Sensors and Transducers
Due to emergence of IoT (Internet of Things) demand for sensors and transducers have increased drastically. Sensors are used throughout the industry verticals including agriculture, power sector, healthcare, automotive , telecommunications , instrumentation and more. Based on these various products have been developed which consist of sensors. To name a few sensors are in our bodies, in aeroplanes, in cellular telephones, in radios, in the chemical plants and industrial plants and more. Let us understand what is the difference between sensors and transducers.
In a common terms, sensor is basically a device which detects change in physical parameters and converts it into a signal which can be recorder or measured. For example, Thermistor which senses the change in temperature and converts it into resistance change.
The transducer is a device which converts energy in primary form into corresponding energy signal in the different form. the primary forms of energy include mechanical, electromagnetic, thermal, chemical, optical and more. As shown in the figure-1, transducer composed of a sensor and an actuator. As depicted microphone is the sensor which converts acoustic signal into electrical form which is being amplified and fed to the loudspeaker which converts electrical signal back to acoustic waves. Here louspeaker is a actuator which generates signal or the stimulus. Sensor basically detects or measures a signal or stimulus.
As we know world is moving towards having automation in all the industries including our home. Due to boom in the wireless standard compliant devices based on WiFi, Zigbee and Bluetooth home automation has become reality. Home automation relies heavily on sensors of various kinds such as proximity sensor or motion sensor, liquid level sensor, smoke sensor, magnetic sensor, temperature sensor, light sensor and more.
Types of Transducers and sensors
There are two types of transducers viz. passive transducer and self generating transducer.
Passive one requires external power source. For example condenser microphone mentioned in the figure-1 is of passive type.
The output of the passive transducer is measure of variation of parameters such as capacitance and resistance.
The self generating transducer do not need external power to function. They will produce current or voltage due to stimulation of some physical form of energy. Thermocouple is self generating type of transducer.
Sensors types are categorized based on the material and functionalities. Sensors are either organic or inorganic. Ogranic sensors are made of materials such as insulator, liquid, gas or plasma etc. Inorganic sensors are made of conductor, semiconductor or biological substances. Based on detection mechanism used in the sensors they are of various types. These include Biological sensor, chemical sensor, physical sensor, temperature sensor, electric or magnetic sensor, light sensor, radioactive sensor etc.
Physical sensors will have following conversion phenomena:
Chemical sensors will have conversion phenomena such as chemical transformation, physical transformation, electrochemical process, spectroscopy etc. Similarly biological sensors will have biochemical transformation, physical transformation, effect on test organism, spectroscopy and more.
Following table summarizes transducer types based on quantity to be measured. The table lists out sensors and actuators used along with quantity to be measured.
|Quantity to be measured||Input device(sensor)||Output device(actuator)|
|Light Level||LDR, photodiode, phototransistor, solar cell||LED and display, fiber optic, lights, lamps|
|Temperature||Thermocouple, thermostate, thermistor,RTD||Heater, Fan|
|Force or pressure||Strain gauge, load cell, pressure switch||Lifts and Jacks, vibration, electromagnetic|
|Position||Potentiometer, encoders, LVDT, reflective or slotted opto switch||Motor, solenoid, panel meter|
|Speed||Tacho generator, reflective or slotted opto coupler, doppler effect sensors||AC and DC motors, stepper motor, brake|
|Sound||Carbon microphone, piezo electric crystal||Bell, Buzzer, loudspeaker|
Sensor or transducer manufacturers
Following are the typical specifications of sensors to be considered before purchase:
• Stimulus range (span)
• Stability (short and long term)
• Speed of response
• Environmental conditions
• Overload characteristics
• Dead band
• Operating life
• Output format
The reputed manufacturers of sensors and transducers are Silicon Labs, Analog Devices and more. Refer IoT Sensors and IoT components pages for IoT compliant sensors and various IoT components and manufacturers.