Abstract:
A meter calibration system and apparatus capable of calibrating meters devoid of process connections. The apparatus are a calibration system and process connection adapters, where in the system is operable for calibrating both linear and nonlinear meters at multiple flow rates, and is suitable for use with both gravimetric and master meter standard references.

Description:
FIELD OF INVENTION 
     This invention pertains to systems that are used in calibrating meters for purposes of assuring accuracy from the meter being calibrated. More specifically, the system enables the calibration of volumetric flowmeters, mass flowmeters, densitometers, and viscometers devoid of process connection. 
     PROBLEM 
     It is desirable to perform a calibration on all meters prior to use in order to ensure accurate and reliable measurement data. The purpose of a meter calibration effort is to ascertain a flow calibration factor that will be used as a multiplier in correcting direct measurements from the meter under test. Coriolis meters, orifice meters, and positive displacement meters are known in the art as linear meters, i.e., the flow calibration factor is a constant with respect to flow rate. Other meters, including magnetic flow and vortex types, are nonlinear meters meaning that the flow calibration factor varies with respect to flow rate. 
     The calibration process typically is performed on a meter with process connections already attached as per a customer order. The meter is inserted into the calibration system having process connections that match those already attached to the meter. After insertion into the calibration system, the calibration process is performed. The most reliable calibration systems include gravimetric standards or master meter transfer standards used as flow rate references during the calibration process. The fluid used within the calibration system and the meter under test has precisely known intrinsic and extrinsic fluid properties, e.g., temperature, density, viscosity, and volume. The meter under test performs flow measurements on this fluid. These measurements are compared with the known fluid properties or flow rate reference to ascertain or validate a flow calibration factor or other calibration factors for the meter under test. 
     The problem with the above procedure is the requirement to have customer-specific process connections attached to the meter prior to performing the calibration. There are several drawbacks associated with this requirement. 
     One drawback is related to capital expenditure. In an effort to minimize warehouse inventory, meter manufacturers defer the process connection attachment step until a customer places an order. Furthermore, in an effort to reduce customer delivery lead-time, meter manufacturers locate customer service facilities around the world as near as possible to customers. As a result, since the calibration step currently follows the process connection attachment step, expensive calibration system hardware must be replicated in several facilities around the world. 
     Another drawback is the inability to test a meter for functional discrepancies immediately following meter assembly and prior to the meter proceeding through the process connection attach, calibration and shipping functions. With the current process, a discrepant meter would not be identified until it has completed its route through the customer service facility. Identifying the discrepant meter at the end of the process results in extremely high scrap costs and a delay in delivery to the customer. 
     For the reasons given above, a need exists for a meter calibration system with sufficient accuracy that enables calibration of meters devoid of process connections. Moreover, the system should be capable of calibrating both linear and nonlinear meters and should not reduce the current system&#39;s performance or capabilities. 
     SOLUTION 
     This invention overcomes the problems outlined above and advances the art by providing methods and apparatus capable of calibrating meters devoid of process connections. The apparatus are a calibration system and process connection adapters, where the system is operable for calibrating both linear and nonlinear meters at multiple flow rates, and is suitable for use with both gravimetric and master meter standard references. 
     One embodiment of the present invention is a process connection adapter used to fluidly connect a calibration system with a test meter devoid of process connections. The process connection adapter is an apparatus composed of a system mating portion, an intermediate portion, and a meter mating portion. The system mating portion is designed to physically match a connection on the calibration system. Typically this connection is in the form of a flange, sanitary fitting, union fitting, or some other type of sealing connection for piping. The intermediate portion transitions the flow area of the system mating portion to the flow area of the meter mating portion. The meter mating portion incorporates mechanical features to physically match a portion of the meter that would typically have a process connection attached to it. Depending on the connection type used by the system, a sealing component may be required to ensure that the interfaces between the process connection adapters, the calibration system, and the test meter are leak-free. Such a component could be an O-ring or gasket seal. During meter installation into the calibration system, the process connection adapters can either be secured to each of its mating members through bolts or other fittings or simply compressed as an assembly between hydraulic or pneumatic actuators. 
     The order fulfillment process begins by receiving a meter, devoid of process connection, from the manufacturing facility. Next, process connection adapters are attached on each end of the meter to form a test assembly. The test assembly is then mounted in the test bed by placing a portion of the test assembly on support structures integrated in the calibration system. Once the test assembly is fixed into the support structures, hydraulic or pneumatic actuators compress the calibration system connectors against the process connection adapters. This compression capability enables quick and easy insertion and removal of the test assembly while also ensuring a leak-free fluid path. Once the test assembly is inserted into the calibration system, the meter signal cabling is attached to the controller and the calibration process is started. 
