Wiring fault detection, diagnosis and reporting for process control
Contents
1. 2 t i t 100 1 1 t 1 1 1 i t 55 102 U S Patent Jun 28 2005 Sheet 1 of 7 US 6 912 671 B2 USER USER DATA INTERFACE INTERFACE STORAGE 12 14 16 20 CONTROLLER 18 LINKING DEVICE SMART FIELD DEVICE 22 SMART FIELD DEVICE 24 SMART FIELD DEVICE 26 FIG 1 US 6 912 671 2 Sheet 2 of 7 Jun 28 2005 U S Patent YOSSJJOYd aINGSHOS JAILOV 151 HOW JILSONSVIG SNOILVOINNAIWOD Old WOVLS NOILVOINNNWOD YOLINOW NOLLVOINNWNOD YON NOILOANNOO HOW ASNAS OLNV 08 LINA NOI1O313Gg 391430 01313 Viva NOILONNA ASVEVLVG wee en nn nw ee ewe ee wd 8 81 1 YATIONLNOS DILSONDVIG LAWS U S Patent OHMMETER 164 NOISE METER TO WIRING FAULT DIAGNOSTIC MGR Jun 28 2005 Sheet 3 of 7 US 6 912 671 B2 wo VOLTMETER peak to peak DC GROUND FAULT DETECTOR CAPACITANCE METER SIGNAL SWITCHING ur STACK FIG 3 U S Patent Jun 28 2005 Sheet 4 of 7 US 6 912 671 B2 DISCONNECT BUS LINES FROM COMMUNICATION 200 CIRCUITRY 204 202 REPORT WIRING FAULT TO USER AT SYSTEM LEVEL POSSIBLE SHORT TO R BETWEEN SIGNAL LINES amp2. gt 50K OHMS YES 208 REPORT WIRING FAULT TO USER AT SYSTEM LEVEL POSSIBLE SHORT CHECK LINES R BETWEEN EACH SIGNAL LINE amp AND SHIELD AND EACH SIGNAL LINE AND GROUND gt 20 M OHMS YES 212 REPORT WIRING FAULT TO USER AT SYSTEM LEVEL POSSIBLE MISSING OR EXTRA TERMINATOR BETWEEN SIGNAL LINES 8 F TO YES 214 216 REPORT WIRING FAULT TO USER AT SYSTEM LEVEL POSSIBLE POOR SHIELD CONNECTION CHECK LINES C BETWEEN EACH SIGNAL LINE AND SHIELD AND EACH SIGNAL LINE AND GROUND lt 300 nF ANY REPORTED FAULTS NO FIG 4 ss U S Patent Jun 28 2005 Sheet 5 of 7 US 6 912 671 B2 CONNECT BUS LINES TO LINKING DEVICE COMMUNICATION CIRCUITRY REPORT WIRING FAULT TO USER AT SYSTEM LEVEL SUPPLY VOLTAGE OUT OF RANGE DC VOLTAGE BETWEEN SIGNAL LINES amp 18 6 TO 19 4 VDC REPORT WIRING FAULT TO PEAK TO PEAK SIGNAL USER AT SYSTEM VOLTAGE amp 500 mV LEVEL INSUFFICIENT TO 900 mV SIGNAL STRENGTH FIG 4B U S Patent Jun 28 2005 Sheet 6 of 7 US 6 912 671 B2 REPORT FATAL COMMUNICATION FAULT TO USER AT SYSTEM LEVEL FATAL COMMUNICATION FAULT INVOKE REPORT COMMUNICATION EXCESSIVE NOISE FAULT PROCEDURE TO USER AT SYSTEM LEVEL SIGNAL LEVEL OUT OF RANGE REPORT SIGNAL LE
3. 4 pages Siemens Quadlog The Safety PLC Critical Discrete Module CDM pp 1 5 U K Search Report issued in GB 0210353 9 dated Nov 11 2002 Examination Report under Section 18 3 issued in GB 0210353 9 application by the United Kingdom Patent Office on May 20 2004 Fieldbus Supplement to Installing Your DeltaV Scalable Process System Fisher Rosemount Systems Inc Jul 1999 Primary Examiner Nadeem Iqbal 74 Attorney Agent or Firm Marshall Gerstein amp Borun LLP 57 ABSTRACT A wiring fault detection diagnostic and reporting technique enables linking devices within a process control system to measure the electrical characteristics of a segment protocol bus and the electrical characteristics of the signals transmit ted via the protocol bus The technique connects a signal line of a segment protocol bus to one of a plurality of measure ment blocks within a wiring fault detection unit The one of the plurality of measurement blocks measures an electrical characteristic associated with the segment protocol bus and sends the measured electrical characteristic to a wiring fault diagnostic manager The wiring fault diagnostic manager analyzes the measured electrical characteristic to determine a type of the wiring fault and reports the type of the wiring fault via a user interface 28 Claims 7 Drawing Sheets COMMUNICATIONS DIAGNOSTIC LINK ACTIVE SCHEDULE MGR
4. 15 sub stantially active 19 The system of claim 18 wherein the second routine is further adapted to cause the wiring fault detection unit to disconnect the signal line of the protocol bus from a com munication circuit 20 The system of claim 18 wherein the second routine is further adapted to measure one of a resistance a capacitance a signal amplitude a noise level and a power supply voltage 21 The system of claim 18 wherein the third routine is further adapted to compare the measured electrical charac teristic to a predetermined value associated with the wiring fault 22 The system of claim 21 wherein the third routine is further adapted to use a predetermined value associated with one of a short circuit an open circuit a ground fault an improper termination an insufficient signal strength a poor quality ground connection and an improper supply voltage 23 A system that detects a wiring fault for use within a process control system having a controller and a protocol bus the system comprising a plurality of measurement blocks communicatively coupled to the controller and adapted to be coupled to the protocol bus wherein the controller is programmed to connect one of the plurality of measurement blocks to the protocol bus to detect the wiring fault and wherein the measurement blocks reside within a linking device wherein the linking device enables the control ler to communicate with a plurality of smart field dev
5. a ground fault detector block 166 and a capacitance meter block 168 Of course any other blocks for measuring the electrical characteristics of the bus 30 or of the signals transmitted via the bus 30 may be included if desired 10 15 20 25 35 40 45 50 55 60 65 10 The signal switching unit 150 includes signal switching circuitry that in response to commands from the wiring fault diagnostic manager 126 connects one or more of the signal lines or wires of the bus 30 to one or more of the measure ment blocks 158 168 Additionally the signal switching unit 150 may connect the signal lines of the bus 30 to commu nication circuitry 1 the physical layer of the communi cation stack 104 within the linking device 28 The signal switching unit 150 may be implemented using electrome chanical devices such as relays reed switches etc and or may use solid state devices such as discrete transistors analog multiplexers etc Of course any other suitable signal switching devices may be used instead without departing from the scope and the spirit of the invention The ohmmeter block 158 is preferably but not necessarily configured to measure resistances between zero ohms and at least twenty megaohms by sending a relatively small direct current DC through a selected pair of signal lines of the bus 30 and measuring a resultant voltage drop However due to the relatively small DC current used by this resistanc
6. faults and FIG 6 is an exemplary schematic block diagram of a portable wiring fault detection and diagnosis device DESCRIPTION OF THE PREFERRED EMBODIMENTS While a technique for detecting diagnosing and reporting wiring faults within a distributed process control system is described in detail in conjunction with a process control system that implements process control functions using Fieldbus devices the wiring fault detection diagnosis and reporting technique described herein may be used with process control systems that perform control functions using other types of field devices and communication protocols including protocols that rely on other than two wire buses and protocols that support only analog or both analog and digital communications such as those mentioned previ ously The Fieldbus protocol is an all digital serial two way communication protocol that provides a standardized physi cal interface to a two wire loop or bus interconnecting field equipment such as sensors actuators controllers valves etc located in an instrumentation or process control envi ronment of for example a factory or a plant The Fieldbus protocol provides in effect a local area network for field devices within a process which enables these field devices to interoperate to perform control functions at locations distributed throughout a process and to communicate with one another before and after the performance of these control functi
7. field devices that are connected to the controller 18 in any conventional or any other desired manner In particular the controller 18 is in communication with smart field devices 22 26 via a linking device 28 The field devices 22 26 are connected in a communication network via a non proprietary protocol databus 30 and communicate with one another and the linking device 28 to execute one or more process control loops either in conjunction with or independently from the controller 18 The smart field devices 22 26 may be for example Fieldbus devices in which case the non proprietary protocol databus 30 employs the Fieldbus signal protocol However other types of devices and protocols could be used as well While the smart field devices 22 26 are illustrated in FIG 1 as being connected to the non proprietary protocol databus 30 in a standard bus type configuration in which multiple devices are connected to the same pair of wires the Fieldbus protocol allows other device wire topologies including point to point connections in which each device is con nected to a controller or a host via a separate two wire pair similar to typical 4 20 mA analog DCS systems and tree or spur connections in which each device is connected to a common point in a two wire bus that may be for example a junction box or a termination area in one of the field devices within a process control system Each of the smart field devices 22 26 is capable of com
