Computers in the Glass Batching Industry

COMPUTERS IN THE GLASS BATCHING INDUSTRY

Willlam C. Susor Toledo Scale - DivIsion of Reliance Electric Company TOledo Toledo, Ohio

Bulk materials required In the preparation of glass have hi storir:ally been conveyed uSing us Ing contact sontact flow and feeding feed ing historically deVises with electromir;hanlcal and electrical or eler;tronir: eler:tronir: deVices devlr:es devl"es serving as loglr logl" control. It is now economlrally economl"ally ': ontrol problem using a mlnl"ompuler feasible to solve the ·:ontrol mlnlr:ompuler inclusion of Inventory "ontrol, " ontral, real time monitorwith the incluSIOn Ing and logging of system status, automatic correr;tlOn for sharar;terlstlcs and Hierarchlal change In material flow characteristics duplex transfer of Information. information.

Proportioning volumetriC means Scales are normally used In preference to volumetrlr: ( 0.1/,0) , Depending upon due to accuracy requirements (0.1/,0). sr:ale may be used for each Ingredient or the time cycle, a scale Ingredients may be weighed on a single scale. multiple ingredients Weighed Batch Transfer and Totalizing System can be used A bucket elevator, conveyor transfer system r;an bat ch to a totalizing scale. ThiS to move the weighed batch bat·-.: h IS scale IS used to verify that the weight of the bat·:h required limits. within the reqUired

Glass Batchlng Process The Glass Batchlng Process requires accurate, rapid proportioning of fluent materials from bulk bUlk unloading areas to portlonlllg the furnace storage hopper. This process can be diVided IIl1tO nto major parts as shown In I n figure 1.

Mixer nllxer is normally used. The :ycle ~ ycle IS A drum or turbine Illlxer r;ontralled -:an be added on controlled on a time baSIS, and liquids r;an volumetrls baSIS. The mixer discharges the a time or volumetriC -.:onveylng system for transportation to mixed batch Into a r;onveylng lhe mixed batch storage hopper above the turnase. furnace.

Unloading Conventional elevator and conveyor unloading systems r:can an be used to move the Ingred ients from cars to silo storunloadin g station. age. A car IS positioned over a hopper unloading The material IS is gravimetrically or mechanically fed to a r: an be Inserted In the r:onbucket elevator. A belt scale r:an conveylng line, after the elevator, to monitor material rer;elvre r:elv veying ed. The material is then conveyed to the proper silo.

Cullet and Furnace Storage Cu Ilet is added to the furnace furna ce by means of a r;onstant constant rate Cullet feeder or batch scale, usually located on the downstream Emergen r:y means are provided to bySide of the mixer. Emergency pass the batch system and add cullet directly to the storag e hopper. age

Storage Silos or Bins construr;ted uSing welded or Storage silos are normally constructed bolted steel, concrete staves, or slip form concrete. The be-::ause of the small quantities Involvminor Ingredients, ber;ause Ided stee e levator or bag ed, are stored In we welded steelI bins. A elevator IIIl device IS used to elevate the bag or drum material to Ilh can be dumped Into the minor an elevatIOn such that they can binS. Ingredient storage bins.

Sensors Material Detectors are used to sense the approximate level of material in a bin. They operate by a rotating mer:hanimechanical means, pressure baffle, or impedance variation and provide a Signal when actuated. meshanLimit SWitches are used to sense t~e position of mechanIcal componets and prOVide a contact closure when actuated.

Material Feeders Depending upon the material flow characteristics and nOise level OSCillatory oscillatory VI'b rator, screw, rotary vane, and / or belt ~eeders ~ee ders may be used in combinagravity gate, and/or ac r: urtion or singularlly ( depending upon the rates and accurac les required) requ ired) , to feed material. aCies

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Consideration must be given to OSHA standards.

Zero Speed Switches are used to sense the velor::lty velor:lty of mechanical devices. They provide a contact closure when actuated. Load Cells are used to sense force or weight. These are ex,;ited with a voltage will strain gauge devices and when ex,:ited voltage levelI pro proportional weight forr::e. output a vo Itage leve portl ona I to we ight or forr:e.

