Abstract:
A current generator that provides a first current level to read a configuration parameter of a field device. The current generator also provides a second current level. The first current level is lower in amperage than the second current level. The first current level does not operate the field device. The second current level operates the field device. A current sensor is connected in circuit with the field device. The current sensor reads the configuration parameter associated with the first current level. A method is provided that creates a current that reads a configuration parameter. The current has less than a minimum amplitude to operate necessary to operate a field device. The configuration parameter is read from the field device through employment of the current. The field device is configured through employment of the configuration parameter.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application is claiming priority of U.S. Provisional Patent Application Ser. No. 60/526,548, entitled “System and Method for the Safe Automatic Detection of a Field Device Communicating With Current Modulated Signal” filed on Dec. 4, 2003, the content of which is incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present disclosure relates to the sensing and configuration of devices, and more particularly, to the sensing and configuration of devices through the use of a reduced current.  
         [0004]     2. Description of the Related Art  
         [0005]     A number of protocol specifications, like the HART® (Registered Trademark of the HART Communications Foundation) communication protocol, are designed to support digital communications. These digital communications can be used for the measurement of various processes and parameters of various control devices. These digital communications, within these protocol specifications, typically occur over a traditional range of 4-20 milliAmps (mA). Generally, these digital communications provide host control systems with process and diagnostic information associated with a field device. The digital communications can occur as the host control system monitors and controls an industrial process.  
         [0006]     One purpose of such protocol specifications is to establish standards so that “hosts” {or “input/output (I/O) masters”} can communicate with field “devices” (“slaves”) developed by different vendors. One subset of the protocol specifications is classified as having “common functions.” “Common functions” requires that the host or device have to meet all standards within this subset of protocol specifications. This allows the host to require only a single interface layer to support a variety of field devices from many different vendors.  
         [0007]     However, other components of the protocol specification are classified as “device-specific,” and are defined by the individual device manufacturer. Since at least some of the digital data that will be passed between a host or I/O Master and the field device is specific to the given field device type, it is important to know what kind of field device is connected to the host control system prior to using the field device within an industrial process in real-time.  
         [0008]     In other words, due to the nature of device-specific components of field devices, it is necessary to obtain and verify pertinent information regarding the identification of the field device prior to configuration load and execution. Generally, configuration load and execution can be defined as the initialization of the field device for use in the field, and the actual employment of the field device. Pertinent information can include a unique identifier for a given field device, the vendor name for the field device, the firmware revision installed in the field device, the tag name (that is, the pseudonym) for the field device, description of the field device, and the various range limits that the field device can measure or apply. Without the above information derived from the initial start-up of a field device, it is difficult to integrate device specific data into a real-time process control strategy.  
         [0009]     Typically, input devices are current sourcing type, and output devices are a current sinking type. A sensor is an example of an input device and a valve is an example of an output device. Employment of a “base signal” of the sourcing current provides at least two functions. It provides the power to charge up, and initially configure, the field devices, and the base signal also is the carrier over which digital information is conveyed. For a current sinking device, the I/O master should drive the current for providing the “base” signal associated with these protocols. Therefore, for output devices, the host or I/O master provides a minimal specified current in order for the digital communication, with aid of the protocol specifications, to function.  
         [0010]     Conventional protocol specifications required users to initially load a control configuration (perhaps with the use of wrong initial control configuration), activate the control strategy, and drive the output (sourcing) current to a base amount required for communication with the field device. This occurred over a traditional range of 4-20 mA. Only then could the actual device identification and configuration data be collected. However, as can be appreciated, this could lead to significant errors in implementing an initial real-time control strategy.  
         [0011]     An alternative approach, used in other conventional protocol specifications, was to always provide a minimal current of 4 mA. However, this approach is not acceptable, as it is unsafe to power up a field device that is not initially configured. In any event, a user would have no control of the output devices if a problem would cause the field device to render itself unresponsive to the current.  
         [0012]     In conventional technologies, to run field devices, current is applied to the field device after configuration, as after configuration it is controllable. However, during a 4 mA power up to the field device, current is applied even without any configuration, and therefore is no way to control the field device. However, if anything goes wrong after applying the 4 mA current, there is no way to control the field device. Another issue is that in this prior art scenario, the minimal current will be omnipresent, which can create safety problems.  
