GB2181274A - Digital controller - Google Patents

Abstract

A front panel 31 of a digital controller comprises display means capable of displaying at least one of: a process variable, a set value, and a manipulation variable, e.g. on respective LED barographs 32a, 32b, 32c and numerical display 35; and a plurality of changing means e.g. switches 37-40 for changing the set value, the manipulation variable, and operation modes. Upon operation of switches 37-40, control is shifted to a function- or parameter-setting mode. Upon subsequent simultaneous operation of the display means and the switches the functions or parameters are displayed and set. With this arrangement, the function-, and parameter-setting can be performed by operating only the front panel of the controller. <IMAGE>

Description

SPECIFICATION Digital controller The present invention relates to a digital controller used for process instrumentation and the like.

In general, when identical products are massproduced in a singlefactory, obtaining uniform quality is a problem. The quality of the products is closely related to process manipulation conditions. Normally, process variables (to be referred to as PV values hereinafter) such astemperature, pressure, flow rate, liquid level, and the like are controlled to coincide with desired set values (to be referred to as SV values hereinafter), thus indirectly stabilizing product quality.

A digital controller performs control calculations of manipulation variables (to be referred to as My values hereinafter) so thatthe PVvalues coincide with the SVvalues. The MVvalues are supplied to manipulation terminals (e.g., a control valve) to change the PV values.

Forexample,when control offlow rate Fb is performed with respect to flow rate Fa to obtain Fb = otFa + (3in an analog way, as shown in Figure 1, flow rate Fa detected by flow rate detector 1 is multiplied with ratio a in ratio-setting circuit 2, and then "aFa + (3" is calculated, adding bias parameter (3thereto. Subsequently, the calculated result is limited by limiter 3, and the limited value is used as the SV val ue. Flow controller4 performs a control calculation so that flow rate Fb detected by flow rate detector 5 (i.e., the PV value) coincides with the SVvalue.The calculated result (i.e., the MV value) is then output from flowcontroller4to control valve 6,so as to control it.

A digital controller executes ali these ratio calculation, limiter, and control calculation functions. Therefore, it must be determined, in advance, which function the digital controller is to be given, in order to process flow rates Fa and Fb (analog inputs) detected by detectors 1 and 5, and with which parameter the controller is to be operated.

Figure 2 shows functional blocks of digital controller 10, which executes the above-mentioned ratio control.

Flow rates Fa and Fb are input to digital controller 10 as signals proportional to the square offlow rates from differential pressure transmitters (not shown). Root arithmetic operation modules 1 la and 11 bare readiedto extract the square roots of signals Fa and Fb,thereby linearizing them. Next, a signal based on flow rate Fb is subjected to a ratio arithmetic operation by ratio/bias module 12, in which the desired ratio a and bias ss are set.

The maximum and minimum values of the signal based on flow rate Fb are limited by limiter module 13, in which given limit values are preset.

Operation modes of the digital controller include a cascade mode (to be referred to as a C mode hereinafter) in which the SV value is externally given, an automatic mode (to be referred to as an A mode hereinafter) which is executed by a local SVvalue, and a manual mode (to be referred to as an M mode hereinafter) in which an operator directly manipulates the MV value. Therefore, switch module 14 is provided to selectcontact S1 when controller 10 is operated in the C mode and to select contact S2 when operated in theA mode. When contactS1 is selected, SV value = aFa + ss, that is, ratio control, can be performed.When contact S2 is selected, the SV value corresponds to a local SVvaluesetfrom a panel or keyboard of controller 10, andtherefore,flow rate Fb is controlled by a constant value.

In PID moduel 15 including proportional action (P), integrate action (I), and derivative action (D) parameters, the PVvalue is given by linearized flow rate Fb, and is compared with the SV value, to perform a PlDcontrol arithmetic operation with respect to a difference therebetween, thereby determining the MVvalue.

The above-mentioned functional system is designed such that necessary data is written in a system PROM using additional equipment (a PROM writer or a so-called system loader), and the system PROM is mounted on the digital controller.

