Abstract:
A vapor recovery system in a fuel dispenser includes the ability to self diagnose the continued viability of a hydrocarbon sensor positioned within the vapor recovery system. A control system associated with the vapor recovery system performs a series of tests including passing pure air over the hydrocarbon sensor and passing a gas known to have hydrocarbons therein over the sensor and evaluating the output of the sensor to see if expected values are output. If the measured values are not within tolerable limits, an alarm is generated.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention pertains to a diagnostic method for checking the accuracy of a hydrocarbon sensor in a vapor recovery system, such as in a fuel dispensing environment. 
     2. Description of the Related Art 
     Vapor recovery equipped fuel dispensers, particularly gasoline dispensers, have been known for quite some time, and have been mandatory in California for a number of years. The primary purpose of using a vapor recovery fuel dispenser is to retrieve or recover the vapors, which would otherwise be emitted to the atmosphere during a fueling operation, particularly for motor vehicles. The vapors of concern are generally those which are contained in the vehicle gas tank. As liquid gasoline is pumped into the tank, the vapor is displaced and forced out through the filler pipe. Other volatile hydrocarbon liquids raise similar issues. In addition to the need to recover vapors, some states, California in particular, are requiring extensive reports about the efficiency with which vapor is recovered and proof that the vapor recovery systems are working as intended. 
     A traditional vapor recovery apparatus is known as the “balance” system, in which a sheath or boot encircles the liquid fueling spout and connects by tubing back to the fuel reservoir. As the liquid enters the tank, the vapor is forced into the sheath and back toward the fuel reservoir or underground storage tank (UST) where the vapors can be stored or recondensed. Balance systems have numerous drawbacks, including cumbersomeness, difficulty of use, ineffectiveness when seals are poorly made, and slow fueling rates. 
     As a dramatic step to improve on the balance systems, Gilbarco, Inc., assignee of the present invention, patented an improved vapor recovery system for fuel dispensers, as seen in U.S. Pat. No. 5,040,577, now Reissue Patent No. 35,238 to Pope, which is herein incorporated by reference. The Pope patent discloses a vapor recovery apparatus in which a vapor pump is introduced in the vapor return line and is driven by a variable speed motor. The liquid flow line includes a pulser, conventionally used for generating pulses indicative of the liquid fuel being pumped. This permits computation of the total sale and the display of the volume of liquid dispensed and the cost in a conventional display, such as, for example as shown in U.S. Pat. No. 4,122,524 to McCrory et al. A microprocessor translates the pulses indicative of the liquid flow rate into a desired vapor pump operating rate. The effect is to permit the vapor to be pumped at a rate correlated with the liquid flow rate so that, as liquid is pumped faster, vapor is also pumped faster. 
     There are three basic embodiments used to control vapor flow during fueling operations. The first embodiment is the use of a constant speed vapor pump during fueling without any sort of control mechanism. The second is the use of a pump driven by a constant speed motor coupled with a controllable valve to extract vapor from the vehicle gas tank. While the speed of the pump is constant, the valve may be adjusted to increase or decrease the flow of vapor. The third is the use of a variable speed motor and pump as described in the Pope patent, which is used without a controllable valve assembly. 
     Various improvements and refinements have been developed to make vapor recovery systems more efficient and provide a better estimate of the type and rate of vapor recovery. Amongst these improvements are vapor flow meters, such as disclosed in commonly owned copending U.S. patent application Ser. No. 09/408,292. Additionally, the use of hydrocarbon sensors positioned within the vapor recovery line is also known as shown in commonly owned U.S. Pat. No. 5,857,500 and its parent U.S. Pat. No. 5,450,883, which are herein incorporated by reference. As the use of such sensors proliferates in the industry, it is being discovered that these sensors deteriorate with age, or otherwise may have their performance degrade over time. Therefore, there is a need for the ability to test the sensors to determine if they are still functioning properly. Additionally, as states begin to require proof that the vapor recovery systems are functioning properly, the ability to test the vapor recovery system is becoming more important. 