         [0013]     Therefore, there is a need to safely and securely establish communication with a field device and acquire the field device identification data using a current modulated signaling technique, prior to a configuration load.  
       SUMMARY OF THE INVENTION  
       [0014]     There is a provided a current generator that provides a first current level to read a configuration parameter of at least one field device. The first current level is lower in amperage than a second current level. The first current level does not operate the field device. The current generator also provides the second current. The second current level operates said field device. A current sensor is connected in circuit with the field device. The current sensor detects the configuration parameter(s) associated with the first current level. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  is diagram of a prior-art control system before configuration;  
         [0016]      FIG. 2  is diagram of a prior-art configuration of a system controller and a master in an inactive status;  
         [0017]      FIG. 3  is a diagram of a prior-art configuration of a system controller and a master in an active status;  
         [0018]      FIG. 4  is a diagram of a prior-art configuration of a configured system controller and master.  
         [0019]      FIG. 5  is diagram of a configuration of devices with employment of an “auto-detect” option;  
         [0020]      FIG. 6  is a diagram of a computer system in which a program for detecting configuration information of field devices could operate; and  
         [0021]      FIG. 7  is a diagram of a current generator that operates in a detection/filed device configuration reading mode and a field device operation mode. 
     
    
     DESCRIPTION OF THE INVENTION  
       [0022]     The term “module” is used herein to demarcate a functional operation that may be embodied either as a stand-alone component or as one of a plurality of modules in an integrated assembly.  
         [0023]     Referring to  FIG. 1 , illustrated is a prior-art unconfigured system  100  having an inactive system controller  110  and an inactive I/O master  120  and one or more field devices  125 . Coupled between inactive system controller  110  and inactive I/O master  120  is a control connection  115 . Control connection  115  is unpowered, and inactive system controller  110  and inactive I/O master  120  are not configured. Therefore there is no current to field devices  125 . Furthermore, no configuration information has been retrieved from the one or more field devices  125 .  
         [0024]     The inactive system controller  110  represents an apparatus device, hardware, software or both, that can execute control algorithms which are used to control one or more field devices  125 .  
         [0025]     In one embodiment, one example of an inactive system controller  110  is a C200 module in an Experion Process Knowledge System™ (PKS). Experion PKS is an integrated platform for which controls, manages and seeks to optimize process operations, diagnostics and domain knowledge. C200 is a device that is employed to control process operations, such as in Experion PKS.  
         [0026]     Turning now to  FIG. 2 , illustrated is a prior-art initially configured system  129  including an inactive system controller  130  with inactive control blocks  131  and an inactive I/O master  140  with inactive channel blocks  141  and one or more field devices  145 . Coupled between inactive system controller  130  and inactive I/O master  140  is a control connection  135 . Control connection  135  conveys information between the inactive system controller  130  and inactive I/O master  140 .  
         [0027]     Inactive system controller  130  is illustrated as having one or more inactive control blocks  131 . Control blocks are the logical representations of real time control algorithms/strategies, such as a “Proportional-Integral-Derivative” control algorithm for controlling and monitoring one or more field devices  145 . However, in inactive system controller  130 , the control blocks are inactive control blocks  131 . Therefore, although control blocks have been created, they are not yet being employed. Inactive control blocks  131  have been configured with initial/preexisting configuration data not derived from a direct reading of one or more field devices  145 .  
         [0028]     Inactive I/O Master  140  is illustrated as having one or more inactive channel blocks  141 . Channel blocks are, generally, logical representations of data associated with one or more field devices  145 . Employment of channel blocks allows the device configurations to be integrated into control strategy. However, in initially configured system  129 , the control clocks are inactive control blocks  141 . Therefore, there is no current to one or more field devices  145 , and inactive control blocks  141  have been configured with initial/preexisting configuration data not derived from a direct reading of one or more field devices  145 .  
         [0029]     Referring to  FIG. 3 , illustrated is a prior-art initially configured system  149  that includes an active system controller  150  with active control blocks  151 , an active I/O master  160  with active channel blocks  161 , and one or more field devices  165 . Coupled between active system controller  150  and active I/O master  160  is a control connection  155 .  
