Arduino Projects    |   Raspberry Pi  |     Electronic Circuits   |   Electronics Reference Design Library  |   AVR    |    PIC    |    8051    |    Electronic Projects

Humidity Sensor

Table of Contents:

Written By: 
Preeti Jain
 
Humidity is the presence of water in air. The amount of water vapor in air can affect human comfort as well as many manufacturing processes in industries. The presence of water vapor also influences various physical, chemical, and biological processes. Humidity Sensor Humidity measurement in industries is critical because it may affect the business cost of the product and the health and safety of the personnel. Hence, humidity sensing is very important, especially in the control systems for industrial processes and human comfort.
 
Controlling or monitoring humidity is of paramount importance in many industrial & domestic applications. In semiconductor industry, humidity or moisture levels needs to be properly controlled & monitored during wafer processing. In medical applications, humidity control is required for respiratory equipments, sterilizers, incubators, pharmaceutical processing, and biological products. Humidity control is also necessary in chemical gas purification, dryers, ovens, film desiccation, paper and textile production, and food processing. In agriculture, measurement of humidity is important for plantation protection (dew prevention), soil moisture monitoring, etc. For domestic applications, humidity control is required for living environment in buildings, cooking control for microwave ovens, etc.  In all such applications and many others, humidity sensors are employed to provide an indication of the moisture levels in the environment.
 
RELEVANT MOISTURE TERMS
To mention moisture levels, variety of terminologies are used. The study of water vapour concentration in air as a function of temperature and pressure falls under the area of psychometrics. Psychometrics deals with the thermodynamic properties of moist gases while the term “humidity’ simply refers to the presence of water vapour in air or other carrier gas.
 
Humidity measurement determines the amount of water vapor present in a gas that can be a mixture, such as air, or a pure gas, such as nitrogen or argon. Various terms used to indicate moisture levels are tabulated in the table below:
 
S.No
Term
Definition
Unit
1
Absolute Humidity
(Vapor Concentration)
Ratio of mass(vapour) to volume.
grams/m3
2
Mixing Ratio OR Mass Ratio
Ratio of mass(vapour) to mass(dry gas)
grams/m3
3
Relative Humidity
Ratio of mass(vapour) to mass(saturated vapour) OR ratio of actual vapor pressure to saturation vapor pressure.
%
4
Specific Humidity
Ratio of mass(vapour) to total mass.
%
5
Dew Point
Temperature(above 0°C) at which the water vapor in a gas condenses to liquid water)
°C
6
Frost Point
Temperature(below 0°C) at which the water vapor in a gas condenses to ice
 
7
Volume Ratio
Ratio of partial pressure(vapour) to partial pressure (dry gas)
% by volume
8
PPM by Volume
Ratio of volume(vapour) X 106 to volume(dry gas)
 
PPMV
9
PPM by Weight
PPMV X
 PPMW
 
Most commonly used units for humidity measurement are Relative Humidity (RH), Dew/Frost point (D/F PT) and Parts Per Million (PPM). RH is a function of temperature, and thus it is a relative measurement. Dew/Frost point is a function of the pressure of the gas but is independent of temperature and is therefore defined as absolute humidity measurement. PPM is also an absolute measurement.
 
Dew points and frost points are often used when the dryness of the gas is important. Dew point is also used as an indicator of water vapor in high temperature processes, such as industrial drying.
Mixing ratios, volume percent, and specific humidity are usually used when water vapor is either an impurity or a defined component of a process gas mixture used in manufacturing.
 
Correlation among RH, Dew/Frost point and PPMv is shown below:

 

HUMIDITY SENSING – CLASSIFICATION & PRINCIPLES
According to the measurement units, humidity sensors are divided into two types: Relative humidity(RH)sensors and absolute humidity(moisture) sensors. Most humidity sensors are relative humidity sensors and use different sensing principles.
 
