Calibration of an air quality sensor in a device

A device (1) comprising a cavity (5) defining an internal volume, an air quality sensor (9) being adapted to measure a concentration of at least one air compound present in the internal volume, the cavity (5) can be alternatively in:

FIELD OF THE DISCLOSURE

The present disclosure concerns a device, for example a wearable device such as a wrist watch or an activity tracker, with an air quality sensor.

BACKGROUND OF THE DISCLOSURE

It is known to embed an air quality sensor into a device like a wrist watch.

The air quality sensor can detect and monitor the presence of air pollution in a surrounding area, for both indoor and outdoor environments. It can provide useful information to a user on the air quality that may negatively impact his health, and cause harmful effects such as cold symptoms or respiratory diseases.

In such a device, the air quality sensor can produce an electric current according to a concentration level of some compounds present in the air.

However, the electrical current may also vary according to other parameters, such as humidity, temperature and aging of other components constitutive of the device which may release gas affecting the accuracy of the air quality sensor located nearby.

It is therefore necessary to recalibrate the sensor on a regular basis. In the absence of recalibration, the air quality sensor is likely to output inaccurate measures that may mislead the user.

However, calibration process is usually difficult and burdensome to implement for a user.

Therefore, there remains a need to provide a device with an air quality sensor able to provide reliable air quality measurements, whatever its conditions of use, and that remains easy to use in the context of everyday life.

SUMMARY OF THE DISCLOSURE

The present disclosure relates to a device comprising a cavity defining an internal volume, an air quality sensor being adapted to measure a concentration of at least one air compound present in the internal volume. The cavity can be alternatively in:

an open state in which air can enter into the cavity from the outside of the cavity, anda closed state in which no air can circulate between the outside and the inside of the cavity,
the air quality sensor being adapted to be calibrated when the cavity is in the closed state once the internal volume no longer comprises the air compound or comprises a concentration of the air compound that is below a predefined threshold.

Thanks to these dispositions, it is possible to perform a reliable measurement of the air compound.

In various embodiments according to the present disclosure, use may also possibly be made of one and/or the other of the following dispositions, taken separately or in combination, according to which:the cavity comprises an opening so that air can exclusively enter the cavity through the opening, the cavity being elsewhere isolated from the device;the air quality sensor is adapted to produce an electric current by consuming the air compound present in the internal volume of the cavity,the air compound is NO2,the internal volume of the cavity is less than 0.3 cm3, less than 0.2 cm3, less than 0.1 cm3, or even less than 0.05 cm3;the cavity comprises a first grid and a second grid, the second grid being adapted to move relative to the first grid so that the cavity can be in the open state or in the closed state;each of the first and second grids comprises a plurality of through apertures, wherein at least some of the through apertures of the first and second grids face each other when the cavity is in the open state and wherein the through apertures of the first and second grids are offset to one another when the cavity is in the closed state;the cavity comprises a door, the door being adapted to move relative to the opening so that the cavity can be in the open state or in the closed state;the device comprises an accelerometer adapted to detect a movement of the user, the air quality sensor being adapted to be calibrated when the accelerometer does no detect any movement of the user;the cavity comprises a hole, the air quality sensor being located into the hole, the cavity and the air quality sensor being sealed together in an airtight manner by using at least one gasket; andthe device is a wearable device, such as a watch.

The present disclosure also relates to a method for calibrating an air quality device of a device as disclosed, comprising at least the steps of:switching the cavity from the open state to the closed state;waiting for the internal volume to no longer comprise the air compound or to comprise a concentration of the air compound that is below a predefined threshold; andcalibrating the air quality sensor.

In the figures, the same references denote identical or similar elements.

DETAILED DESCRIPTION OF THE DISCLOSURE

Device

FIG. 1shows a device1according to the present disclosure.

The device1can be a wearable device, such as a watch, a wrist watch or an activity tracker.

However, the device1can also be any other device, such as glasses, a necklace, a ring, a weight scale, etc.

