Abstract:
Providing a fast response to a process step while allowing a sensor response to remain relatively slow. A mechanical component generates a response to a step change in a physical property and an electrical component generates an analog electrical signal indicative of the response generated by the mechanical component over a period of time. The analog electrical signal is converted into digital values and the digital values are used to indicate the final value of the step change in the physical property before the period of time has elapsed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application Ser. No. 61/835,236, filed Jun. 14, 2013, the entire contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     A sensing system includes a collection of mechanical and electrical components used to detect or measure a physical property and to indicate the detected or measured physical property. The mechanical components require an amount of time to respond to changes in the physical property. Additionally, one or more of the electrical components may intentionally slow the sensing time for the sensing system to reduce noise that would have otherwise been present when the sensor system is sampling under stable process conditions. 
     The amount of time required for the sensing system to respond to changes in the physical property may be decreased by reducing the amount of signal filtering or other electrical circuit alterations. However, these approaches introduce undesirable side effects, such as increased noise or susceptibility to vibration effects. 
     SUMMARY 
     Aspects of the present invention relate to a sensor system that provides a fast response to a change in a physical property. In particular, aspects of the invention minimize delay while the sensor system slews to a final value after the change that occurs in the physical property. 
     In one aspect, a sensor generates an analog electrical signal over a period of time in response to a step change in a physical property. The sensor comprises at least one mechanical component configured to generate a response to the step change in the physical property and at least one electrical component in communication with the mechanical component for generating the analog electrical signal. The analog electrical signal is indicative of the response generated by the mechanical component. An analog-to-digital (A/D) converter is connected to the electrical component for receiving and converting the analog electrical signal into a plurality of discrete digital values as a function of time. A control circuit is connected to the A/D converter for receiving the discrete digital values and the control circuit is configured to infer a final value of the step change in the physical property before the period of time has elapsed as a function of one or more of the received discrete digital values. 
     In another aspect, a mechanical response is generated in a sensing system during a first period of time. The mechanical response is indicative of a change from an initial value to a final value of a sensed physical property. A continuous electrical signal is generated in the sensing system during the first period of time in response to the change of the sensed physical property and the continuous electrical signal is indicative of the mechanical response. The continuous electrical signal is converted into a plurality of discrete digital values as a function of time and the final value of the change in the sensed physical property is indicated as a function of one or more of the plurality of discrete digital values before the first period of time has elapsed. 
     In yet another aspect, a physical computer-readable medium stores computer-executable instructions for determining the magnitude of a change in a physical property. A computer-executable instruction applies a first time-dependent relationship to an analog electrical signal outputted by an electrical sensing element for determining a mechanical step change inputted to the electrical sensing element. The first time-dependent relationship characterizes the response of the electrical sensing element to the mechanical step change and the mechanical step change is outputted by a mechanical sensing element. A computer-executable instruction also applies a second time-dependent relationship to the determined mechanical step change outputted by the mechanical sensing element for determining a physical step change inputted to the mechanical sensing element. The second time-dependent relationship characterizes the response of the mechanical sensing element to the physical step change. And a computer-executable instruction applies a third time-dependent relationship to the determined physical step change inputted to the mechanical sensing element for determining the magnitude of a change in a physical property of an object. The third time-dependent relationship characterizes a response of the object to the change in the physical property of the object. In this instance, the physical step change is indicative of the response generated by the object, the mechanical step change is indicative of the response generated by the mechanical sensing element, and the analog electrical signal is indicative of the response generated by the electrical sensing element. 
     Other objects and features will be in part apparent and in part pointed out hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates components of an exemplary sensing system in accordance with an embodiment of the invention. 
