- Email: [email protected]
Simplification of Man-Machine Communication in a Flexible Digital Computer Process Control System
SIMPLIFICAnON OF MAN-MACHINE COMMUNICAnON IN A FLEXIBLE DIGITAL COMPUTER PROCESS CONTROL SYSTEM J. B. Williams, Automation Systems Division, Ferranti Ltd., Manchester, U. K. SUMMARY Examples are given of a simple man·machine interface in a digital computer process control system known as CONSUL B. The system provides a wide range of control facilities using pre-programmed building blocks that are assembled and modified on line from a central console. Cost and maintenance problems are reduced by the avoidance of a backing store and the restriction of the man-machine interface to a level below that of a full 'conversational mode' whilst remaining easy and safe to use.
1. INTRODUCTION Since the last PRP Congress in 1966, third-generation Ferranti ARGUS process control computers have been used on-line in a wide range of industries, with proven reliability (1) in a range of environments. These computers and associated input-output equipment are modular in concept, giving full hardware flexibility. Compatible process control software known as CONSUL B, which forms the subject of this paper, combines with an ARGUS computer to form an extremely powerful tool for digital process control . The position in the process computer field occupied by CONSUL B is intermediate between the min i-com· puter application (2) illustrated by the ARGUS 600 and CONSUL (without the 'B', (3) which uses an AR GUS 500 plus disc backing store for the control, pro· duction scheduling, optimising, process modelling and history recording of large complexes such as oil refineries . . CONSUL B is designed to avoid the costly task of writing 'special to project' programs and also to avoid a backing store which undoubtedly is the hardware item needing most maintenance. It greatly simplifies manmachine communication whilst providing a wide range of pre-programmed building blocks for various levels of control. These building blocks, properly called 'algorithms' , are assembled and changed as required on -line by simple button operation on a central keyboard.
CONSUL B requires a minimum of 12K (12,288) 24bit words of core store. Typ ically this would provide space for approximately 50 simple control loops, or for fewer more complex loops, in addition to standard logging facilities. A useful comparison here is with the mini-computer ARGUS 600, whose maximum core store is 8K of 8-
IU~
PAPER 3.5
bit words, giving space for approximately 60 simple control loops but with no logs and without the more advanced control features, the flexibility and the optimised man-machine interface of CONSUL B. The core store of a CONSUL B system is expandable in 4K blocks, from the m i nimum 12K to a maximum of 60K. Each 4K addition provides space for a further 60 (approximately) simple control loops, or for fewer more complex loops. There is, therefore, virtually no cor est 0 re restriction on the number of control loops or their complexity. The pract ical restriction, apart from cost, is t i m e; CONSUL B can handle approximately 300 loops per second , or 600 loops per two seconds, etc. It has been stressed that CONSUL B has been designed as a core resident system, distinct from the CONSUL system which uses a backing store. Nevertheless, it is interesting to note that two recent sales, including one to the Plastics Industry, of CONSUL B systems have been to multi-process installations where ARGUS 500 computers with core resident CONSUL B are to be su pervised by another ARGUS 500 with a disc backing store. 2.2. Levels of Control The following 'levels' of control are provided by CONSUL B. It is emphasised that, apart from item (xii). all these levels are implemented by the building up of preprogrammed algorithms from the CONSUL B key-board; absolutely no programming knowledge is required from the user. (i)
D. D. C., that is, direct contro l of a plant actuator, optionally via a Computer/Manual Station.
(ii)
Set Point Control , that is, direct digital control of the setpoint of an analogue controller.
(iii)
Cascade control whereby the set point of one control loop is driven by the output of another control loop. Ratio control, a common requirement in the Pulp and Paper Industry, is a simple example of cascade control.
(iv)
Feedforward control, whereby a plant actuator is moved to compensate for some process effect which has been predicted by the computer on the basis of plant measurements supplied to it.
(v)
Non-linear control, whereby the gain of a control loop is a function of its error Signal.
(vi)
The abiiity to control from a 'calcu lated measurement' , i. e. the computer uses several process measurements to calculate a process parameter wh ich cannot be measured directly.
