Abstract:
A method and apparatus for deploying a luminescent dissolved oxygen sensor where the luminescent material is already stable, is disclosed. The luminescent material of the sensor is shipped immersed in fluid. The luminescent material of the sensor may be pre-saturated in a fluid before shipping or may be allowed to saturate during shipping.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention is related to the field of sensors, and in particular, to a system and method for shipping a replacement part for a luminescent dissolved oxygen sensor in a saturated condition.  
         [0003]     2. Statement of the Problem  
         [0004]     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.  
         [0005]     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&#39;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.  
         [0006]     Luminescent quenching of the luminescent material varies dependent on how long the luminescent material has been immersed in water. A dry sensor, when first immersed in water, will have a stable response for the concentration of oxygen in the water for a short period of time, typically up to two hours. As the luminescent material slowly becomes saturated with water, the luminescent response for a given oxygen concentration will slowly change. Once the luminescent material becomes fully saturated with water, typically after about three days, the luminescent response stabilizes. A user that replaces a luminescent oxygen sensor in the field with a dry sensor, may not get an accurate reading from the sensor for up to three days. After the probe stabilized, the user would still need to recalibrate the instrument to ensure the accuracy of the readings. Most users would like to start accurately measuring the oxygen concentration in the water as soon as the sensor is deployed.  
         [0007]     Therefore there is a need for a system and method for deploying a luminescent dissolved oxygen sensor that is already stable.  
       SUMMARY OF THE INVENTION  
       [0008]     A method and apparatus for deploying a luminescent dissolved oxygen sensor where the luminescent material is already stable, is disclosed. The luminescent material of the sensor is shipped immersed in fluid or enclosed in a container with water saturated air. The luminescent material of the sensor may be pre-saturated before shipping or may be allowed to saturate during shipping. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is an exploded view of luminescent dissolved oxygen sensor  100 .  
         [0010]      FIG. 2  is an exploded view of shipping container  200 , in an example embodiment of the invention.  
         [0011]      FIG. 3 a  cross-sectional view of a side sensing luminescent dissolved oxygen sensor  300 .  
         [0012]      FIG. 4  is a cross-sectional view of an end sensing luminescent dissolved oxygen sensor  400 .  
         [0013]      FIG. 5  is an isometric view of field replaceable part  330 .  
         [0014]      FIG. 6  is a cross-sectional view of a lid for a shipping container in an example embodiment of the invention.  
         [0015]      FIG. 7  is an exploded view of shipping container  700  in another example embodiment of the invention.  
         [0016]      FIG. 8  is an exploded view of shipping container  800  in another example embodiment of the invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]      FIGS. 1-9  and the following description depict specific examples to teach those skilled in the art how to make and use the best mode of the invention. For the purpose of teaching inventive principles, some conventional aspects have been simplified or omitted. Those skilled in the art will appreciate variations from these examples that fall within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific examples described below, but only by the claims and their equivalents.  
         [0018]     Luminescent dissolved oxygen sensors (also called probes) are immersed in water during use. The luminescent material must be exposed to the water for the sensor to operate properly. The surface of the sensor exposed to the water may become fouled over time by biological growth or sediment. The fouled sensor may have reduced response time, inaccurate performance, or both. Removing the growth or sediment may damage the luminescent material and affect the sensor performance or accuracy. Some sensors solve this problem by using a field replaceable part that contains the luminescent material.  
         [0019]      FIG. 1  is an exploded view of luminescent dissolved oxygen sensor  100 . Luminescent dissolved oxygen sensor  100  comprises probe body  102 , cap  108 , O-ring  106 , and seal  104 . Cap  108  has a luminescent material deposited on face  110 . Luminescent material  112  is typically a mix of Polystyrene and Platinum Porphynin. The luminescent material is covered by an optically opaque hydrostatically transparent material that allows water to penetrate to the luminescent material but prevents light from penetrating to the luminescent material. One example of an optically opaque hydrostatically transparent material is a mix of carbon lamp black and Polybutyl Methacrylate. Cap  108  is configured to screw onto threads  112  on probe body  102 . O-ring  106  and seal  104  help form a water tight seal between cap  108  and body  102 . Cap  108  is designed to be field replaceable. A user can remove the probe from the water, remove the fouled cap from the probe and replace it with a new cap, then re-install the probe back into the water. Unfortunately, if the field replaceable cap is dry, the probe readings may not stabilize for up to three days as the luminescent material on the new cap slowly becomes saturated with water.  
         [0020]      FIG. 2  is an exploded view of shipping container  200 , in an example embodiment of the invention. Shipping container  200  comprises main body  220  and lid  222 . Main body  220  has a cavity formed to hold liquid. Lid  222  is configured to attach to main body  220  and seal the cavity, forming a water tight container. Lid  222  can use a number of different fastening methods to attach to main body  220 , for example lid may screw onto main body, lid may snap onto main body, or the like. An O-ring or gasket (not shown) may be used to help form the seal between lid  222  and main body  220 . There is a mounting structure on the bottom side of lid  222  configured to hold field replaceable cap  208 . The mounting structure on the bottom of lid  222  may take any number of shapes. In one example embodiment of the invention, the mounting structure replicates the threaded end of the probe body. The field replaceable cap is screwed onto the bottom of lid  222  that replicates the threaded end of the probe. A mounting structure may alternately be formed inside the cavity in the main body of the shipping container, instead of on the bottom of the lid.  
