lnle?ece Feedback Gain
Contents
1. ENABLE DATA ENTRY FIELDS FOR LEAD LAG FILTER COEFFICIENTS DISABLE DATA ENTRY FIELDS FOR LEAD LAG FILTER COEFFICIENTS DISPLAY MESSAGE E G INTERNAL STIMULUS WILL CAUSE THE VALVE TO MOVE OK TO PROCEED DISPLAY MESSAGE E G WARNING THE VALVE WILL TRACK SET POINT OK TO PROCEED RAMP SET POINT TO VALUE IN DATA ENTRY FIELD FOR NOMINAL SET POINT AT RATE OF 10 PER SECOND DISPLAY GRAPH PROPERTY GRAPHICS AND INITIATE STEP SEQUENCE 917 233 B2 US 7 Sheet 5 of 5 Mar 29 2011 U S Patent Oliva SVVdva7 OLLVY SVVdV31 mo ae SO eee se a o ee a YASN 319VSIQ y3sn INaVsIa Oliva 9VV0VIN Y43SN 378VSIO Oliva 9V1 0V37 INISOT9 e rd 3SV8VIVO NI t 3NTVA OUVE i l i ONISOT9 NOS H OMLNOD S9VUVAVN 5 JOVABIINI ONISOTO 1 r Masnanavna SLAdNIYASN 1 ONISO19 HOS 0FUOLS INTVA OYINO9 OL IIS OlLVY 39V3Y3LNI 9V1 0v31 ONISOTO y Ollva 9VVQV3 na ONISOTD OS sou TOMLNOD yan JOVANIINI ONISOTO t 0001 ONISOTI AOA o OYINOO i 30V4YILNI EL ONISOT9 e cm co lO O tek te ee OLIVY 9V10V37 i 3 11 OVI ANTVA OILVY i I 1 ONIN3dO NOS ONIONVHO YOY MIL 9Y1 l 104LNO9 pele TOYINO9 gos ana J0VIYILNI Nado JOVANIANI SiNgNI Nash i SLNdNI Y3SN i Y3SN 319VN3 if MISNITBVNI i OLIVA 9VVAV31 3svaviva NI 3WIL OVI ONI2. Marshall Gerstein amp Borun application No PCT US2005 037810 on Oct 20 LLP 2005 now Pat No 7 593 802 67 ABSTRACT 60 Provisional application No 60 620 537 filed on Oct A lead lag input filter is connected ahead of a positioner 20 2004 provisional application No 60 652 546 feedback loop having one or more valve accessories such as filed on Feb 14 2005 a volume booster or a QEV to overcome slow dynamics experienced by the accessories when receiving low amplitude 51 Int Cl change control or set point signals A user interface is con GO6F 19 00 2006 01 nected to the lead lag input filter and enables an operator or AA A AAA 700 28 700 65 Other control personnel to view and change the operating 58 Field of Classification Search 700 1 29 37 characteristics of the lead lag input filter to thereby provide 4 20mA 50 Travel Set Point Reference T 5 1 T2St1 700 55 71 74 65 44 45 91 24 137 82 701 66 138 105 45 101 120 See application file for complete search history 30 10 Forward Path Gain Lead Lag 20 Input Filter 40 90 94 110 80 Minor Loop Feedback Gain Velocity Feedback Gain the control loop with any of a number of desired response characteristics 22 Claims 5 Drawing Sheets 85 65 55 Volume Boosters QEVs US 7 917 233 B2 Page 2 U S PATENT DOCUMENTS 5 504 608 A 4 1996 Neeves et al 5 504 672 A 4 19
3. 2 adjusts the ratio of the lead time to the lag time in the opening direction The slider 230 of FIG 2 adjusts the ratio of the lead time to the lag time in the closing direction This ratio determines the initial response of the lead lag input filter 20 As indicated above the lead lag filter 20 is generally config ured to provide a large amplitude but short duration spike in the travel set point 50 which allows the valve 60 to move in smaller steps A fast decay rate which translates to a small lag time also mitigates overshoot for larger steps because the valve 60 tends to slew allowing the filter response to decay away completely before the valve 60 gets close to the set point Additionally the filter response graph 150 FIG 2 pro vides the operator or technician with the ability to predict or view the filter response when particular settings are selected for the various user adjustable parameters such as lag time and ratio of lag time to lead time The filter response graph 150 of FIG 2 illustrates the predicted response of the lead lag filter 20 to a unit step change before the parameters changes are applied to the lead lag filter 20 to thereby enable the operator or technician to view a graphical representation of the predicted filter response before the dynamics of the con trol system are actually adjusted Thus there is a virtual ratio of lead to lag that an operator may manipulate in order to generate a predicted response o
4. lead tag filter said user interface including at least one adjustable interface control wherein adjustment of each of said at least one adjustable interface controls alters at least one tuning coefficient associated with the lead lag filter 15 The system of claim 14 wherein the user interface is located at a remote location from the lead lag filter 16 The system of claim 14 wherein the user interface communicates with the lead lag filter through at least one of a group of telephone lines satellite transmission coaxial cable Ethernet fiber optic cable and the Internet 17 The system of claim 14 wherein the user interface further includes a display for a monitoring a predicted response ofa position of the valve plug of the control valve in response to adjustments of each of the at least one adjustable interface controls US 7 917 233 B2 13 18 The system of claim 17 wherein the user interface is provided with at least one control mechanism to control a latency period between the predicted response of the position of the valve plug of the control valve to adjustments of each of the at least one adjustable interface controls and application of the adjustments of each of the at least one adjustable interface controls to the lead lag filter to effect an actual response of the position of the valve plug of the control valve 19 The system of claim 14 wherein the lead lag input filter is in communication with a controller sa
5. tons 310 315 320 and slider 330 shown at the top of the display 120 of the user interface 107 may be manipulated with an appropriate computer input device such as those listed above to control a latency period or delay between the predicted response depicted in the filter response graph 150 and real world application of the settings to effect actual adjustment of the control system dynamics In the event an operator determined that the predicted response to a particu lar adjustment or set of adjustments to the tuning coefficients by manipulation of one or more of the virtual interface con trols 200 was an undesired result the operator can manipulate the graphically depicted buttons 310 315 320 or the slider 330 to increase the latency period and readjust the tuning coefficients until a desired result is depicted in the filter response graph 150 preventing the undesired result from ever occurring in the actual real world control system Other operations such as printing may be performed by a technician s or operator s selection of other graphically depicted buttons 335 340 345 350 355 360 on the display 120 The user interface allows the stimulus for tuning the valve 60 to be applied externally e g through a DCS or inter nally with a computer software program such as ValveLink configured to send a digital step command to the positioner Using an external stimulus the user manipulates the 4 mA 20 mA input sign