(vii)
Alternative control actions, determined by logic-
2. THE PLACE OF CONSUL B IN DIGITAL PROCESS CONTROL 2. 1. System Size
AUTCJ'V1AI
154
al
board, which form the main interface between the user and the computer. The purpose of the three windows on the panel is to display information requested by the pushing of the keyboard buttons. Generally, this information is presented in a way very easily understood by the user. The way in which the buttons are used is perhaps best illustrated by building up, bringing on line, tuning and subsequently modifying a simple D . D.C. control loop. As example, let us take the case of a paper machine', main stock flow loop, under cascade control from a weight changing loop . A CONSUL B control loop may consist of many algorithms as in the case of the weight changing loop, but our flow loop will contain only 3 algorithms (see Fig. 2) :
decisions made by the computer.
(viii) 'Deadtime' compensation, whereby a control loop may be near optimally tuned for the control of a process with a significant delay. (ix)
Non-interactive control , whereby the computer reduces undesirable interaction between certain measured process variables.
(x)
Simple optimisation of production by, for example, automatically increasing the production rate until anyone of a number of production constraints is met.
(xi)
Grade changing , by , for example, ramping set point changes in a phased manner dependent upon production rate.
(xii)
Limited communication between control loops and a 'background' area of core store . This would enable, for example, a FORTRAN background program to use the computer free time for the reading of a number of setpoints and for a production analysis based upon them.
SPMV which calculates the control deviation between the SP (setpoint) and MV (measured value), INTC which applies integral control action to the deviation , VALV which stores the output from I NTC in an output data list.
2.3. Main Limitations
Before building up this simple flow loop, the engineer must decide on the following items.
There are three main facilities lacking in CONSUL B. Each of them has been omitted in order to restrict the minimum core store requirement and also to avoid duplicating some advanced features, used in the petro· chemical industry, of a ' CONSUL - Backing Store' System . (i)
(ii)
(iii)
(i)
The IDENTITY of the loop, that is, the code by means of which the computer will distinguish it from all other loops.
(ii)
The ENGINEERING UNITS (for example Gallons/Minute, Litres/Hour) in which it is desired to display appropriate loop parameters.
(iii)
The RANGE of the loop in Engineer ing Units, which should correspond to the range of the flowmeter.
(iv)
The Setpoint Address, to which the weight changing loop will be cascaded .
S p e cia I - t 0 - Pro j e c t 'B a c kg r 0 u n d' Programs The standard CONSUL B system has a restricted, all core resident, background facility. FORTRAN programs may be compiled on line only if 8K of core store is reserved for this purpose. Communication between a FORTRAN prog r am and a control loop is limited.
(v)
The Measured Value address, that is, the input data list location into which the flowmeter signal, suitably converted, is placed by CONSUL B's input scanning program .
(vi)
The Output Address, that is, the output data list location from which CONSUL B's valve output program sends a control signal to the hardware modules which drive the valve.
Conversationa l Mode Whilst assembling or modifying a CONSUL B control loop, the user is not told by the computer what particular piece of information it needs next. I n other words, there is no conversational mode because the computer does not 'talk ' to the user. Rather, CONSUL B prevents the user from inserting data except in a predefined sequence and format which he obtains from a handbook . Experience has shown that users of CONSUL B very rapidly become expert in the operation of the keyboard buttons.
(vii)
Optionally , the Valve Position Feedback address, t hat is, the input data list location into which a feedback of va lve position, suitably converted , is placed by CONSUL B's input scanning program .
I n t e r - cas cad e Sw i t chi n g CONSUL B omits some advanced switching facilities required by complex control schemes in which , for example, interconnections between multiple cascaded systems may be switched automatically w ithout 'bumping' the plant actuators.
(vi ii) Optionally, the identifying number of the Computer/Manual Station to be associated with the loop . 3.2 . Building a Control Loop The eng i neer builds the flow control loop by pressing the buttons in a predefined way , using the 'ENTER' button to complete each data insertion. Should he push buttons in the wrong order the FORMAT ERROR lamp will light and he will be unable to continue until
3. THE CONSUL B MAN-MACHINE INTERFACE 3. 1. Preface Fig . 1 shows the CONSUL B display panel and key·
155
'r.::;;"
'---'
~
"."
--l
51
F
'/0
CUIIIIIIII,,,,
CO.TIIIICM.
