2016年2月29日星期一

What is a Humidity sensor or Dew Sensor?

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 / dew 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 / Dew 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.



Infrared CO2 sensor working principle

In nature, plants use CO2 for photosynthesis. CO2 combinate with moisture under the action of the sun to produce sugar (and oxygen). We know about how much  Infrared CO2 sensor? How does it work?

CO2 can absorb infrared wavelengths of light. The absorption can be used to measure the concentration of carbon dioxide per unit volume. The infrared absorption function of CO2 is causing part of the greenhouse effect. The greenhouse effect is one of the characteristics of all the planet's atmosphere, it makes the planet's surface temperature is higher than without the atmosphere. Any gas absorbs the sun's rays will lead to the greenhouse effect, the most important greenhouse gas for surface of the earth include: water vapor, CO2 and methane, they can absorb infrared wavelengths of light.

Most of gas sensors could give the corresponding signal according to the molecular density, even down to one over one million as units. According to the ideal gas law, when the pressure and/or temperature change, density of molecules will change, and PPM value is displayed on the sensor. Accuratly say this is wrong, as density of the gas (in PPM) will not change with the change of temperature and pressure. The change of gas sensor readings can also be used to correct for the temperature and the pressure change of gas sensor readings errors.

Considering the water vapor to the effect of CO2 sensor, the information is very important. For example: in the same pressure, temperature and volume, add water vapour in the process of gas drying, then water had taken over of general mixture of other gas molecules.

Our CO2 gas sensors could be used for accurate CO2 detection.

iSweek(http://www.isweek.com/)- Industry sourcing & Wholesale industrial products

Garment industry sourcing model fundamentally flawed

 A new report from the Clean Clothes Campaign is further evidence that the garment industry sourcing supply chain is unsustainable and unjust, no matter where it is in the world.
The report, ‘Stitched Up’, released 11 June, surveyed garment workers in Turkey and Eastern Europe producing clothes for labels such as Hugo Boss, Adidas, Zara and H&M in 10 different countries.
It found that garment workers in the area were subject to poverty wages, poor working conditions and long working hours, mirroring the experiences of workers in other parts of the world.

Some three million people are employed in the garment industry in Turkey, Georgia, Bulgaria, Romania, Macedonia, Moldova, Ukraine, Bosnia & Herzegovina, Croatia and Slovakia.
Jenny Holdcroft, policy director at IndustriALL Global Union, which represents garment unions in the surveyed countries, said:

It comes as no surprise that workers in Turkey and Eastern Europe are subjected to similar poor wages and working conditions as those in countries such as Bangladesh or Cambodia. The sourcing model for the garment industry is based on paying the lowest possible wages and so is fundamentally flawed. Made in Europe is not a guarantee of better rights or wages for garment workers.

The survey found a considerable gap between the legal minimum wage and the estimated minimum living wage in all the countries. The report said:

Jobs with such a tremendously low wage create poverty rather than fighting it.

A seamstress in Belarus spoke of working 0.45 Euro per hour embroidering blouses for Zara for a contract that had been outsourced by a Greek agent. In some cases, workers told of growing their own vegetables and doing a second job in order to survive. Others complained of damage to their eyesight after sewing for long days without breaks.

The report also found that garment workers, the majority of whom are women, suffer sexual harassment, discrimination in pay and treatment, and limited union representation.

A Croatian unionist stated that “unions do not have the opportunity to bargain for higher wages since they have to constantly fight illegal practices such as long-term unpaid overtime and unpaid social contributions or long-term unpaid wages.”

Holdcroft said:
“The report’s findings are a reflection of the endemic practices throughout the global garment industry. Wages are squeezed through brand purchasing practices and furthermore the absence of collective bargaining leads to a reliance on the legal minimum wage, which is in many cases a poverty wage."

 iSweek(http://www.isweek.com/)- Industry sourcing & Wholesale industrial products


Reducing Warm Up Time of NDIR Gas Sensors

MEMS-based electrically-efficient infrared sources from Axetris — In a number of gas detection applications, a short warm-up time of the NDIR gas sensor is critical. Especially for applications where discrete measurements need to be made, and where the gas sensor is not continuously switched on, a short warm-up time is absolutely essential. This is the case for portable gas detection devices, e.g. for combustible and toxic gas detection, refrigerant leak detection or breath alcohol measurement.

Gas sensors based on non-dispersive infrared (NDIR) spectroscopy can guarantee accurate gas concentration values only after a thermally stable state is achieved. The MEMS-based infrared sources from Axetris are produced using a unique thin-film process, and exhibit very high electrical efficiency. This leads to lower optical losses in the form of dissipated heat. Additionally, the emitting blackbody structure has a very low thermal mass, leading to a quick heating time constant of 11 milliseconds.

Besides the inherent advantages offered by the design of the infrared sources, Axetris supports its customers with comprehensive characterization information, as well as by suggesting efficient integration practices in order to achieve a quick warm-up phase. Thermal management thus becomes an easy task, and a quick warm-up time of the NDIR gas sensor can be achieved.

 iSweek(http://www.isweek.com/)- Industry sourcing & Wholesale industrial products

2016年2月25日星期四

Liquid Level Sensors & Switches

Gems liquid level sensors and switches provide high-reliability monitoring and detection of a wide range of fluid media. Requirements can range anywhere from the sensing of cooking oil, to hydraulic fluids, to diesel fuel tanks (gas level indicator), to water and wastewater, to biohazards, to even deionized or potable water.

To effectively address such a wide variety of measurement challenges, Gems offers a broad range of contact, non-contact, and non-intrusive liquid level sensors and switches. These are available in multiple technology types, including magnetic reed switch-based floats, solid-state electro-optical, conductivity, capacitive, ultrasonic, and piezo-resonant. Multiple liquid level sensing technologies may also be incorporated within a single application. Sometimes, more than one “best fit” solution may also exist, with the ultimate decision simply a matter of customer preference.

Standard catalog products for liquid level sensing include single point level switches, continuous level transmitters, multi-point level switches, chemical vapor deposition (CVD) pressure transducers, coolant level sensors, and visual level indicators. Detailed specifications on these and other liquid level sensors and switches may be found in the links below.

Please consult our fully digital online standard product catalog for an up-to-date listing of available models for immediate customer shipment. Most Gems standard catalog products can be easily modified with alternate connectors and housings. Or, a custom solution can also be developed, many times delivered in OEM volumes with shorter lead times than most industry off-the-shelf solutions.

Still not sure what your application requires?  We are happy to help. Please give us a call on 1-855-877-9666. Or, feel free to simply use our convenient Contact Us form, and a member of our sales and engineering team will be in touch within one business day.

Find out why a growing number of liquid level sensing customers have placed their trust in Gems. Contact us today for a free application assessment.

iSweek(http://www.isweek.com/)- Industry sourcing & Wholesale industrial products


Developing Methane Sensors for Leak Detection in Oil and Gas Operations

HARC is working with the Environmental Defense Fund (EDF) to identify inexpensive methane sensors that can be deployed in a variety of oil and gas operations to rapidly identify and facilitate repair of natural gas leaks. 

