Humidity , Humidity Sensor, Circuit of Humidity Sensor and block diagram of the Humidity Circuit

Humidity Definition

§  Humidity   is  a  term  used  to  describe  the  presence  of  moisture  or  water  vapor  in  the  air .  The  amount   of  moisture  that  the  air  will  hold  depends  upon  the  temperature  of  the  air .  Warm  air  will  hold  more  moisture  than  cold   air.  Dry  air  causes  rapid  evaporation  .  Moist  ( humid )  air  prevents  rapid  evaporation  making  it  feel  warmer  than  the  temperature  indicated  by  thermometer .

§  Relative  humidity   is   defined  as  the  actual  vapor  pressure  on  the  value  that  would  occur in  the  space  was  occupied  by  steam  in  saturation  conditions  and  expressed  in %

                          

§  Absolute humidity  is the weight of water vapor in a given volume of atmosphere (air) and is expressed in kg of water vapor per cubic of dry air .

Effect  Of Humidity On The Greenhouse Climate

Humidity is one of the environmental factors that must be in proper balance for satisfactory greenhouse cultivation .

Plants have to  transpirate water to transport nutrients , to cool and to regulate growth . 

The transpiration depends on the saturation deficit between the Stomata’s and the air .

Problem  definition:

The following can be said :

 *Too high and low saturation deficits have unfavourable influence on plant ; physiology and growth :

•         When air humidity is too high ,the gas exchanges are restrained causing low transpiration of the plant and therefore low nutrient absorption.
•        When air humidity is too low ,the stomates close, reducing photosynthesis rate .

*  High humidity  can also induce difficulties in pollination because wet pollen cannot be released .

             *  The humidity of the air in the plant favours diseases.

Solving of the problem:

By designing greenhouse control system we can control some parameters which have agreat effect on plants grow and one of  the most effective factors on plants is humidity.

Controlling of humidity can be realized by using humidity sensor which provides accurate measures of relative humidity according to this measures we can control the humidity and generating the right action that leads to maxmimum product of plant.

humidity sensor that we used in our system is 

 HS1101Relative Humidity Sensor

Why  HS1101 Relative Humidity Sensor?

Features 

                         

Ø Simple calibration required when operating in standard conditions.

Ø Fast response time.

Ø Simple, RCTIME output corresponds to  relative humidity when directly connected to BASIC Stamp.

Ø Compatible with automatized assembly  processes , including wave soldering , reflow and water immersion.

Ø Suitable for linear voltage or frequency output circuitry.

Ø High reliability and long term stability.

 Circuit & equation:

Connecting and Testing

Connecting the HS1101 to a microcontroller is demonstrated here with a BASIC Stamp module. It is a straightforward application, requiring only one I/O pin.

 Since the HS 1101 is based on a unique capacitive cell, relative humidity can be obtained using a simple RC wiring diagram, 

TDecay = 2.4 %RH + Rhconstant

Key Specifications

Ø Power requirements: 5 to 10 VDC.

Ø Communication: Analog output of varying capacitance in response to change in relative humidity.

Ø Humidity Measuring Range:

       1 to 99% RH

Ø Operating temperature: -40 to 212 °F (-40 to 100 °C)

Application Ideas

Ø Home and office automation

Ø Humidity component for weather station applications

Ø Industrial process control systems

 The block diagram of the humidity circuit is as the following: