A humidity sensor (or hygrometer) senses, measures and reports the
relative humidity in the air. It therefore measures both moisture and
air temperature. Relative humidity is the ratio of actual moisture in
the air to the highest amount of moisture that can be held at that air
temperature. The warmer the air temperature is, the more moisture it can
hold.
Humidity sensors use capacitive measurement, which relies on
electrical capacitance. Electrical capacity is the ability of two nearby
electrical conductors to create an electrical field between them. The
sensor is composed of two metal plates and contains a non-conductive
polymer film between them. This film collects moisture from the air,
which causes the voltage between the two plates to change. These voltage
changes are converted into digital readings showing the level of
moisture in the air.
Types of Humidity Sensors
There are many different kinds of humidity / dew sensors and at Future
Electronics we stock many of the most common types categorized by
accuracy, operating temperature range, humidity range, supply voltage,
packaging type and supply current. The parametric filters on our website
can help refine your search results depending on the required
specifications.
The most common sizes for supply voltage are 3 to 5.5 V and 4.75 to 5.25
V. We also carry humidity / dew sensors with supply voltage as high as
15 V. Supply current can be between 100 µA and 15 mA, with the most
common humidity / dew sensor chips using a supply current of 100 µA, 500
µA and 2.8 to 4 mA.
Humidity / Dew Sensors from Future Electronics
Future Electronics has a full chip selection of humidity / dew sensors
from several manufacturers that can be used to design a relative
humidity sensor, temperature and humidity monitor, moisture sensor,
humidity sensor IC (integrated circuit), humidity sensor switch, digital
home humidity sensor, wireless humidity sensor, digital humidity meter,
soil moisture sensor, dew point sensor, remote humidity sensor or for
any other application that needs humidity measurement. Simply choose
from the humidity / dew sensor technical attributes below and your
search results will quickly be narrowed to match your specific humidity /
dew sensor application needs.
If you have a preferred brand, we deal with Digi International, GE
Measurement & Control, Measurement Specialties or Vishay as
manufacturers. You can easily refine your humidity / dew sensor product
search results by clicking your preferred humidity / dew sensor brand
below from our list of manufacturers.
Applications for Humidity / Dew Sensors:
Humidity sensors can be used as a monitoring and preventive measure in
homes for people with illnesses that are affected by humidity. They are
also found as part of home heating, ventilating, and air conditioning
systems (HVAC systems). They can also be found in offices, cars,
humidors, museums, industrial spaces and greenhouses and can be used in
meteorology stations to report and predict weather. Dew sensors are used
in the coating industry because the application of paint and other
coatings may be extremely sensitive to dew point.
Choosing the Right Humidity / Dew Sensor:
When you are looking for the right humidity / dew sensors, with the
FutureElectronics.com parametric search, you can filter the results by
various attributes: by Accuracy (±5 %RH, ±3 %RH, ±2 %RH,…), Supply
Current (100 µA, 500 µA , 2.8 to 4 mA,…) and Supply Voltage (up to 15 V)
to name a few. You will be able to find the right semiconductor chip
from several manufacturers that can be used to design a temperature and
humidity monitor, moisture sensor, relative humidity sensor, humidity
sensor IC (integrated circuit), wireless humidity sensor, digital
humidity meter, humidity sensor switch, digital home humidity sensor,
soil moisture sensor, remote humidity sensor, dew point sensor or for
any other application that might need humidity or dew measurement.
Humidity / Dew Sensors in Production Ready Packaging or R&D Quantities
If the quantity of humidity / dew sensors required is less than a full
reel, we offer customers many of our humidity / dew sensor products in
tube, tray or individual quantities that will avoid unneeded surplus.
In addition, Future Electronics offers clients a unique bonded inventory
program that is designed to eliminate potential problems that may arise
from an unpredictable supply of products containing raw metals and
products with erratic or long lead times. Talk with your nearest Future
Electronics branch and find out more on how you and your company can
avoid possible shortages.
iSweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrial products
2016年1月5日星期二
How to choose a Humidity Sensor?
he most important specifications to keep in mind when selecting a humidity sensor are:
• Accuracy
• Repeatability
• Interchangeability
• Long-term stability
• Ability to recover from condensation
• Resistance to chemical and physical contaminants
• Size
• Packaging
• Cost effectiveness
Additional significant long-term factors are the costs associated with sensor replacement, field and in-house calibrations, and the complexity and reliability of the signal conditioning and data acquisition (DA) circuitry. For all these considerations to make sense, the prospective user needs an understanding of the most widely used types of humidity sensors and the general trend of their expected performance. Definitions of absolute humidity, dew point, and relative humidity are provided in the sidebar, "Humidity Basics").
