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Computer Control of a Glass Fibre Process
COMPUTFll. CON'IROL OF A GLASS FIBRE PROCESS A. Thomson
Gullfiber AB Billesholm, Sweden
B.K. Josefsson ASEA Vas terAs , Sweden
ABSTRACT This paper describes the preparations and experience of a process computer installation at Gullfiber AB, Billesholm, Sweden. IN'IRODTK: TION
In the autumn of 1967 Gullfiber decided to investigate how the manufacture of glass fibre could be rationally controlled during the 1970's. Three different alternatives were considered in this respect: Continuous data logging Centralised, analog control Process computer control This investigation gave the following results:
through the nozzles in a jet to the spinners, which are of the double centrifuge type. Here the glass is converted with the aid of a very powerful and rapid gas flame into fibres having a diameter of 56 microns. The fibres are sucked down on to a conveyor, while at the same time they are sprayed with a binder of phenolic resin type. The fibres, which are now in the form of a mat, then pass through a curing oven, where the final polymerisation of the binder takes place. During this process the product receives its final shape and colour. The weight by volume of the product is determined by the speed of the conveyor and the setting of the curing oven. After the curing oven, the glass-fibre mat is trimmed and cut to suitable lengths and shape, and in certain cases, lined with paper, foil, etc. The quality of the glass fibre is primarily determined by the composition of the glass, its homogeneity and the temperature during the fibre formation.
The data logging al ternative was rejected, since this would only provide a history of faults that had occurred, while it would not prevent their occurrence.
The exhaust gases from the furnace have a very high temperature and their energy is recovered in recuperators for heating the incoming combustion air.
Centralised analog control would not provide any advantages compared to the existing control system, apart from the geographical concentration of the equipment.
The entire level, temperature and pressure control forms a closely inter-related system, in which both rapid and slow oscillations may occur.
The alternative based on a process computer was found to be the only one that would give the desired advantages.
Scope of the project
These conclusions led to an agreement being signed with ASEA, Vaster~s, Sweden, for the delivery of an ASEA System 1700 process computer with associated software.
The installation described below forms the first stage of an integrated process control system. This first part embraces the control of the furnace (raw material feed, temperature, level, exhaust gases, etc.), the forehearth channel (temperature profile, outflow) and the spinners.
Process
Software
Glass fibre is manufactured at Gullfiber according to the TEL process.
Apart from the programs required for administrating the use of the memory and peripheral units on a time-sharing basis (monitor, drivers, etc.), a number of standardised programs have been used. These perform the major part of the tasks for which the computer is responsible.
The ten different raw materials are batched by an automatic weighing installation according to the set formula and are then mixed. Sand and soda account for about two-thirds of the finished mix. The batched material is transported via conveyors, bins and flowmeters to the glass furnace for melting at a temperature of about 1400oC. After being retained for about 24 hours in the furnace, the glass runs out into a forehearth channel, where the final temperature control takes place. At the other end of the channel there are a number of platinum bushings at the bottom. Molten glass runs
PIA (Process Input Acquisition) is a program system used for reading, conversion and scaling to process quantities of sensor signals. In addition, it checks various limit values of signals received. When a signal exceeds any limit, an alarm is automatically transmitted, and information is given when the signal returns to the normal state. This program system also takes care of composite measuring
408
limits, output signals to actuators, circuits in alarm state, computer-controlled loops, back-upcontrolled loops, console-controlled loops, etc. In addition, he can request logging by a typewriter of all measuring points with associated actual values, set-point values and actuator positions. As already indicated, there are three different control modes for a loop: computer control, back-up control and console control. The latter means that the operator can position the actuator directly from the console.
points (from several sensor signals) as well as computed measuring points. A program system, Direct Dig! tal Control, is provided for control purposes. This calculates interventions by the control systems according to certain standard algorithms (PI, PID action, etc.). This program system is designed so that different control loops can be easily connected in cascade. Both the program systems mentioned above are wri tten in modular form so that only those parts required for a certain plant need be included to form a system. To match the software with a certain plant, various lists must be filled in with parameters specific to the installation (limit values, parameters in control algorithms, text describing individual points, etc.).