     SUMMARY OF THE INVENTION 
     The present invention periodically tests a sensor for determining hydrocarbon concentration within a vapor recovery system for proper operation. Specifically, the control system which controls the vapor recovery system within a fuel dispenser, checks the reading on the sensor every fueling transaction at the beginning of the fueling transaction and at a subsequent time during the same fueling transaction. If the two readings are roughly equivalent, the control system determines if this is the appropriate fueling transaction to trigger a more comprehensive diagnostic test of the sensor. If an appropriate number of fueling transactions have occurred since the last full diagnostic test, the sensor checks to see if the last measured value of hydrocarbon concentration is within an expected range. Further, the diagnostics test the readings of the sensor against a flow of pure air, to make sure that the last measured value is greater than that of pure air. Still further, the sensor can test itself by measuring a flow of vapor known to contain hydrocarbons and comparing the resultant reading to an expected value. If any of these diagnostic tests fail, the control system may generate an alarm indicating that the sensor has potentially failed and needs to be serviced or examined further to determine the cause of the failure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of a fuel dispenser incorporating a vapor recovery system; 
     FIG. 2 is a flow diagram of the diagnostics performed by the present invention; and 
     FIG. 3 is a flow diagram of an alternate set of diagnostics that could be implemented with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning now to FIG. 1, a fuel dispenser  10  is adapted to deliver a fuel, such as gasoline or diesel fuel to a vehicle  12  through a delivery hose  14 , and more particularly through a nozzle  16  and spout  18 . The vehicle  12  includes a fill neck  20  and a tank  22 , which accepts the fuel and provides it through appropriate fluid connections to the engine (not shown) of the vehicle  12 . 
     Presently, it is known in the field of vapor recovery to provide the flexible delivery hose  14  with an outer conduit  30  and an inner conduit  32 . The annular chamber formed between the inner and outer conduits  30 ,  32  forms the product delivery line  36 . The interior of the inner conduit  32  forms the vapor return line  34 . Both lines  34  and  36  are fluidly connected to an underground storage tank (UST)  40  through the fuel dispenser  10 . Once in the fuel dispenser  10 , the lines  34  and  36  separate at split  51 . The UST  40  is equipped with a vent shaft  42  and a vent valve  44 . During delivery of fuel into the tank  22 , the incoming fuel displaces air containing fuel vapors. The vapors travel through the vapor return line  34  to the UST  40 . 
     A vapor recovery system is present in the fuel dispenser  10  and includes a control system  50  and a vapor recovery pump  52 . Control system  50  may be a microprocessor with an associated memory or the like and also operates to control the various functions of the fuel dispenser including, but not limited to: fuel transaction authorization, fuel grade selection, display and/or audio control. The vapor recovery pump  52  may be a variable speed pump or a constant speed pump with or without a controlled valve (not shown) as is well known in the art. A hydrocarbon sensor  54 , such as that disclosed in the previously incorporated, commonly owned U.S. Pat. No. 5,857,500 and its parent U.S. Pat. No. 5,450,883 or the equivalent sensor is positioned in the vapor recovery line  34  and communicatively connected to the control system  50 . 
     Sensor  54  may also be an alternative sensor which through the detection of other vapor within the vapor return line  34  indirectly measures the level of hydrocarbon concentration within vapor return line  34 . Such a sensor may sense the oxygen concentration, the nitrogen concentration, or other appropriate gas and from that reading the control system  50  may determine a hydrocarbon concentration. For example, hydrocarbon concentration would be inversely proportional to oxygen or nitrogen concentration. The determination would be precalibrated to provide an accurate indication of hydrocarbons based on the measured level of the gas in question. 
     While the sensor  54  is depicted in the vapor recovery line  34  upstream of the vapor pump  52 , other placements of the sensor  54  are also possible. For example, the sensor  54  could be in a parallel vapor recovery path to reduce the likelihood of exposure to liquid fuel; the sensor  54  could be downstream of the vapor pump  52 ; sensor  54  could be placed in the ventilation line  42  or the like as needed or desired. Additionally, although a particular arrangement is shown for the vapor recovery system, it should be appreciated that other arrangements are possible, and the present invention encompasses all vapor recovery systems that include a sensor for determining hydrocarbon concentration. 