Capacitive Humidity Sensors
Relative Humidity. Capacitive relative humidity (RH) sensors (see Photo 1) are widely used in industrial, commercial, and weather telemetry applications.
Capacitive RH sensors are produced in a wide range of specifications, sizes, and shapes including integrated monolithic electronics. The sensors shown here are from various manufacturers.
They consist of a substrate on which a thin film of polymer or metal oxide is deposited between two conductive electrodes. The sensing surface is coated with a porous metal electrode to protect it from contamination and exposure to condensation. The substrate is typically glass, ceramic, or silicon. The incremental change in the dielectric constant of a capacitive humidity sensor is nearly directly proportional to the relative humidity of the surrounding environment. The change in capacitance is typically 0.2–0.5 pF for a 1% RH change, while the bulk capacitance is between 100 and 500 pF at 50% RH at 25°C. Capacitive sensors are characterized by low temperature coefficient, ability to function at high temperatures (up to 200°C), full recovery from condensation, and reasonable resistance to chemical vapors. The response time ranges from 30 to 60 s for a 63% RH step change.
State-of-the-art techniques for producing capacitive sensors take advantage of many of the principles used in semiconductor manufacturing to yield sensors with minimal long-term drift and hysteresis. Thin film capacitive sensors may include monolithic signal conditioning circuitry integrated onto the substrate. The most widely used signal conditioner incorporates a CMOS timer to pulse the sensor and to produce a near-linear voltage output.
A near-linear response is seen in this plot of capacitance changes vs. applied humidity at 25°C. The term "bulk capacitance" refers to the base value at 0% RH.
The typical uncertainty of capacitive sensors is ±2% RH from 5% to 95% RH with two-point calibration. Capacitive sensors are limited by the distance the sensing element can be located from the signal conditioning circuitry, due to the capacitive effect of the connecting cable with respect to the relatively small capacitance changes of the sensor. A practical limit is 10–100 M makes the response an impedance measurement. A distinct advantage of resistive RH sensors is their interchangeability, usually within ±2% RH, which allows the electronic signal conditioning circuitry to be calibrated by a resistor at a fixed RH point. This eliminates the need for humidity calibration standards, so resistive humidity sensors are generally field replaceable. The accuracy of individual resistive humidity sensors may be confirmed by testing in an RH calibration chamber or by a computer-based DA system referenced to standardized humidity-controlled environment. Nominal operating temperature of resistive sensors ranges from –40°C to 100°C.
In residential and commercial environments, the life expectancy of these sensors is >>5 yr., but exposure to chemical vapors and other contaminants such as oil mist may lead to premature failure. Another drawback of some resistive sensors is their tendency to shift values when exposed to condensation if a water-soluble coating is used. Resistive humidity sensors have significant temperature dependencies when installed in an environment with large (>10°F) temperature fluctuations. Simultaneous temperature compensation is incorporated for accuracy. The small size, low cost, interchangeability, and long-term stability make these resistive sensors suitable for use in control and display products for industrial, commercial, and residential applications.
One of the first mass-produced humidity sensors was the Dunmore type, developed by NIST in the 1940s and still in use today. It consists of a dual winding of palladium wire on a plastic cylinder that is then coated with a mixture of polyvinyl alcohol (binder) and either lithium bromide or lithium chloride. Varying the concentration of LiBr or LiCl results in very high resolution sensors that cover humidity spans of 20%–40% RH. For very low RH control function in the 1%–2% RH range, accuracies of 0.1% can be achieved. Dunmore sensors are widely used in precision air conditioning controls to maintain the environment of computer rooms and as monitors for pressurized transmission lines, antennas, and waveguides used in telecommunications.
