Introduction

Sensors-
A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. Sensors are devices that are used to measure physical variables like temperature, pH, velocity, rotational rate, flow rate, pressure and many others. For example, a mercury thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated glass tube. A thermocouple converts temperature to an output voltage which can be read by a voltmeter. For accuracy, all sensors need to be calibrated against known standards.
Today, most sensors do not indicate a reading on an analog scale (like a thermometer), but, rather, they produce a voltage or a digital signal that is indicative of the physical variable they measure. Those signals are often imported into computer programs, stored in files, plotted on computers and analyzed to death.

Working
The sensors work on the principle of analog to digital conversion. In order to collect data from the sensors, the signals from the sensors need to be converted into digital numbers that the processor can handle. The sensors generate a varying voltage based on what is measured and the processor cannot understand it. Remember, the processor is digital so it only understands ones and zeros.
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An analog¬to-digital converter or ADC allows a processor to measure voltages. The world outside the computer does not have discrete steps such as on/off, high/low, one/zero. It’s an analog world. The
ADC allows the computer to measure the analog world with the ADC.
Take a temperature sensor as an example. A temperature sensor can convert the temperature it is measuring to a voltage that corresponds to the temperature. The ADC is used to measure the voltage and convert it to a digital number that the computer can use.