What Is A Position Sensor?

As one of the most diverse sensors used across a range of industries in various applications, position sensors can be used to measure either linear or rotary position using different sensing technologies. They can detect the movement of an object or determine its relative position measured from an established reference point. Position sensors can also be used to detect the absence of an object.

What are the different typs of position sensors?

Position sensors are used to detect an object and relay its position through the generation of a signal that provides positional feedback. This feedback can be used to control automated responses in a process, sound an alarm or trigger other activity determined by the specific application. The main types of position sensors come under the type of movement they measure: linear or rotary.

• Linear position sensors

Linear position sensors convert linear movements or measurements into output signals for processing. Linear position sensors can be either contacting or non-contacting.

• Rotary position sensors

Rotary position sensors convert rotary movements into output signals. Rotary position sensors can also be contacting or non-contacting. They can be single turn or multi-turn; therefore, it is crucial to understand the degree of rotation or number of turns being measured.

To ensure they are taking measurements in the most effective way for the specific application, different position sensors utilise different technologies. The primary technologies include potentiometric position sensors, inductive position sensors and draw-wire sensors.

Potentiometric position sensors

Potentiometric position sensors are resistance-based sensors that use a resistive track with a wiper that is attached to the object whose position is being monitored. Movement of the object causes the wiper to change its position along the resistance track and therefore alter the measured resistance value between the wiper position and the end of the track. The resistance measured can be used to indicate the position of the object. This technology works for both linear and rotary displacements.

Potentiometric position sensors offer relatively low cost because their technology is simple but they can be hindered by low accuracy, repeatability and size limitations as well as sensitivity to extreme temperatures.

Inductive position sensors

Inductive position sensors detect the position of an object by changes in the characteristics of a magnetic field that is induced in the coils of the sensor. A common inductive position sensor type is an LVDT (Linear Variable Differential Transformer). In an LVDT position sensor, three separate coils are wound on a hollow tube. One of these is a primary coil and the other two are secondary coils. A metal target placed into this magnetic field will induce eddy currents that oppose the magnetic field and drop the field strength to zero at the target. By being placed in different physical locations, the two receiving coils will detect a different voltage. The position of the target can be determined by calculating the ratio of the two coil voltages.

LVDT position sensors provide good accuracy and resolution, they have high sensitivity and offer good linearity across the sensing range. These sensors are frictionless and heavy-duty, making them ideal for use in conditions where they might be exposed to extreme environments. As these sensors are non-contacting, they offer a longer life but are typically high cost.

While LVDT position sensors track linear movement, an equivalent device called an RVDT (Rotary Voltage Differential Transformer) can provide tracking of the rotational position of an object. The RVDT functions identically to the LVDT and varies only in the specifics of their construction.

Draw-wire sensors

In the instance where the environment, application or installation space doesn’t permit attaching critical measuring equipment to the object, a draw-wire sensor solves the problem. Relatively simple in construction, draw-wire sensors measure linear movements using a highly flexible steel wire. The cable drum is attached to a sensor element which provides a displacement-proportional output signal. Measurements are performed with high accuracy and high dynamic response. The use of high-quality components guarantees a long service life and high operational reliability.

What are position sensors used for?

Position sensors are used in many applications across various industries including automotive, motorsport, medical, agriculture, robotics, industrial processing, mobile vehicle, test and lab applications, food and beverage, packaging, wrapping and more. Position sensors may also be used in a number of appliances in the home.

Key specifications to consider when selecting a position sensor

• Measurement range – indicates the distance range from the sensor a measured value can be obtained.
• Resolution – defines the value of the smallest position increment that the sensor can measure.
• Accuracy – a measure of the degree to which the measured position agrees with the actual position of the object being measured.
• Repeatability – reflects the range of values obtained for the measured position when the sensor performs an identical measurement over time.
• Linearity – the extent of deviation from linear behaviour of the output signal measured over the range of output for the sensor.

Other selection considerations for position sensors include:

• The size and weight of the sensor
• Whether the sensor provides absolute or incremental position information
• The operating temperature range for the device
• The sensor’s ability to withstand extreme environmental and operating conditions
• Ease of installation
• The initial cost

Talk to the sensor experts

Additional performance of a system can be revealed by the right sensor, but there are many factors to be considered and therefore it is important to be clear about what the sensor is required to do.

As industry leaders, Applied Measurement specialise in and supply both contact and non-contact options to support different applications. We have been providing innovative and effective solutions for applications that involve measurement of physical parameters since 1976. We have the experience and expertise to supply the correct sensor for your application.

To discuss sensor solutions, talk to the sensor experts today!