8. linking device having a wiring fault detection unit and a wiring fault diagnostic manager therein the wiring fault detection unit including a plurality of measure ment blocks and a signal switching unit the system com prising a computer readable medium a first routine stored on the computer readable medium and adapted to be executed by the processor that causes the wiring fault detection unit to connect a signal line of the protocol bus to one of the plurality of measure ment blocks a second routine stored on the computer readable medium and adapted to be executed by the processor that causes the wiring fault detection unit to measure an electrical characteristic associated with the protocol bus using the one of the plurality of measurement blocks while the protocol bus is substantially active a third routine stored on the computer readable medium and adapted to be executed by the processor that determines a type of the wiring fault based on the measured electrical characteristic a fourth routine stored on the computer readable medium and adapted to be executed by the processor that automatically reports the type of the wiring fault to the user interface and a fifth routine stored on the computer readable medium and adapted to be executed by the process that auto 10 15 20 25 30 35 40 45 50 55 18 matically detects a communications problem associated with the protocol bus while the protocol bus
9. otherwise block 214 passes control to block 216 Block 216 reports a wiring fault to the user at the system level and indicates that a poor shield connection may be present on those lines within a particular segment having excessive capacitances greater than 300 nF After block 216 reports wiring faults the procedure terminates Block 218 determines if any of blocks 204 212 have reported a wiring fault if a fault has been reported the procedure terminates otherwise if no faults have been reported then control passes to block 220 Block 220 reconnects the lines of the bus 30 to the communication circuitry 1 the physical layer within the communication stack 104 of the linking device 28 As a result of this connection power is supplied to the field devices 22 26 and Fieldbus communications between the field devices 22 26 and the controller 18 may resume Block 220 then passes control to block 222 Block 222 measures the DC voltage between the and signal lines of the bus 30 and if the measured DC voltage falls between 18 6 volts DC and 19 4 volts DC control passes to block 226 otherwise control passes to block 224 Block 224 reports a wiring fault to the user at the system level and indicates that the power supplied on the bus 30 is out of range Block 224 then passes control to block 226 Block 226 measures the peak to peak voltage between the and signal lines and if the measured pea
10. VEL OUT OF RANGE TO USER AT SYSTEM LEVEL FIG 5 U S Patent Jun 28 2005 Sheet 7 of 7 WIRING DISPLAY K406 DIAGNOSTIC MANAGER KEYPAD M408 WIRING FAULT DETECTION UNIT FIG 6 US 6 912 671 B2 400 402 MEMORY 404 PROCESSOR 410 POWER SOURCE US 6 912 671 2 1 WIRING FAULT DETECTION DIAGNOSIS AND REPORTING FOR PROCESS CONTROL SYSTEMS FIELD OF THE INVENTION The present invention relates generally to process control systems and more specifically to automatically detecting diagnosing and reporting wiring faults within communica tion segments of a process control system DESCRIPTION OF THE RELATED ART Modern process control systems are typically microprocessor based distributed control systems DCSs A traditional DCS configuration includes one or more user interface devices such as workstations connected by a databus e g Ethernet to one or more controllers The controllers are generally located physically close to a con trolled process and are connected to numerous electronic monitoring devices and field devices such as electronic sensors transmitters current to pressure transducers valve positioners etc that are located throughout the process In a traditional DCS control tasks are distributed by providing a control algorithm within each of the controllers The controllers independently execute the control algo rithms to control the field devices coupled to the controllers T
11. a United States Patent Christensen et al US006912671B2 US 6 912 671 B2 Jun 28 2005 10 Patent No 45 Date of Patent 54 WIRING FAULT DETECTION DIAGNOSIS AND REPORTING FOR PROCESS CONTROL SYSTEMS 75 Inventors Daniel D Christensen Austin TX US Steven D Bonwell Austin TX US Michael L Marshall Georgetown TX US 73 Assignee Bisher Rosemount Systems Inc Austin TX US Notice Subject to any disclaimer the term of this patent is extended or adjusted under 35 U S C 154 by 436 days 21 Appl No 09 850 300 2 Filed May 7 2001 65 Prior Publication Data US 2002 0194547 1 Dec 19 2002 51 E 11 00 GOIR 31 28 52 US CER 714 25 714 721 58 Field of Search 714 25 26 27 714 32 37 43 47 48 721 742 33 44 324 513 539 702 109 122 56 References Cited U S PATENT DOCUMENTS 6 107 807 A 8 2000 Fluhrer 324 533 6 115 831 A 9 2000 Hanf etal 714 43 FOREIGN PATENT DOCUMENTS DE 198 13 964 A1 8 1999 DE 101 04 908 A1 8 2002 EP 556 991 A1 8 1993 DATABASE MEMORY WIRING WIRING FAULT DETECTION UNIT AUTO SENSE MGR 118 MGR MGR FUNCTION CONNECTION LIVE LIST MGR 122 COMMUNICATION MONITOR OTHER PUBLICATIONS Horner Bus Interface Unit for use with Interbus S and GE Fanuc Field Control User Manual for HE670IBU100 May 7 2002
12. a basic device or a bridge device etc that are associated with one or more of the field devices 22 26 and compare the identification information to commissioning 1 configuration information stored in the database manager 118 and or the memory 106 Based on the comparison the auto sense manager 112 determines if there is a discrepancy such as for example if a device has been added to or removed from the protocol bus 30 To further improve the diagnostic capabilities of the linking device 28 the auto sense manager 112 may be adapted to automatically report any discrepancy to the user The wiring fault diagnostic manager 126 receives signals indicative of measured electrical characteristics associated with the signal lines or wires of the bus 30 from the wiring fault detection unit 128 and further processes these signals to determine whether there are any wiring faults on the bus 30 In particular the wiring fault diagnostic manager 126 may determine that a wiring fault exists on a particular segment protocol bus within the system 10 such as the bus 30 and may further identify the specific nature or type of the wiring fault For example the wiring fault diagnostic man ager 126 may determine that a particular one of the signal lines of the bus 30 is shorted is an open circuit is improp erly terminated is excessively noisy etc Any such wiring fault information generated by the wiring fault diagnostic manager 126 may be communic
13. ated to the controller 18 which in turn may report the wiring fault information to the user via one of the user interfaces 12 and 14 Thus the wiring fault detection unit 128 and the wiring fault diag nostic manager 126 enable a system user at one of the interfaces 12 and 14 to identify a wiring fault within any segment protocol bus of the process control system 10 thereby eliminating the requirement for a field technician to physically inspect every communication segment during system check out or commissioning The wiring fault diag nostic manager 126 also sends control signals and com mands to the wiring fault detection unit 128 to control the operations of the wiring fault detection unit 128 For example the wiring fault diagnostic manager 126 may send commands to the wiring fault detection unit 128 that cause the wiring fault detection unit 128 to carry out a particular electrical characteristic measurement or sequence of mea surements at particular times FIG 3 is a more detailed exemplary block diagram of the wiring fault detection unit 128 shown in FIG 2 As shown in FIG 3 the wiring fault detection unit 128 includes a signal switching unit 150 a plurality of measurement blocks 152 a light emitting diode LED drive circuit 154 and a plurality of LEDs 156 By way of example only the plurality of measurement blocks 152 includes an ohmmeter block 158 a voltmeter block 160 a signal generator block 162 a noise meter block 164