The system PROM is mounted on the side panel of the controller. When a powerswitch of the controlleris turned on, the content written in the system PROM is transferred to a RAM incorporated in the controller, and the controller is operated based on this. Setting and updating operations of parameters are performed upon operation of a keyboard, which is mounted on the side panel of the controller or is externally provided.

The above conventional digital controller has been described in, for example, U.S.P. No.4,528,623 issued on July 9,1985, or U.S.P. No, 4,542,452 issued on September 17, 1985.

In the conventional digital controller, special purpose equipment (e.g., a system loader) is required for designating functions of the controller, and a special-purpose keyboard is also required for setting or updating parameters, resulting in increased cost. In a normal digital controller, only a front panel of limited area is exposed, and remaining portions are housed in a casing or a rack. Therefore, when functions and parameters areto be set, afterthe digital controller has been temporarily drawn outfrom the casing, mounting ofthe system PROM and operation ofthe keyboard must be performed. This procedure is cumbersome and results in poor operability.

A conventional digital controller, which is supposed to moderate the above drawbacks, has been disclosed in U.S.P. No. 4,514,798 issued on April 30,1985. However, this digital controller requires an open/close operation of a front panel coverwhen parameter/function is set, and isfarfrom satisfactory.

It is an object of the present invention to provide a digital controllerwhich can allow the setting of functions and parameters by simply operating a front panel of limited area,thus improving its operability.

In order to achieve the above object of the present invention, a front panel (Figure4) comprises display means (32,35) capable ofdisplaying at least one of: a process variable, a set value, and a manipulation variable; and a plurality of changing means (37 to 40) for respectively changing the set value, the manipulation variable, and operation modes. Upon operation of one or a combination of the changing means, control is shifted to a parameter/function setting mode (step ST10 in Figure 6).Upon simultaneous operation ofthe display means and one or a combination ofthe changing means, the function of parameters are displayed and set (step ST20). In addition, upon operation of one or a combination of the changing means (37 to 40),the parameter-/fu nction-setting mode is canceled (step ST40).

This invention can be more fully understood from the following detailed description when taken in conjunction withthe accompanying drawings, in which: Figure lisa circuit diagram for explaining conventional ratio control; Figure2 is a functional block diagram of a conventional digital controller; Figure 3 is a perspective view of a digital controller according to an embodiment of the present invention; Figure4is a plan view showing an arrangement of displays and switches on a front panel ofthecontroller shown in Figure3; Figure5is a block diagram of a system configuration ofthe controller shown in Figure 3; Figure 6is a flow chart showing a basic operation of processing routines of a CPU shown in Figure 5, according to the present invention;; Figure 7is a flow chart showing another operation ofthe processing routines of the CPU in Figure 5; Figure 8 is a flow chart for exemplifying a function-setting routine when ratio arithmetic operation control is performed; Figure 9 is a diagram showing functions for executing ratio control; and Figures lOA and lOB are flow charts for exemplifying a parameter-setting routine when the ratio arithmetic operation control is performed.

Figure 3 is a perspective view of digital controller 30 according to an embodiment of the presentinvention.

Digital controller 30 comprises front panel 31. Modeshiftcommand swtich 370 can be arranged on the side surface of controller30, if necessary.

Figure4 is a plan viewoffront panel 31. Front panel 31 comprises: LED bargraphs 32a, 32b, and 32cfor respectively indicating PV, SV, and MV values; indication display gauge 34consisting of LEDs (i.e., HALT display HLT,ALARM displayALM, computer/local display CMP, and remote manual display RM) 33 for displaying conditions of controller 30; numeric display 35forselectively displaying the PV, SV, and MV digital values; numeric item-indication display LED 36 for indicating the type of item displayed on display 35 to an operator (forexample, in the PVvalue display mode it is illuminated in red, in the SVvaluedisplay mode itis green, and in the MVvalue display mode it isturned off);SVvalue-setting switches 37a and 37b for setting and changing a local SVvalue in theA mode; mode-selection switches 38a, 38b, and for switching an operation mode to one ofthe C,A, and M modes; manual switches39a and 39bfor manipulating the MV value in M mode; and FAST/SEL switch 40 which changes the speed of manual operation to high speed when used togetherwith switches 39a and 39b, and changes the item displayed on display 35 from the PV value to the SV valueandthen to the MVvalue.