         [0030]     Active control blocks  151  have been loaded with an initial configuration. Control connection  155  is illustrated as an “Output Percent” of 0% to 100% (OP). OP is equivalent to output current 4 mA to 20 mA. When channel blocks are active and OP is 0%, 4 mA is driven to the current path  163  by the system and when it is 100%, 20 mA is driven. Active channel blocks  161  have also been loaded with the initial/pre-existing configuration parameters. Active channel blocks  161  of active I/O master  160  are actively interfacing with one or more field devices  165  over a current path  163 . Therefore, there is a 4-20 mA current sent to one or more field devices  165 . The 4-20 mA current powers one or more field devices  165 , but uses the parameters loaded within the initial configuration of active control blocks  151  and active channel blocks  161  to do so.  
         [0031]     Referring to  FIG. 4 , illustrated is a prior-art reconfigured system  169  illustrating the reconfiguration of a reconfigured system controller  170 , a reconfigured I/O master  180  after both have received updated actual configuration parameters from one or more field devices  185  over a current path  183 . A control connection  175  couples reconfigured system controller  170  and reconfigured I/O master  180 .  
         [0032]     In reconfigured system  169 , after one or more field devices  185  are activated through application of the 4-20 mA current, the final identification/configuration data for each one or more field device  185  is retrieved from one or more field device  185  over current path  183 . The final configuration of reconfigured active control blocks  171  of reconfigured system controller  170  and reconfigured active channel blocks  181  of reconfigured I/O master  180  is, therefore, modified in accordance therewith with the discovered final one or more field device  185  reconfiguration information. In reconfigured system  169 , this can be digital information stored within one or more field devices  185 , conveyed over the 4-20 mA current over current path  183 .  
         [0033]     Generally, as can seen from  FIGS. 1-4 , the 4-20 mAs which is employed to power one or more field devices, is first driven in initial configuration of the active control blocks  151  and active channel blocks  161 . However, the actual digital configuration parameters of one or more field devices  185  are not read until after the current is applied, as illustrated in reconfigured system  169 . Therefore, the initial configurations of active control blocks  151  and active channel blocks  161  could be based upon erroneous information and parameters. Only after the initial system power up is completed in reconfigured system  169  are the actual configuration parameters associated with one or more field devices  185  taken into account within reconfigured system controller  170  and reconfigured I/O  180 . This can lead to serious errors in configuration, which can create safety or work concerns when employing a real-time control strategy that relies upon the accuracy of this initial configuration information.  
         [0034]     One such problem is that when the initial configuration load is done and the devices are put into run state, a contact with the device has not yet been established. If there are some problems with the device, system  100 ,  200 ,  300 , or  400  will be able to detect only some time after a field device is in its run state. This could be catastrophic.  
         [0035]     Turning now to  FIG. 5 , illustrated is a configuration system  200  using a configuration detection feature for the digital information programmed in one or more field devices  250 . Generally, configuration system  200  employs a safe and a secure method to provide control system users with digital identification parameters prior to configuring the various system controllers and I/O masters. Configuration system  200  includes a system controller  205 , an I/O master  220 , and an auto-detector  240  that provides for the detection of actual digital configuration information from one or field devices  250  prior to applying the standard 4.0-20.0 mA of current. The actual configuration parameters that were originally digitally stored in one or more field devices  250  are then used in I/O master  220  or system controller  205 , as opposed to using user-defined configuration parameters. The choice of which one or more field devices  250  to detect can be displayed on and input in a system controller interface  223  or I/O master interface  225 .  
         [0036]     By enabling auto-detection, a safe current, less than 4 mA, is driven through a current pathway  230  to one or more field devices  250 . The safe current, such as 3.2 mA, is adequate to power the device electronics of one or more field devices  250  to enable current modulated digital communication therewith. For instance, an application of 3.2 mA will not make a change in a state of one or more field devices  250 , such as a valve stem position, but will enable the reading of the actual digital configuration parameters of one or more field devices  250 . These parameters are then used to configure system controller  205  and I/O master  220 . Disabling auto-detector  240  will remove this safe current, thereby giving the user full control of the output current to one or more field devices  250 , even though the 3.2 mA current is within safe limits.  
