Quick Guide to Precision Measuring Instruments
Linear Scales
Glossary
ABSOLUTE (ABS) system A measurement mode in which every point measurement is made relative to a fixed origin point. Incremental system A measurement mode in which every point measurement is made relative to a certain stored reference point. Origin offset A function that enables the origin point of a coordinate system to be translated to another point offset from the fixed origin point. For this function to work, a system needs a permanently stored origin point. Restoring the origin point A function that stops each axis of a machine accurately in position specific to the machine while slowing it with the aid of integrated limit switches. Sequence control A type of control that sequentially performs control steps according to a prescribed order. Numerical control A way of controlling the movements of a machine by encoded commands created and implemented with the aid of a computer (CNC). A sequence of commands typically forms a ‘part program’ that instructs a machine to perform a complete operation on a workpiece. Binary output Refers to output of data in binary form (ones and zeros) that represent numbers as integer powers of 2. RS-232C An interface standard that uses an asynchronous method of serial transmission of data over an unbalanced transmission line for data exchange between transmitters located relatively close to each other. It is a means of communication mainly used for connecting a personal computer with peripherals. Line driver output This output features fast operating speeds of several tens to several hundreds of nanoseconds and a relatively long transmission distance of several hundreds of meters. A differential-voltmeter line driver (RS-422A compatible) is used as an I/F to the NC controller in the linear scale system.
RS-422 An interface standard that uses serial transmission of bits in differential form over a balanced transmission line. RS-422 is superior in its data transmission characteristics and in its capability of operating with only a single power supply of 5 VDC. Accuracy The accuracy specification of a scale is given in terms of the maximum error to be expected between the indicated and true positions at any point, within the range of that scale, at a temperature of 20 ºC. Since there is no international standard defined for scale units, each manufacturer has a specific way of specifying accuracy. The accuracy specifications given in our catalog have been determined using laser interferometry. Narrow range accuracy Scale gratings on a scale unit normally adopt 20 µm pitch though it varies according to the kind of scale. The narrow range accuracy refers to the accuracy determined by measuring one pitch of each grating at the limit of resolution (1 µm for example).
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