Abbreviations 41, necessary for setting functions and parameters of digital controller 30 (i.e., in which mode, and with which parameter controller 30 isto be operated) are printed on a scale plated of LED bargraphs 32a to 32c of gauge 34 to respectively correspond with predetermined items.For example, the abbreviations used for designating thetype of controller30 (e.g., "PID" indicating a one-input/one-output PID controller, "R-SV" indicating a PID controller with remote SVvalues, and the like) are printed on the upper portion of the plate; the abbreviations used for designating functions (e.g., "ROT" indicating a root arithmetic operation module, "LMT" indicating a limiter module, and the like) are printed on the intermediate portion ofthe plate; andthe abbreviations usedforsetting parameters (e.g., "DV" indicating an alarm setvaluefordeviation of SV-PV, "TD" indicating a differentiating time of PiD operation "Tl" indicating an integrating time of PVD operation, "KP" indicating a proportional gain constant of PID operation, and the like) are printed on the lower portion of the plate. Note that abbreviations 41 are printed in an unobtrusive color when compared with that of the numerals printed on the scale plate or the scale thereof. Therefore, when abbreviations 41 are seen from a distant location, they cannot be clearly perceived.

Abbreviations on front panel in Figure4are: PID ... General PID control R-SV ... Remote SetValue TRK ... Tracking (Output is controlled to follow Input) A/M ... Auto/manual ROT ... Root Arithmetic Operation D/R ... Direct/Reverse (Output increases for Direct when SV-PV < 0, and it increases for Reverse when SV-PV > 0) RB ... Ratio/Bias LMT ... Limiter DV ... Alarm Set Value for Deviation of SV-PV PL .. LowAlarmingPointofPV PH ... High Alarming Point of PV RL ... Low End of Range of PV (0%, e.g.,0 C) RH ... High End of Range of PV (100%, e.g., 1000"C) TD ... Differentiating Time of PiD Operation TI ... Integrating Time of PID Operation KP ...Proportional Gain Constant of PID Operation Figure 5 is a block diagram of a main part of the system configuration according to this embodiment.

Referring to Figure 5, reference numeral 51 denotes an A/D converter for converting analog inputs PV1 and PV2 into digital signals. The digital signals from A/D converter 51 are supplied to CPU 53 through bus line 52. CPU 53 executes known arithmetic operation control with respect to the inputs from A/D converter 51, based on desired functions and parameters written in memory 54. The control operation result, i.e.,the MV value, is outputfrom MV value output section 55 to a section to be controlled (e.g., control valve 6 in Figure 1).

Reference numeral 56 denotes a panel controller, which has a function for receiving signalsfrom switches 37 to40 on front panel 31,through bus line 52, so asto output them to CPU 53, and a function for performing display control ofdisplays 34to 36 in response to a command from CPU 53. Functions and parameters of controller30,written in memory 54, can be set based on the signal input to CPU 53, through panel controller56.

Processing routines executed by CPU 53, which are associated with the present invention, will be schematically described below with reference to the flow chart of Figure 6.

CPU 53 receives a mode-shift command signal for commanding shifting to the parameter-/function-setting mode, through panel controller 56. The mode-shift command signal is generated upon turning on the mode-shift command switch 370 arranged on the side surface of digital controller 30, or upon simultaneous turning on of switches 37a and 37b arranged on front panel 31. When the mode-shift command signal is generated (YES in step ST1 0 in Figures 6), the processing routine of CPU 53 advances to the parameter-/function-setting mode (step ST20). In this mode, desired parameters and functions are set.

However, as long as the setting operation continues (NO in step ST30), the processing routine of CPU 53 is left in the parameter-/function-setting mode.

When FAST/SELswitch 40 on front panel 31 (Figure 4) isturned on afterthe desired parameters and functions are set, the parameter-/function-setting mode in cancelled (YES in ST30). The processing routine of CPU 53 then returns to the committed routine, and arithmetic operation processing essential to digital controller 30 is performed (step ST40).

