Recent Advances in Glass Level Control Systems

STSTDfS RlCD'r ADVAlfeJ:S ADVAlfOlS IJr U GLASS LnEL CORnOL COlmtOL STS'l'DfS

lied Wed W. Lowry LoW1'7 !echnicel Technical Director Control Sytlte.e S7Itells Engineering Generel General n-velopment neYelopment Laboretoriee Laboratories Anchol'-Hock:int Corporet1on Anchol'-Hockint Corporation Lancaeter, Lancaster, Ohio, U. S. A. ABS'rRAC!' ABS'l'RAC'1'

'!'he typical typioel modern automatic glass glBee leTel 'l'he level control .yetem ie shown in block diegrem aystem is diagram form in 'igure Pigure 1. It is ie compoeed oomposed of a eeneor aenaor or ~ee8uring ~eaauring device, device. a continuous continuoua recordel'-controller and a device to modulate the feed-rete feed-rate of the betch batch charger. Recent edvencell Bnd advances in the fields fielda of Phytlice, Ph7lica, Electronics and Control Systeme Syateme have heTe provided techniques which have hsve permitted the development of new typell types of level control syetems cBpabilitiee. a7ltems with extended capabilities.

The eutoeetic glaee autoaatic meesarement mea~rement ead and control of glass level in ea gless glass melting tenk tank hes has been en an importent important fector factor in qul1ty quality glen glaaa aeking making for I18ny many yeers. years. With increeses increases in melting retee, ratea, I18nufecturing manufacturing speede speeds and quality requirements hes has cOlle the need for lIore accurete accurate meesurement measurement end and 1I0re rewponsiTe, rewponsive, reliable control. Recent advances BdTencee in the fielde fields of electronice electronics and control eyetelle aystema heTe heve provided technique. technique a which heve heTe permitted the development of new typee types of level control syeteme syatems with extended capBbilitiee. !'hie eeverel such euch capabilities. '1'his peper paper deecribee deacribes several eysteme Bre in uee aystems which are use et at Anchol'-Hocking.

ADV.AWC!S IlII GLASS L!VEL MEASUREMDT ADV.AWC!S 1111 MEASUREMD'T

SYS'l'J.:M EVOLlJ1'IOli SYSTEM EVOLur10W

Por many yeare, years, oscillating oacillating probe syBtemll syatems heve hsve been 'or ueed glalle level. 'rhese eyeteme heTe uaed to measure glass 'l'heae systema have dO reqUire proved to be quite reliable but d. require periodic meiatenance. MBny such euch systems eyeteme are still in uee maiatenance. Many use at Anchol'-Hocking today. Recent advencell advances in nucleBr nuclear phYllioe physica have hsve permitted the development of !'Bdiation radiation type level meosaring syeteme. The8e systems eyetems are Bre meosuring systems. compoeed composed of an isotope source package which emits beta !'Bdiation Bnd aB scintillation ecintillation detector which radiation and totalizes the number of particles detected per unit time. 'l'he The detector also provides an electrical 8ignel BverBge number signal which is proportional to the average of pBrticle8 particle8 deteoted. detected. BecBuBe Because glB8e gla8s i. i8 quite dense it ver,y effectively blocke blocks the betB beta pBrticlee particlea and thus aB meesuring thie type can be made to mea8uring system syetem of this function quite eatisfBctorily. aatisfactorily. Level meBlIurement measurement 8yste.e 8ystema of thie this type are manufBctured manufactured and 80ld sold by eeveral aeveral American companie8. cOMpaniea.

