Patent Publication Number: US-2017350782-A1

Title: Fill fluid thermal expansion compensation for pressure sensors

Description:
TECHNICAL FIELD 
     This disclosure relates generally to pressure sensors. More specifically, this disclosure relates to a fill fluid with thermal expansion compensation for pressure sensors. 
     BACKGROUND 
     Pressure sensors designed for process measurements of a process fluid typically utilize a fill fluid, which is an inert secondary fluid, to transmit pressure signals to relatively delicate internal sensing systems. The fill fluid is separated from process fluid by a flexible membrane typically in the form of a metallic diaphragm. 
     SUMMARY 
     This disclosure provides a fill fluid thermal expansion compensation for differential pressure sensors. 
     In a first embodiment, a pressure sensor including a housing with a cavity is provided. The cavity includes a fill fluid and a compensation material. The fill fluid conveys a pressure from a process fluid through a diaphragm to a sensor. The compensation material reduces a difference of thermal expansion between the cavity and the fill fluid. 
     In a second embodiment, a system is provided. The system includes a control system and a pressure sensor. The control system is configured to communicate data with one or more pressure sensors. The pressure sensor includes a housing, a cavity, a compensation material and a fill fluid. The fill fluid conveys a pressure from a process fluid through a diaphragm to a sensor. The compensation material reduces a difference of thermal expansion between the cavity and the fill fluid. 
     In a third embodiment, a method thermal expansion compensation of a fill fluid in a pressure sensor is provided. The method includes reducing a difference of thermal expansions between a cavity and a fill fluid by using a compensation material inserted in the cavity. The method further includes conveying a pressure from a process fluid through the fill fluid, separated by a diaphragm, to a sensor. 
     Other technical features may be readily apparent to one skilled in the art from the following figures, descriptions, and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of this disclosure, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates an example industrial control and automation system according to this disclosure; 
         FIG. 2  illustrates an example differential pressure sensor according to this disclosure; 
         FIG. 3  illustrates another example differential pressure sensor according to this disclosure; and 
         FIG. 4  illustrates an example method for fluid fill thermal expansion compensation for pressure sensors according to this disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 through 4 , discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any type of suitably arranged device or system. 
     Pressure sensors designed for measurements of a process fluid typically utilize a fill fluid, an inert secondary fluid, to transmit pressure signals to relatively delicate internal sensing systems. The disclosure describes how to reduce the effective thermal expansion of a fill fluid within a closed system to more closely match the expansion coefficient of the cavity of the housing such that extra volumetric loading of barrier diaphragms can be reduce over wide temperature ranges (e.g., −50° C. to 130° C.). 
       FIG. 1  illustrates an example industrial process control and automation system  100  according to this disclosure. As shown in  FIG. 1 , the system  100  includes various components that facilitate production or processing of at least one product or other material. For instance, the system  100  is used here to facilitate control over components in one or multiple plants  101   a - 101   n . Each plant  101   a - 101   n  represents one or more processing facilities (or one or more portions thereof), such as one or more manufacturing facilities for producing at least one product or other material. In general, each plant  101   a - 101   n  may implement one or more processes and can individually or collectively be referred to as a process system. A process system generally represents any system or portion thereof configured to process one or more products or other materials in some manner. 
     In  FIG. 1 , the system  100  is implemented using the Purdue model of process control. In the Purdue model, “Level 0” may include one or more sensors  102   a  and one or more actuators  102   b . The sensors  102   a  and actuators  102   b  represent components in a process system that may perform any of a wide variety of functions. For example, the sensors  102   a  could measure a wide variety of characteristics in the process system, such as temperature, pressure, flow rate, or a voltage transmitted through a cable. Also, the actuators  102   b  could alter a wide variety of characteristics in the process system. The sensors  102   a  and actuators  102   b  could represent any other or additional components in any suitable process system. Each of the sensors  102   a  includes any suitable structure for measuring one or more characteristics in a process system. Each of the actuators  102   b  includes any suitable structure for operating on or affecting one or more conditions in a process system. 
     At least one network  104  is coupled to the sensors  102   a  and actuators  102   b . The network  104  facilitates interaction with the sensors  102   a  and actuators  102   b . For example, the network  104  could transport measurement data from the sensors  102   a  and provide control signals to the actuators  102   b . The network  104  could represent any suitable network or combination of networks. As particular examples, the network  104  could represent an Ethernet network, an electrical signal network (such as a HART or FOUNDATION FIELDBUS (FF) network), a pneumatic control signal network, or any other or additional type(s) of network(s). 
