According to [Lee Teschler], The classic representation of encoders showing code rings is outdated. His post states that most industries use a special magnetic sensor known as Wigand to control the cost of the absolute encoder. He teardown an encoder created by Nidec Avtron Automation for display and if you’ve ever wondered what’s inside something like this, you enjoyed the post.
This is a large industrial unit and when you open it, you get a glimpse. Most of the inside is empty! Inside there is a very small encoder. The core body protects the inside and holds the large bearings. The original encoder looks more like a toy car motor than anything else.
The inner can is also almost empty. But it is part of our interest. Here is a Melexis Hall effect sensor Weigand Wire Hall is a special magnetic wire that has an outer sheath which is resistant to its magnetic field reversal and an inner core which is not. Until an applied magnetic field reaches a certain force, the wire will remain magnetic on one side. When the field exceeds the threshold, the magnetic polarity of the whole wire changes rapidly. The effect is independent of the rate of change of the applied magnetic field.
In other words, like the old original memory, the wire has strong magnetic hysteresis. From the data from the Weigand cable pulse and the Hall effect sensor, you can accurately determine the location of the trench.
It always amazes us how many modern gears are now mostly empty The size of the device is driven by physical limitations and not the electronics inside.