14. ch as a failure of a device to transmit data properly to a subscribing device and or may include timing problems that may be identified using statistical information such as for example the number of times a device has failed to provide fresh data to a subscribing device Of course a wide variety of other communication related diagnostic information can be gen erated by making appropriate comparisons and analyses of the actual and scheduled communication activities The linking device 28 also provides wiring fault detection diagnostic and reporting capabilities As will be described in greater detail below the linking device 28 can measure the electrical characteristics such as for example the resistance capacitance etc of the protocol bus 30 and can also measure the electrical characteristics of the signals being transmitted via the bus 30 such as for example the amplitude frequency noise level etc of the signals The linking device 28 may further process or analyze these measured electrical characteristics to determine whether a wiring fault exists on the bus 30 and may diagnose the specific nature of a wiring fault For example the linking device 28 may measure one or more resistances associated with one or more bus wires or signal lines of the bus 30 and based on a comparison of the measured resistances to predetermined resistance values or ranges of resistance values determine that a wiring fault exists on one or more of th
15. col bus while the protocol bus is substantially active connecting a signal line of the protocol bus to one of the plurality of measurement blocks measuring an electrical characteristic associated with the protocol bus using the one of the plurality of measure ment blocks while the protocol bus is substantially active sending the measured electrical characteristic to the wir ing fault diagnostic manager determining a type of the wiring fault based on the measured electrical characteristic and automatically reporting the type of the wiring fault to the user interface 11 The method of claim 10 wherein the step of connect ing the signal line of the protocol bus to the one of the plurality of measurement blocks includes the step of con necting the signal line to one of an ohmmeter block a voltmeter block a signal generator block a noise meter block a ground fault detector block and a capacitance meter block 12 The method of claim 10 wherein the step of connect ing the signal line of the protocol bus to the one of the plurality of measurement blocks includes the step of con necting the signal line to the one of the plurality of mea surement blocks in response to a signal from the wiring fault diagnostic manager US 6 912 671 2 17 13 The method of claim 10 wherein the step of measur ing the electrical characteristic associated with the protocol bus using the one of the plurality of measurement blocks inclu
16. des the step of disconnecting the signal line of the protocol bus from a communication circuit 14 The method of claim 10 wherein the step of measur ing the electrical characteristic associated with the protocol bus includes the step of measuring one of a resistance a capacitance a signal amplitude a noise level and a power supply voltage 15 The method of claim 10 wherein the step of deter mining the type of the wiring fault based on the measured electrical characteristic includes the step of comparing the measured electrical characteristic to a predetermined value associated with the wiring fault 16 The method of claim 15 wherein the step of com paring the measured electrical characteristic to the prede termined value includes the step of using a predetermined value associated with one of a short circuit an open circuit a ground fault an improper termination an insufficient signal strength a poor quality ground connection and an improper supply voltage 17 The method of claim 10 wherein the step of auto matically reporting the type of the wiring fault to the user interface includes the step of sending wiring fault informa tion to the user interface via a controller 18 A system for detecting a wiring fault for use within a process control system having a user interface a controller a protocol bus a processor and a linking device that enables a controller to communicate with the plurality of smart field devices the
17. dule as a communication template to identify communication and linking problems such as where a field device fails to provide fresh data at the correct time to the correct recipient or fails to provide any data Because the linking device 28 can communicate freely with the control ler 18 the diagnostic information can be easily conveyed to the user at the system level 1 a user interface which US 6 912 671 2 7 eliminates the need for the user to locally monitor and manually determine field device communication problems The linking device 28 automatically subscribes to all communications on the protocol bus 30 using for example the link active schedule Because the link active schedule contains a communication template for the protocol bus 30 the linking device 28 can determine the precise times at which particular field devices are scheduled to communicate on the bus 30 Thus by comparing the link active schedule to the actual communications on the bus 30 deviations from the link active schedule can be identified as possible com munication problems with particular field devices These deviations from the link active schedule can be used by the linking device 28 to generate communication diagnostic information associated with the smart field devices 22 26 that may be useful in troubleshooting and or configuring the process control system 10 FIG 1 For example the diag nostic information may include linking problems su
18. e bus wires e g a short circuit an open circuit an improper termination etc The linking device 28 may then convey or report the detected wiring fault information which may include wiring fault diagnostic information to the controller 18 which in turn may report this information to the user via one or more of the user interfaces 12 and 14 As shown in FIG 2 the linking device 28 includes a plurality of functional blocks 100 which are controlled by a processor 102 to publish and subscribe to communications on the protocol bus 30 via a communications stack 104 and to enable detection diagnosis and automatic system level reporting of wiring faults on the protocol bus 30 The functional blocks 100 may be implemented using any desired combination of hardware and software Generally the functional blocks 100 may be efficiently implemented using the processor 102 to execute a number of software code segments or modules that are retrieved from a local computer readable memory 106 However other combina tions of hardware and software using for example algo rithm specific integrated circuits 1 ASICs or other types of hardware may be used to accomplish the same functions without departing from the scope and the spirit of the invention The functional blocks 100 within the linking device 28 include but are not limited to a communication monitor 10 15 20 25 30 35 40 45 50 55 60 65 8 108 a co
19. e measurement technique the ohmmeter block 158 requires the signal switching unit 150 to disconnect the signal lines of the bus 30 from the communication circuitry within the linking device 28 while the ohmmeter block 158 carries out the resistance measurement The voltmeter block 160 on the other hand is configured to measure peak to peak alternating current AC voltage DC voltage AC root mean squared RMS voltage etc while the signal lines of the bus 30 are connected to the communication circuitry of the linking device 28 and while Fieldbus communications are active on the bus 30 Con necting the voltmeter block 160 to the signal lines of the bus 30 in this manner does not have any practical effect on active communications because the voltmeter block 160 has a high input impedance e g greater than one megaohm In operation the voltmeter block 160 may be used to measure any DC supply voltage on the bus 30 the signal amplitude or strength using for example a peak to peak voltage measurement function on the bus 30 or any other voltage that may be indicative of the quality of the signals trans mitted via the bus 30 The signal generator block 162 is configured to generate AC signals that may be transmitted via one or more signal lines of the bus 30 and measured by for example the voltmeter block 160 to determine the transmission charac teristics of the bus signal lines The signal generator block 162 may provide any variety o