     In the Purdue model, “Level 1” may include one or more controllers  106 , which are coupled to the network  104 . Among other things, each controller  106  may use the measurements from one or more sensors  102   a  to control the operation of one or more actuators  102   b . For example, a controller  106  could receive measurement data from one or more sensors  102   a  and use the measurement data to generate control signals for one or more actuators  102   b . Multiple controllers  106  could also operate in redundant configurations, such as when one controller  106  operates as a primary controller while another controller  106  operates as a backup controller (which synchronizes with the primary controller and can take over for the primary controller in the event of a fault with the primary controller). Each controller  106  includes any suitable structure for interacting with one or more sensors  102   a  and controlling one or more actuators  102   b . Each controller  106  could, for example, represent a multivariable controller, such as a Robust Multivariable Predictive Control Technology (RMPCT) controller or other type of controller implementing model predictive control (MPC) or other advanced predictive control (APC). As a particular example, each controller  106  could represent a computing device running a real-time operating system. 
     Two networks  108  are coupled to the controllers  106 . The networks  108  facilitate interaction with the controllers  106 , such as by transporting data to and from the controllers  106 . The networks  108  could represent any suitable networks or combination of networks. As particular examples, the networks  108  could represent a pair of Ethernet networks or a redundant pair of Ethernet networks, such as a FAULT TOLERANT ETHERNET (FTE) network from HONEYWELL INTERNATIONAL INC. 
     At least one switch/firewall  110  couples the networks  108  to two networks  112 . The switch/firewall  110  may transport traffic from one network to another. The switch/firewall  110  may also block traffic on one network from reaching another network. The switch/firewall  110  includes any suitable structure for providing communication between networks, such as a HONEYWELL CONTROL FIREWALL (CF9) device. The networks  112  could represent any suitable networks, such as a pair of Ethernet networks or an FTE network. 
     In the Purdue model, “Level 2” may include one or more machine-level controllers  114  coupled to the networks  112 . The machine-level controllers  114  perform various functions to support the operation and control of the controllers  106 , sensors  102   a , and actuators  102   b , which could be associated with a particular piece of industrial equipment (such as a boiler or other machine). For example, the machine-level controllers  114  could log information collected or generated by the controllers  106 , such as measurement data from the sensors  102   a  or control signals for the actuators  102   b . The machine-level controllers  114  could also execute applications that control the operation of the controllers  106 , thereby controlling the operation of the actuators  102   b . In addition, the machine-level controllers  114  could provide secure access to the controllers  106 . Each of the machine-level controllers  114  includes any suitable structure for providing access to, control of, or operations related to a machine or other individual piece of equipment. Each of the machine-level controllers  114  could, for example, represent a server computing device running a MICROSOFT WINDOWS operating system. Although not shown, different machine-level controllers  114  could be used to control different pieces of equipment in a process system (where each piece of equipment is associated with one or more controllers  106 , sensors  102   a , and actuators  102   b ). 
     One or more operator stations  116  are coupled to the networks  112 . The operator stations  116  represent computing or communication devices providing user access to the machine-level controllers  114 , which could then provide user access to the controllers  106  (and possibly the sensors  102   a  and actuators  102   b ). As particular examples, the operator stations  116  could allow users to review the operational history of the sensors  102   a  and actuators  102   b  using information collected by the controllers  106  and/or the machine-level controllers  114 . The operator stations  116  could also allow the users to adjust the operation of the sensors  102   a , actuators  102   b , controllers  106 , or machine-level controllers  114 . In addition, the operator stations  116  could receive and display warnings, alerts, or other messages or displays generated by the controllers  106  or the machine-level controllers  114 . Each of the operator stations  116  includes any suitable structure for supporting user access and control of one or more components in the system  100 . Each of the operator stations  116  could, for example, represent a computing device running a MICROSOFT WINDOWS operating system. 
     At least one router/firewall  118  couples the networks  112  to two networks  120 . The router/firewall  118  includes any suitable structure for providing communication between networks, such as a secure router or combination router/firewall. The networks  120  could represent any suitable networks, such as a pair of Ethernet networks or an FTE network. 
     In the Purdue model, “Level 3” may include one or more unit-level controllers  122  coupled to the networks  120 . Each unit-level controller  122  is typically associated with a unit in a process system, which represents a collection of different machines operating together to implement at least part of a process. The unit-level controllers  122  perform various functions to support the operation and control of components in the lower levels. For example, the unit-level controllers  122  could log information collected or generated by the components in the lower levels, execute applications that control the components in the lower levels, and provide secure access to the components in the lower levels. Each of the unit-level controllers  122  includes any suitable structure for providing access to, control of, or operations related to one or more machines or other pieces of equipment in a process unit. Each of the unit-level controllers  122  could, for example, represent a server computing device running a MICROSOFT WINDOWS operating system. Although not shown, different unit-level controllers  122  could be used to control different units in a process system (where each unit is associated with one or more machine-level controllers  114 , controllers  106 , sensors  102   a , and actuators  102   b ). 
