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It is hard to imagine the tremendous role that sensors play in our daily lives. They have become a part of our day-to-day activities. We come across various types of sensors in our homes, offices, shopping malls, etc.
These sensors have made our life easier by adjusting the room temperature, opening the garage door when the car is near, detecting smoke and toxic gases, making coffee or even turning the lights on as we enter the room are just a few instances.
What are Sensors?
It is a device which has the ability to detect and measure a physical quantity and convert the measurement into a signal which can be read. The physical quantity which is the input can be heat, light, pressure, moisture, etc and the output is a human readable signal. Some of the criteria which have to be considered while choosing sensors are accuracy, environmental condition, range, resolution, and cost.
Types of Sensors
Sensors can be categorized on the basis of different signals it can detect. Some of them are active and passive sensors; analog and digital sensors; temperature, proximity, infra-red, ultrasonic, pressure, gas and touch sensors. Some of the commonly used sensors are described below.
Active and Passive Sensor
Active sensors are the sensors where an external excitation signal or a power signal is required. In passive sensors, the external excitation signal is not required it directly generates output response.
Analog and Digital Sensor
Analog sensors give an analog output whereas digital sensors work with digital data. The analog output is a continuous output signal with respect to the quantity which is being measured.
Temperature sensor is one of the most popular and common sensor. This sensor measures the changes in temperature which corresponds to change in its physical property like voltage or resistance. These sensors are used in mobile phones, computer, automobiles, industries, air conditioning systems, etc. Thermocouples, Thermistors, Resistive Temperature Devices (RTD) and Temperature Sensors ICs are a few kinds of temperature sensors usually used.
Touch sensors are one of the simplest and useful sensors. These sensors detect touch, force or pressure and are also known as tactile sensors. Touch sensor behaves like a simple switch i.e., a current flows when there is a contact with the touch sensor and when the contact is released the circuit is open and no current flows. These sensors have application in mobile phones, remote controls, control panels, and many others.
Touch sensors are further categorized into capacitive touch sensors and resistive touch sensors. Capacitive touch sensors measure the capacitance and they are robust, durable and have smart product design. These sensors do not have any moving parts and are more durable than their mechanical counterparts. These are mostly used in portable devices like mobile phones, home appliances, automotive and industrial applications. Resistive touch sensors sense the pressure on the surface and can be used with non-conducting materials like stylus or glove finger. They have simple control circuits and are more durable than the capacitive touch sensor.
Proximity sensor detects the presence of an object without any physical contact with the object. These sensors find application in cars as parking sensors, ground proximity in aircrafts, object alignment in industries, mobile phones, manufacturing systems and many others. These sensors are highly reliable and durable as it does not contain any mechanical parts. Proximity sensors can be applied using various techniques like ultrasonic, capacitive, optical, Hall Effect, etc.
Infrared (IR) sensor detects infrared radiation to sense its surroundings. It is a light based sensor and there are two types: transmissive type and reflective type IR sensor.
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In the transmissive type, the transmitter and the receiver are placed facing each other. The sensor detects the object when it passes between the transmitter and the receiver. On the other hand, in reflective type the transmitter and the receiver are placed adjacent to each other. The sensor detects the object when it comes in front of the sensor. Some of the applications of IR sensors are as proximity sensors in mobile phones, automobiles, robots, industrial assembly, etc.
Ultrasonic sensor measures the distance and the velocity of the object. It is a non-contact type of sensor which senses the sound waves, whose frequency is greater than that of the human audible range. It uses the time of flight of the sound wave to measure the distance of the object and Doppler shift property to measure the velocity of the object. This sensor is mainly used by the ships and submarines.
Pressure sensor senses pressure and converts it into electrical signal. The magnitude of the electrical signal depends on the applied pressure. Pressure sensors have application in automotive industry, touch screen devices, biomedical instrumentation, aviation, marine industry, air conditioning, hydraulic measurement, and many more. In automotive industry, the pressure sensor monitors the oil and coolant pressure. It also regulates the power that the engine should deliver whenever the brake or accelerator is applied.
Whenever high pressure is experienced by the vehicle, the air bag system gets activated to ensure the safety of the passengers. In biomedical instrumentation, the blood pressure monitors and ventilators use pressure sensors to optimize the parameters according to the patient’s requirement and health. In aviation industry, the pressure sensors are needed to maintain a balance between the atmospheric pressure and control system of the airplanes. The air pressure is maintained inside the airplane to provide normal breathing condition.
Sources and Further Reading