resistive Sensing: Definition, Examples & Sensors

Resistive sensing is one of the most fundamental and simple techniques for transforming forces of the physical world into electrical signals. Therefore, it is one of the most common sensing principles used in modern electronics. There is a high chance that resistive sensors are integrated into any of your electronic devices.

What is Resistive Sensing?

Resistive sensing is one of the most fundamental and simple techniques for transforming forces of the physical world into electrical signals. Therefore, it is one of the most common sensing principles used in modern electronics. There is a high chance that resistive sensors are integrated into any of your electronic devices.

Due to the simplicity of their working principle, these sensors are used in:

  • Consumer electronics

  • Modern consumer wearables

  • Smart power tools and other equipment

  • Electronic medical equipment

  • Presence detection in seats

  • Industrial Human Machine Interface (HMI)

  • Automotive HMI

The main benefits of these types of sensors are:

  • Small size

  • Easy to integrate

  • Simple readout electronics

  • Flexibility

  • Cost

The Science of Resistive Sensing

Resistive sensing is based on the conceptof electrical resistance, which in simple terms means how easily electriccharges can move through a component in an electric circuit. This depends inboth the geometrical dimensions as well as the material of the component.Therefore the resistance  can be described with the formula

Where ρ is the specific electric resistance of the material, l is the length of the component and A is the cross-section area of the component. Changing any of these quantities will change the electrical resistance of the components. While changing the specific electric resistance is technically difficult. When force is applied on a force-sensing resistor the contact area between the sensing layer and the electrodes increases or decreases directly proportional to the force, which therefore increases or decreases A in the formula.

How is this helpful? In 1827 German physicist and mathematician Georg Simon Ohm discovered that when applying a voltage to a circuit if the resistance (in his case the length l of the cable) increased or decreased the current would respectively increase or decrease. Therefore, Ohm’s law was born: V=R∙I . With this relationship we can measure the changes in the drop of voltage across the sensor when its resistance changes.

How can you read out resistive sensors?

FSR elements can be read out from an electronic circuit by applying a constant driving voltage to one line and measuring the current passing through the connecting element. This current is further digitized for processing in a microcontroller. There are different electric circuits that allow for the measurement of the resistive sensor.

Voltage divider

A voltage divider configuration is the simplest readout circuit to determine sensor resistance. Given that Rref and Vin are known when applying a constant voltage to the circuit, the resistance Rsens can be calculated by measuring the voltage drop Vout across the reference resistor Rref.

The output voltage can be expressed as:

Transimpedanceamplifier (I-V converter)

A transimpedance amplifier (TIA) converts the current flowing through the sensor (Vin/Rsens) to a voltage signal (Vout), providing a more ideal transfer function than a voltage divider.

Under the assumption of an ideal op-amp, the output voltage is calculated as:

Example Applications of Force Sensing Resistors

The Force Sensing Resistor is a versatile piece of equipment that is exceptionally good for human-machine interface applications. They are also good for IoT devices, meaning that they can enable smarter edge computing applications. This means that they can transform analog devices into digital ones. An example of this would be traditional touch devices that don't have a lot of sensitivity. These devices can be upgraded to improve how sensitive they are by using this sensor.

In automotive applications, these sensors are excellent for touch surfaces where plainly capacitive elements are not enough. In comparison to capacitive sensors, they enable efficient human interaction with less influence of environmental conditions, allowing you to have more options in front of the driver. On top of that, many of the pressure, temperature, and flow sensors inside the car use resistive sensing at a fundamental level. These sensors are made bulky because they require this functionality in such environment, but they don't necessarily have to be that way. Currently a new generation of resistive sensors is being developed, which are smaller, more affordable, and faster to manufacture.

In the robotics field, these resistive sensors are useful for creating human-machine interaction and sensors with gripping handles. They are also valuable for collision detection, as they enable the robot to know when they have contacted a surface or any physical object.

The Innovative tacterion Resistive Sensor

plyon - a flexible sensor technology for proximity, touch, and force detection

Proprietary force sensors - plyon®’s thin and durable sensor architecture differentiates itself with its excellent signal integrity under bending - the perfect fit for the application

One of the best innovations in resistive sensing come from tacterion. Their new sensor is called plyon®, which enables you to apply resistive and capacitive measurements to give you the best of both worlds. It is thin and durable, and it provides a simple interface to process its signals relatively easily, which is one of its major advantages. The Plyon sensor is quite inexpensive and has great characteristics such as its TrueZero capability, meaning it is flexible and does not lose signal integrity on bending up to a radius of 1 cm. You can integrate this sensor into flexible screens, making it perfect for integration in your applications.

The other great benefit of this technology is the data processing capability you get. The electronics interface is quite easy to use, meaning you won't have to worry about the signal processing side of the sensor. You can integrate it into your robotics, hand tools, touchscreens, and even your automobile. There is no limit to what you can do, and it will be dependent on your imagination. Best of all, these sensors are easy to manufacture and quite affordable, which means you don't have to increase unit costs, and you don't have to worry about how much it will cost to add next-level tactile technology to your device.

The final benefit of this device is how robust it is. Traditional resistive sensors can be affected by humidity, moisture, and other contaminants on the surface. This typically degrades performance, meaning you get outputs with more errors. However, the plyon® sensor includes technology to read signals accurately while dealing with the problems from nonideal environmental conditions. Moreover, the sensor is robust enough to also resist very high amounts of strain much above its sensitive range before they are damaged.

The signal processing capability of tacterion’s electronics and software is also extremely effective. It even adds the power of artificial intelligence and machine learning as well as traditional signal processing algorithms to enable personalization on a level never seen before. It makes resistive sensors even smarter, and they are perfect for the future of modern smart devices that will need the benefits you get from machine learning and artificial intelligence.

tacterion was founded in 2015 as a spin-off of the German Aerospace Center.

The unique force and touch sensor technology plyon® was developed as a sensor-skin for robotics which provides the sense of touch to products and machines. With a team of world class engineers, software developers, data scientists and industrial designers, tacterion develops smart surface solutions and smart components to enable the next generation of interactive and responsive products in the field of interactive handlebars, industrial robotics, and consumer electronics. Together with its clients tacterion enables the tactile internet of the future.

Frequently Asked Questions

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