The back-up cubicles contain for each loop an instrument for the measured variable and another one for the actuator position. In addition, there are potentiometers for positioning the actuators and balancing between the back-up station and the computer outputs. The choice between manual and computer control of each loop can be requested from the back-up stations.
The operating console for the computer is provided with a section to be used together with the abovementioned software. After a selector has been unlocked, IIlOdifica tions of a trimming nature can be made from the console (changing of limit values for alarms, control parameters, etc.). This allows a process technioian to trim the plant in a corresponding manner as he is familiar with from previous analog equipment.
Since a high availability of the computer system was foreseen from the beginning and the process is relatively slow, it was not considered necessary to provide any form of controller in the back-up stations. Installation
The software system used allows not only process control tasks to be performed, but also programs to be assembled and compiled. Since the core memory from the dynamic point of view can be divided into protected and unprotected areas, programs developed in the future can be tested without this influencing the control programs.
Up to the delivery of the computer, less than 10 months after the signing of the contract, the work did not deviate by IIlOre than ±. 2 weeks from the most optimistic estimates in the time-table. The actual preparations for the installation involved the arranging of computer and operator rooms, laying of the cables, and the replacement and supplementing of certain sensors and actuators.
Hardware The configuration for the tasks outlined above as well as for a later stage consists of:
The programming work was split up between Gullfiber and ASEA, since Gullfiber by actively participating in this work wished to become familiar with the software. The computer and the associated programs were tested as far as possible prior to delivery.
Central processor with 32 K core memory (one word. 16 bits + parity + program protect). Disc melllOry for 1500 K
Despi te careful planning of the cooling system and air filters, certain air pollution problems arose. The computer room is located in the iIImediate vicini ty of the factory hall (less than 5 metres from the nearest furnace) and the air in it became contaminated, which lead to breakdown of the disc memory.
Tape reader/punch Console typewriter Logger/alarm typewriter 112 analog inputs, mainly for thermocouples
64 analog outputs
After better air filters had been installed, this problem was eliminated, and the availability of the computer has been practically 100% since then.
256 dig! tal inputs 192 dig! tal outputs
The rest of the commissioning took place according to plan and the first loop was closed two months after the delivery of the computer. At present, 64 loops are controlled by the computer, of which 6 are connected in cascade and 2 are subject to quotient control.
All the cables to and from-the process pass via terminal cubicles for matching the signals and insulation between computer and process. These cubicles also contain a reference unit for the cold junction points of the thermocouples. The operator controls the process with the aid of the console, which can be seen on the photo in Figure 1 from the operator's room. From this he can obtain particulars about actual values, their alarm limits, deviations, set-point values, their
Training and infOrM tion To create a positive attitude within Gullfiber to the computer installation, the employees were
409
informed in different ways: Those who were only peripherally concerned or not at all, received information about the project from their staff magazine. A four-day course was arranged for supervisors, foremen and machine and furnace opera tors. This embraced analog and digital control, the design of the process computer, and, above all, the use of the operating console. The above-mentioned training program appears to have bad the intended effect. All operators today are familiar with the computer and show a very positive attitude towards its operation. Resul ts Up to now a period of about 10 man-years has been devoted to investigations, installation and design work and commissioning. In addition, the sum of about 0.5 million Sw. Kr. has been invested in buildings, sensors, cables and actuators. On the income side it can be mentioned that it has proved possible to take out of service analogcontrolled equipment to a value of 0.3 million Sw. Kr. and to use this elsewhere. The running costs pay for themselves if the efficiency or yield can be raised by 1%. After one year of operation, it can be stated that the anticipations have been met and during this period the yield has been increased by 2"fo. The major gain in terms of service with a computer
in this case is the stability achieved with the control, where decoupling of the physical relationship between process quantities can be accomplished. Stable temperature and level will result in a controlled, constant glass flow. This is a necessary condition for the maintaining of a constant fibre diame ter • The re sul t has been tha t the previous major source of rejects has been largely speaking eliminated. Figure 2 shows the number of fibre defects per 24 h before and after the installation of the computer.
