Group C Humidity Sensor Week 7

                                                             Humidity Sensor

Humidity is the amount of water vapor in car. It could affect human comfort and some industrial systems as well. So humidity sensor is needed in order to control systems for industrial process and human comfort. Humidity controls are important for semiconductor industry, medical applications and biological products. So humidity sensors are employed to provide an indication of moisture levels in the environment.

Common units for humidity measurement are relative humidity, Dew/Frost point and parts per million. Relative humidity indicates temperature; Dew/Frost indicates pressure of gas and parts per million is an absolute measurement. Dew point is used as an indicator of water vapor in high temperature processes.

Humidity sensors are divided into two types, the relative humidity sensors and absolute humidity sensors. But most of the humidity sensors are relative humidity sensors. Humidity sensors are consists of a hygroscopic dielectric material in the small capacitor. 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.

Relative humidity is a function of both the ambient temperature and water vapor pressure. The relationship between relative humidity, the amount of moisture and the sensor capacitance can governs the operation of a capacitive humidity instrument.

Basic structure of capacitive type humidity sensor is shown below:

Lower electrode is formed using gold, a polymer layer such as PVA is deposited on the electrode and this layer senses humidity. On top of this polymer film, gold layer is deposited which acts as top electrode. The top electrode also allows water vapor to pass through it, into the sensing layer. The vapors enter or leave the hygroscopic sensing layer until the vapor 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.

Basic structure of resistive type humidity sensor is shown below

Resistive type humidity sensors pick up changes in the resistance value of the sensor element in response to the change in the humidity. 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.

Reference:http://pasternack.ucdavis.edu/files/6213/7271/8210/hyd151_read13.pdf
http://www.engineersgarage.com/articles/humidity-sensor

To Qian: I found that the movement sensor is useful from your post. I learnt the difference between radar sensor and infrared sensor, but they are both movement sensor. They are used in automatic doors, automatic lights and building security. I agree with you that the sensor technology will continue to grow and contribute to modern age.

To Qi: I just figure out that the flow sensor can be used in the automobile industry. It’s interesting that the airflow can tell the computer to adjust how much fuel need to be added into the motor. And I agree with you that the accurate flow sensors ensure the safety of the process.

Week 7 - Humidity sensor Group C Kyung Yoon

Humidity Sensor

There are many things required to condition indoor air quality to human comfort. Especially cold winter like this term, it is easy to experience what low humidity can do to human comfort. However, too high of humidity can also create discomfort for indoor environment. That's when the humidity sensor takes a role.

Humidity is not only effecting human comfort, but many others that could be affected like followings;

(1) Many industrial processes are humidity sensitive; product quality, yield, and cost often depend on controlling the humidity within some acceptable band.

(2) Human health, comfort, and productivity are adversely affected by extreme relative humidity.

(3) Optimal functioning of various home appliances necessitates humidity sensing and control.

(4) Modern, solid-state electronic equipment is susceptible to damage by the discharge of electrostatic energy that can accumulate if the environment is too dry.

                                                                                                                 - Kulwicki, 1991

Among many different sensors out there, there are two main sensors being used the most: ceramic and polymeric humidity sensor. Ceramic sensor is based on the absorption of water molecules through porous semi-conductor. Polymeric sensors can be divided into two categories: one using capacity of sensing principle, while the other uses resistant effects. Capacitive effect is basically sandwich the hygroscopic dielectric material with a pair of electrode forming a small capacitor. This capacitor will determine the values based on presences of moisture. Resistive effect is based on number of movable ions sensed by polymeric film. Change in humidity will change in resistance of the film.

Despite the fascinating process of sensors, they are not always accurate. For ceramic sensors, it requires integral heater to calibrate the system. The system often be contaminated by oil vapors or smoke. The cost of the sensor would go proportion with frequent of self heating process and the complexity. On the other hand, polymeric humidity senors are bulk effective sensors that it's less sensitive, slower respond time required, and hysteresis, but it has lesser chance to get contaminated like porous ceramics.

Different sensors will be used in different environment and preferences. It goes same to BIM as well. BIM model will analyze the building before it was built. It will analyze the indoor air quality to make sure it is in good shape for people to living in. However, BIM model does not consider long term effects like how oil vapors and smoke affect on humidity sensors, at least, revit doesn't. BIM can be very useful in many different way, but putting all the trust in BIM could cost owner more money than without BIM. BIM is relatively new to the industry. There are many tasks that could be done in BIM, but many many people, especially owners, expect more than what it can do. All the owners and BIM users should study and understand the process of construction and maintenance while understanding the program itself.

Sources:

Kulwicki, 1991, Humidity sensors

http://www.engineersgarage.com/articles/humidity-sensor

Group C: Humidity Sensor

Humidity can be defined as the quantity of moisture (water) in the air. The warmer the air is, the more moisture it can hold. Relative humidity is a percentage that helps quantify the amount of moisture in the air. It is the ratio of the moisture present in the air to the maximum amount of moisture the air can hold at that temperature. A humidity sensor would measure and report this quantity. Most humidity sensors work by using a “capacitive measurement” system [1]. These sensors use two metal plates and a non-conductive film that will collect the moisture in the air. The moisture will cause voltage changes between the two plates, which in turn will be converted into digital readings of the air relative humidity. 
   

