I have prepared nanocrystalline TiO2 powder and I am looking for gas sensor applications.
Firstly, most of the gas sensors are specified only for a certain
temperature. Since cooling is more difficult, the heating temperature is
set well above room temperature in order to be sure that the simple
Joule-heating does the job.
Secondly, the gas sensor itself needs to be water-free. Usually, all
objects at room temperature (or lower) around us are covered with a
multi-molecular H2O-film, coming from the air humidity and sticking on
the surface due to the high polarity of the H2O-molecule. In heating,
you get rid of that, like baking of ultrahigh-vacuum chambers.
The key process in the response of the semiconductor to a reducing gas
involves the modulation of the concentration of adsorbed oxygen species.
By withdrawing electron density from the semiconductor surface,
adsorbed oxygen gives rise to Schottky potential barriers at grain
boundaries, and thus increases the resistance of the sensor surface.
Reducing gases decrease the surface oxygen concentration and thus
decrease the sensor resistance. The temperature dependence of this
process arises in part from the differing stabilities of the surface
oxygen species over different temperature ranges. The different gases
have characteristic optimum oxidation temperatures, and therefore give
rise to characteristic conductance temperature profiles, which can be
modified by doping the semiconductor with noble metals or other
catalytic materials.
most gas sensor is built from materials and these materials have maximum
working temperature to detect the gases, so increasing the temperature
of detecting materials to the best sensitivity like ZnO is has very good
sensitivity at 200C for methane gas so they using heater to increase
the ZnO temperature to 200 C to be always at maximum sensitivity. this
type of work cause the draw back the sensitivity of sensor with time and
can effect on the accuracy of detector
Generally metal oxide based gas sensors operate at relatively higher
temperatures to facilitate the chemical reaction to produce the sensor
response (as endothermic chemical reaction requires some activation
energy that can be provided in form of heat) and to reduce the effects
of humidity.
iSweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrial products
2016年3月7日星期一
Ultra-sensitive photosensor ignores ambient light
Since
photosensors must not trigger on ambient light changes, it limits their
sensitivity. That’s because large ambient light variations cause large
changes in photocell resistance and sensitivity. In attempts to increase
sensitivity, users typically resort to shielding, filtering the ambient
light, or restricting the application. Ambient light changes are slow,
so the circuit described here combines this characteristic with
electronic feedback to produce an ultrasensitive photo detector.
With the lamp voltage set at 9 V, the change in photocell resistance from ambient room light to dark is 100 Ω (from 600 to 700 Ω). The resistance change generated by clear plastic moving between the cell and light is 20 Ω. The only way to sense the plastic under all light conditions is to make the cell resistance independent of ambient light changes. A dc-coupled circuit accomplishes this by varying the lamp voltage to compensate for ambient light changes.
The current source (Q1) shown in the figure biases the photo cell with 5 mA, and this yields a cell voltage of 3.25 V for the average cell resistance of 650 Ω. The divider string consisting of R5, R6, and R7 puts 3.25 V on the noninverting lead of the CA3140 op amp. The CA3140 was selected for the op amp because it has very small input currents required for an integrator. The integrator causes Q2 to push current through the lamp until the voltage at the inverting lead of the op amp equals 3.25 V.
The integration time constant consists of R4 and the series combination of C1 and C2. C1 and C2 are connected in series to create a largevalue, non-polarized capacitor. The integration time constant is 110 seconds, so the feedback loop can only respond to very slow changes in the light level. The loop is fast enough to correct for ambient light changes, but when the plastic moves rapidly between the lamp and the cell, the cell responds by producing a positive 100-mV change across the photocell. When the time constant is selected to be as fast as ambient light changes allow, fast signals have no discernible effect on the feedback circuit.
The voltages at both op-amp inputs are equal at 3.25 V when no signal is present. No current flows through R4, so the voltage drop across R6 biases the comparator output to the low state. The HA4905 comparator was chosen for this application because it can sense input voltages close to the 15-V supply rail, yet it still has a logic-compatible output voltage. The current flowing through R6 generates 10.7 mV of bias, which is large enough to overcome voltage and current offsets.