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4) Other sensors are employed In this type of a system; however, they are similar In operation to those described.

will fetsh fetc:h the The CPU via the program counter Will instruction from memory. will decode and execute the Instruction. The CPU Will The instructions may consist of more than one word. The program counter advances prior to the execution of each word. de..e0sit the If data is transmitted the CPU will dejOsit data in the destinatIOn address. ***

As one follows this operation on a step by step basis It seems rather straight forward. The computer IS sur:cessful In solVing solving problems due to ItS speed ( approximately ser;ond) . 200,000 instructions per sesond)

Actuators Motors: AC and dc motors are used through the system to drive screw feeders, conveyors, mixers, blowers, e levators, etc. The sizes vary from fractional to hundreds of horsepower. Vibrators: Vibratory devices are used to drive material feeders. Air Cylinders: These devices are used to control material flow gates.

Computers have been used to solve process problems for a penal ity had to be number of years; however, an economic penallty r::onventional process control equippaid for this use over r:onventional pro r: ess ment. The computer IS Ideally structured to solve pror:ess problems in that processess Involve logical and algorithmic progression of data toward a result that requires the changing of variables depending upon external ,:onditions. With the advent of low rost minicomputers It IS is now feasible to solve these problems by using the computer at a 10 ,: onventional equipment. to 2 D/'o cost savings over r:onventional

Why Use a Computer pror::ess Why should a computer be used to solve this pror:ess problem? What advantages does it have over other methods? To understand the answer to these questions one must first understand the basIc operation of a computer. The computer consists of four functional elements (figure 2) •

Type of Computer Once the decision has been made to use a computer as a part of the process control system its configuration must dedlr:ated r;omcombe determined, e.g. whether it shall be a dedlr;ated process) , or puter (used solely to operate this specific pror;ess) a time-share computer In a central operation. The dedsignificant advantages over the Icated computer has some Significant time-shared computer: - The initial equipment cost of the dedicated computer IS about equal to the requ Ired portion of the central computer. - The programming, verificatIOn, and modification cost IS reduced because the programmer need not be concerned with intervening programs, program disruption due to improper safeguards, or unexper;ted unexpected timing problems. Subprogram standards may be structured to allow sommon maintenance and Information information flow between computers; however, application of these subprograms is controlled by the vir::e versa. programmer without affecting other software or vir:e - The process problems in most industries involve a number of vendors. Each IS an expert in implementing hiS

The Central Process Unit controls the operation of the whl r:: h computer. It generally consists of a program counter whlr:h points to a memory location, a stack pointer to permit the use of subroutines, a status register to set levels of operatIOn and indicate the logl':al logl';al result of an operation, Instration uctIOn set decoders to Interpret b II nary operation codes, r::odes and rontrol and the logic elements to execute these r:odes the flow of informatIOn. A series of registers are generally available for temporary data storage. The arithmetic unit adds and subtracts binary numbers. Other mathematical functIOns are obtained through the software program. ** The memory unit consists of elements that store binary bits of information. These elements are generally Wire wound Ferrite cores although other solid state devices may be used depending upon the problem being solved.

*These elements may not be physically dlstin'lUlshable in the computer hardware. ** Hardware "Multiply and Divide" are available as options in many computers. *** A program IS a series of binary words. There are generally 16 binary bits per binary word. The program IS pro'lrammer to solve the problem in constructed by the pro'lralllmer question. computer is identified with a **** Every location In the r;omputer unique address. The CPU receives and transmits data by controlling the address location.

The Input/output unit acts as a buffer and control for all dev Ir;es. data transmitted between the computer and other devises. In order for the computer to function, a program *** must be loaded into ItS memory. This program is generally refphysl r: ally erred to as "software" (can be changed without physlr:ally altering the computer) whi le "hardware" represents the physical configuration of the unit. The computer ran be programmed to solve any type of problem. The computer can perform only one function at a time and Will will operate as follows:

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portion of the process. It is highly improbable that a group of vendors could efficiently solve their problem using a common computer. computer -With -Wi th a dedicated ded icated computer, the degree of supervisory superv i sory control can be altered by direct communication to a supervisory vi sory central computer. The supervisory superv i sory computer will command the dedicated ded icated computer to perform predetermined predeterm i ned major functions, i.e. alter the formulation. A failure in the supervisory superv i sory computer will not shut down the process, but only require manual input of major supervisory information. -If one of a number of dedicated ded icated computers fails, fai Is, that portion of the process can be continued on a manual basis untilI the fault has been corrected. If the plant were operunti ated from a single computer and a failure occured, It is doubtful that an automated plant could muster enough manpower to maintain manual operation.

that process engineers rapidly learn to apply software to process solutions.