Gullfiber, this will result in a saving of many hours per year. On tne personnel side the results have also been good. 'l'he VTork of the furnace opera tors is ph;ysically very demanding and this has previously had the resul t that there has been a large turnover of personnel for these jobs. Thanks to the installation of the computer, such a working environment has been created that the personnel turnover for this work has been entirely eliminated. The computer also constitutes a form of insurance for the future. The need for prior knowledge of new employees decreases in that the personnel can be trained more smoothly with the aid of the computer. Other positive effects, which were not included in the preliminary calculations, can also be reported. It can be mentioned, for example, that the National Swedish Nature Conservancy Board has permitted Gullfiber to monitor the content of phenols in the effluent with the aid of the computer. The alternative to this was to construct a large tank for the effluent. The savings for this are estimated to be 0.1 million Sw. Kr. The introduction of the computer has also necessitated new technical solutions to, for example, level meters for liquid glass. The signal from the old meter was too unstable for connection to the computer. The new meter provides a stable signal and permits a much better control. In addition, it has been found tba t this meter does not .require any maintenance compared to the previous type, for which Gullfiber incurred considerable maintenance costs. In this way the computer contributes towards increased process knowledge and increased know-how. Future developments Considerable pressure is being exerted from all levels within the production area, from the workshop floor to the production management, for the speeding up of the continued extension and for the installation of a similar system in the other factory belonging to Gullfiber.
The automatic weighing plant for hatching the raw materials described previously is responsible for about 100 hatches per 24 h. This plant is completely unmanned and if a hatching error should arise, there is a great risk that it will not be discovered, resulting in a service interruption.
A direct consequence of the positive results obtained from the project described here will be that further tasks will be entrusted to the installed computer. Preparations are now under way for a second stage. This will embrace the manufacturing process after the fibre formation, i.e., control of the fibre mat thickness, addition of the binder, curing and cutting to the correct length and width. When this stage has been completed, the entire manufacturing chain will be under the control of the computer.
Two such incidents were detected with the aid of the computer. If this had not been done, these might have lead to stoppages of several days. Each of these incidents might have cost about 0.1 to 0.2 million Sw. Kr. Power failures are a major problem facing a process industry of Gullfiber's type. A brief interruption can cause a stoppage of 10 to 12 hours. The standby power plants prevent a catastrophe, but these only supply the most essential loads. Wi th the aid of the computer it is now possible to start up the process aoain within 3 to 4 hours. 1fi th the number of power failures experienced by
410
Figure 1 - Photo of the operat or's room with console and log/ala rm typewr iter. To the left the termina l cubicle s can be seen and in the backgro und are the back-up station s. The TV-set s are used for moni tor(the ing the state at critica l points in the process burner flames in the furnace s, spinne rs, etc.).
411
,20
FEB -69
LINE T2
/s 10
1.5
20 /5 FEB -69 LINE T3
It)
10
IS
.to
FEB -69
LINE T4
10
15 OCT -70 LINE T2
10
5 2.0
OCT -70 LINE T3
10
s
.zs
.10
IS
OCT -70 LINE T4
10
.ts Figure 2 - Comparasion between number on fibre rejects per day for three production lines (T2, T3, T4) before (FEB -69) and after (OCT -70) the computer installation. (Y-axis ~ number of fibre rejects, X-axis _ date.)
412
Discussion on Paper XI:S by A. Thomson, B. K. Josefsson
w.
Brand, Bel§ium: 1. \~at is your measuring accuracy in % , possibly as an average of some kind?
2. Can you elaborate on longer power failure stability? For example, I would expect an infinite time stability (on stand-by power source); some 2 min. for the process part. K. Josefsson: 1. The accuracy of the measurements is for tne glass temperature 1 degree centigrade at 10SO°C and for glass level 0.03 mm. The accuracy of the absolute signals has not been verified against any norrnals, but the variation is also reflected in fibre diameter and measurements in laboratory have verified that the repeatability of the signal is in this order of magnitude. 2. No computer control is performed during power failures as there is no auxiliary power supply existing which permits control of the process under such conditions. The improvement as compared to the time before the computer installation lies solely in simplified and centralized start-up procedure.