'l'odey's 'l'odayls eutometic automatio glB8s gla8s level control syeteme syatems ere are the result cf of the typicel typical evolutioner,y evolutionar,y developmeat development proceBB. procen. Eerly Early approechee approaches provided for periodic meB8urement gleee level through the uee measurement of glass use of a eimple, siaple, menully manually operBted operated probe which located the surface of the gIB.. gIB .. with reepect respect to a fixed reference. Prom thi8 lIeasurement meaeurement ea men man then made the neceeeBr,y Bdjuetmente to the feed-rate of raw necessar,y adjuatments materiel material into the tBnk. tank. Ae As technology advBnoed, advanced, the level leTel lIea8urement mea8urement wee was meohanized mechanized end and provided ea oontinuoue indioBtion of the level. With advance8 Bdvence8 continuous indication in the field of induetrial industrial controle controls it beceme became p088ible glBe8 level and possible to record continuouely continuously the glass thue Bnd enelyze thus obeerve observe and analyze fluctuatione fluctuations which might occur. Concurrent with thie this evolution, bBtch batch charging devicee devices were developed whioh which provided methode adjusting the feed-rate feed-!'Bte sutomatically. automBticBlly. methods of edjueting When it becalle became p08eible poaaible to oonnect connect the level meaBurement systell eyetell to the batch ohBrger lIeasurement charger to regulBte regulate the feed-rate, feed-rBte, the glass glBee level control 8yBtem s7ltem of today todey well was born.

Anchor-Hocking currently haB has in operation six of the8e syetems. syatems. Figure 2 illustrates ea typicel typical instBllation. '!'he eource inatallation. 'l'he aource housings are lead-lined steel with ea shaped aperatllre ape!'Bture and are extremely heevy. heavy. The largest large8t one in use at Anchol'-rtockiag Anchol'-rtocking weigha epproximetely apprOXimately 1200 pounds. The red18t1on radiation ""igbe pattern is in the form of ea nBrrow fBn euch narrow vertical fan auch thBt most of the particlee that particlea ere are ebsorbed absorbed in the glas. glaaa or refractory. The detector is ia mounted opposite the eource and aligned Bligned in ite senBitive position. source ita most senaitlve Five of the 8Y8tells Bre mounted on foreheBrthe sy8tema are foreheertha where the span epBn between the source and detector is ebout Bbout 48 inchee. Bmall refiner with inchea. '!'he 8ixth is mounted on a small epBn of 10 feet. '!'he Source8 aB spen source8 do not require epecial cooling however ell Bre weter special all the detectors ere water oooled. cooled. One of the 8yetems 8ystems hes been in operation for one yeer meintenence or year without requiring requlring any maintenance edju8tment. adjustment. 'l'he The rest of the 8yt1tems systems have been in operBtion operation less lesa than one yeer. year. BecBuse Because radio-i80topel redio-isotopes slowly dec87, anticipBted that occa8ionel decay. it lt is entlclpated occa8ional re-calibration re-calibratlon will be required. '!'he half-life of

INTRODUC'l'IOW 1NTRODUC'l'10Il With the edvent glBse melting eyeteme advent of continuoue oontinuoua glass and eutollBtic glBse forming proceesee autollatic glass proceasea celle came the requirement for eutomatic automatio controle. controla. !heBe These were required to l18intBin maintain preeet preset vBluee values of vBrioue various parametere ie the parameters in the melting eyetem. aystell. Among theee these is requirement conetBnt dapth of glass glaee requirellent to l18intein maintain aB constant in the melting tank. Thie ie necee8Br,y This is neces8ar,y becauee because the method of feeding molten glass glBss to the forming procese constBnt proceas reliee relies on grevity. greTity. !'o '1'0 maintBin maintain aB constant feed-rete feed-rate i t is therefore neces8llry necenary to provide a conetant head of glass in the melting tenk. constant tank.

