Automation Fundamentals
Measuring Angle and Travel With Simple Sensors
Understand position feedback, potentiometers and practical sensor choices.
You are applying “Measuring Angle and Travel With Simple Sensors” to a real system and need the concept, assumptions and verification boundary to stay clear.
Learn how potentiometers, incremental and absolute encoders, linear sensors and non-contact distance sensors measure motion—and how range, resolution, loading, mounting and calibration determine whether that measurement represents the real machine.
- Select or check first
- Define the required outcome, operating conditions and exact component or system boundary before choosing a part or method.
- Controlling assumption
- Sensors, controller logic, actuator limits, timing, fault response and environmental conditions are defined together.
- Top risk
- Do not use a small signal potentiometer to control actuator power. A position potentiometer is normally an information device. Respect its total dissipation, voltage, wiper-current, rotational-life and environmental ratings.
- Proof
- Check the exact manufacturer data, units and limits, then verify the result by calculation, measurement or a controlled acceptance test.
Start with the basics Optional foundation before “Measuring Angle and Travel With Simple Sensors”
Automation-and-control basics
An automatic system measures a condition, decides what it means and commands an actuator while checking whether the expected result actually happened.
- Sensor
- A sensor converts a physical condition into a signal. Its range, uncertainty, response time, environment and failure behaviour matter as much as its nominal output.
- Controller
- A controller reads inputs, applies logic or a control law and issues outputs. Software cannot correct missing measurements, inadequate hardware authority or unsafe architecture.
- Actuator
- An actuator turns a command into physical action, such as motor torque, valve position or switching. Its real limits depend on load, supply, drive and duty.
- Feedback
- Feedback compares measured behaviour with the desired state so error can be corrected. Open-loop command assumes the action occurred; closed-loop control checks it.
- Fault and safe state
- A fault is an abnormal condition that may invalidate control. The safe response must be defined from the hazard and may require independent hardware, not only software.
How to use this article: Trace one complete chain—physical condition, sensor, signal conditioning, controller, drive, actuator and feedback—then ask how each link can fail.
On this page
A controller cannot regulate the position it only assumes. Position feedback converts a mechanical quantity—angle, linear travel or distance—into an electrical value the controller can read. The sensor must measure the coordinate that matters, over the complete travel, with enough resolution and repeatability, while surviving the environment and the mechanism's real alignment errors. A precise sensor on the motor can still miss backlash or a loose coupling at the load.
Angle, travel and distance are different measurements
Diagram description
The drawing compares sensor categories conceptually. It does not specify range, accuracy, mounting geometry, environmental rating or a particular control architecture.
| Method | What it reports | Strength | Limitation to design around |
|---|---|---|---|
| Rotary potentiometer | Wiper voltage related to shaft position | Simple continuous analog signal | Contact wear, finite travel, loading and taper error |
| Linear potentiometer | Wiper voltage related to slider travel | Direct absolute travel after power-up | Mechanical contact, sealing and mounting alignment |
| Incremental encoder | Pulses as the shaft moves | High resolution and speed/direction information | Requires counting and usually a reference after power loss |
| Absolute encoder | A code for position within its stated range | Position can be available immediately | Cost, interface, multi-turn assumptions and mounting error |
| Non-contact distance sensor | Distance along a sensing path | No mechanical linkage to the target | Target reflectivity, angle, atmosphere, blind zone and field of view |
| Discrete limit switch | One position or boundary state | Simple end or home indication | Does not provide continuous position |
Omron's encoder guidance distinguishes incremental encoders, which produce pulses that a controller counts from a reference, from absolute encoders, which output a position code. That distinction is about how position information is represented—not a promise of final machine accuracy. Resolution, edge timing, missed counts, coupling eccentricity, shaft play, installation zero and the sensor's own specified error all remain in the measurement chain.
A potentiometer can turn position into a voltage ratio
Diagram description
Terminal letters are conceptual rather than product pin numbers. The displayed divider equation assumes negligible wiper loading and does not include contact resistance, end resistance or taper tolerance.