6. FIELD OF THE DISCLOSURE This disclosure relates generally to the field of servo con trollers for use in logical processes or control loops and more particularly to the augmentation of electro pneumatic con trol loops and other logical processes for improvement of performance of control valves and pneumatic actuator acces sories BACKGROUND Electro pneumatic control systems are increasingly being employed with process control devices such as valve actua tors and piston actuators in order to provide better or more optimal control of fluid within a process plant Some such electro pneumatic control systems include one or more accessories for controlling valve and piston actuators such as volume boosters and quick exhaust valves QEVs A volume booster which is typically coupled to a pneumatic actuator for a valve increases the rate of air supplied to the pneumatic actuator or increases the rate of air exhausted from the pneu matic actuator This increased air movement amplifies the actuator stroke speed thereby increasing the speed at which the actuator is able to stroke the valve plug toward its open or closed position and thus enables the valve to respond more quickly to process fluctuations Similar to volume boosters QEVs increase the speed at which an actuator is able to stroke a valve toward an open or closed position Currently volume boosters are utilized with pneumatic actuators in a manner that makes the actuators move
7. controller by adding dynamics within the control routine Instead operators gen erally prefer to effect or change dynamics at the valve level The lead lag filter 20 which can be modified to vary the process dynamics at the valve or loop level provides the operator with just such control As illustrated in FIG 1 the lead lag input filter 20 is preferably implemented in combination with a user interface 107 such as a computer program with user friendly real time graphics One or more routines and one or more processors in operable communication with the user interface 107 the lead lag input filter 20 and one or more devices or components within the control loop 40 may be employed to implement the functionality and features disclosed herein The user interface 107 is preferably implemented in com munication with a graphical user interface GUI to facilitate a user s interaction with the various capabilities provided by the user interface 107 and lead lag input filter 20 The GUI may include one or more software routines that are imple mented using any suitable programming languages and tech niques Further the software routines making up the GUI may be stored and processed within a single processing station or unit such as for example a workstation a controller etc 20 25 30 35 40 45 50 55 60 65 4 such as in a control room within a process control plant or a central control room facility for o
8. in real time the filter output and travel feedback data concerning the actual control valve or control loop to which the lead lag input filter 20 has been added Using a computer software program for the control of parameters associated with a control valve such as the AMS ValveLink Software program available from the Fisher Controls division of Emerson Process Management the user interface 107 may be configured to display real time filter output and travel feedback data from the control valve or other device with which the lead lag input filter 20 is employed Additional data may also be displayed such as reference signal to the device For example as illustrated in FIG 2 by the graph 130 the user interface 107 may plot on the GUI the real time travel set point Tvl Set Pt and travel feedback data TvI displayed as percentages against time to enable an operator to easily view the response of the control valve to changes in the reference signal The improved control achieved by using the lead lag filter 20 at low amplitudes can be appreciated by comparing the plot 130 shown in the graphics display 120 shown in FIG 2 reflecting real time data for the travel set point 50 and the travel feedback 79 collected while the lead lag filter 20 is engaged to the plot 135 shown in the graphics 140 displayed in FIG 3 reflecting data collected while the lead lag filter is turned off or disengaged after the 0 02 12 time mark wh
9. in the filter response to mitigate overshoot for larger steps While a distributed control system DCS typically updates at a frequency on the order of 1 Hz or slower a positioner within the control loop 40 can update at a frequency of 100 Hz or more As a result the response time provided by the lead lag filter 20 in series with the positioner can be on the order of 100 ms which is much faster than can be provided by the control dynamics of the DCS alone Additionally the lead lag filter 20 can provide inherent protection against over driving the valve plug of the valve 60 into the valve seat or into the upper travel stop In particular algorithms or control routines can be implemented within or as part of the filter 20 to clip the valve s response near a valve seat or a travel stop and thereby prevent the lead lag filter 20 from bouncing the valve plug of the valve 60 off of the valve seat or an upper travel stop Still further as will be understood with respect to FIGS 2 and 3 the operating characteristics ofthe lead lag filter 20 can be easily adjusted using the user interface 107 which may be stored in a computer and operably coupled to the control loop 40 and one or more display screens Because many processes that use large actuators with complex accessory configura tions generally require complicated and highly customized control algorithms to control the process loop operators are typically reluctant to modify the process