413
Gullfiber AB Billesholm, Sweden
B.K. Josefsson ASEA Vas terAs , Sweden
ABSTRACT This paper describes the preparations and experience of a process computer installation at Gullfiber AB, Billesholm, Sweden. IN'IRODTK: TION
In the autumn of 1967 Gullfiber decided to investigate how the manufacture of glass fibre could be rationally controlled during the 1970's. Three different alternatives were considered in this respect: Continuous data logging Centralised, analog control Process computer control This investigation gave the following results:
through the nozzles in a jet to the spinners, which are of the double centrifuge type. Here the glass is converted with the aid of a very powerful and rapid gas flame into fibres having a diameter of 56 microns. The fibres are sucked down on to a conveyor, while at the same time they are sprayed with a binder of phenolic resin type. The fibres, which are now in the form of a mat, then pass through a curing oven, where the final polymerisation of the binder takes place. During this process the product receives its final shape and colour. The weight by volume of the product is determined by the speed of the conveyor and the setting of the curing oven. After the curing oven, the glass-fibre mat is trimmed and cut to suitable lengths and shape, and in certain cases, lined with paper, foil, etc. The quality of the glass fibre is primarily determined by the composition of the glass, its homogeneity and the temperature during the fibre formation.
The data logging al ternative was rejected, since this would only provide a history of faults that had occurred, while it would not prevent their occurrence.
The exhaust gases from the furnace have a very high temperature and their energy is recovered in recuperators for heating the incoming combustion air.
Centralised analog control would not provide any advantages compared to the existing control system, apart from the geographical concentration of the equipment.
The entire level, temperature and pressure control forms a closely inter-related system, in which both rapid and slow oscillations may occur.
The alternative based on a process computer was found to be the only one that would give the desired advantages.
Scope of the project
These conclusions led to an agreement being signed with ASEA, Vaster~s, Sweden, for the delivery of an ASEA System 1700 process computer with associated software.
The installation described below forms the first stage of an integrated process control system. This first part embraces the control of the furnace (raw material feed, temperature, level, exhaust gases, etc.), the forehearth channel (temperature profile, outflow) and the spinners.
Process
Software
Glass fibre is manufactured at Gullfiber according to the TEL process.
Apart from the programs required for administrating the use of the memory and peripheral units on a time-sharing basis (monitor, drivers, etc.), a number of standardised programs have been used. These perform the major part of the tasks for which the computer is responsible.
The ten different raw materials are batched by an automatic weighing installation according to the set formula and are then mixed. Sand and soda account for about two-thirds of the finished mix. The batched material is transported via conveyors, bins and flowmeters to the glass furnace for melting at a temperature of about 1400oC. After being retained for about 24 hours in the furnace, the glass runs out into a forehearth channel, where the final temperature control takes place. At the other end of the channel there are a number of platinum bushings at the bottom. Molten glass runs
PIA (Process Input Acquisition) is a program system used for reading, conversion and scaling to process quantities of sensor signals. In addition, it checks various limit values of signals received. When a signal exceeds any limit, an alarm is automatically transmitted, and information is given when the signal returns to the normal state. This program system also takes care of composite measuring
408
limits, output signals to actuators, circuits in alarm state, computer-controlled loops, back-upcontrolled loops, console-controlled loops, etc. In addition, he can request logging by a typewriter of all measuring points with associated actual values, set-point values and actuator positions. As already indicated, there are three different control modes for a loop: computer control, back-up control and console control. The latter means that the operator can position the actuator directly from the console.
points (from several sensor signals) as well as computed measuring points. A program system, Direct Dig! tal Control, is provided for control purposes. This calculates interventions by the control systems according to certain standard algorithms (PI, PID action, etc.). This program system is designed so that different control loops can be easily connected in cascade. Both the program systems mentioned above are wri tten in modular form so that only those parts required for a certain plant need be included to form a system. To match the software with a certain plant, various lists must be filled in with parameters specific to the installation (limit values, parameters in control algorithms, text describing individual points, etc.).