A table showing important parameters of different types of humidity sensors is given below:
Active Material
Thermo-set
Polymer
 
Thermoplastic
Polymer
Thermoplastic
Polymer
Bulk Thermoplastic
Bulk
AlO3
 
Lithium
Chloride Film
 
Substrate
Ceramic or
Silicon
Ceramic or
silicon
Polyester or
mylar film
N/A
N/A
Ceramic
Sensed Parameter
Capacitance
Capacitance
Capacitance
Resistance
Resistance
Conductivity
Measured Parameter
%RH
%RH
%RH
%RH
%RH
%RH
RH Change
0% to 100%
0% to 100%
0% to 100%
20% to 100%
2% to 90%
15% to <100%
RH Accuracy
±1% to ±5%
±3% to ±5%
±3% to ±5%
±3% to ±10%
±1% to ±5%
±5%
Interchangability
±2% to
±10% RH
 
±3% to
±20% RH
 
±3% to
±20% RH
 
±5% to
±25% RH
 
poor
±3% to
±10% RH
 
Hysterisis
<1% to 3% RH
2% to 5% RH
2% to 5% RH
3% to 6% RH
<2% RH
very poor
Linearity
±1% RH
±1% RH
±2% RH
poor
poor
Very poor
Risetime
15 s to 60 s
15 s to 90 s
15 s to 90 s
2 min to 5 min
3 min to 5 min
3 min to 5 min
Temperature
Range
 
-40 °C to
185 °C
 
-30 °C to
190 °C
 
-25°C to
100 °C
 
10 °C to
40 °C
 
-10 °C to
75 °C
 
-
Long Term
Stability
±1%RH/5 yr
±1%RH/yr
±1%RH/yr
±3%RH/yr
±3% RH/yr
>1% RH/°C
 
·         Sensing Principle
Humidity measurement can be done using dry and wet bulb hygrometers, dew point hygrometers, and electronic hygrometers. There has been a surge in the demand of electronic hygrometers, often called humidity sensors.
 
Electronic type hygrometers or humidity sensors can be broadly divided into two categories: one employs capacitive sensing principle, while other use resistive effects
 
Sensors based on capacitive effect:
Humidity sensors relying on this principle consists of a hygroscopic dielectric material sandwiched between a pair of electrodes forming a small capacitor. Most capacitive sensors use a plastic or polymer as the dielectric material, with a typical dielectric constant ranging from 2 to 15. In absence of moisture, the dielectric constant of the hygroscopic dielectric material and the sensor geometry determine the value of capacitance.
 
At normal room temperature, the dielectric constant of water vapor has a value of about 80, a value much larger than the constant of the sensor dielectric material. Therefore, absorption of water vapor by the sensor results in an increase in sensor capacitance.
 
At equilibrium conditions, the amount of moisture present in a hygroscopic material depends on both the ambient temperature and the ambient water vapor pressure. This is true also for the hygroscopic dielectric material used on the sensor.
 
By definition, relative humidity is a function of both the ambient temperature and water vapor pressure. Therefore there is a relationship between relative humidity, the amount of moisture present in the sensor, and sensor capacitance. This relationship governs the operation of a capacitive humidity instrument.
 
Basic structure of capacitive type humidity sensor is shown below:

 

On Alumina substrate, lower electrode is formed using gold, platinum or other material. A polymer layer such as PVA is deposited on the electrode. This layers senses humidity. On top of this polymer film, gold layer is deposited which acts as top electrode. The top electrode also allows water vapour to pass through it, into the sensing layer .  The vapors enter or leave the hygroscopic sensing layer until the  vapour content is in equilibrium with the ambient air or gas.Thus capacitive type sensor is basically a capacitor with humidity sensitive polymer film as the dielectric.  
 
Sensors based on Resistive effect:
Resistive type humidity sensors pick up changes in the resistance value of the sensor element in response to the change in the humidity. Basic structure of resistive type humidity sensor from TDK is shown below

 

Thick film conductor of precious metals like gold, ruthenium oxide is printed and calcinated in the shape of the comb to form an electrode. Then a polymeric film is applied on the electrode; the film acts as a humidity sensing film due to the existence of movable ions. Change in impedance occurs due to the change in the number of movable ions.