         [0037]     In other words, at 4 mA field devices  250  are just at the beginning of the normal operating range. By providing a current less than that, there will not be enough current to make any change in the one or more field devices  250 , other than just establishing the digital communication.  
         [0038]     Generally, configuration system  200  provides a mechanism in I/O master  220  or system controller  205 , perhaps through employment of system controller interfaces  223  or I/O master interface  225 , to enable and disable automatic field device digital information detection for current sinking devices, such as one or more field devices  250 , before a control strategy or configuration is loaded to controller  205  and the I/O master  220 . Generally, when auto-detector  240  is enabled for one or more field devices  250 , I/O master  220  drives a “safe” current, such as of 3.2 mA, to one or more field devices  250 . This current is enough to power up most of one or more field devices  250  to establish digital communication. Generally, one reason a current such as 3.2 mA is safe is because it does not allow circuitry, such as valve circuitry, to operate on or within one or more field devices  250 . This current is below 4 mA, which is the 0% output value as per 4-20 mA current HART signal standards.  
         [0039]     When auto-detector  240  is disabled, (the default setting) for any particular device  251 - 255 , pathway  230  to that particular devices is unpowered, providing drive zero current such that the digital configuration parameters for that particular device can not be read. When automatic device detection is enabled in the auto-detector  240  for any given one or more field devices  250  (or alternatively, all field devices) communication with one or more field devices  250  is established to collect device identification/configuration data from the one or more field devices  250 . The collected digital information/configuration parameters collected can then also presented to the user in system controller interface  223  or I/O master interface  225  which also provided the option to enable/disable automatic detection for each field devices of one or more field devices  250 .  
         [0040]     After detection of one or more field devices  250  is complete, the digitally read and detected field device or field devices  250  can still be continuously monitored, using a low-priority polling scheme, as long as automatic device detection is enabled by auto-detector  240 . Any change in one or more field device  250  configuration is therefore automatically updated on system controller interface  223  or I/O master interface  225  mentioned above, and can be used in reconfiguring system controller  205  and/or I/O master  220 , respectively. This low-priority polling should have minor bandwidth loading on I/O master  220 . In one embodiment of configuration system  200 , if one or more field devices  250  are defective in some manner, system  200  removes minimal (less than 4.0 mA) current by disabling auto-detector  240 . Both using a smaller current than minimally required to drive one or more field devices  250 , such as 3.2 mA, and the capability of disabling auto-detector  240  enhance the safety of configuration system  200 .  
         [0041]     The auto-detector  240  is disabled when a control strategy is loaded. This helps to avoid two separate controls for the output current of I/O master  220  being applied at the same time. Once the control strategy is loaded, current to one or more field devices  250  is controlled only though the control strategy.  
         [0042]     In the case of redundant I/O masters (not illustrated), the auto-detector  240  feature will take effect only in the currently-designated primary I/O master  220 . However, the secondary I/O master will remember the user selections for each field device  250  and perform automatic device detection as soon as the secondary I/O master becomes a primary I/O Master following a switch-over. Finally, auto-detector  240  selection will not block the capability of I/O master  240  to shed outputs to a safe unpowered state in case of a failure.  
         [0043]     In one embodiment, the loading of the control strategy does not disturb the current applied over current path  183 , nor does loading the control strategy overwrite the configuration data that was loaded to system controller  205  and I/O master  220  derived from one or more field devices  250 . An initial user configuration, that is, the configuration information that a user has before the actual reading of the digital information embedded in one or more field devices  250  can thus be validated by comparing it with actual device configuration data read from one or more field devices  250 . After the comparison is made and perhaps the initial user configuration is corrected, the collection of one or more field devices  250  dynamic data, that is, data that configuration system  200  collects through monitoring events in real time, can be started immediately without the need to go through an entire power up and reading of configuration readings and reconfiguration of system controller  205  and I/O master  220  at 4-20 mA.  