When no mode-shift command signal is generated (NO in step ST10), steps ST20 and ST30 are not executed.

Figure 7 shows a processing routine executed by CPU 53, differentfrom that in Figure 6.

CPU 53 always detects the presence/absence of a mode-shift command signal, designating the shifttothe parameter-/function/setting mode, among signals inputtheretothrough panel controller 56 (step ST10). When no mode-shift command signal is detected (NO in step ST10), the normal arithmetic operation control (committed routine) is executed (step ST40).However, if the mode-shift command signal is detected (YES in step ST1 0), the flow first advances to the parameter-setting mode (step ST21 When another mode-shift command signal is detected (YES in step ST1 1) without dismissing the current mode (NO in step ST31 ),the control enters the function-setting mode (step ST22). Eachtimethemode-shiftcommand signal is inputto CPU 53 (YES in steps Sit11 and ST12) without dismissing the current mode (NO in steps ST31 and ST32),the parameter-setting mode (step ST21) and the function-setting mode (step ST22) are alternately executed.

When the signals, inputto CPU 53 through panel controller 56, include a signal for dismissing orcancelling the function-, and parameter-setting modes (YES in steps ST31 and ST32), the control enters the committed routine (step ST40), and executes the arithmetic operation.

In this embodiment, the shift command forthe parameter-/function-setting mode is produced, for example, by simultaneous depression of switches 37a and 37b. The mode-cancellation command forthe parameter4function-setting mode is produced upon depression ofFAST/SELswitch 40. In the parameter-/function-setting mode, LED bargraph 32b for indicating the SVvalue on front panel 31, is switched from bargraph displayto point display, thereby illuminating the corresponding abbreviation 41. Numeric data necessaryforsetting the functions or parameters is displayed on numeric display 35, and can be changed upon operation of switches 37a and 37b.

Acas will be described in detail with reference to Figures 8 to 10, wherein digital controller 30 executes a ratio arithmetic operation among thefunction-, and parameter-setting operations, using front panel 31.

Referring to Figure 8, when a function-setting operation is to be performed from the operation mode (step ST100), both switches 37a and 37b are simultaneously depressed twice (YES in step ST102). The control is switched from the operation mode to the function-setting mode (step ST104), and bargraph 32b is switched to point display, thereby indicating a function to be currently set with the corresponding abbreviation 41 (e.g., "PID") (step ST106). Atthe sametime, a control number(N = 1)indicating,e.g.,aPIDcontroller,isdisplayed on display 35 (step ST108). In addition, numericterm item-indicating display LED 36 is illuminated in red (step ST110).

In this case, since ratio control is to be performed by digital controller 30, controller 30 must designate a PID controllerwith remote SV value "R-SV". For this purpose, if switch 37a is depressed (YES in step Sty 12), a numeral displayed atthe least significant digit position (LSD) (in this case, "1") of display 35 flashes (step ST1 14). When switch 37a is continuously depressed (YES in step ST116),theflashing numeral is incremented one-by-one (step ST1 18). Thereafter (NO in step ST120), if the numeral is incremented and "2" (= N)flashes (YES instep ST120), switch 37a is released (NO in step ST1 16). Then, "2" (= N) is displayed on display 35 (step ST122), and bargraph 32b displays a point-indicator "R-SV" of abbreviations 41 (step ST124).

Next, when switch 37b is depressed (YES in step ST126), controller 30 is set in a setting-enable state, and the color of LED 36 is turned from red to green (step ST128). If FAST/SEL switch 40 is depressed in this state (YES in step ST130), "2" (= N) is set in CPU 53 (step ST132) and the color of LED 36 is turned from green to red (step ST134), thereby indicating that the necessary data is set.

Afterthe mode of controller 30 is set with the processing routine in Figure 8, a detailed function is set as shown in Figure 9.

