Benefits of magnetic linear encoder over optical version.
One advantage of magnetic linear encoders over optical versions is that the magnetic tape can be provided in very long lengths — . But for incremental encoding, this means the homing sequence to a single reference mark could require traversing the entire length of the encoder. This is why magnetic linear encoders often include distance-coded reference marks. These marks are magnetic poles that are included on the scale in addition to the standard magnetic poles. The reference marks are spaced individually (i.e. their spacing is not the same along the length of the tape) and independently of the standard magnetic poles. After traversing two reference marks, the encoder can determine absolute position based on the position of the first reference mark, the distance between the two marks, the direction of travel, the length of each magnetic pole, and the basic increment (distance between odd reference marks).
Magnetic encoder technology virtually eliminates one of the primary drawbacks of optical encoders — sensitivity to dirt, dust, liquids, and other debris. Because optical designs rely on either the reflection or refraction of light, anything that interferes with the light’s transmission can cause a problem with the signal. Because magnetic coders don’t rely on “line of sight” to measure position, contamination doesn’t affect their performance.