10. very slowly in response to very small set point or control signal changes In particular some volume boosters are designed with a built in dead band to actually prevent the volume booster from becoming active in response to small amplitude change control signals While some volume boosters have small dead bands at the lower amplitude signal range these volume boosters still move very slowly in response to small amplitude signal changes becoming fast only in response to larger amplitude input signals DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING FIG 1 is a block diagram of an electro pneumatic control system augmented with a lead lag input filter FIG 2 is an example screen display generated by a user interface routine of an electro pneumatic control system such as that shown schematically in FIG 1 illustrating travel set point plotted against time and lead lag filter response plotted against time when the lead lag input filter is engaged FIG 3 is an example screen display generated by a user interface routine of an electro pneumatic control system 20 25 30 35 40 45 50 55 60 65 2 such as that shown schematically in FIG 1 illustrating travel set point plotted against time and lead lag filter response plotted against time when the lead lag input filter is disen gaged FIG 4 is an example screen display of a menu enabling a user to select a stimulus source for the lead lag filter of the co
11. 10 220 and 230 Also the virtual interface controls 200 may alternatively be graphically rep resented by for example dials not shown or other graphics Additionally as illustrated in FIG 2 at the areas 205 207 209 to the left of the sliders 210 220 230 the filter coefficients or ratios selected by the sliders 210 220 and 230 may be dis played in numerical form and buttons 214 and 216 shown in 20 25 30 35 40 45 50 55 60 65 6 the area designated 212 of the display 120 may be used to apply the current settings or to reset the current setting ofthe lead lag filter 20 Valid values for the lag time filter coefficient 205 include 0 00 which results in bypassing the filter and values in a range from 0 10to 10 00 seconds Preferably the range oflag time filter coefficients 205 is shown in a logarithmic scale on the plot 130 of the display 120 inasmuch as most lag time filter coefficients are selected in a range from 0 10 to 2 00 seconds Valid values for the lead time to lag time ratio in the opening direction 207 and lead time to lag time ratio in the closing direction 209 range from 0 0 to 2 0 and are shown in a linear scale on the display 120 As illustrated in FIG 2 the slider 210 adjusts the lag time which determines the decay rate of the filter response The larger the lag time the slower the lead lag input filter 20 returns its output to the reference signal 10 The slider 220 of FIG
12. 85 65 4 20mA Volume Reference T 5 1 Boosters QEVs 55 Actuator amp Valve 60 Forward Path Gain Minor Loop Feedback Gain Velocity Feedback Gain 40 70 FIG 2 130 310 315 320 i A AD a a MIO Latency 120 360 355 350 345 340 230 to la 335 220 Lead Lag Ratio 228 h Options a O No Filter 2 0 Filter Response 150 O Lag 200 O Lead Lag O Aysm Lead Lag 205 a Filter Coefficients Lag Time xxx sec 214 Opening Ratio xxx Closing Ratio xxx 207 200 209 200 212 U S Patent Mar 29 2011 Sheet 2 of 5 US 7 917 233 B2 FIG 3 135 O E Latency TMi Set Pt Tvi 0 01 58 0 02 08 0 02 18 0 02 28 0 02 38 0 02 49 Lead Lag Ratio Options 2 9 Filter Response O Lag O Lead Lag 5 Filter Coefficients Lag Time sec 0 Lead Lag Ratio 0 U S Patent Mar 29 2011 Sheet 3 of 5 US 7 917 233 B2 FIG 4 O External Stimulus OValveLink Stimulus Square Wave Nominal Set Point Step Size er Step Hold Time sec FIG 7 Setup Wizard Stabilize Optimize A ee m e a Remote Tuning b Performance Tuner Detailed Setup b Mode gt Change Protection Instrument Actions b Travel Pressure Control Enhanced Stabilize Optimize Lead Lag Input Filter U S Patent Mar 29 2011 Sheet 4 of 5 US 7 917 233 B2 FIG 5 IS SELECTED STIMULUS EXTERNAL STIMULUS
13. 96 Hardiman et al 5 511 863 A 4 1996 Suh 5 521 824 A 5 1996 Eagan et al 5 568 389 A 10 1996 McLaughlin et al 5 576 976 A 11 1996 White 5 587 896 A 12 1996 Hansen et al 5 615 593 A 4 1997 Anderson et al 5 789 987 A 8 1998 Mittel et al 5 838 561 A 11 1998 Owen 5 951 240 A 9 1999 Mirsky et al 6 085 940 A 7 2000 Ferri Jr 6 108 609 A 8 2000 Qian et al 6 198 246 Bl 3 2001 Yutkowitz 6 281 650 Bl 8 2001 Yutkowitz 6 330 483 B1 12 2001 Dailey 6 453 261 B2 9 2002 Boger et al 6 466 893 B1 10 2002 Latwesen et al 6 760 692 Bl 7 2004 Rose 6 862 199 B2 3 2005 Escobar et al 7 349 745 B2 3 2008 Junk 2002 0040284 Al 4 2002 Junk 2002 0055790 Al 5 2002 Havekost 2003 0105535 Al 6 2003 Rammler 2004 0194101 Al 9 2004 Glanzer et al 2006 0012414 Al 1 2006 Goldman 2006 0118169 Al 6 2006 Junk 2007 0162214 Al 7 2007 Junk et al FOREIGN PATENT DOCUMENTS EP 0869204 Al 10 1998 JP 4 000601 A 1 1992 JP 7 503082 T 3 1995 JP 2000 39901 A 8 2001 JP 2002 149207 A 5 2002 WO WO 93 09481 Al 5 1993 OTHER PUBLICATIONS Rudolph Muijtjens Praktisches Positionieren mit pneumatischen Linearantrieben Olhydraulik und Pneumatik vol 42 No 7 Mainz DE 1996 Practical Positioning with Pneumatic Linear Drives 3031 Oil Hydraulics and Pneumatics vol 42 No 7 11 pages International Preliminary Report on Patentability for International Application No PCT US2005 037810 dated Oct 20 2004 1 page Bridgeview User Manual Nati
14. NIdO JO GSYOLS INTIVA i i ONI NYH YO4 INU DY TOYINO9 OLLAS Ollwy OYINO9 Od INTIVA JOVINAINI 9V1 0V371 JOVIMALNI SLNANI YISN MISNINAVAI ONINAdO Y3SN ITIVN3 i I OLIVA 9VVQV31 O INIL 9V7 ONINIdO NOS ONIONVHO NOS SLL V7 toy1no9 PAS OWE omiNoo X04 INVA MUA SLNdNI Y3sn 30VIY3LNI ONINadO JOVANBANI MaISNINAVSIa iy MasnaINgvAI Ollva 9VV10V31 3 11 91 im i tie QNINSdO X04 eo OLII ONIONVHO yog SONO93S MINOS Las ove 0001 i ovvavat _OBINO9 cana JOVANILNI JOVAMIINI ONINadO MIL 9v1 wasn 319VSIO ils Y3SN Jl8VSIO I ta 1 OLIVA SVVGVaT tt ONINSdO Va 9y 9 Old ovT dva1 OIMLAWWASY 9V1 0V31 em 03193138 si NOILdO AdAL 43 014 HOIHM 3NINY3130 US 7 917 233 B2 1 LEAD LAG FILTER ARRANGEMENT FOR ELECTRO PNEUMATIC CONTROL LOOPS REFERENCE TO RELATED APPLICATIONS This disclosure is a Continuation of U S patent application Ser No 10 595 116 filed Feb 21 2006 and issued as U S Pat No 7 593 802 which was the United States national stage under 35 U S C 371 of International Application No PCT US05 37810 having an international filing date of Oct 20 2005 and is entitled to the benefit of the filing date of U S Provisional Application Nos 60 620 537 filed Oct 20 2004 and 60 652 546 filed Feb 14 2005 as to all subject matter commonly disclosed therein
15. US007917233B2 az United States Patent 10 Patent No US 7 917 233 B2 Junk et al 45 Date of Patent Mar 29 2011 54 LEAD LAG FILTER ARRANGEMENT FOR 56 References Cited ELECTRO PNEUMATIC CONTROL LOOPS U S PATENT DOCUMENTS 75 Inventors Kenneth William Junk Marshalltown 4 417 312 A 11 1983 Cronin et al IA US Annette L Latwesen ado A at hoe Puman ca gt gt rovat e Marshalltown IA US 4 805 126 A 2 1989 Rodems E 4 808 126 A 2 1989 Wilson wee 439 607 18 73 Assignee Fisher Controls International LLC St 5 043 863 A 8 1991 Bristol et al Louis MO US 5 195 028 A 3 1993 Hiroi 5 272 647 A 12 1993 Hayes x ci g 5 394 322 A 2 1995 Hansen Notice Subject to any disclaimer the term of this 5 406474 A 4 1995 Hansen patent is extended or adjusted under 35 Continued U S C 154 b by 0 days ontinued This patent is subject to a terminal dis FOREIGN PATENT DOCUMENTS claimer EP 0 869 104 Al 10 1998 Continued 21 Appl No 12 556 036 OTHER PUBLICATIONS 22 Filed Sep 9 2009 Instruction Manual Form 5122 Aug 2003 Type 2625 and 2625NS Volume Boosters 12 pages 65 Prior Publication Data Jack L Johnson P E The Final Word on Non symmetrical Valves Hydraulics and Pneumatics Oct 2003 3 pages US 2009 0326682 A1 Dec 31 2009 Continued Related U S Application Data Primary Examiner Kidest Bahta 63 Continuation of application No 10 595 116 filed as 74 Attorney Agent or Firm
