Edited by Zak Khan || Multi-turn measuring encoders are absolute encoders that can count multiple turns. Three main technologies enable such encoder design — batteries, gearing, and self-powering setups. Batteries and gears are traditional implementations of multi-turn technology; self-powering setups are newer.
Batteries: Simple but incur replacement costs
Batteries maintain power supply even during machine shutdowns to keep track of multiple turns. In other words, power to the encoder is constant so all turns are tracked. The main caveat is that batteries wear out and require replacement and disposal. So, there’s more regular maintenance and expense.
Gears: Proven technology, but sometimes costly
Gears are mechanical devices that allow tracking of multiple turns. One train of gears fitted with feedback can mechanically describe an encoder’s unique turn count. The gear positions are tracked by optical, electric or magnetic means. Gears don’t need regular replacement, but still wear out. They can also be expensive and relatively bulky.
Self-powering: No wear but less tested
Self-powering multi-turn encoders use the Wiegand effect. The Wiegand effect occurs in specialty wire engineered with an alloy called Vicalloy.
During manufacture, a machine repeatedly twists the wire until it exhibits quantum magnetic properties. When a magnet comes near a Wiegand wire, it rapidly switches its magnetic polarization. Because the switching is so fast, it produces usable voltage.
Wiegand-effect multi-turn encoders harness this voltage and require no outside voltage from batteries or gearheads. Rather, they supply their own power to keep track of multiple turns.
This greatly increases longevity and reduces maintenance and upkeep expenses. The Wiegand wire was patented and as such had royalties associated with it. Now that the patent has expired, however, it is seeing increasing usage in encoders.
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