New High-Resolution Linear Position Sensors Replace Magnetostrictive and Potentiometer Devices

By Marty Cwach, Product specialist, TURCK, Inc., Minneapolis, Minn.

Linear position sensors are used to determine the position of a mechanical, component in a broad range of applications, including medical, automotive, electrical and more. Traditional sensor types used to determine the linear position of a moveable object include magnetostrictive sensors—which measure the space from a position magnet and the head of a sensing rod through the use of magnetic signals—as well as potentiometer sensors that generate a resistance output in proportion to the position of the mechanical component. Newly designed linear position sensors now provide an accurate and robust alternative to magnetostrictive and potentiometer devices for applications including metal processing machines, rolling mills, or injection molding machines.

These linear position sensors replace magnetostrictive and potentiometer devices and deliver precise, repeatable measurements in metal-processing machines, rolling mills, or injection-molding machines.

How they work
These new linear position sensors deliver precise, repeatable measurements through the use of an inductive oscillating circuit coupling positioned between the actuator and sensor. Emitter and receiver coil systems are precisely arranged on a printed circuit board. A high frequency ac field activates the coil system and produces an inductive RLC circuit with the positioning element, also referred to as the resonator. As a result, the resonator is inductively coupled with the receiver coils. Different voltages are induced into the coils, depending on the position of the resonator, and these voltages serve as a measure for the sensor signal.

linear-position-sensor-rlc
The linear position sensors use emitter and receiver coil
systems that are activated with a high frequency ac field
and produce an inductive RLC circuit with the positioning
element (resonator).

To increase the speed and accuracy of measurement, the new linear position sensors have a coarse and a fine measuring coil system that is controlled by a micro-processor. This processor then analyzes the sensor signals to determine the position of the actuator and provides an output signal in different formats: 0 to 10 V, 4 to 20 mA, IO-Link, or SSI.

Unique advantages
Unlike potentiometers, these linear position sensors operate with no mechanical contact, reducing downtime and contributing to longer operational life. While potentiometers include an internal rod, the new linear position sensors do not require this rod, delivering a significant advantage for many space-constricted applications. The sensors are available in 10 lengths from 100 mm to 1,000 mm, and they feature rugged, extruded aluminum housings with polycarbonate inserts rated for IP67 protection. Additionally, new linear position sensors are simpler to seal and have no moving parts, providing a durable sensing approach—even in challenging environments.

The low-profile sensors feature smaller blind zones than magnetostrictive systems, providing a greater sensing area within a smaller package.

Linear position sensors are usually more accurate than magnetostrictive systems. Unlike magnetostrictive sensors, they have no magnet to attract ferrous debris, which could interfere with sensing accuracy. These linear positions sensors are also immune to stray magnetic fields, which can create issues for magnetostrictive sensors. Additionally, magnetostrictive sensors have processors and dampening electronics on each end and the overall package is lengthened. The linear position sensors are configured so that the coil system and processing electronics exist on two separate printed circuit boards and are then able to be stacked inside its housing. This provides a sensor with smaller blind zones than magnetostrictive systems—with just 29 mm on each end—allowing for a greater sensing area within a smaller package.

The new linear position sensors provide up to one µm resolution and can achieve measuring ranges between 100 mm and 1,000 mm with analog voltage/current, SSI, or I/O Link outputs. They have extremely short blind zones of only 29 mm on each side, along with a wide temperature range of -25 to 70°C. The sensors may be programmed for different measuring ranges. These versatile features paired with their high accuracy and repeatable performance make newly designed linear position sensors a suitable replacement for magnetostrictive and potentiometer devices in many applications.

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