The magnetic scales are a form of linear quadrature encoder, it uses a magnetized strip with precisely spaced poles to read the position. Since the strip often has an adhesive backing, it’s more commonly referred to as magnetic tape. The reading head contains a sensor that can detect changes in the magnetic field and convert them to precise position data.
Magnetic quadrature encoders are much more complicated devices compared to the use of the optical encoder in linear glass encoders. While they possess some properties that are very desirable for digital readout applications, they also have some serious drawbacks. In order to understand the tradeoffs of using magnetic scales in a DRO, it’s important to have a good grasp of how these scales work.
Magnetic tape used in these scales is made of ferromagnetic powder that is held together by a rubber-like binding agent and is magnetized in a way that produces a series of precisely spaced poles running perpendicular to the long dimension. Common scales use tape with pole-to-pole distances ranging from 1mm to 10mm.
Magnetic scales offer properties that make them very desirable in some DRO systems, however, due to the higher complexity of the interpolation mechanism these scales have some notable drawbacks. Traditionally, magnetic scales were seldom used in mainstream digital readout models and were mostly relegated to specialized applications. When shopping for magnetic scales, it’s important to remember that good scales cost real money and inexpensive scales are able to hit the price point by cutting corners.