The 100-mV signal resulting from the clear plastic passing between the lamp and cell overcomes the bias causing the output voltage to go high. There’s no capacitor in the signal path, thus there are no recovery time problems associated with this design. This circuit preserves the photocell sensitivity across a wide range of ambient light changes. It has been adapted for interior and exterior use. Moreover, the sensor can be adjusted to sense the presence of clear glass.
iSweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrial products
With the lamp voltage set at 9 V, the change in photocell resistance from ambient room light to dark is 100 Ω (from 600 to 700 Ω). The resistance change generated by clear plastic moving between the cell and light is 20 Ω. The only way to sense the plastic under all light conditions is to make the cell resistance independent of ambient light changes. A dc-coupled circuit accomplishes this by varying the lamp voltage to compensate for ambient light changes.
The current source (Q1) shown in the figure biases the photo cell with 5 mA, and this yields a cell voltage of 3.25 V for the average cell resistance of 650 Ω. The divider string consisting of R5, R6, and R7 puts 3.25 V on the noninverting lead of the CA3140 op amp. The CA3140 was selected for the op amp because it has very small input currents required for an integrator. The integrator causes Q2 to push current through the lamp until the voltage at the inverting lead of the op amp equals 3.25 V.
The integration time constant consists of R4 and the series combination of C1 and C2. C1 and C2 are connected in series to create a largevalue, non-polarized capacitor. The integration time constant is 110 seconds, so the feedback loop can only respond to very slow changes in the light level. The loop is fast enough to correct for ambient light changes, but when the plastic moves rapidly between the lamp and the cell, the cell responds by producing a positive 100-mV change across the photocell. When the time constant is selected to be as fast as ambient light changes allow, fast signals have no discernible effect on the feedback circuit.
The voltages at both op-amp inputs are equal at 3.25 V when no signal is present. No current flows through R4, so the voltage drop across R6 biases the comparator output to the low state. The HA4905 comparator was chosen for this application because it can sense input voltages close to the 15-V supply rail, yet it still has a logic-compatible output voltage. The current flowing through R6 generates 10.7 mV of bias, which is large enough to overcome voltage and current offsets.
The 100-mV signal resulting from the clear plastic passing between the lamp and cell overcomes the bias causing the output voltage to go high. There’s no capacitor in the signal path, thus there are no recovery time problems associated with this design. This circuit preserves the photocell sensitivity across a wide range of ambient light changes. It has been adapted for interior and exterior use. Moreover, the sensor can be adjusted to sense the presence of clear glass.
iSweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrial products
CO2 Sensor SKU:SEN0159
Introduction
Greenhouse Effect is melting the iceberg every minute,. By knowing the exact concentration of CO2, we can do something to reduce the CO2 and to protect our earth. For that reason, a HQ CO2 sensor is designed by DFRobot engineer . This is the first CO2 sensor in OSHW market. The output voltage of the module falls as the concentration of the CO2 increases. The potentiometer onboard is designed to set the threshold of voltage. As long as the CO2 concentration is high enough (voltage is lower than threshold), a digital signal (ON/OFF) will be released.
• Features:
o It has MG-811 sensor module onboard which is highly sensitive to CO2 and less sensitive to alcohol and CO, Low humidity & temperature dependency.
o Onboard heating circuit brings the best temperature for sensor to function. 5V power input will be boosted to 6V for heating.
o This sensor has an onboard conditioning circuit for amplifying output signal.
Specification
• Operating voltage: 5V
• Interface: Analog
• One digital output (Once the CO2 concentration is over the set threshold value, it will output digital HIGH, 5V)
• Onboard heating circuit
o Heating Current: 200mA
o Heating Power: 1200mW
• Size: 32x42mm
iSweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrial products
Greenhouse Effect is melting the iceberg every minute,. By knowing the exact concentration of CO2, we can do something to reduce the CO2 and to protect our earth. For that reason, a HQ CO2 sensor is designed by DFRobot engineer . This is the first CO2 sensor in OSHW market. The output voltage of the module falls as the concentration of the CO2 increases. The potentiometer onboard is designed to set the threshold of voltage. As long as the CO2 concentration is high enough (voltage is lower than threshold), a digital signal (ON/OFF) will be released.