     As noted, sensor  54  may deteriorate over time as a result of the harsh environment in which it is positioned, or a state regulatory commission may require proof that the vapor recovery system is working as intended. Therefore, it is imperative that the operator of the fueling station have some means to ascertain the accuracy of any readings provided by the sensor  54 . The present invention addresses this concern by providing a diagnostic routine performed by the control system  50  of the fuel dispenser  10  as shown in FIG.  2 . The diagnostics are designed to check the output of the sensor  54  against an expected output for a fueling transaction and further check the output of the sensor  54  to see if it varies as a result of varying input conditions. The diagnostic tests are preferably performed at predetermined intervals based on the number of fueling transactions that the sensor  54  has endured. 
     The process starts (block  100 ) when a fueling transaction begins or at some other predetermined time as needed or desired, such as five seconds after a fueling transaction begins. Further the definition of a the beginning of a fueling transaction is not necessarily when payment is authorized, but rather is preferably the time at which fuel begins to be dispensed. At the time the process starts, the output of sensor  54  is checked by the control system  50  (block  102 ). A reading of the sensor  54  is labeled A. 
     The control system  50  then determines if this is a new transaction (block  104 ). If the answer to block  104  is no, the process restarts at block  102 . If the answer to block  104  is yes, the control system  50  checks the output of the sensor  54  after a predetermined amount of time, for example after “X” seconds and labels this output A x  (block  106 ). In the preferred embodiment, X is approximately 10 to 20 seconds, although other time frames are also contemplated. The average fueling transaction for a private vehicle is approximately two minutes in length. The average fueling transaction for a tractor-trailer or large commercial vehicle is substantially longer. X is preferably less than the expected length of the fueling transaction. 
     The control system  50  then determines if A equals A x ±Y %, wherein Y % is a predetermined confidence interval (block  108 ). This tests to see if the sensor  54  is getting a consistent reading from the vapor recovery line. Further, this may help determine if there is an Onboard Recovery Vapor Recovery system present. If an inconsistent reading is rendered, this anomaly is generally indicative that the sensor  54  is working, and the error, if there is one, may lie in other hardware within the system. However, additional diagnostics could be performed if desired or needed prior to restarting at block  102  as will be explained below. 
     Absent these potential additional diagnostics, if the answer to block  108  is no, then the diagnostic process restarts at block  102 . If the answer to block  108  is yes, then the control system  50  determines if this is the Nth transaction, where N is a predetermined number, preferably between 50 and 200 (block  110 ), although other ranges from 3 to 10,000 or larger are also feasible. In one embodiment, the number would be empirically calculated to correspond to testing the system approximately once a day. If the answer to block  110  is no, the process restarts at block  102 . Thus, the control system  50  may only run the diagnostic tests every Nth fueling transaction. A memory or counter associated with the control system  50  can easily be implemented to keep track of the number of transactions since the last diagnostic test. 
     In the preferred embodiment, multiple measurements are taken during a fueling transaction, even if A=A x ±Y % and it is not the Nth transaction. This is a result of decisional logic shown in FIG.  2 . Sensor  54  takes an initial reading A at the beginning of the fueling transaction. Block  104  is answered affirmatively, that this is a new transaction. A subsequent reading is taken to create A x . If A does not roughly equal A x , a third reading is taken when the routine cycles back to block  102 . Fourth and more readings are taken as the routine cycles through blocks  102  and  104  until the end of the fueling transaction. Even if A=A x ±Y %, but this is not the Nth transaction, a third reading is taken when the routine cycles back to block  102 . Again, fourth and more readings are taken as the routine cycles through blocks  102  and  104  until the end of the fueling transaction. All of these readings can be stored in memory associated with the control system  50  to track the performance of the sensor  54  over the course of many fueling transactions. These historical data points can be used to evaluate when a sensor  54  failed, or extrapolate a linear degradation curve associated with the sensor  54  or the like. Some states may require such data to show vapor recovery rates or the like. However, if this data is determined to not be helpful, it may be deleted as needed or desired. While it is useful to have this information, this still does not test per se if the sensor  54  is functioning properly. Thus every Nth transaction, the control system  50  runs a more in depth diagnostic test. 