         [0021]     In operation, field replaceable cap  208  is mounted onto the bottom of lid  222 . Fluid is added to the cavity in main body  220 . Lid  222  is attached to main body  220  sealing the cavity and holding field replaceable cap  208  into the cavity. In one example embodiment of the invention, the end of field replaceable cap  208  is held in the fluid when the lid  222  is attached to the main body  220 . In another embodiment of the invention, the end of field replaceable cap  208  is held above the top level of the fluid and does not contact the fluid. In this embodiment, the fluid in the sealed cavity keeps the air in the cavity saturated with the fluid, thereby saturating the luminescent material. In one example embodiment of the invention, a sponge (not shown) may be installed in the cavity. The sponge may reduce the amount of fluid required in the cavity to keep the bottom of the field replaceable cap  208  saturated with the fluid. A heat shrink band (not shown) may be installed around the lid  222  of the shipping container to help prevent unwanted separation of the lid  222  from the main body  220 .  
         [0022]     In one example embodiment of the invention, a water tight seal is formed between the field replaceable cap  208  and the lid  222 . An O-ring or gasket may be used to help form the water tight seal between the field replaceable cap  208  and the lid  222 . The water tight seal prevents fluid in the shipping container from getting into the inner surface of field replaceable cap  208 . Installing the field replaceable cap  208  onto a probe with water on the inner surface of the field replaceable cap  208  may cause inaccurate sensor measurements. Drying the inner surface of the field replaceable cap  208  may be difficult in the field. With a water tight seal between the field replaceable cap  208  and the lid  222 , the user can just remove the lid from the body, remove the cap  208  from the lid  222 , and attach the cap  208  to the probe body  102 .  
         [0023]     The luminescent material on the field replaceable part may take some time to fully saturate after being immersed in fluid. The time to saturate may be dependent on the thickness of the luminescent material, the thickness of the optically opaque hydrostatically transparent material covering the luminescent material, the part geometry, or the like. The saturation time can easily be determined. In some cases, the time needed to ship the field replaceable part to its destination may be less that the saturation time. In one example embodiment of the invention, the luminescent material on the replacement part is pre-saturated before being inserted into the shipping container. In another example embodiment of the invention, the replacement part is installed into the shipping container and then allowed to saturate in the shipping container before being shipped. A combination of pre-saturation time and shipping time may also be used to ensure that the luminescent material on the replacement part is fully saturated when the replacement part reaches its destination.  
         [0024]     The field replaceable part containing the luminescent material need not be in the shape of a cap.  FIG. 3  is a cross-sectional view of a side viewing luminescent dissolved oxygen sensor  300 . Sensor  300  has field replaceable sensor part  330  comprising a hydrostatic barrier  310 , a luminescent material  312 , and an optically opaque hydrostatically transparent material  314  covering the luminescent material  312 .  FIG. 4  is a cross-sectional view of an end sensing luminescent dissolved oxygen sensor  400 . Sensor  400  also has a field replaceable part comprising a hydrostatic barrier  410 , a luminescent material  412 , and an optically opaque hydrostatically transparent material  414  covering the luminescent material  412 .  FIG. 5  is an isometric view of field replaceable part  530  having hydrostatic barrier  510 , a luminescent material  512 , and an optically opaque hydrostatically transparent material  514 . The drawings are not to scale and some thicknesses have been increased for clarity in explaining the invention, for example, in practice the optically opaque hydrostatically transparent material may only be a thin layer (10-20 microns) deposited over the other layers.  
         [0025]      FIG. 6  is a cross-sectional view of a lid for a shipping container in an example embodiment of the invention. Lid  622  is configured to attach to the main body (not shown) of a shipping container. Lid  622  has a mounting feature formed in the bottom side of the lid used to hold a field replaceable part  630  containing a luminescent material similar to the part shown in  FIG. 5 . Field replaceable part  630  comprises a hydrostatic barrier  610 , a luminescent material  612 , and an optically opaque hydrostatically transparent material  614  covering the luminescent material  612 . Field replaceable part  630  is held onto the mounting structure with retaining ring  608 . A water tight seal may be formed between the mounting structure and field replaceable part  630  such that one side of field replaceable part  630  is kept dry during shipment. Lid  622  is attached onto the main body (not shown) of the shipping container thereby holding field replaceable part immersed in fluid. Because field replaceable part  630  is essentially flat, it may not be difficult to dry one side in the field. This may allow more flexibility in the design of the shipping container.  
         [0026]      FIG. 7  is an exploded view of shipping container  700  in another example embodiment of the invention. Shipping container  700  comprises sealable bag  732  and shipping box  734 . In operation, field replaceable part  730  is inserted into sealable bag  732 . Fluid is added to sealable bag and then the bag is sealed. The sealed bag is inserted into shipping box  734 . Shipping box  734  is configured to protect sealable bag  732  from rupture during shipment. When a user receives field replaceable part  730 , the user will remove the bag from the shipping box, remove the part from the bag, dry the hydrostatic barrier side of the part, and then install the part into the probe.  
         [0027]      FIG. 8  is an exploded view of shipping container  800  in another example embodiment of the invention. Shipping container  800  comprises main body  820  and lid  822 . Main body  820  has a cavity configured to hold fluid. Slot  836  is formed on the inner sides of the cavity. Lid  822  is configured to attach to main body  820  and seal the cavity, forming a water tight compartment in the shipping container. In operation, field replaceable part  830  is inserted into slot  836 . Fluid is added to the cavity, immersing field replaceable part  830 . Lid is attached to main body  820 , thereby sealing the cavity. Lid may also be configured to hold field replaceable part into slot  836 .