This will allow for the reduction of greenhouse gas emissions in an industry that is extremely important to Texas, the U.S. and world energy needs and will be for many decades to come.

The project is lead by Alex Cuclis, Research Scientist in Air Emissions and Monitoring. Alex is working with EDF to identify methane monitors suitable for testing based on their current level of development. 

The project team will design a lab or field-based testing protocol to detect natural gas emissions at oil and gas facilities. The goal of the project is to find ways to mass produce methane emissions sensors at a low cost so that oil and gas operators will purchase, install and make full use of these analyzers.


Fiber optic sensor

A fiber optic sensor is a sensor that uses optical fiber either as the sensing element ("intrinsic sensors"), or as a means of relaying signals from a remote sensor to the electronics that process the signals ("extrinsic sensors"). Fibers have many uses in remote sensing.

Depending on the application, fiber may be used because of its small size, or because no electrical power is needed at the remote location, or because many sensors can be multiplexed along the length of a fiber by using light wavelength shift for each sensor, or by sensing the time delay as light passes along the fiber through each sensor.

Time delay can be determined using a device such as an optical time-domain reflectometer and wavelength shift can be calculated using an instrument implementing optical frequency domain reflectometry.

Fiber optic sensors are also immune to electromagnetic interference, and do not conduct electricity so they can be used in places where there is high voltage electricity or flammable material such as jet fuel. Fiber optic sensors can be designed to withstand high temperatures as well.

iSweek(http://www.isweek.com/)- Industry sourcing & Wholesale industrial products

Force sensor for chameleon and Casimir force experiments with parallel-plate configuration

The search for non-Newtonian forces has been pursued following many different paths. Recently it was suggested that hypothetical chameleon interactions, which might explain the mechanisms behind dark energy, could be detected in a high-precision force measurement.

In such an experiment, interactions between parallel plates kept at constant separation could be measured as a function of the pressure of an ambient gas, thereby identifying chameleon interactions by their unique inverse dependence on the local mass density.

During the past years we have been developing a new kind of setup complying with the stringent requirements of the proposed experiment. In this article we present the first and most important part of this setup—the force sensor.

We discuss its design, fabrication, and characterization. From the results of the latter, we derive limits on chameleon interaction parameters that could be set by the forthcoming experiment. Finally, we describe the opportunity to use the same setup to measure Casimir forces at large surface separations with unprecedented accuracy, thereby potentially giving unambiguous answers to long-standing open questions.


iSweek(http://www.isweek.com/)- Industry sourcing & Wholesale industrial products

Learn the Working of a Gas Sensor

 In current technology scenario, monitoring of gases produced is very important. From home appliances such as air conditioners to electric chimneys and safety systems at industries monitoring of gases is very crucial. Gas sensors are very important part of such systems. Small like a nose, gas sensors spontaneously react to the gas present, thus keeping the system updated about any alterations that occur in the concentration of molecules at gaseous state.
 
Gas sensors are available in wide specifications depending on the sensitivity levels, type of gas to be sensed, physical dimensions and numerous other factors. This Insight covers a methane gas sensor that can sense gases such as ammonia which might get produced from methane. When a gas interacts with this sensor, it is first ionized into its constituents and is then adsorbed by the sensing element. This adsorption creates a potential difference on the element which is conveyed to the processor unit through output pins in form of current. What is this sensing element? Is it kept in some chamber or is kept exposed? How does it get current and how it is taken out? Let’s find out in this Insight!!!

The gas sensor module consists of a steel exoskeleton under which a sensing element is housed. This sensing element is subjected to current through connecting leads. This current is known as heating current through it, the gases coming close to the sensing element get ionized and are absorbed by the sensing element. This changes the resistance of the sensing element which alters the value of the current going out of it.

Image 01 shows externals of a standard gas sensor module: a steel mesh, copper clamping ring and connecting leads. The top part is a stainless steel mesh which takes care of the following:
{C}{C}{C}{C}1. {C}{C}{C}{C}Filtering out the suspended particles so that only gaseous elements are able to pass to insides of the sensor.
{C}{C}{C}{C}2. {C}{C}{C}{C}Protecting the insides of the sensor.
{C}{C}{C}{C}3. {C}{C}{C}{C}Exhibits an anti explosion network that keeps the sensor module intact at high temperatures and gas pressures.

In order to manage above listed functions efficiently, the steel mesh is made into two layers. The mesh is bound to rest of the body via a copper plated clamping ring.

The connecting leads of the sensor are thick so that sensor can be connected firmly to the circuit and sufficient amount of heat gets conducted to the inside part. They are casted from copper and have tin plating over them. Four of the six leads (A, B, C, D) are for signal fetching while two (1,2) are used to provide sufficient heat to the sensing element.

The pins are placed on a Bakelite base which is a good insulator and provides firm gripping to the connecting leads of the sensor.

 iSweek(http://www.isweek.com/)- Industry sourcing & Wholesale industrial products


2016年2月24日星期三

Mass flow sensor

A mass flow sensor (MAF) is used to find out the mass flowrate of air entering a fuel-injected internal combustion engine.

The air mass information is necessary for the engine control unit (ECU) to balance and deliver the correct fuel mass to the engine. Air changes its density as it expands and contracts with temperature and pressure. In automotive applications, air density varies with the ambient temperature, altitude and the use of forced induction, which means that mass flow sensors are more appropriate than volumetric flow sensors for determining the quantity of intake air in each cylinder. (See stoichiometry and ideal gas law.)

There are two common types of mass airflow sensors in use on automotive engines. These are the vane meter and the hot wire. Neither design employs technology that measures air mass directly. However, with additional sensors and inputs, an engine's ECU can determine the mass flowrate of intake air.

Both approaches are used almost exclusively on electronic fuel injection (EFI) engines. Both sensor designs output a 0.0–5.0 volt or a pulse-width modulation (PWM) signal that is proportional to the air mass flow rate, and both sensors have an intake air temperature (IAT) sensor incorporated into their housings for most post OBDII vehicles. Vehicles prior to 1996 could have MAF without an IAT. An example is 1994 Infiniti Q45.

When a MAF sensor is used in conjunction with an oxygen sensor, the engine's air/fuel ratio can be controlled very accurately. The MAF sensor provides the open-loop controller predicted air flow information (the measured air flow) to the ECU, and the oxygen sensor provides closed-loop feedback in order to make minor corrections to the predicted air mass.




Brief Introduction about CO2 Gas Sensor

 The Carbon Dioxide Gas Sensor - Ultra 1000-IR is a microprocessor based sensor specializing in the detection of CO2 gas using Infrared sensor technology. The self-contained sensor features user friendly interface and menu driven calibration procedure and configuration.

The CO2 gas sensor uses Non Dispersive Infrared (NDIR),a technique to monitor the CO2 vapors. The detection principle is based on measuring the absorption of infrared radiation using dual wavelength infrared detectors. The IR detectors measure the intensity of two wavelengths, one absorbed by the target gases and other unaffected by the target gases (the gas concentration is determined by comparing the detector signals).

