Linear encoders 101: Choosing the right encoder for your application

You require a linear encoder for length measurement, but you’re not sure which type of encoder is best suited for your application — sealed linear encoders or exposed linear encoders. 

You’re not alone. Below is a brief summary to help you in your decision-making process.   

Sealed linear encoders are protected from dust, chips and splash fluids, and are ideal for operation on machine tools. The aluminum housing of a Heidenhain sealed linear encoder, for example, protects the scale, scanning carriage and its guideway from chips, dust and fluids. Downward-oriented elastic lips seal the housing. The scanning carriage travels along the scale on a low-friction guide. It is connected to the external mounting block by a coupling that compensates unavoidable misalignment between the scale and the machine guideways.

Exposed linear encoders operate with no mechanical contact between the scanning head and the scale or scale tape. Typical areas of application for these encoders include measuring machines, comparators and other precision devices in linear metrology, as well as production and measuring equipment, for example, in the semiconductor industry. They are designed for use on machines and installations that require high accuracy of the measured value. 

There are also incremental and absolute linear encoders. With incremental linear encoders, the current position is determined by starting at a datum and counting measuring steps, or by subdividing and counting signal periods. Incremental encoders from Heidenhain feature reference marks, which must be scanned after switch-on to reestablish the datum. This process is especially simple and fast with distance-coded reference marks. 

Absolute linear encoders require no previous traverse to provide the current position value. The encoder transmits the absolute value through the EnDat interface or another serial interface. 

For more information, contact Heidenhain. 

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