• Features:
o It has MG-811 sensor module onboard which is highly sensitive to CO2 and less sensitive to alcohol and CO, Low humidity & temperature dependency.
o Onboard heating circuit brings the best temperature for sensor to function. 5V power input will be boosted to 6V for heating.
o This sensor has an onboard conditioning circuit for amplifying output signal.
Specification
• Operating voltage: 5V
• Interface: Analog
• One digital output (Once the CO2 concentration is over the set threshold value, it will output digital HIGH, 5V)
• Onboard heating circuit
o Heating Current: 200mA
o Heating Power: 1200mW
• Size: 32x42mm
iSweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrial products
The semiconductor gas sensing technique
Semiconductor gas sensors rely on a gas coming into contact with a
metal oxide surface and then undergoing either oxidation or reduction.
The absorption or desorption of the gas on the metal oxide changes
either the conductivity or resistivity from a known baseline value. This
change in conductivity or resistivity can be measured with electronic
circuitry. Usually the change in conductivity or resistivity is a linear
and proportional relationship with gas concentration. Therefore, a
simple calibration equation can be established between
resistivity/conductivity change and gas concentration.
An example of a calibration equation for a change in resistivity is given by Fine et al (2010) for carbon monoxide:
R/Ro = 1+A[CO]
where R is the resistance following contact with a gas, Ro is the baseline resistance, A is a constant, and CO is carbon monoxide.
The metal oxide surface is usually a thin film of a transition or heavy metal. The exact metal that is used will depend on the application and example metals include tin dioxide (SnO2) or tungsten oxide (WO3). The film overlies a layer of silicon and is heated to a temperature between 200 and 400C, again depending on the application. In this way, the chemical processes is hastened and the effects of fluctuating external temperatures is minimised.
Semiconductor sensors work best when they have a large surface area. Such a sensor can absorb as much of the target gas as possible particularly at low concentrations.
example CO sensor calibration output
The figure above is an example calibration output from a CO sensor taken from the ESCOD-200 Carbon Monoxide Detector Manual. The graph on the left is a sensor with a voltage output and the graph on the right is a sensor with a 4..20mA output. Both graphs show a simple, linear relationship. At 2V, CO level is 0ppm where as at 10V the CO level is 300ppm. Similarly, for the current sensor, at 4mA the CO level is 0ppm and at 20mA the CO level is 300ppm. A simple algebraic extraction will determine what the CO levels are between 0 and 300ppm for a given voltage or mA output.
advantages of semiconductor sensors
Semiconductor sensors are relatively inexpensive to manufacture due to their simplicity and scalability.
Specific sensors can be designed for particular applications. For example, a sensor can be designed for low concentration applications whereas an alternative sensor can be designed for high concentration applications.
limitations of semiconductor sensors
Non-target gases may absorb on the oxide surface and provide false measurements. Important disrupting gases include ozone, water and volatile organic compounds.
One of the advantages of semiconductor sensors is their flexibility in sensor design for specific applications (see above in Advantages section). However, this can also be a limitation. A user will need to purchase multiple sensors depending on the application.
The relationship between R/Ro and CO2 is not necessarily linear leading to issues with consistent calibration across sensors. Individual calibration of sensors may be necessary, leading to increased sensor costs associated with resources and labour time.
Fine et al (2010) state that semiconductor CO2 sensors perform best in the range between 2,000 and 10,000 ppm. This limited range means the semiconductor CO2 sensors will not be suitable for a number of applications. For example, in plant physiology, atmospheric CO2 concentrations are most important in the range between 280ppm and 800 ppm. For indoor air quality applications, an ideal monitoring range is in the order between 500 and 1,000 ppm.
Semiconductor CO2 sensors can also be unreliable at high relative humidity and varying temperatures.
iSweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrial products
An example of a calibration equation for a change in resistivity is given by Fine et al (2010) for carbon monoxide:
R/Ro = 1+A[CO]
where R is the resistance following contact with a gas, Ro is the baseline resistance, A is a constant, and CO is carbon monoxide.