0
II0lAT,
o
'----'
~
~
,000
'''\,IU
LOO' tOIN'
.......
.... .......,G.,,.... .....
" ,
'r---J ..co ..
_on
"IIIIA",T,IIII ,
'
VALout
6
9
3 .8
+ 7
1
5 .0
5P +
0
,. ,.. ~ L..:, G/M1 N
.'ICIAl
,,,,,cno ••
CD
156
~~:
.... 110
CM
"" I
0
LOG
IC'
•
ac;,
+
... ...
IT .. LDL
••
lIP DlC .. T UNIT ADD DU., L" 2
+
Iir~G 0 ..
ALG
". "" 0" • • •
I
AT
11-
-
LOOt' ALL LG
•
-
2
7
A
L
I
•
>.
tl
"
•
12
•
M
2
7
DIY
'/11
IITIO
13
C
.
3
I
• •
I.
0
11
•
•
IAT
AILT AILT MGM L_
• • •
IWCM IawcM CLD
"
T
•
0
OAT
0/"
I
I'
IU" UN... 11., All' AL" 7
I
II
jo..L 011
.."
+
'uu
ALG DATA "ALUI
TIID IICD
-
I.
, •
DIY LT
ACK ILL ENTIIY TEIT D.... LAY
3
.. I
O"IN CA le
ACCE ..T ALAII"
E.. UII
LT
CLII CAIC
Fig. 1. Consul B Panel and Keyboa rd
0" AUTO
0
MANUAL
TEIT LA .....
I
CANCEL
TIMI
Panel Inserted Set pOint I Dry BasIs wtl
Consistency Compensation
Converts to incremental demand
SI BI25 BASIS WT CONTROL LOOP (Primary Loop)
Cascade SWitch
Provides positive only output
Machine Speed Measurement
Consistency Main Meter Stock Flow Valve
Measured Dry Basis Weight
Flow Meter
Fig. 2. Example of consul B algorithms for paper machine control
he pushes the correct button . As soon as he has entereel 'FINI' his loop is held in the computer store. Whilst the engineer has been building up the loop, a teleprinter will have been recording all his button actions, -esulting in the kind of printout shown in the following table. Explanatory comment has been added . ASSEMBLY OF SIMPLE FLOW LOOP TELEPRINTER PRINTOUT
EXPLANATORY COMMENT
NEWLOOP
03
New loop requiring 3 algorithms.
FREQ
01
Perform this loop's calcu !ations every 1 second_
9999
{ Th. loop ;d.ntity ;, 10 '"
SlF001 SF* SF+ DEC
PT
ENG UNITS
STN NO
0000 1 02
010
SlF001 and it is to have a range from 0 to 999 .9 Engineering Units. Engineering Units are to be Gallons/Minute_ [Anyone of 12 Engineering Units may be specified by a predefined code]. ComputerjManual Station No. 10.
LDL NO
01
Specification of the 1st. illgorithm follows.
ALG NO
07
SPMV algorithm.
ALGDATA
04
Setpoint address follows.
VALUE REF ALGDATA VALUE LDL NO
048 05 *007 02
48th position in Reference List. Measured Value address follows_ 7th position in Input Data List. Specification of the 2nd algorithm follows.
ALG NO
11
INTC algorithm.
LDL NO
03
Specification of the 3rd algorithm follows.
ALG NO
10
VALValgorithm.
08
Output address follows.
ALGDATA VALUE ALGDATA VALUE
157
*005 06 *001
5th position in Output Data List. Valve Position Feedback address follows. 1st position in Input Data List .
FINISH
3.7. Comment
The loop is now held in the computer, but has not yet been brought on line.
."Simplification of man·machine communication in a flexible dig ital computer process control system".
(i)
Loop SlF001 is an example of the simplest possible type of control loop. More complex loops are built, tuned, modified and logged in exactly the same manner.
(ii)
During the building or modification of a loop, other loops remain fully on line.
(iii)
There are 21 algorithms in CONSUL B. These comprise arithmetic, dynamic, cascade switching, ~ogical switching and special algorithms which have been shown necessary by common experience in a range of industries. Additional algorithms specified by a customer often are added to meet some special-to-project need; examples of these are an AVERAGE algorithm wh ich calculates the arithmetic average of a measurement from a profiling instrument and a RAMP algorithm which ramps set points at a grade change.
