Fluid Level Encoder
Fluid level measurement is of vital importance in many circumstances. As such, many techniques have been invented to measure fluid level. We have invented a fundamentally new technique which is analogous to rotary optical encoders. In this case, we build an optical structure which blocks the transmission of light only when the fluid is within a certain range of levels. These structures can be serially stacked to create encoder channels which respond to fluid levels in a plurality of ranges. Multiple stacks can then be combined to create incremental, absolute, or any of a variety of standard encoder topologies. This provides a direct, calibration-free, digital measurement of fluid level that can be mass produced at minimal cost.
Background & Objective: There are many methods of measuring fluid level. One of the most elegant uses a cylindrical lens which comes to a point. In air, light sent through the lens is reflected back by total internal reflection. However, when immersed in fluid, the difference in index in refraction gets smaller, allowing the light to escape, so little is returned. The one draw back of this otherwise elegant technique is that a separate sensor is needed for each detection level. Our goal was to create a method which had similar desirable properties (inexpensive, reliable, explosion proof, no moving parts, etc.) but that only needed log2(n) sensors to detect n levels.
Technical Discussion: The key to the optical fluid level encoder is to create a structure which blocks the transmission of light only when the fluid is within a certain range of levels. If you imagine a flashlight held under water, perpendicular to the surface, you would be able to see much of the light escaping through the surface. As the angle of the flashlight is changed, the amount of light escaping decreases until the critical angle is reached, at which point all of the light is reflected off the air-water interface and none escapes. However, if one were to place a glass rod along the line of the beam, the light would then be able to escape, following the clear path of the rod through the surface. If we instead had sections of rod all lined up along the beam path, light would be able to pass through, unless the water surface lay in between rod segments. This creates an encoder channel.
Contacts:
Darren Leigh
Joseph Katz
William Yerazunis
Technology Area: Sensor and Data Systems
Modification Date: November 1, 2007
