Patent Description:
<CIT> describes a formaldehyde technique field, specifically, relating to a kind of low concentration formaldehyde sensor.

<CIT> describes a method of selectively sensing the concentration of a target gas in polluted ambient air comprises the steps of providing a target gas sensor (<NUM>) sensitive to the target gas; providing a first gas flow derived from the ambient air, from which first flow the target gas is substantially removed.

<CIT> describes a portable formaldehyde detecting method, in particular to a hardware anti-interference circuit based on a subtractor and a digital filtering formaldehyde detecting method, belonging to the field of detecting technology.

<CIT> describes an electrochemical formaldehyde sensor and a method of detecting formaldehyde are disclosed. The electrochemical formaldehyde sensor may comprise a housing; an electrolyte disposed within the housing; and a plurality of electrodes in contact with the electrolyte within the housing, wherein the plurality of electrodes comprise a working electrode comprising iridium and an applied potential of between approximately <NUM> to IV relative to a reversible hydrogen electrode; and a counter electrode.

The invention is defined in the independent claims, to which reference should now be made. Advantageous features are set out in the dependent claims. In an embodiment, a method for determining the concentration of a second target gas while in the presence of a first target gas may comprise operating a first sensor under a first operating condition, wherein the first sensor is part of a sensor assembly; operating a second sensor under a second operating condition, wherein the second sensor is part of the sensor assembly, and wherein the second operating condition is different from the first operating condition; detecting at least one target gas by the first sensor; detecting at least one target gas by the second sensor; processing a signal output from the first sensor with a signal output from the second sensor; and determining a concentration of the first target gas and second target gas based on the processed output signals.

In an embodiment, a sensor assembly configured to detect a second target gas in the presence of a first target gas may comprise a first sensor comprising a first operating condition; a second sensor comprising a second operating condition, wherein the first operating condition is different from the second operating condition; and a processor configured to receive a first output signal from the first sensor; receive a second output signal from the second sensor; process the received output signals by comparing them; and determine a concentration of the first target gas and second target gas based on the processed output signals.

It should be understood at the outset that although illustrative implementations of one or more embodiments are illustrated below, the disclosed systems and methods may be implemented using any number of techniques, whether currently known or not yet in existence. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, but may be modified within the scope of the appended claims.

Embodiments of the disclosure include systems and methods for detecting formaldehyde without a cross-sensitivity to carbon monoxide. Demand for domestic formaldehyde detectors (for personal use) may increase in areas with growth in the housing market, where people may be exposed to health damage due to exposure to low levels of formaldehyde, particularly in newly built homes (as formaldehyde exists in construction supplies and paints). Current detectors for formaldehyde typically suffer from cross-sensitivity to carbon monoxide (CO), where CO may exist in larger concentrations (when compared to the levels of formaldehyde). This cross-sensitivity may cause false alarms and prevent effective detection of formaldehyde. Also, high quality detectors currently available (that may not suffer from these cross-sensitivity issues) may be prohibitively expensive.

Embodiments of the disclosure may employ two solid electrolyte sensors (SECS) operating under two different conditions. For example, the sensors may operate with two different bias potentials and/or with two different filters. The two sensors may respond differently when exposed to formaldehyde than they do when exposed to CO (and other cross-sensitivity gases), allowing the response related to formaldehyde to be isolated and detected. The low cost of the SECS may allow for more widespread domestic use, providing users with an affordable selective formaldehyde detector. Additionally, by comparing the outputs from the two sensors, noise in the signal(s) may be cancelled out, allowing for high resolution in the detected signal. This improved resolution may allow for lower concentrations of formaldehyde to be detected.

It may be known in the art for a gas detector to use multiple sensors to provide selectivity. However, the disclosed embodiments comprise two sensors operating under different conditions, which may provide additional detection benefits, as described here. For example, a formaldehyde detector may comprise two different bias voltages applied to the two sensors. As another example, a formaldehyde detector may comprise different filters for the two sensors, which may provide increased resolution and selectivity for formaldehyde. These two examples of different operating conditions are used simultaneously in the same formaldehyde detector.

The two-sensor design can be utilized by determining a difference in the response of the two sensors. The sensor response may vary due to the difference in bias voltage, which may provide a difference in sensitivity, response time, and noise towards gases (e.g., formaldehyde, CO, and other organic gases). The differences in the response of the two sensors can be interpreted to identify two or more gases. Noise in the signals may also be canceled out to achieve selectivity and high resolution.

