JPS62502774A - Self-heated sensor package - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] self-heated sensor package Zirconia stabilized with Y2O3, CaO, MgO, etc. is used for various industrial and Widely used for automotive oxygen sensors. stabilized zirconia is a solid oxygen ion conductor that selectively carries oxygen ions with a high oxygen partial pressure. from a gas stream with low oxygen partial pressure to a gas stream with low oxygen partial pressure. This goes without saying This is the case when the two gas streams are separated. Transport speed (response time) depends on working temperature more controlled. The E, M, and F of this oxygen cell are calculated using Nelson's equation: % formula % ( ) where R is the gas constant, T is the temperature in K, N is the electric charge, and F is the faraday The constants PO□(1) and Pot(I) are the oxygen partial pressures on the two sides, respectively.

Several models are on the market today. These are all based on two things: 1) current place type 2) Sampling type are categorized.

In the on-site type, a sensor is placed inside the furnace and detects atmospheric oxygen. . This sensor is heated by the furnace heat or, if insufficient, wrapped around it. The external platinum or nichrome plate is heated by a heater to give the appropriate working temperature. It gets heated. The heating element must be protected from the furnace atmosphere, which complicates and add weight. The complexity of field sensors depends on the sampling type of equipment. in which case the probe is inserted into the furnace or other atmosphere to be measured. and a sample is taken, which is then placed in an external chamber maintained at the desired temperature. part of the sensor. This type of device is also useful as a portable unit. be. However, the line from the furnace to be measured to the sensor unit The problem of condensation of gases arises. The line must be heated to avoid condensation. In order to obtain the correct PO□, the working temperature of the sensor must Consideration must be given to the calibration of the sensor to the working temperature. Pay attention to the above circumstances chemically inert materials that are stable to atmosphere and temperature and are less expensive. There is a need for efficient field-type equipment for real-time atmosphere monitoring of heating elements. exist. Some of the applications for such equipment are diffusion furnaces, gas analysis, sintering furnaces and Applications include melting furnaces, glass melting furnaces, combustion furnaces, heat treatment furnaces, and nitriding furnaces.

light skin hikidake return An in-situ oxygen sensing device accomplishing the objectives of this invention surrounds a solid electrolyte and A ceramic resistor (preferably silicon carbide) that heats the quality sensor by radiation and convection. resistance is provided by the use of thermal elements.

Margin below Embryo] Kunihiro FIG. 1 is a perspective view of the sensor of the invention.

FIG. 2 is a cross-sectional view of the sensor element.

FIG. 3 is a top view of one of the heating elements.

FIG. 4 is a side view of the heating element.

Happan Dan Pregnant Mouse Plate Silicon carbide igniters are used commercially to ignite gases, and It works well in typical atmospheres such as These igniters will last for a long time. withstands the most demanding demands of heat and gas circulation. Therefore, they are household goods market It has been accepted in the field. Needless to say, these markets are dependent on reliability and Very conservative in product selection due to cost consciousness. A typical ignition system No. 3,875,477.

Two plano-concave SiC heating elements 11 surrounding the ZrO□ sensor tube 13, A working unit node using 12 is shown in FIG.

This entire assembly is placed on an insulating ceramic disc 14 which is placed in the furnace. and completely seals the furnace atmosphere.The electronic device connects connector 1. 5. Process E, M, F from 16 and relate this to the oxygen partial pressure in the furnace. regulated from a separate uni-nod. The heater is connected to connectors 17, 18, and 19. and 20.

FIG. 3 shows a longitudinal section through the sensor element 13 and the associated annular electrodes 21 and 22. , shown in more detail with the connectors 23 and 24 in the base 14. . This lead may be protected by a thermal spray coating 23' and 24'. . Similarly, the porous electrodes 21 and 22 are plasma-molded with a material of the same composition as the solid electrolyte. by spray or flame spray coatings 21', 22' or by cordierite (co of materials that are difficult to melt, such as rdierit, e) or spinel. It may be protected by a porous coating.

Connectors from electrodes to high impedance voltmeters or other measuring or regulating devices These devices are not part of this invention and are well known in the art. Are known.

3 shows a top view of one of the heating elements 11 or 12, and FIG. 4 shows a top view of one of the heating elements 11 or 12, and FIG. Figure 3 shows a left side view of the heating element. This element has notches 31, 32, and 33. , the elements act as outer legs 35 and 36 which act as electrical terminals of opposite pairs of conductors. As a result, the voltage drop applied across terminals 35 and 37 is The device is arranged to generate a heating current in the silicone body. directed towards sensor 13 The surface shown at 50 in Fig. is pointed at the sensor. Other concave shapes such as circular can also be used. Ru.