The complete CO2 sensor comes with a stainless steel sensor head assembly, a user connection board and a transmitter board assembly - all of the sensor's electronics are enclosed in an explosion proof instrument box. Ultra 1000-IR provides a 4-20mA signal proportional to 0-100% LEL gas at the sensor. In addition the sensor may be addressed via MODBUS RTU interface. The MODBUS output provides sensor status, alarm & fault conditions.

Ultra 1000-IR CO2 Gas Sensor Features:
• Low Maintenance.
• 4-20mA Analog Output
• Optional RS485 MODBUS RTU Serial Communication
• 12-28 VDC Operation
• Automated Non-Intrusive Calibration
• Optional Adjustable Alarm Relay Contacts
• Liquid Crystal display with back light

 iSweek(http://www.isweek.com/)- Industry sourcing & Wholesale industrial products


Microwave sensors

 Microwave sensors, also known as Radar, RF or Doppler sensors, detect walking, running or crawling human targets in an outdoor environment.

Southwest Microwave developed the industry’s first bi-static microwave sensor in 1971, and has pioneered the development of flexible, reliable microwave links and transceivers for the protection of open areas, gates or entryways and rooftop or wall applications.

Microwave sensors generate an electromagnetic (RF) field between transmitter and receiver, creating an invisible volumetric detection zone. When an intruder enters the detection zone, changes to the field are registered and an alarm occurs.

Our microwave sensors are easy to install, provide high probability of detection, low nuisance alarms and resistance to rain, fog, wind, dust, falling snow and temperature extremes. Most operate at K-Band frequency, maximizing detection performance and minimizing interference from external radar sources.

 iSweek(http://www.isweek.com/)- Industry sourcing & Wholesale industrial products

What does Photosensor mean?

Definition - What does Photosensor mean? 

A photosensor is a type of electronic component that enables the detection of light, infrared and other forms of electromagnetic energy.

It is used in electronic and computing devices to receive input and/or transmit data in the form of light or electromagnetic signals.
Photosensors are also known as photodetctors.
Techopedia explains Photosensor

Photosensors are primarily used as a means to send or receive data. Typically, photosensors help in detecting change or intensity of electromagnetic energy or signals transmitted from a sending device. Depending on the receiving or interpreting device, this change or intensity of light results in a specific action. For example, when an infrared-based remote control transmits a signal to the television, the photosensor in the TV translates it into an action such as increasing or deceasing volume or changing channels.

Some of the common electronic and computing devices and technologies that utilize photosensors include:
• Optical disk drives
• Fiber optics
• Remote control devices
• Wireless networks

iSweek(http://www.isweek.com/)- Industry sourcing & Wholesale industrial products 

Humidity Sensors

Measurement Principle

Capacitive RH sensors consist of a ceramic substrate on which a thin film of polymer is deposited between two conductive electrodes.
The sensing surface is coated with a micropourous metal electrode, allowing the polymer to absorb moisture while protecting it from contamination and exposure to condensation. As the polymer absorbs water, the dielectric constant changes incrementally and is nearly directly proportional to the relative humidity of the surrounding environment. Thus, by monitoring the change in capacitance, relative humidity can be derived.

Product Overview

IST thin film capacitive relative humidity sensors are capable of measuring 0 to 100% relative humidity and operating at temperature ranges of -80°C to +190°C.  The humidity sensor product line features sensors with excellent linearity, low hysteresis, fast response times, and high chemical resistance.
IST provides exclusive humidity sensors with directly integrated platinum temperature sensors that cater to a wide range of applications. A variety of different layouts and connections such as SMD and wired configurations are available.

Application Services


Need some help with your application development? Our technical teams can offer you consulting, development, and production assistance for your project.


iSweek(http://www.isweek.com/)- Industry sourcing & Wholesale industrial products

CO2 Sensor (Carbon dioxide sensor)

A carbon dioxide sensor or CO2 sensor is an instrument for the measurement of carbon dioxide gas. The most common principles for CO2 sensors are infrared gas sensors (NDIR) and chemical gas sensors. Measuring carbon dioxide is important in monitoring indoor air quality, the function of the lungs in the form of a capnograph device, and many industrial processes.
Nondispersive Infrared NDIR CO2 Sensors
NDIR sensors are spectroscopic sensors to detect CO2 in a gaseous environment by its characteristic absorption. The key components are an infrared source, a light tube, an interference (wavelength) filter, and an infrared detector. The gas is pumped or diffuses into the light tube, and the electronics measures the absorption of the characteristic wavelength of light. NDIR sensors are most often used for measuring carbon dioxide.[1] The best of these have sensitivities of 20–50 PPM.[1] Typical NDIR sensors cost in the (US) $100 to $1000 range.
New developments include using microelectromechanical systems to bring down the costs of this sensor and to create smaller devices (for example for use in air conditioning applications). NDIR CO2 sensors are also used for dissolved CO2 for applications such as beverage carbonation, pharmaceutical fermentation and CO2 sequestration applications. In this case they are mated to an ATR (attenuated total reflection) optic and measure the gas in situ.
Another method (Henry's Law) can be also be used to measure the amount of dissolved CO2 in a liquid, if the amount of foreign gases is insignificant.
Chemical CO2 sensors
Chemical CO2 gas sensors with sensitive layers based on polymer- or heteropolysiloxane have the principal advantage of a very low energy consumption, and can be reduced in size to fit into microelectronic-based systems. On the downside, short- and long term drift effects as well as a rather low overall lifetime are major obstacles when compared with the NDIR measurement principle.[2] Most CO₂ sensors are fully calibrated prior to shipping from the factory. Over time, the zero point of the sensor needs to be calibrated to maintain the long term stability of the sensor.
Applications
• Examples:
o Modified atmospheres
o Indoor air quality
o Stowaway detection
o Cellar and gas stores
o Marine vessels
o Greenhouses
o Landfill gas
o Confined spaces
o Cryogenics
o Ventilation management
o Mining
o Rebreathers (SCUBA)
• For HVAC applications, CO2 sensors can be used to monitor the quality of air and the tailored need for fresh air, respectively. Measuring CO2 levels indirectly determines how many people are in a room, and ventilation can be adjusted accordingly. See demand controlled ventilation (DCV).
• In applications where direct temperature measurement is not applicable, NDIR sensors can be used. The sensors absorb ambient infrared radiation (IR) given off by a heated surface.
iSweek(http://www.isweek.com/)- Industry sourcing & Wholesale industrial products

Electrochemical gas sensor

Electrochemical gas sensors are gas detectors that measure the concentration of a target gas by oxidizing or reducing the target gas at an electrode and measuring the resulting current.

