An open encoder is frictionless since the scan head and linear scale have no physical contact. Also, EMI protection has to be separately provided. Some open encoders have still finer resolution, down to 0.001-mm. Sophisticated electronic interpolation circuits and multipliers are needed to obtain these high resolutions. The flexible strip comes in precut lengths or in continuous rolls.
Gold plating is used to improve reflectivity and corrosion resistance.
Other surface coatings serve to make the scale more durable. It produces an ac output proportional to the core s movement and is linear over a specified range. An LVDT is limited to measuring relatively short displacements due to its inherent construction. However, device resolution is virtually unlimited, as set by capability of the external electronics. Capacitive sensing methods provide still another choice.