Referring now to <FIG>, an exemplary embodiment of a sensor <NUM> is shown, wherein the sensor <NUM> may comprise a plurality of layers attached to a substrate <NUM>. The substrate <NUM> may comprise an alumina ceramic material, and may comprise one or more diffusion channels <NUM> through the thickness of the substrate, where the diffusion channels <NUM> may allow gas flow into the sensor <NUM> from the surrounding environment. In some embodiments, the sensor <NUM> may comprise a first layer <NUM> (e.g., which may be a catalytic and/or electrode layer) configured to allow gas transfer into the sensor <NUM> and to the other layers of the sensor <NUM>. In some embodiments, the first layer <NUM> may comprise a platinum (Pt) and ionic solution material. Although the diagram of <FIG> only shows one electrode layer (i.e., catalytic layer, first layer <NUM>), the sensor <NUM> may comprise two or three electrodes that are co-planar with each other. In some embodiments, the first layer <NUM> may comprise between one and three electrodes, which may include a sensing (or working) electrode, a counter electrode, and/or a reference electrode.

In some embodiments, the sensor <NUM> may comprise a second layer <NUM> (e.g., which may be a humidification layer) configured to absorb any humidity within the sensor <NUM> which may prevent electrolyte from a third layer <NUM> from flooding the electrodes located within the first layer <NUM>. In some embodiments, the second layer <NUM> may comprise silicon dioxide (SiO<NUM>) and an ionic solution material. In some embodiments, the sensor <NUM> may comprise a third layer <NUM> (e.g., which may comprise an electrolyte layer) configured to provide electrolyte to facilitate ionic conduction between the electrodes. Optionally, the third (electrolyte) layer <NUM> may also be configured to provide a reservoir of water to enable the sensor to be operated over a range of humidity conditions. In some embodiments, the third layer <NUM> may comprise a mixture of sulfuric acid (H<NUM>SO<NUM>) and/or polyvinylpyrrolidone (PVPY), where the PVPY may serve to immobilize the sulfuric acid electrolyte.

In some embodiments, the sensor <NUM> may comprise a fourth layer <NUM> (e.g., which may comprise a sealing layer) configured to seal with the substrate <NUM> to provide an air-tight seal for the sensor <NUM>. This sealing layer <NUM> may prevent air flow into the sensor <NUM> except for at the diffusion channels <NUM>. In some embodiments, the sealing layer <NUM> may comprise a silicone material. In some embodiments, the sensor <NUM> may comprise one or more electrical contacts <NUM> that extend out of the sensor <NUM> to provide electrical connection(s) to other elements of a gas detector. In some embodiments, the sensor <NUM> may comprise up to three electrical contacts <NUM> for each of three electrodes that are located within the first layer <NUM>.

Referring to <FIG>, a sensor assembly <NUM> is shown where the sensor assembly <NUM> may comprise at least part of a formaldehyde gas detector. The sensor assembly <NUM> may comprise at least two sensors <NUM> and <NUM> located within the sensor assembly <NUM>. In some embodiments, the sensors <NUM> and <NUM> may comprise electrochemical sensors. In some embodiments, the first sensor <NUM> may operate under a first condition and the second sensor <NUM> may operate under a second condition, wherein the outputs from the first sensor <NUM> and/or the second sensor <NUM> may be adjusted by adjusting the operating conditions. In some embodiments, the sensor assembly <NUM> may comprise a power source <NUM> (e.g., a battery) configured to power the elements of the sensor assembly <NUM>. In some embodiments, the sensor assembly <NUM> may comprise one or more other components, such as component <NUM>, which may comprise additional sensor elements, communication elements, electrical elements, and/or any other component <NUM> that may be located within the sensor assembly <NUM>.

The different operating conditions applied to the first sensor <NUM> and the second sensor <NUM> are a difference in bias voltage and a difference in filtering conditions. By comparing the signal outputs from the two sensors <NUM> and <NUM>, the gas concentrations may be predicted without the sensor(s) <NUM> and <NUM> needing to reach a steady-state. Additionally, any common mode signals (e.g., temperature, pressure, and/or humidity transients, and/or electrical interference) in the signal output from each of the sensors <NUM> and <NUM> may be cancelled out by comparing the signals.

The sensor assembly <NUM> may comprise a printed circuit board (PCB) <NUM> which may comprise one or more electrical connection elements configured to connect with the sensors <NUM> and <NUM>. In some embodiments, the PCB <NUM> may be configured to apply one or more controls to the sensors <NUM> and <NUM> (i.e., the PCB <NUM> may control one or more operating conditions of the sensors <NUM> and <NUM>). For example, the PCB <NUM> comprises one or more elements configured to apply a bias voltage to one or both of the sensors <NUM> and <NUM>. The PCB <NUM> may comprise a processor, a memory, and other elements as would be known to those skilled in the art.

