Analog Computer Systems in Blending Processes

42 IRE TRANSACTIONS ON INDUSTRIAL ELECTRONICS May

Analog Computer Systemsin Blending Processes*

HAROLD H. ROTH, t MEMBER, IRE

Summary-Analog computers especially engi- for it is the nature of such processes that quanti-neered to program and control specific blending ties, qualities, prices, and supplies of raw materi-processes, are establishing themselves as prac- als are uncontrollable variables, yet the endtical solutions to scores of industrial blending pro- products must be uniform in quality and price, andblems. They reduce productton costs, eliminate produced in quantities consistent with varyingraw material waste and mulitply product output market demands.many times over. An important consideration is Webster's definition of blending exemplifiesthat non-technical personnel can be quickly trained these process industries: "preparation by minglingto a high degree of operational proficiency. different varieties or grades." More specifically,

blending processes usually involve a number ofINTRODUCTION mixing functions. Various means must be used to

perform those mixing functions; the compositions-Automation is an exciting word. Say it to an and therefore the prices-of the raw materials are

uninitiated industrial purchasing agent and what it not always known and an adequate supply of allexcites might well be some outlandish estimates necessary raw materials is not always available;of costs. Mention it to a personnel man and he may market demand for the end product is not alwayspale at the thought of those "unmentionable" labor predictable. These are the variables inherent inproblems. Speak on the virtues of automation to virtually all industrial blending processes.people who live and work in an old-fashioned mill The fact is that, in many instances, differenttown and there's a fair chance you'll find yourself proportions can yield the same desired end productplucking feathers from your hide. But what about so that the choice of the most economical blendthe more sophisticated levels of industrial man- procedure must be a consideration of all theseagement-the men who live with the problem of the variables. When the composition and supply of theclassic profit squeeze? To them, automation is raw materials are erratic, the choice becomesnot merely an exciting word, but a stimulating and even more complex. Then too, when the marketdramatic concept. . . a practical solution to the demand for the end product-whether it is icegrowing probleyn of the shrinking profit margin, cream or rolled steel-is inconsistent, the blendIt's a buyers' market. The customer is king. process must be so regulated. The selection ofPurchasing agents are playing their budgets close ingredients in compensating proportions, and theto the vest. They want the most and the best they choice of the proper blending sequence can be ex-can get for the least amount of dollars. Their job pressed mathematically. The constraints areis to shop for it. Yet, labor is being better paid known. The proportions of raw materials andfor fewer hours and retiring earlier. The cost of their costs are the unknowns. The solution of theraw materials and transportation are still spiral- mathematical equations gives the most economi-ing. Federal, state and local taxes, happy as we cal mixture of variable raw materials needed toare to pay, are taking bigger and bigger chunks. produce the desired end product. But, can pro-Just what can automation do? How can it help? duction personnel be expected to be proficient inWhere could it apply? the formation and solution of mathematical ex-

pressions? Even if they were, solving them manu-BLENDING PROCESSES ally would be time-consuming, tedious, and subject

Among the first industries to prove the feasi- to human error. Put analog computer to the taskbility of automation enmasse and to incorporate of solving these intricate equations and the answerthe concept operationally are the dynamic blending is virtually immediate and unfailingly accurate.processes. Their acceptance is understandable,

COMPUTER APPLICATION IN BLENDING* Received September 20, 1961. Cranyadgtlcmue ol epot Special Systems Division, Minneapolis-Honeywell Regu- g ertammed to dogithe job, puttereconomi senep oflator Company, Pottstown, Pa. gamdt otejb u h cnmcsneo

1962 ROTH: ANALOG COMPUTER SYSTEMS IN BLENDING PROCESSES 43

integrating one of these comprehensive giants for AN ANALOG COMPUTER FOR ICE CREAv-this relatively simple job is questionable at best. BLENDINGMost of their tremendous capacity would be unused The answer to that can best be demonstrated byand wasted. The savings realized would hardly illustrating the special purpose analog computerjustify the investment. An analog computer, on the system in operation today in Boston's Hood Iceother hand, can be specifically designed to accom- Cream Platplish an assigned function. It need be only as large Cream P ant.Some time ago Hood's management expressedas a given situation demands, but can be engineered an interest in automating their ice cream blendingfor future expansion. An analog computer per- process. It was decided that to be of any value toforms with optimum efficiency and delivers great- them, the system would have to satisfy these ex-er returns-immediate and long range-on a far pressed qualifications:lower initial investment.