     The basic meter calibration system includes a mechanism for supplying fluid to use in flow calibration measurements, a flow and density measurement reference, a controller for automating the system in order to optimize the accuracy or sensitivity of the measurements, and, of course, a meter under test. The flow measurements are used to ascertain or validate a flow calibration factor for the meter under test. The same principles apply for mass flow rate, volumetric flow rate, density, or viscosity calibrations. 
     The fluid supply mechanism can provide any fluid type; e.g., a liquid reservoir and a pump; a multiphase fluid including multiple immiscible liquid phases and gas; an attachment to a pressurized water supply, such as plant process fluids, a city water supply, artesian well, or gravimetric system; or a pressurized gas supply, such as natural gas, air, or plant process gases. For most meter calibrations, a constant-pressure source of water is the preferred supply mechanism. 
     The meter is operably configured, as described above, to receive fluid from the fluid supply mechanism. The meter under test is positioned in the flow piping between the fluid supply and either a scale, as in the case of a gravimetric system, or a master meter array as in a master meter system, described in U.S. Pat. No. 6,360,579 issued to DeBoom et al. 
     Once the calibration process is started, the meter under test provides flow measurement signals to a supervisory CPU-based controller. The controller adjusts valves leading to the meter for the purpose of controlling flow through the meter within the range of optimal measurement sensitivity corresponding to relatively low uncertainty for the meter. The controller interprets these electrical signals as flow measurement data and calibrates the meter under test using a flow calibration factor obtained from flow data. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other advantages and features of the present invention may be better understood in connection with a reading of the following detailed description of one possible exemplary embodiment thereof taken in conjunction with the drawings in which: 
     FIG. 1 is a process schematic diagram showing the flow process for a meter calibration system according to the prior art; 
     FIG. 2 discloses a calibration installation according to an embodiment of the present invention; 
     FIG. 3 depicts a process connection adapter; 
     FIG. 4 depicts an additional process connection adapter; 
     FIG. 5 is a process schematic diagram showing the flow process for a meter calibration system according to the present invention; 
     FIG. 6 depicts a block schematic diagram of the flow process for a meter calibration system according to the present invention; 
     FIG. 7 depicts a block schematic diagram of the flow process for a meter calibration system according to another embodiment; 
     FIG. 8 discloses a process schematic diagram showing the calibration process. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is directed toward methods and apparatus used in calibrating meters devoid of process connections for the purposes of assuring measurement accuracy. The apparatus can include a flow calibration unit and associated adapters for connecting and calibrating meters without process connections. Many specific details of certain embodiments of the invention are set forth in the following description and in FIGS. 1-8 to provide a thorough understanding of such embodiments. One skilled in the art, however, will understand that the present invention may have additional embodiments and that they may be practiced without several of the details described in the following description. 
     FIG. 1 is a process schematic diagram showing a process  100  of how a meter is routed from production to shipment to a customer according to the prior art. Step  105  involves the production of a meter from component or piece parts. This production includes all assembly, welding and finishing processes up to but not including the attachment of process connections. After the meter has completed production, the meter is then shipped to a storage area in step  110  to await a customer order 
     In step  115 , a customer orders a meter based on customer requirements, including flow rate, fluid type and line pressure. Based on the customer&#39;s requirements, an order is placed in manufacturing for a meter with a specific process connection attached. Various types of process connections exist, including flanges, union fittings, sanitary, etc. 
     Step  120  entails the connection of the process connections ordered by the customer. The meter and process connections are attached using either an automated or manual welding station. 
     After the meter has been built, it is calibrated as shown in step  125 . Depending on the meter type and size, a calibration facility requires between 2 and 3 calibration systems. Calibration units can cost as much as $450,000 dollars and can take up as much as 800 sqft. Due to the cost and size of these systems, limiting the number of installations is desirable. Not only is the size and cost a consideration, but also calibration is a time-consuming process. The calibration process is subsequently described in further detail. 