In some embodiments of the sensor assembly <NUM>, the first sensor <NUM> comprises a first bias voltage while the second sensor <NUM> comprises a second bias voltage, where the second bias voltage is different from the first bias voltage. When the two sensors <NUM> and <NUM> are operating at different bias voltages, the relative sensitivity of the sensors to different gases may be adjusted and compared. As an example, the sensors <NUM> and <NUM> may comprise sensors configured to detect a first gas, where the sensor response to the first gas may not change with changes in bias voltage (e.g., because of diffusion limitations). However, the response of the sensors <NUM> and <NUM> to other gases, or a second gas, may be changed by adjusting the bias voltage applied to the sensors. In some embodiments, the sensitivity to other gases may be increased by increasing the bias voltage. If two different bias voltages are applied to the two different sensors <NUM> and <NUM>, the signals from the two sensors <NUM> and <NUM> may be compared and/or processed to determine the response that is caused by a gas other than the first gas (i.e., the second gas). This information may be used to determine a concentration of the first and second gas. Algorithms that may be used to process the sensor outputs may consider the specific type of sensor(s), the gas flow rate(s) to the sensor(s), the effects of the bias voltage(s) applied to the sensor(s), operating conditions (e.g., temperature, pressure, humidity), among other things. Additionally, the transient behavior of the sensors <NUM> and <NUM> may be different due to the different operating conditions (i.e., different bias voltages), and therefore time dependence may be accounted for in an algorithm that processes the signals from both of the sensors <NUM> and <NUM>.

As an example, the first gas may comprise CO and the second gas may comprise formaldehyde. The sensor assembly may be configured to detect both CO and formaldehyde based on the outputs of the two sensors <NUM> and <NUM>. The bias voltages applied to the two sensors may be between zero (i.e., no bias voltage) and approximately <NUM> mV.

In some embodiments, only one sensor may have an applied bias voltage. In some embodiments, both sensors may have an applied bias voltage, where the applied bias voltage is different for the two sensors. In some embodiments, the sensor assembly <NUM> may comprise more than two sensors (i.e., a plurality of sensors), where each sensor of the plurality of sensors may comprise a different bias voltage, and wherein the number of gases that can be detected by the sensor assembly <NUM> may be equal to the number of sensors.

Each of the two (or plurality) of sensors <NUM> and <NUM> may comprise a gas channel configured to allow gas flow into the sensor(s) <NUM> and <NUM> from the external environment (e.g., similar to the diffusion channels <NUM> described in <FIG>). In some embodiments, the gas channels to the sensors <NUM> and <NUM> may be separate from one another. In some embodiments, the gas channels to the sensors <NUM> and <NUM> may be configured to provide an equal gas flow to each of the sensors.

In the sensor assembly <NUM>, the sensors <NUM> and <NUM> comprise different filtering elements configured to filter certain gases from the airflow into the sensor. For example, the first sensor <NUM> may comprise a first filter while the second sensor <NUM> may comprise a second filter, wherein the first filter is configured to filter differently than the second filter.

As an example, the sensors <NUM> and <NUM> may comprise sensors configured to detect a first gas, and the sensor assembly <NUM> may be configured to also detect a second gas. To accomplish detection of the second gas, the first sensor <NUM> may comprise a filter configured to capture/block the second gas, while the second sensor <NUM> does not comprise a filter. Therefore, the first sensor <NUM> may produce a signal in response to the first gas, while the second sensor <NUM> may produce a signal in response to the first gas and the second gas.

During operation, the output of the first sensor <NUM> (that does not include the second gas) may be compared to the output of the second sensor <NUM> (that does include the second gas) to determine a concentration of the second gas. In some embodiments, the signal generated by the sensor(s) <NUM> and <NUM> in response to the first gas may be significantly higher than the signal generated by the sensor(s) <NUM> and <NUM> in response to the second gas. In some embodiments, the first gas may typically be present in much higher concentrations than the second gas. As an example, the determined concentration of formaldehyde may be approximately <NUM> times less than the concentration of carbon monoxide. As an example, the ratio of the carbon monoxide concentration to the formaldehyde concentration may be approximately <NUM>:<NUM>. As another example, the ratio of the carbon monoxide concentration to the formaldehyde concentration may be approximately <NUM>:<NUM>. In some embodiments, it may be more difficult to filter the first gas from entering the sensor(s) <NUM> and <NUM> than to filter the second gas.

Algorithms that may be used to process the sensor outputs may consider the specific type of sensor(s), the gas flow rate(s) to the sensor(s), the effects of the bias voltage(s) applied to the sensor(s), operating conditions (e.g., temperature, pressure, humidity), among other things. Testing may be completed on a prototype sensor assembly to determine the preferred or optimum algorithm processing. Additionally, the transient behavior of the sensors <NUM> and <NUM> may be different due to the different operating conditions (i.e., different filtering conditions), and therefore time dependence may be accounted for in an algorithm that processes the signals from both of the sensors <NUM> and <NUM>. For example, the gas flow into the first sensor <NUM> may be slower than the gas flow into the second sensor <NUM> when the first sensor <NUM> comprises a filter and the second sensor <NUM> does not.