More specifically, the presence/absence of various processing with respect two controlled amount PV1 or auxiliaryanalog input PV2 is set by selecting "0" (OFF) or "1" (ON). An initial value is set in advance and, inthis case, is "0". When ratio control offlow rate is executed, all the designations shown in Figure 9 must be altered from "0" to "1". These alternations can be made in the same manner as in the mode-setting operation described with reference to Figure 8.For example, when a root arithmetic operation module is set, switch 37b is depressed (step Sty 12) to flash the LSD of display 35 (step ST1 14), and switch 37a is kept depressed (step Sot1 16)to incrementtheflashing LSD (step Sty 18). When the LSD indicates a number representing thatthe rootarithmeticoperation module is "ON" (e.g., "1 YES instep ST1 20), switch 37a is released (NO in step ST1 16). Next, after switch 37b is depressed (step ST1 26) to set the setting-enable state (step ST1 28), switch 40 is depressed (step ST130). In this way, the root arithmetic operation module is set (step ST1 32).

Notethat it can be distinguished, by 1-or 2-point display of bargraph 32b, whetherthe rootarithmetic operation module is set for input PV1 or PV2. More specifically, when the function is selected in association with input PVl,the point display of bargraph 32b is indicated by 1 point, and when associated with input PV2, it is indicated by 2 points.

As described above, afterthe mode of controller 30 and detailed functions are set, FAST/SEL switch 40 is depressed (YES in step S138). The function-setting mode is then cancelled or dismissed, and the control enters the committed operation mode (step ST200).

In the operation mode (step ST200) in Figure 1 0A, when parameter-setting is to be performed, both switches 37a and 37b are simultaneously depressed once (YES in step ST202). The control enters the parameter-setting mode (step ST204), and bargraph 32b is switched to the point display, thus indicating "KP" of abbreviations 41 (step ST206). At the same time, a current ratio gain (e.g., "2.00") is displayed on display 35 (step ST208), and LED 36 is turned on in red (step ST210).

In this case, when the parameter item is to be changed, switch 37a is depressed (YES in step ST2l 2). The poi nt display of ba rg raph 32b is then shifted upward (step ST214), and numeric data corresponding to the indicated parameter is displayed on display 35 accordingly (step ST216).

When the parameter (initial value "2.00") of ratio gain "KP" isto be changed, switch 37b is depressed (YES in step ST218). Next, numeral "2", at the mostsignificantdigit position (MSD) to be changed, flashes (step ST220). When switch 37b is then depressed (YES in step ST222), the flashing numeral is incremented by one.

When the flashing numeral reaches desired numeral (Nx) (YES in step ST226), switch 37a is released (step ST228).

When switch 37b is then depressed (YES in step ST 230), the flashing digit is sequentially shifted toward lower digit positions (step ST232). When a numeral at a desired digit position (Dx) flashes (YES in step ST234), switch 37b is released (step ST236), and switch 37a is depressed (YES in step ST 238) to increment numeral (Nx) at the digit position (Dx) (step ST240). When the desired numeral is obtained (YES in step ST238), switch 37a is released (step ST244), thus setting the desired numeral.

Referring to Figure lOB, when the parameterto be set includes a decimal point, the current decimal point flashes afterthe LSD flashes, thus setting the decimal point selection mode. When switch 37a is depressed in this state (YES in step ST254), the position ofthe decimal point is shifted from the left to the right (step ST256).

Switch 37a is released (step ST260) when the decimal point has reached the desired position (YES in step ST258), thus setting the position ofthe decimal point.

In this way, after the LSD or the decimal point is set, switch 37b is depressed (YES instep ST262). Next,the color of LED 36 is changedfrom red to green (stop ST264),thus allowing a setting operation. When switch 40 is then depressed (YES in step ST266),the changed parameter is set (step ST268), and the color of LED 36 is returned to red (step ST 272).

Thereafter, when switch 40 is depressed again (YES in step ST274), the control returns to the normal operation mode (step ST276).