20. etermined threshold etc Of course the LED drive circuit 154 and the LEDS 156 may be configured to illuminate in any manner desired to provide a local 1 at the segment location visual indication that particular wiring faults exist thereby enabling a field technician to quickly identify the location and nature of a segment protocol bus wiring fault FIGS 4A and 4B are exemplary flow diagrams depicting one manner in which the linking device 28 shown in FIGS 1 and 2 may be used to detect diagnose and report segment protocol bus wiring faults Preferably but not necessarily the blocks shown in FIGS 4A and 4B are carried out by the diagnostic manager 126 working in conjunction with the wiring fault detection unit 128 Alternatively some of the blocks shown in FIGS 4A and 4B may be carried out by the controller 18 and or one or both of the user interfaces 12 and 14 Furthermore while the wiring fault diagnostic manager 126 is depicted as residing entirely with the linking device 28 some or all of the functions of the wiring fault diagnostic manager 126 may instead reside within the controller 18 within one or both of the user interfaces 12 and 14 or within any other device within the process control system 10 As shown in FIG 4A block 200 disconnects the signal lines of the segment protocol bus 30 from the communica tion circuitry 1 the physical layer of the communication stack 104 of the linking device 28 Block 202 uses t
21. f waveforms desired such as for example square waves sawtooth waveforms sinusoidal waveforms impulses step function waveforms frequency modulated waveforms amplitude modulated waveforms etc Thus the signal generator block 162 may be used to measure the response of the bus 30 to various types of communications or signals thereby enabling these measure ments to be used to diagnose a variety of wiring faults For example the signal generator 162 may output a fixed amplitude sinusoidal current waveform on one or more of the signal lines of the bus 30 and the resulting peak to peak voltage may be measured by the voltmeter block 160 The peak to peak voltage measured by the voltmeter block 160 may be indicative of the load on the bus 30 and in a case where the peak to peak voltage is substantially near zero volts it may be indicative of a short circuit on one or more bus lines In general use of the signal generator block 162 to transmit signals on the bus 30 requires the signal switch ing unit 150 to disconnect the communication circuitry of the linking device 28 from the bus 30 The noise meter block 164 may be connected via the signal switching unit 150 to the bus 30 while Fieldbus US 6 912 671 2 11 communications are active on the bus 30 to measure noise levels present on one or more signal lines of the bus 30 within one or more frequency bands The noise meter block 164 may use any conventional or any other suitable filter
22. gs etc associated with a field device may be conveyed to a user terminal and communication diagnostic information such as timing and linking problems associ ated with the field device protocol bus 30 can be generated by detecting a deviation between the actual communications on the bus 30 and the scheduled communications in accor dance with a link active schedule that is stored in the linking device 28 FIG 2 is a more detailed exemplary block diagram of the linking device 28 shown in FIG 1 The linking device 28 allows an integration of the field devices 22 26 FIG 1 with the process control system 10 FIG 1 For instance in addition to providing conventional communication links between the function block parameters of the smart field devices 22 26 on the non proprietary protocol bus 30 the linking device 28 also enables communication links between function blocks of the field devices 22 26 and function blocks that reside within the controller 18 Thus the linking device 28 allows a user to define control loops using combinations of function blocks that reside in the controller 18 and in one or more of the field devices 22 26 As noted above the linking device 28 provides diagnostic capabilities for facilitating the troubleshooting of commu nication problems on the field device protocol bus 30 The linking device 28 monitors and analyzes substantially all of the communications on the protocol bus 30 and uses the link active sche
23. h segment i e each interconnected group of smart field devices and a controller These linking devices enable the smart field devices within a segment to interoperate via a protocol data bus e g a Fieldbus databus with the function blocks of a controller and with smart field devices connected to other segments of the process control system Thus these linking devices enable a seamless inte gration of smart field devices within a distributed process control system because they enable the linking of field device information such as function block information resident in one or more of the field devices with function block information resident in the controller or other field devices and controllers distributed throughout the process control system While the protocol bus wiring for the multitude of seg ments that are typically used within a distributed process control system is being installed one or more bus wires may be inadvertently connected to the wrong terminal the wrong signal port power supply voltage etc one or more bus wires may be left unconnected 1 an open circuit condition and or one or more bus wires may be improperly terminated Additionally even if all protocol bus wiring is initially installed properly one or more of the bus wires may become severed or shorted to another wire or potential a voltage source ground line etc during subsequent opera tion of the process control system De
24. he ohmmeter block 158 FIG 3 to measure the resistance between the and signals lines of the bus 30 and determines whether the measured resistance is greater than 50 kilohms kohms If the measured resistance is greater than 50 kohms control passes to block 206 On the other hand if the measured resistance is less than or equal to 50 kohms control passes to block 204 Block 204 reports a wiring fault to the user at a system level and indicates that the and signals lines of a particular segment e g the segment associated with the bus 30 may be shorted to each other and then passes control to block 206 To report the wiring fault to the user at the system level the diagnostic manager 126 may convey the wiring fault information to the controller 18 which in turn may convey the wiring fault information to one or both of the user interfaces 12 and 14 Block 206 measures the resistances between the each of the and signal lines and the shield line of the bus 30 Additionally block 206 measures the resistances between the and signal lines and system ground potential e g a system grounding bar Block 206 then determines whether any of the measured resistances is greater than 20 megaohms Mohms and if any of the resistances measured by block 206 is greater than 20 Mohms control passes to block 210 otherwise control passes to block 208 Block 208 reports a wiring fault to
25. he computer readable medium and adapted to be executed by the processor that causes the wiring fault detection unit to measure an electrical characteristic associated with the protocol bus using the one of the plurality of measurement blocks Still further the system may include a third routine stored on the computer readable medium and adapted to be executed by the processor that determines a type of the wiring fault based on the measured electrical characteristic Additionally the system may include a fourth routine stored on the computer readable medium and adapted to be executed by the processor that automatically reports the type of the wiring fault to the user interface BRIEF DESCRIPTION OF THE DRAWINGS FIG 1 is a schematic block diagram of an exemplary process control system having a linking device that detects diagnoses and reports segment protocol bus wiring faults FIG 2 is a more detailed exemplary block diagram of the linking device shown in FIG 1 FIG 3 is a more detailed exemplary block diagram of the wiring fault detection unit shown in FIG 2 FIGS 4A and 4B are exemplary flow diagrams depicting one manner in which the linking device shown in FIGS 1 and 2 may be used to detect diagnose and report segment protocol bus wiring faults FIG 5 is an exemplary flow diagram depicting another manner in which the linking device shown in FIGS 1 and 2 may be used to detect diagnose and report segment protocol bus wiring