History
Beginning his research in 1962, Mr. Naoyoshi Taguchi became the first person in the world to succeed in the development of a semiconductor device which could detect low concentrations of combustible and reducing gases when used with a simple electrical circuit. Devices based on this technology are often called "TGS" (Taguchi Gas Sensors).
Construction
The sensors contain two or three electrodes, occasionally four, in contact with an electrolyte. The electrodes are typically fabricated by fixing a high surface area precious metal on to the porous hydrophobic membrane. The working electrode contacts both the electrolyte and the ambient air to be monitored usually via a porous membrane. The electrolyte most commonly used is a mineral acid, but organic electrolytes are also used for some sensors. The electrodes and housing are usually in a plastic housing which contains a gas entry hole for the gas and electrical contacts.
Theory of operation
The gas diffuses into the sensor, through the back of the porous membrane to the working electrode where it is oxidized or reduced. This electrochemical reaction results in an electric current that passes through the external circuit. In addition to measuring, amplifying and performing other signal processing functions, the external circuit maintains the voltage across the sensor between the working and counter electrodes for a two electrode sensor or between the working and reference electrodes for a three electrode cell. At the counter electrode an equal and opposite reaction occurs, such that if the working electrode is an oxidation, then the counter electrode is a reduction.
Diffusion controlled response
The magnitude of the current is controlled by how much of the target gas is oxidized at the working electrode. Sensors are usually designed so that the gas supply is limited by diffusion and thus the output from the sensor is linearly proportional to the gas concentration. This linear output is one of the advantages of electrochemical sensors over other sensor technologies, (e.g. infrared), whose output must be linearized before they can be used. A linear output allows for more precise measurement of low concentrations and much simpler calibration (only baseline and one point are needed).
Diffusion control offers another advantage. Changing the diffusion barrier allows the sensor manufacturer to tailor the sensor to a particular target gas concentration range. In addition, since the diffusion barrier is primarily mechanical, the calibration of electrochemical sensors tends to be more stable over time and so electrochemical sensor based instruments require much less maintenance than some other detection technologies. In principle, the sensitivity can be calculated based on the diffusion properties of the gas path into the sensor, though experimental errors in the measurement of the diffusion properties make the calculation less accurate than calibrating with test gas.
Cross sensitivity
For some gases such as ethylene oxide, cross sensitivity can be a problem because ethylene oxide requires a very active working electrode catalyst and high operating potential for its oxidation. Therefore gases which are more easily oxidized such as alcohols and carbon monoxide will also give a response. Cross sensitivity problems can be eliminated though through the use of a chemical filter, for example filters that allows the target gas to pass through unimpeded, but which reacts with and removes common interferences.
While electrochemical sensors offer many advantages, they are not suitable for every gas. Since the detection mechanism involves the oxidation or reduction of the gas, electrochemical sensors are usually only suitable for gases which are electrochemically active, though it is possible to detect electrochemically inert gases indirectly if the gas interacts with another species in the sensor that then produces a response. Sensors for carbon dioxide are an example of this approach and they have been commercially available for several years.
 iSweek(http://www.isweek.com/)- Industry sourcing & Wholesale industrial products

Grove - Barometer Sensor

 This Grove - Barometer Sensor features a Bosch BMP085 high-accuracy chip to detect barometric pressure and temperature. It can widely measure pressure ranging from 300hPa to 1100hPa, AKA +9000m to -500m above sea level, with a super high accuracy of 0.03hPa(0.25m) in ultra-high resolution mode. The chip only accepts 1.8V to 3.6V input voltage. However, with outer circuit added, this module becomes compatible with 3.3V and 5V. Therefore, it can be used on Arduino/Seeeduino or Seeeduino Stalker without modification. It is designed to be connected directly to a micro-controller via the I2C bus.

Features
• Digital two wire (I2C) interface
• Wide barometric pressure range
• Flexible supply voltage range
• Ultra-low power consumption
• Low noise measurement
• Fully calibrated
• Temperature measurement included

Application Ideas
• Enhancement of GPS navigation
• Indoor and outdoor navigation
• Leisure and sports
• Weather forecast
• Vertical velocity indication (rise/sink speed)

 iSweek(http://www.isweek.com/)- Industry sourcing & Wholesale industrial products

2016年2月23日星期二

Choosing a Humidity Sensor: A Review of Three Technologies

 The 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.

photo
Photo 1. 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 (see Figure 1).

figure
Figure 1. 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 ft.
Direct field interchangeability can be a problem unless the sensor is laser trimmed to reduce variance to ±2% or a computer-based recalibration method is provided. These calibration programs can compensate sensor capacitance from 100 to 500 pF.
Dew Point. Thin film capacitance-based sensors provide discrete signal changes at low RH, remain stable in long-term use, and have minimal drift, but they are not linear below a few percent RH. These characteristics led to the development of a dew point measuring system incorporating a capacitive sensor and microprocessor-based circuitry that stores calibration data in nonvolatile memory. This approach has significantly reduced the cost of the dew point hygrometers and transmitters used in industrial HVAC and weather telemetry applications.
The sensor is bonded to a monolithic circuit that provides a voltage output as a function of RH. A computer-based system records the voltage output at 20 dew point values over a range of –40°C to 27°C. The reference dew points are confirmed with a NIST-traceable chilled mirror hygrometer. The voltage vs. dew/frost point values acquired for the sensor are then stored in the EPROM of the instrument. The microprocessor uses these values in a linear regression algorithm along with simultaneous dry-bulb temperature measurement to compute the water vapor pressure.
Once the water vapor pressure is determined, the dew point temperature is calculated from thermodynamic equations stored in EPROM. Correlation to the chilled mirrors is better than ±2°C dew point from –40°C to –7°C and ±1°C from –7°C to 27°C. The sensor provides long-term stability of better than 1.5°C dew point drift/yr. Dew point meters using this methodology have been field tested extensively and are used for a wide range of applications at a fraction of the cost of chilled mirror dew point meters.
Resistive Humidity Sensors
Resistive humidity sensors (see Photo 2) measure the change in electrical impedance of a hygroscopic medium such as a conductive polymer, salt, or treated substrate.

photo
Photo 2. Resistive sensors are based on an interdigitated or bifilar winding. After deposition of a hydroscopic polymer coating, their resistance changes inversely with humidity. The Dunmore sensor (far right) is shown 1/3 size.
The impedance change is typically an inverse exponential relationship to humidity (see Figure 2).

figure
Figure 2. The exponential response of the resistive sensor, plotted here at 25°C, is linearized by a signal conditioner for direct meter reading or process control.
Resistive sensors usually consist of noble metal electrodes either deposited on a substrate by photoresist techniques or wire-wound electrodes on a plastic or glass cylinder. The substrate is coated with a salt or conductive polymer. When it is dissolved or suspended in a liquid binder it functions as a vehicle to evenly coat the sensor. Alternatively, the substrate may be treated with activating chemicals such as acid. The sensor absorbs the water vapor and ionic functional groups are dissociated, resulting in an increase in electrical conductivity. The response time for most resistive sensors ranges from 10 to 30 s for a 63% step change. The impedance range of typical resistive elements varies from 1 k to 100 M.
Most resistive sensors use symmetrical AC excitation voltage with no DC bias to prevent polarization of the sensor. The resulting current flow is converted and rectified to a DC voltage signal for additional scaling, amplification, linearization, or A/DRconversion (see Figure 3).

