Liquid level sensor

1. A liquid level sensor comprising:

a sleeve disposed so as to extend in a vertical direction,

a float configured so as to move along said sleeve according to fluctuation of liquid level,

a resistor string including a plurality of resistors connected in series and having both ends always connected with a direct current power supply,

a plurality of grounding means disposed inside said sleeve respectively corresponding to junction parts between adjacent resistors included in said resistors in said resistor string, and configured such that said junction part is grounded when said float is located within a predetermined distance from the corresponding junction part and said junction part is not grounded when said float is not located within the predetermined distance from the corresponding junction part, and

a liquid level signal output means configured so as to take out an electric signal detected between a positive electrode side end part that is an end part connected with a positive electrode of said direct current power supply among said both end parts of said resistor string and said junction part grounded by said grounding means as a liquid level signal that is a signal corresponding to said liquid level,

characterized by further comprising:

a warning signal output means configured such that a warning signal is output when said float is located within a predetermined distance from a warning position that is a predetermined position within a movable range of said float and the warning signal is not output when said float is not located within the predetermined distance from said warning position, and

a positive electrode grounding means configured such that said positive electrode side end part or said junction part closest to said positive electrode side end part is grounded when said float is located within a predetermined distance from said grounding means corresponding to said junction part closest to said positive electrode side end part among a plurality of said grounding means or when said float is located outside the grounding means, and

a negative electrode grounding means configured such that said junction part closest to a negative electrode side end part, which is an end part on a side opposite to said positive electrode side end part of said resistor string, is grounded when said float is located within a predetermined distance from said grounding means corresponding to said junction part closest to said negative electrode side end part among a plurality of said grounding means or when said float is located outside the grounding means.

2. The liquid level sensor according to claim 1 , characterized in that:

said warning signal output means is constituted by a power source different from said direct current power supply.

3. The liquid level sensor according to claim 1 , characterized in that:

said direct current power supply comprises a constant current circuit, and

resistance values of said resistors which constitute said resistor string are all identical.

4. The liquid level sensor according to claim 3 , characterized in that:

said warning signal output means is constituted by a power source different from said direct current power supply.

5. The liquid level sensor according to claim 1 , characterized in that:

said float comprises a magnet,

said grounding means is configured such that said corresponding junction part is grounded when a magnetic field generated by said magnet is detected and said corresponding junction part is not grounded when a magnetic field generated by said magnet is not detected, and

said warning signal output means is configured such that said warning signal is output when a magnetic field generated by said magnet is detected and said warning signal is not output when a magnetic field generated by said magnet is not detected.

6. The liquid level sensor according to claim 5 , characterized in that:

said warning signal output means is constituted by a power source different from said direct current power supply.

7. The liquid level sensor according to claim 5 , characterized in that:

said direct current power supply comprises a constant current circuit, and

resistance values of said resistors which constitute said resistor string are all identical.

8. The liquid level sensor according to claim 7 , characterized in that:

said warning signal output means is constituted by a power source different from said direct current power supply.

9. The liquid level sensor according to claim 5 , characterized in that:

said grounding means and said warning signal output means comprise either a reed switch or a Hall IC.

10. The liquid level sensor according to claim 9 , characterized in that:

said warning signal output means is constituted by a power source different from said direct current power supply.

11. The liquid level sensor according to claim 9 , characterized in that:

said direct current power supply comprises a constant current circuit, and

resistance values of said resistors which constitute said resistor string are all identical.

12. The liquid level sensor according to claim 11 , characterized in that:

said warning signal output means is constituted by a power source different from said direct current power supply.

13. The liquid level sensor according to claim 1 , characterized in that:

said warning signal output means comprises a logic inverting means.

14. The liquid level sensor according to claim 13 , characterized in that:

said warning signal output means is constituted by a power source different from said direct current power supply.

15. The liquid level sensor according to claim 13 , characterized in that:

said direct current power supply comprises a constant current circuit, and

resistance values of said resistors which constitute said resistor string are all identical.

16. The liquid level sensor according to claim 15 , characterized in that:

said warning signal output means is constituted by a power source different from said direct current power supply.

17. The liquid level sensor according to claim 13 , characterized in that:

said float comprises a magnet,

said grounding means is configured such that said corresponding junction part is grounded when a magnetic field generated by said magnet is detected and said corresponding junction part is not grounded when a magnetic field generated by said magnet is not detected, and

said warning signal output means is configured such that said warning signal is output when a magnetic field generated by said magnet is detected and said warning signal is not output when a magnetic field generated by said magnet is not detected.

18. The liquid level sensor according to claim 17 , characterized in that:

said warning signal output means is constituted by a power source different from said direct current power supply.

19. The liquid level sensor according to claim 17 , characterized in that:

said direct current power supply comprises a constant current circuit, and

resistance values of said resistors which constitute said resistor string are all identical.

20. The liquid level sensor according to claim 19 , characterized in that:

said warning signal output means is constituted by a power source different from said direct current power supply.

21. The liquid level sensor according to claim 17 , characterized in that:

said grounding means and said warning signal output means comprise either a reed switch or a Hall IC.

22. The liquid level sensor according to claim 21 , characterized in that:

said warning signal output means is constituted by a power source different from said direct current power supply.

23. The liquid level sensor according to claim 21 , characterized in that:

said direct current power supply comprises a constant current circuit, and

resistance values of said resistors which constitute said resistor string are all identical.

24. The liquid level sensor according to claim 23 , characterized in that:

said warning signal output means is constituted by a power source different from said direct current power supply.