26. his decentralization of control tasks provides greater over all system flexibility For example if a user desires to add a new process or part of a process to the DCS the user can add an additional controller having an appropriate control algorithm connected to appropriate sensors actuators etc Alternatively if the user desires to modify an existing process new control parameters or control algorithms may for example be downloaded from a user interface to an appropriate controller via the databus To provide for improved modularity and inter manufacturer compatibility process controls manufacturers have more recently moved toward even further decentrali zation of control within a process These more recent approaches are based on smart field devices that communi cate using an open protocol such as the HART PROFIBUS WORLDFIP Device Net CAN and Fieldbus protocols These smart field devices are essentially microprocessor based devices such as sensors actuators etc that in some cases such as with Fieldbus devices also perform some control loop functions traditionally executed by a DCS controller Because some smart field devices provide control capability and communicate using an open protocol field devices from a variety of manufacturers can communicate with one another on common digital databus and can interoperate to execute a control loop without the intervention of a traditional DCS controller As is well kno
27. ices the linking device being operable to automati cally detect a communications problem associated with the protocol bus while the protocol bus is substantially active 24 The system of claim 23 wherein the plurality of measurement blocks includes one of an ohmmeter block a voltmeter block a signal generator block a noise meter block a ground fault detector block and a capacitance meter block 25 The system of claim 23 wherein the wiring fault is one of a short circuit an open circuit a ground fault an improper termination an insufficient signal strength a poor quality ground connection and an improper supply voltage 26 The system of claim 1 wherein the automatic detec tion of the communications problem occurs during an asyn chronous communication interval 27 The method of claim 10 wherein automatically detecting the communications problem associated with the protocol bus occurs during an asynchronous communication interval 28 The system of claim 18 wherein the fifth routine automatically detects a communications problem associated with the protocol bus during an asynchronous communica tion interval UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO 6 912 671 B2 DATED June 28 2005 INVENTOR S Dantel D Christensen et al Page 1 of 1 It is certified that error appears in the above identified patent and that said Letters Patent is hereby corrected as shown below Ti
28. ing techniques to selectively measure peak noise power average noise power etc within a desired frequency band The ground fault detector block 166 may be connected via the signal switching unit 150 to the bus 30 when the signal lines of the bus 30 are disconnected from the communication circuitry of the communication stack 104 to determine whether the ground signal line or wire of the bus 30 is improperly connected to another potential The ground fault detector block 166 detects an unusually low resistance e g a short between a bus signal line and system ground such as for example the unusually low resistance that would result from the ground signal line or wire of the bus 30 shorting to a shield line or to any other signal line or wire of the bus 30 The capacitance meter block 168 may be connected via the signal switching unit 150 when the signal lines of the bus 30 are disconnected from the communication circuitry of the linking device 28 to measure a capacitance between a pair of bus lines The capacitance meter block 168 may be implemented using any conventional technique such as techniques that measure a charging rate i e a time based technique or that measure an impedance or any other technique In general the measurement blocks 158 168 may be implemented using any suitable technique for measuring the electrical characteristics of signal lines and signals trans mitted via signal lines For example the measurement b
29. k to peak voltage is between 500 millivolts mV and 900 mV the procedure terminates Otherwise block 226 passes control to block 228 Block 228 reports a wiring fault to the user at the system level and indicates that the signal strength on the bus 30 is insufficient As is known an insufficient signal strength on a segment protocol bus may result from exces sive bus length i e wire lengths too many devices being connected on the segment and or one or more field devices having insufficient signal drive Of course an excessive number of terminators on a segment may also cause the signal strength to fall below 500 mV However the capaci tance test described in connection with block 210 may be used to specifically identify an improperly terminated seg ment bus After block 228 reports any wiring faults the procedure terminates 10 15 20 25 30 35 40 45 50 55 60 65 14 FIG 5 is an exemplary flow diagram depicting another manner in which the linking device 28 shown in FIGS 1 and 2 may be used to detect diagnose and report segment protocol bus wiring faults Block 300 determines if a fatal communication fault has occurred on the bus 30 Fatal communication faults include those faults which preclude the field devices on a segment protocol bus from interoper ating properly Fatal communication faults may be detected by comparing the actual communications and the timing of the communications to schedu
30. led communications stored within the link active schedule For example if a device failed to communicate at a scheduled time according to the link active schedule block 300 may determine that a fatal communication fault has occurred If a fatal communication fault has occurred control passes to block 302 Block 302 reports the fatal communication error to the user at the system level and block 302 then passes control to block 304 Block 304 invokes a communication fault diagnosis proce dure For example block 304 may invoke the procedure depicted in FIGS 4A and 4B thereby enabling the system user to determine if the communication fault is a result of a wiring related problem If block 300 does not detect a fatal communication error control passes to block 306 Block 306 measures the noise level on the bus 30 and compares the measured noise level to a predetermined threshold value If the measured noise level is greater than the predetermined threshold level control passes to block 308 otherwise control passes to block 310 Block 308 reports to the user at the system level that excessive noise is present on the bus 30 and then passes control to block 310 Block 310 measures the signal level e g the peak to peak voltage across the and signal lines of the bus 30 and compares the measured signal level to a predeter mined range of values If the measured signal level falls outside of the predetermined range of values co
31. locks 158 168 may be implemented using digital signal processing techniques or analog signal processing tech niques or alternatively any combination of analog and digital processing techniques without departing from the scope and the spirit of the invention Although the measurement blocks 158 168 are shown by way of example as separate functional blocks one or more of the measurement functions carried out by the blocks 158 168 may be combined if desired For example the voltmeter block 160 and the noise meter block 164 may be implemented using a digital oscilloscope block that converts bus signals to digital values and processes these digital values to measure voltages and or to measure noise using for example digital filtering techniques spectral analysis techniques e g fast Fourier transform based techniques etc Additionally while some of the measurement blocks 158 168 are described as being connected to the bus 30 while communications are inactive thereby preventing these measurement blocks from interfering with communications other methods of preventing interference may be used instead For example measurement blocks that could inter fere with Fieldbus communications may be connected dur ing asynchronous Fieldbus communication intervals which enables the Fieldbus devices on the bus 30 to communicate in an unimpaired manner during scheduled synchronous intervals Alternatively these measurement blocks may be scheduled t
32. lts are not necessarily reported to a user interface at the system level Instead wiring fault information is displayed as graphic and or textual informa tion within the display 406 A user may request particular test sequences may retrieve information stored in the memory 404 or may enter or change test parameters etc using the keypad 408 Preferably but not necessarily the power source 410 includes a battery so that the bus 30 may be tested without requiring a local power source near each segment that is to be tested In operation a field technician may connect the device 400 to a segment suspected of having a wiring fault or any segment which needs to be commissioned and invokes a desired test sequence While the invention has been described with reference to specific examples which are intended to be illustrative only and not to be limiting of the invention it will be apparent to those of ordinary skill in the art that changes additions or deletions may be made to the disclosed embodiments with out departing from the spirit and scope of the invention What is claimed is 1 A system that detects a wiring fault for use within a process control system having a plurality of smart field devices communicatively coupled to a protocol bus the system comprising a linking device that enables a controller to communicate with the plurality of smart field devices the linking device being further operable to automatically detect a com
