Abstract:
A method and system are described for detecting a fluid level within a fluid vessel by disposing a wireless fluid sensor module in the fluid vessel, measuring at least one characteristic of a fluid in the fluid vessel, and wirelessly transmitting the measured at least one characteristic to a receiver disposed external to the fluid vessel.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No. 61/529,757, filed on Aug. 31, 2011, which is herein incorporated by reference in its entirety. 
     
    
     BACKGROUND OF INVENTION 
       [0002]    The present invention pertains, in general, to instrumentation for field and process vessels and, in particular, to the determination of fluid level inside vessels. In most situations, determination of fluid level inside of a vessel is accomplished by installing a sensor device inside the vessel with wiring connected to a collection point outside of the vessel from which the data are often forwarded to a local or remote monitoring system. The sensors can be based on many phenomena, such as position of floats on top of the fluid level interface(s), measurement of fluid pressure which can be converted to level height, ultrasonic travel time measurement to the fluid level, microwave, optical travel time sensors or time delay reflectometry techniques. 
       SUMMARY OF INVENTION 
       [0003]    In general, in one aspect, one or more embodiments of the invention are directed to a fluid level detection system. The detection system includes a wireless fluid sensor module disposed within a fluid vessel and a wireless receiver device disposed external to the fluid vessel. 
         [0004]    In general, in one aspect, one or more embodiments of the invention are directed to a fluid level detection module. The fluid level detection module includes a power source, one or more sensors configured to detect a characteristic of a fluid in a fluid vessel, a processing module configured to process and to store data of the detected fluid characteristic, and a wireless transceiver configured to transmit the data to a wireless receiver disposed external to the fluid vessel. 
         [0005]    In general, in one aspect, one or more embodiments of the invention are directed to a method to detect a fluid level within a vessel. The method includes disposing a wireless fluid sensor module in the fluid vessel, measuring at least one characteristic of the fluid, and wirelessly transmitting the measured at least one characteristic to a receiver disposed external to the fluid vessel. 
         [0006]    Other aspects and advantages of the invention will be apparent from the following description and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0007]      FIG. 1  shows a system in accordance with one or more embodiments of the invention. 
           [0008]      FIG. 2  shows a system in accordance with one or more embodiments of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    In the following detailed description of embodiments, numerous specific details are set forth in order to provide a more thorough understanding of the system and method of wireless tank level monitoring. However, it will be apparent to one of ordinary skill in the art that these embodiments may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description. 
         [0010]    In general, one or more embodiments of the invention relate to a system and method to estimate fluid levels in vessels using wireless telemetry. The estimated fluid levels are based on data derived from pressure measurements taken by a standalone sensor module located inside the vessel. The sensor module is normally placed on the bottom of the vessel and reports readings wirelessly to a receiver-processor module located on the outside of the vessel wall. 
         [0011]      FIG. 1  shows a system for wireless tank level monitoring in accordance with one or more embodiments of the invention. A vessel  1  includes the fluid of interest (for instance, oil, water, or other liquid) that is filled to a certain fluid level  2  inside the vessel. The vessel can be of any size and can be either fully enclosed or open or accessible at the top. A sensor module  3  is placed inside the vessel, ideally installed by simply dropping it into the vessel via a hatch or opening  4 . One of ordinary skill will appreciate that typical storage vessels employ various types of hatches or openings. Thus, the particular shape of the opening  4  depicted in  FIG. 1  is for illustrative purposes only, and is not meant to limit the invention in any way. In accordance with one or more embodiments, the sensor module  3  may be powered by a power source, e.g., a battery (not shown) or other energy source. 
         [0012]    Furthermore, in accordance with one or more embodiments, the sensor module  3  is sealed and environmentally protected from the fluid in the vessel  1 . The sensor module  3  includes one or more sensors  7   a  and  7   b.  In accordance with one or more embodiments, the sensor module  3  may employ a microelectromechanical (MEMS) pressure sensor, e.g., a Freescale MPXH6115A. MEMS sensors include various beneficial characteristics for wireless tank level monitoring, including their extremely small size, environmentally ruggedness, low power requirements (typically 5V at 6 mA, or 30 mW), and high resolution (on the order of 10 mV per inch of water). 
         [0013]    In accordance with one or more embodiments, the sensor module  3  wirelessly communicates with a collection module  5  that is located on the outside of the vessel. The collection module  5  may include similar processing and transmission electronics as the sensor module itself and also may additionally employ a cellular modem (e.g., a Telit CC864-Dual, or the like) for incorporating the collection module and thereby the wireless sensor module into a cellular network. Advantageously, no external wiring is necessary to install the system and the sensor data may be made available to a remote server. Advantageously, this wireless aspect makes the system portable in addition to being simple and easy to maintain. The collection module  5  may be a wireless transceiver configured to communicate with the sensor module  3 . One of ordinary skill will appreciate that many protocols for wireless communication are presently known in the art and that the sensor module  3  and collection module  5  may employ any known method without departing from the scope of the present invention. In accordance with one or more embodiments, the sensor module  3  and collection module  5  may include wireless transceiver chipsets, including, e.g., the RFM12B, RFM 22B, or the like. One of ordinary skill will appreciate that in accordance with one or more embodiments of the invention, any transceiver, receiver, and/or transmitter chipsets may be used without departing from the scope of the present invention. 
