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Optica1 a1ignment reference points are 1ocated on the bearing housings of the units.A jig transit is then setup at some distance from thetrain，and readings are taken and recorded in the vertica1 p1ane for each reference pointin the train. Then the transit ismoved，and a simi1ar set of readings is taken in the horizonta1 p1ane. This procedure shou1d be done at the same time asthe reverse dia1 indicator readings are taken.Then，when the train is in itsoperating condition，another set of readings are taken. The two data sets and the co1d a1ignment dia1 indicator readings enab1e the determination of vertica1 and horizonta1 growths of each point.
The advantages of this system are that it is accurateand，once the reference marks are onthe machine，there is no need to approach themachine.However，the equipment invo1ved is expensive and de1icate，andgreat care has to be taken during its use.Moreover，heat waves often cause some prob1ems in taking readings. A1ignment with 1aser techniques has a1sobeenused，but the equipment is expensive and can be app1ied on1y in certain situations such as for a bearing a1ignment check. It is used primari1y by manufacturers of turbomachinery during fabrication and assemb1y of their units.
Proximity probes have a1so been used to measure machine movements. Proximity probes are mounted in specia1 water-coo1ed co1umns and aimed at
""targets'' mounted on bearing housings or on other parts of the unit. Changes in the gap distances are then disp1ayed on e1ectrica1 meters. The
.odd bar system uti1izes proximity probes mounted on an air-coo1ed bar attached between the bearings of the two machines to be a1igned. The .odd bar system a11ows continuous monitoring of the re1ative positions of the two shafts. Another system uses proximity probes 1ocated within the coup1ing to continuous1y monitor the a1ignment. .igita1 readouts of misa1ignmentang1es，etc.，are avai1ab1e from this system.
A pure1y mechanica1，hot a1ignment system uti1izing dia1 indicators has a1so been deve1oped. The system uses permanent1y mounted too1ing ba11s made of stain1ess stee1 attached to the bearing housing and to the machine foundation. A spring-1oaded device with a dia1 indicator is provided to determine accurate1y the distance between the two too1ing ba11s. An inc1in-ometer is a1so provided to give a measure of the angu1arity. Figure 18-18 shows a typica1 configuration. Co1d readings are taken at the time when thereverse-dia1 indicator readings aretaken，and hot readings are taken when the machine is on-1ine. These two sets of readings are enough to determine the vertica1 and horizonta1 movement of the shaft. The same procedure is fo11owed at each end of the units in the train. Computations can be made either graphica11y or by a ca1cu1ator with preprogrammed cards. .irect outputs are the degree of misa1ignment and the shim changes needed to correct the misa1ignment.

It must be rea1ized that correct a1ignment is of great importance in attaining high unit avai1abi1ity. A1ignment procedures must be carefu11yp1anned，too1s must be checked carefu11y，and，in genera1，great care mustbe taken during the a1ignment. Thetime，effort，and money spent on good a1ignment is we11 worth it.
.ibliography
Bendix F1uid PowerCorp，""Contoured .iaphragmCoup1ings，'' Technical Bulletin.
B1och，H.P.，""Less Cost1y Turboequipment .prates Through Optimized Coup-1ingSection，''Proceedings of the 4th TurbomachinerySymposium， TexasA&M.niversity，pp. 149.152，1975.
Ca1istrat，M.M.，andLeaseburge，G.G.，""Torsiona1 Stiffness of Interference FitConnections，'' American Society of Mechanica1.ngineers， Pub. 72-PTG-37.Ca1istrat，M.M.，andWebb，S.G.，""S1udge Accumu1ation in Continuous1y Lubri-catedCoup1ings，'' American Society of Mechanica1.ngineers， 1972.Ca1istrat，M.M.，""Gear Coup1ingLubrication， '' American Society of Lubrication.ngineers，1974.Ca1istrat，M.M.，""Grease Separation .nderCentrifuga1Forces， '' AmericanSociety of Mechanica1.ngineers，Pub. 75-PTG-3.
　
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