figure
Figure 3. Resistive sensors exhibit a nonlinear response to changes in humidity. This response may be linearized by analog or digital methods. Typical variable resistance extends from a few kilohms to 100 MV.
Nominal excitation frequency is from 30 Hz to 10 kHz.
The "resistive" sensor is not purely resistive in that capacitive effects >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.
The latest development in resistive humidity sensors uses a ceramic coating to overcome limitations in environments where condensation occurs. The sensors consist of a ceramic substrate with noble metal electrodes deposited by a photoresist process. The substrate surface is coated with a conductive polymer/ceramic binder mixture, and the sensor is installed in a protective plastic housing with a dust filter.
The binding material is a ceramic powder suspended in liquid form. After the surface is coated and air dried, the sensors are heat treated. The process results in a clear non-water-soluble thick film coating that fully recovers from exposure to condensation (see Figure 4).

figure
Figure 4. After water immersion, the typical recovery time of a ceramic-coated resistive sensor to its pre-immersion, 30% value is 5-15 min., depending on air velocity.
The manufacturing process yields sensors with an interchangeability of better than 3% RH over the 15%–95% RH range. The precision of these sensors is confirmed to ±2% RH by a computer-based DA system. The recovery time from full condensation to 30% is a few minutes. When used with a signal conditioner, the sensor voltage output is directly proportional to the ambient relative humidity.
Thermal Conductivity Humidity Sensors
These sensors (see Photo 3) measure the absolute humidity by quantifying the difference between the thermal conductivity of dry air and that of air containing water vapor.

photo
Photo 3. For measuring absolute humidity at high temperatures, thermal conductivity sensors are often used. They differ in operating principle from resistive and capacitive sensors. Avbsolute humidity sensors are left and center; thermistor chambers are on the right.
When air or gas is dry, it has a greater capacity to "sink" heat, as in the example of a desert climate. A desert can be extremely hot in the day but at night the temperature rapidly drops due to the dry atmospheric conditions. By comparison, humid climates do not cool down so rapidly at night because heat is retained by water vapor in the atmosphere.
Thermal conductivity humidity sensors (or absolute humidity sensors) consist of two matched negative temperature coefficient (NTC) thermistor elements in a bridge circuit; one is hermetically encapsulated in dry nitrogen and the other is exposed to the environment (see Figure 5).

figure
Figure 5. In thermal conductivity sensors, two matched thermistors are used in a DC bridge circuit. One sensor is sealed in dry nitrogen and the other is exposed to ambient. The bridge output voltage is directly proportional to absolute humidity.
When current is passed through the thermistors, resistive heating increases their temperature to >200°C. The heat dissipated from the sealed thermistor is greater than the exposed thermistor due to the difference in the thermal conductively of the water vapor as compared to dry nitrogen. Since the heat dissipated yields different operating temperatures, the difference in resistance of the thermistors is proportional to the absolute humidity (see Figure 6).

figure
Figure 6. The output signal of the thermal conductivity sensor is affected by the operating temperature. Maximum output is at 600°C; output at 200°C drops by 70%.
A simple resistor network provides a voltage output equal to the range of 0–130 g/m3 at 60°C. Calibration is performed by placing the sensor in moisture-free air or nitrogen and adjusting the output to zero. Absolute humidity sensors are very durable, operate at temperatures up to 575°F (300°C) and are resistant to chemical vapors by virtue of the inert materials used for their construction, i.e., glass, semiconductor material for the thermistors, high-temperature plastics, or aluminum.
An interesting feature of thermal conductivity sensors is that they respond to any gas that has thermal properties different from those of dry nitrogen; this will affect the measurements. Absolute humidity sensors are commonly used in appliances such as clothes dryers and both microwave and steam-injected ovens. Industrial applications include kilns for drying wood; machinery for drying textiles, paper, and chemical solids; pharmaceutical production; cooking; and food dehydration. Since one of the by-products of combustion and fuel cell operation is water vapor, particular interest has been shown in using absolute humidity sensors to monitor the efficiency of those reactions.
In general, absolute humidity sensors provide greater resolution at temperatures >200°F than do capacitive and resistive sensors, and may be used in applications where these sensors would not survive. The typical accuracy of an absolute humidity sensor is +3 g/m3; this converts to about ±5% RH at 40°C and ±0.5% RH at 100°C.

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


Infrared CO2 sensor

 Cal Sensors announces the global launch of the IRCO2, an infrared CO2 sensor for HVAC applications. Designed to meet the challenging accuracy and reliability requirements of Demand Controlled Ventilation systems (DCVs), the IRCO2 combines superior sensitivity and reliability with lower costs and power consumption.

Cal Sensors' IRCO2 sensor applies the latest in non-dispersive infrared (NDIR) technologies. The optical path consists of a state-of-the-art emitter and detector that optimize the signal to noise performance while minimizing costs. Unlike traditional CO2 sensors that produce a signal by reacting with the gas, thus degrading over time, NDIR sensors generate a signal passively, by measuring the absorption of infrared light through the gas. Consequently, the infrared system eliminates degradation concerns, reduces maintenance, and provides accurate measurements more reliably.

Cal Sensors can support prototyping to high volume manufacturing requests with lead times depending on quantities desired.

The IRCO2 was first introduced at the SPIE Photonics West 2013 exhibit held February 2-7, 2013 in San Francisco, California.


iSweek(http://www.isweek.com/)- Industry sourcing & Wholesale industrial products

Semiconductor gas sensor

 A semiconductor gas sensor for use in equipment for detecting small amounts of H2 S. The method of sensor fabrication comprises spray deposition of a mixture of metal oxides mixed together with various metal and non-metal materials which serve in the finished product as activators, dopants, and/or film binder materials, and including in suspension a molecular sieve material, for enhancing and defining porosity on a scale of molecular dimensions in the finished sensor.

All of the foregoing materials are suspended in a suitable solution and preferably sprayed onto a heated insulating substrate to form the finished product. The example sensor, capable of selective detection of H2 S in air and a sensitivity of less than 1 PPM (part per million), is comprised of a platinum activated alumina, tin oxide, and zeolite molecular sieve material.

FIELD OF THE INVENTION

This invention relates to semiconductor gas sensors and to methods of fabrication thereof, and more particularly to a unique spray deposition method wherein an improved semiconductor sensor is fabricated which comprises preselected gas sensor components in combination with a molecular sieve material to enhance and define porosity in the final semiconducting film. A specific example of a sensor and its method of fabrication is described which is capable of a selective detection of H2 S by changes in the conductivity of the sensor relative to the concentration of H2 S in the gas sample.

BACKGROUND OF THE INVENTION
Various semiconducting metal oxides have been used in conjunction with a variety of metal and non-metal additives in the fabrication of gas sensitive films suitable for use in gas detection apparatus. Exposure of such gas sensitive films to the gas of interest generally is detected as a change in conductivity of the film. In general, these prior devices exhibited inherent deficiencies in sensitivity, selectivity, response and recovery times, and/or calibration stability.

The electrical characteristics and subsequent gas response characteristics of such materials when employed as gas sensors in previous gas sensing equipment have been found to be highly dependent upon film properties such as thickness, uniformity of composition, purity, film porosity, and density. Since it has previously been difficult to adequately control the foregoing factors this art has been seeking a technique of fabrication which would be capable of producing films with the above mentioned and other properties well controlled.