The metal oxide surface is usually a thin film of a transition or heavy metal. The exact metal that is used will depend on the application and example metals include tin dioxide (SnO2) or tungsten oxide (WO3). The film overlies a layer of silicon and is heated to a temperature between 200 and 400C, again depending on the application. In this way, the chemical processes is hastened and the effects of fluctuating external temperatures is minimised.
Semiconductor sensors work best when they have a large surface area. Such a sensor can absorb as much of the target gas as possible particularly at low concentrations.
example CO sensor calibration output
The figure above is an example calibration output from a CO sensor taken from the ESCOD-200 Carbon Monoxide Detector Manual. The graph on the left is a sensor with a voltage output and the graph on the right is a sensor with a 4..20mA output. Both graphs show a simple, linear relationship. At 2V, CO level is 0ppm where as at 10V the CO level is 300ppm. Similarly, for the current sensor, at 4mA the CO level is 0ppm and at 20mA the CO level is 300ppm. A simple algebraic extraction will determine what the CO levels are between 0 and 300ppm for a given voltage or mA output.
advantages of semiconductor sensors
Semiconductor sensors are relatively inexpensive to manufacture due to their simplicity and scalability.
Specific sensors can be designed for particular applications. For example, a sensor can be designed for low concentration applications whereas an alternative sensor can be designed for high concentration applications.
limitations of semiconductor sensors
Non-target gases may absorb on the oxide surface and provide false measurements. Important disrupting gases include ozone, water and volatile organic compounds.
One of the advantages of semiconductor sensors is their flexibility in sensor design for specific applications (see above in Advantages section). However, this can also be a limitation. A user will need to purchase multiple sensors depending on the application.
The relationship between R/Ro and CO2 is not necessarily linear leading to issues with consistent calibration across sensors. Individual calibration of sensors may be necessary, leading to increased sensor costs associated with resources and labour time.
Fine et al (2010) state that semiconductor CO2 sensors perform best in the range between 2,000 and 10,000 ppm. This limited range means the semiconductor CO2 sensors will not be suitable for a number of applications. For example, in plant physiology, atmospheric CO2 concentrations are most important in the range between 280ppm and 800 ppm. For indoor air quality applications, an ideal monitoring range is in the order between 500 and 1,000 ppm.
Semiconductor CO2 sensors can also be unreliable at high relative humidity and varying temperatures.
iSweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrial products
Smart sensor board for electrochemical gas sensors
A smarter way to use electrochemical gas sensors
Perhaps the most promising near-term technology for accurately detecting many atmospheric pollutant gases within modest cost, power, and size constraints is the electrochemical sensor cell. Recent "echem" sensors from Alphasense in particular (-A4 and -B4 models, for example see CO-B4 datasheet) provide:
• impressively low noise and sensitivity down to the very low ppb range
• low cross-sensitivities to other gas species
• ridiculously linear response across a wide detection range
• 1% gain accuracy from the factory
• built-in temperature compensation mechanism that provides an offset error signal on a fourth "Aux" pin
All for less than $100 per unit in volume. Sounds fantastic, right? These are specs that usually match up with a $$$$ benchtop gas analyzer. Except...
How do you get a good signal out of this thing?
And here's the rub. It turns out to be somewhat tricky to actually achieve those specs in a real-world circuit. Not impossible, but it takes a fair amount of analog-type thinking and careful design considerations to make sure various noise and calibration error sources don't creep in and ruin all those sparkly numbers on the sensor's datasheet. I'll get into error budgets and noise sources in future Research Notes, but it's not hard to imagine that any attempt to measure parts per billion of anything requires a perhaps fanatical attention to these sorts of details.
And the sensors turn out to have something of their own personalities as well. Depending on their deployed environment, they may drift in gain and offset over time and temperature, and since they are typically gel-filled electrolytes exposed to air, they can dry out or become more saturated depending on moisture content in atmosphere. Oh well, here we are in the real world, what happened to that shiny datasheet again?
iSweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrial products
Perhaps the most promising near-term technology for accurately detecting many atmospheric pollutant gases within modest cost, power, and size constraints is the electrochemical sensor cell. Recent "echem" sensors from Alphasense in particular (-A4 and -B4 models, for example see CO-B4 datasheet) provide:
• impressively low noise and sensitivity down to the very low ppb range
• low cross-sensitivities to other gas species
• ridiculously linear response across a wide detection range
• 1% gain accuracy from the factory
• built-in temperature compensation mechanism that provides an offset error signal on a fourth "Aux" pin
All for less than $100 per unit in volume. Sounds fantastic, right? These are specs that usually match up with a $$$$ benchtop gas analyzer. Except...