Both general purpose and special purpose ana- 1) It would have to increase their productivelog computers can be used to solve mathematical capacity from 1300 gallons of ice cream perexpressions. Both can calculate the exact pro- hour to 2500 gallons.portions of ingredients needed for specific blending 2) hour to2500lgallons.2)The system would have to consolidate theirprocesses. But, considering the stated prerequi- existing production processes without ad-sites of lowest possible cost, compactness, high ditional equipment.specific performance, and design simplicity, a 3) The equipment would have to be reliable, andspecial purpose analog computer is the more easy to maintain and service.sensible choice for application to variable blend- 4) With the flow of the ingredients automated,ing processes. A special purpose analog com- the system would minimize 'unidentified"puter, thoughtfully designed to meet the needs of a dairy losses and reduce the need for physi-specific process, will increase productivity, solve cal movement of heavy tanks.the complex mix problems of varying quantities 5) The quality and consistency of their iceand qualities, and can be operated competently by cream would have to be improved.properly oriented, nontechnical personnel. 6) Above all, there would have to be a sharp re-An analog computer solves for unknowns by duction in their operating and finishedcomparing them to knowns. Physical quantities of product costs.a given problem are represented by dc voltages.The main computing elements are reliable dc

opeatinalamplifiers with resistive and capaci- Their over-all objective was to find a systemoperational apiirwihrssieadcai- that could make rapid and accurate batch calcu-tive feedback networks. Therefore, complicated lat asul means ard opte th caltsindustrial mix problems are solved by means of lations as a means toward optimizing the resultsrelatively simple electrical circuits. of their blending processes.

An analog computer can translate its solutions The Special Systems Division of Minneapolis-to digital form, then record its answers on punched Honeywell established these criteria:cards for programming and for automated controlof blending processes. An analog computer may 1) Precise solutions to the problems of ingredi-also be used as an integral part of a closed loop ent proportions for mixing blends with noprocess system using transduced information to less than four variables.perform the control functions. By this method 2) Fastest practical solution time.coefficient settings, output indications, program- 3) The solutions would have to be transcribedming and control are accomplished rapidly and on punched cards to serve both as controlwithin an error margin of less than one-tenth of instructions and as a permanent record ofone per cent. operations.

In addition to low cost initial cost and low oper- 4) The system should be simple enough to beating expenses, a well-engineered analog com- operated by nontechnical personnel.puter has the inherent qualities of reliability and 5) It would have to be easy to service and main-ease of maintenance. A computer-controlled tam.blending process, therefore, increases the efficien-cy and productivity of manpower, and alleviates A special purpose analog computer was chosenmanagement's vexing problems of rising pro- for these reasons:duction costs and erratic product quality. Arethose contentions merely theoretical? How well 1) It performs calculations accurately and con-do these principles prove themselves in practical sistently.applications? 2) Properly designed and engineered, a special


purpose analog computer system would yield cost of that particular batch. Then too, when somethe desired increase in product output most of the ingredients are scarce, available quantitieseconomically and with no production delay. may be introduced and the computer will auto-

3) A special purpose analog computer is simple matically calculate the compensating proportion ofto operate. the ingredients that are readily available.

4) Its cost would be considerably less than a The batch is described by the following mathe-digital computer programmed to perform the matical expressions:same functions.

The system, as finalized, accomplished all of amount oA2BQ A3BQ3 + AtBQ = total (1)those objectives. Fig. 1 shows the system in oper-ation. To use the system, the operator presses a AlSQ1 + A2SQ2 + A3SQ3 = AtSQ = total (2)button for each of the dairy and non-dairy ingredi- amount of batch solid seruments indicated by a particular recipe. Whole milk,skimmed milk, cream, ice cream powder, butterfat and solid serum contents each has its own "in- Q b

+ Q2 + Q3 + Qw + Qln + Q2n = Q = total (3)gredient button"-so do corn sugar, cane sugar, batch quantitywater and the other non-dairy ingredients. Now where (1), (2) and (3) = subscripts identifying dairythe computer automatically determines the exactquantities of each ingredient necessary for the de- ingredients,sired recipe, actuates the controls linking the in- Qntirgredients to the main blending tanks, and records Qw = ents,the operation on punched cards for the use of the Qn, Q2n = quantities of non-dairy in-accounting and production control departments. gredients,The operation can be repeated as many times a AlB, A2B, A3B = butter fat percentages inday as is necessary to satisfy the demand for the the dairy ingredients,various batches. The speed of solving mathe- AtB = total butter fat percentagematical expressions by computer, and the direct in the batch,and positive control of the blending processes has AlS, A2S, A3S = solid serum percentagesvery nearly doubled the plant's production ca- in the dairy ingredients,pacity. AtS =total serum percentage in