         [0044]     In one embodiment, auto-detector  240  selection is fully supported by one or more redundant I/O masters. If auto-detector  240  is enabled in a primary I/O master, and if it fails over (switches over to the secondary), the new primary I/O master will preserve the auto-detector  240  selection. In configuration system  200 , if primary I/O master loses communication with the control system, outputs are then driven to some configured safe states. Unpowering, or removing the current, helps to ensure safe state configuration. The use of a safe current, such as 3.2 mA with auto-detector  240  does not obstruct this safety activity.  
         [0045]     Referring to  FIG. 6 , illustrated is a block diagram of a computer system  300  adapted for employment of auto-detector  240  and the reading of the digital configuration information embedded in one or more field devices  350 . Computer system  300  includes a workstation computer  310  with a storage media  325  and a user interface  305  coupled to workstation computer  310 . User interface  305  includes an input device, such as a keyboard or speech recognition subsystem, for enabling a user to communicate information and command selections to workstation computer  310 . A cursor control such as a mouse, track-ball, or joy stick, allows the user to manipulate a cursor on the display for communicating additional information and command selections to workstation computer  310 . Computer system  300  presents an image of one or more field devices  250  and auto-detector  240  on system controller interface  223  or I/O master interface  225  as displayed on user interface  305 , and provides a hardcopy of one or more field devices  250  digital configuration data via a printer.  
         [0046]     Workstation computer  310  is coupled to a network  330 . The network  330  is also coupled to a data depository  307 . Network  330  is also coupled to a slave processor  340 . Slave processor  340  is coupled to a memory  315 . Memory  315  is a memory for storing data and instructions for controlling the operation of slave processor  340 . An implementation of memory  315  could include a random access memory (RAM), a hard drive and a read only memory (ROM). One of the components of memory  315  is a program  320 . Slave processor  340  is also coupled to one or more field devices  350 .  
         [0047]     Program  320  can includes instructions for controlling slave processor  340 , system controller  205 , I/O master  220 , or current control to drive either the safe current or HART current to one or more field devices  350  by employing auto-detector  240 . As a result of execution of program  320 , slave processor  310  can reads the digital configuration data into memory  315  from one or more field devices  250 , and can use this configuration data to configure system controller  205  or I/O master  220 . Program  320  may be implemented as a single module or as a plurality of modules that operate in cooperation with one another.  
         [0048]     While program  320  is indicated as already loaded into memory  315 , it may be configured on a storage media  325  for subsequent loading into memory  315  by way of network  330 . Storage media  325  can be any conventional storage media such as a magnetic tape, an optical storage media, a compact disk, or a floppy disk. Alternatively, storage media  325  can be a random access memory, or other type of electronic storage, located on a remote storage system.  
         [0049]     Slave processor  340 , through an I/O master  345 , then configures one or more field devices  350  with the configuration data. Slave processor  340  then controls and monitors one or more field devices  350 . I/O master  345  can correlate to I/O master  220 .  
         [0050]     In  FIG. 7 , in a current generation system  400 , a slave processor  410  is coupled to a current generator  420 . Both slave processor  410  and current generator  420  are coupled to a switch  430 . Switch  430  has a plurality of connections to field device  440 . Field device  440  has a feedback loop  450  coupled back to slave processor  410 .  
         [0051]     Generally, slave processor  410  instructs current generator  420  whether to generate a current in a safe mode, perhaps 3.2 mA, or the standard 4.0 to 20.0 mA. 4-20 mA is standard instrumentation signal range. Slave processor  410  instructs switch  430  to which field devices or field devices of field device  440  should have the current applied. Slave processor  410  then reads the configuration data embedded within field device  440  over feedback loop  450 . Slave processor  410  can sense this configuration data, or alternatively, another device can extract the configuration data and then convey the configuration data to slave processor  410 . In one embodiment, this configuration data is then conveyed to system controller  205  and I/O master  220  (not shown in this FIGURE). Then, slave processor  410 , through switch  430 , uses configuration parameter read from field device  440  to configure field device  440 , using the a lower, safe current of less than 4.0 mA. Then, current generator  440  increases the current to the 4.0 to 20.0 mA range to operate field device  440 .  
         [0052]     It should be understood that various alternatives, combinations and modifications of the teachings described herein could be devised by those skilled in the art. The present invention is intended to embrace all such alternatives, modifications and variances that fall within the scope of the present invention.