What is a sensor and types of sensors

What is a sensor

Sensors are a device that measures the physical quantity or produces a signal relating to the quantity being measured and the physical quantities are temperature, pressure, light, current, weight…

what are the types of sensors

What are the performance characteristics of a sensor

Transfer function – it shows the functional relationship between the physical input signal and electric output signal

Sensitivity – it is the relationship between the input physical signal and output electrical signal it can be described as the ratio between the small change in electrical signal to a small change in the physical signal

Dynamic range – it is the range of input physical signal that is converted into electrical signals by the sensor and the signals outside of this range could cause inaccuracy

Uncertainty – it is the largest expected error between the actual and measured output signals

Precision – it can be considered as the reliability of the instrument. The ability of an instrument to reproduce a certain set of readings within a given accuracy

Stability – it is the ability of a sensor to give the same output when used to measure a constant input over a period of time.

Repeatability – the ability of the sensor to give the same output for repeated applications of the same input value

What is the use of a sensor in industrial automation

Sensors are devices that are capable to measure a physical quality and it will produce a signal according to the measured physical quality. This device can identify the progression in electrical, physical or other quality. According to physical quality, these sensors can provide a signal. In industrial automation, many devices can work automatically and it is with the help of the sensors.

How to select a sensor and what are their required features

  • Repeatability
  • Linearity
  • Ruggedness
  • High stability and reliability
  • Good dynamic response
  • Excellent mechanical characteristic
  • Convenient instrumentation

How to choose a sensor and what are the factors that must be considered while choosing a sensor

Environmental factors such as temperature range, humidity, corrosion, size, over-range protection, susceptibility to EM interferences, ruggedness, power consumption and self-test capability. Certain economical factors must be considered such as cost and availability. There is some required characteristic for a sensor and it should be considered they are the stability and sensitivity of the sensor, repeatability, and linearity.

**How sensors are Classified **

  • Based on signal characteristics – analog and digital
  • Based on power supply – active and passive
  • It is also classified according to the subject of measurement - acoustic, biological, chemical, electric, mechanical, optical, radiation, thermal…

Analog sensors

Its output will be proportional to the variable being measured and the output changes in a continuous way.

Digital sensors

Its output will be in digital form, a sequence of on/off signals spells out a number whose value is related to the size of the variable being measured. They are known for their accuracy and precision and does not need any converters when interfaced with a computer monitoring system.

Active sensors

This type of sensor needs an external source of excitation, resistor based sensors such as thermistors, RTD, and strain gauges are an example of active sensors, current will be passed through them and the resistance value is determined by measuring the corresponding voltage. It is a modulator so it can deliver more energy to the next stage than it draws from the measurand.

Passive sensors

The passive sensor doesn’t need an excitation system and it generates its own electrical output signal. Thermocouples and photodiodes which generate thermoelectric voltages and photocurrent are examples of passive sensors. Passive sensors are also called as self-generating sensors.

Position sensors

Position sensors are used to detect the position of an object with reference to some reference point. Potentiometers and encoders are examples of position sensors. While selecting position sensors we must consider certain things like the size of the displacement, linear or angular, the material of the measuring object. Encoders are widely used as position detectors. Potentiometers can be used for linear or rotary displacements, by converting displacement into the potential difference.

Velocity sensor

Tacho-generator is a velocity sensor it is an electromechanical generator that is capable of producing electrical power from mechanical energy mostly by the turning of a generator. Tacho-generators are mostly used to measure the speed of electric motors and engines

Light sensors

Photodiodes are light sensors which are a p-n junction diode connected in reverse bias conditions. Reverse bias junction has high resistance. Incoming lights can excite the electrons which are bounded in the crystal lattice and it can generate free electron-hole pairs in the junction, because of this the resistance drops and current increases proportional to the intensity of the light. A phototransistor is another type of light sensor when light falls on the collector-base junction reducing the junction resistance and rises the collector current which is sufficient enough for detecting its capability to convert the light energy to electrical energy is called as quantum efficiency.

Flow sensors

Flow sensors are devices that can measure the fluid flow without any discrimination in the nature of the fluid and transforms it into signals. Ultrasonic sensors are an example of a flow sensor it will measure fluid velocity by passing high-frequency sound waves through the fluid. its operation is by measuring the transmission time difference of an ultrasonic beam passed through a homogeneous fluid contained in a pipe both upstream and downstream location

Proximity sensors

The proximity switch is a non-contact switch is a proximity sensor which works on the principle of inducing changes in an electromagnetic field. Proximity sensors can detect an object which is close to it without any physical contact. The most commonly used proximity switches are inductive proximity switch and capacitive proximity switch.

Tactile sensors

Tactile sensors are devices that can measure the details from its interaction between the environment these sensors are used in robotics. Types of tactile sensors are optical, piezoelectric, resistive, capacitive and magnetic.

Vision system

Machine vision is the acquisition of the image data followed by the processing and interpretation of these data by a computer for some useful application. The operation of the machine vision is divided into three they are Image acquisition and digitization, image processing and analysis, interpretation

What are the applications of sensors

  • Sensors are used in cameras, infrared detectors, and ambient lighting applications and these sensors are light sensors
  • Many sensors are used for automotive applications in order to know the vehicle’s vibration, skid, roll…
  • Sensors are used in safety devices such as stability control and antilock braking system
  • Sensors are used in electronic devices such as cell phones
  • Sensors are used for safety purposes such as motion and vibration detection
  • Speed of an object can be detected by using a speed sensor
  • The amount of oxygen in the exhaust can be determined by using oxygen sensors
  • In order to measure the current in a transmission line magnetic sensors can be used
  • Position measurement can be done by the help of ultrasonic sensor
  • Sensors are widely used in industrial automation.