         [0014]      FIG. 2  shows an example of a sensor module in accordance with one or more embodiments of the invention. The module  7  can be fashioned of any shape or size, but preferably, the module  7  includes a very small device body  8 , which is of a higher density than the fluid in the vessel so that the module  7  may be lowered by a cord or wire (not shown) attached to the device at a convenient point  10  on the device body  8 . Alternatively, the module  7  may be dropped into the vessel without being attached to a cord or wire. The device body  8  may be fluidly and/or environmentally sealed from the fluid to be measured and/or monitored, such that the internal components of the module  7  may not interact with the fluid. A series of one or more small sensors  11  of the module  7  are exposed to the fluid and thereby detect the fluid pressure and/or other fluid characteristics. 
         [0015]    The sensors  11  may be pressure sensors, salinity sensors, and/or other fluid characteristic sensors. Sensor readings are collected in internal electronics  9 , which may include a processing module  13 . In accordance with one or more embodiments, the processing module may include any microprocessor module known in the art, e.g., microprocessors such as the TI MSP430F2003, MSP430G2231, or the like, and one of ordinary skill will appreciate that the processing module may further include a processor  15 , memory  16 , and a wireless transceiver  12 , where the sensor data are processed, stored, and transmitted wireles sly, respectively. As discussed above in reference to the collection module  5 , suitable wireless transceivers  12  include, but are not limited to the RFM12B, RFM 22B, or the like. 
         [0016]    In accordance with one or more embodiments, the data is transmitted by wireless transceiver  12  wireles sly through the tank wall to the external collection module (not shown), e.g. through the use of RF signals  17  near a carrier frequency of 315 MHz. One of ordinary skill will appreciate that the precise frequency chosen depends on the tank material and the skin depth of the RF radiation within the tank material. Field tests performed by the inventor indicate that 315 MHz are suitable for tanks having steel walls of ⅜ in. However one of ordinary skill will appreciate that lower or higher frequencies may be used without departing from the scope of the present invention. In accordance with one or more embodiments, the electronics located within the module  7  may be powered by power source  14 , which may include a battery, or the like. As used herein, the term transceiver in meant broadly to encompass units known in the art to have wireless transmission capabilities only, wireless reception capabilities only, or both transmission and reception capabilities within a single unit. 
         [0017]    In accordance with one or more embodiments, the sensor module  7  functions by taking periodic pressure measurements of the surrounding fluid. A preferred sensor type is a small MEMS device. Recent advancements in sensor technology driven by automobile real-time tire pressure measurement and medical products have driven cost and power requirements of these devices to extremely low levels. A key enabling factor has been the associated lowering of the operating pressure range of these sensors. Common and inexpensive sensors now operate in the range of 0-20 psi, providing an excellent fit for fluid pressure measurement in most vessel heights which normally do not exceed heights of ten to twenty feet. 
         [0018]    One of ordinary skill will appreciate that the fluid height can be estimated based on the sensor module&#39;s pressure reading and knowledge of the specific gravity of the fluid in the vessel. For example, in accordance with one or more embodiments, for tanks with fluids having a density that does not vary in time, calibration may be performed in an initial two-point calibration. Subsequent measurements may then be calibrated based on a linear formula relating pressure to height using the initial two point calibration. 
         [0019]    According to other embodiments, a more robust solution can include onboard capability to determine the fluid density. Methods of determining the fluid density include, for example, salinity based measurements. For example, in the case of water, an accurate estimate of water density can be made if the resistivity and temperature of the water are known. Thus, a sensor module including two or more electrical pads (not shown) in contact with the fluid can be used to measure the electrical resistance of the fluid in order to calculate the salinity-to-density transform. One of ordinary skill will appreciate that the conversion between salinity and density may be employed using any known method in the art without departing from the scope of the present disclosure. 
         [0020]    In accordance with one or more embodiments, the system may be configured to undertake a differential pressure measurement. In a differential measurement method, two or more pressure sensors, or a sensitive differential pressure sensor, may be installed in a vertical array on the tank sensor module. A pressure gradient between the sensors may then be determined and used in a calculation to derive fluid height. 
         [0021]    One of ordinary skill will appreciate that many other methods may be employed to measure fluid level in addition to the two types of methods disclosed herein. Furthermore, one of ordinary skill will appreciate that the sensors used in the sensor module disclosed herein may be of any type known in the art to measure fluid characteristics that may be used to determine a fluid level. 
         [0022]    In accordance with one or more embodiments, several methods of wireless communication are possible. One example of a wireless communication method employs acoustic transmission, wherein sensor readings are encoded in an acoustic pulse signal. The acoustic pulse signal is transmitted by the sensor module and received by the collection module. However, because the information transfer rate in acoustic methods is normally extremely low—on the order of 1 to 5 bytes per transmission—low frequency RF (VLF) can also be used. Higher frequency RF is possible if the transmission distance is small. 
         [0023]    In accordance with one or more embodiments, the communication is normally one-way from sensor module to collection module. In other embodiments, the system may be configured to employ bi-directional communication. 
         [0024]    In accordance with one or more embodiments, the sensor module is normally ‘sleeping’ in very low power draw mode. For many applications, level measurements are often needed only hourly or perhaps daily. Thus, the sensor module can be operated on a small battery for a long period of time, thereby minimizing the frequency of sensor module replacement. 
         [0025]    In accordance with one or more embodiments, the sensor module is constructed from common electronics parts and can be manufactured cheaply—at a fraction of the cost of systems that are common today. Advantageously, one or more embodiments of the invention employ a sensor module that can be easily replaced by simply lowering (or dropping) a replacement into the vessel. This greatly reduces the maintenance time, cost, and skill required to use this system. Furthermore, the sensor module is designed to maintain function in harsh environmental conditions, such as wide temperature variations and corrosive fluid environments. 
         [0026]    While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.