In addition it is of course desireable that any new technique should be reproducible and cost effective. Further, the previous sensors were sometimes of limited utility if they were not capable of low temperature operation. This property is advantageous when sensing flammable gases in that there would be a reduced hazard of flammable gas ignition by the operating sensor, as well as an increased realiability and sensor life, reduced sensor power requirements, and better compatibility with on-chip integrated signal processing circuitry.

iSweek(http://www.isweek.com/)- Industry sourcing & Wholesale industrial products 


How Does an NDIR CO2 Sensor Work?

In our industry, many of us use the term "NDIR CO2 sensor", without thinking about what it stands for, or how NDIR sensors actually work.

NDIR is an industry term for "nondispersive infrared", and is the most common type of sensor used to measure CO2.

An infrared (IR) lamp directs waves of light through a tube filled with air toward an IR light detector, which measures the amount of IR light that hits it. As the light passes through the tube, any gas molecules that are the same size as the wavelength of the IR light absorb the IR light light only, while letting other wavelengths of light pass through.

Next, the remaining light hits an optical filter that absorbs every wavelength of light except the exact wavelength absorbed by CO2.

Finally, an IR detector reads the amount of light that was not absorbed by the CO2 molecules or the optical filter.

The difference between the amount of light radiated by the IR lamp and the amount of IR light received by the detector is measured. The difference is proportional to the number of CO2 molecules in the air inside the tube.

Of course, this is a very simplified explanation. If you want to learn more about NDIR, this Wikipedia article is a great place to start.

iSweek(http://www.isweek.com/)- Industry sourcing & Wholesale industrial products 

2016年2月22日星期一

Measuring methane with a simple open-path gas sensor

Methane is the second most prevalent greenhouse gas sensor after carbon dioxide, and influences tropospheric ozone and water vapor, further increasing its importance to the Earth's radiation budget.1 Due to its short atmospheric lifetime compared with carbon dioxide, a reduction in methane emissions can produce a rapid response in moderating climate change.2 Therefore, methane monitoring will be an important component of a greenhouse gas regulatory framework. However, constraining the atmospheric budget of methane has proved difficult, notably because of its numerous sources.

In remote and rural areas, problems with space, gas and electric supply, dust, and temperature can present challenges when establishing ground-based stations for atmospheric gas measurements. Often there is insufficient infrastructure available to install valuable and delicate methane analyzers, such as gas chromatograph and cavity ring-down spectroscopy instruments. As a result, there are often uncertainties in quantitative estimation of methane emissions. Satellite observations can enable sensing of methane and retrieval of information on abundances of the gas, but these can be compromised in areas with frequent cloud cover and high aerosol optical depth.4 Ultimately, we require detailed comparisons between satellite and ground-based measurements, which necessitates in situ atmospheric measurements over vast and fast-growing regions for an improved, more detailed understanding of methane budgets.

To obtain in situ observations in remote regions, one conventional and reliable method of gas measurement is air vessel sampling followed by laboratory analysis. However, to be effective, this technique requires frequent samplings and measurements to investigate regional emissions and advection (bulk motion of fluids).

To overcome these issues, we developed an in-field methane concentration measurement system that provides continuous observations, and it interpolates the data obtained by the traditional sampling method with a one-week interval. We operated the system at a barn in a paddy field in rural northern India close to methane sources. We used the LaserMethane miniG (LMm) detection system, which was originally designed to identify gas leaks.5 The instrument is small (W70 × D179 × H42mm), cost-effective, has low electric consumption (∼1W), requires very little maintenance, and is highly durable. It can measure atmospheric methane concentration continuously, and is therefore suitable for field observations in rural areas.


The LMm senses and measures methane by an open-path method, using a near-IR diode laser for IR absorption spectroscopy. In field measurements, the laser light is returned by a reflector located tens of meters from the unit, and is detected by a photodetector in the instrument (see Figures 1, 2). The LMm can quickly and selectively detect the methane concentration integrated over the open optical path, and achieves high sensitivity by second-harmonic detection using wavelength-modulation spectroscopy. The relative error of the methane concentration for a 10min integration time is less than 2% when measuring the typical atmospheric concentration with a path length of 50m. We provided an instrument chassis and frame for adjustment of the laser alignment, as well as a battery-backed power supply system to enable continuous operation since the region has only intermittent AC power supply.

We conducted continuous measurement of methane at the Indian paddy field since December 2014 to investigate diurnal and seasonal variations of methane concentration and their relationship with sources and meteorological conditions. We calibrated the concentration values of methane by the data obtained using the vessel sampling method once a week at the same site. The measurement system has not only provided the seasonal variation characteristics, such as enhancement of methane in the monsoon season relating to the rice vegetation phenology, but also provided detailed information on diurnal and day-to-day variations related to the local meteorological conditions and local emissions. Figure 2 (inset) shows typical results of the diurnal variations. The observation results obtained prove the durability of the instrument for methane network observations.

Our system achieved low-cost, easily installed, almost maintenance-free performance, supplying measurements at hard-to-access sites close to methane sources. Our future work will focus on extending the observation network over a larger area from the plains to the mountain regions. In this way, we may further the studies of satellite retrievals that show a plume-like enhancement of methane over south Asia during the monsoon season, suggesting enhanced emissions and deep convection during that time of year.



Advanced NDIR Sensor for SF6 or Refrigerants Detection

 The IR series of infrared gas detection sensors, from N.E.T. (Italy), use the technique of NDIR sensor (Non Dispersive Infrared) to monitor the presence of SF6 or refrigerants.

This technique is based on the fact that the gas has a unique and well defined light absorption curve in the infrared spectrum that can be used to identify the specific gas. The gas concentration can be determined by using a suitable infrared source and by analysing the quantity of energy absorbed from the gas inside the optical path.

The IREF-P sensor is equipped with electronics and firmware in order to provide an output that is linearised and temperature compensated. The output is analogue voltage type [0.4 V—2 V] dc (other voltages are available on request). IREF P is now SIL2 approved.

The main features are: analogue voltage standard output, incorporated signal, linearisation and temperature compensation suited for instrument manufacturers without any specialist knowledge in IR technology, standard sensor size 32 mm, fast response, solid, rugged construction, wide operating temperature and humidity range (-20°C +60°C) and new optics “Variable Geometry".

iSweek(http://www.isweek.com/)- Industry sourcing & Wholesale industrial products 

Feasibility of a novel NDIR CO2 sensor in North Atlantic

Researchers from Germany and Cape Verde fitted an oceanographic profiling float (i.e. able to adjust internal buoyancy to either float or sink in the water column) with a Non-Dispersive Infrared NDIR CO2 sensor, as well as with an O2 sensor, to determine the feasibility of combining these two sensors to collect continuous measurements of both gases.

The float was deployed near the Cape Verde Ocean Observatory (CVOO) on four separate occasions between November 2010 and June 2011.

Despite the relatively slow sensor response time, the pCO2 data collected were reliable and a comprehensible drift pattern allowed the researchers to easily account for any sensor drift.

The combination of pCO2 and O2 sensors was found to be feasible and collected data with accuracy similar to that of a more typical but heavier set up. Remarkably, the large changes in pressure and temperature during short-interval upcasts (~1.5 h) of the float did not cause any significant sensor drift.