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A number of languages are available avai lable for the engineer to work With. with. The lowest level is machine language (the ( the language used by the computer in executing a program) • A binary (machine language) program can be toggled into the computer using switches on the front of the unit, for example: Core Condition Core Address

** 013737 8a** 0010008 001000a 002000 8a 000001 0000018 a If the computer is started at location 5008, 500a, the first word it fetches is 013737 8 a-, This word is examined by the CPU. The 01 is unique and tells the processor that the instruction is a move-data instruction. The first 37 ind iindi500 502 504 506

Control Console and I/O The control console is preferably located in an env environironmentally controlled area. The console houses most of the control logic, sensor transducing equipment, visual aids, I/O equipment, computer, associated peripherals, and 1/0 manual controls, as shown in Fig. 3. Subpanels are located throughout the process area. They house motor starters, valve actuators, subloop controls ( such as automatic chain starting of motors) and some alarm indicators. I/O printers can be located where required for schedule inputs, inventory reporting, and system monitoring.

cates the address of the source of the data as being be i ng in location 502 R R', and the second 37 indicates ind icates the address of the destinaTion as being in location 504 8 ,. After det8 ermining this, the processor will execute the instruction by moving the contents of location 1000 1000 B R to location 2000g. The processor then will fetch OOOOOTa. 00000I8' This instruction tells the computer to wait for an interrupt. Due to the difficulty in working with a pure number system to solve logical flow problems, mneumonic ( assembly) languages were devised to allow the programmer to use symbols to represent numbers. Using an assembly language the above program would be written as follows:

The equipment housed in the main control console must be located to minimize electrical noise. All low level *equipment is located in an isolated section of the cabinet. Th is equ ipment cons i sts of computer, mass memory, local This I/O printer (for ( for program modification and service) , integrated circuit logic for signal conditioning, scale transducers and associated manual control, and isolated interface.

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WAIT These languages move the programming symbols closer to the English language. In writing thiS this program, the programmer generates a source tape which must be converted into binary. This IS accomplished by using an assembler software program. The assemb ler program wi II assembler I1 accept the source tape and reduce it to the binary data for execution by the computer. Assembly and binary languages are unique to a processor and therefore not usable on processors of different manufacture. manu facture.

The connection between the high and low level equipment IS is through an electrically isolated interface ( fig. 4) • The high level input wires are connected to terminals on the high level side of the cabinet. The incoming signal will excite a photodiode which in turn excites a photocell. The photocell transfers this information to the low level circuitry. There is no electrical connection between the high and low level signals. This process operates in reverse when outputting information. The high level equipment consists of hardwired logic for chain starting, field terminals, and visual display. display_

Compiler languages are higher level languages ( one command may encompass several assembly instructions) whose statements have been standard standardized, i zed, nationally and/ or internationally.

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* Low level cirCUitry circuitry is defined as Integrated circuit compatable generally 5 vdc. High level is defined as all other power. A number to the base 8 represents an octal number ( as compared to decimal base 10). Since the computer has a bi nary base, direct communication must be In binary. Octal binary represents a binary number in that 013737 013737a8 =

The successful application of the minicomputer will not depend upon a computer programmer ( who may not know the process) , but rather on a process design engineer familiar with programming. The minicomputer provides the process engineer with a tool to allow him to solve the process problem at a higher degree of sophistication than has been permissible in the past. Experience has shown

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Although these languages are powerfu I and universally applicable to most computers (specifically FORTRAN) , they were generated to solve r.ompllcated algorithmic and file mani pu lation prob lems. The process env ironment generally requires the solutIOn solution of a series of boolean equations with min min imal fi le structures. As such; compi ler languages have some disadvantages when applied to the solution of many process prob lems.

1. The memory requirement r.an be two to three times

tive parts of the program. Sub-programs will evolve which will yield the same benefits as printed cirCUit cards in a hardwired system. Software programs have an additIOnal advantage from a development and maintenance standpoint over hardware in that the engineer has a natural location to insert comments ( Fig. 5). Comments are non-operative parts of the program which describe the . purpose of the instruction in questIOn. question. In fl gure 5 they are located to the right of the semi-colon. In addition to comments, the engineer mayor may not use flow charts ( Fig. 6) •

that required for an assembly language program. The operating speed can be reduced by a factor of 10 which may result In marginal real time performance. 3. It is difficult to use debugging routines on r.omplier compiler programs. 4. It is difficult to manipulate machine priority and input-output logic bits using compiler languages. 2.