(iv)
The safety features of CONSUL B include Illegal Entry protection from the keyboard and selective button lockout provided by the three panel keys engraved 'Control Engineer' , 'Parameters' and 'Special Functions'.
3.3. Bringing the Loop On Line The buttons 'DEV LT', 'ABLTHIGH ' , 'ABLTLOW' are used to enter Alarm Limits in gallons/minute. 'IAT' is used to enter an estimated Integral Action Time. 'AUTO' puts the loop on line 'bumplessly '. 'SP' dis· plays the setpoint, 'MV' the measured value, in the Current Value window. 3.4. Trend Recorder Facility I n order to tune the loop, ~he engineer may assign setpoint and measured value to two pens of a trend recorder. For example, ' SlFOOl SP TRD RCD 0136' as- ' signs the setpoint to Pen 1 and scales Pen 1 so that its fullscale movement represents 30 % to 60 % of the control loop range. Using the trend recorder and the 'lAd' button, the engineer can tune the loop for a suitable response to a setpoint change.
3.8 . Data Logging
3.5. Loop Modification The engineer may find that he cannot tune SlF001 loop just using the integral control provided by the algorithm INTC. In this case he would wish to change the INTC algorithm for a PIDC algorithm, which would enable him to try any combination of proportional, integral or derivative control. CONSUL B prevents his changing the loop structure whilst the loop is on line. He takes the loop off line simply by entering 'MANUAL', then changes the INTC for a PIDC algorithm by 'LDL No 02 ALG No 12' (see the table) Finally, ' AUTO' places the loop back on line, and tuning is carried out via the PB (Proportional Band), IAT (I ntegral Action Time) and OAT (Derivative Action Time) buttons. 3.6. Loop Logging
(wh ich assigns the loop to the) (5th position of Log Table 02)
/ENTER \
'5F*\
8500'ENTER \
'sF'+ \
1000/ENTER \ 2'ENTER \
/ENG UNITS'
01/ENTER \
fl/P ADD'
*003/ENTER ,
~
The symbO'r--\ denotes a Single button operation.
3.9 . Visual Display Units In addition to the central panel with keyboard and teleprinters, Visual Display Units (V .D.U's) also are interfaced by CONSUL B. Hence V .D .U's may be used, for example, to display control loop parameters at remote parts of a plant and, if the V.D .U's are equipped with keyboards, to change setpoints and other parameters. 3.10. Multi-Process Installations The modular nature of the computer and its input-output equipment, together with the modularity and flexibility of CONSUL B, combine to form an ideal system for the control of more than one Paper or Plastics Machine using one computer.
then : LOG 02 EVERY 0100
W087
/NEWRD\
I DEC pl\
The engineer, having replaced one algorithm by another in some other way modified SlF001100p so that the above table is no longer an accurate record .of its structure or data, may well enter 'SlF001 LOOP LG' , which will produce the modified version of the table on logging teleprinter. He also may wish to monitor the measured value of the loop for a while by printing it at specified time intervals. To do this, he first assigns SlF001 to a Log Table by entering: SlF001 LOG 025
There is a common requirement in the Paper and Plastics industries for the alarm monitoring of certain process measured variables and their inclusion in Logs without, or prior to, using these measured variables for control. CONSUL B meets this requirement economically but with its usual flexible features. The following keyboard button operations assemble a 'Read Only Loop' of 'Identity S6T087 and Range 100 C to 95 0 C, receiving its measured temperature input from the third position in the Input Data List.
(which prints the contents of ) (Log Table 02 every 10 min . )
158
4 . CONCLUSIONS
5. REFERENCES
1. CONSUL B provides a unique medium sized process control capabil ity for applications without a backing store.
1. MacLAURIN M . I., "Optimum Complexity for Com-
2. In no way does CONSUL B remove the need for the basic necessities of any successful computer application, namely
2. LONG J., "The Minis. The Market Scene in Europe' Supplement to Computer Weekly, November 12, 1970.
(i)
well planned control objectives,
(ii)
adequate, accurate and reliable measurements and actuators.