33. municating over the non proprietary protocol databus 30 and is capable of independently performing one or more process control functions using data acquired by the field device from the process or from a different field device via communication signals on the bus 30 In particular Fieldbus devices are capable of directly implementing portions of an overall control strategy that in the past were performed entirely within a DCS controller To implement any control strategy using function blocks distributed throughout a process control system the execu tion of the function blocks must be precisely scheduled with respect to the execution of other function blocks in a particular control loop Likewise communication between different function blocks must be precisely scheduled on the bus 30 so that the proper data is provided to each function block before that block executes For communication to occur on the bus 30 the link active scheduler LAS which can be the linking device 28 or any 10 15 20 25 30 35 40 45 50 55 60 65 6 other smart field device having link master capability e g one of the field devices 22 26 must actively schedule and control communications on the protocol bus 30 The LAS stores and updates a communication schedule i e a link active schedule containing the times that each function block of each device is scheduled to start periodic 1 synchronous communication activity o
34. munications problem associated with the protocol bus while the protocol bus is substantially active and wherein the linking device has a wiring fault detection unit and a wiring fault detection unit residing therein the wiring fault detection unit being adapted to be coupled to the protocol bus to measure an electrical character istic associated with the protocol bus while the protocol bus is substantially active and the wiring fault diagnostic manager being communica tively coupled to the wiring fault detection unit and using the measured electrical characteristic to deter mine a type of the wiring fault 2 The system of claim 1 wherein the wiring fault detection unit and the wiring fault diagnostic manager reside within a portable unit that is adapted to be locally coupled to the protocol bus 3 The system of claim 2 wherein the portable unit includes 10 15 20 25 30 35 40 45 55 60 65 16 a memory a processor communicatively coupled to the memory a display communicatively coupled to the processor that is adapted to display wiring fault information a keypad communicatively coupled to the processor and a power source that supplies power to the portable unit 4 The system of claim 1 wherein the wiring fault detection unit includes a signal switching unit and a plurality of measurement blocks coupled to the signal switching unit 5 The system of claim 4 wherein the signal switching
35. n diagnostic and reporting tech nique enables linking devices 1 the interfaces between smart field devices and controllers within a process control system to measure the electrical characteristics of a segment protocol bus and the signals transmitted via the protocol bus The technique described herein also enables the linking devices to analyze the measured electrical characteristics to determine whether a wiring fault exists on a protocol bus connected to that linking device Additionally the technique described herein enables the linking devices to report the wiring fault information such as electrical characteristic information signal quality information diagnostic information etc to respective controllers which in turn may automatically report this wiring fault information to a user via a user interface In this manner the wiring fault detection diagnostic and reporting technique described herein enables a user to perform commissioning activities such as for example wiring check outs in an efficient and convenient manner from an operator s terminal thereby reducing or eliminating the need for a field technician to physically inspect every segment throughout the process control system as is required with current systems In accordance with one aspect of the invention a system and method for use within a process control system having a user interface a controller and a protocol bus includes a wiring fault detection uni
36. n monitor 108 monitors all communica tions on the bus 30 and routes the information to one or more of the other functional blocks 110 124 for further process ing The connection manager 110 uses the communication stack 104 to coordinate communications on the protocol bus 30 For instance the connection manager 110 may use the link active schedule a copy of which is stored in the memory 106 to send receive information from the field devices 22 26 during either asynchronous or synchronous commu nication intervals of a macrocycle on the bus 30 Some of the information transmitted synchronously may include func tion block information needed by or sent by function blocks within the controller 18 In this manner the connection manager 110 allows the linking device 28 to emulate the synchronous communication characteristics of a field device The field device manager 114 controls the downloading of configuration information to the Fieldbus devices 22 26 For example virtual communication relationships VCRs addresses tags etc may be sent by a user via the user interfaces 12 and 14 the controller 18 and the linking device 28 to one or more of the field devices 22 26 The link active schedule manager 120 controls the loading of the link active schedule in any other link active schedulers that may be present on the protocol bus 30 The database manager 118 stores Fieldbus information for reporting to the controller 18 The Fieldbus informa
37. n the bus 30 and the length of time for which this communication activity is to occur While there may be one and only one active LAS device on the bus 30 other smart field devices having link master device capability such as the device 22 may serve as backup LASs and become active when for example the current LAS fails Generally speaking communication activities over the bus 30 are divided into repeating macrocycles each of which includes one synchronous communication for each function block having external links active on the bus 30 and one or more asynchronous communications for one or more of the function blocks or devices active on the bus 30 To conserve bandwidth on the bus 30 communications between two function blocks within a single device need not be published on the bus 30 and may be accomplished using communication links that are completely internal to the device Generally speaking the linking device 28 provides a communication gateway or bridge between the smart field devices 22 26 that communicate using a non proprietary protocol and a controller 18 that may not be using the non proprietary protocol More specifically the linking device 28 monitors all the communications on the smart field device protocol bus 30 and processes the monitored communications so that function block information sub scribed to by the controller 18 may be conveyed to the controller 18 as needed identification information e g addresses ta
38. nnection manager 110 an auto sense manager 112 a field device manager 114 a function block data manager 116 a database manager 118 a link active schedule manager 120 a live list manager 122 a communications diagnostic manager 124 and a wiring fault diagnostic manager 126 The linking device 28 also includes a wiring fault detection unit 128 which as described in greater detail below includes functional blocks that can measure the electrical character istics of the bus 30 and the electrical characteristics of the signals being transmitted on the bus 30 As shown in FIG 2 the wiring fault detection unit 128 is communicatively coupled to the wiring fault diagnostic manager 126 and provides electrical characteristic information to the wiring fault diagnostic manager 126 for further processing and reporting to a user at the system level A general outline of the operations of the above noted functional blocks 100 will be provided below and will be followed with a more detailed discussion of how the various functional blocks cooperate to provide communication troubleshooting capabilities that enable a system user to remotely troubleshoot a segment protocol bus from for example a user interface The communication stack 104 is a conventional Fieldbus communication stack which allows the functional blocks 100 to communicate 1 receive and send information along the protocol bus 30 to the field devices 22 26 FIG 1 The communicatio
