JPH0119241B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a resistance temperature detector that measures the temperature of a fluid or solid by utilizing a change in electrical resistance due to a change in temperature, and a resistance temperature detector that measures the temperature of a fluid or solid by using a change in electrical resistance due to a change in temperature. This relates to a flow rate measurement sensor that detects a change and measures the flow rate of a fluid, or a method for fixing and protecting a resistance wire such as a sheathed heater inside a thin tube.

Conventionally, this type of resistance thermometer, sensor for measuring instruments, etc. is made by using a thin wire (5 to 40 microns) with a large temperature coefficient of resistance, such as a tungsten wire, nickel wire, or platinum wire, as a resistance wire, as a straight or spiral bare wire. Alternatively, it is used by wrapping it around the surface of an insulator, but if it is used as a bare wire, it is often cut and becomes unusable, whereas resistance wire is used by wrapping it around the surface of an insulator. It is unstable and extremely difficult to clean if dust in the fluid adheres to it, and it is easily affected by humidity, resulting in a major loss of measurement accuracy.Furthermore, such sensors are unable to measure the temperature or flow rate of the fluid. It is possible.

In order to eliminate this drawback, methods have been implemented in which the heat-sensitive resistor of the sensor is sealed in a hard tube together with an inorganic insulating powder such as magnesia or an insulating organic polymer adhesive. In this method, if the inner diameter of the hard tube is minute, it is impossible to insert inorganic insulating powder, etc. Therefore, it is impossible to manufacture a minute sensor, and the sensor itself becomes large, making it difficult to separate the fluid and resistor to be measured. It takes time for the liquid to reach thermal equilibrium, making it unsuitable for measuring fluctuating temperatures or flow rates of fluids, and the method of encapsulating it with an organic polymer adhesive generally has the drawback of not being able to withstand high temperatures of around 200°C or higher. It was hot.

The present invention eliminates the above-mentioned drawbacks and provides a sensor for measuring instruments (thermal sensitive resistor) or a sheathed heater for high temperatures that is small, has quick response, can withstand high temperatures, and can accurately measure temperature or fluid flow velocity. According to the present invention, this object is achieved by filling a thin tube into which a resistance wire is inserted, using centrifugal force, with ceramic powder or a dispersion thereof, and firing the ceramic powder or its dispersion.

To explain the example below with reference to the drawings, as shown in Fig. 1, a fine platinum wire of 20 microns in diameter was
Platinum lead wires 1, 1 with a diameter of 0.2 mm are connected to both ends of the spirally wound resistance wire 2 by electric welding or the like, and a wire with an inner diameter of 0.5 mm and a length of about 4 mm is made of alumina, silica, or a mixture thereof. The thin platinum resistance wire 2 is inserted into the ceramic thin tube 3 so that the welded portion of the lead wires 1, 1 and the thin resistance wire 2 is accommodated, and a mold 5 made of, for example, a heat-shrinkable plastic tube is fitted on the outside of the ceramic thin tube 3. Then, a part of the platinum lead wire 1 is made to protrude from the mold 5 and temporarily fixed with an appropriate adhesive, and the other platinum lead wire 1 is fixed to a part of the mold 5 with an instant adhesive 6, and then ceramic powder, e.g. A slurry-like dispersion 4 obtained by mixing a fine powder mixture of 50% alumina powder and 50% silica powder with a diameter of 7 microns or less with approximately three times the amount of water, methyl alcohol, or other suitable volatile liquid is placed in the mold 5. As shown in Fig. 2, the ceramic powder is clamped in the holder 8 of the centrifuge 7 with a diameter of 30 cm and rotated at 1000 rpm, and centrifugal force C is applied. After reaching 95%, the supernatant liquid is removed and dried by heating at 80 to 100°C for about 1 hour.
In some situations, injection and centrifugation of the dispersion may be necessary.
Do it in stages.

Thus, as shown in FIG.
After filling both openings of the ceramic capillary tube 3 with
Ceramic slurry sintered at about 1200°C as shown in b and 4b, for example, is obtained by mixing a mixture of 70% alumina powder and 30% hard glass powder with about twice the amount of water, methyl alcohol, or other suitable volatile liquid. After additionally filling with the slurry dispersion and drying at 80 to 100℃ for about 1 hour,
The temperature was raised to about 400°C in 1 hour and maintained at about 400°C for 2 hours to burn out the plastic mold 5. The temperature was raised to about 1200°C in 3 hours and maintained at about 1200°C for about 30 minutes to form ceramic powder 4a. The thin platinum resistor wire 2 is placed inside the ceramic tube 3 by firing, completely expelling air, adsorbed gas, water vapor, etc. inside the ceramic tube, and then sintering the ceramics 4b and 4b and slowly cooling them to room temperature for about 10 hours. Fixed by If the filling ceramic 4a is of the same quality as the ceramic 4b, it can be sintered integrally with the platinum resistance thin wire 2.