The computer does not automatically produce a the batch.recipe with a minimum of high-cost ingredientsand a maximum of low-cost ingredients. However, These expressions are reconstructed to form thethe operator has only to specify a particular quan- equations solvable by the computer:tity of low-cost ingredients for the computer toautomatically determine the compensating pro- 12A2BQ2 + c3A3BQ3 = Lt(AtBQ - AIBQI), (4)portion of higher-cost ingredients to optimize the

___ a2A2SQ2 + a3A3SQ3 = L(AtSQ - AlsQ1), (5)

a w f V X * EQw = Q Q1 - Q2 - Q3 - Q1N - Q2N- (6)

The unknown ingredients are Q2, Q3, and Qw. Theremainder of the variables are known: butter fatpercentages, AlB, A2B, and A3B; the desiredbatch size and butter content, Q and AtB; the solid-serum percentages, AiS, A2S, and A3S; the desiredbatch solid-serum content, AtS; and total quanti-ties of dairy and non-dairy ingredients, Q1 and Qlnand Q2n, respectively. These are all introducedmanually into the computer. The factors alpha,alpha two, and alpha three are scaling factors.Their function is to calibrate the equations so thatgreater accuracy is achieved in solving for thequantity of unknown ingredients.

Fig. 1-Analog computer installation used in ice cream Fig. 2 shows the computer in block diagramblending process. form. After the known variables are manually


INGREDIENTMAbUAL aX SCALED 59OLUTIONS i ll

TOTrAL aOUT

BATCOH BTC

gADDcCRM911503Xi|

SCALL} SELECTION l lO

Fig. 2-Block diagram of blending process computer.Fig. 4-Blending process computer.

introduced and scaled, the computer equations areprepared by multiplication and addition circuitry. due to amplifier saturation, card-punching is pre-They are then scaled to simulate the final process vented by an alarm interlock. The input to A-liequations which are solved, descaled and identi- corresponds to the second computer equation. Thefled. The analog voltmeter and the digital volt- solution to these equations must be identical to themeter accomplish visual display. The factors are computer quantities at the outputs of A-12 and A-rescaled if the readout is incorrect. Production 14 if A-il and A-i5 are to have zero outputs.instructions for the control units are performed by A full view of the computer is shown in Fig. 4.the card punch unit. With this system, solution In order to make the best use of the computer attime is approximately 50 msec. the production level, all controls have been ar-

Fig. 3 shows the interconnections of the com- ranged to provide maximum simplicity of oper-puter amplifiers. All amplifiers are of the dc ation. Pushbutton switches vertically mounted areoperational type and function as follows: A-9 and provided for selection of the three dairy ingredi-A-13 are integrators; A-10 and A-14 are invert- ents. The selected ingredient button is illuminat-ers; and A-li and A-i5 are summers with a gain ed for clear indication. Scaling switches of theof 200. When amplifiers A-li and A-15 have zero unknown dairy ingredients provide automatic se-outputs, the equations have been properly solved. lection for satisfactory operating voltage levels.If the equations are improperly solved, perhaps The switching circuitry on the recessed service

control panel (Fig. 5) allows amplifier output andFEF O - I [Q,~ calibration test points to be conveniently scanned.e Q-Ae The panel also contains eight calibration adjust-

i aT. t 0 ~~~A+, E, ments. The entire computer is modularindsgREF i;1 j ^ (Fig. 6), and all amplifiers and individual net-

A AD DWITHISALSAa works are plug-in units. These networks are~~~~~- -- r SESUALINGJ F packaged in a sealed unit to minimize the effects

0 11^> X62Qz s I^h)-<T of temperature changes and atmospheric con-W__ _V_j__ ditions.

- _ --- - The automated system has greatly increased2lo d . productivity. Labor hours once spent in moving

A[ +LO~QN A,4 <, F heavy cans, manual weighing, and tedious cleaningintre ad s e operations are eliminated. Waste of raw material

preparedbymultiplication and adito circuitry. duhas been reduced, and unidentified losses haveThey are then scaled tosimulatbeen eliminated by precise transduced measuring

fied.- Te a and the automatic recording of all ingredientmovements. The card computing and measuring

Fig. 3-Amplifier function diagram, equipment enables management to choose mixing


PORK & FATi

BEEF a FAT '.ARYINSG COMPOSITIONS

CONSTRAINTS QUANTITY

PRODLCTSFAT CONTENTQOALITYCOST

LINEAR PROGRAMMING

ANALOG COMPUTER

COMMAND(ORDERS)_

FEEDBACK B CONTROL CIRCUITS

SOLUTION

Fig. 5-Control panel. Fig. 7-Meat blending problem.