How do you get a good signal out of this thing?
And here's the rub. It turns out to be somewhat tricky to actually achieve those specs in a real-world circuit. Not impossible, but it takes a fair amount of analog-type thinking and careful design considerations to make sure various noise and calibration error sources don't creep in and ruin all those sparkly numbers on the sensor's datasheet. I'll get into error budgets and noise sources in future Research Notes, but it's not hard to imagine that any attempt to measure parts per billion of anything requires a perhaps fanatical attention to these sorts of details.
And the sensors turn out to have something of their own personalities as well. Depending on their deployed environment, they may drift in gain and offset over time and temperature, and since they are typically gel-filled electrolytes exposed to air, they can dry out or become more saturated depending on moisture content in atmosphere. Oh well, here we are in the real world, what happened to that shiny datasheet again?
iSweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrial products
2016年3月4日星期五
Nanoscale optical force sensor made with living probes
Run
a quick [search engine of your choosing] query for the phrase "Apple bezel
patent," and you'll see a ton of news, dating back a number of years,
related to all the possible improvements that Apple has considered regarding
the black border around its iPhones and iPads.
According to the website, Patently Apple, the U.S. Patent and Trademark Office has recently published a patent application related to force detection on the bezel of Apple's devices.
As the related figure illustrates, Apple's ambitions – at least, as part of the patent application – involve slapping four different sensors in the four corners of an iPad (for example). These would be able to detect finger-pushing at any length along the device's bezel. In other words, you wouldn't just be stuck tapping one of the four corners in order to activate a particular action; you could tap any portion of the bezel to, say, raise and lower the iPad's volume via virtual buttons.
Presumably, the force sensors on the Apple device would be able to differentiate between single or multitouch gestures and, we hope, be able to discern whether you're just gripping the device near the bezel with your fingers or actively trying to engage a virtual button.
Since this is just a patent application, there's no indication that Apple actually plans to roll this technology out in future iterations of its iPad, iPhone, or who-knows-what-else.
Additionally, it's unclear just how Apple's patented technology would work with its more recent design update to its bezels. If you've taken a gander at an iPhone 5S or 5C lately, or an iPad Air, you'll note that there really isn't all that much bezel to speak of. The virtual buttons we previously mentioned would be more the size of a scrollbar's "thumb," if that.
If anything, we wonder if this wouldn't be a way for Apple to eliminate bezels entirely. If force-sensitive sensors could better discern between how one grips an iDevice versus how one actively manipulates it, what's to stop Apple from slapping these sensors under the display itself and extending the total viewing area to cover the entirety of an iPad or iPhone?
According to the website, Patently Apple, the U.S. Patent and Trademark Office has recently published a patent application related to force detection on the bezel of Apple's devices.
As the related figure illustrates, Apple's ambitions – at least, as part of the patent application – involve slapping four different sensors in the four corners of an iPad (for example). These would be able to detect finger-pushing at any length along the device's bezel. In other words, you wouldn't just be stuck tapping one of the four corners in order to activate a particular action; you could tap any portion of the bezel to, say, raise and lower the iPad's volume via virtual buttons.
Presumably, the force sensors on the Apple device would be able to differentiate between single or multitouch gestures and, we hope, be able to discern whether you're just gripping the device near the bezel with your fingers or actively trying to engage a virtual button.
Since this is just a patent application, there's no indication that Apple actually plans to roll this technology out in future iterations of its iPad, iPhone, or who-knows-what-else.
Additionally, it's unclear just how Apple's patented technology would work with its more recent design update to its bezels. If you've taken a gander at an iPhone 5S or 5C lately, or an iPad Air, you'll note that there really isn't all that much bezel to speak of. The virtual buttons we previously mentioned would be more the size of a scrollbar's "thumb," if that.