The preferred sensor solid electrolyte is doped zirconia; The specific chemistry is not part of this invention, and the sensor transmits oxygen ions. and generates a voltage across its electrodes in response to the oxygen partial pressure difference. can be made from any suitable material.

While referring to the drawings, the geometry of the heating elements of the heater should be determined by the maximum resistance of the heater ( Note that the cross-section (minimum conductivity) is such that it is inside the ends and sides of the element. Should. That is, the highest temperature is directed to the sensor. metallic conductor resistance Using a conductive ceramic material with a relatively high resistance compared to the heating element and by adjusting the geometry of the unit such that the heating position can be Adjustable.

Exemplary geometries when battery power is used or when power supply is limited The increased efficiency of the heater provided by the shape is an additional advantage.

If the heater surrounds the outside of the sensor, as in Figures 2 and 3, A chamber is formed around the heater, which is in immediate direct contact with the ambient gas outside the heater. It functions as a buffer to prevent the area from getting too close. Furthermore, between the heater and the sensor Does the gas entering and exiting the space have to flow in close proximity to the hot surfaces of the heating elements? Excess oxygen tends to react with some green products, thereby causing This will ensure equilibrium oxygen partial pressure conditions for the gas being sensed. Furthermore, heating The buffer chamber formed by the chamber protects the sensor against contamination by solid combustion products. will.

Conventionally manufactured SiC heating elements suffer from oxygen content errors after 3 to 6 months of use. It has been found to be of no use in obtaining accurate readings. This is probably It is caused by the gradual oxidation of free silicon and free carbon in the device. Oxidizing atmosphere Extensive heating of the device at 1200°C in air for 10-15 hours circumvents this problem. However, fill the surface holes of the SiC heater with ceramic fine powder such as 543Na. and heat to oxidize any substances that may interfere with accuracy. Additional protection of the element can be achieved by this. 5i3Na is preferably Applied in the form of a rally.

For a comparative test of an atmosphere at a pressure of 1 atm containing an oxygen partial pressure of approximately 10-4 atm. , untreated SiC heater and ceramic coated but not evacuated. Both heaters gave false oxygen partial pressure readings of IQ-16 atmospheres. 12 When using a SiC element treated at 00°C for 10 to 15 minutes, the pressure of 10-4 atm. The correct pressure is obtained and this is done in a temperature controlled atmosphere without the use of SiC elements. It was the same as when using the sensor. Therefore, the relevant temperature range (approximately 70 Treat the SiC to remove all materials that can be oxidized at 0"C) and/or prevent the access of oxidizable substances to the atmosphere to be tested. It is necessary to process it for this purpose.

For additional protection of the heating element against oxidation, a combination of finely divided silicon carbide and sodium silicate The mixture can be filled into the pores and flamed to a dry glass state.

such as finely divided silicon nitride, as taught in U.S. Pat. No. 4,187,344. Pore-filling materials can also be used.

Other types of ceramic heating elements are disclosed in a pending application filed November 11, 1984. as described in U.S. patent application Na 669,399, in which nitrogen Electricity controlled by a mixture of aluminum oxide, molybdenum disilicide and silicon carbide A structure is formed that has specific properties. According to the teaching of this patent specification, the nitride phase Silicon nitride or boron nitride can be used as the material.

U.S. Patent +1h3,890,250, floor 3,649,310, and 3'; 875.476 also discloses ceramic heating elements.

Margin below international search report IAII, lll6. , ll　Apoll+l+16A　N. PCT/US85 100630

Claims (4)

[Claims] 1. A device for measuring the partial pressure of oxygen in a gas, the device having an inside and an outside. with one end closed, one side exposed to a comparative pressure of oxygen and the other side a solid electrolyte element exposed to the oxygen partial pressure to be measured; a heating element separated from one side and surrounding it to form a chamber; the heating element is made of ceramic and heated by electrical resistance; a thermally radiating surface spaced from and concentric with the solid electrolyte element; and the heating element does not contain any substance that can be oxidized. . 2. The heating element has a concave inner radiating surface and a centrally concentrated heating area. 2. A device as claimed in claim 1, comprising at least two members. 3. Claim wherein the heating element is located at one end in a non-conductive ceramic base. Apparatus according to scope 1. 4. The ceramic heating element is made of silicon carbide, silicon nitride, molybdenum disilicide, and the like. The device according to claim 1, consisting of a material selected from the group consisting of a mixture of Place. Margin below