Linear Sensors

Things to know about displacement sensors

Guide for Linear Sensors

Linear Sensors

Linear potentiometers, magnetical and optical linear transducers and measuring probes

Our displacement sensors have an optimal focus on space-saving, robustness and precision. With our linear sensors you can measure mechanical measuring distances up to 4000 mm. A wide selection of mechanical and electrical interfaces allows the best possible constructive and electrical integration into your application.

We cover high demands in protection class, EMC, shock, hydraulic pressure (up to 350 bar), accuracy (up to 1 µm) and measuring dynamics (up to 10 m/s @ max. 100 m/s²). Each measuring principle has its own advantages, which we will determine with you during our consultation.

Only the requirements of the application determine the choice of the suitable displacement transducer. In many cases, demanding applications require technical product adaptation. MEGATRON is your specialist for this adaptation process - even for small quantities.


Guide for Linear Sensors
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Measuring principle of linear sensors

The task of displacement sensors is to convert linear movements into electrical signals. To do this, a push rod or a guided or loose actuator is used to mechanically move along the travel distance linearly. 
In the displacement transducer, the mechanical measuring path is electrically detected via a sensor element (electrical measuring path) and converted into electrical signals. The electrical signal acquisition depends on the measuring principle or sensor technology. The acquired signals are either transferred as analogue signals directly to a transducer for further processing or via an internal signal conditioning (measuring amplifier / transducer).
These signals represent the recorded measuring path. Displacement measuring systems are used in all areas of industry and medical technology. Just where linear mechanical movements are converted into electrical signals for further processing of control tasks, distance measurements and position detection.


Linear sensor technologies

For linear displacement measurement, linear sensors are available in five different measuring principles:


Potentiometric

A linear potentiometer is a passive component whose resistance value can be continuously adjusted. The wiper is guided over the resistance track, which outputs the resistance value depending on its position. The linear potentiometer has three connections for this purpose: two for the resistor and one for the pickup.
Application example: injection moulding machine, pneumatics, simple presses

  • Simple sensor principle, mostly without electronics
  • Measured value is available immediately
  • Resolution almost infinite
  • Reasonably priced and very many differentiated designs
  • Works with low voltages (hardly any power consumption)
  • But works with wear
  • Sensory characteristics change in the course of operation
  • Insensitive to magnetic interference fields

Magnetostrictive

The sensor consists of a robust housing, a waveguide inside, a permanent magnet that deflects the generated pulses and a converter that converts the returning vibrations into an electrical signal. As a result, the position of the magnet is determined by means of magnetostriction.
Application example: injection moulding machine, hydraulic cylinders, presses, tank level measurement, rolling mills.

  • Sealed sensor (high IP protection) with electronics
  • Contactless measuring principle
  • Maintenance- and wear-free
  • Durable, consistent accuracy
  • Long measuring distances up to 4000 mm
  • Insensitive to shock and vibration
  • Withstands high pressures - ideal for hydraulically moved axes
  • Insensitive to various chemical media
  • But sensitive to magnetic interference fields

Inductive (LVDT)

The LVDT is an analogue sensor in which a coil system operates - consisting of a primary coil and two secondary coils. These coils convert the linear motion into electrical signals.
Application example: probes, quality monitoring, manufacturing automation, food production

  • Sealed sensor (high IP protection) with or without electronics
  • With very good linearity
  • Recording of small measurement changes
  • Resolution almost infinite
  • Durable, consistent accuracy
  • Maintenance- and wear-free
  • Suitable for high dynamics
  • Zero point is reproducible
  • Signal output absolute
  • Insensitive to many chemical media
  • But sensitive to magnetic interference fields

Hall effect

Hall sensors use a permanent magnet placed on a moving plunger. One or more Hall ICs are located on the travel path. They measure the field strength on the path and identify the position of the magnet and thus the distance of the measuring path.
Application example: Position detection in elevators or hinges, where space is limited