As an example, <FIG> illustrate a first sensor <NUM> and a second sensor <NUM> comprising different filtering conditions (where the sensors <NUM> and <NUM> may be similar to the sensors <NUM> and <NUM>). The first sensor <NUM> and the second sensor <NUM> may comprise a bottom housing <NUM> and a top housing <NUM>, where the top housing <NUM> comprises an air inlet <NUM>. The first sensor <NUM> and the second sensor <NUM> may also comprise a substrate <NUM> (e.g., as described in <FIG>), as well as one or more diffusion channels <NUM> in the substrate <NUM> and one or more electrical contacts <NUM>. The bottom housing <NUM> may comprise a cavity <NUM> configured to hold the substrate <NUM> (and other layers described in <FIG>). In some embodiments, the first sensor <NUM> and/or the second sensor <NUM> may comprise a dust filter <NUM> configured to prevent particulate matter from entering through the air inlet <NUM>.

Additionally, the first sensor <NUM> comprises a filter <NUM> (which may be configured to filter the second (target) gas) located in the airflow pathway from the air inlet <NUM> to the diffusion channels <NUM>. The filter <NUM> may comprise one or more materials configured to filter the second gas (as described above). As an example, the filter <NUM> may comprise a potassium permanganate impregnated glass fiber sheet. In some embodiments, the first sensor <NUM> may also comprise a membrane <NUM>, configured to hold the filter <NUM> in place so that it does not move around within the sensor housing <NUM> and <NUM>.

Some embodiments of the invention comprise a method for detecting a second target gas in the presence of a first target gas. A method may comprise detecting at least one target gas by a first sensor of a sensor assembly, where the first sensor may comprise a first operating condition. The method may comprise detecting at least one target gas by a second sensor, where the second sensor comprises a second operating condition, and the second operating condition is different than the first operating condition. The method may comprise comparing and/or processing the output signal from the first sensor and the second sensor to determine a concentration of at least one target gas. In some embodiments, the method may comprise determining a concentration of a first target gas and determining a concentration of a second target gas. In some embodiments, the method may comprise determining the concentration of the second target gas while in the presence of the first target gas. In some embodiments, the first target gas may comprise CO, while the second target gas may comprise a volatile organic compound (VOC). In some embodiments, the second target gas may comprise formaldehyde.

While various embodiments in accordance with the principles disclosed herein have been shown and described above, modifications thereof may be made by one skilled in the art without departing from the scope defined by the independent claims. The embodiments described herein are representative only and are not intended to be limiting. Many variations, combinations, and modifications are possible and are within the scope of the claims.

Accordingly, the scope of protection is not limited by the description set out above, but is defined by the claims which follow that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated as further disclosure into the specification and the claims are embodiment(s) of the present invention(s). Furthermore, any advantages and features described above may relate to specific embodiments, but shall not limit the application of such issued claims to processes and structures accomplishing any or all of the above advantages or having any or all of the above features.

Use of broader terms such as "comprises," "includes," and "having" should be understood to provide support for narrower terms such as "consisting of," "consisting essentially of," and "comprised substantially of. " Use of the terms "optionally," "may," "might," "possibly," and the like with respect to any element of an embodiment means that the element is not required, or alternatively, the element is required, both alternatives being within the scope of the embodiment(s). Also, references to examples are merely provided for illustrative purposes, and are not intended to be exclusive.

While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods may be embodied in many other specific forms without departing from the scope as defined by the independent claims. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted or not implemented.

Claim 1:
A method for determining the concentration of a second target gas while in the presence of a first target gas, the method comprising:
operating a first sensor (<NUM>) under a first operating condition, wherein the first sensor is part of a sensor assembly (<NUM>);
operating a second sensor (<NUM>) under a second operating condition, wherein the second sensor is part of the sensor assembly (<NUM>); and wherein:
the second operating condition is different from the first operating condition, and
the first operating condition comprises a first bias voltage and the second operating condition comprises a second bias voltage, the second bias voltage being different from the first bias voltage, wherein the first sensor comprises a first filter and the second sensor comprises a second filter different from the first filter, and wherein the first sensor comprises a membrane (<NUM>) configured to hold the first filter;
detecting at least one target gas by the first sensor;
detecting at least one target gas by the second sensor;
processing a signal output from the first sensor with a signal output from the second sensor; and
determining a concentration of the first target gas and determining a concentration of the second target gas based on the processed output signals.