16. a lead lag filter 20 connected to the input thereof In particular a reference control signal 10 such as a 4 20 mA set point signal or control signal generated by a process controller or user interface is applied to the input ofthe lead lag input filter 20 which operates on the reference signal which can be a set point or other control signal to provide a filtered output 50 also called a travel set point signal to a summer 30 associ ated with the electro pneumatic control loop 40 As illustrated in FIG 1 the summer 30 compares the valve travel with the travel set point signal 50 to generate an error signal which is provided to an amplifier or gain unit 90 called a forward path gain unit which applies a gain K The output of the forward path gain unit 90 is provided to a further summer 94 which sums in this case subtracts a velocity feedback gain devel oped by a gain unit 95 and a minor loop feedback gain devel oped by a gain unit 105 from the output of the forward path gain unit 90 The output 110 of the summer 94 is provided to a current to pressure 1 P transducer 80 which develops and provides a pneumatic or pressure signal to a pneumatic relay 85 As illustrated in FIG 1 a measurement of the relay position 100 is provided to the gain unit 105 and is used to develop the minor loop feedback gain The pneumatic output of the relay 85 is provided to the volume booster or QEV 65 This pneumatic signal is used to control the valve
17. actuator of an actuator 55 associated with a valve 60 As illustrated in FIG 1 the measured valve travel of the valve plug or the position of the valve stem with which the valve plug is associated is provided to the summer 30 for comparison to the travel set point signal as well as to the velocity feedback gain unit 95 to develop the velocity feed US 7 917 233 B2 3 back gain At least one sensor not shown is employed to detect the measured valve travel of the valve plug or the position of the valve stem Generally speaking the transfer function and operation of lead lag input filter 20 is configurable via a user interface 107 In particular a technician can remotely adjust the travel set point signal 50 for driving the pneumatic actuator 55 and the control valve 60 or other device controlled by the electro pneumatic control loop 40 by adjusting parameters of the lead lag filter 20 The user interface 107 may be provided to enable remote monitoring of control of or communication with the electro pneumatic control loop 40 from a remote location or from a location in the immediate vicinity of the control loop 40 During operation the lead lag filter 20 will generally pro vide a large amplitude but short duration spike at the begin ning of any step change in the received reference signal 10 which allows the valve 60 to move in smaller steps Addition ally a fast decay rate which translates to a small lag time is provided
18. al and the valve responds accordingly In addi tion the lead lag filter 20 may be implemented either directly in a device such as in a valve positioner or in a distributed control system connected to the device e g in a controller Generally speaking the lead lag filter 20 may be imple mented as a digital control program or routine stored in a computer readable memory and executed on a processor but may be implemented as an analog filter as well The user interface 107 may be provided with an option screen allowing the user to readily select an external stimulus or an internal stimulus When the external stimulus is selected operator adjustment of the adjustable interface con trols alters at least one tuning coefficient associated with the lead lag filter to cause modifications to the reference control signal When the internal stimulus is selected the adjustable interface controls are at least partially disabled such that the disabled interface controls no longer alter tuning coefficients associated with the lead lag filter Instead the tuning coeffi cients of the lead lag filter are modified in response to a controller including programming adapted to cause predeter mined modifications to the reference control signal For instance as shown in FIG 4 a menu is provided from which a user may select either External Stimulus or ValveLink Stimulus Square Wave which will be under stood to be an internal stimulus Select
19. ator or technician to predict or view the filter response when particular settings are selected for various user adjust able parameters of the lead lag input filter 20 While there is inherent delay when signals or data are transmitted via one or a combination of the various commu nication technologies especially over long distances the user interface 107 can be employed in a manner to adjust for such delays provided the extent of the delays are known or can be calculated or determined For example the user interface 107 may provide the user or operator with the option of imple menting a particular set of adjustments to the user adjustable parameters of the lead lag input filter 20 which the user or operator has first plotted using the predicted response capa bilities of the user interface 107 discussed in more detail below If the new set of adjustments is to be implemented for US 7 917 233 B2 5 a valve or loop in a distant location at a time selected by the user or operator the user interface 107 may factor the delay into a calculation of the timing for sending actual signals to the lead lag input filter 20 of a particular valve or loop For instance if the user or operator wants the new set of adjust ments to be implemented in 10 seconds and there is a known or calculated delay of 0 5 second the actual signal to the lead lag input filter 20 may be sent in 9 5 seconds This assumes the user or operator is receiving and displaying
