Understanding How Linear Transducers Work

A displacement transducer is any device with an electromechanical working principle used in converting the motion or vibration of an object into an electrical output. Displacement transducers are generally actuating devices used in control systems, automation, and measurement. Classifying displacement transducers typically relies on the principle applied to convert the movement into a corresponding output signal.

What is a linear displacement transducer?

A transducer is a device that emits an output signal as a voltage as opposed to a transmitter that emits a current signal. The different conversion principles that categorise displacement transducers are:

• Inductive
• Electrostatic
• Magnetoelectric
• Electromagnetic

The signal emitted by these transducers may be analogue or digital.

Types of linear displacement transducers

One of the most common types of linear displacement transducer used in various applications is a linear variable differential transducer which also comes in different variations:

• Force-extended armature. This type of sensor uses an internal spring or a pneumatic force to push the sensor armature to its maximum extension. A force-extended armature is used for displacement transducers used in slow applications.
• Unguided armature. A displacement transducer using an unguided armature design has infinite resolution and is not susceptible to wear and tear.
• Captive armature. A displacement transducer with a captive armature is best for applications requiring an extended working range. A captive armature sensor design can prevent misalignment due to the guide and restraint provided by a low-friction assembly.

These design variations also determine the suitability of a linear transducer for the specifications required by the intended application.

Linear displacement transducer specifications

Selecting a linear displacement sensor usually begins by considering the following specs:

• The percentage equivalent of the sensor’s measurement deviation to actual data.
• Type of output. The sensor output type can be in frequency, current, or voltage.
• Sensor linearity refers to the maximum measurement deviation in relation to the proportion of distance measured and output distance as designated along a pre-set measurement range.
• Operating temperature. Each sensor can operate optimally within a range of temperature.

Apart from these parameters, it is also crucial to consider the sensor’s sensitivity and the corresponding interface used in interpreting the signal output.

Applications of linear displacement transducers

Linear transducers are versatile devices which are compatible with industrial applications. The following are specific applications of linear transducers.

• Hydraulic cylinders. Linear sensors used in hydraulic cylinders function as charge sensors, or as a unique external sensor subject to rugged conditions. Sensors used in hydraulic applications need to have an excellent stroke-to-length ratio and high immunity to friction, shock, and vibration.
• Machine automation. Linear transducers used in machine automation typically include a hermetic sealing for improved performance in factories, processing plants, and the mining industry.
• For most aerospace and aircraft applications, position sensors need to be compact and miniaturised. Manufacturers can custom-build displacement transducers suitable for the high-precision requirements of this industry.

Apart from the examples provided, linear transducers are also used for power turbines, power plants, and in sophisticated satellite technology. Some everyday uses of linear sensors include transportation such as cars, buses, and subway trains.