Nidec Industrial Solutions offers both encoders and resolvers.
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.
Encoders are typically powered with simple DC voltage.
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.
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.
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:
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.
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.