humidity sensor is nothing but a device which can measure the amount of water or moisture present in air.this is also known as HYGROMETER.
BEFORE GO FAR I WANT TO TELL SOME IMPORTANT ABOUT THE HUMIDITY
1.their is a important point to remember that the amount of moisture present in air changes with change in the temperature.
2.Also we know that the As the temperature of the air is increases then it can held more water vapor or moisture contains than the cold air.
3. As we know that the air contains some amount of evaporated vapor . this amount of vapor is helpful to detect the weather condition .
Humidity can affect the human comfort as well as affect many industries environment condition.due to the humidity their are many chemical reaction can take place which affects the working of the industries.these are designed to improve the environment condition and also increase the safety.
THERE ARE TWO TYPES OF HUMIDITY sensor
SENSOR can sense the moisture present in the air relative to the amount of the maximum moisture can held by air is known as relative humidity .
in other words relative humidity sensor is the sensor which the ratio of the ACTUAL amount of moisture present in air to the maximum amount of moisture held by air at their air temperature.
ACTUAL AMOUNT OF MOISTURE PRESENT IN AIR
RELATIVE HUMIDITY = ___________________________________________
MAXIMUM AMOUNT OF MOISTURE HELD BY AIR AT
THEIR AIR TEMPERATURE
Absolute humidity is the measure of water vapor (moisture) in the air, regardless of temperature. It is expressed as grams of moisture per cubic meter of air (g/m3).
ABSOLUTE HUMIDITY is the total mass of water present in given amount of water.
MASS OF VAPOR PRESENT IN THE AIR
ABSOLUTE HUMIDITY = _____________________________________
Volume of the air and the vapor mixture
WORKING PRINCIPLE OF HUMIDITY SENSOR (SENSOR BASED ON CAPACITIVE EFFECT)
It consist of two conductive plates and a hygroscopic dielectric material placed between these conductive plates.this combination forms a capacitor.In absence of moisture, the dielectric constant of the hygroscopic dielectric material and the sensor geometry determine the value of capacitance.at the normal room temperature condition the value of the capacitance is about 80.when moisture is detect by the sensor then the value of capacitance will increases which results to change in the voltage and these voltage signals are converted into the digital value of humidity.
WORKING PRINCIPLE OF HUMIDITY SENSOR (SENSOR BASED ON RESISTIVE EFFECT
the working principle of this type of humidity sensor is to change in the resistance of a material due to the humidity.this resistance will give the amount of the humidity because change in resistance is proportional to the humidity present in the air. these are less sensitive than the capacitive type of humidity sensor.
WORKING PRINCIPLE OF HUMIDITY SENSOR (SENSOR BASED ON thermal EFFECT)
this is the hygrometer which measure the change in conductivity of the air which is directly proportional to the humidity.these type of humidity devices measure the absolute humidity.
WORKING PRINCIPLE OF HUMIDITY SENSOR(SENSOR BASED ON gravimetric EFFECT )
this type of the sensor MEASURES the mass of the air which have moisture contents and compare the same amount of dry air . the difference between these measured amount and dry air mass will give us the amount of moisture which is also known as humidity.