3. BAI LEY S. J., "Pushbutton Programm ing for Onl ine Control" . Control Engineering, August 1968, p . 76-79.
Rather, the fulfilment of these two conditions enables a high return from investment in the flexible, easy to use and readily expandable features of CONSUL B.
159
puter Control ". 13 th EUCEPA Conference, April 1970.
1. INTRODUCTION Since the last PRP Congress in 1966, third-generation Ferranti ARGUS process control computers have been used on-line in a wide range of industries, with proven reliability (1) in a range of environments. These computers and associated input-output equipment are modular in concept, giving full hardware flexibility. Compatible process control software known as CONSUL B, which forms the subject of this paper, combines with an ARGUS computer to form an extremely powerful tool for digital process control . The position in the process computer field occupied by CONSUL B is intermediate between the min i-com· puter application (2) illustrated by the ARGUS 600 and CONSUL (without the 'B', (3) which uses an AR GUS 500 plus disc backing store for the control, pro· duction scheduling, optimising, process modelling and history recording of large complexes such as oil refineries . . CONSUL B is designed to avoid the costly task of writing 'special to project' programs and also to avoid a backing store which undoubtedly is the hardware item needing most maintenance. It greatly simplifies manmachine communication whilst providing a wide range of pre-programmed building blocks for various levels of control. These building blocks, properly called 'algorithms' , are assembled and changed as required on -line by simple button operation on a central keyboard.
CONSUL B requires a minimum of 12K (12,288) 24bit words of core store. Typ ically this would provide space for approximately 50 simple control loops, or for fewer more complex loops, in addition to standard logging facilities. A useful comparison here is with the mini-computer ARGUS 600, whose maximum core store is 8K of 8-
IU~
PAPER 3.5
bit words, giving space for approximately 60 simple control loops but with no logs and without the more advanced control features, the flexibility and the optimised man-machine interface of CONSUL B. The core store of a CONSUL B system is expandable in 4K blocks, from the m i nimum 12K to a maximum of 60K. Each 4K addition provides space for a further 60 (approximately) simple control loops, or for fewer more complex loops. There is, therefore, virtually no cor est 0 re restriction on the number of control loops or their complexity. The pract ical restriction, apart from cost, is t i m e; CONSUL B can handle approximately 300 loops per second , or 600 loops per two seconds, etc. It has been stressed that CONSUL B has been designed as a core resident system, distinct from the CONSUL system which uses a backing store. Nevertheless, it is interesting to note that two recent sales, including one to the Plastics Industry, of CONSUL B systems have been to multi-process installations where ARGUS 500 computers with core resident CONSUL B are to be su pervised by another ARGUS 500 with a disc backing store. 2.2. Levels of Control The following 'levels' of control are provided by CONSUL B. It is emphasised that, apart from item (xii). all these levels are implemented by the building up of preprogrammed algorithms from the CONSUL B key-board; absolutely no programming knowledge is required from the user. (i)
D. D. C., that is, direct contro l of a plant actuator, optionally via a Computer/Manual Station.
(ii)
Set Point Control , that is, direct digital control of the setpoint of an analogue controller.
(iii)
Cascade control whereby the set point of one control loop is driven by the output of another control loop. Ratio control, a common requirement in the Pulp and Paper Industry, is a simple example of cascade control.
(iv)
Feedforward control, whereby a plant actuator is moved to compensate for some process effect which has been predicted by the computer on the basis of plant measurements supplied to it.
(v)
Non-linear control, whereby the gain of a control loop is a function of its error Signal.
(vi)
The abiiity to control from a 'calcu lated measurement' , i. e. the computer uses several process measurements to calculate a process parameter wh ich cannot be measured directly.
(vii)
Alternative control actions, determined by logic-
2. THE PLACE OF CONSUL B IN DIGITAL PROCESS CONTROL 2. 1. System Size
AUTCJ'V1AI
154
al
board, which form the main interface between the user and the computer. The purpose of the three windows on the panel is to display information requested by the pushing of the keyboard buttons. Generally, this information is presented in a way very easily understood by the user. The way in which the buttons are used is perhaps best illustrated by building up, bringing on line, tuning and subsequently modifying a simple D . D.C. control loop. As example, let us take the case of a paper machine', main stock flow loop, under cascade control from a weight changing loop . A CONSUL B control loop may consist of many algorithms as in the case of the weight changing loop, but our flow loop will contain only 3 algorithms (see Fig. 2) :
decisions made by the computer.