39. ntrol passes to block 312 otherwise control returns to block 300 Block 312 reports that the measured signal level is outside of the predetermined range to the user at the system level and then returns control to block 300 The wiring fault detection diagnosis and reporting tech nique described above by way of example in connection with FIGS 4A and 4B may be used during commissioning of the system 10 FIG 1 thereby eliminating the require ment for a field technician to physically inspect the wiring of the bus 30 or the wiring of any other segment protocol bus within the system 10 In other words the system 10 may be commissioned in an economical manner by a user stationed at one of the user interfaces 12 and 14 Further the technique may be invoked periodically during operation of the system 10 either automatically and or in response to a request by the system operator to perform system wiring integrity checks Still further the wiring fault detection diagnosis and report ing technique described herein may be carried out automati cally in response to a detected communication fault as shown by way of example in FIG 5 If implemented in software the functional blocks and process control routines discussed herein may be stored in any computer readable memory such as on a magnetic disk a laser disk or other storage medium in a RAM or ROM of a computer controller field device etc Likewise this software may be delivered to a use
40. o perform measurement activities during particu lar synchronous intervals in a manner that does not interfere with other synchronous communications on the bus 30 In any event it should be recognized that it is not necessarily required that the wires or lines of the bus 30 are discon nected from the communication stack 104 while resistance measurements capacitance measurements or any other measurements are being made 10 15 20 25 40 45 50 55 60 65 12 The LED drive circuit 154 may receive signals or com mands from one or more of the measurement blocks 152 and or from the wiring fault diagnostic manager 126 to illuminate one or more of the LEDs 156 Each of the LEDs 156 may uniquely correspond to a particular type of wiring fault and or may correspond to a particular signal line of the bus 30 For example one of the LEDs 156 maybe illumi nated when the ohmmeter block 158 detects a short circuit between the and signal lines of the bus 30 another one of the LEDs 156 may be illuminated when the wiring fault diagnostic manager 126 determines using for example the capacitor meter block 168 that the signal line is improperly terminated still another one of the LEDs 156 may be illuminated when the wiring fault diagnostic manager 126 determines using for example the voltmeter block 160 that the signal strength measured between the and signal lines is below a minimum pred
41. ons to implement an overall control strategy Although the Fieldbus protocol is a relatively new all digital communication protocol developed for use in process con trol systems the Fieldbus protocol is known in the art and US 6 912 671 2 5 is described in detail in numerous articles brochures and specifications published distributed and available from among others the Fieldbus Foundation a not for profit organization headquartered in Austin Tex FIG 1 illustrates an exemplary process control system 10 that uses for example Fieldbus field devices The process control system 10 includes user interfaces 12 and 14 which may be for example workstations connected in a commu nication network to a number of other devices such as a data storage device 16 and a controller 18 via a system level databus 20 The system level databus 20 may be an Ethernet databus or any other databus suitable for the transmission of data The controller 18 may be a DCS controller and may communicate with the user interfaces 12 and 14 using a proprietary communication protocol or in any other suitable manner via the system level databus 20 For example the controller 18 may send alarm status and diagnostic infor mation to the user interfaces 12 and 14 and may additionally receive user commands requests from the user interfaces 12 and 14 via the system level databus 20 The controller 18 may further include control algorithms for use in controlling
42. r or a device via any known or desired delivery method including for example over a communication channel such as a telephone line the Internet etc Although the wiring fault detection diagnosis and report ing technique is described herein as being integrated within US 6 912 671 2 15 one or more linking devices of a distributed process control system the technique may be alternatively embodied within a portable device Such a portable device may be imple mented by incorporating the features and functions of the wiring fault diagnostic manager 126 and the wiring fault detection unit 128 into a portable unit that may be carried by a field technician for example and locally connected to a segment protocol bus to thereby determine whether a wiring fault exists on that segment protocol bus FIG 6 is an exemplary schematic block diagram of a portable wiring fault detection and diagnosis device 400 As shown in FIG 6 the portable wiring fault detection and diagnosis device 400 includes the wiring fault diagnostic manager 126 and the wiring fault detection unit 128 which are described in detail above in connection with FIGS 2 and 3 The device 400 further includes a memory 402 a pro cessor 404 that is communicatively coupled to the memory 404 a display 406 a keypad 408 and a power source 410 The wiring diagnostic manager 126 and the wiring fault detection unit 128 function generally as described above except that wiring fau
43. t having a plurality of measurement blocks and a signal switching unit and a wiring fault diagnostic manager The system and method may connect a signal line of the protocol bus to one of the plurality of measurement blocks Additionally the system and method may measure an electrical characteristic associated with the protocol bus using the one of the plurality of measurement blocks and may send the measured electrical characteristic to the wiring fault diagnostic manager Still further the system and method may determine a type of the wiring fault based on the measured electrical characteristic and may automatically report the type of the wiring fault to the user interface In accordance with another aspect of the invention a system for detecting a wiring fault for use within a process control system having a user interface a controller a pro tocol bus and a processor includes a wiring fault detection unit The wiring fault detection unit may include a plurality of measurement blocks and a signal switching unit The system may further include a computer readable medium and a first routine stored on the computer readable medium 10 15 20 25 30 35 40 45 50 55 60 65 4 and adapted to be executed by the processor that causes the wiring fault detection unit to connect a signal line of the protocol bus to one of the plurality of measurement blocks The system may further include a second routine stored on t
44. tecting diagnosing and reporting a wiring fault within a segment is typically very difficult because current linking devices cannot measure or analyze the electrical character istics such as the resistance capacitance etc of the segment protocol bus or the amplitude frequency noise level etc of the signals being transmitted via the segment protocol bus As a result users at the system level e g at an operator s terminal having a graphical user interface cannot easily identify a wiring fault on a particular segment and are typically only informed by the system that the overall process is not operating properly and or that a communica tion error has occurred For example in the case where two or more protocol bus wires within a segment become shorted to one another or to another common potential the con troller may report to the user via a user interface that the smart field devices on that segment are not responding However the controller typically does not provide the user with any additional information that could be used to determine why the devices failed to respond In fact neither the controller nor the linking device can measure the resis tance of the bus wires to detect the shorted condition thereby preventing the detection and reporting of such a wiring fault With existing process control systems the diagnosis of a segment protocol bus wiring fault is typically accomplished by dispatching a field technician to vis
