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[[Quadrature]] encoders are nowadays the most common feedback device type in servo motors. Quadrature encoders are incremental sensors so they require position zeroing/homing to get absolute position feedback. | [[Quadrature]] encoders are nowadays the most common feedback device type in servo motors. Quadrature encoders are incremental sensors so they require position zeroing/homing to get absolute position feedback. | ||
| − | Another type of encoder is ''absolute encoder''. Absolute encoders typically output serial data of absolute position thus they may not need to be zeroed | + | Another type of encoder is ''absolute encoder''. Absolute encoders typically output serial data of absolute position thus they may not need to be zeroed. The drawback of absolute sensors is higher price and lower compatibility & interchangeability. |
| − | + | ===Resolver/synchro=== | |
| − | + | Resolver is an analog technology based on rotary transformer that can provide absolute position (single turn absolute, for multiturn absolute position zeroing is still needed). Resolvers are good for harsh conditions but don't provide as high precision as encoders. | |
| − | ===Resolver | + | |
| − | Resolver is an analog technology based on rotary transformer that can provide absolute position (single turn absolute, for multiturn absolute position zeroing is still needed). Resolvers are good for harsh conditions but | + | |
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===Tachometer=== | ===Tachometer=== | ||
| − | Tachometer is a small DC generator that outputs DC voltage proportional to rotation speed. It can be used as velocity feedback device but not as position sensor. Tachometers are often seen in dual-loop configurations | + | Tachometer is a small DC generator that outputs DC voltage proportional to rotation speed. It can be used as velocity feedback device but not as position sensor. Tachometers are often seen in dual-loop configurations with position sensor. |
===Hall sensors=== | ===Hall sensors=== | ||
| − | Hall sensors are | + | Hall sensors are found in AC & BLDC motors only. Halls provide commutation information (drive current phase angle) for drive. Modern drives such as all GD drives don't require Hall sensors but can utilize them to make faster power-up possible. Hall sensors are too low resolution for position or high performance velocity control. |
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==Comparison== | ==Comparison== | ||
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| Absolute encoder | | Absolute encoder | ||
| Medium | | Medium | ||
| − | | Serial | + | | Serial, [http://en.wikipedia.org/wiki/Gray_code Gray signals] |
| Yes (single or multiturn) | | Yes (single or multiturn) | ||
| Medium to very high | | Medium to very high | ||
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==See also== | ==See also== | ||
*[[Motor types]] | *[[Motor types]] | ||
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