CO2 Concentration in Eastern Tropical North Atlantic Studies
All-in-all, this set up appears to be feasible for continuous in situ measurements of CO2 and O2 profiles in the ocean.

iSweek(http://www.isweek.com/)- Industry sourcing & Wholesale industrial products 

Principles of NDIR Gas Sensors

How does a non-dispersive infrared NDIR gas sensor work?

-Using the characteristics of different gas molecules absorbing infrared rays with specific wavelengths, NDIR sensors measure the ratio of absorbed infrared rays and compute the density of gas (e.g. CO2 absorbs 4.26㎛ , and CO absorbs 4.64)

-NDIR is contactless and highly accurate while having an extensive longevity.

-Previously only used in manufacturing highly-priced measurement instruments,,

NDIR technologies have been recently applied in mass-producing low-cost CO2 sensors for everyday use.


iSweek(http://www.isweek.com/)- Industry sourcing & Wholesale industrial products 

2016年2月19日星期五

Portable gas sensors improve atmospheric pollution measurements

Remote-controlled robotic helicopter in flight with a laser-based greenhouse gas sensor extending from its nose. The aerial detector is easy to deploy, inexpensive to operate, can be guided by GPS, and provides measurements in both vertical and horizontal directions. Credit: Department of Civil and Environmental Engineering, Princeton University
Different types of compact, low-power portable sensors under development by three independent research groups may soon yield unprecedented capabilities to monitor ozone, greenhouse gases, and air pollutants. The three teams will each present their work at the Conference on Lasers and Electro-Optics (CLEO: 2012 ), to be held May 6-11, in San Jose, Calif.

Princeton University engineer Amir Khan and colleagues, working with space scientists at the University of Texas at Dallas, will discuss how their teams combined a compact, low-power, open-path (exposed directly to the environment) laser sensor with a robotic helicopter to measure the three most important greenhouse gases – carbon dioxide, methane and water vapor – in the atmosphere. The biggest advantage of the combination is that it provides high-resolution mapping in both the vertical and horizontal directions near emissions sources – something that ground-based networks or satellite-based sensors cannot do. Additionally, the sensor on the robotic helicopter is easy to deploy, inexpensive to operate, can be programmed to fly a preset monitoring pattern using GPS coordinates, and can handle challenging situations such as measuring emissions from industrial plants where the plumes move sideways as well as up.

A first-time demonstration of a system with the potential to become a portable, low-power, low-cost, and long-lasting optical sensor for ozone (O3) measurements will be presented by a team of engineers from the University of Rostock in Germany and Sensor Electronic Technology Inc. in South Carolina. The sensor uses light-emitting diodes (LEDs) to produce light in the deep ultraviolet range of the spectrum (wavelengths less than 300 nanometers) that allows the detection of small amounts of ozone – trace concentrations ranging anywhere from approximately 10 parts per billion to approximately 100 parts per million. The team showed in tests that this sensitivity compares favorably to conventional sensors that use less durable and more expensive mercury or electrochemical light sources. The team also discovered that coupling the deep ultraviolet LED to the detection equipment with fiber-optic cables produced a sturdy sensor that could be used in harsh environments, such as areas with strong electromagnetic fields, high temperatures, or strong vibrations.

Finally, engineer David Miller, also from Princeton University, will discuss his team's use of an open-path quantum cascade laser to create a portable sensor that can detect extremely small quantities of atmospheric ammonia (NH3) in harsh field environments. This molecule commonly forms unhealthy particulate matter, but measurements of this pollutant in the atmosphere are lacking. The Princeton sensor has performed well when deployed in harsh environments – everything from dusty deserts to jungle-like conditions to sub-freezing temperatures – providing an ability to measure concentrations of NH3 as small as 200 parts per trillion. Data from the high-sensitivity ammonia sensor will significantly improve air quality forecasts.



New Universal Inductive Conductivity Sensor Simplifies Accurate Process Measurement

Designed with matched dual toroidal magnetic coils for precision accuracy, the intelligent S80 Inductive Conductivity Sensor from Electro-Chemical Devices (USA) simplifies process measurement in rugged industrial water treatment applications.
The measurement of conductivity in liquid water-based solutions is an essential requirement in a wide range of municipal water treatment and industrial processes. Conductivity sensors measure the electrical conductivity of a solution, which correlates to the purity of the water or the amount of dissolved ions in the liquid.
The versatile S80 Inductive Conductivity Sensors are ideal for a wide range of rugged environment municipal and industrial water applications. They are suitable for service in applications that include: wastewater treatment effluent, petrochemical refinery cooling tower water, food/beverage concentration control and clean-in-place (CIP) systems, electronic component resin regeneration, rinsing systems for metals and mining production, paper pulp stock processes and electric power generation cooling tower water. The 0.75-inch diameter allows for easy installation using the fittings common to all S80 sensors.
The S80 Inductive Conductivity Sensors convert the analogue signals from their dual toroid magnetic coils into a digital protocol that allows two-way communications with ECD’s universal T80 transmitter. The identity of the sensor, the measurement type and the serial number are stored in the sensor’s memory along with three calibration registers.
When connected to an ECD digital analyser the sensor’s conductivity measurement information is uploaded from the sensor to the analyser. This system configures the displays and outputs of the transmitter to the values appropriate for the parameter measured by the sensor. Set-up is easy with this virtually plug-and-play sensor/transmitter/analyser technology.
The S80’s conductivity sensors feature a chemically resistant PVDF (KYNAR) body, which is excellent for highly corrosive industrial process environments. The standard contacting sensor configuration can measure from very low conductivity, < 50 µS, to very high conductivity ranges, but they can be subject to coating and corrosion issues in some applications. When those conditions are present the non-contacting configuration sensors excel. The contacting conductivity S80 sensors come in three ranges, low range, 0.05μS – 50μS, high range, 50μS – 50mS and Resistivity, 0 – 20MΩ. The inductive sensors measure from 50µS to 1000mS.
The S80 Sensors are designed for use with the ECD Model T80 transmitter, which is available as a single or dual channel transmitter for the measurement of conductivity, resistivity, pH, ORP, pION, dissolved oxygen and turbidity. The Model T80 transmitter digitally communicates with any ECD intelligent S80 digital sensor, automatically configuring the transmitter’s menus and display screens to the measured parameter.
The ECD S80 digital sensor product line facilitates two way communication with the Model T80 transmitters. With the optional SENTINEL configuration, the transmitter automatically activates a “remaining life” diagnostic graphic alert for the S80 sensor’s replaceable cartridge.

 iSweek(http://www.isweek.com/)- Industry sourcing & Wholesale industrial products


Zirconia Oxygen Sensors - Principles of Operation and Design

Many processes use zirconia based oxygen sensors for monitoring and control. Solid-state sensors have found uses in a wide range of applications, including, control of atmosphere in materials processing and control of air-to-fuel ratio in combustion.

Technox Zirconia Oxygen Sensors

Technox® 802 a fully stabilised Yttria zirconia (FSZ) material is used to produce a wide range of components for application as oxygen sensors. Typically these include thin walled, open and closed end tubes, flat plates and sheets.