Unloaded potentiometer divider
V_out = V_in × R_bottom / (R_top + R_bottom)
This is the ideal high-impedance case. A finite controller-input resistance appears in parallel with the lower part of the track and changes the ratio. Supply variation also changes the voltage unless the ADC uses the same supply as its reference or software compensates for it.
- V_out
- wiper voltage relative to the low terminal, volts
- V_in
- voltage across the full track, volts
- R_top
- resistance from high terminal to wiper, ohms
- R_bottom
- resistance from wiper to low terminal, ohms
| Effect | What the controller sees | Useful response |
|---|---|---|
| Track taper/tolerance | Voltage ratio differs from an ideal straight line | Calibrate several known positions or use a specified precision sensor |
| Wiper contact variation | Small jumps or noise during motion | Filter only after checking wiring, wear and required response time |
| Input loading | Position-dependent ratio error | Use a sufficiently high input impedance or buffer designed for the ADC |
| Mechanical play | Sensor repeats while the load shifts | Mount at the load or characterize backlash in both directions |
| End stops | Electrical travel may not match mechanical travel | Preserve mechanical margin; do not use the pot as a hard stop |
| Open wiper/wire | Reading may float or rail | Provide bias, plausibility checks and a defined fault response |
The same component can be wired for a different job
Diagram description
The rheostat diagram is a low-power teaching configuration. Tying the wiper to one end may retain full-track resistance if the wiper opens, but it is not a safety guarantee and does not increase track or wiper current ratings.
Calibrate the complete mechanical path
Two-point linear calibration
x = x_1 + (C − C_1)(x_2 − x_1)/(C_2 − C_1)
This maps a measured ADC count or encoder count C to position x between two known points. It assumes the relation is linear over that interval. More calibration points or a fitted lookup table may be needed for nonlinear linkage geometry, taper error or non-contact sensor response. Never extrapolate beyond validated travel without an explicit policy.
- x
- estimated angle or linear position
- C
- current sensor reading
- x_1, x_2
- known reference positions
- C_1, C_2
- readings measured at those reference positions
| Check | Evidence to record |
|---|---|
| Move slowly through full intended travel | No collision, cable strain, sensor over-travel or discontinuity |
| Measure independent reference points | Calibration error at low, middle and high positions |
| Approach from both directions | Backlash, hysteresis and direction-dependent offset |
| Apply expected load and temperature range | Compliance, drift and mounting stability |
| Disconnect or short each signal safely | Fault is detected and motion response is bounded |
| Cycle power | Absolute recovery or a controlled homing/reference sequence |
The difference between commanded and measured motion is developed in Open-Loop Commands Versus Real Feedback. For mechanisms that turn motor rotation into travel, continue with Inside a Ball Screw and Lead Screw Versus Ball Screw.
Selection boundary and evidence to keep with the decision
Treat “Measuring Angle and Travel With Simple Sensors” as a selection problem, not only a definition. Record the required result, alternatives considered, the controlling assumption and the condition that would change the choice.
Keep evidence proportional to consequence: Check the exact manufacturer data, units and limits, then verify the result by calculation, measurement or a controlled acceptance test. Revisit the decision when the load, environment, duty, interface, regulation or maintenance plan changes.
One-minute questions
Questions to answer before you apply this lesson
What should I select or check first for Measuring Angle and Travel With Simple Sensors?
Define the required outcome, operating conditions and exact component or system boundary before choosing a part or method.
Which assumption can change the conclusion?
Sensors, controller logic, actuator limits, timing, fault response and environmental conditions are defined together.
What can go wrong if I copy the example directly?
Do not use a small signal potentiometer to control actuator power. A position potentiometer is normally an information device. Respect its total dissipation, voltage, wiper-current, rotational-life and environmental ratings.
How do I verify the result in the real system?
Check the exact manufacturer data, units and limits, then verify the result by calculation, measurement or a controlled acceptance test.
Sources and further reading
- Rotary Encoders Technical GuideOMRON Industrial Automation · 2026-10-13Manufacturer technical guide reviewed for rotary and linear displacement terminology, incremental pulse counting, absolute position coding, direction and sensor-selection constraints.
- The Potentiometer HandbookBourns · 2026-10-13Manufacturer handbook reviewed for potentiometer construction, resistance taper, loading, resolution, contact behavior and precision-position applications.