20. ck sig nals 70 100 vary proportionally in response to changes in a process parameter with which they are associated in this case the position of the actuator 55 or the relay 85 so graphically depicting changes in the feedback signals 70 100 provides an accurate indication of actual variation in valve stem position Such real time graphics allows the control valve 60 to be tuned remotely and provides quantifiable results Addition ally remote tuning of the control valve loop via the user interface 107 significantly reduces maintenance costs by avoiding physical maintenance visits to individual control valves A control room with one or more computer terminals for accessing the user interface 107 may be provided in the geo graphic vicinity of the valves or loops to be controlled Alter natively satellite communication telephone lines coaxial cable Ethernet fiber optic cable connections an intranet the Internet or other long distance communication technology may be employed to provide remote access to the user inter face 107 at geographically distant locations A central control facility may be provided in which one or more computer terminals for accessing the user interfaces 107 associated with valves or loops provided with lead lag filters 70 in a plurality of locations separated by long distances from the central control facility As explained in greater detail below the user interface 107 is provided with a plot allowing the oper
21. e lead lag input filter 20 may be implemented with four states or stages of execution includ ing a prefilter stage a filter stage a post filter stage and an initial condition stage In the prefilter stage the filter 20 checks to determine if the reference signal 10 has exceeded a predefined upper limit has dropped below a predefined lower limit or if the filter 20 has been turned off altogether When the reference signal 10 exceeds the predefined upper limit or drops below the predefined lower limit or the filter 20 is turned off or disengaged via the user interface 107 the lead lag input filter 20 bypasses processing of the reference signal and instead provides the reference signal 10 directly to the input 30 of the servo loop As indicated above the predefined upper and lower limits are preferably set so that output of the lead lag input filter 20 will not trip a cutoff or hit a hard stop in the actuator The following pseudo computer programming code dem onstrates one manner in which a controller associated with the lead lag input filter 20 may be programmed so as to set the upper and lower filter limits to desirable threshold levels Filter limit high min ivp cutoff high high cut off deadband 100 high cutoff deadband Filter limit low max ivp cutoff low low cut off deadband 0 low cutoff deadband These limits may be calculated in firmware and are calcu lated every time the input characteristic lower travel c
22. ere the times displayed on the horizontal axis of the plot are in hours minutes and seconds Here it can be seen that without the lead lag filter 20 the response of the valve 60 deteriorates in and slows as a resultofa simple step change in the travel set point reference signal Real time graphics such as those illustrated in FIGS 2 and 3 are particularly advantageous for tuning the lead lag input filter 20 given the sensitivity and complexity associated with the valve dynamics even at low amplitudes Referring again to FIG 2 for ease of operation tuning coefficients associated with the lead lag input filter 20 may be represented in the display 120 of the user interface routine using a filter response plot 150 Additionally the tuning coef ficients and thereby the transfer function associated with the lead lag filter 20 may be changed using one or more virtual interface controls 200 depicted in FIG 2 as graphical repre sentations of slider bars 210 220 and 230 A control operator or technician may manipulate the slider bars 210 220 and 230 using for example a computer input device not shown such as a mouse knob trackball keyboard touch screen monitor voice activation or stylus pad to thereby change the transfer function or dynamics of the lead lag input filter 20 Of course this list of computer input devices is intended to be exemplary only and other input devices may likewise be used to manipulate the sliders 2
23. example on a computer readable disk or other transportable computer storage mechanism or over a communication channel such as a telephone line the Internet etc which are viewed as being the same as or interchange able with providing such software via a transportable storage medium While certain embodiments have been described herein claims to the disclosed invention are not intended to be lim ited to these specific embodiments We claim 1 A method for controlling a process parameter of a con trol loop comprising providing a reference control signal at an input to a control loop providing a lead lag filter in communication with the ref erence control signal prior to amplification of the refer ence control signal providing a user interface in operable communication with the lead lag filter said user interface facilitating remote manipulation of a ratio of lead to lag produced by the lead lag filter and operating the user interface to remotely manipulate the ratio of lead to lag of the lead lag filter to produce an alteration in the process parameter to be controlled 2 The method of claim 1 wherein operating the user interface includes adjusting at least one tuning coefficient associated with the lead lag filter by manipulating at least one virtual interface control provided ona display associated with the user interface 3 The method of claim 2 and displaying data associated with the process parameter to be co
24. f a process parameter to be controlled or tuned and that predicted response is displayed on a display associated with the user interface 107 A similar filter response graph 155 in FIG 3 displays the response when the lead lag input filter 20 is turned off or disengaged Additionally an operator may use the selection buttons in the area 228 of the user interface display 120 of FIG 2 to configure the lead lag filter 20 to be turned off or disengaged to adjust just the lag element of the response to adjust or select both the lag and the lead lag ratio of the filter response or to enable asymmetric lead lag ratios i e where there is a non zero lag time coefficient and the coefficients for the lead time to lag time ratio in the opening direction differs from the lead time to lag time ratio in the closing direction When the lag time coefficient is zero and there are non zero but iden tical lead time to lag time ratio coefficients the lead lag dynamics are symmetrical By storing collected and predicted data displayed in the plots 130 150 in a buffer or readable memory of or opera tively coupled to a computer the plots 130 150 may be paused rewound and replayed at the operator s or techni cian s convenience or for future quality control efficiency and optimization purposes educational purposes regulatory compliance purposes or other purposes US 7 917 233 B2 7 Control mechanisms such as the graphically depicted but
