Resistive Sensors
A sensor is a device that detects physical or chemical changes including pressure, force, or an electrical quantity. Simply put, a sensor is a device that helps send a signal from an object to a human operator. After detection, the signal is sent to the processor before the sensor ultimately produces an output signal that corresponds to the input signal. A resistive sensor is an electromechanical device that converts a mechanical change into an electrical signal that can be monitored after conditioning. There are three types of resistive sensors: resistive transducers, potentiometers, and strain gauges. This blog will cover each in detail.
The most common type of resistive sensor is the resistive transducer. These devices measure temperature, pressure, displacement, force, vibrations, and more. To understand how a resistive transducer works, consider a conductor rod. They work on the principle that the conductor rod’s length is proportional to the resistance of the conductor and is inversely related to the area of the conductor. This principle is represented by the equation R=pL/A. L is the conductor length, A is the area of the conductor, p is the resistivity, and R is the resistance of the conductor. A transducer’s resistance varies based on external environmental factors as well as the physical properties of the conductor.
The most common example of a resistive transducer is the sliding contact device. In these devices, one end of the conductor is fixed while the other end is connected to a slider or a brush that moves along the length of the conductor. The slider is connected to the object whose displacement is being measured. When a force is applied to move the object, the slider also travels all along the length of the conductor. This changes the length of the conductor, which is reflected by a change in resistance of the conductor.
The second type of resistive sensor is the potentiometer. Also called a pot, this device is a variable resistor with three terminals - two fixed and one variable. In potentiometers, the current flow is controlled by manually varying the resistance. These devices carry out the function of an adjustable voltage divider. Potentiometers are passive components that work by moving a slider across the conductor. The input supply voltage is applied to the entire length of the resistor, and the output voltage is measured as a voltage drop between fixed and movable contact. The slider is adjusted manually over the resistive strip to alter the resistance value. When the resistance changes, the current flowing through the circuit also changes. In turn, according to Ohm’s law, the resistive material also changes. There are two types of potentiometers: rotary and linear.
The final resistive sensor is the strain gauge. This is a type of sensor that applies a force resulting in a change of resistance. Parameters such as force, pressure, etc. are converted into measurable electrical resistance. In a stationary object, when external forces are applied, it undergoes stress and strain. Here, stress is defined as internal resistance of the object and strain is represented by displacement and deformation. As stress is applied to the conductor, the length and area of the conductor changes, causing the resistance to change as well.
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