(viii) 'Deadtime' compensation, whereby a control loop may be near optimally tuned for the control of a process with a significant delay. (ix)
Non-interactive control , whereby the computer reduces undesirable interaction between certain measured process variables.
(x)
Simple optimisation of production by, for example, automatically increasing the production rate until anyone of a number of production constraints is met.
(xi)
Grade changing , by , for example, ramping set point changes in a phased manner dependent upon production rate.
(xii)
Limited communication between control loops and a 'background' area of core store . This would enable, for example, a FORTRAN background program to use the computer free time for the reading of a number of setpoints and for a production analysis based upon them.
SPMV which calculates the control deviation between the SP (setpoint) and MV (measured value), INTC which applies integral control action to the deviation , VALV which stores the output from I NTC in an output data list.
2.3. Main Limitations
Before building up this simple flow loop, the engineer must decide on the following items.
There are three main facilities lacking in CONSUL B. Each of them has been omitted in order to restrict the minimum core store requirement and also to avoid duplicating some advanced features, used in the petro· chemical industry, of a ' CONSUL - Backing Store' System . (i)
(ii)
(iii)
(i)
The IDENTITY of the loop, that is, the code by means of which the computer will distinguish it from all other loops.
(ii)
The ENGINEERING UNITS (for example Gallons/Minute, Litres/Hour) in which it is desired to display appropriate loop parameters.
(iii)
The RANGE of the loop in Engineer ing Units, which should correspond to the range of the flowmeter.
(iv)
The Setpoint Address, to which the weight changing loop will be cascaded .
S p e cia I - t 0 - Pro j e c t 'B a c kg r 0 u n d' Programs The standard CONSUL B system has a restricted, all core resident, background facility. FORTRAN programs may be compiled on line only if 8K of core store is reserved for this purpose. Communication between a FORTRAN prog r am and a control loop is limited.
(v)
The Measured Value address, that is, the input data list location into which the flowmeter signal, suitably converted, is placed by CONSUL B's input scanning program .
(vi)
The Output Address, that is, the output data list location from which CONSUL B's valve output program sends a control signal to the hardware modules which drive the valve.
Conversationa l Mode Whilst assembling or modifying a CONSUL B control loop, the user is not told by the computer what particular piece of information it needs next. I n other words, there is no conversational mode because the computer does not 'talk ' to the user. Rather, CONSUL B prevents the user from inserting data except in a predefined sequence and format which he obtains from a handbook . Experience has shown that users of CONSUL B very rapidly become expert in the operation of the keyboard buttons.
(vii)
Optionally , the Valve Position Feedback address, t hat is, the input data list location into which a feedback of va lve position, suitably converted , is placed by CONSUL B's input scanning program .
I n t e r - cas cad e Sw i t chi n g CONSUL B omits some advanced switching facilities required by complex control schemes in which , for example, interconnections between multiple cascaded systems may be switched automatically w ithout 'bumping' the plant actuators.
(vi ii) Optionally, the identifying number of the Computer/Manual Station to be associated with the loop . 3.2 . Building a Control Loop The eng i neer builds the flow control loop by pressing the buttons in a predefined way , using the 'ENTER' button to complete each data insertion. Should he push buttons in the wrong order the FORMAT ERROR lamp will light and he will be unable to continue until
3. THE CONSUL B MAN-MACHINE INTERFACE 3. 1. Preface Fig . 1 shows the CONSUL B display panel and key·
155
'r.::;;"
'---'
~
"."
--l
51
F
'/0
CUIIIIIIII,,,,
CO.TIIIICM.
0
II0lAT,
o
'----'
~
~
,000
'''\,IU
LOO' tOIN'
.......
.... .......,G.,,.... .....
" ,
'r---J ..co ..
