Liquid level sensor which prevents liquid absorption

• US 5,148,708 A
• Filed: 04/29/1991
• Issued: 09/22/1992
• Est. Priority Date: 05/08/1990
• Status: Expired due to Term

• Current Assignee: Murata Manufacturing Co Limited
• Original Assignee: Murata Manufacturing Co Limited
• Inventors: Murata, Michihiro, Matsuo, Kenji, Yamazaki, Shigeo, Kumada, Akira
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): Bennett, G. Bradley
• Application Number:
  US07/692,660
• Time in Patent Office: 512 Days
• Field of Search: 73/290 R, 73/304 R, 73/304 C, 73/305, 73/314, 73/319, 338/36, 338/38, 338/44, 338/27, 338/81, 338/94, 338/231, 128/761
• US Class Current: 73/304.00R
• CPC Class Codes: G01F 23/242 Mounting arrangements for electrodes

Abstract

A liquid level sensor for detecting a level of an electrolyte where: a pair of resistance films are formed on an insulating substrate: a plurality of electrodes are intermittently mounted on the resistance films in the longitudinal direction; the resistance films are soaked in the electrolyte in the vertical direction along the longitudinal direction; the liquid surface is detected from the variation of the resistance value of the resistance films caused by the short-circuiting of pairs of the electrodes in the electrolyte. The exposed surface of the resistance film is covered by a moisture-resistance film. The result is that undesirable change of resistance value of the resistance film caused by being moistened can be reliably prevented.

Claims

1. A liquid level sensor for detecting the level of a liquid including an electrolyte matter, comprising:

(a) an insulating substrate made of plastic thin film;

(b) a pair of resistance films disposed in parallel to each other with a predetermined space therebetween on said insulating substrate, said resistance films each having a lengthwise dimension which is larger than a widthwise dimension of said resistance films;

(c) a plurality of detecting electrodes mounted intermittently in a longitudinal direction on said resistance films, each electrode including an arm portion extending from said resistance films;

(d) lead electrodes mounted at one end of said resistance films, respectively; and

(e) a water-proof film for covering an exposed surface of said resistance films;

wherein the resistance between said lead electrodes, upon application of a voltage, depends on the liquid level of the electrolyte.

2. A liquid level sensor according to claim 1, wherein said arm portion of each said detecting electrode projects partially from said water-proof film.

3. A liquid level sensor according to claim 2, wherein each said arm portion extends on a surface of said insulating substrate in a horizontal direction from said resistance films.

4. A liquid level sensor according to claim 1, wherein water-repellent layers are formed between said detecting electrodes.

5. A liquid level sensor according to claim 1, wherein said insulating substrate is made of polyethylene-type plastic.

6. A liquid level sensor for detecting the level of a liquid including an electrolyte matter, comprising:

(a) an insulating substrate made of plastic thin film;

(b) a pair of resistance films disposed in parallel to each other with a predetermined space therebetween on said insulating substrate, said resistance films each having a lengthwise dimension which is larger than a widthwise dimension of said resistance films;

(c) a plurality of detecting electrodes mounted intermittently in a longitudinal direction on said resistance films, each electrode including an arm portion extending from said resistance films;

(d) a water-proof film for covering an exposed surface of said resistance films; and

(e) a water-proof layer at least for covering said detecting electrodes, a part of each said arm portion remaining uncovered by said water-proof layer;

wherein the resistance between said lead electrodes, upon application of a voltage, depends on the liquid level of the electrolyte.

7. A liquid level sensor according to claim 6, wherein said arm portion of each said detecting electrode projects partially from said water-proof layer.

8. A liquid level sensor according to claim 7, wherein each said arm portion projects in a horizontal direction from said resistance films.

9. A liquid level sensor according to claim 6, wherein said water-proof layer has a window for exposing said arm portion in contact with said liquid.

10. A liquid level sensor for detecting the level of a liquid including an electrolyte matter, comprising:

(a) an insulating substrate made of plastic thin film;

(b) a pair of resistance films disposed in parallel to each other with a predetermined space therebetween on said insulating substrate, said resistance films each having a lengthwise dimension which is larger than a widthwise dimension of said resistance films;

(c) a plurality of detecting electrodes formed intermittently in a longitudinal direction on said resistance films, each electrode including an arm portion extending from said resistance films;

(d) lead electrodes mounted at one end of said resistance films, respectively; and

(e) a water-proof film for covering an exposed surface of said resistance films;

wherein the resistance between said lead electrodes, upon application of a voltage, depends on the liquid level.

11. A liquid level sensor for detecting the level of a liquid according to claim 10, wherein said arm portion of each of said detecting electrodes projects partially from said water-proof film.

12. A liquid level sensor according to claim 10, wherein each said arm portion extends on a surface of said insulating substrate in a horizontal direction from said resistance films.

13. A liquid level sensor according to claim 10, wherein, wherein water-repellent layers are formed between said detecting electrodes.

14. A liquid level sensor according to claim 10, wherein said insulating substrate is made of polyethylene-type plastic.

15. A liquid level sensor according to claim 10, further comprising a water-proof layer at least for covering said detecting electrodes, a part of said arm portion remaining uncovered by said water-proof layer.

16. A liquid level sensor for detecting the level of a body fluid, comprising:

an insulating substrate;

a pair of resistance films disposed in parallel to each other with a predetermined space therebetween on said insulating substrate, said resistance films each having a lengthwise dimension which is larger than a widthwise dimension of said resistance films;

a plurality of detecting electrodes formed in a longitudinal direction on said resistance films, each electrode including an arm portion extending from said resistance films;

lead electrodes formed at one end of said resistance films, respectively; and

a water-proof film for covering an exposed surface of said resistance films;

wherein the resistance between said lead electrodes, upon application of a voltage, depends on the liquid level.

17. A liquid level sensor according to claim 16, wherein said arm portion of each said detecting electrode projects partially from said water-proof film.

18. A liquid level sensor according to claim 16, wherein each said arm portion extends on said insulating substrate in a horizontal direction from said resistance films.

19. A liquid level sensor according to claim 16, wherein water-repellent layers are formed between said detecting electrodes.

20. A liquid level sensor according to claim 16, wherein said insulating substrate is made of polyethylene-type plastic.

21. A liquid level sensor according to claim 16, further comprising a water-proof layer at least for covering said detecting electrodes, a part of each said arm portion remaining uncovered by said water-proof layer.