SENSORS

What are Sensors?

Sensors are devices that provide an interface between electronic equipment and the physical world. They Help electronics to "see," "hear," "smell," "taste," and "touch" the physical world by converting input objective physical or chemical signals into electrical signals.

How are sensors classified?

• There are many sorts of categorization methods available. The most popular way is based upon the kinds of the targeted signals to be sensed. Roughly, there are six signal domains and related sensors.
  
• The thermal signal domain: the most common signals are temperature, heat flux, or heat flow. Related sensors are called thermal signal sensors.
  
• The mechanical signal domain: the most common signals are force, pressure, velocity, acceleration, and position. Related sensors are called mechanical signal sensors.
  
• The chemical signal domain: the signals are the internal quantities of the matter such as concentration of a certain material, composition, or reaction rate. Related sensors are called chemical signal sensors.
  
• The magnetic signal domain: the most common signals are magnetic field intensity, flux density, and magnetization. Related sensors are called magnetic signal sensors.
  
• The radiant signal domain: the signals are quantities of the electromagnetic waves such as intensity, wavelength, polarization, and phase. Related sensors are called radiant signal sensors.
  
• The electrical signal domain: the most signals are voltage, current, and charge. Related sensors are called electrical signal sensors.

How to Parameterize a Sensor

• Absolute sensitivity - the ratio of the change of output signal to the change of the measured (physical or chemical quantity)
  
• Relative sensitivity - the ratio of a change of the output signal to a change in the measurand normalized by the value of the output signal when the measurand is zero.
  
• Cross sensitivity - the change of the output signal caused by more than one measurand.
  
• Direction dependent sensitivity - a dependence of sensitivity on the angle between the measurand and the sensor.
  
• Resolution - the smallest detectable change in the measurand that can cause a change of the output signal.
  
• Accuracy - the ratio of maximum error of the output signal to the full-scale output signal expressed in a percentage.
  
• Linearity error - the maximum deviation of the calibration curve of the output signal from the best-fitted straight line that describes the output signal.
  
• Hysteresis - a lack of the sensor’s capability to show the same output signal at a given value of measurand regardless of the direction of the change in the measurand.
  
  
• Offset - the output signal of the sensor when measurand is zero.
  
• Noise - the random output signal not related to the measurand.
  
• Cutoff frequency - the frequency at which the output signal of the sensor drops to 70.7% of its maximum.
  
• Dynamic range - the span between the two values of the measurand (maximum and minimum) that can be measured by sensor.
  
• Operating temperature range - the range of temperature over which the output signal of the sensor remains within the specified error.

The Broad Applications of Sensors:

Factory Automation-Computer, Automobile, Environmental Monitoring, Industry Monitoring, Telecommunication, Transportation, Health Care, Space Exploration, and Military Uses indicate that sensors can be used in almost every aspect of our life.

As more and more advanced technology brings numerous opportunities for human beings to pursue better quality of life and explore new living space, the importance of accurate, reliable, fast and economic approaches to better existing technology solutions are based upon more precise control of machines and devices. Signal technology is becoming more and more crucial for all these attempts. This is the basis of a rapid boost in the sensor industry. New sensor technology brings new dimensions to emerging products in the form of convenience, energy savings, and safety. Sensors are the machinerized eyes, ears, noses, and nerves we use to touch the world around us. They are applied to a tremendous variety of fields and are influencing our life in previously unimagined ways.

How Does a Sensing System Work?

Primary Sensor System

look at the block diagram above.

the second diag is not clear it goes like this

-> input transducer ---> Signal processing--->output transducer-->