As illustrated onFIG. 1, the device1may comprise a casing2, a dial plate3aand a top cover3bof the dial plate3a. The casing2, the dial plate3aand the top cover3bare arranged one on top of another in a vertical direction Z. The thickness of the device1is thus defined along this vertical direction Z.

The device1can be a digital watch, such that the dial plate3acomprises a display31. As a variant or complementarily, the device1may be an analog type watch, such that the dial plate3acomprises stick-like hands32with a traditional clock face for instance.

To be attached to a wrist of a user, the casing2may comprise projections21for attachment to a wristband (not illustrated) as known per se and thus not described in more details.

As illustrated onFIG. 1, the device1can have a round shape. However, other shapes, such as square or rectangle, are also possible. Similarly, the device1can be relatively small, as for a watch for example, or can have bigger dimensions when it comes to objects having larger dimensions, as for a weight scale for another example.

The device1also comprises an internal part4illustrated onFIG. 2. As illustrated onFIG. 1, the internal part4can be sandwiched between the casing2and the dial plate3a.

As illustrated more particularly onFIGS. 4 and 9, the internal part4comprises a cavity5. The cavity5may be molded, in particular as a single piece.

The cavity5comprises a wall51and an opening52.

The wall51forms at least the lateral portion of the cavity5.

The cavity5also comprises a bottom portion53and a top portion54.

The bottom portion53can comprise a first hole55and a second hole56. As illustrated onFIGS. 4 and 9, the holes55,56can have a circular shape.

The top portion54can be closed by a cover6.

The cavity5defines and delimits an internal volume. The internal volume is suited and intended to receive an air volume coming from the outside of the cavity5, and more precisely from the outside of the device1, through the opening52. The cavity5may take any form, notably cylindrical, parallelepipedal or other so as to form the internal volume.

The terms “internal”, “inside” and “external”, “outside” when applied to the cavity5reflect the fact that the cavity5delimits the internal volume comprising a quantifiable amount of air, distinguishable from the air present in the surrounding of the device1or present elsewhere in the device1. It is therefore with reference to this situation that these terms should be understood.

The cavity5can be arranged on, or fixed to, a printed circuit board7. The printed circuit board7can comprise a control unit, an oscillator, a battery either conventional or rechargeable (not illustrated), or any known elements for the functioning of the device1.

In order for the internal volume of the cavity5to be in fluid communication with the outside of the device1, the casing2can comprise a perforated area22, wherein through bores23opens on the cavity5and the outside of the device1.

The through bores23may be aligned in the perforated area22, facing the opening52of the cavity5.

As illustrated onFIG. 1, the casing2comprises six through bores23. Each through bore23may have a diameter comprised between 0.5 mm (millimeter) and 1.5 mm, for example about 1 mm.

In an embodiment, the device1can also comprise a membrane8which is impermeable to water but permeable to air. The water-impermeable membrane8is placed facing the opening52so that air entering the cavity5passes through the membrane8.

As illustrated more particularly onFIGS. 3, 4, 6 and 7, the water-impermeable membrane8can be placed in front of the opening52toward the outside of the cavity5.

As a variant, the water-impermeable membrane8may as well be inside the cavity5on the inside face of the opening52.

As another variant, the water-impermeable membrane8may also be placed on the internal or external side of the perforated area22. This way, the water-impermeable membrane8can ensure that the whole device1is waterproof.

The water-impermeable membrane8prevents the ingress of water inside the cavity5. This way, the user can for example immerse briefly the device1in water without any damage.

The water-impermeable membrane8may be formed as a thin wall manufactured in synthetic material having a microporous structure.

Air Quality Sensor

The device1comprises an air quality sensor9. The air quality sensor9is arranged in the cavity5of the internal part4.

“The air quality sensor is arranged in the cavity” means that the air quality sensor9is located inside, opens on, or is at least is in fluid communication with the internal volume of the cavity5.

More particularly, as illustrated onFIG. 3, the air quality sensor9is placed in the first hole55of the cavity5. This way, the air quality sensor9is in direct contact with the air present in the internal volume of the cavity5.