25. id controller includ ing programming adapted to cause the lead lag input filter to curtail movement of a valve stem of the control valve opera tively coupled to the valve plug as the valve plug approaches at least one of a valve seat and a travel stop of the control valve 20 A method for optimally tuning adjustment of a param eter of a control loop comprising providing a lead lag input filter in communication with an input of a control loop 5 10 14 supplying an unamplified reference control signal to an input of the lead lag input filter providing at least one of a user interface and a controller in operable communication with the lead lag input filter and facilitating remote manipulation of the lead to tag ratio and operating the user interface or controller to signal the lead lag input filter to modify the reference control signal prior to application of the control signal to the input of the control loop 21 The method of claim 20 and providing both the user interface and the controller in operable communication with the lead lag input filter and selecting among the user inter face and the controller 22 The method of claim 21 wherein upon selecting the controller at least partially disabling the user interface
26. im 8 wherein the user interface includes a display on which variations in the at least one feedback signal are graphically displayed 11 The system of claim 7 wherein the user interface further includes a display for a monitoring a predicted response of the process parameter in response to adjustments of each of the at least one adjustable interface controls 12 The system of claim 11 wherein the user interface is provided with at least one control mechanism to control a latency period between the predicted response of the process parameter to adjustments of each of the at least one adjustable interface controls and application of the adjustments of each of the at least one adjustable interface controls to the lead lag filter to effect an actual response of the process parameter 13 The system of claim 7 wherein said user interface is provided in a location remote from the lead lag input filter 14 A system for tuning the response of a control valve and facilitating remote manipulation of the lead to lag ratio com prising a control loop including a valve controller a current to pressure transducer a control valve and a valve actuator in operable communication with a valve plug of the control valve a lead lag filter in communication with an input to the control loop a process controller supplying an unamplified reference control signal to an input of the lead lag filter and a user interface in operable communication with the
27. ing the internal stimu lus option enables the user to enter values for the data entry fields Nominal Set Point Step Size and Step Hold Time sec When External Stimulus is selected these data entry fields become disabled When the internal stimulus option is selected the program may be configured to automatically populate the data entry fields with initial default values such as the following DATA ENTRY FIELD DEFAULT VALUES Nominal Set Point Step Size Step Hold Time 50 15 8 seconds FIG 5 is a flow chart diagramming the results performed and displayed on the user interface depending on whether an 20 25 35 40 45 50 55 60 65 8 external stimulus or an internal stimulus is selected Warning messages or other alerts are preferably displayed before ini tiating control valve operation to remind the user that in the case of selection of an external stimulus the valve will track the set point and in the case of selection of an internal stimu lus the internal stimulus will cause the valve to move If the internal stimulus option is selected the set point value pref erably ramps to the value entered for the nominal set point at 10 per second before the step sequence is initiated FIG 6 is a flow chart diagramming the status of various input controls of the user interface in response to particular filter type selections For instance when an asymmetric lead lag fi
28. lter type is selected the user interface is configured to enable the user interface control for manipulating lag time The user interface also is configured to enable the user inter face control for manipulating the opening lead lag ratio and the closing lead lag ratio Conversely if a symmetric or simple lead lag filter is selected an initial value from a data base is provided in a data entry field of the user interface for the opening lead lag ratio the user interface is configured to enable the user interface controls for manipulating the lag time and opening lead lag ratio but the user interface control for setting the closing lead lag ratio is disabled Still further as indicated above the filter 20 may be pro vided with an automatic reset of the lead lag filter dynamics to prevent the filter 20 from inadvertently activating above or below a cutoff In particular the lead lag input filter 20 may in some situations have the undesirable capability to bounce the valve plug of the valve 60 off the seat or offofa travel stop This is a particularly difficult problem because positioners typically have built in travel cutoffs that fully saturate the 1 P transducer 80 when set point approaches 0 or 100 For a Fisher DVC6000 digital valve controller the problem asso ciated with the use of lead lag filters at the high or low range of the valve is avoided by establishing travel cutoffs using default values of 0 5 and 99 5 meaning that if
29. ne or a number of geo graphically remote process control plants or alternatively the software routines of the GUI may be stored and executed in a distributed manner using a plurality of processing units that are communicatively coupled to each other Preferably but not necessarily the GUI may be imple mented using a familiar graphical windows based structure and appearance in which a plurality of interlinked graphical views or pages include one or more pull down menus that enable a user to navigate through the pages in a desired manner to view and or retrieve a particular type of informa tion The features and or capabilities of the user interface 107 described herein may be represented accessed invoked etc through one or more corresponding pages views or displays of the GUI Furthermore the various displays making up the GUI may be interlinked in a logical manner to facilitate a user s quick and intuitive navigation through the displays to retrieve a particular type of information or to access and or invoke a particular capability of the user interface 107 and lead lag input filter 20 An example of such a GUI is generally depicted in a dis play 120 illustrated in FIG 2 As depicted in FIG 2 the display 120 graphically depicts the filter output or travel set point signal 50 and the position feedback utilizing for example data collected from the actuator feedback signal 70 or the relay position feedback signal 100 The feedba
