Linear Technology Mechanical limit switches
Robust, directly switching end-position detection – proven and simple, with no auxiliary power at the switching point. The classic choice for "open/closed".
Knowledge · Control & feedback
Control and feedback for electric linear actuators
Which feedback options and interfaces are possible with an electric linear actuator – and when do they become relevant? This page brings together end positions, position feedback, motion control and the control-open interface. The guiding idea: feedback is derived from the machine function, not from an accessory list.
In brief
End positions, position feedback, force control and synchronisation are not a fixed add-on list; they follow from what the machine reliably needs. S+R supplies the mechanics with motor and a defined electrical interface at the terminal box – the control system remains control-open with you. You do not have to specify the sensors in advance: describe the function and your control environment, and S+R classifies the rest.
Principle
Why feedback is derived from the machine function.
Limit switches, potentiometers, encoders or positioning control are not "more equipment" but part of the function. What matters is which position, end limit, force limitation or synchronisation the machine reliably needs.
That is why sizing the control system does not start with a sensor list but with the task: what should be detected, held, controlled or reported? From this function follow the sensor type, signal type and interface – not the other way around. A rough description of the motion and the existing control system is enough to get started; S+R then clarifies the exact feedback and connection.
End positions
Detect end positions reliably.
For detecting end and switching positions, various limit switches are available depending on the requirements for robustness, switching rate and safety.
Inductive limit switches
Contactless and wear-free. A good fit for high switching rates, dirt, moisture and long service life.
Safety limit switches
Additional, safety-oriented monitoring of the end position – when overtravel beyond the position must be reliably prevented.
Position
Position feedback and signal types.
When not just the end position but the actual position is needed, sensors supply the position – as an analog signal, matched to your control system.
Potentiometer
Simple, cost-effective absolute position feedback across the full stroke – sufficient for many positioning and adjustment tasks.
Encoder
Incremental or absolute, for repeatability, position control and higher dynamics – the basis for clean positioning and synchronisation.
Measuring systems
Integrated or external measuring systems for precise, robust position sensing even under harsh conditions.
0–10 V
Analog voltage signal of the actual position – widely used and easy to connect to a PLC or control system.
4–20 mA
Analog current signal of the actual position – immune to interference over longer cables, and a wire break is detectable.
Motion control
When motion needs to be controlled.
Via encoder, position control and matching drives, "travelling" becomes a controlled motion – three typical tasks.
Positioning
Repeatable approach to defined positions via encoder and position control – process-reliable instead of just "open/closed".
Synchronous control
Several actuators run synchronised – for flaps, gates and adjustments that must operate without binding.
Force control
Defined pressing, holding and actuating forces: the motion follows the process, not just a mechanical stop.
Control openness
The interface stays control-open.
S+R builds the actuator; which control system runs it remains your decision. What matters is a clearly documented interface.
Your control system stays in charge
S+R supplies the proven mechanics with motor; which control system runs them remains your decision – not tied to any control brand or generation.
Document the interface clearly
Pin assignment, signals and end positions are described cleanly, so the connection to your control system is unambiguous and traceable.
Handover at the motor terminal box
The electrical interface is the motor terminal box. The control cabinet and commissioning stay with you; a frequency inverter or servo drive is provided on request.
Decision
Typical questions before sizing.
These questions narrow down sensors, signal and interface. You do not have to answer them conclusively – a rough estimate per point is enough.
Is a limit switch enough – or do you need position feedback?
"Open/closed" gets by with limit switches. Defined intermediate positions, repeatability or synchronisation call for an encoder, potentiometer or measuring systems.
Do several actuators need to run synchronously?
Synchronisation can be engineered – important for flaps, gates and wide adjustments that must not bind.
Is a defined force needed instead of a fixed end position?
Then force control is the topic: pressing, holding or actuating force follows the process rather than a mechanical stop.
Which signal does your control system expect?
0–10 V, 4–20 mA, digital limit switches or fieldbus/servo – the interface follows your control world, not the other way around.
Where does our interface end and your control cabinet begin?
Handover at the motor terminal box; the control cabinet, wiring and commissioning remain control-open with you.
FAQ
Frequent questions on control & feedback.
Does S+R supply the complete control system?
No. S+R supplies the proven mechanics with an attached motor and a defined electrical interface at the terminal box. The control cabinet and control system remain control-open with you – a frequency inverter or servo drive is provided on request.
Do I have to specify the sensors in advance?
No. Limit switches, encoders, potentiometers or measuring systems are derived from the machine function. Describe which position, end limit or force is reliably needed – S+R classifies the selection.
0–10 V or 4–20 mA – which is better?
Both are possible. 4–20 mA is more immune to interference over longer cables and detects a wire break; 0–10 V is simple and widely used. What matters is what your control system expects.
Can several actuators travel synchronously?
Yes. Via encoder and position control, synchronisation can be engineered – typical for flaps, gates and wide adjustments that must run without binding.
What happens after the inquiry?
Outline your control environment roughly (signals, fieldbus, control cabinet). S+R clarifies the interface together with you and proposes the right feedback. The data basis is set out in the knowledge overview on sizing.
Outline your control environment – clarify the interface together.
Signals, fieldbus, control cabinet and the desired feedback in keywords are enough. S+R proposes the right sensors and defines the interface at the terminal box – control-open and traceable.