The air quality sensor9is sealed with the cavity5in an airtight manner with a gasket11. To ensure that the air quality sensor9is sealed with the cavity5, the device1can comprise a supporting element10. The supporting element10holds the air quality sensor9against the cavity5.

More precisely, the cavity5can be fixedly attached to the supporting element10. As illustrated onFIGS. 3 and 8, the device1may comprise screws14that go through the cavity5and the printed circuit board7and that are fixed to the supporting element10.

Spring elements15are compressed between the printed circuit board7and the air quality sensor9. The spring elements15can be electrical conductors that ensure electrical contact between the air quality sensor9and the printed circuit board7.

As a variant, to ensure that the air quality sensor9is sealed with the cavity5, the air quality sensor9may be soldered to the printed circuit board7and the cavity5may be screwed on the printed circuit board7, thus compressing the gasket11.

The device1can also comprise other types of sensors, such as a temperature sensor, a humidity sensor, a pressure sensor, or the like.

As illustrated onFIGS. 3 and 8, the device1comprises a humidity sensor13arranged in the cavity5of the internal part4. The humidity sensor13is placed in the second hole56of the cavity5. The humidity sensor13is sealed with the cavity5in an airtight manner with a gasket12. The gasket12can seal the humidity sensor13with the cavity5in the same manner as the gasket11seals the air quality sensor9with the cavity5.

Air can exclusively circulate between the outside and the inside of the cavity5through the opening52, the cavity5being elsewhere isolated from the device1. In particular, the cavity5is isolated from the other elements of the internal part4of the device1, and more precisely from the other elements of the printed circuit board7.

The air quality sensor9is adapted to measure a concentration of one or several air compounds in the vicinity of the device1.

“In the vicinity of the device” means that the air compound(s) measured by the device1are not substantially different from the air compound(s) that the user of the device1is breathing or that surrounds the device1.

The one or several air compounds are of interest. This way, the device1is adapted to detect compounds in the general environment of the device1and/or detect some chemical species present in the breath of the user when the user exhales or blows toward the device1. The air quality sensor9is particularly suited to measure a concentration of some air compounds which may have an impact on human health (also called “pollutants”).

The air quality sensor9may be adapted to measure a concentration of an air compound chosen among NO2(nitrogen dioxide), O3(ozone), NO (nitric oxide), CO (carbon monoxide), SO2(sulphur dioxide), CO2(carbon dioxide), H2S (hydrogen sulfide), CI (chlorine), benzene, CH4 (methane), NH4(ammonia), (CH3)2CO (acetone) and alcohol vapours. The air compound can be a volatile organic compound.

When the air quality sensor9is used to detect some chemical species present in the breath of the user for instance, the air compound can be more precisely NH4(ammonia), (CH3)2CO (acetone) and alcohol vapours.

The air quality sensor9may be adapted to measure a concentration of only one air compound or of several air compounds, in particular simultaneously. For instance, the air quality sensor9may be adapted to measure a concentration of two air compounds, such as those mentioned-above. The air quality sensor9may be reactive both to NO2and O3.

According to an embodiment, the air quality sensor9can be an amperometric sensor. The air quality sensor9produces an electric current when a potential is applied between electrodes.

A first chemical occurs at least at one working electrode (or catalyst) when in contact with the air, which takes place with regard to at least one auxiliary electrode (or reference).

For example, if the air quality sensor9is adapted to measure a concentration of CO, the first chemical reaction may be:
CO+H2O<=>CO2+2e−+2H+ (electrons are released in the working electrode)

According to another example, if the air quality sensor9is adapted to measure a concentration of NO2, the first chemical reaction may be:
NO2+2e−+2H+<=>NO+H2O (electrons are captured in the working electrode)

These chemical reactions are purely illustrative and non-limitative. More complex chemical reactions involving a larger number of chemical species are also possible.