     Once the meter has been calibrated, a quality check is performed in step  130 . Then, the meter is shipped to the customer as denoted by step  135 . The quality check involves, among other things, the meter&#39;s adherence to strict performance standards as well as its conformity to manufacturing standards. If, for any reason, the meter does not meet the quality standards, it is routed back to manufacturing for further disposition while a replacement meter is substituted for order fulfillment. Unfortunately, the labor and materials expended during the process connection attachment and calibration steps are wasted since the quality assurance check occurs at the end of all manufacturing steps. 
     Description of FIG. 2 
     FIG. 2 discloses a calibration installation according to an embodiment of the present invention. A meter support  200  is comprised of a back support  202  and two side supports  204 . The back support  202  has attached to it guides  206  for enabling process connection supports  208  to be installed and adjusted, up or down, depending on the size and type of flow meter under test. Incorporated on the side supports are the process fluid inlet  210  and outlet  211  for conveying process fluid through the process connection adapters  216  and the test meter  220 . 
     Once the test meter  220  has the process connection adapters attached onto each end of the test meter  220 , the assembly is placed on process connection supports  208  and locked down with clamps  218 . The process fluid inlet  210  and outlet  211  are then pressed against the process connection adapters, thereby creating a leak-free fluid path. 
     Description of FIGS. 3 and 4 
     FIGS. 3 and 4 are exploded views of different types of process connection adapters that may be used to install a meter devoid of process connections into a calibration system. FIG. 3 is a process connection adapter  300  that is designed to act as a mock flange connection. The process connection adapter  300  comprises a disc portion  305  with bolt holes  310  that may be used to connect to a mating flange on the calibration system. From the disc  305 , the adapter reduces in size to a neck portion  315  and truncates at the meter mating portion  320 . The meter mating portion  320  may further contain a sealing mechanism  325  (e.g. an O-ring) to ensure a leak-free seal between the test meter  220  and the process connection adapter  300 . 
     FIG. 4 is a process connection adapter  400  designed to act as a mock sanitary connection. The process connection adapter  400  comprises a disc portion  405  that interfaces with either the process fluid inlet  210  or outlet  211  of the calibration system piping. From the disc  405 , the adapter reduces to a meter mating portion  410 . The meter mating portion  410  may further contain a sealing mechanism  415  (e.g. an O-ring) to ensure a leak tight seal between the test meter  220  and the process connection adapter  400 . 
     Description of FIG. 5 
     FIG. 5 is a process schematic diagram showing a process  500  of how a meter is routed from production to shipment to a customer according to one possible exemplary embodiment of the invention. Step  505  involves the production of a meter from component or piece parts. This production includes all assembly, welding and finishing processes up to but not including the attachment of process connections. 
     After the meter has completed production, the meter is then calibrated as shown in step  510 . The calibration process differs for that in FIG. 1 step  125  in that the meter is calibrated without process connections. Compared to the process in FIG. 1, this process enables completion of more steps prior to customization based on a customer&#39;s order. Once the meter has been calibrated, it is put through a battery of tests to verify its adherence to strict quality standards as denoted by step  515 . If the meter fails to pass any of the quality tests, it is routed back to meter production for further disposition. However, if the meter passes the quality test, it is forwarded to meter storage as depicted by step  520 . Due to the fact that all calibration and quality check procedures have been performed on the meter, the storage facility can be located in any part of the world. It is not necessary, as in the prior art process denoted by FIG. 1, for the storage facility to have costly calibration systems. It is only necessary that the facility have capabilities for attaching process connections, a relatively inexpensive capital investment and relatively less labor-intensive operation. 
     In step  525 , a customer orders a meter based on many criteria, including flow rate, fluid type and line pressure. Based on the customer&#39;s requirements, an order is placed in manufacturing for a meter with a specific type of process connection. 
     The meter type ordered by the customer is retrieved from storage and the process connection attachment is performed as shown in step  530 . The meter and process connections are attached using either an automated or manual welding station. As mentioned above, the relatively low cost of the welding stations enable their use in many locations. 
     After the meter has the process connections attached, it is shipped to the customer as shown in step  535 . The benefit of the described process over the prior art is the ability to maintain meter inventories at multiple locations throughout the world while minimizing capital cost. This strategy improves the response time to a customer&#39;s order by locating the customer specific operations close to the customer, while limiting the locations performing labor and capital-intensive operations such as manufacturing, calibration, and quality testing. 