Comments (10)

i like this type of sensor  

i like this type of sensor

 

 

it is good.

it is good.

its good 

its good

 

what is the cost of humidity

what is the cost of humidity sensor

Can i get the model name of

Can i get the model name of this humidity sensor?

 

 

plz give me protous model!!

plz give me protous model!!

What type of sensor is being

What type of sensor is being used in the sensing project please provide the part no. and manufacturer's details. Which compiler has been used to compile the code?

Good info it helps me

Good info it helps me

THREE: When shopping around

THREE: When shopping around for weight loss pills, it is best for the dieter to make sure they are dealing with companies of repute and which were proved by other dieter that their weight reduction products actually works. garcinia cambogia vitacost Oz has featured an increasing variety of celebrities on his show, showcasing their fat loss secrets. Also tend not to consume sugar, oily and fatty substances like clarified butter, butter and sweet potato. It will be the science that's based on the Tridosha principle. You'll fare best with healthy fat loss diet plans if you realise about correct portions. The chemicals present inside fruit helps the body dissolve stubborn fatty cells so that more and much more fat loss can be done. I choosing a lump sum 18 pounds now considering that the first in the year. Once you might have achieved your desired weight level, simply have one more 100-200 calories a day for the calorie budget. A couple in the programs that you can find available today will only be suitable for certain kinds of people, so although a lot of people will discover success with this program there is no guarantee that you will discover results. s talk nutrition as well as perhaps we should mention some types of drugs and what drugs probably have an effect. Fast weight reduction which targets low calorie intake and fat reducing without right nutrition is indeed a starvation practice. It does not affect the guts the way in which other diet pills do. You begin in My Fitness Pal by setting your overall weight, your goal weight, specifics about the body and lifestyle, and then how soon you wish to slim down. Weight loss, while you now know, is a very important part of maintaining a healthy lifestyle. A slimmer healthier you is achievable providing you follow a number of simple directions from the diet and weight-loss doctor. Various general obesity health issues that persons that are obese often are confronted with include diabetes, high-cholesterol, high hypertension, coronary disease, increased risk for heart attack and stroke, increased risk in the formation of blood clots, breathing problems such as asthma and COPD, lung related infections including pneumonia and bronchitis and back and leg pain due towards the presence of extreme quantities of more weight that the body is obligatory to keep as well as several other matters that may expand higher than the evolution of moment in time. Just squeeze and tighten your abs for 15-20 seconds at a time. Check the subsequent reviews about the Anabolic Cooking and The Fat Loss Factor and understand 2 with the most recommended weight-loss systems available nowadays. While you might be convinced which you must don't use anything but the high end items, you ought to know that you have other lines that you'll be able to use just too. Eating breakfast helps to obtain the metabolism going within the morning and may set a bad tone for the rest from the day. >> Tip: When your eating meals everyday try to be. When searching for a great fat loss program, look for the following features:. Sustainable weight reduction is much more about creating smart choices than strict dieting. Basically the way it operates is basically that you pay a weekly fee to attend a live, local meeting or join an internet support community. While it just isn't a miracle pill, it allows you to succeed in your fat loss goals at a considerably quicker pace. resources: http://www.spiritofindia.org/locating-straightforward-products-weight-loss http://www.europamusic.co.uk/events/2013/july/choosing-simple-techniques... http://www.oxyzenfitness.gr/forum/information-upon-simple-options-fat-loss http://m.phonewarrior.mobi/forums/index.php?p=/discussion/1739/is-the-ga... http://mostlymarketing.com/articles/discovering-no-hassle-solutions-with... http://en.wikipedia.org/wiki/Garcinia_cambogia http://www.youtube.com/watch?v=dX3pdxi9dZ0

Hey can u suggest me with

Hey can u suggest me with some humidity sensor ?

 

APPLICATIONS & TECHNOLOGIES

Learn about the latest applications and industry trends with tutorials and white paper design resources on vertical markets.

Automotive
Energy Harvesting
MEMS Technology
OpenSource Hardware
RFID & NFC
RF Wireless
Sensor
Solar
Touch
Wireless Charging

 

You are here