45. the user at the system level and US 6 912 671 2 13 indicates that a short circuit may exist between particular signals lines of a particular segment If multiple faults such as multiple shorts are found then block 208 reports all of the faults to the user at the system level Block 208 then passes control to block 210 Block 210 measures the capacitance between the and signal lines and compares the measured capacitance value to a predetermined range of capacitance values such as for example 0 8 microfarads uF to 1 2 uF If the capacitance measured by block 210 falls outside of the predetermined range of capacitance values control passes to block 212 otherwise control passes directly to block 214 Block 212 reports a wiring fault to the user at the system level and indicates that a particular segment may not be properly terminated Typically a measured capacitance value of less than 0 5 uF indicates that there is no terminator coupled to the segment whereas a measured capacitance value of 2 indicates that two terminators i e an extra terminator are coupled to the segment Block 212 then passes control to block 214 Block 214 measures the capacitance value between the and signal lines and the shield line and between the and signal lines and system ground If any of the measured capacitance values are less than 300 nanofarads nF block 214 passes control to block 218
46. tion stored in the data base manager 118 may include view list information data subscribed to by the controller 18 function block information statistical information relating to the commu nications on the bus 30 etc The communications diagnostic manager 124 detects communication problems e g timing problems on the protocol bus 30 and reports the problems to the user via one of the user interfaces 12 and 14 the controller 18 and the system level network 20 The auto sense manager 112 the live list manager 122 and the communications diagnostic manager 124 work together to automatically analyze detect and report to the user communication problems associated with communica US 6 912 671 B2 9 tions on the protocol bus 30 thereby enabling the user to engage in communication troubleshooting from the system level e g the user interface 12 and 14 The auto sense manager 112 uses the link active schedule and the live list to identify and to communicate with the field devices 22 26 via the connection manager 110 and the communication stack 108 The live list manager 122 detects when field devices are added to or are no longer communicating on the protocol bus 30 and reports changes to the auto sense manager 112 and the communications diagnostic manager 124 The auto sense manager 112 may collect and produce identification information such as addresses tags serial numbers functional roles e g whether the field device is
47. tle page Item 73 Assignee delete Bisher and insert Fisher Item 56 References Cited U S PATENT DOCUMENTS insert the following 5 066 919 6 230 109 6 046 594 5 848 238 4 792 950 5 168 237 5 539 306 3 701 848 5 521 903 6 037 779 Column 12 11 1991 05 2001 04 2000 12 1998 12 1988 12 1992 07 1996 10 1972 05 1996 03 2000 Klassen et al Miskimins et al Mavretic Anton Shimomura et al Volk et al Fieau et al Riggio Jr Salvatore R Joseph W Dehn English et al Deweerdt et al Line 7 delete maybe and insert may be Signed and Sealed this Thirtieth Day of May 2006 JON W DUDAS Director of the United States Patent and Trademark Office UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO 6 912 671 2 Page of 1 APPLICATION NO 09 850300 DATED June 28 2005 INVENTOR S Daniel D Christensen et al It is certified that error appears in the above identified patent and that said Letters Patent is hereby corrected as shown below In the Claims At Column 15 lines 52 53 a wiring fault detection unit and a wiring fault detection unit should be a wiring fault detection unit and a diagnostic manager At Column 16 lines 35 36 a wiring fault detection unit and a wiring fault detection unit should be a wiring fault detection unit and a diagnostic manager Signed and Sealed this Twen
48. ty third Day of September 2008 WD JON W DUDAS Director of the United States Patent and Trademark Office
49. ually inspect each suspect segment Additionally the field technician typically uses a variety of test equipment such as an ohmmeter a voltmeter an oscilloscope a signal generator a capacitance meter etc to measure and compare the electrical charac teristics of the segment protocol bus to expected ranges or US 6 912 671 2 3 levels and to assess the qualities such as for example the noise level amplitude frequency etc of the communication and power supply signals transmitted via the bus wires The measured electrical characteristics of the segment protocol bus and the measured electrical characteristics of the signals transmitted via the bus wires may be used by the field technician to diagnose the specific nature or type of a wiring fault e g a short circuit an open circuit an improper termination etc thereby enabling the field technician to take appropriate corrective action Thus with existing systems a field technician typically does not have any information other than that a communication problem exists indicating on which segment the wiring fault has occurred or what type of wiring fault is likely to have caused the communication problem As a result the field technician must carry a relatively large amount of equipment to the location of each suspect or possibly every segment bus to guarantee that a proper diagnosis can be made at the segment location SUMMARY OF THE INVENTION A wiring fault detectio
50. unit is adapted to be coupled to the protocol bus and to couple a signal line of the protocol bus to one of the plurality of measurement blocks 6 The system of claim 5 wherein the signal switching unit is further adapted to disconnect the signal line of the protocol bus from a communication circuit 7 The system of claim 4 wherein the signal switching unit is responsive to signals sent by the wiring fault diag nostic manager 8 The system of claim 4 wherein the plurality of mea surement blocks includes one of an ohmmeter block a voltmeter block a signal generator block a noise meter block a ground fault detector block and a capacitance meter block 9 The system of claim 1 wherein the type of the wiring fault is one of a short circuit an open circuit a ground fault an improper termination an insufficient signal strength a poor quality ground connection and an improper supply voltage 10 A method of detecting a wiring fault for use within a process control system having a user interface a protocol bus a linking device that enables a controller to communi cate with the plurality of smart field devices and wherein the linking device has a wiring fault detection unit and a wiring fault detection unit residing therein the wiring fault detec tion unit including a plurality of measurement blocks and a signal switching unit the method comprising automatically detecting a communications problem asso ciated with the proto
51. wn smart field devices such as for example Fieldbus devices may include one or more logical function blocks that perform control functions or portions of a control function These function blocks may for example perform analog input functions analog output functions proportional integral derivative PID control functions or any other desired control functions As discussed in greater detail below the function blocks within a smart field device may be communicatively linked with other function blocks within that smart field device or with function blocks within other smart field devices to carry out any desired control function For example an analog input block may be used to monitor a fluid flow via a flow sensor and a PID block may process a fluid flow value provided by the analog input block 10 15 25 30 35 40 45 50 55 60 65 2 to provide responsive signals via an analog output block to an actuator that modulates the position of a valve plug Thus these function blocks may be communicatively linked to one another to form a PID based control loop that controls the flow of a fluid through a valve Smart field devices typically communicate using an open protocol that is different from the protocol used by the controllers within a process control system As a result an interface device such as an input output I O device or linking device is typically used to provide a communication gateway between eac
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