Patent Application
20070141695
1. FIELD OF THE INVENTION
The invention is related to the field of sensors, and in particular, to a luminescent dissolved oxygen sensor with a system and method for visual verification.
2. STATEMENT OF THE PROBLEM
The concentration of oxygen in water can be measured with a probe. The oxygen in the water interacts with a luminescent material on the outside of the probe. This interaction between the oxygen and the luminescent material results in a phenomenon known as luminescent quenching. Thus, the amount of luminescent quenching indicates the concentration of oxygen in the water.
In operation, the probe directs a light source centered at one wavelength onto the luminescent material. The light causes the luminescent material to generate luminescent light centered at a different wavelength. Luminescence quenching affects the amount of time that the luminescent material continues to luminescence light. Thus, if the light source's signal varies sinusoidally, the luminescence quenching affects the phase shift between the excitation light and the luminescent light. The probe uses an optical sensor to measures the phase shift between the excitation light and the luminescent light to assess the amount of luminescent quenching. As a result, the probe processes the phase shift to determine the concentration of oxygen in the water. An example of such a probe is disclosed in U.S. Pat. No. 6,912,050 entitled “Phase shift measurement for luminescent light” filed Feb. 3, 2003, which is hereby incorporated by reference.
Sinusoidally varying the signal to the light source causes the light source to pulse on and off. In some probes, the light source is visible, allowing a user to determine when the probe is operating by viewing the pulsing light. Unfortunately, daylight hitting the luminescent material or the optical sensor can cause inaccuracies in the measurement of the concentration of oxygen in the water. Therefore the luminescent material and the optical sensor are now typically shielded from daylight. This may be done by enclosing the light source, the optical sensor, and the luminescent material inside a light tight container. The light tight container shields the light source in the probe from view and prevents a user from visually detecting when the probe is operating. Without a visual means for verifying that the probe is operating, the senor must be connected to a computer or other device to verify operation. A user may not have access to a computer when checking or installing the probe in the field. Even when the user has access to a computer, connecting the probe to a computer to verify probe operation takes more time than a simple visual verification.
Therefore there is a need for a system and method for allowing a user to visually detect when a luminescent dissolved oxygen sensor is operating.
A method and apparatus for visually detecting when a luminescent dissolved oxygen sensor is operating is disclosed. In one example embodiment of the invention, a shutter is placed into the light tight container. When the shutter is open, a user can see into the light tight container and verify probe operation. When the shutter is closed, external light is prevented from entering the light tight container and affecting measurement accuracy. In another example embodiment of the invention, one end of a light pipe is placed on the outside of the light tight container, and the other end is positioned to view the light source of the probe. In another example embodiment of the invention a second light source, visible on the outside of the light tight container, is used to verify operation of the probe. In another example embodiment of the invention, a predetermined area is left open in the optically opaque hydrostatically transparent on the face of the sensor window, allowing a user to see light from the sensor when the sensor is operating properly.
Luminescent dissolved oxygen sensors (also called probes) can be made using a number of different layouts. Some sensors place the luminescent material on the end of the sensor and some place the luminescent material on the side of the sensor. Sensors with different layouts typically have a number of common design elements.
Body 102 contains light source 104 and optical detector/sensor 106 as well as electronics (not shown) used to drive the light source 104 and the optical detector 106. Light source 104, optical sensor 106, and electronics typically need to be kept dry. A hydrostatic barrier 110 forms a seal against body 102 to prevent fluids from entering the cavity formed by body 102. An O-ring or gasket (not shown) may be used to help form the seal between the hydrostatic barrier 110 and the body 102. The hydrostatic barrier 110 can be made from any material that is optically transparent and hydrostatically opaque, for example plastic, glass, crystal, or the like. The luminescent material 112 is placed on top of the hydrostatic barrier 110. An optically opaque hydrostatically transparent material 114 is placed on top of the luminescent material 112. A retaining cap 108 is used to hold the hydrostatic barrier 110, luminescent material 112, and optically opaque hydrostatically transparent material 114 onto the body 102. The retaining cap is made from an optically opaque material or coated with an optically opaque material. The body 102, the retaining cap 108, and the optically opaque hydrostatically transparent material 114 form a light tight container around light source 104, optical detector 106, and luminescent material 112.
In operation, the probe is immersed in water. The optically opaque hydrostatically transparent material 114 allows water to penetrate to the luminescent material 112. Hydrostatic barrier 110 prevents the water from entering the cavity formed by the body 102. The wet luminescent material is illuminated by light source 104 through hydrostatic barrier 110. The luminescent material 112 emits light in response to the illumination from light source 104. The duration of the response is dependent on the concentration of oxygen in the water. Optical sensor 106 detects the light emitted from the luminescent material 112.