Summary
Rapid advancements in semiconductor technology, such as thin film deposition, ion sputtering, and ceramic/silicon coatings, have made possible highly accurate humidity sensors with resistance to chemicals and physical contaminants?at economical prices. No single sensor, however, can satisfy every application. Resistive, capacitive, and thermal conductivity sensing technologies each offer distinct advantages. Resistive sensors are interchangeable, usable for remote locations, and cost effective. Capacitive sensors provide wide RH range and condensation tolerance, and, if laser trimmed, are also interchangeable. Thermal conductivity sensors perform well in corrosive environments and at high temperatures. For most applications, therefore, the environmental conditions dictate the sensor choice.
iSweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrial products
• Accuracy
• Repeatability
• Interchangeability
• Long-term stability
• Ability to recover from condensation
• Resistance to chemical and physical contaminants
• Size
• Packaging
• Cost effectiveness
Additional significant long-term factors are the costs associated with sensor replacement, field and in-house calibrations, and the complexity and reliability of the signal conditioning and data acquisition (DA) circuitry. For all these considerations to make sense, the prospective user needs an understanding of the most widely used types of humidity sensors and the general trend of their expected performance. Definitions of absolute humidity, dew point, and relative humidity are provided in the sidebar, "Humidity Basics").
Capacitive Humidity Sensors
Relative Humidity. Capacitive relative humidity (RH) sensors (see Photo 1) are widely used in industrial, commercial, and weather telemetry applications.
Capacitive RH sensors are produced in a wide range of specifications, sizes, and shapes including integrated monolithic electronics. The sensors shown here are from various manufacturers.
They consist of a substrate on which a thin film of polymer or metal oxide is deposited between two conductive electrodes. The sensing surface is coated with a porous metal electrode to protect it from contamination and exposure to condensation. The substrate is typically glass, ceramic, or silicon. The incremental change in the dielectric constant of a capacitive humidity sensor is nearly directly proportional to the relative humidity of the surrounding environment. The change in capacitance is typically 0.2–0.5 pF for a 1% RH change, while the bulk capacitance is between 100 and 500 pF at 50% RH at 25°C. Capacitive sensors are characterized by low temperature coefficient, ability to function at high temperatures (up to 200°C), full recovery from condensation, and reasonable resistance to chemical vapors. The response time ranges from 30 to 60 s for a 63% RH step change.
State-of-the-art techniques for producing capacitive sensors take advantage of many of the principles used in semiconductor manufacturing to yield sensors with minimal long-term drift and hysteresis. Thin film capacitive sensors may include monolithic signal conditioning circuitry integrated onto the substrate. The most widely used signal conditioner incorporates a CMOS timer to pulse the sensor and to produce a near-linear voltage output.
A near-linear response is seen in this plot of capacitance changes vs. applied humidity at 25°C. The term "bulk capacitance" refers to the base value at 0% RH.
The typical uncertainty of capacitive sensors is ±2% RH from 5% to 95% RH with two-point calibration. Capacitive sensors are limited by the distance the sensing element can be located from the signal conditioning circuitry, due to the capacitive effect of the connecting cable with respect to the relatively small capacitance changes of the sensor. A practical limit is 10–100 M makes the response an impedance measurement. A distinct advantage of resistive RH sensors is their interchangeability, usually within ±2% RH, which allows the electronic signal conditioning circuitry to be calibrated by a resistor at a fixed RH point. This eliminates the need for humidity calibration standards, so resistive humidity sensors are generally field replaceable. The accuracy of individual resistive humidity sensors may be confirmed by testing in an RH calibration chamber or by a computer-based DA system referenced to standardized humidity-controlled environment. Nominal operating temperature of resistive sensors ranges from –40°C to 100°C.
In residential and commercial environments, the life expectancy of these sensors is >>5 yr., but exposure to chemical vapors and other contaminants such as oil mist may lead to premature failure. Another drawback of some resistive sensors is their tendency to shift values when exposed to condensation if a water-soluble coating is used. Resistive humidity sensors have significant temperature dependencies when installed in an environment with large (>10°F) temperature fluctuations. Simultaneous temperature compensation is incorporated for accuracy. The small size, low cost, interchangeability, and long-term stability make these resistive sensors suitable for use in control and display products for industrial, commercial, and residential applications.
One of the first mass-produced humidity sensors was the Dunmore type, developed by NIST in the 1940s and still in use today. It consists of a dual winding of palladium wire on a plastic cylinder that is then coated with a mixture of polyvinyl alcohol (binder) and either lithium bromide or lithium chloride. Varying the concentration of LiBr or LiCl results in very high resolution sensors that cover humidity spans of 20%–40% RH. For very low RH control function in the 1%–2% RH range, accuracies of 0.1% can be achieved. Dunmore sensors are widely used in precision air conditioning controls to maintain the environment of computer rooms and as monitors for pressurized transmission lines, antennas, and waveguides used in telecommunications.