Flow charts are similar to the function of block deSigns in designs In a hardwired system. They are used to reduce the verbal description of theproblem into functional blocks. While comments shou Id be mandatory, flow diagrams may be left to the discretion of the deSign design engineer. System Documentation As with hardwired systems software programs must be properly documented. The typical flow of a software design is shown in fig. 7. The customer should be supplied with sufficient documentation to allow him to maintain the system. This documentation should include:

The argument for compiler compi ler languages is that they are machine Independent and therefore a standard program can be applied to any computer to solve the same problem. This statement is generally true In the data processing environment. The fallacy when applied to the process env ironment IS that different computers solve similar compiler language problems differently. The memory, timing, and input-output handling will be different. The fact remains that the data processing problem and the process control is an problem are different. The process control problem IS engineering problem, whether a r.omputer r:omputer is used or not. If a computer is used,the used, the selection of languages should SUit the prob lem.

1. Abstract - a short deScription description of the major functions of the program 2. Listing - source list of the program including comments. 3. Source tape - listing on paper tape 4. Core map- areas in memory where the program IS stored 5. Symbol table - area in memory where symbols are stored 6. Binary tape - funr;tional program.

Assembly language is generally preferable for the solution of process problems. The engineer readily adapts to ItS structure which can produce minimum time cycles with optimum memory allocation at minimum cost.

System Checkout After the software design IS completed and assembled It should be installed and executed in the system prior to shipment. It must be recognized that the most time consuming part of software design is not necessarily the coding and initial assembly of the program, but detecting and r.orrectcorrecting errors when running the system.

System Design The process design engineer uses the computer as a tool which forms a part of the system dedicated to solving a problem. With a hardwired system he drew symbols for'>( for">( logic elements * and Interconnected them to form schematics. The schematics are then reduced to hardware. With a computer he follows a Similar process; instead of logic symbols he uses mneumonic symbols; Instead of sr.hematics he generates a program; instead of reduction to hardware the program IS is assembled and entered into a computer. The computer system will solve the same problems as the hardwired system and in addition can be programmed to solve background ** problems such as inventory and production control.

To minimize field startup time the be simulated and run at the source of standard software will minimize

system operation should plant. The application checkout time.

System Startup Prior to startup of a software system the hardware shOUld should * i.e. "and" gates, "nor" gates, "or" gates, counters, buffers, serializers, etc. **In the process control environment certain functions funr.tlons must occur on a real time basis; that is, if a quantity of material is being measured to a predeterminal amount the computer must stop the process when that amount is rear.hed and not be so Iv i ng other prob lems at the time. Thus the terms foreground, background. Foreground programs are with the real process (high priority) while those involved With background programs can run as time perm its.

As in the design of hardwired systems, software programs should be structured for reuse. In a hardwired system repetitive solutions are reduced to printed circuit cards. The reasons for this are somewhat obvious; engineering deSign design time is minimized, the design can be tested and proven, the board~ can be stocked, and documentation can be standarized. The same concept applies with software. The program should be structured to maximize reuse of repeata-

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be verified in a manual mode of operation. It is necessary to allocate sufficient time for startup of these systems even after simulation at the source plant. Depending upon interface complexity and size, startup may take from two week s to three months. weeks

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After the system IS up and running, system changes are normally easy to make. Assuming the system is properly deSigned, hardware 1/0 and software changes can be made designed, with little disruption to the process, and at minimal expense.

preset weight "zone" the computer will adjust preact, make a log entry of the overweight condition, accept the error, and continue. is over-tolerance and outside outSide the If the weighment IS preset" accept zone" the computer will make a preact adjustment and hold the scale cycle while making a log entry of the alarm condition. This condition must be corrected or overriden by the operator before the cycle can continue.

ContrOl; The computer will function as the master Mix Control; timer and sequence controller In the cycle. All downstream equipment, as well as the mixer itself, is initiated by a signal from the furnace mixed batch storage hopper. The Will o~cur or;cur automatically. following sequence will

Operation thiS type of a system could be as Typical operation of this follows: Formula Formu la Storage; All production formulas formu las are loaded into mass memory to be accessed by the used via entry of the formula number. To place a formula into production, the supervisor need only Input the formula number of each furnace. Level controls in the mixed batch storage hopper of each furnace signals the starting of a particular partiCUlar formula. To change any part of a formu la in storage, the superv Isor formula supervisor can recall as desired, and replace the corrected formula into storage.