_on
"IIIIA",T,IIII ,
'
VALout
6
9
3 .8
+ 7
1
5 .0
5P +
0
,. ,.. ~ L..:, G/M1 N
.'ICIAl
,,,,,cno ••
CD
156
~~:
.... 110
CM
"" I
0
LOG
IC'
•
ac;,
+
... ...
IT .. LDL
••
lIP DlC .. T UNIT ADD DU., L" 2
+
Iir~G 0 ..
ALG
". "" 0" • • •
I
AT
11-
-
LOOt' ALL LG
•
-
2
7
A
L
I
•
>.
tl
"
•
12
•
M
2
7
DIY
'/11
IITIO
13
C
.
3
I
• •
I.
0
11
•
•
IAT
AILT AILT MGM L_
• • •
IWCM IawcM CLD
"
T
•
0
OAT
0/"
I
I'
IU" UN... 11., All' AL" 7
I
II
jo..L 011
.."
+
'uu
ALG DATA "ALUI
TIID IICD
-
I.
, •
DIY LT
ACK ILL ENTIIY TEIT D.... LAY
3
.. I
O"IN CA le
ACCE ..T ALAII"
E.. UII
LT
CLII CAIC
Fig. 1. Consul B Panel and Keyboa rd
0" AUTO
0
MANUAL
TEIT LA .....
I
CANCEL
TIMI
Panel Inserted Set pOint I Dry BasIs wtl
Consistency Compensation
Converts to incremental demand
SI BI25 BASIS WT CONTROL LOOP (Primary Loop)
Cascade SWitch
Provides positive only output
Machine Speed Measurement
Consistency Main Meter Stock Flow Valve
Measured Dry Basis Weight
Flow Meter
Fig. 2. Example of consul B algorithms for paper machine control
he pushes the correct button . As soon as he has entereel 'FINI' his loop is held in the computer store. Whilst the engineer has been building up the loop, a teleprinter will have been recording all his button actions, -esulting in the kind of printout shown in the following table. Explanatory comment has been added . ASSEMBLY OF SIMPLE FLOW LOOP TELEPRINTER PRINTOUT
EXPLANATORY COMMENT
NEWLOOP
03
New loop requiring 3 algorithms.
FREQ
01
Perform this loop's calcu !ations every 1 second_
9999
{ Th. loop ;d.ntity ;, 10 '"
SlF001 SF* SF+ DEC
PT
ENG UNITS
STN NO
0000 1 02
010
SlF001 and it is to have a range from 0 to 999 .9 Engineering Units. Engineering Units are to be Gallons/Minute_ [Anyone of 12 Engineering Units may be specified by a predefined code]. ComputerjManual Station No. 10.
LDL NO
01
Specification of the 1st. illgorithm follows.
ALG NO
07
SPMV algorithm.
ALGDATA
04
Setpoint address follows.
VALUE REF ALGDATA VALUE LDL NO
048 05 *007 02
48th position in Reference List. Measured Value address follows_ 7th position in Input Data List. Specification of the 2nd algorithm follows.
ALG NO
11
INTC algorithm.
LDL NO
03
Specification of the 3rd algorithm follows.
ALG NO
10
VALValgorithm.
08
Output address follows.
ALGDATA VALUE ALGDATA VALUE
157
*005 06 *001
5th position in Output Data List. Valve Position Feedback address follows. 1st position in Input Data List .
FINISH
3.7. Comment
The loop is now held in the computer, but has not yet been brought on line.
."Simplification of man·machine communication in a flexible dig ital computer process control system".
(i)
Loop SlF001 is an example of the simplest possible type of control loop. More complex loops are built, tuned, modified and logged in exactly the same manner.
(ii)
During the building or modification of a loop, other loops remain fully on line.
(iii)
There are 21 algorithms in CONSUL B. These comprise arithmetic, dynamic, cascade switching, ~ogical switching and special algorithms which have been shown necessary by common experience in a range of industries. Additional algorithms specified by a customer often are added to meet some special-to-project need; examples of these are an AVERAGE algorithm wh ich calculates the arithmetic average of a measurement from a profiling instrument and a RAMP algorithm which ramps set points at a grade change.
(iv)
The safety features of CONSUL B include Illegal Entry protection from the keyboard and selective button lockout provided by the three panel keys engraved 'Control Engineer' , 'Parameters' and 'Special Functions'.