30. ntrol loop and to input values in data entry fields when such fields are enabled FIG 5 is a flow chart diagramming actions performed and information displayed as a result of various inputs in a user interface of an electro pneumatic control system FIG 6 is a flow chart diagramming the status of various input controls ofa user interface in response to particular filter type selections and FIG 7 is an example screen display of a menu enabling a user to select among various instrument control settings including a setting Remote Tuning DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Generally speaking a lead lag input filter is provided ahead of a positioner feedback loop in conjunction with one or more valve accessories such as a volume booster ora QEV to overcome slow dynamics experienced by the accessories when receiving low amplitude change control or set point signals Additionally a user interface enables an operator or other control personnel to view and change the operating characteristics of the lead lag input filter to thereby provide the control loop with any of a number of desired response characteristics Through manipulation of the ratio of lead to lag of the lead lag input filter a process parameter such as displacement or travel of a valve stem may be controlled and in particular fine tuned FIG 1 illustrates a control loop 40 such as an electro pneumatic control loop or other logical process having
31. ntrolled 4 The method of claim 3 wherein the data is displayed on the display associated with the user interface 5 The method of claim 1 and manipulating a virtual ratio of lead to lag to generate a predicted response of the process 20 25 30 35 40 45 50 55 60 65 12 parameter to be controlled and displaying the predicted response on a display associated with the user interface 6 The method of claim 1 wherein the reference control signal is a 4 20 mA control signal 7 A system for tuning a process parameter of a control loop comprising a lead lag input filter in communication with an input to the control loop a controller applying an unamplified reference control sig nal to an input of the lead lag input filter a user interface facilitating remote manipulation of the lead to lag ratio in operable communication with the lead lag filter said user interface including at least one adjustable interface control wherein adjustment of each of said at least one adjustable interface controls alters at least one tuning coefficient associated with the lead lag filter 8 The system of claim 7 wherein the user interface further includes a display for monitoring a process parameter affected by alteration of the at least one tuning coefficient 9 The system of claim 8 wherein the control loop includes at least one feedback signal that varies with changes in the process parameter 10 The system of cla
32. onal Instruments May 1998 49 pages Tewksbury Instruments and Measurements Laboratory Facilities Lab View Software Tool Suite Capabilities Feb 26 1999 7 pages International Search Report for International Application No PCT US05 37810 dated Jul 10 2006 3 pages Written Opinion for International Application No PCT USOS 37810 dated Jul 10 2006 3 pages Translation of Chinese Office Action for corresponding Application No 200580025123 x dated Sep 5 2008 17 pages J B Calvert Electronics 12 The Phase Locked Loop 8 pages Jul 22 2001 ControlGlobal com Three Alternative Approaches to Better Loop Control referenced by Examiner in parent case U S Appl No 10 595 116 3 pages 2004 ControlGlobal com Three Alternative Approaches to Better Loop Control referenced by Examiner in parent case U S Appl No 10 595 116 6 pages 2005 Translation of Substantive Examination Report from Argentina Patent Application No POS 01 04380 May 5 1996 Nov 19 1996 Bridge VIEW M and LabVIEW PID Control Toolkit for G Ref erence Manual National Instrument Jan 31 1998 URL http www ni com pdf manuals 320563b pdf Supplementary European Search Report for Application No 05814806 dated Jun 11 2010 Notice of Rejection for Japanese Patent Application No 2007 538048 dated Nov 16 2010 cited by examiner U S Patent Mar 29 2011 Sheet 1 of 5 US 7 917 233 B2 FIG 1
33. out changing closed loop dynamics Augmenting the feedback controller with a lead lag filter on the set point is one such technique while other techniques involve augmenting the controller with set point velocity feedforward elements The lead lag filter could be used in these situations as well The technique in which a feedback controller is augmented with a lead lag input filter is particularly useful in applica tions in which accessories for increasing actuator stroke speed such as volume boosters and QEVs are used In order to compensate for slow dynamics at low amplitude changes a lead lag filter may be used to over drive the set point for a brief amount of time so as to engage volume boosters even at lower amplitudes such as amplitudes at which conventional volume booster arrangements would not be effectively acti vated due to low dead bands While the lead lag filter 20 may be implemented in a desired manner including in software and hardware or firm ware when implemented in software the software 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 or proces sor such as an application specific integrated circuit ASIC a standard multi purpose CPU or other hard wired device etc Likewise the software may be delivered to a user or a process control system via any known or desired delivery method including for
