The workhorses of the machine alignment field, optical alignment instruments have been used for precision measurement in industrial settings for many years. Rugged and dependable – and highly accurate to one arc second (0.001″ over 17 feet) – optical alignment tooling continues to be the tool of choice for many applications where the measuring environment is less than ideal. Paper mills, steel mills, converting and corrugating facilities, power generating plants, and more, benefit from the accuracy and reliability of optical tooling and alignment methods. In this post we provide you with definitions for terminology that you may hear during a machine alignment inspection or alignment procedure where optical alignment instruments are being used. 

Optical Instruments 
Alignment (Control) InstrumentAn optical instrument used to establish a reference Line of Sight (LOS) from which other optical instruments can be collimated or collineated. Usually this control instrument is bucked-in to the machine baseline.
Sight LevelAn optical instrument used for measuring the level to earth condition of machine components.
Telescopic Transit Square (TTS)An optical instrument which consists of two optical systems arranged exactly 90 degrees to each other. These systems form accurate perpendicular Lines of Sight (LOS).

References 
BaselineA parallel reference line which represents the machine centerline. It is usually established by Stainless Steel Target Bushings (SSTBs) or brass plugs embedded in the floor on the operator side of the machine. In the case of newer free standing equipment, this reference is installed in the cross-machine direction directly in the frame or sole plates. 
Brass PlugA monument embedded in the floor with an affixed prick punch mark used as a reference point on a baseline
Line of SightA line projected by an optical instrument from which all measurements are made.
Optical ScaleA device that has accurately positioned increments which can be measured optically.
Optical TargetA device inserted into a Stainless Steel Target Bushing (SSTB), with accurately positioned patterns which can be measured using optical tooling. 
Stainless Steel Target Bushing (SSTB)A machined busing designed and used exclusively by OASIS in the installation of baselines. It performs the same function as a brass plug, but is far more accurate due to its ability to accept and optical target
Stick on TargetAn adhesive backed optical target used as a temporary reference where permanently fixed target bushings are not always practical.

Procedures 
Buck-InSetting a Line of Sight (LOS) parallel to at least two reference points such as Stainless Steel Target Bushings (SSTBs), brass plugs (BPs), or both ends of a machine component.
CollimationSetting two optical instruments so that their Lines of Sight (LOS) are parallel but not coincident. 
CollineationSetting two optical instruments so that their Lines of Sight (LOS) are coincident. 
PlanizingSetting an instrument's Line of Sight (LOS) parallel to a given plane. This plane can be defined by three points, or by two points and a level instrument. 

For an in-depth description of the Telescopic Transit Square (TTS), check out this article Measurement Tool Spotlight: The Telescopic Transit Square (TTS). If you would like to learn how precision machine alignment can increase efficiency at your location, please contact us and be sure to subscribe to our email list for regular updates on precision measurement tools and technologies, alignment methodologies, case studies and more. 

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