3.3. Bringing the Loop On Line The buttons 'DEV LT', 'ABLTHIGH ' , 'ABLTLOW' are used to enter Alarm Limits in gallons/minute. 'IAT' is used to enter an estimated Integral Action Time. 'AUTO' puts the loop on line 'bumplessly '. 'SP' dis· plays the setpoint, 'MV' the measured value, in the Current Value window. 3.4. Trend Recorder Facility I n order to tune the loop, ~he engineer may assign setpoint and measured value to two pens of a trend recorder. For example, ' SlFOOl SP TRD RCD 0136' as- ' signs the setpoint to Pen 1 and scales Pen 1 so that its fullscale movement represents 30 % to 60 % of the control loop range. Using the trend recorder and the 'lAd' button, the engineer can tune the loop for a suitable response to a setpoint change.
3.8 . Data Logging
3.5. Loop Modification The engineer may find that he cannot tune SlF001 loop just using the integral control provided by the algorithm INTC. In this case he would wish to change the INTC algorithm for a PIDC algorithm, which would enable him to try any combination of proportional, integral or derivative control. CONSUL B prevents his changing the loop structure whilst the loop is on line. He takes the loop off line simply by entering 'MANUAL', then changes the INTC for a PIDC algorithm by 'LDL No 02 ALG No 12' (see the table) Finally, ' AUTO' places the loop back on line, and tuning is carried out via the PB (Proportional Band), IAT (I ntegral Action Time) and OAT (Derivative Action Time) buttons. 3.6. Loop Logging
(wh ich assigns the loop to the) (5th position of Log Table 02)
/ENTER \
'5F*\
8500'ENTER \
'sF'+ \
1000/ENTER \ 2'ENTER \
/ENG UNITS'
01/ENTER \
fl/P ADD'
*003/ENTER ,
~
The symbO'r--\ denotes a Single button operation.
3.9 . Visual Display Units In addition to the central panel with keyboard and teleprinters, Visual Display Units (V .D.U's) also are interfaced by CONSUL B. Hence V .D .U's may be used, for example, to display control loop parameters at remote parts of a plant and, if the V.D .U's are equipped with keyboards, to change setpoints and other parameters. 3.10. Multi-Process Installations The modular nature of the computer and its input-output equipment, together with the modularity and flexibility of CONSUL B, combine to form an ideal system for the control of more than one Paper or Plastics Machine using one computer.
then : LOG 02 EVERY 0100
W087
/NEWRD\
I DEC pl\
The engineer, having replaced one algorithm by another in some other way modified SlF001100p so that the above table is no longer an accurate record .of its structure or data, may well enter 'SlF001 LOOP LG' , which will produce the modified version of the table on logging teleprinter. He also may wish to monitor the measured value of the loop for a while by printing it at specified time intervals. To do this, he first assigns SlF001 to a Log Table by entering: SlF001 LOG 025
There is a common requirement in the Paper and Plastics industries for the alarm monitoring of certain process measured variables and their inclusion in Logs without, or prior to, using these measured variables for control. CONSUL B meets this requirement economically but with its usual flexible features. The following keyboard button operations assemble a 'Read Only Loop' of 'Identity S6T087 and Range 100 C to 95 0 C, receiving its measured temperature input from the third position in the Input Data List.
(which prints the contents of ) (Log Table 02 every 10 min . )
158
4 . CONCLUSIONS
5. REFERENCES
1. CONSUL B provides a unique medium sized process control capabil ity for applications without a backing store.
1. MacLAURIN M . I., "Optimum Complexity for Com-
2. In no way does CONSUL B remove the need for the basic necessities of any successful computer application, namely
2. LONG J., "The Minis. The Market Scene in Europe' Supplement to Computer Weekly, November 12, 1970.
(i)
well planned control objectives,
(ii)
adequate, accurate and reliable measurements and actuators.
3. BAI LEY S. J., "Pushbutton Programm ing for Onl ine Control" . Control Engineering, August 1968, p . 76-79.
Rather, the fulfilment of these two conditions enables a high return from investment in the flexible, easy to use and readily expandable features of CONSUL B.
159
puter Control ". 13 th EUCEPA Conference, April 1970.