If anything, we wonder if this wouldn't be a way for Apple to eliminate bezels entirely. If force-sensitive sensors could better discern between how one grips an iDevice versus how one actively manipulates it, what's to stop Apple from slapping these sensors under the display itself and extending the total viewing area to cover the entirety of an iPad or iPhone?
Elmos Semiconductor AG: SMI: Highly Stable, Highly Accurate Medium Pressure Sensors
SMI (Silicon
Microstructures, Inc.), a subsidiary of Elmos, is proud to introduce the SM3041
fully digital, medium pressure MEMS differential and gauge sensor family. The
sensor has better than 1% initial accuracy and less than 1% accuracy shift over
life (1% shift over 1000hr HTOL at 150C). This makes it one of the most stable
medium pressure sensors in the market. Furthermore it is the first SMI sensor
with the AccuStable marking. Only products combining an extraordinary accuracy
with a long-time stability are allowed to have this high quality label.
The pressure sensor family is developed with special focus on the following markets: Medical (ventilators, oxygenators, wound therapy, fluid evacuation and others), Industrial (gas flow, pneumatic gages, pressure switches) and Consumer (sport equipment, appliances). The manufacturing line is qualified to the highest industry standards (ISO9001 & ISO/TS 16949).
The SM3041 Series is developed and manufactured with state-of-the-art pressure transducer technology and CMOS mixed signal processing technology. It produces a digital, fully signal conditioned output. The integrated temperature compensation ranges from -20 to +85 C. Standard differential parts are offered at +/-5 and +/-15psi, but the device can be fully customized per customer requirements anywhere in the range of +/-2.5psi to +/-15psi. The SM3041 family has an I2C digital communication interface. The device is offered in several JEDEC SOIC16 package configurations, with dual vertical ports, dual horizontal ports or a single vertical port.
Combining the pressure sensor with a signal-conditioning ASIC in a single package simplifies their use. The pressure sensor can be mounted directly on a standard printed circuit board and a calibrated pressure signal can be acquired from the digital interface. This eliminates the need for additional circuitry, such as a compensation network or microcontroller containing a custom correction algorithm.
The SM3041 is shipped in sticks or tape & reel.
SMI is offering proven solutions to a range of industries, based on application-specific ICs, sensors and complete microsystems. SMI is an ISO/TS16949:2009 certified premier developer and manufacturer of MEMS-based pressure sensors for a broad range of markets, with over 25 years of experience. SMI's design, production and quality control processes have enabled it to develop both the most sensitive and smallest MEMS pressure sensors available on the market today.
The pressure sensor family is developed with special focus on the following markets: Medical (ventilators, oxygenators, wound therapy, fluid evacuation and others), Industrial (gas flow, pneumatic gages, pressure switches) and Consumer (sport equipment, appliances). The manufacturing line is qualified to the highest industry standards (ISO9001 & ISO/TS 16949).
The SM3041 Series is developed and manufactured with state-of-the-art pressure transducer technology and CMOS mixed signal processing technology. It produces a digital, fully signal conditioned output. The integrated temperature compensation ranges from -20 to +85 C. Standard differential parts are offered at +/-5 and +/-15psi, but the device can be fully customized per customer requirements anywhere in the range of +/-2.5psi to +/-15psi. The SM3041 family has an I2C digital communication interface. The device is offered in several JEDEC SOIC16 package configurations, with dual vertical ports, dual horizontal ports or a single vertical port.
Combining the pressure sensor with a signal-conditioning ASIC in a single package simplifies their use. The pressure sensor can be mounted directly on a standard printed circuit board and a calibrated pressure signal can be acquired from the digital interface. This eliminates the need for additional circuitry, such as a compensation network or microcontroller containing a custom correction algorithm.
The SM3041 is shipped in sticks or tape & reel.
SMI is offering proven solutions to a range of industries, based on application-specific ICs, sensors and complete microsystems. SMI is an ISO/TS16949:2009 certified premier developer and manufacturer of MEMS-based pressure sensors for a broad range of markets, with over 25 years of experience. SMI's design, production and quality control processes have enabled it to develop both the most sensitive and smallest MEMS pressure sensors available on the market today.
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