  • Contactless measuring principle
  • Maintenance- and wear-free
  • Durable, consistent accuracy
  • Reliable measurement even with vibration
  • Detection of wire breaks and short circuits
  • But sensitive to magnetic interference fields

Optoelectronic

At the end of the push rod there is a glass scale. The transmitter and receiver are arranged opposite to each other. The glass scale moves between them. Electrical impulses are converted into light pulses by the transmitter and into electrical signals by the receiver. This way, a glass scale linear encoder is implemented and is the principle of this kind of sensor. The downstream amplifier compares the received signal with a predetermined switching wave. With our optical probes, exact positions can be detected.
Application example: Probes, quality monitoring, dial gauges, precision engineering

  • Precise sensor with electronics
  • Contactless measuring principle
  • Maintenance- and wear-free
  • Durable, consistent accuracy
  • Very high resolution
  • Temperature stable
  • Easy mounting
  • Insensitive to magnetic interference fields
  • But the glass scale is fragile

Technology comparison

Measurement method / Technical requirements Potentiometric LVDT Magnetostrictive Hall effect Optoelectronic
High resolution (100 μm) + + + + +
Very high resolution (1 μm) - - + + +
Operating speed 0 0 + + -
Small shape + + 0 + 0
High protection class (IP65) 0 0 + + 0
Use in magnetic field + - 0 - +
Very small measuring distances (±1 mm) - + - 0 -
Digital processing required - - - - +
Lateral forces occur (transverse) 0 0 0 - -
High measuring rate/strongly oscillating movements 0 + + + +

Electrical interfaces and signals

To serve a variety of applications in different industries, we offer displacement sensors with corresponding electrical interfaces.

Potentiometric and inductive
Our potentiometric and inductive linear sensors have also been realized with integrated electronics to simplify electronic integration. This allows direct connection to the typical analogue signals 0…5 V / ±5 V / 0…10 V / ±10 V / 0…20 mA / 4…20 mA without external amplifier.

Hall effect
Our contactless Hall sensors have an analogue output with 0.5…4.5 V. This enables wire break and short circuit detection.

Magnetostrictive
In the magnetostrictive displacement encoder, the signal processing after the travel time measurement is always integrated. The electrical connection is made via 5, 6 or 8-pin plugs with M12 or M16 screw threads. Some sensors have a potted cable with a length of one meter (standard) or on request up to 15 m.
In addition, these sensors offer analogue outputs in voltage or current for direct measurement of displacement and speed or digital outputs.

Optoelectronic
The incremental displacement measurement outputs the counting pulses in TTL, OC or LD level.


Mechanical interfaces

Guided push rod with mechanical interfaces

  • With spring return as probe
  • With ball joints - ideal for compensation of lateral misalignment
  • With threaded coupling (with or without return spring)

Loose push rod

  • Only for LVDT sensors - with threaded coupling - the application requires an appropriately matched interface. Core extensions from 50 mm to 315 mm optionally available

Guided carriage (actuator/cursor)

  • Carriage is mechanically or magnetically connected to the displacement sensor, the application requires a correspondingly matched interface

Loose carriage (actuator/cursor)

  • The carriage is moved at a defined distance above the surface of the displacement sensor, the application requires a correspondingly adapted interface

There are two types of mechanical integration of push rods in the displacement sensor:

  • The push rod is guided on both sides. This means that the push rod "projects" horizontally in both directions of the sensor housing. This offers greater robustness with miniaturized displacement sensors, because the push rod is securely guided linearly in both slide bearings. In addition, there is no need for elaborate bearing arrangements.
  • The push rod is guided on one side. This means that the push rod only protrudes on the measuring side. Bearings inside the housing give the connecting rod its stability.

Mounting

We have a wide range of accessories for installation - depending on product and application. Many accessories are already enclosed with the sensor. Please also note our information on the product data sheets.

As a general rule: Each sensor requires a clean and even support surface. For longer measuring distances, additional support should be considered to prevent deflection. Please do not apply any mechanical stress to the sensor housing.

Many sensors are already supplied with fixing clamps. Some have mounting blocks, flanges or ball joints.

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