34. own menu screen captioned Instrument Setup as shown in FIG 7 The menu screen s preferably provide adequate indi cia to inform the user that the control valve loop may be remotely tuned For instance a menu option in FIG 5 reads Remote Tuning When selected the user may select Enhanced Stabilize Optimize Lead Lag Input Filter The lead lag input filter 20 may be implemented in any number of different types of servo loops Thus while the lead lag input filter 20 is illustrated in FIG 1 as being used in one type of electro pneumatic control system comprising a high gain closed loop servo controller used to set stem or shaft position on control valves it could be used in other control systems or control loops as well For example another application in which a lead lag filter associated with a set point is effective is in combination with ball valves where shaft windup between the actuator and the plug introduces dead band in flow control Shaft windup may be overcome by briefly over driving the actuator and allowing the ball to move to the desired location Because this is an open loop tech US 7 917 233 B2 11 nique the response is not perfect but a considerably better response is obtained than without a lead lag filter Still further there are various techniques available to improve performance by driving the servo to set point faster than what would normally be achieved by closed loop com pensation alone with
35. patory control by correct ing for error prior to occurrence of such error When plotted the operator of the user interface 107 would see positive phase with respect to the controlled element So long as the lead lag ratio is greater than 1 0 the initial lead response will dominate If the lead lag ratio is 2 there is an initial lead response of 2 0 as a result of which any cor rection in the position of the control valve stem or shaft is substantially reduced prior to error propagating through the control circuit and will then gradually move the control valve stem position or other process variable being controlled to the travel set point 50 If the lead lag ratio is less than 1 0 then the lag correction will dominate By recognizing the change in performance in various valve performance scenarios resulting from various possible lead lag ratios operators may become easily adept at fine tuning process parameters and correcting for errors and may easily optimize control valve performance It will be recognized that additional components may advantageously be provided that benefit from the use of a lead lag filter 20 For example feedforward components may be provided which are adapted to respond to data including the reference signal 10 velocity of the reference signal 10 and acceleration of the reference signal 10 The display 120 of the user interface 107 is preferably accessed through one or more menu screens such as a pull d
36. t reference value Of course in order to provide inverse dynamics to nonlinearities in the pneumatics filter coefficients may be separately adjusted for the opening direction and the closing direction of a control valve 60 35 40 45 50 65 10 In a preferred embodiment the lead lag input filter s result i e the effect of the lead lag input filter 20 on the set point or the valve input signal is given by the formula 1 s 1 1 28 1 By adjusting the values of t and T the ratio is changed effecting pure lag pure lead or some combination of lead and lag When applied to a control valve the resulting ratio cor relates to the amount of overshoot that the lead lag filter will provide Thus in different valve performance scenarios the Operator may use the user interface 107 to adjust the ratio to achieve desired alterations For instance if it is desired for the lead lag input filter 20 to produce pure lag then 1 s is set to zero producing a result of 1 t s 1 In a control loop when pure lag is generated by the lead lag input filter 20 error is driven towards zero As a result the position of the control valve stem with which the lead lag filter 20 is employed or other process variable being controlled will creep to the travel set point 50 Ifit is desired for the lead lag input filter 20 to produce pure lead then T s is set to zero producing a result of t s 1 1 In a control loop this provides antici
37. the refer ence signal or set point falls below 0 5 or exceeds 99 5 the servo controller is bypassed and the I P transducer 80 is either saturated at full supply or vented to the atmosphere depending on the required saturation state As a result during normal throttling operation the lead lag input filter 20 should not trip a cutoff A pseudo computer programming code provided below demonstrates an example computer program code implemen tation that may be used to assure that a controller associated with or that implements the lead lag input filter 20 prevents cutoffs from being tripped In this case the lead lag input filter 20 is bypassed and the dynamics are reset ifthe output of the filter 20 exceeds a predefined limit near the cutoff value such as at 0 5 or 99 5 although other values can be used as well Begin lead lag filter Prefilter stage if r gt filter limit high r lt filter limit low lag time 0 0 x r bypass filter when in or near cutoffs else Filter stage x a r old x old x old b r r old check filter output to make sure we do not bump into cutoffs if x gt filter limit high x filter limit high else if x lt filter limit low US 7 917 233 B2 9 continued x filter limit low Post filter stage x_old x update old values r_old r In one embodiment th
38. utoff or upper travel cutoff values are changed Moreover because the cutoff processing algorithm is downstream of the charac terizer these limits are passed through an inverse character istic with x and y data vectors reversed so that the charac terized limits are below the cutoff thresholds In the filter stage the lead lag input filter 20 operates as a standard discrete time filter Generally speaking the lead lag input filter 20 may be represented as having two coefficients a and b Coefficient a is the coefficient for the lag contribution and coefficient b is the coefficient for the ratio of the lead time to lag time which may be expressed formu laically as Trad Tag TO prevent the lead lag input filter 20 from activating a cutoff or hitting a hard travel stop the output of the filter 20 is preferably reset to the same upper and lower values used in the prefilter stage During the filter stage or state the filter 20 applies the filter coefficients ratio to the reference signal in any known or desired manner to create the filtered input signal for the servo loop During the post filter stage the previous values used in the filter calculations are updated based on new inputs from the user interface or from the servo loop Finally during the initial conditions stage which occurs for example when an instrument is started up the initial conditions of the lead lag input filter 20 are set to the present inpu
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