combinations which reduce the overall cost of the production lines at the Hypothetical Meat Productsdairy ingredients in the final mix recipe to a mini- Company. To optimize all of the company's pro-mum. duction lines a digital computer might prove more

What is the difference between this system and economical, but for automation of a single line, aa closed loop automatic process. The ice cream special purpose analog computer system is moreblend operator depressed the buttons for whatever appropriate.ingredients were required for a given recipe. In a Hypothetical produces five different kinds ofclosed-loop system, all the computer needs to know meat products from this production line (Fig. 7).are the characteristics desired in the end product. Each one is a recipe of different quantities of beefScale factoring is eliminated along with the need and pork. These raw materials composed of un-to manually program the ingredients. known and varying percentages of fat content are

ground and stored in bins. The computer-controlled blending process must produce five

A CLOSED-LOOP COMPUTER SYSTEM different products-each one able to qualify forTo examine a closed-loop system with its sens- federal grading and local inspection for quality and

ing devices, computer and computer operated con- uniformity-and each at a cost commensurate withtrols, consider the automation of one of the nine established price and profit latitudes. The com-

puter must be programmed according to definedmathematical interrelationships to calculate theprecise proportions of meat and fat contents. Allthat is necessary to initiate the automatic, close-loop process is to "tell" the computer how muchand what qualities of end products are wanted, andhow much Hypothetical Meat Packing Companywants to spend to produce them. The computerwill make all necessary calculations, automatical-ly actuate and control the blending process, andmonitor the end products to assure that they arewithin prescribed government standards.

Factors which make a special purpose analogcomputer system a more practical choice than adigital computer for this application are:

1) A digital computer handles data in discreteblocks and performs its functions in pre-programmed sequences. Its precision and

Fig. 6-View of computer showing plug-in amplifier. accuracy are dictated largely by its designed


I Special purpose analog computer systems have/.4a vast number of applications in industrial blend-

j PROBLNEMS Sj- - ing processes By controlling process tempera-tures and pressures, and the temperatures and

<+1DIGITAL pressures of the ingredients intended for blending,they effectively inhibit costly "overshoot.' The

COST water flooding and refining operations in petrole-um, the carbon introduction phase of steel process-ing, the bleaching of wood pulp, and sterilizing and

OFINSTALLy1 ATION filling in food canning are examples of industrialblending processes in which analog computer con-trol is applicable. Analog computer control sys-

________/_____ tems designed for the separation processes inA0 CCUCY 0.01 0.0 petroleum, metals and chemicals are invaluable

assets to those industries. Any blending process,regardless of how often its blending demands mayFig. 8-Cost-accuracy comparison of analog and digital change, can be more effectively and economicallysystems. controlled by analog computer methods.

capacity. Furthermore, a digital computer CONCLUSIONis comparatively expensive. There is strong evidence that industry is be-

2) An analog computer, on the other hand, coming more aware of the possibility of analog-handles a continuous flow of data, performs controlled automation as a means toward increasedits operations simultaneously, and has an productivity without increased costs. The objectiveaccuracy directly proportional to the quality question is not where automation might apply, butof its components. The blending process that rather where it might accomplish sufficient resultsrequires an accuracy greater than one-tenth to justify the initial investment. Just as theof one per cent is a rarity. That accuracy is characteristics of industrial blending processeswell within the operational capabilities of a are more favorable to analog computer systemswell-engineered, yet relatively inexpensive than to digital computer systems, so the specificsanalog computer. of blending processes make special purpose analog

3) The last comparison, cost vs accuracy, has computers more applicable than general purposeperhaps the greatest influence on our se- systems. Special purpose systems are especiallylection. The lined area on Fig. 8 (chart from designed to solve specific blending problems andKorn and Korn's 'Electronic Analog Com- to control specific blending processes with noputers") is where most of this type of appli- wasted capacity. By closing the process loop withcation will fall. The digital computer transducers and controls, optimized ratios ofnormally does not apply as a suitable so- quality to price can be accomplished automatically.lution on a cost basis. The savings of an As the professional stature of industry grows-analog computer are further amplified by as attitudes mature-as new approaches penetratelow maintenance costs, design simplicity, archaic restraints, special purpose analog com-ease of operation and high reliability, and the puter systems and the advances they represent willcomparatively short time and expense in- be called upon with increasing frequency to satisfyvolved in training personnel to full oper- the challenges of our expanding and dynamicational proficiency. economy.

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Analog Computer Systems in Blending Processes