         FIG. 2  is an exemplary graph illustrating various signals that represent various delays that occur within the sensing system of  FIG. 1 . 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the drawings. 
     DETAILED DESCRIPTION 
       FIG. 1  illustrates the components of an exemplary sensing system  100  in accordance with an embodiment of the invention. The illustrated sensing system  100  is a pressure transmitter (e.g., differential pressure transmitter) but it should be noted that the sensing system  100  could be any other type of sensing system (e.g., temperature sensor, density meter, etc.) and the below teachings correspond to sensing the other types of physical properties (e.g., temperature, density, etc.). Exemplary pressure transmitters include the Invensys® Foxboro® family of pressure transmitters. 
     The sensing system  100  includes mechanical sensing elements  102 , electrical sensing elements  104 , analog-to-digital (A/D) converter  106 , control circuit  108 , and digital-to-analog (D/A) converter  110 . The mechanical sensing elements  102  and electrical sensing elements  104  may be included within a single sensor. In one embodiment, the mechanical sensing elements  102  include a metal diaphragm and a fluid-filled chamber and the electrical sensing elements  104  include filtering elements. For further details about an embodiment of the mechanical sensing elements  102  and electrical sensing elements  104 , see U.S. Pat. No. 6,279,401 by Karas, which is incorporated herein by reference. The control circuit may be comprised solely of a microcontroller and program code but it should be noted that alternative or additional circuitry may be used without departing from the scope of the invention. 
     In the sensing system  100 , the mechanical sensing elements  102  are in communication with the electrical sensing elements  104 . In an embodiment in which the mechanical sensing elements  102  include a metal diaphragm and a fluid-filled chamber, the metal diaphragm is operatively connected to the fluid-filled chamber. The electrical sensing elements  104  are electrically coupled to the A/D converter  106 . In an embodiment in which the mechanical sensing elements  102  include a fluid-filled chamber, the electrical sensing elements  104  are connected to the fluid-filled chamber. In one embodiment, the A/D converter  106  is electrically coupled to the control circuit  108 . In another embodiment, the A/D converter  106  is in communication with the control circuit  108 . In an embodiment in which the control circuit  108  is part of a control circuit, the A/D converter  106  is connected to the control circuit. The control circuit  108  is connected to the D/A converter  110 . 
     In operation, the mechanical sensing elements  102  generate a response in reaction to a pressure step, and the electrical sensing elements  104  generate an analog electrical signal that is indicative of the response generated by the mechanical sensing elements  102 . In an embodiment in which the mechanical sensing elements  102  and the electrical sensing elements  104  are included within a single sensor, the sensor generates an analog electrical signal over a period of time in response to a pressure step. In an embodiment in which the mechanical sensing elements  102  include a metal diaphragm and a fluid-filled chamber, the metal diaphragm flexes away from a resting point in response to applied pressure, transferring pressure to the fluid-filled chamber and causing the electrical sensing elements  104  to generate an analog electrical signal that is proportional to the applied pressure. 
     The A/D converter  106  then receives the analog electrical signal generated by the electrical sensing elements  104  and converts it to a digital value. In operation, A/D converter  106  converts the analog electrical signal that is generated by electrical sensing elements  104  over a period of time into discrete digital values as a function of time. In one embodiment, the A/D converter  106  samples the analog electrical signal generated by the sensor that includes mechanical sensing elements  102  and electrical sensing elements  104  and converts each sample into a digital value. 
     The control circuit  108  receives the digital values from the A/D converter  106 . In an embodiment in which the control circuit  108  is part of a control circuit, the control circuit receives the digital values from the A/D converter  106 . The control circuit  108  is configured to apply one or more algorithms to the received digital values to produce a digital measurement value that represents the applied pressure. The D/A converter  110  then receives the digital measurement values from the control circuit  108  and converts them to an analog output signal that represents the applied pressure. 
     In general, there is a delay between the time at which a step occurs in the applied pressure and the time at which the step is represented in the analog output signal from the D/A converter  110 .  FIG. 2  is a graph illustrating various signals that exemplify various delays that occur within the sensor system  100 . In the illustrated embodiment, Signal A represents the applied pressure and illustrates a pressure step that occurs at a first time, t 0 . Signal B represents the analog electrical signal that is generated by the electrical sensing elements  104 . Signal C represents the digital values generated by the A/D converter  106 . Signal D represents the analog output signal that is produced by the D/A converter  110 . 
