Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1989-11-15
1991-03-05
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
250903, 73293, 356136, G01N 1506
Patent
active
049980220
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates generally to the field of optical liquid level sensors, and, more particularly, to an improved liquid level sensor which is particularly adapted for use with corrosive liquids that would otherwise chemically attack a conventional optical sensor.
BACKGROUND ART
It is frequently necessary to measure or monitor the level of liquid in a tank or container. This has commonly been done by means of a float-type device.
However, it is also known to measure the liquid level by means of a plurality of optical sensors, which are positioned on the tank wall at various vertically-spaced elevations. Basically, a transparent body is provided with a conical or prismatic tip end portion. Light is propagated within the body toward the tip end portion, and is reflected by two surfaces at the tip end portion back toward a receiver. The body is typically glass and has a refractive index of about 1.50. If the tip end portion is exposed to air above the surface of the liquid, the "critical angle", at which all light is reflected within the body, may be calculated from the equation: refraction of the fluid (i.e., air) to which the tip is exposed, and n.sub.1 is the index of refraction of the material (i.e., glass) of the tip end portion. Thus, for air, n.sub.2 =1.00; and for glass, n.sub.1 =1.50. Hence, this equation may readily be solved, and the "critical angle" for a glass body with respect to air is about 42.degree.. On the other hand, if the tip end portion is submerged in a liquid, such as water (i.e., n=1.33), then the "critical angle" with respect to water is about 62.5.degree..
If the prismatic surfaces are ground such that the angles of incidence are equal to or greater than the "critical angle", then all of the light propagated along the sensor body will be reflected internally of the body, and no portion of such incident light will be refracted into the surrounding fluid. This is known as the phenomenon of "total internal reflection". On the other hand, if the angle of incidence is less than the "critical angle", then only a portion of the light will be reflected, with the balance being refracted into the fluid surrounding the tip end portion.
Upon information and belief, such prior art devices have been commonly formed such that the angle of incidence (.theta..sub.i) is about 45.degree.. Hence, incident light strikes a first surface, is reflected to a second surface, and is thereafter reflected back through the body in a direction substantially parallel to the incident light beam. At the same time, such angle (i.e., 45.degree.) is greater than the "critical angle" for air/glass (i.e., .theta..sub.c =42.degree.), such that "total internal reflection" occurs when the tip end portion is exposed to air. However, if the tip end portion is submerged in water, the angle of incidence is less than the "critical angle" for water/glass (i.e., .theta..sub.c =62.5.degree.). Hence, an incident light beam will be twice refracted into the liquid. The first refraction would occur at the first surface, and the second at the second surface.
This principle (i.e., that "total internal reflection" occurs if the tip end portion is exposed to air, but that light is refracted if the tip end portion is submerged in liquid) has been used to measure the level of liquid in a tank. See, e.g., Rakucewicz, "Fiber-Optic Methods of Level Sensing", Sensors (Dec. 1986) [at p. 5 et seq] As indicated above, a plurality of such sensors are typically mounted on the tank wall at various vertically-spaced locations. Those sensors which are arranged above the liquid level will reflect light at a greater intensity than those which are submerged in the liquid. Thus, depending on the intensity of the internally-reflected light, one can infer whether such sensor is above or below the liquid surface.
However, in some instances, the serviced fluid may chemically attack the material of which the sensor body is made. For example, one common optical material, glass, is chemically attacked by hydroflouric acid (HF). Another com
REFERENCES:
patent: 4320291 (1982-03-01), Uramoto
patent: 4322713 (1982-03-01), Duck et al.
patent: 4354180 (1982-10-01), Harding
patent: 4427293 (1984-01-01), Harmer
patent: 4440022 (1984-03-01), Masom
patent: 4676638 (1987-06-01), Yasuda
patent: 4783599 (1988-11-01), Borden
patent: 4859864 (1989-08-01), Smith
patent: 4881487 (1989-11-01), Moore
patent: 4882499 (1989-11-01), Luukkala et al.
Allen Stephone B.
Conax Buffalo Corporation
Nelms David C.
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