The back-up cubicles contain for each loop an instrument for the measured variable and another one for the actuator position. In addition, there are potentiometers for positioning the actuators and balancing between the back-up station and the computer outputs. The choice between manual and computer control of each loop can be requested from the back-up stations.
The operating console for the computer is provided with a section to be used together with the abovementioned software. After a selector has been unlocked, IIlOdifica tions of a trimming nature can be made from the console (changing of limit values for alarms, control parameters, etc.). This allows a process technioian to trim the plant in a corresponding manner as he is familiar with from previous analog equipment.
Since a high availability of the computer system was foreseen from the beginning and the process is relatively slow, it was not considered necessary to provide any form of controller in the back-up stations. Installation
The software system used allows not only process control tasks to be performed, but also programs to be assembled and compiled. Since the core memory from the dynamic point of view can be divided into protected and unprotected areas, programs developed in the future can be tested without this influencing the control programs.
Up to the delivery of the computer, less than 10 months after the signing of the contract, the work did not deviate by IIlOre than ±. 2 weeks from the most optimistic estimates in the time-table. The actual preparations for the installation involved the arranging of computer and operator rooms, laying of the cables, and the replacement and supplementing of certain sensors and actuators.
Hardware The configuration for the tasks outlined above as well as for a later stage consists of:
The programming work was split up between Gullfiber and ASEA, since Gullfiber by actively participating in this work wished to become familiar with the software. The computer and the associated programs were tested as far as possible prior to delivery.
Central processor with 32 K core memory (one word. 16 bits + parity + program protect). Disc melllOry for 1500 K
Despi te careful planning of the cooling system and air filters, certain air pollution problems arose. The computer room is located in the iIImediate vicini ty of the factory hall (less than 5 metres from the nearest furnace) and the air in it became contaminated, which lead to breakdown of the disc memory.
Tape reader/punch Console typewriter Logger/alarm typewriter 112 analog inputs, mainly for thermocouples
64 analog outputs
After better air filters had been installed, this problem was eliminated, and the availability of the computer has been practically 100% since then.
256 dig! tal inputs 192 dig! tal outputs
The rest of the commissioning took place according to plan and the first loop was closed two months after the delivery of the computer. At present, 64 loops are controlled by the computer, of which 6 are connected in cascade and 2 are subject to quotient control.
All the cables to and from-the process pass via terminal cubicles for matching the signals and insulation between computer and process. These cubicles also contain a reference unit for the cold junction points of the thermocouples. The operator controls the process with the aid of the console, which can be seen on the photo in Figure 1 from the operator's room. From this he can obtain particulars about actual values, their alarm limits, deviations, set-point values, their
Training and infOrM tion To create a positive attitude within Gullfiber to the computer installation, the employees were
409
informed in different ways: Those who were only peripherally concerned or not at all, received information about the project from their staff magazine. A four-day course was arranged for supervisors, foremen and machine and furnace opera tors. This embraced analog and digital control, the design of the process computer, and, above all, the use of the operating console. The above-mentioned training program appears to have bad the intended effect. All operators today are familiar with the computer and show a very positive attitude towards its operation. Resul ts Up to now a period of about 10 man-years has been devoted to investigations, installation and design work and commissioning. In addition, the sum of about 0.5 million Sw. Kr. has been invested in buildings, sensors, cables and actuators. On the income side it can be mentioned that it has proved possible to take out of service analogcontrolled equipment to a value of 0.3 million Sw. Kr. and to use this elsewhere. The running costs pay for themselves if the efficiency or yield can be raised by 1%. After one year of operation, it can be stated that the anticipations have been met and during this period the yield has been increased by 2"fo. The major gain in terms of service with a computer
in this case is the stability achieved with the control, where decoupling of the physical relationship between process quantities can be accomplished. Stable temperature and level will result in a controlled, constant glass flow. This is a necessary condition for the maintaining of a constant fibre diame ter • The re sul t has been tha t the previous major source of rejects has been largely speaking eliminated. Figure 2 shows the number of fibre defects per 24 h before and after the installation of the computer.