     The amount of time that is required for the entire process input step (e.g., pressure step) to be represented by the analog electrical signal generated by the electrical sensing elements  104  (i.e., Signal B) that is provided to the A/D converter  106  is referred to as the slew time. The slew time is represented by the period of time between t 0  and t 4  in  FIG. 2 . The slew time may be due to, for example, time needed for fluid within the fluid-filled chamber to move such that the pressure change is communicated to the electrical sensing elements  104 . Other factors that may contribute to the slew time include the time required for calculations by the control circuit  108  and time required for the D/A converter  110  to respond to a change in the signal produced by the control circuit  108 . 
     The amount of time of the delay between the occurrence of the pressure step (i.e., Signal A) and any indication of a pressure change in the analog electrical signal (i.e., Signal B) provided to the A/D converter  106  is referred to as dead time. The dead time is represented by the period of time between t 0  and t 1  in  FIG. 2 . The dead time may be caused by, for example, the time needed for the mechanical sensing elements  102  to communicate with electrical sensing elements  104 . Another exemplary cause of dead time is the time needed for propagation through additional electrical components that may exist to intentionally slow the signal&#39;s transitions to reduce noise that would otherwise be seen when the sensor is sampled under stable process conditions. 
     The amount of time of the delay between the arrival at the A/D converter  106  of the analog electrical signal generated by the electrical sensing elements  104  (i.e., Signal B) and the detection of that signal by the control circuit  108  (i.e., Signal C) is referred to as the conversion cycle time. The conversion cycle time is represented by the period of time between t 1  and t 2  in  FIG. 2 . The conversion cycle time may be caused by, for example, timing constraints associated with the control circuit  108 . Another exemplary cause of conversion cycle time is that the A/D converter  106  may be used to read multiple inputs in sequence and the A/D converter  106  may be processing another input when the present input appears. In this instance, the A/D converter  106  must complete the processing of that input and potentially other inputs before the cycle returns to the point where the present input is examined. 
     Aspects of the present invention provide a reduction in the impact of the slew time for optimizing the step response time of the sensor system  100 . Aspects of the present invention also reduce the need to make other changes to a sensing system that have less desirable consequences, such as increased noise or susceptibility to vibration effects. In particular, a model is developed to indicate how the analog electrical signal (i.e., Signal B) that is received at the A/D converter  106  slews when various process steps (i.e., pressure steps) occur. Based on this information, the control circuit  108  is configured to infer a final value of the pressure step before the control circuit  108  has received digital values from the A/D converter  106  that are proportional to the final value of the pressure step. In particular, digital values initially provided from the A/D converter  106  to the control circuit  108  in response to a pressure step (e.g., initial sequence of sensor readings) are used by the control circuit  108  to determine the final value of the pressure step. 
     In one embodiment, a model sensor system includes a set of reference sensors and electronic components. The model sensor system collects data as the reference sensors experience steps of different magnitudes and polarities (e.g., low-to-high pressure, high-to-low pressure) under varying ambient conditions. The collected data is used to develop a model characterizing how the analog electrical signal (i.e., Signal B in  FIG. 2 ) provided to the A/D converter  106  slews when particular process steps (e.g., pressure steps) occur. In one embodiment further discussed below, the collected data may be modeled using a resistor-capacitor (RC) curve. Alternatively, the collected data may be modeled using other known techniques such as neural networking. In addition to the collected data noted above, the model may consider other parameters such as initial conditions, including the initial pressure and/or the sensor temperature. 
     In one embodiment, the control circuit  108  is configured to monitor the digital values to detect a process step. For example, the control circuit  108  is configured to detect a process step when a threshold change in magnitude of the sensor readings (e.g., digital values) occurs in a pre-defined time span. In response to detecting a process step, the control circuit  108  is configured to collect two or more digital values from the A/D converter  106  and to determine the change in magnitude of the digital values over a defined amount of time. The control circuit  108  then applies the determined change in magnitude and duration of time to the model to generate the magnitude of the process input step that occurred. 
     In one embodiment, the model sensor system is operated to examine three stages: (1) external environment response to a pressure step; (2) mechanical sensing elements response to a pressure step; (3) analog electrical signal response to filtering components that are included in the electrical sensing elements. Each stage is modeled mathematically using an RC equation shown below to model how each stage&#39;s output (O) will vary as a function of time (t) in response to a step (S). 
     