     Description of FIG. 6 
     As mentioned previously, the ability to calibrate meters early in the work-flow process is beneficial because of the time and costs associated with a calibration system. One such system is a master meter calibration system of the present invention, as shown in FIG.  6 . FIG. 6 depicts a meter calibration system  600 . A reservoir  602  contains water or another liquid, which is pressurized in tubing  604  by the action of gravity and an optional pump  606 . An automated valve  608  may be partially opened to permit a portion of the flow from pump  606  to bypass flow through system  600 . A first meter array  612  is positioned to receive liquid from tubing  604  under the pressure influence of pump  606 . The term “array” is used to denote a grouping of flow meters. A meter under test or test unit  614  is positioned between first meter array  612  and a second meter array  616 . The term “test unit” is used here because a single meter may be tested or a plurality of similar meters may be connected in series for simultaneous calibration testing. The testing of meters in series significantly enhances the test process efficiency because flow measurement data from a single test perceived by first meter array  612  and second meter array  616  can be used to calibrate each meter in series within test unit  614 , as opposed to having to run separate volumes through the arrays while testing each meter. 
     Test unit  614  receives liquid through tubular segment  618  and, in turn, passes this liquid to second meter array  616  through tubular segment  620 . A CPU-based controller  622  is in electrical contact with each of first meter array  612 , test unit  614  and second meter array  616  through corresponding cables  624 ,  626 , and  628 . Controller  622  is also in electrical contact with pump  606  and valve  608  through corresponding cables  630  and  632 . Tubing  634  provides a return of fluid from second meter array  616  to reservoir  602 . 
     A pressure indicating recorder  636  and a temperature indicating recorder  638  are mounted in tubular segment  618 , i.e., upstream of test unit  614 . A temperature indicating recorder  640  is mounted in tubular segment  620 , i.e., downstream of test unit  614 . These devices are in operable contact with controller  622  through cables  642 ,  644 , and  646  for the receipt and transmission of signals. The pressure indicating recorder  636 , temperature indicating recorder  638 , and temperature indicating recorder  640  provide data that is used according to conventional practices in obtaining density measurements from test unit  614  when it contains a Coriolis flowmeter. Pressure and temperature data from the positions shown for pressure indicating recorder  636 , temperature indicating recorder  638 , and temperature indicating recorder  640 , are also required to perform volumetric measurements when the test unit  614  contains a volumetric flow meter, such as a positive displacement meter or orifice meter. 
     In operation, the meter under test  614  has been newly manufactured or recently removed from a normal service position (not depicted in FIG.  6 ). Meter under test  614  has just been installed into position contacting tubular segments  618  and  620  for calibration test purposes, and the portion of system  600  downstream of reservoir  602  has been bled of air and other gasses. Controller  622  actuates pump  606  to flow liquid from within reservoir  602  in series into first meter array  612 , meter under test  614  and second meter array  616 , which each perform simultaneous flow measurements on the liquid. Controller  622  synchronizes these simultaneous measurements. The synchronous measurements avoid the possibility of obtaining flow measurements at different times where the flow measurements may be influenced by pressure surges or pulses from the action of pump  606 . Controller  622  operates, as described in greater detail below, to assure that respective meters within second meter array  616  are operating at flow rates making it at least ninety-five percent certain that the uncertainty of measurements obtained from second meter array  616  are at least three times more accurate than the manufacturer&#39;s performance specification that is allocated to meter under test  614 . 
     Description of FIG. 7 
     FIG. 7 depicts another form of the calibration system called a gravimetric scale system  700 . A reservoir  702  contains water or another liquid, which is pressurized in tubing  704  by the action of gravity and an optional pump  706 . An automated valve  708  may be partially opened to permit a portion of the flow from pump  706  to bypass flow through system  700 . A meter under test or test unit  714  is positioned between first meter array  712  and a second meter array  716 . The term “test unit” is used here because a single meter may be tested or a plurality of similar meters may be connected in series for simultaneous calibration testing. The testing of meters in series significantly enhances the test process efficiency because flow measurement data from a single test can be used to calibrate each meter in series within test unit  714 . 
     Test unit  714  receives liquid through tubular segment  718  and, in turn, passes this liquid to a scale  716  through tubular segment  720 . A CPU-based controller  722  is in electrical contact with each of test unit  714  and scale  716  through corresponding cables  726 , and  728 . Controller  722  is also in electrical contact with pump  706  and valve  708  through corresponding cables  730  and  732 . Tubing  734  provides a return of fluid from scale  716  to reservoir  702 . 