     Access to the unit-level controllers  122  may be provided by one or more operator stations  124 . Each of the operator stations  124  includes any suitable structure for supporting user access and control of one or more components in the system  100 . Each of the operator stations  124  could, for example, represent a computing device running a MICROSOFT WINDOWS operating system. 
     At least one router/firewall  126  couples the networks  120  to two networks  128 . The router/firewall  126  includes any suitable structure for providing communication between networks, such as a secure router or combination router/firewall. The networks  128  could represent any suitable networks, such as a pair of Ethernet networks or an FTE network. 
     In the Purdue model, “Level 4” may include one or more plant-level controllers  130  coupled to the networks  128 . Each plant-level controller  130  is typically associated with one of the plants  101   a - 101   n , which may include one or more process units that implement the same, similar, or different processes. The plant-level controllers  130  perform various functions to support the operation and control of components in the lower levels. As particular examples, the plant-level controller  130  could execute one or more manufacturing execution system (MES) applications, scheduling applications, or other or additional plant or process control applications. Each of the plant-level controllers  130  includes any suitable structure for providing access to, control of, or operations related to one or more process units in a process plant. Each of the plant-level controllers  130  could, for example, represent a server computing device running a MICROSOFT WINDOWS operating system. 
     Access to the plant-level controllers  130  may be provided by one or more operator stations  132 . Each of the operator stations  132  includes any suitable structure for supporting user access and control of one or more components in the system  100 . Each of the operator stations  132  could, for example, represent a computing device running a MICROSOFT WINDOWS operating system. 
     At least one router/firewall  134  couples the networks  128  to one or more networks  136 . The router/firewall  134  includes any suitable structure for providing communication between networks, such as a secure router or combination router/firewall. The network  136  could represent any suitable network, such as an enterprise-wide Ethernet or other network or all or a portion of a larger network (such as the Internet). 
     In the Purdue model, “Level 5” may include one or more enterprise-level controllers  138  coupled to the network  136 . Each enterprise-level controller  138  is typically able to perform planning operations for multiple plants  101   a - 101   n  and to control various aspects of the plants  101   a - 101   n . The enterprise-level controllers  138  can also perform various functions to support the operation and control of components in the plants  101   a - 101   n . As particular examples, the enterprise-level controller  138  could execute one or more order processing applications, enterprise resource planning (ERP) applications, advanced planning and scheduling (APS) applications, or any other or additional enterprise control applications. Each of the enterprise-level controllers  138  includes any suitable structure for providing access to, control of, or operations related to the control of one or more plants. Each of the enterprise-level controllers  138  could, for example, represent a server computing device running a MICROSOFT WINDOWS operating system. In this document, the term “enterprise” refers to an organization having one or more plants or other processing facilities to be managed. Note that if a single plant  101   a  is to be managed, the functionality of the enterprise-level controller  138  could be incorporated into the plant-level controller  130 . 
     Access to the enterprise-level controllers  138  may be provided by one or more operator stations  140 . Each of the operator stations  140  includes any suitable structure for supporting user access and control of one or more components in the system  100 . Each of the operator stations  140  could, for example, represent a computing device running a MICROSOFT WINDOWS operating system. 
     Various levels of the Purdue model can include other components, such as one or more databases. The database(s) associated with each level could store any suitable information associated with that level or one or more other levels of the system  100 . For example, a historian  141  can be coupled to the network  136 . The historian  141  could represent a component that stores various information about the system  100 . The historian  141  could, for instance, store information used during production scheduling and optimization. The historian  141  represents any suitable structure for storing and facilitating retrieval of information. Although shown as a single centralized component coupled to the network  136 , the historian  141  could be located elsewhere in the system  100 , or multiple historians could be distributed in different locations in the system  100 . 
     In particular embodiments, the various controllers and operator stations in  FIG. 1  may represent computing devices. For example, each of the controllers could include one or more processing devices  142  and one or more memories  144  for storing instructions and data used, generated, or collected by the processing device(s)  142 . Each of the controllers could also include at least one network interface  146 , such as one or more Ethernet interfaces or wireless transceivers. Also, each of the operator stations could include one or more processing devices  148  and one or more memories  150  for storing instructions and data used, generated, or collected by the processing device(s)  148 . Each of the operator stations could also include at least one network interface  152 , such as one or more Ethernet interfaces or wireless transceivers. 