Gullfiber, this will result in a saving of many hours per year. On tne personnel side the results have also been good. 'l'he VTork of the furnace opera tors is ph;ysically very demanding and this has previously had the resul t that there has been a large turnover of personnel for these jobs. Thanks to the installation of the computer, such a working environment has been created that the personnel turnover for this work has been entirely eliminated. The computer also constitutes a form of insurance for the future. The need for prior knowledge of new employees decreases in that the personnel can be trained more smoothly with the aid of the computer. Other positive effects, which were not included in the preliminary calculations, can also be reported. It can be mentioned, for example, that the National Swedish Nature Conservancy Board has permitted Gullfiber to monitor the content of phenols in the effluent with the aid of the computer. The alternative to this was to construct a large tank for the effluent. The savings for this are estimated to be 0.1 million Sw. Kr. The introduction of the computer has also necessitated new technical solutions to, for example, level meters for liquid glass. The signal from the old meter was too unstable for connection to the computer. The new meter provides a stable signal and permits a much better control. In addition, it has been found tba t this meter does not .require any maintenance compared to the previous type, for which Gullfiber incurred considerable maintenance costs. In this way the computer contributes towards increased process knowledge and increased know-how. Future developments Considerable pressure is being exerted from all levels within the production area, from the workshop floor to the production management, for the speeding up of the continued extension and for the installation of a similar system in the other factory belonging to Gullfiber.
The automatic weighing plant for hatching the raw materials described previously is responsible for about 100 hatches per 24 h. This plant is completely unmanned and if a hatching error should arise, there is a great risk that it will not be discovered, resulting in a service interruption.
A direct consequence of the positive results obtained from the project described here will be that further tasks will be entrusted to the installed computer. Preparations are now under way for a second stage. This will embrace the manufacturing process after the fibre formation, i.e., control of the fibre mat thickness, addition of the binder, curing and cutting to the correct length and width. When this stage has been completed, the entire manufacturing chain will be under the control of the computer.
Two such incidents were detected with the aid of the computer. If this had not been done, these might have lead to stoppages of several days. Each of these incidents might have cost about 0.1 to 0.2 million Sw. Kr. Power failures are a major problem facing a process industry of Gullfiber's type. A brief interruption can cause a stoppage of 10 to 12 hours. The standby power plants prevent a catastrophe, but these only supply the most essential loads. Wi th the aid of the computer it is now possible to start up the process aoain within 3 to 4 hours. 1fi th the number of power failures experienced by
410
Figure 1 - Photo of the operat or's room with console and log/ala rm typewr iter. To the left the termina l cubicle s can be seen and in the backgro und are the back-up station s. The TV-set s are used for moni tor(the ing the state at critica l points in the process burner flames in the furnace s, spinne rs, etc.).
411
,20
FEB -69
LINE T2
/s 10
1.5
20 /5 FEB -69 LINE T3
It)
10
IS
.to
FEB -69
LINE T4
10
15 OCT -70 LINE T2
10
5 2.0
OCT -70 LINE T3
10
s
.zs
.10
IS
OCT -70 LINE T4
10
.ts Figure 2 - Comparasion between number on fibre rejects per day for three production lines (T2, T3, T4) before (FEB -69) and after (OCT -70) the computer installation. (Y-axis ~ number of fibre rejects, X-axis _ date.)
412
Discussion on Paper XI:S by A. Thomson, B. K. Josefsson
w.
Brand, Bel§ium: 1. \~at is your measuring accuracy in % , possibly as an average of some kind?
2. Can you elaborate on longer power failure stability? For example, I would expect an infinite time stability (on stand-by power source); some 2 min. for the process part. K. Josefsson: 1. The accuracy of the measurements is for tne glass temperature 1 degree centigrade at 10SO°C and for glass level 0.03 mm. The accuracy of the absolute signals has not been verified against any norrnals, but the variation is also reflected in fibre diameter and measurements in laboratory have verified that the repeatability of the signal is in this order of magnitude. 2. No computer control is performed during power failures as there is no auxiliary power supply existing which permits control of the process under such conditions. The improvement as compared to the time before the computer installation lies solely in simplified and centralized start-up procedure.
413