Corrosion-resistant diaphragm pressure sensor

[0002] The present invention pertains generally to a pressure sensor and, more particularly, to a corrosion-resistant diaphragm pressure sensor used for liquid chemical containers, liquid chemical piping, etc.

[0003] In general, a diaphragm pressure sensor is constructed in such a way as to sense pressure by converting the displacement of a diaphragm generated by pressure applied to the diaphragm into an electronic signal. In particular, a diaphragm pressure sensor for sensing pressure of strong acid, strong alkaline liquid chemicals, etc. conventionally has had a diaphragm. The surface of the diaphragm can be coated with fluoroplastics, if the diaphragm is made of metal, or the diaphragm can be made of a highly corrosion-resistant material such as alumina ceramic, etc. with a view to minimization of corrosion by liquid chemicals such as mentioned above.

[0004] However, a metal diaphragm coated with fluoroplastics employed in a conventional diaphragm pressure sensor has a limited life due to poor uniformity of coating, pinholes, etc. Further, a diaphragm made of alumina ceramic, although it has satisfactory corrosion resistance properties, slightly dissolves in strong acid or strong alkaline liquid chemicals.

[0005] It is an object of the present invention to provide an improved diaphragm pressure sensor for sensing fluid pressure, characterized by excellent corrosion resistance to strong acid, strong alkaline liquid chemicals, etc.

[0006] A diaphragm pressure sensor of the present invention comprises a pressure guide member made of fluoroplastics for the admission of liquid chemicals, pressure of which is measured, and a pressure frame made of perfluoroalkoxy resin (pheno-lformaldehyde) integrated with the pressure guide member to constitute a container for holding the liquid chemicals. A ceramic diaphragm is provided for housing a pressure sensor portion, which is bonded to the surface of the pressure frame opposite to the surface against which pressures of the liquid chemicals are applied. A body houses the pressure guide member, pressure frame and diaphragm.

[0007] Since a diaphragm pressure sensor of the present invention does not have an O-ring, etc. as an airtight seal for liquid chemicals installed between a ceramic diaphragm housing a pressure sensor part and a liquid contact portion, it is free from leakage of liquid chemicals caused by deterioration of an O-ring, etc. Therefore, the diaphragm in the present sensor can be fully protected from highly-corrosive liquid chemicals.

[0008] Further, a pressure guide member made of perfluoroalkoxy resin and a pressure frame also made of perfluoroalkoxy resin in the present invention are integrated such that they form a single component made of perfluoroalkoxy resin. Therefore, the present sensor can achieve excellent corrosion-resistance to strong acid, strong alkaline liquid chemicals, etc.

[0009] FIG. 1A shows a constitution of a diaphragm pressure sensor in accordance with the present invention, and

[0010] FIG. 1B shows a detail of the ceramic diaphragm 8 and pressure frame 4.

[0011] The drawings show a constitution of the diaphragm pressure sensor 1 of the present invention.

[0012] The pressure guide member 3 made of perfluoroalkoxy resin is fitted into the opening side of the body 2 of the diaphragm pressure sensor 1. The pressure frame 4 also made of perfluoroalkoxy resin is welded to the pressure guide member 3 such that the pressure frame 4 and pressure guide member 3 are integrated to form a wetted part 6 (liquid containing part) for containing liquid chemicals as is indicated by the arrow 5, pressure of which chemicals is measured.

[0013] The pressure sensor portion 7 comprises, for example, a strain resistance gauge deposited on the interior surface of the ceramic diaphragm 8, which interior surface is adjacent to the wetted part 6, such that the strain resistance gauge constitutes a part of a Wheatstone bridge. The pressure sensor portion 7 senses a fluid pressure by converting the displacement of the diaphragm 8 generated by pressure from the wetted part 6 of the liquid chemicals into the change in resistance, and then outputting the change as an electronic signal.

[0014] The diaphragm 8 and pressure frame 4 are bonded to each other by bonding a bonding surface of the ceramic diaphragm onto a sensing surface of the film-treated portion 9 of the pressure frame 4 opposite to the pressure-receiving surface to which pressure is applied. The surface of the diaphragm 8 is treated with perfluoroalkoxy resin for surface protection (indicated by slanting lines in the drawing).

[0015] In the past, it was believed that fluoroplastics such as perfluoroalkoxy resin, PTFE, etc. couldn't be bonded by bonding adhesive. However, the present inventors have found that if a small amount of organic amine compounds is added to a cyanoacrylate adhesive and the bonding surface of the ceramic diaphragm 8 is roughly worked (i.e., roughened), the pressure frame 4 made of fluoroplastics can be tightly bonded to the diaphragm 8.

[0016] The diaphragm 8 is fixed by the sensor holding portion 10 at the top of the body 2 and holding O-ring 11 so as to be stably contained in the body 2 of the diaphragm pressure sensor 1.