Figure 1. Technox® 802 zirconia oxygen sensors.
Operating Temperatures for Oxygen Sensors
The characteristics required for an oxygen monitoring device will vary with its application. Thus a flue gas monitor would be required to operate between 200°C and 600°C when interpretation of the EMF generated would be difficult, due to the temperature dependence of the electrode kinetics and the variation in EMF due to temperature.
As the boiler output is changed the flue gas temperature will change similarly so that the EMF output would vary. To obtain a constant and representative EMF the zirconia electrolyte is maintained at constant high temperature (700°C-800°C) as shown in figure 2 by incorporating the sensor in an oven.

Figure 2. Schematic of an oxygen level sensor.
Atmosphere Control
Atmosphere control using a dedicated monitor requires operation at low partial pressure of oxygen and temperatures in the range 800°C-1200°C. The gas carburising process used to harden steel components is a typical application. However at the high end of this temperature range the electronic conductivity can become significant.
Care must be taken to avoid impurities such as Fe3+ which could enhance this reaction. Further problems are encountered:
• With the removal of grain boundary phases by volatilisation allowing the electrolyte to become permeable and
• With the high thermal stresses often generated when carbon deposits are regularly burnt off.
Reducing Emissions
The legal requirements in some countries to control exhaust gas emission and the rapid increase in fuel prices have led to the demand for greater control of the internal combustion engine.
Control of Air/Fuel Ratios
The effectiveness of the equipment added to reduce pollution depends on accurate control of the air to fuel ratio, which may be monitored with an oxygen sensor, either before combustion or more usually from the exhaust gas composition.
The exhaust gas is usually reducing, hence there is only a small pO2 present. Since the amount of O2 present under thermodynamic equilibrium depends greatly on the air to fuel ratio, it is essential for the sensor, particularly the electrode surfaces, to have catalytic properties in order to equilibrate the pO2 as quickly as possible.
Oxygen Sensor Design
The device most widely used at present consists of a stabilised zirconia electrolyte tube with platinum electrodes deposited on the inner and outer surfaces. With different pO2 on inner and outer surfaces an EMF is generated. If carbon monoxide is present a further reaction is possible:
CO (gas) + O2 (electrolyte) -> CO2 (gas) + 2e- (electrode)
The catalytic reaction at the platinum electrode
CO (gas) + ½ O2 ->CO2
can minimise the above effect. Further reactions can occur when H2, H2O and NOx are present. The successful application of an exhaust monitor requires a simple and inexpensive device which is able to operate in a harsh environment at temperatures in the region of 900°C in the presence of thermal shock.
A typical sensor is shown in the diagram, figure 2, with the format being similar to an 18mm diameter sparking plug.

Figure 2. Schematic of a section through a ZrO2 oxygen sensor for use in an internal combustion engine.
Electrolytes and Electrodes
Yttria stabilised zirconia (YSZ) is used as the electrolyte with platinum coated electrodes, with the outer layer of Pt coated with a porous oxide to protect the electrode from erosion. The microstructure of this layer is of importance since it governs the oxygen equilibrium conditions and also the response time of the device.
For control devices, a well made zirconia electrode has a response time < 200ms above 350°C.
Degradation of the Oxygen Sensor
Another factor of importance is the degradation of the sensor due to ageing of the system, where the main change is an increase in the response time and a decrease in the EMF output. Poisoning of the catalytic activity of the Pt electrode can occur by the deposition of lead oxides or the formation of oil rich deposits on the sensor.
Summary
In spite of these difficulties, zirconia exhaust sensors have been developed successfully particularly for applications with stoichiometric air to fuel mixtures.

 iSweek(http://www.isweek.com/)- Industry sourcing & Wholesale industrial products


lobal Semiconductor gas sensor Markets Size, Analysis, Share, Growth and Forecasts 2015

2015 Global Semiconductor gas sensor Industry Report is a professional and in-depth research report on the world’s major regional market conditions of the Semiconductor gas sensor industry, focusing on the main regions (North America, Europe and Asia) and the main countries (United States, Germany, Japan and China).

The report firstly introduced the Semiconductor gas sensor basics: definitions, classifications, applications and industry chain overview; industry policies and plans; product specifications; manufacturing processes; cost structures and so on. Then it analyzed the world’s main region market conditions, including the product price, profit, capacity, production, capacity utilization, supply, demand and industry growth rate etc. In the end, the report introduced new project SWOT analysis, investment feasibility analysis, and investment return analysis.

The report includes six parts, dealing with: 1.) basic information; 2.) the Asia Semiconductor gas sensor industry; 3.) the North American Semiconductor gas sensor industry; 4.) the European Semiconductor gas sensor industry; 5.) market entry and investment feasibility; and 6.) the report conclusion.

Part I Semiconductor gas sensor Industry Overview
Chapter One Semiconductor gas sensor Industry Overview
1.1 Semiconductor gas sensor Definition
1.2 Semiconductor gas sensor Classification Analysis
1.2.1 Semiconductor gas sensor Main Classification Analysis
1.2.2 Semiconductor gas sensor Main Classification Share Analysis
1.3 Semiconductor gas sensor Application Analysis
1.3.1 Semiconductor gas sensor Main Application Analysis
1.3.2 Semiconductor gas sensor Main Application Share Analysis
1.4 Semiconductor gas sensor Industry Chain Structure Analysis
1.5 Semiconductor gas sensor Industry Development Overview
1.5.1 Semiconductor gas sensor Product History Development Overview
1.5.1 Semiconductor gas sensor Product Market Development Overview
1.6 Semiconductor gas sensor Global Market Comparison Analysis
1.6.1 Semiconductor gas sensor Global Import Market Analysis
1.6.2 Semiconductor gas sensor Global Export Market Analysis
1.6.3 Semiconductor gas sensor Global Main Region Market Analysis
1.6.4 Semiconductor gas sensor Global Market Comparison Analysis
1.6.5 Semiconductor gas sensor Global Market Development Trend Analysis
Chapter Two Semiconductor gas sensor Up and Down Stream Industry Analysis
2.1 Upstream Raw Materials Analysis
2.1.1 Upstream Raw Materials Price Analysis
2.1.2 Upstream Raw Materials Market Analysis
2.1.3 Upstream Raw Materials Market Trend
2.2 Down Stream Market Analysis
2.1.1 Down Stream Market Analysis
2.2.2 Down Stream Demand Analysis
2.2.3 Down Stream Market Trend Analysis

Part II Asia Semiconductor gas sensor Industry (The Report Company Including the Below Listed But Not All)
Chapter Three Asia Semiconductor gas sensor Market Analysis
3.1 Asia Semiconductor gas sensor Product Development History
3.2 Asia Semiconductor gas sensor Process Development History
3.3 Asia Semiconductor gas sensor Industry Policy and Plan Analysis
3.4 Asia Semiconductor gas sensor Competitive Landscape Analysis
3.5 Asia Semiconductor gas sensor Market Development Trend

 iSweek(http://www.isweek.com/)- Industry sourcing & Wholesale industrial products