Magnetic measurement is using a scale where the patterns are defined with magnetic north and south poles. The different types of sensor technology – Hall sensors or magneto resistive sensors – are used to read the magnetic pattern and convert them to a electric signal that is used for a motion controller or other electronic controller to assess the information.
The different types of sensor technology can be used for distinctive tasks. Hall sensors are available as switching or linear sensors. Switching hall sensors can be best used for detecting positions on a scale, while linear hall cells provide an output, that is different over different parts of a scale. Magneto resistive element provide an information that is similar to linear Hall sensors.
The challenge in scale production is to create a very precise pattern, where the borders between the north and south poles are placed on the ideal position. For a scale with 2 mm pole pitch, i.e. the length of one single pole, the production system must ensure, that exactly at every 2 mm there is a pole border. For quality control HSMAG describes the quality of the scale by determining, how much each pole is deviating from its ideal position. If any pole is less than 10 micron away from the ideal position in 1 meter, the scale is defined as having quality A10.
The advantages of magnetic measurement are numerous.
Reading at distance
As a rule of thumb, the distance between the scale and the sensing head is half a pole pitch. Using a scale with 5 mm pole pitch means, that the distance between the sensing head and scale must be smaller than 2.5 mm. This distance can be air, but it could also any paramagnetic material such as most fluids.
Reading in dirty environment
In many applications, dirt, dust or sprinkles of liquid will accumulate on scales. The magnetic scale can be read regardless of these disturbances, since only the magnetic field is used for the sensor.
Adapting the scale to different geometries
Magnetic scales can be produced to any length with different scale width.