4 to 6 show another embodiment of the present invention, in which a ceramic cylindrical body 3a with two through holes is prepared as shown in FIGS. 4 and 5, and a lead wire 1 is prepared. , 1 electrically welded at both ends is inserted into the two through holes, and a ceramic cylinder body 3 is inserted.
A mold 5 is fitted on the outside of the lead wires 1, 1.
After a part of the mold 5 is made to protrude from the mold 5 and temporarily fixed with an appropriate adhesive, the ceramic powder 4a is injected into the mold 5, and the centrifugal force C is applied as explained with reference to FIG.
The filling rate of the ceramic powder 4a into the ceramic cylinder 3a was increased by increasing the filling rate of the ceramic powder 4a into the ceramic cylinder 3a, and then dried at 80 to 100°C for about 1 hour. After the ceramic slurry exemplified in Example 1 is additionally filled and dried, the ceramic powder 4a is fired or sintered, and the ceramics 4a and 4b are sintered.

In the above embodiments, platinum was used as the lead wire 1 and the thin resistance wire 2, ceramic such as alumina was used as the thin tube 3, and a mixture of alumina powder and silica powder or hard glass powder was used as the ceramic powders 4a and 4b to be filled. An appropriate conductor can be used for the wire 1 and the resistance wire 2 as long as the surface does not oxidize due to the outside air, and the material for the thin tube 3 can be ceramic such as mullite or zirconia or metal, ceramic powder 4a, 4b, etc. As the material, alumina, silica, magnesia, quartz glass, etc. or a mixture thereof can be used. Furthermore, the ceramic tube 3, the ceramic powder for filling 4a, and the resistance wire 2
It is necessary to select and combine the respective materials so that their coefficients of thermal expansion are as equal as possible, and when used as a sensor for a measuring instrument that utilizes changes in electrical resistance due to changes in temperature, it is necessary to select and combine the respective materials so that the coefficients of thermal expansion are as equal as possible. Use conductors made of platinum, tungsten, nickel, stainless steel, nickel silver, phosphor bronze, etc., which have a large temperature coefficient. Of course, the resistance thin wire 2 is not limited to a spiral shape, and a straight wire may be used.

Since the present invention is constructed as described above, for example, a ceramic tube 3 having an outer diameter of 0.8 mm, an inner diameter of 0.5 mm, and a length of 4 mm is used, and the diameter of the thin platinum resistance wire 1 is set to 20 to 50 microns, and the length of the helical portion is set to 20 to 50 microns. By configuring the platinum lead wire 2 to have a diameter of 3 mm (resistance 1.0 to 3 ohms) and a diameter of approximately 0.2 to 0.4 mm, it can be used as a resistance temperature detector from -200 to +
It can be measured accurately and quickly within a response time of 0.1 to 2 seconds in the range of 600℃, and when measuring the fluid flow rate based on the amount of heat transfer between the sensor and the surrounding fluid, -200℃ is the same as above. In the range of ~+200℃
Flow velocity of about 0.1 to 50 m/sec. can be measured accurately with an error within ±2% and quickly with a response time of about 0.5 seconds. Active gas in fluid with excellent impact resistance and heat resistance. It also has extremely high resistance to chemicals. When a conductor other than platinum is used as the resistance wire 1 or the lead wire 2, there are restrictions on the fluid to be measured or its temperature depending on its heat resistance, oxidation resistance, and chemical resistance.

As described above, the present invention allows the resistance wire and inorganic insulator to be filled in an extremely small tube at a high density. Therefore, the sensor for measuring instruments manufactured by this method has an extremely small heat capacity compared to conventional sensors for measuring instruments. As a result, the thermal response can be measured extremely quickly and accurately, and the physical strength is strong. Sheathed heaters can be manufactured in the same manner, and in either case, they can be easily and reliably manufactured without requiring any special equipment or technology, and can be supplied at low cost.

[Brief explanation of drawings]

FIG. 1 is a central sectional view showing an embodiment of the present invention;
FIG. 2 is a plan view showing the centrifugation process, FIG. 3 is a central sectional view of a thin resistance wire fixed in a thin tube by the method shown in FIG. 1, and FIG. 4 is a central sectional view showing another embodiment of the present invention. 5 is a sectional view taken along the line A--A in FIG. 4, and FIG. 6 is a central sectional view of the thin resistance wire fixed in the thin tube by the method shown in FIGS. 4 and 5. Note that 5 in the figure indicates a mold.

Claims (1)

[Claims] 1. A resistance wire 2 with lead wires 1 and 1 welded to both ends is inserted into a thin tube 3, and ceramic powder or its dispersion 4 is filled into the thin tube 3. After increasing the packing density of the ceramic powder by centrifugal force, firing is performed. A method for fixing a resistance wire in a thin tube, characterized in that the ceramic is integrally formed with the resistance wire 2.