Body 202 contains light source 204 and optical detector/sensor 206 as well as electronics (not shown) used to drive the light source and the optical detector 206. Light source 204, optical sensor 106, and electronics typically need to be kept dry. A hydrostatic barrier 210 forms a seal against body 202 to prevent fluids from entering the cavity formed by body 202. An O-ring or gasket (not shown) may be used to help form the seal between the hydrostatic barrier 210 and the body 202. The hydrostatic barrier 210 can be made from any material that is optically transparent and hydrostatically opaque, for example plastic, glass, crystal, or the like. The hydrostatic barrier is shaped as a cap that screws onto body 202. The luminescent material 212 is placed on top of the hydrostatic barrier 210. An optically opaque hydrostatically transparent 214 material is placed on top of the luminescent material 212 and surrounds hydrostatic barrier 210. The body 202 and the optically opaque hydrostatically transparent material 214 form a light tight container around light source 204, optical detector 206, and luminescent material 212. Shutter 216 is placed on top of luminescent material 212. Shutter can be opened or closed. When closed, shutter is optically opaque. When open, shutter is optically transparent and allows light from luminescent material 212 or from light source 204 to exit the light tight container and be seen by a user, allowing visual verification of probe 200 operation. In one example embodiment of the invention, a user would open the shutter and visually verify that the probe was operating. Once the user has visually verified that the probe was operating, the user would close the shutter. Shutter 216 can be an optical shutter, for example a liquid crystal shutter, a mechanical shutter, or the like.
Mechanical shutters are well known in the arts. Any type of mechanical shutter can be used as shutter 216. Some of the possible embodiments include a sliding or rotating door, a rotating vain, a folded flexible material (like Venetian blinds), an iris, or the like. Shutter 216 can be manually operated or power driven, for example using an electro-magnetic force. Shutter 216 is not required to be located on top of luminescent material 212. Shutter 216 can be located anywhere in the perimeter of the light tight container such that when the shutter is open it allows light to exit the light tight container.
In operation the PC board is mounted inside a probe with the light source and the optical sensor facing a luminescent material. A first end of light pipe 430 is directed towards light source 404. The first end of the light pipe 430 may be clamped, held or glued in place. The optical axis of the first end light pipe 430 may be directed towards the light source with an orientation directed away from the optical sensor 406 and directed towards the PC board. With this orientation, any light that exits the first end of the light pipe is directed away from the optical sensor and away from the luminescent material. In one example embodiment of the invention, the optical axis of the light pipe is perpendicular to a line running between the light source and the optical sensor. When sensor board 400 is installed into a probe, the second end of the light pipe is mounted such that it can be seen on the outside of the light tight container. This allows a user to look at the second end of the light pipe and determine when the light source in the probe is functioning. A band pass filter (not shown) corresponding to the wavelength of the light source may optionally be attached to either end of the light pipe. The band pass filter would prevent any light not corresponding to the wavelength of the light source from being transmitted through the light pipe. This would limit the amount of external light entering the probe through the light pipe.
Body 502 contains light source 504 and optical detector/sensor 506 as well as electronics (not shown) used to drive the light source 504 and the optical detector 506. The hydrostatic barrier is shaped as a cap that screws onto body 502. The luminescent material 512 is placed on top of the hydrostatic barrier 510. An optically opaque hydrostatically transparent 514 material is placed on top of the luminescent material 512 and surrounds hydrostatic barrier 510. The body 502 and the optically opaque hydrostatically transparent material 514 form a light tight container around light source 504, optical detector 506, and luminescent material 512. A first end of light pipe 526 is directed towards light source 504. The second end of light pipe 526 is mounted such that it is visible from the outside of the light tight container.
In another example embodiment of the invention, the probe would have two light sources. The first light source would be used to illuminate the luminescent material, and the second light source would be use to signal the user that the probe was operating. The second light source would be mounted such that the light from the second source would be visible outside the light tight container while preventing external light from entering the light tight container. In one example embodiment of the invention, the second light source 628 would fit into an opening in the body of the probe (see
In one example embodiment of the invention, at least one small area is left uncovered by the optically opaque hydrostatically transparent material. The uncovered or exposed area can be on the flat sensor face, for example small area 744. The uncovered or exposed area can be on the chamfer, for example small area 750. The uncovered or exposed area can be on the side face, for example small area 746. In one embodiment of the invention, there are a plurality of uncovered or exposed areas distributed at different places on the sensor cap. By limiting the uncovered or exposed area to a small portion of the total area of the sensor, the effect on the accuracy of the sensor can be minimized while providing the user with visual verification that the sensor is operating properly. In one example embodiment of the invention, the exposed or uncovered area is smaller than 5% of the total sensor area, where the total sensor area is the area covered by the luminescent material. The position or location of the uncovered area may allow the size of the area to be increased. When the uncovered area is placed in a location as far away from the optical sensor as possible, the size of the uncovered area may be increased. The uncovered areas can be formed by removing the optically opaque hydrostatically transparent material or by masking small areas during the application of the optically opaque hydrostatically transparent material to the sensor cap.
