Force Sensitive Resistor
Introduction Force Sensitive Resistor:
A force sensitive resistor is a type of variable resistor whose resistance decreases when the applied force increases. Force sensitive resistors are also known as force sensing resistors, FSR, force sensor, or pressure sensor.The force sensitive resistor consists of conductive polymer whose resistance changes when the force is applied. It is normally supplied as polymer sheet or ink that can be applied by a technique called screen-printing. Screen-printing is a technique used to transfer ink into a substrate.
The sensing film consists of both electrically non-conducting and conducting particles suspended in matrix. When the force is applied, the sensing film causes particles to touch the conducting electrodes. As a result, the resistance of the film decreases.The resistance of the force sensitive resistor is depends on the amount of force applied. If large amount of force is applied, the resistance of the force sensitive resistor decreases and provides low resistance to the electric current. On the other hand, if little force or no force is applied to the force sensitive resistor, the resistance remains same and provides high resistance to the electric current.
Spceifications:
-
The maximum current is: 1 mA/Cm
-
FSR must be from : 20-100 g
-
The operating temperature is from : 30v
Circuit Operation:
A force sensing resistor senses the force applied to it and correspondingly changes its resistance. The resistance is inversely proportional to force. This means when the applied force high, it reduces its resistance and vice-versa.The “force sensing resistor” or FSR is not an ideal term, since it is actually sensing the pressure and the output is dependent on the pressure on the surface of the resistor. The more appropriate name would be pressure-sensitive resistor. But force-sensing resistor became common term to refer it.
It has a wide range of resistance, it can vary from few ohm to >1M ohm. An unloaded FSR would have around 1M ohm and fully loaded would have around few ohm resistance.The force-sensing resistor comes in various shapes; the common shapes are circle and square. It can sense weight ranging from 100g to 10Kg. The major disadvantage is that, it is not very accurate and has very high tolerance value. The accuracy reduces overtime due to usage. But it is reliable enough to be used for hobby projects and non critical industrial measurements.
The force sensing resistor consists of three layers: an active area, plastic spacer and conductive film.The active area where the force is applied, the plastic spacer which isolates the two layers and an air vent is provided for discharge of air bubbles. The accumulation of air bubble leads to unreliable results.The conducting film consists of both electric and dielectric particles which are suspended in matrix form.When force is applied it changes its resistance in predictable manner. These are microscopic particles ranges few micrometers. The conductive film is basically a kind of an ink coated on plastic film. When pressure is applied the conducting particles come close together and reduce resistance and vice-vers.
The contact resistance takes place between the sensor electrodes and the conductive particles, and between neighboring particles, but for simplicity, the sketch from Figure 1a only shows the former scenario. The particles shown in Figure 1a may be formed by nanoparticle agglomerates that behave as greater-microscopic-particles. These neighboring nanoparticles also exhibit contact resistance among them.Both resistances, Ribulk and Ric, are stress-dependent but only Ribulk is modified by the driving voltage (VFSR). A detailed discussion on the tunneling resistance, Ribulk, is later addressed in Section 2.1 Conversely, the contact resistance, Ric, only depends on the physical constriction occurring at the interface between two materials, and therefore, Ric is voltage-independent. Computer simulations and experimental results have demonstrated the validity of the authors’ model in that it is able to predict a lower drift error for incremental values of VFSR [20]. This implies that the drift error can be minimized by trimming VFSR in the driving circuit. Note that this is opposed to what the manufacturers of FSRs have stated in their product datasheets [11,12,13], i.e., a constant drift error regardless of VFSR.
The development of a physical model for the current conduction of FSRs is of paramount importance for the definition of strategies that enhance the accuracy of such devices; this can be done in a two-folded strategy. From the standpoint of a nanocomposite designer, the physical model provides a full overview of the design parameters that impact the FSRs’ performance the most. For instance, it may be interesting to simulate—prior to assembly—the influence of choosing carbon black or metallic particles as the nanocomposite filler. Multiple simulations can be performed with a wide range of design parameters, such as the mass ratio of nanoparticles to polymer, the type of polymer, the particles’ dimensions and shape, etc. From the standpoint of a final user, the physical model aims to design the most appropriate driving circuit that maximizes the sensors’ performance. Based on the latter statement, the target of this study is to design and test a driving circuit that minimizes—or even removes—most of the error sources of FSRs, where drift, hysteresis, and sensitivity degradation are the most important error sources.
Read Also:
How the Force Sensitive Resistor] Work:
The FSR is made of 2 layers separated by a spacer. The more one presses, the more of those Active Element dots touch the semiconductor and that makes the resistance go down. FSRs are basically a resistor that changes its resistive value (in ohms O) depending on how much it is pressed.It converts an input mechanical force such as load, weight, tension, compression or pressure into another physical variable, in this case, into an electrical output signal that can be measured, converted and standardized. As the force applied to the force sensor increases, the electrical signal changes proportionally.Force-sensitive resistors, commonly referred to as FSRs, are a versatile and cost-effective sensor technology used in a wide range of applications. They are particularly popular for their ability to detect the presence and magnitude of force or pressure applied to their sensing area.
This article will provide an in-depth look at FSR technology, its working principles, and the advantages and The working principle of an FSR is based on the piezoresistive effect, which is the change in electrical resistance that occurs in certain materials when subjected to mechanical stress. The FSR consists of two primary layers: the conductive layer, which contains conductive particles such as silver or carbon, and the resistive layer, which contains particles of a resistive material like a polymer. When force is applied to the sensor, the conductive particles move closer together, creating more pathways for electrical current to flow, thus decreasing the overall resistance of the sensor.
The change in resistance can be measured using a simple voltage divider circuit, where the FSR is connected in series with a known resistor. As the resistance of the FSR changes, the voltage across it also changes, providing an electrical signal that can be used to determine the applied force. This signal can then be fed into a microcontroller or other processing unit for further analysis or control purposes.
Frequently Asked Questions
What is the principle of force-sensitive resistor?
A force-sensing resistor is a material whose resistance changes when a force, pressure or mechanical stress is applied. They are also known as force-sensitive resistor and are sometimes referred to by the initialism FSR.
.What is the latest FSR?
FSR 2, our next-level temporal upscaling technology, is designed to deliver similar or better than native image quality and boosts framerates in supported games across a wide range of products and platforms.
What is FSR full form?
Financial Stability Report (FSR) is a biannual report released by the Reserve Bank of India (RBI). The FSR reflects the collective assessment of the Sub-Committee of the Financial Stability and Development Council (FSDC) on risks to financial stability, as also the resilience of the financial system.
What sensor detects force?
Force Sensors detect and respond to the presence or a change in the amount of pressure on their actuator, which can be a ball, button, diaphragm, flat membrane, plunger, or pushbutton. The three sensor types are force sensing resistor, load cell, and resistive.
What is a force probe?
The force sensors essentially measure the deformation of an elastic support subject to the force: the elastic constant (k) of the substrate that connects applied force (F) and supports displacement (s) through Hooke's law F = k's, to establish the sensor's sensitivity and range.
