Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2001-03-08
2004-03-09
Strecker, Gerard R. (Department: 2862)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S900000, C073S293000, C073S305000, C073S322500, C073S705000, C340S619000, C385S013000
Reexamination Certificate
active
06703635
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of measuring a height of liquid level (water level) and a liquid-level gauge and more particularly, to a method and liquid-level gauge for measurement of a water level of liquid by measuring a change in force acted by liquid (buoyancy or hydrostatic pressure) on a body movably arranged in the liquid as a change in strain or strain level in an optical fiber.
Liquid-level gauges for measurement of a height of liquid level (water level) based on various principles have hitherto been proposed. For example, an electrostatic capacitance type liquid-level gauge (JP-A-2000-097750 or JP-A-11-030544), a barometric liquid-level gauge (JP-A-2000-088629), a float type liquid-level gauge (JP-A-10-148565 or JP-A-11-326015), an electrode type liquid-level gauge (JP-A-11-023346) and an electric wave type liquid-level gauge (JP-A-10-197617) have been known. Specifically, the present invention contemplates a float or comparable type liquid-level gauge and a barometric or comparable type liquid-level gauge, especially, using an optical fiber.
The float type liquid-level gauge detects a height of a float that ascends/descends as the liquid-level changes and conventionally, it is classified into two kinds of which one uses reed switches and a magnet and the other uses a wire or a tape. Structurally, the former float type liquid-level gauge using reed switches and a magnet has many reed switches that are operated by the magnet as the float ascends or descends. On the other hand, in the latter float type liquid-level gauge using a wire, a measuring wire attached to a float is wound up to calculate a liquid water level from a windup amount.
On the other hand, a barometric liquid-level gauge as exemplified in
FIG. 20
has hitherto been employed. In the barometric liquid-level gauge, an air supply pipe
300
having an open lower end is dipped vertically in liquid
200
stored in a tank
100
and compressed air
500
is supplied to the air supply pipe
300
by means of a pump
400
. As the supply of compressed air
500
to the air supply pipe
300
proceeds, air fills in the air supply pipe
300
in opposition to a pressure of the liquid
200
stored in the tank
100
. When saturated in the air supply pipe
300
, the air is discharged to the liquid
200
in the form of bubbles through the lower open end of the air supply pipe
300
. At that time, a pressure P in the air supply pipe
300
equals a head pressure &rgr;H when no gas pressure is applied onto the liquid level, the liquid level in the tank
100
is H and density of the liquid
200
is &rgr;. Therefore, the pressure P in the air supply pipe
300
is measured by means of a pressure sensor
700
and a measured value is indicated in terms of liquid level height on an indicator.
SUMMARY OF THE INVENTION
In the conventional float type liquid-level gauge, especially, using reed switches and a magnet, however, it is necessary that the magnet be built in the float and a great number of reed switches be incorporated in guide pipes for guiding the float, raising a problem that the number of parts increases and the structure is complicated.
On the other hand, in the float type liquid-level gauge using a wire, many parts such as a windup drum for the wire, a windup motor and a pulley are needed, so that the apparatus is increased in scale and is often troubled because of mechanical windup, thus requiring laborious and time-consuming work for repairs and maintenance.
Further, the conventional barometric liquid-level gauge faces problems that the pump
400
for supplying the compressed air
500
to the air supply pipe
300
is needed and during measurement, the pump
400
must be driven constantly to supply the compressed air
500
.
Under the circumstances, the present inventors have studied and conducted experiments in various ways by noticing a change in buoyancy which a body receives from liquid as the liquid level changes in the float type or comparable type (suspension type) liquid-level gauge to confirm that the water level of the liquid can be measured by detecting the change in buoyancy as a change in strain in an optical fiber.
Experiments have been conducted also in the barometric or comparable type liquid-level gauge to confirm that the liquid level height can be measured by displacing a pressure receiving member in accordance with a change in liquid pressure, applying tension to an optical fiber in accordance with the displacement to generate strain in the optical fiber and detecting the strain.
The present invention has been made in the light of the conventional problems and the results of experiments and it is an object of the invention to provide liquid-level measuring method and liquid-level gauge which can measure a water level accurately by using an optical fiber connected to force receiving means movably arranged in liquid to receive force from the liquid and detecting a change in force due to a change in liquid level as strain in the optical fiber or a change in strain therein.
To accomplish the above object, in a method of measuring a liquid level according to the present invention, an optical fiber connected at its one end portion to force receiving means movably arranged in liquid to receive force from the liquid is dipped in the liquid together with the force receiving means, and a change in the force acting on the force receiving means when the liquid level changes is detected as a change in strain in the optical fiber by means of an optical fiber strain gauge connected to the other end of the optical fiber.
The precedently determined correlation between changes in strain in the optical fiber and changes in liquid level of the liquid is consulted on the basis of the detected value to determine a water level of the liquid.
A liquid-level gauge according to the invention comprises an optical fiber, force receiving means connected to one end portion of the optical fiber and movably arranged, together with the optical fiber, in liquid to receive force from the liquid, and optical fiber strain measuring means connected to the other end portion of the optical fiber to detect, as a change in strain in the optical fiber, a change in the force acting on the force receiving means when the liquid level of the liquid changes.
Preferably, the optical fiber strain measuring means is a Brillouin-optical time domain reflector (hereinafter simply referred to as B-OTDR).
According to one aspect of the invention, in a method of measuring a liquid level, a float having a cross-sectional form that is uniform in the height direction and a specific weight value less than that of liquid is dipped in the liquid, the float is supported by an optical fiber in such a manner that an upper end of the optical fiber constantly protrudes from the liquid level, the optical fiber is connected at its upper end to an optical fiber strain gauge, and a change in buoyancy acting on the float as the water level of the liquid changes is detected as a change in strain in the optical fiber by means of the optical fiber strain gauge, thus measuring a water level of the liquid.
According to a second aspect of the invention, in a method of measuring a liquid level, a suspension member having a cross-sectional form that is uniform in the height direction and a specific weight value not less than that of liquid is suspended by an optical fiber so as to be dipped in the liquid in such a manner that an upper end of the suspension member constantly protrudes from the liquid level, the optical fiber is connected to an optical fiber strain gauge, and a change in buoyancy acting on the suspension member as the water level of the liquid changes is detected as a change in strain in the optical fiber by means of the optical fiber strain gauge, thus measuring a water level of the liquid.
In embodiments of the float type liquid-level gauge according to the invention, a liquid-level gauge comprises a float having a cross-sectional form that is uniform in the height direction and a specific weight value less than that of liq
Mochizuki Satoshi
Yashiro Takamasa
Yoshitomi Takaharu
Blakely & Sokoloff, Taylor & Zafman
NTT Advanced Technology Corporation
Strecker Gerard R.
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