Summary
Rapid advancements in semiconductor technology, such as thin film deposition, ion sputtering, and ceramic/silicon coatings, have made possible highly accurate humidity sensors with resistance to chemicals and physical contaminants?at economical prices. No single sensor, however, can satisfy every application. Resistive, capacitive, and thermal conductivity sensing technologies each offer distinct advantages. Resistive sensors are interchangeable, usable for remote locations, and cost effective. Capacitive sensors provide wide RH range and condensation tolerance, and, if laser trimmed, are also interchangeable. Thermal conductivity sensors perform well in corrosive environments and at high temperatures. For most applications, therefore, the environmental conditions dictate the sensor choice.
iSweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrial products
2016年1月4日星期一
【industry sourcing】Scientists developed a miniature gas sensor for mobile devices | ISweek
VTT Technical Research Centre of Finland has developed a miniature gas sensor that can be connected to mobile devices. Gas measurements made with smartphones will make activities such as the detection of internal air problems easier. In addition, sleep quality will be measurable with greater precision, using mobile healthcare applications which gauge carbon dioxide quantities.
Many sensor developers are interested in using smartphones to measure gas concentrations.
"This is probably due to the spread of the Internet of Things (IoT), which enables indirect observations of a range of environmental factors based on data gathered from single sensors or sensor networks. Many day-to-day issues, such as precision and efficiency in the workplace, can depend on carbon dioxide levels and internal air quality," says Anna Rissanen, leader of the VTT research team.
Using a mobile device to measure carbon dioxide will also enable new applications for smartphones: for example, sleep quality can be monitored by measuring the sleeper's exhalations.
The miniaturised gas sensor is based on Fabry-Pérot interferometers (FPI) -- adjustable optical filters. Over the years, VTT has developed these for various spectroscopy-based applications, such as hyperspectral cameras for nanosatellite- and drone-based environmental monitoring, the early detection of skin cancer and fuel analysis for emission minimisation.
The tiny gas sensor developed by team's senior scientist Rami Mannila is based on channelling light through the sample being analysed. Penetrability at various light wavelengths can be used to determine the composition of the compound. Carbon dioxide is identified based on its strong absorption of light at a wavelength of 4.2 µm. In addition, a corresponding sensor technology can be used to simultaneously differentiate and detect other gases or substances based on the spectrum of their absorption peaks at various infra-red wavelengths.
MEMS sensor technology can be mass produced, enabling the manufacture of new types of large-volume products based on the spectral analysis of substances. Thanks to microspectrometers and other optical devices, VTT is creating new kinds of business and expertise for Finland: the start-up, Spectral Engines, which provides spectral sensors based on FPI technology, has already been established on the basis of microspectrometer technology. VTT Memsfab, on the other hand, offers manufacturing services of MEMS chips.
iSweek（http://www.isweek.com/）- industry sourcing,wholesale industrial products
Many sensor developers are interested in using smartphones to measure gas concentrations.
"This is probably due to the spread of the Internet of Things (IoT), which enables indirect observations of a range of environmental factors based on data gathered from single sensors or sensor networks. Many day-to-day issues, such as precision and efficiency in the workplace, can depend on carbon dioxide levels and internal air quality," says Anna Rissanen, leader of the VTT research team.
Using a mobile device to measure carbon dioxide will also enable new applications for smartphones: for example, sleep quality can be monitored by measuring the sleeper's exhalations.
The miniaturised gas sensor is based on Fabry-Pérot interferometers (FPI) -- adjustable optical filters. Over the years, VTT has developed these for various spectroscopy-based applications, such as hyperspectral cameras for nanosatellite- and drone-based environmental monitoring, the early detection of skin cancer and fuel analysis for emission minimisation.
The tiny gas sensor developed by team's senior scientist Rami Mannila is based on channelling light through the sample being analysed. Penetrability at various light wavelengths can be used to determine the composition of the compound. Carbon dioxide is identified based on its strong absorption of light at a wavelength of 4.2 µm. In addition, a corresponding sensor technology can be used to simultaneously differentiate and detect other gases or substances based on the spectrum of their absorption peaks at various infra-red wavelengths.
MEMS sensor technology can be mass produced, enabling the manufacture of new types of large-volume products based on the spectral analysis of substances. Thanks to microspectrometers and other optical devices, VTT is creating new kinds of business and expertise for Finland: the start-up, Spectral Engines, which provides spectral sensors based on FPI technology, has already been established on the basis of microspectrometer technology. VTT Memsfab, on the other hand, offers manufacturing services of MEMS chips.
iSweek（http://www.isweek.com/）- industry sourcing,wholesale industrial products
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