According to this embodiment as described above, when switches 37a, 37b, and 40 are selectively operated while observing display sections 34to 36 arranged on front panel 31 of digital controller 30, function-, and parameter-setting operations of controller 30 can be performed. Therefore, the functions and parameters need not be set by operating a keyboard on the side surface of the controller or a system PROM as in the conventional digital controller. All the operations can be performed on front panel 31, and digital controller30 need not be withdrawn from a casing orthe like, thus improving its operability. In addition, special equipment (e.g., a system loader (PROM writer)) is not required in the system arrangement, and a keyboard for setting parameters can be omitted. Thus, a relatively low-cost, high-performance digital controller can be realized. In the above embodiment, abbreviations 41 are printed adjacent to LED bargraphs 32a to 32c, in addition to the components of the conventional digital controller. However, this need not be provided, in view of cost.

The present invention is not limited to the above embodiment. Forexample, in the above embodiment, the parameter-/function-setting mode is set upon operation of switches 37a and 37b,functions and parameters are also set by operating switches 37a and 37b based on the display content of display sections 34 and 36, and the committed operation mode is reset by FAST/SEL switch 40. However, the present invention is not limited to this. The digital controller can be designed so that mode-shifting,-setting, and -cancelling can be performed by operating any of the switch groups arranged on front panel 31. Alternatively, the parameter-/function-setting mode can be set by operating a special-purpose switch (370 in Figure 3). With this arrangement, the committed operation mode of digital controller 30 will not be interfered with by unnecessary depression of switches 37a and 37b, and this arrangement causes no problem in view of cost, since only one switch is added. In the above embodiment, abbreviations 41 are arranged as indications of function-, and parameter-setting modes.

Abbreviations 41 are not limited to those in the above embodiment, and can be other symbols if they playthe role of identification. Various changes and modifications may be made within the spirit and scope ofthe invention.

Claims (10)

1. Adigital controllerwhich can obtain a munipulation variable corresponding to a difference between a process variable and its set value based on a predetermined function and parameter, a front panel of said digital controller comprising: first display means for displaying at least one of: the process variable, the setvalue, and the manipulation variable; second display means fordisplaying a value of at ieast one of: the process variable, the set value, and the manipulation variable; first designating means for designating the set value; second designating means for designating the manipulation variable; third designating means for designating an operation mode of said digital controller; mode-shifting meansforshifting the operation mode of said digital controllerto function-, and parameter-setting modes; function-/parameter-setting display meansforsetting and displaying the function and the parameterin accordance with displays of said first and second display means and the designation of at least one ofsaidfirst to third designating means; and mode-resuming meansforcancelling thefunction-, and parameter-setting modes in accordance with the designation of at least one of said first to third designating means, to resume the operation mode of said digital controller.

2. A controller according to claim 1, wherein the mode shifting by said mode-shifting means is performed in accordance with the designation of at least one of said first to third designating means.

3. A controller according to claim 1,wherein said digital controller comprises a mode-shift command switch arranged on a predetermined portion otherthan said front panel, the mode shifting by said mode shifting means being performed upon turning on of said mode-shift command switch.

4. Acontrolleraccording to claim 1, wherein said first display means comprises a symbol fordesignating the type ofthe predetermined function and parameter.

5. A controller according to claim 1, wherein said function-/parameter-setting display means includes function-setting means which sets the predetermined function in accordance with said mode-shifting means.

6. A controller according to claim 1,wherein said function-/parameter-setting display means includes parameter-setting means which sets the predetermined parameter in accordance with said mode-shifting means.

7. A controller according to claim 1,wherein said first designating means includes a first setting switch and a second setting switch arranged on said front panel, the mode shifting to the function-, and parameter-setting modes by said mode-shifting means is performed upon simultaneous turning on of said first and second setting switches, and the predetermined function setting and the predetermined parameter setting are performed by turning on one of said first and second setting switches.

8. A controller according to claim 1,wherein said front panel comprises a cancellation switch for cancelling the mode shifting to said function-, and parameter-setting modes, to reset the mode of said digital controllerto that before the mode shifting.

9. A controller according to claim 1,wherein an indicator for indicating which one of the process variable, the set value, and the manipulation variable corresponds to a displayed value on said second display means, is arranged adjacent to said second display means.

10. A digital controller, substantially as herein before described with reference to the accompanying drawings of Figures 3 to 10.