     If the answer to block  110  is yes, enough transactions have elapsed to necessitate a new test of the sensor  54 , the control system  50  waits until the end of the presently occurring fueling transaction (block  1   12 ) and proceeds to run a more in depth diagnostic test. At the conclusion of the Nth fueling transaction, the control system  50  determines if A x =STA±Y %, wherein STA is the typical hydrocarbon concentration in the fill-neck  20  of the vehicle  12  (block  114 ). This step determines if the sensor  54  is getting an expected reading within a predetermined confidence interval. If the answer to block  114  is yes, the control system  50  then instructs the fuel dispenser  10  to run air through the vapor recovery system, and more particularly through the vapor return line  34  by operating the vapor recovery pump  52  for a predetermined amount of time (labeled “T”). Sensor  54  then takes a subsequent reading while air is passing over the sensor  54  (labeled At) (block  116 ). The control system  50  then determines if A t &lt;A x  (block  118 ). This step verifies that A x , the concentration of hydrocarbons within the vapor recovery line  34  during a fueling transaction, is greater than a value corresponding to what the sensor  54  reads when pure air is passed thereover. If the answer to block  118  is yes, the control system  50  stops the vapor recovery pump  52  and closes any valves associated therewith (block  120 ). The diagnostic test resumes at block  102  as previously described. The diagnostic test has confirmed that the sensor  54  is operating as intended, and no further action is immediately required. 
     If the answer to block  114  is no, A x  is not within a predetermined acceptable range, the control system  50  instructs the sensor  54  to perform a series of self diagnostic tests to determine whether the sensor  54  is presently working. Specifically, the sensor  54  has gas known to have hydrocarbon vapor therein passed over the sensor  54 , and the response of the sensor  54  is measured. If no hydrocarbons are detected, there is a problem with the sensor  54 . Passing hydrocarbon laden gas over the sensor  54  can be achieved by reversing the flow of pump  52  for a few seconds, preferably approximately 10 seconds. This brings vapor from the UST  40  to the sensor  54 . Alternatively, a pipe with a valve may be positioned upstream of the sensor  54  and connect the vapor return line  34  to the UST  40  (not shown). The valve can be opened and the pump  52  operated as normal to draw vapor from the UST  40  past the sensor  54  and back to the UST  40 . This gas with known vapors therein should register on the sensor  54 . If no hydrocarbons are detected, the sensor  54  has probably suffered a failure of some sort. Finally, gas with known hydrocarbon vapor may be introduced to the vapor return line  34  manually. 
     Further, the control system  50  checks the power input to the sensor  54 . Turning the power off and on again can do this. Some sort of change in the reading provided by sensor  54  should be achieved in response to this power fluctuation. Still further, the control system  50  tests the sensor  54  output by varying the power input to the sensor  54  (block  122 ). In sensors  54  with an optical element or a heating element, the element&#39;s intensity will vary according to the power input. For example, an LED may glow with a greater intensity as the power is increased; the receptor should reflect this greater intensity. If the readings gathered by sensor  54  do not vary as a result of the variance of the power input, the sensor  54  may have failed. Control system  50  determines if the sensor  54  passed the tests enumerated in block  122  (block  124 ). If the answer to block  124  is yes, the control system  50  determines that the answer to block  114  was an anomaly and restarts the diagnostic process at block  100 . If however, the answer to block  124  is no, or the answer to block  118  is no, then control system  50  sends an appropriate warning signal to one or more of the following locations: the station attendant, a central office location, a maintenance log, or other appropriate locations local or remote to the fuel dispenser  10  wherein the warning signal includes an instruction to check further, and preferably manually, the sensor  54  for proper performance (block  126 ). 
     There are occasions when A will dramatically fluctuate compared to A x . Further diagnostics may be required to ascertain whether the result was an anomaly or whether the sensor  54  is in fact not functioning properly. This optional diagnostic routine is seen in FIG.  3 . The control system  50  determines how much A differs from A x  (block  130 ). The control system  50  then determines if this difference exceeds some preselected criteria. If the answer is no, the results of block  108  are viewed as a random anomaly and the process restarts at block  102 . If the answer is yes, then the control system  50  proceeds with further diagnostic testing at block  112 . 
     While shown as being positioned within the fuel dispenser  10 , it should be appreciated that the control system  50  could be remote from the fuel dispenser  10 , such as in the gas station building or the like as needed or desired. Further the sensor  54  could be positioned in a number of places within the vapor recovery system as needed or desired. The diagnostic routine described herein could be implemented through software associated with said control system  50 , or it could be performed by dedicated hardware or the like as needed or desired. 
     The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the spirit and essential characteristics of the invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.