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isot~e is ebout about 30 years end and thus this rethe isot~e calibration vill will occur ebeut abeut once rrery rre17 two yeare. yeara. ceHbretion total span of the measurement is one inoh and !he totel aeasured to en an aceureoy accuracy of less than 0.01 level is aeesured inches. Al Although though the cost of ~f the systell syetem is higher then than other systells syetems currently in use, it is predicted that thet the reduced maintenence maintenance cost viII will more than offset the tha higher initial cost. offeet

measuring gless glass level ere are Other methods of meesuring continually being developed. Preeently Presently the continuelly lasere and electrical c8pecitence capacitance utilization of lesers investigated. Although no results of are being inveetigeted. these investigations heTe have yet been pUblished, published, it is ineviteble inevitable that more accurate and end relieble reliable systems vill will evolve in the future. !DV.\NOES IN GLASS I.EVm. CONTROL DEVICES .AI:'V ANOES 11 In the field of control systems and devices, the advent of solid-state electronics has permitted instrument inltrument manufacturers to develop instruments with better reliability and eccurecy. accuracy. Solid-stete Solid-state vith are now available perfor. the sellle lame devices ere evellable which perfoN function as earlier electra-mechanical electra-mechanioal devices. many ysars years probe type glees glaes level control Por lIIeny syeteme systems have used ueed a reoorder recorder to monitor and display the poeition position of the probe. The input signal to the controller vss VBS taken from the recorder, so, the ae~lraoy aC~lraoy of control vss VBS dependent on both the performance of the probe system end and the recorder. Plgure Pigure 3 illustrates such a system. Today it is possible to use solid-stete solid-state devices called Mpea~ "pea~ pickers" or "sample-and-hold· "sample-and-hold" units whioh monitor and store the poeition position of the probe end and provide an output signal to a recorder end and controller simultaneeusly. se devices simultaneously. ,be 'hese devioes are much more aceurate and reliable than eerlier earlier methods end and require no maintenance. figure 4 illustrates this control arrangement. Systeme Systems of this type have been in operetion Anchor-Rocking for OYer five years year& operation at Anohor-Rocking vith with excellent results. Reliability is very high end and accuracies aoouracies of lees less than plus or minue minus 0.01 inchee inohes are maintained.

reciprocatio~ is controlled by varying the speed of reciprocetio~ methods utilized a constant speed electric aotor and a variable ratio, belt type reducer to the pusher lIechenisll. mechenism. !he speed cf of the connected te system syetem W88 ws adjusted lIanually manually lIy by changing the ratio of the reducer reduoer so that the chergillg chargilig rete rate ves ws snfficient sufficiont to maintaia maintain the proper glass gleee level in tha tank. pneumatic oontrol the hDk. With the advent of pneWllatic systems, charger ves ws eutollated automated aysteme, the control of the cherger lIy positioner to adjuet adjust the by utilizing a pneumatic poeitioner eleotronic control ratio of the reduoer. Later, electronic systems positioners to acoomplish the eystells used electric positionere selle sa.. result. Soae of these syeteas systems ere are still ia use et at Anohor-Hocking however mnch meintenanoe maintenanoe is required to maintain proper aperetion. operation. The varieble variallle ratio speed reducer is not designed to tolerete tolerate the automatic control continued speed adjustment which autometic systems produoe and the result is a high rate of weer wear and ea resulting reeulting high level of maintenence. maintenance.