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Material Control; The computer will control the unloading and weighing sequence which may include performing multiple checks on material versus silo si 10 location to prevent improper silo assignment.

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Automatic Tare; Prior to commencing an automatir; weigh cyc le, the computer will e cycle, ele--:troni-:;ally ler:tron i -:ally zero the scale. This will ensure a true scale zero at the beginning of ea~h ea~h cycle. If the accumulated r;orrections reach a maximum preset value Indicating a material bui Idup ldup in the hopper or a scale malfunction; the computer will initiate a scale alarm, stop the cycle, and Identify the alarm on the I/O ledge and correct printer. The operator then must acknow acknowledge corre ct the condition. cond it ion •

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Automatic Preact; A certain preactuation value wi II 11 be stored in the computer for each of the materials in the system. These preact values will be updated, as required, by automatic computer analysis and averaging of the cutoff accuracy each time the material is weighed. This function will eliminate the need to adjust preact settings manually as material densities vary. Automatic Tolerance Control; ContrOl; In addition to determining cutoff accuracy and stopping the system in event of an offtolerance condition, the computer can control the acsura cy acr;urar;y of the cutoff in the following manner: 1)

Within a If the weighment is over-tolerance but wlthlll

When final cutoff occurs, the computer will interrograte the scale for an out-of tolerance condition. r;ondltion. 1n ighment is under-to lerance in the event that the we weighment under-tolerance the computer will adjust preact and jog the feeder until the weighment IS within tolerance.

Alarms and System Faults; FaUlts; All alarm functions are monitored, either directly or indirectly, by the computer. The action taken is dependent on the type of alarm. Each alarm condition, upon occurrence, will command printout of the faUlt took place. Alarms alarm type and time at which the fault will allow the cycle to progress where possible and the Will prevent start of a new cyc r:ycle. le. mixer to discharge but will Scale alarms, i.e. , overload, maximum tare and overtolerance, will cause the weigh cycle on that particular partir;ular scale to "hold". Data Logging Logg ing and Inventory Control Contro I The following series of logs can be recorded on an 1/0 printer ( logging these reports does not interfere with With the control of the cycle) :

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All mixer and downstream auxilliaries will Will start in a predetermined sequence. All scales will start weighing their respective materials. delay, sr;an After a short time de lay, the computer will scan all alarm and sensing points on the ma shinery and ma,:hinery downstream equ II pment to be sure that no fau It IS present. With all conditIOns normal and all scales weighed up and ready, the transfer cycle will start. The scales will dis discharge charge onto the conveyor which will convey the material to the totalizing scale, then to the mixer. With material transferred to the mixer, the mix cycle is started. When required the computer also controls the addition of liquids to the mixer. When the mix IS complete, the batch IS discharged from the mixer into the m ixed batch storage hopper. mixed The addition of cullet is controlled on a per batch basis. Depending upon the condition of the batch storage hoppers, a weigh cycle will commense commen':e Immediately after scale discharge is complete.

number of 0 f batches batche s rUIl ru n per formula; formu la; alarm-type malfunctions; changes made to formu las;

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materia ls left inventory of matertals used and matertals in storage.

Manual Control The reliability of this system is the best available ( an electrome chanorder of magnitude above the conventional electromechanoc ,:ur and ical discrete systems) i however, fai lures can oc,;ur therefore the system must be safely operable in a manual mode. se le ct in g the desIn manual, the scales are weighed up by selecting mate rial / feeder and pressing the feed pushbutton. ired material/feeder Material control equipment is started and monitored from controls on the main panel. A sound soun d but basic manual capability enhances startup, simplifies maintenanr:e, maintenan~e, and reduces downtime. SoncluslOn ost minicomputers and the With the advent of reliable low -:~ost promise of Improved improved cost In the near future, industry must Incorporate these components In process design. The problem with a hardrisks are no greater than solving the problem lon g as the computer is used as a tool to wired system as long solve a known problem. As in any system the solution must be properly documented and retrievable. As operating experience is gained the computer system can and should be used to solve increasingly complex problems remembering the risk IS is not in the computer, but rather in the engineers ability to properly define the prosolution . blem and implement the solution.

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