These sensors are used in residential, office, and even industrial settings. Humidity sensors can be integrated into the HVAC system in order to constantly monitor and control indoor air moisture levels. Humidity sensors are important because humidity affects human comfort, and can even cause health concerns. Indeed low humidity can cause breathing problem or joint pain, and high humidity can cause mold and fungus growth [2]. In an industrial setting, certain processes are very sensitive to humidity, and the moisture in the air must be maintained around a certain level. Paper production or pharmaceutical processes for instance.  

Sensors definitely play a very important role in the development of intelligent buildings. Sensors help with the automation of certain processes in the building. A robots functioning with a humidity sensor could automatically regulate the amount of air blown into a room to maintain an appropriate relative humidity.

I had a basic understanding of the use of humidity sensors, although I did not know exactly how they functioned. Doing research actually made me aware of the crucial role humidity sensor play in day to day operation of a building. When think about indoor air comfort, we often focus on temperature, but relative humidity is very important. As I stated bellow, certain levels of moisture are responsible for health problems in residential homes. In a city like Philadelphia where temperature range from 10°F to 95°F annually, constantly monitoring the humidity in the air becomes even more important.

Comments on others posts:

Matt’s post: I found your post very interesting. As I stated in my own, I have taken for granted a lot of the things sensors do in a building. I would have thought pressure sensors would only be useful in medical settings when keeping a patient in isolation. I had never considered how it is used in the HVAC and plumbing system. Your pictures were also a very good idea. I helped understand the concepts and the functioning of the sensors better. Your post mentioned the use of pressure sensor to keep workers and occupant safe in high rise building. Is the technology already being used, or is it a prediction?

Yoon’s post: I liked that you found so many more example of humidity sensor. It was nice to see the different options out there. I only discussed the “Capacity” polymeric sensor. I also like that you mentioned the limitation of both system. I chose to focus on their role, as well as their possible future application. Reading the other blog posts, I felt that sensor are getting more and more precise and effective. Do you think that there are less common sensors that can perform better than the ones you mentioned? 

References:

[1] "Humidity Sensor." EngineersGarage. N.p., 2012. Web. 18 Feb. 2014.

[2] Erdemir, J.S. Metzker, and C. Wilborn. "What Is a Humidity Sensor." WiseGeek. Conjecture, 17 Jan.
      2014. Web. 18 Feb. 2014.

Week 7 - Humidity Sensors

D. Barbalace

A humidity sensor, or hygrometer, is used to measure moisture content in the atmosphere.  These instruments usually base their readings off of a more easily obtained quantity and are then calibrated to calculate a measurement of humidity.  The most common quantities used to measure humidity in modern hygrometers are the dew point and the electrical capacitance or resistance of the air.  For as little as $10, someone can purchase a simple Arduino humidity sensor (that utilizes electrical capacitance) for use in a home project.  This sensor is the size of a quarter!  While this type of sensor is not preferable in an industrial setting, its perfect for small projects at home or school.

Humidity sensors are an essential part of the operations of many building systems.  They are often used in manufacturing when a certain process needs to take place in a particularly dry or moist environment.  Greenhouses need hygrometers to ensure that the humidity is at a healthy level for the plants growing within.  Saunas rely heavily on comfortably high humidity levels.  Museums must ensure that humidity sensors are installed near sensitive artifacts so that the old materials are not damaged by moisture levels in the air that are too high or too low.  High quality musical instruments, especially acoustic guitars and string instruments like the violin and cello, must be kept in a controlled, humid environment to keep the wood in its best condition.

Moisture control is equally important in residential buildings.  HVAC systems contain humidity sensors that help keep humidity at comfortable and healthy levels.  Dry conditions can cause skin irritation and dehydration, while overly moist conditions can increase growth of unfavorable organisms.  Since humidity is such an essential part of human comfort, nearly all modern HVAC systems contain some type of hygrometer.

References:

https://www.sparkfun.com

http://en.wikipedia.org/wiki/Hygrometer

Comments:

On Ian Lagrange's Post:

Why is there an option to sign out directly under the comment box? I just wrote an entire comment and then I hit 'sign out', thinking it was 'publish,' and I deleted my entire damn comment. So here we go again:

I like how you focused on the safety aspects of motion sensors. They're widely used in alarm systems, automatic lights, and automatic doors, but it seems like people have started forgetting they're even there. When I was in 8th grade, they installed motion sensitive lights in the new addition to the middle school, and everyone thought it was amazing. Since then, I haven't seen a single building in the medical, business, or education fields get constructed without automatic lights somewhere in the building.

On Tyler Woyshner's Post:

I wanted to read your post because it is closely related to my post, which is about humidity sensors. Both temperature sensors and humidity sensors are incredibly important in HVAC design, and humidity is dependent on temperature. Both are important for health and comfort in a building. As you mentioned, closed-loop A/C systems can be optimized by turning off the system once a space has reached the desired temperature. Keeping humidity at a desired level will also aid in energy optimization, as the temperature is more likely to remain constant when the moisture content remains steady as well.