     A pressure indicating recorder  736  and a temperature indicating recorder  738  are mounted in tubular segment  718 , i.e., upstream of test unit  714 . A temperature indicating recorder  740  is mounted in tubular segment  720 , i.e., downstream of test unit  714 . These devices are in operable contact with controller  722  through cables  742 ,  744 , and  746  for the receipt and transmission of signals. The pressure indicating recorder  736 , temperature indicating recorder  738 , and temperature indicating recorder  740  provide data that is used according to conventional practices in obtaining density measurements from test unit  714  when it contains a Coriolis flowmeter. Pressure and temperature data from the positions shown for pressure indicating recorder  736 , temperature indicating recorder  738 , and temperature indicating recorder  740 , are also required to perform volumetric measurements when the test unit  714  contains a volumetric flow meter, such as a positive displacement meter or orifice meter. 
     In operation, the meter under test  714  has been newly manufactured or recently removed from a normal service position (not depicted in FIG.  7 ). Meter under test  714  is installed into position contacting tubular segments  718  and  720  for calibration test purposes, and the portion of system  700  downstream of reservoir  702  has been bled of air and other gasses. Controller  722  activates pump  706  to flow liquid from within reservoir  702  in series into meter under test  714  and scale  716 , which each perform simultaneous measurements on the liquid. Controller  722  synchronizes these simultaneous measurements. 
     Description of FIG. 8 
     FIG. 8 depicts a schematic block process diagram showing a process  800  of meter calibration as described in step  510  from FIG.  5 . The discussion of the steps of FIG. 8 is framed in the context of reference numbers of the apparatus of FIG.  6 . 
     Step  802  entails inserting a unit under test. This assembly typically includes inserting process connection adapters on to each end of the test unit  614  and compressing the process connection adapters between tubular segments  618  and  620 . Test unit  614  is typically held in place between tubular segments  618  and  620  by a hydraulic or pneumatic actuator. 
     Test unit  614  is normally filled with air after the unit under test has been properly installed in step  802 . A pressurized air source is used to blow liquid from the system, if needed, prior to determining an air density reference value from each individual meter in the test unit  614 , pursuant to step  804 . 
     According to step  806 , air is next bled from the system and water or another test fluid is introduced into the test unit  614 . The test fluid can be air, in which case air does not need to be bled from the system and step  806  can be skipped. 
     Controller  622  opens automated valves (not shown) and uses liquid from pump  606  to purge the test unit  614 . Alternatively, controller  622  can open valves for return of fill liquid to reservoir  602  if residual fluid and/or particles inside test unit  614  will not contaminate the fluid in the reservoir. 
     In step  808 , controller  622  activates pump  606  to flow water from reservoir  302  or permits fluid from another source to flow fluid through flow calibration system  600 . Controller  622  also determines the flow rate for the calibration test based upon operator input identifying the type or types of meters in the unit under test and a lookup table or database of appropriate test profile information for each meter. The operator can also input the test profile information to override or supplement test profile information in the database. Controller  622  then selectively opens and closes the automated valves to match the test profile. 
     Controller  622  is preferably configured to obtain simultaneous readings from each active meter in first meter array  612 , second meter array  616 , and the test unit  614 . This synchronization avoids the possibility that pressure surges through the system  600  could skew the measurement results if controller  622  polls the respective meters at different times. This flow measurement data can be quickly obtained, e.g., seven measurement points can be obtained in two to three minutes. 
     In step  810 , the flow measurement data from second meter array  616  is used to calculate a flow calibration factor or calibration equation that is compatible with the type of meter under test in test unit  614 . The flow calibration factor calculation is performed according to the manufacturer&#39;s specifications, and the manner of this calculation is preferably kept in the same database or lookup table that is used to identify the test profile in step  808 . 
     Step  812  entails additional flow measurement testing to verify performance of the meter under test using the flow calibration factor that was calculated in step  810 . Controller  622  again synchronizes measurements from all of the active meters in flow calibration system  600 . 
     In step  814 , the controller  622  checks each measurement signal from steps  808  and  812  and compares the cumulative signals (e.g., representing total flow rate amounts from two meters in first meter array  612 ) that are obtained from one array at a single time against the cumulative signals from the other array at the same time. The comparison entails subtracting one signal from the other and determining whether the difference exceeds an uncertainty limit. 
     It is to be expressly understood that the claimed invention is not to be limited to the description of the preferred embodiment but encompasses other modifications and alterations within the scope and spirit of the inventive concept. For example, the term “material” encompasses fluids, gases, liquids and any other element that can be made to flow through a meter.