~rly ~r17

Recent advances in electronic eleotronio controls oontrols haTe hrre provid. provid.. . a aethod of controlling the speed of reciprocation reCiprocation aocurately and reliebly. reliallly. A direct current lIotor motcr very aocuretely coupled to e gear geer box provides the reciprocating reCiprocating power. The speed of the motor ls is controlled contrOlled by an eleotronic electronic control commonly celled called an ·SCR "SCR control·. control". Figure 5 illustrates illuetrates this system. SCR controllers BVaileble which utilize the stendard standard output are evailable current signels si~als frOll from ae conventional eleotronic electronic industrial industriel controller as en an input signel signal to regulete regulate the speed of the motor. Meny Many batoh batch chargers chergere at Anchor-Hocking system Anchor-Hccking hsYe h8ve been converted to this syetem with good results. Charging rates retes cen can be controlled very accurately and the speed of response exterBel respcnse to external ohanges or up-sets is much faster thus better control is echieved. aohieved. An elternate been alternate approach approaoh to the above system has ieen worked out which employs an air cylinder to provide the reciproceting reoiprooating ecUoD action directly, direotly, thereby eliminating the electric motor Rnd gearbox. motcr "Dd g8arllox. The sir air cylinder is controlled through an electric solenoid operated valve. The valve is operated by en an electronic electronio device celled called a current to pulse converter. Ag8ia, Again, the advent of solid-stete solid-state electronics electronios has permitted instrument lIanufacturers manufaoturers to develop this device. Several American companies now sell thie this device. It is designed to eccept, accept, ss an input. input, stendard standard current signels signals from froll industrial controllers and provides, ss en an output, ea series of cf on-off eleotric electric pulse•• pulses. The pulse rate is directly direotly proportional to the current input. Pigure 6 illustrates such a system. Severel Several systems are in operation at Anchor-Hocking Anohor-Hocking and performance an~ reliebility to that of d.c. motor systems. reliability are equal tc

Solid-etete Solid-state electronic electronio controllere controllers heve have also enhanced enhanoed the control of glass level by providing ea broader range of tuning. This hes has allowed improved responee response to upsets and helps to minimize fluctuetione in glasp level which fluctuations whioh are caused by external factore. factors. The next level of sophieticetion sophisticetion in gless glass level control ie being achieved oontrol is aohieved by replacing analog controls vith with ea digitel digital computer system. ~fort ~fort is underV8Y undervay at Anchor-Hocking Anohor-Rocking in thie this area and the first !yetem system is in operation. Glass level is only one of several parameters being controlled contrOlled end and the overall control scheme is muoh more sophisticeted oontrol soheme sophisticated then than can be achieved aohieved vith with enelog analog type systems.

SUMMARY AND CONCLUSIONS This piper psper has attempted to present severel several new methods and techniquee teohniques which heve hrre been applied to glase level control glass oontrol systems. Because the devices and methods are basicelly besically electrio and electronic eleotronic it is possible to employ them in various combinations, poesible depending on the specific application. !he The intent here hes bes been to try to ecquaiat acqueint the readpr readl!'r vith with some of the recent developments end and how hoy they have as the past ten years heve been applied. Just es have producpd major producl!'d mejor strides in the field of eutometic autOlletie control. e%citing control, the future holds even more excitlng developments.

JJJV.\NOES ATJV ANCES IN IW COlmlOL CONTROL OP BATCH CHARGERS Anchor-Rocking uses only one type of betch batoh charger, s8 reciprocating, reoiprocating, pusher type charger, however the methode methods and techniques desoribed in this pgper paper can be epplied applied to other typee types of chergere chargers also. With a reciprocating type charger, the charging rate

184

LXVEL UVEL

unt LEnL

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RECORDER AND RECORnER Mm

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CONTROt:ER CONTROL:.ER

BATCH CliARGER CIiARGER

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GLAS~ GLAS::

TANK TAl<"'K

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RADIATION ftPl LEVEL MElSURING MEASURING SYSrIM. RADIA'l'ION nPJ: LE'VJ:L SYS'l'IM.

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LEVEL GAGE CONTROLLER

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J'IGUR! J'IGURE 3.

EARLY 'flPE GLASS LEVEL :RECORDING RECORDING .iNn EARLY'I'lPE .iND CONTROL SYSTEM. 185

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MODElm ELECTRONIO ELEOTRONIO TYPE GLASS LEVEL RECORDING REOORDING AND CONTROL OONTROL SySTEM. MODERN SYSTEM.

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BATOH ~TOH OHt.RGER

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SOR TYPE BATOH CHARGER OHARGER SPEED CONTROL SYSTEM. SCR

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AIR CYLINDER

BATCH OHARGER nGUR!: 6. AIR CYLIWDER OYLIWDER OPERATED BATOH CHARGER. nGURE

186