Guide · 6 min read · Updated October 2026

Encoder, resolver or Hall sensor: how each works and how each fails

Every brushless servo or BLDC motor needs to know where its rotor is. Three kinds of device do that job: Hall sensors, encoders and resolvers. They fail in different ways, and knowing which one your motor has tells you what to check first.

By Suresh Sankaran, founder of Star Automations, servo motor repair since 1998.

01Compare

The three at a glance

	Hall sensors	Encoder	Resolver
What it is	Three magnetic switches	Optical or magnetic disc read by electronics	Rotary transformer, no electronics
What it gives	Six positions per electrical cycle	Thousands to millions of positions per turn	Continuous sine and cosine of the angle
Typical use	BLDC fans, pumps, EV hub motors	Servo motors on machines and robots	Hot, vibrating or high-reliability axes
Typical faults	Failed sensor, board shifted, wrong 60/120° setting	Contamination, LED or chip failure, data errors, lost memory, battery loss	Open winding, insulation breakdown, slipped stator
First check	Watch the three outputs while turning the shaft	Encoder supply, cable and drive alarm code	Winding resistance and insulation

02Encoders

Encoder types you will meet

Incremental A, B and Z, often with U, V and W commutation tracks
Incremental 1 Vpp sine and cosine, such as Heidenhain ERN 1387
Serial absolute, single-turn or multi-turn: Fanuc, Mitsubishi, Tamagawa, Yaskawa, Sanyo Denki
Open-standard serial: EnDat, Hiperface, SSI, BiSS
Multi-turn absolute types that keep the turn count with a battery or a gear stage

03Resolvers

Why resolvers are still used

A resolver has no LED, no chip and no glass disc. It tolerates heat, shock and coolant better than an encoder, which is why it survives on presses, robots and older drives. The trade-off is lower accuracy and the need for a resolver-to-digital converter in the drive.

04Hall sensors

Hall sensors in BLDC motors

Hall sensors give only six positions per electrical cycle, which is enough to switch a BLDC motor's phases but not enough for precise positioning. They are cheap and simple, and the most common fault is not a dead sensor but a Hall board fitted a few degrees off after a repair.

05Help

When to send it to us

If you are not sure which feedback your motor has, the nameplate and the number of pins on the feedback connector are usually enough for us to tell. Send the nameplate or WhatsApp +91 97866 22233. Related: encoder repair, resolver repair, Hall sensors.

Free downloads for your maintenance file

Printable one-page sheets from our bench. More on the resources page.

Motor feedback selection guide

For motor makers and machine builders: Hall sensors, incremental encoders, absolute encoders and resolvers compared on cost, resolution, temperature, noise immunity and drive compatibility.

PDF · 1 page · 4 KB · free, no sign-up

Download PDF

Servo motor encoder quick reference

Encoder families, interfaces, counts per revolution and the motors they sit on: Fanuc pulsecoders (alpha A64, A1000), Mitsubishi OBA/OSA, Yaskawa UTOPH, Tamagawa, Heidenhain ECN/EQN/ERN and SICK SKS/SRS/SRM.

PDF · 2 pages · 8 KB · free, no sign-up