Capacitive Sensing: A New Technology in Linear Position Sensors

With the various functions that a linear position sensor delivers, innovators have developed more and more types to address the diverse needs of users further when it comes to technology. Linear position sensors are usually bought from manufacturing companies and are used to detect linear movement that then helps in the laboratory and industrial automation. Now, it does more than that. Linear position sensors do capacitive sensing.

What is capacitive sensing?

Capacitive sensing is a new technology that can detect and measure anything conductive, or can help in the continuation of the flow of electrons. More specifically, this is a measurement done by a linear position sensor called a capacitive sensor by detecting the effects on electrical fields of nearby objects. It measures the capacitance, the ability of a capacitor to store an electrical charge, produced by a body as the input.

Sensors used in this technology typically operate at ranges of one centimetre or less. At one metre, the capacitance change in the body is smaller. Capacitive sensors are made of many different materials, such as indium tin oxide (ITO), copper, and printed ink. Size and spacing of the capacitive sensor are both significant to the sensor’s performance.

How is it applied?

The measurement of brake disc deformation uses the mechanism of capacitive sensors. Brake discs are a type of car brake that uses callipers for squeezinga pair of pads against a disc that creates friction, thus allowing the car to stop. Due to the high-temperature development from the friction, very few sensors are suitable for operating close to the measurement object. Capacitive transducers detect changes in the nanometre range and measure the wear on the brake disc.

Apart from that, capacitive sensing is used in the touchscreens of digital audio players, mobile phones, and tablet computers for input detection. Capacitive sensors have long replaced mechanical buttons. Most smartphones do not even use buttons but rather a touchscreen – all thanks to capacitive sensing. Laptops do not use a computer mouse now, as trackpads that run on capacitive sensing continue to replace them.

Surprisingly, to detect threatening objects hidden in shoes, envelopes or small parcels, different capacitive sensor arrays have been designed and manufactured using printed circuit boards (PCBs). On the other hand, an older application of capacitive sensing is a computer graphic input tablet manufactured by Shintron Co., Concord, Massachusetts. The said company developed the tablet in 1967, but the company and researchers from all over still use the principles of its operation today.

Certainly, linear position sensors have evolved since their creation way back then. Aside from just being used in automation, linear position sensors now serve electronic devices that we use daily like smartphones, tablets, and laptops. And these are all due to this new technology of capacitive sensing. In addition to the current applications, adding more significant contributions to technology is highly likely. Innovators are encouraged to explore this field of electronics more.

How capacitive sensors differ from inductive sensors?

In most industrial applications of a capacitive sensor, it is often equated to inductive sensors because of the similarities in function. But when compared closely, a capacitive sensor differs from an inductive sensor in operating parameters and certain design principles.

The standard design of a capacitive sensor is cylindrical containing electrodes and wirings. The capacitive principle allows the device to detect minute objects and is compatible with both insulating and conductive materials. In proximity sensor applications, the output of a capacitive sensor is in pulses or contact closure, which is activated as the object reaches a specific distance within the sensor’s measurement range.

Features of capacitive sensors

Hysteresis is an essential principle in the function of a capacitive sensor. To determine hysteresis, you need to get the difference between the distance of the target and the sensing face of the device, as well as the difference between the target’s release distance and the device’s sensing face.

The following notable features should be observed in distinguishing a capacitive sensor from other types of sensors:

  • Capacitive sensors can detect non-metallic objects
  • Unlike a mechanical limit switch, capacitive sensors can detect minute and lightweight objects.
  • Capacitive sensors produce output in a solid state which does not bounce the corresponding contact signal.
  • Capacitive sensors are suitable for counting applications because it reacts quickly and has a high switching rate.
  • Long lifespan
  • Ideal for detecting liquid targets but limited only when the liquid passes through specific barriers.

Overall, capacitive sensors are highly versatile and useful for a variety of laboratory and industrial applications. Along with inductive sensors, capacitive sensors are some of the most commonly used sensing devices in manufacturing consumer products. Nevertheless, if the application is exposed to high levels of moisture and humidity, the sensor’s performance will be affected negatively. Furthermore, capacitive sensors also require a broad sensing field for effective detection.

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