view of a conventional ceramic heater/sensor. A circuit diagram when two conventional ceramic heater sensors or one ceramic heater sensor according to the present invention are used. Figure 6 is a circuit diagram of a bridge connection according to the present invention. Figure 7 is a circuit diagram using two heater sections. FIG. 3 is a circuit diagram of an electrically isolated embodiment of the present invention.

Claims (1)

[Scope of utility model registration request] Two or more heaters are embedded in a columnar or cylindrical ceramic body at different positions in the axial direction, one of these heaters is used for heating and the other is used for detection, and the temperature change of the detection heater is A ceramic heater sensor characterized by measuring a liquid level by detecting a change in resistance.