Sensors: An Overview

A sensor is a device that detects a physical quantity from the environment and converts it into an electrical signal that can be measured, displayed or processed. Sensors are the input components of measurement and control systems, translating the physical world into voltages, currents or digital data. The quantities they respond to are diverse, including temperature, pressure, light, force, displacement, magnetic field, humidity and the concentration of gases.

Sensors are often grouped by the physical principle they exploit. Resistive sensors change their resistance in response to a stimulus, as in strain gauges and thermistors. Capacitive sensors register changes in capacitance caused by displacement or by the presence of a material. Piezoelectric sensors generate a charge when mechanically stressed, which suits them to pressure and vibration measurement. Thermoelectric devices such as thermocouples produce a voltage from a temperature difference, while semiconductor sensors integrate the sensing element with signal-conditioning circuitry on a single chip, as in the LM75 digital temperature sensor.

Key characteristics distinguish one sensor from another: sensitivity, the range of values it can measure, accuracy, linearity, response time and resistance to drift and noise. Many practical applications combine several sensor types, for example using temperature compensation to correct a pressure reading. Understanding the underlying principle of each type, and its strengths and limitations, is essential to selecting and applying sensors correctly in electronics, instrumentation and control.

Frequently asked questions

What is the basic job of a sensor?

To convert a physical quantity, such as temperature or pressure, into an electrical signal that a circuit or instrument can measure and process.

How are sensors usually classified?

Often by the physical principle they use, such as resistive, capacitive, piezoelectric, thermoelectric or semiconductor, and by the quantity they measure.

What properties matter when choosing a sensor?

Sensitivity, measuring range, accuracy, linearity, response time and resistance to drift and noise all affect whether a sensor suits a given task.