     In accordance with this disclosure, various components of the system  100  support a process for fill fluid thermal expansion compensation for pressure sensors in the system  100 . For example, one or more of the sensors  102   a  could include a pressure sensor that can compensate for thermal expansion over a wide temperature range, as described in greater detail below. 
     Although  FIG. 1  illustrates one example of an industrial process control and automation system  100 , various changes may be made to  FIG. 1 . For example, a control system could include any number of sensors, actuators, controllers, servers, operator stations, and networks. Also, the makeup and arrangement of the system  100  in  FIG. 1  is for illustration only. Components could be added, omitted, combined, or placed in any other suitable configuration according to particular needs. Further, particular functions have been described as being performed by particular components of the system  100 . This is for illustration only. In general, process control systems are highly configurable and can be configured in any suitable manner according to particular needs. 
       FIG. 2  illustrates an example differential pressure sensor  200  according to this disclosure. The embodiment of differential pressure sensor  200  illustrated in  FIG. 2  is for illustration only.  FIG. 2  does not limit the scope of this disclosure to any particular implementation. The pressure sensor  200  may represent (or be represented by) the sensor  102   a  of  FIG. 1 . 
     As shown in  FIG. 2 , the pressure sensor  200  is configured for mounting in a pipe containing a process fluid  210 , such as oil or gas. The pressure sensor  200  measures the pressure of the process fluid  210  and transmits pressure readings to a system, such as the system  100 . The process fluid  210  flowing through the pipe passes across a flexible membrane  215  exerting pressure on the flexible membrane. As shown in  FIG. 2 , a fill fluid  205  is separated from the process fluid  210  by a flexible membrane  215  typically in the form of a metallic diaphragm. The fill fluid  205  is an incompressible fluid, such as silicone oil. Because the fill fluid  205  is incompressible, when the process fluid  210  exerts pressure, that pressure is conveyed from the process fluid  210  through the flexible membrane  215  and the fill fluid  205  to a sensor  245 . The fill fluid  205  works with the sensor  245  to measure the pressure from the process fluid  210 . The cavity  220  in the housing  225  of the differential pressure sensor  200  that the fill fluid  205  is located in has a significantly lower thermal expansion coefficient than the fill fluid  205 . As the differential pressure sensor  200  may be operated over a wide temperature range, relative shrinkage or expansion of the fill fluid  205  places extra stress on the barrier diaphragm  230  that must move to compensate for the volumetric changes. Since there is a practical lower limit to fill fluid  205  volumes, the volumetric changes caused by temperature place a lower limit on barrier diaphragm  230  size in a given design to keep the barrier diaphragm  230  stresses within acceptable limits. The barrier diaphragm  230  size constrains overall sensor size and cost due to material and manufacturing requirements. 
     Although  FIG. 2  illustrates an example of a differential pressure sensor  200 , various changes may be made to  FIG. 2 . For example, while a configuration of the components is illustrated in  FIG. 2 , other embodiments can include more or fewer components. 
       FIG. 3  illustrates another example differential pressure sensor  300  according to this disclosure. The embodiment of differential pressure sensor  300  illustrated in  FIG. 3  is for illustration only.  FIG. 3  does not limit the scope of this disclosure to any particular implementation. 
     The fill fluid  305  is separated from the process fluid  310  by a flexible membrane  315  typically in the form of a metallic diaphragm. The fill fluid  305  conveys a pressure from a process fluid  310  through a flexible membrane  315  to the sensor. The process fluid  310  works with a sensor  345  to measure the pressure from the process fluid  310 . The cavity  320  in the housing  325  of the differential pressure sensor  300  that the fill fluid  305  is located in has a significantly lower thermal expansion coefficient than the fill fluid  305 . A compensation material  330  is added to the cavity  320  to accommodate the difference in thermal expansion. 
     Construction of a compensation material  330  involves increasing the cavity  320  in a controlled manner that allows close fitting insertion of the compensation material  330  with a low or negative thermal expansion coefficient. The volume of low thermal expansion material is proportional to the fill fluid volume and the ratio of the fill fluid to enclosure expansion coefficients. For an enclosure constructed from stainless steel with a silicone fill fluid  305 , the amount of low expansion material required would be about 20× the fill fluid volume. 
