Position and Rotation Sensors: 8 Myths Technicians Still Believe

POSITION & ROTATION SENSORS

Position sensing has a lot of folklore. Some of it was true twenty years ago and some never was. Here are eight common beliefs and what is actually correct.

PART 6 OF 25 | 4 MIN READ | BY SUBODH RAJ

Myth 1: An encoder with more pulses is always more accurate.

Fact: Resolution is not accuracy. An encoder with 10,000 pulses per turn can still be off by several hundred pulses because of shaft eccentricity or coupling error. Accuracy comes from the whole mechanical chain, not just the disc.

Myth 2: Incremental and absolute encoders are basically the same.

Fact: An incremental encoder forgets its position when power is lost and must be homed. An absolute encoder reports a unique code for every angle and knows where it is the moment it powers up.

Myth 3: Resolvers are old technology.

Fact: They remain popular in electric vehicle motors and harsh sites because they have no electronics inside. They survive heat, shock and vibration that kill optical encoders.

Myth 4: Potentiometers are useless in industry.

Fact: They are simple, cheap and fine for slow, low-cycle jobs such as control panels and manual setpoints. The limit is wear, not capability.

Myth 5: Hall sensors cannot measure angle.

Fact: Hall and magnetic angle sensors read the direction of a magnet and give accurate angle in a small, contactless package. They are common in pedals, valves and steering.

Myth 6: Limit switches are obsolete because of proximity sensors.

Fact: Mechanical limit switches handle direct physical contact, switch real loads, and are easy to understand and fix. Many safety circuits still prefer them.

Myth 7: Any coupling will do between the shaft and the encoder.

Fact: A rigid coupling transfers misalignment into the encoder bearing and shortens its life. Use a flexible coupling, and for hollow-shaft types, use the supplied torque arm.

Myth 8: Noise problems mean the encoder is faulty.

Fact: Most encoder faults come from cable routing. Run encoder cable away from motor cables, use shielded twisted pair, and ground the shield at one end.

The 9 sensors in this part

Each card below shows the sensor in use, what it is and how it works, and where you will find it.

SENSOR 1 OF 9

Rotary Encoder

A rotary encoder is attached to a shaft and gives digital pulses as the shaft turns. By counting the pulses, the controller knows the angle, the direction and the speed. Incremental encoders give pulses, while absolute encoders give a unique code for every angle. It is used on servo motors and conveyors.

USED IN

servo motorsconveyors

SENSOR 2 OF 9

Linear Encoder

A linear encoder reads a very fine scale along a straight path and gives pulses for each small step of movement. The controller counts these pulses to know the exact position, down to micrometres. It is used on CNC machine tools and other equipment where accurate positioning is needed.

USED IN

CNC machines

SENSOR 3 OF 9

Resolver

A resolver looks like a small motor, with a rotor winding and two stator windings. As the rotor turns, it gives two analogue voltages whose values depend on the shaft angle. It has no electronics inside, so it works very reliably in heat, vibration and dirt. It is widely used in EV motors.

USED IN

EV motorsharsh environments

SENSOR 4 OF 9

Rotary Potentiometer

A rotary potentiometer has a resistive track and a wiper that turns with a shaft or knob. The output voltage changes with the angle of the shaft. It is a simple, cheap way to measure angle and is used in control panels, volume controls and simple feedback, but it wears out with use.

USED IN

control panelsvolume controls

SENSOR 5 OF 9

Linear Potentiometer

A linear potentiometer (slide type) gives a voltage that depends on the position of its slider along a resistive track. The slider is moved by the part whose position needs to be known. It is simple and cheap and used for sliders and basic position feedback, but it wears over time.

USED IN

sliderssimple position feedback

SENSOR 6 OF 9

Hall-Effect Position Sensor

A Hall-effect position sensor measures the position or angle of a magnet using a Hall chip. As the magnet moves, the magnetic field at the chip changes and so does the output voltage. It is contactless, so it does not wear out and is used in pedals, valves and throttles.

USED IN

pedalsvalves

SENSOR 7 OF 9

Magnetic Angle Sensor

A magnetic angle sensor reads the angle of a small magnet fixed on a rotating shaft. The sensor chip measures the direction of the magnetic field and gives the angle as an analogue or digital output. It is compact and contactless, so it is used in robots, steering and motor control.

USED IN

robotssteering

SENSOR 8 OF 9

Limit Switch

A limit switch is a mechanical switch with an actuator, such as a lever or plunger. When a moving part touches the actuator, the contacts change state. This tells the machine that the part has reached a limit, so it can stop or reverse. It is simple, strong and widely used for travel limits.

USED IN

machine travel limitslifts

SENSOR 9 OF 9

Inductive Position Sensor

An inductive position sensor measures the position of a metal target using the change in a coil's magnetic field. As the target moves, the coil's inductance changes, and the electronics convert it into a position signal. It is non-contact and strong, so it works well in dirty, oily or wet places such as valve actuators.

USED IN

valve actuators

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Written by Subodh Raj, EngineerX Academy. Part 6 of 25 in the Industrial Sensors series.