Encoders vs. Resolvers

Nidec offers both Encoders and Resolvers.

How are incremental encoders different than resolvers?

Output Signal

Incremental vs. Absolute Encoders 

Encoders produce pulses indicating movement over a short distance; counting these pulses indicates distance (and speed over time) and checking the order of pulses in channel A vs. channel B indicates direction (quadrature).

Resolvers produce a set of sine/cosine waves (analog voltage) indicating absolute position within a single revolution; these signals are typically converted with a resolver interface board to a digital signal.

Input Signal

Encoders are typically powered with simple DC voltage.

Incremental vs. Absolute EncodersIncremental vs. Absolute Encoders

Resolvers are "excited" by an AC reference sine wave, typically created with a dedicated resolver power supply; this power supply is typically powered with simple DC voltage.

Location of Electronics

Incremental vs. Absolute Encoders Incremental vs. Absolute Encoders

Encoders typically have all their electronics onboard, minimizing interconnections, but limiting operating temperatures.

Resolver systems typically mount the resolver power supply and resolver interface board near the input device, requiring substantial inter-device wiring, but allowing the resolver to withstand higher temperature environments.

Typical Applications

Encoder Applications:

  • AC Induction Motor Speed and Position Control
  • DC Motor Speed and Position Control
  • AC & DC Servo Motors (with commutation tracks added)

Resolver Applications

  • Permanent Magnet (PM) Motor Commutation and Speed Control
  • AC & DC Servo Motor Commutation and Speed Control

Can I replace a Resolver with an Encoder?

For existing installations, encoders can only replace resolvers if the input device (drive, PLC, etc.) can accept encoder quadrature input signals as an alternative to resolver input.

For new installations, encoders can replace all resolvers except under the following situations:

  • The environment is below -40°F/-40°C or above 212°F/100°C ambient
  • The input device cannot accept encoder signals
  • The input device requires absolute position feedback

Virtually all modern AC and DC drives can use encoders for feedback; very few can use resolvers. Most servo and permanent magnet motor drives can use resolvers and encoders.

Can I replace an Encoder with a Resolver?

For existing and new installations, resolvers can only replace encoders if the input device (drive, PLC, etc.) can accept resolver sine/cosine input signals as an alternative to encoder pulse input.