     As an example, the compensation material  330  can be manufactured as a cylindrical component of low expansion metal, such as a low expansion metal, ultra-low expansion glass or ceramic may be inserted into a close tolerance hole such that addition of extra fill fluid trapped within the gap between the two parts is minimized. During thermal expansion, the housing  325  will expand away from the compensation material  330  and produce a gap into which the fill fluid  305  can expand into rather than the diaphragm cavity. Ideally, the cylindrical shape of the compensation material  330  is advantageous since precise OD tolerances can be easily obtained by centerless grinding or lathe operations. The pocket can also be economically produced accurately by reaming operations. This close fit allows for a minimum of extra fill fluid  305  to be added to the system in the corners and gaps between the compensation material  330  and housing  325 . 
     The differential pressure sensor  300  includes a low side sensor  350  and a high side sensor  355 . The low side sensor  350  measures the pressure before a compressor. The high side sensor  355  measures the pressure after a compressor. Both the low side sensor  350  and the high side sensor  355  include a cavity where compensation material  330  can be inserted. 
     Although  FIG. 3  illustrates an example of a differential pressure sensor  300 , various changes may be made to  FIG. 3 . For example, while a configuration of the components is illustrated in  FIG. 3 , other embodiments can include more or fewer components. 
       FIG. 4  illustrates an example method  400  for fill fluid thermal expansion compensation for pressure sensors according to this disclosure. The process depicted in  FIG. 4  is described as being performed in conjunction with the differential pressure sensor  300  illustrated in  FIG. 3 . Of course, this is merely one example; the process may be performed in conjunction with other sensors, such as the differential pressure sensor  200  of  FIG. 2 . 
     In operation  405 , a compensation material  330  is inserted in a cavity  320  of a differential pressure sensor  300 . The compensation material  330  is a material with a thermal expansion coefficient lower than a thermal expansion coefficient of the housing. In other embodiments, the compensation material  330  can also be chosen to reduce a difference for other reasons of change in volume, such as external pressure. The amount and shape of the compensation material  330  is determined based on the ratio compared to the fill fluid  305  in order for the changes in volume due to changes in temperature to not affect the pressure of the fill fluid  305 . Increasing the pressure of the fill fluid  305  will increase the pressure on the barrier diaphragm resulting in inaccurate results or possible damage to the differential pressure sensor  300 . The compensation material  330  is sized such that an average thermal expansion coefficient of both the volume of the fill fluid and the compensation material is less than the thermal expansion coefficient of the housing. A gap between the compensation material  330  and the housing  325  is minimized at a lowest operating temperature of the pressure sensor  300 . The amount of the compensation material  330  and the amount of the fill fluid  305  has a net thermal expansion value that is zero or negative. 
     In operation  410 , a net thermal expansion of zero is maintained within the cavity  320  for a range of operating temperatures. The range of operating temperatures is based on the temperature patterns at the location of the installation. The differential pressure sensor could be installed in a location where the operating temperature, for example, is in the temperature range from −50° C. to 130° C. 
     In operation  415 , a net pressure expansion of zero is maintained within the cavity  320  due to exterior pressures. While a change in external pressure may not produce as great a difference in pressure within the cavity, any slight exterior pressure change could affect the reading of the pressure from the sensor. The compensation material  330  could balance any difference in pressure or volume between the fill fluid  305  and the housing  325  due to exterior pressure changes. 
     In operation  420 , the fill fluid  305  conveys a pressure from a process fluid  310  to a diaphragm. The fill fluid  305  is an incompressible fluid to transmit the pressure from the process fluid  310  accurately. Due to the compensation material  330 , the fill fluid  305  conveys an accurate reading at all operating temperatures. 
     Although  FIG. 4  illustrates one example of a method  400  for fill fluid thermal expansion compensation for pressure sensors, various changes may be made to  FIG. 4 . For example, various steps shown in  FIG. 4  could overlap, occur in parallel, occur in a different order, or occur any number of times. 
     It may be advantageous to set forth definitions of certain words and phrases used throughout this patent document. The terms “transmit,” “receive,” and “communicate,” as well as derivatives thereof, encompasses both direct and indirect communication. The terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation. The term “or” is inclusive, meaning and/or. The phrase “associated with,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, have a relationship to or with, or the like. The phrase “at least one of,” when used with a list of items, means that different combinations of one or more of the listed items may be used, and only one item in the list may be needed. For example, “at least one of: A, B, and C” includes any of the following combinations: A, B, C, A and B, A and C, B and C, and A and B and C. 
     While this disclosure has described certain embodiments and generally associated methods, alterations and permutations of these embodiments and methods will be apparent to those skilled in the art. Accordingly, the above description of example embodiments does not define or constrain this disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of this disclosure, as defined by the following claims.