       
         
           
             
               O 
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                 ( 
                 t 
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             = 
             
               S 
               * 
               
                 ( 
                 
                   1 
                   - 
                   
                     e 
                     
                       - 
                       
                         ( 
                         
                           t 
                           RC 
                         
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     An RC value for each stage of the model sensor system is empirically determined to generate a model that is used by the sensor system (e.g., control circuit  108 ) for a particular change in magnitude of the digital values. Alternatively, each stage may be modeled using other known techniques, such as neural network algorithms or more sophisticated time-dependent models. 
     Continuing with the above embodiment, the analog electrical signal received at the A/D converter  106  represents the output value for the third stage. Once this third stage output value is determined, the RC value for the third stage (e.g., the RC value for electrical sensing elements  104 ), may be used to determine the input into the third stage, which is also the output of the second stage. The output of the second stage is used with the RC value for the second stage (e.g., the RC value for mechanical sensing elements  102 ) to determine the input to the second stage, which is also the output for the first stage. Similarly, the output from the first stage is used with the RC value for the first stage to determine the magnitude of the process step that must have occurred for the sensor to generate the sequence of values having the particular change in magnitude. Thus, the control circuit  108  is able to use the equations and the empirically determined RC values to determine the applied pressure value. 
     Accordingly, aspects of the present invention allow a sequence of sensor readings to be collected relatively early in the time period required for the sensor to respond to a process step, and use those sensor readings to determine the final value of the process step. As such, the magnitude of the process step can be provided at a time prior to the sensor fully reacting to the change in pressure. Thus, aspects of the present invention minimize delays due to signal slew time and eliminate the need for alternative modifications to the sensor system  100 , which would impose noise and susceptibility to vibration effects. 
     Although described in connection with an exemplary processing environment, including computer-executable instructions, embodiments of the aspects of the invention are operational with numerous other general purpose or special purpose computing system environments or configurations. The computing system environment is not intended to suggest any limitation as to the scope of use or functionality of any aspect of the invention. Moreover, the computing system environment should not be interpreted as having any dependency or requirement relating to any one or combination of components illustrated in the exemplary operating environment. Examples of well-known computing systems, environments, and/or configurations that may be suitable for use with aspects of the invention include, but are not limited to, personal computers, server computers, hand-held or laptop devices, multiprocessor systems, microprocessor-based systems, set top boxes, programmable consumer electronics, mobile telephones, network PCs, minicomputers, mainframe computers, distributed computing environments that include any of the above systems or devices, and the like. 
     Embodiments of the aspects of the invention may be described in the general context of data and/or processor-executable instructions, such as program modules, stored one or more tangible, non-transitory storage media and executed by one or more processors or other devices. Generally, program modules include, but are not limited to, routines, programs, objects, components, and data structures that perform particular tasks or implement particular abstract data types. Aspects of the invention may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules may be located in both local and remote storage media including memory storage devices. 
     In operation, processors, computers and/or servers may execute the processor-executable instructions (e.g., software, firmware, and/or hardware) such as those illustrated herein to implement aspects of the invention. 
     Embodiments of the aspects of the invention may be implemented with processor-executable instructions. The processor-executable instructions may be organized into one or more processor-executable components or modules on a tangible processor readable storage medium. Aspects of the invention may be implemented with any number and organization of such components or modules. For example, aspects of the invention are not limited to the specific processor-executable instructions or the specific components or modules illustrated in the figures and described herein. Other embodiments of the aspects of the invention may include different processor-executable instructions or components having more or less functionality than illustrated and described herein. 
     The order of execution or performance of the operations in embodiments of the aspects of the invention illustrated and described herein is not essential, unless otherwise specified. That is, the operations may be performed in any order, unless otherwise specified, and embodiments of the aspects of the invention may include additional or fewer operations than those disclosed herein. For example, it is contemplated that executing or performing a particular operation before, contemporaneously with, or after another operation is within the scope of aspects of the invention. 
     When introducing elements of the present invention or the preferred embodiments(s) thereof, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
     In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained. 
     Not all of the depicted components illustrated or described may be required. In addition, some implementations and embodiments may include additional components. Variations in the arrangement and type of the components may be made without departing from the spirit or scope of the claims as set forth herein. Additional, different, or fewer components may be provided and components may be combined. Alternatively or in addition, a component may be implemented by several components. 
     The above description illustrates the aspects of the invention by way of example and not by way of limitation. This description enables one skilled in the art to make and use the aspects of the invention, and describes several embodiments, adaptations, variations, alternatives and uses of the aspects of the invention, including what is presently believed to be the best mode of carrying out the aspects of the invention. Additionally, it is to be understood that the aspects of the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The aspects of the invention are capable of other embodiments and of being practiced or carried out in various ways. Also, it will be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 
     Having described aspects of the invention in detail, it will be apparent that modifications and variations are possible without departing from the scope of aspects of the invention as defined in the appended claims. It is contemplated that various changes could be made in the above constructions, products, and processes without departing from the scope of aspects of the invention. In the preceding specification, various preferred embodiments have been described with reference to the accompanying drawings. It will, however, be evident that various modifications and changes may be made thereto, and additional embodiments may be implemented, without departing from the broader scope of the aspects of the invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative rather than restrictive sense.