Measurement of concentration of the air compound can also depend on other parameters, such as the ambient temperature, ambient humidity (more particularly measured by the humidity sensor13described above), ambient pressure or the electric intensity flowing through the air quality sensor9.

Electrolyte may be provided between two or more electrodes to transport the ions produced by the chemical reactions from one electrode to the other electrode.

The air quality sensor9may have a low electric consumption, for example an average electric consumption when powered of less than 10 μA (microampere), or less than 2 μA. The electric current produced by the air quality sensor9can be comprised between 0.1 nA (nanoAmp) and 20 nA depending on the concentration of the air compound measured.

The lifetime of the battery of the device1can be sufficient to ensure a sufficiently long working life of the air quality sensor9.

By way of example, the battery of the device1may have a capacity of 120 mAh (milliampere hour), with an autonomy of 25 days or 600 hours without using the air quality sensor9. Its average electric consumption is 200 μA.

By considering that the average consumption of the air quality sensor9is 10 μA, the average electric consumption of the air quality sensor9is equal to 5% of the average electric consumption of the device1without using the air quality sensor9. The device1may thus have an autonomy of around 24 days or around 570 hours when powering the air quality sensor9.

The air quality sensor9is connected to the control unit of the device1which collects and processes the measurements of concentrations of the air compounds.

Such measurements can then be provided to the user, for instance on the display31of the device1. As an alternative or complementarily, the device1may wirelessly communicate with another external terminal (not illustrated), such as a smartphone or a server, to send the collected measurement data.

Opening and Closing of the Cavity

Measurements made by the air quality sensor9can become out of calibration over time for a number or reasons.

For instance, external reasons, such as humidity and temperature, or internal reasons such as aging of components (e.g. electronic component, battery or coating material), may affect the accuracy of the air quality sensor9.

It is therefore necessary to recalibrate the air quality9on a regular and/or periodic basis.

To this end, the cavity5can be alternatively in an open state or a closed state.

In the open state, air can enter into the cavity5, so that the air present in the internal volume is constantly renewed from the outside of the cavity5, and more particularly from the outside of the device1.

In the closed state, no air can circulate between the outside and the inside of the cavity5. The air present in the internal volume cannot be renewed and remains trapped in the cavity5as long as the cavity does not switch to the open state. The cavity5is hermetically sealed or airtight with respect to the air located outside the cavity5, whether this air is located elsewhere inside the device1or outside the device1.

In the closed state, concentration of the air compound can decrease over time, in particular since air cannot enter anymore into the cavity5.

More precisely, the air quality sensor9is adapted to consume the air compound that is present in the internal volume of the cavity5.

When the cavity5is in the closed state, the air quality sensor9can thus consume the entire air compound present in the internal volume of the cavity5, so that the cavity5no longer comprises the air compound or comprises the air compound having a concentration that is below a predefined threshold, such as the detection threshold of the air quality device9.

When the air compound is NO2, such predefined threshold can be 5 ppb (parts per billion), 1 ppb or even 0.1 ppb.

For instance, the air quality sensor9can be adapted to measure the concentration of NO2according to the chemical reaction mentioned above, so that the air compound NO2can be progressively consumed by chemical reaction by the air quality sensor9when the cavity5is in the closed state, so that no NO2is finally left in the internal volume of the cavity5or only in trace amounts.

The air quality sensor9can consume the air compound in less than 8 hours, or in less than 4 hours, or in less than one hour, or even in less than 30 minutes. Consumption time of the air compound may depend on the air quality sensor parameters and on the size of the internal volume of the cavity5.

To this end, the internal volume of the cavity5can be less than 0.3 cm3(cubic centimetre), less than 0.2 cm3, less than 0.1 cm3, or even less than 0.05 cm3.

Then, the air quality sensor9can be calibrated. Calibration can encompass several possibilities, such as setting a new baseline measurement or the sensitivity of the air quality sensor9. Calibration can also permit to obtain a calibration function in the form of a curve, a look-up table, or any other form in order to describe the linear or non-linear relation between the air compound concentration and the measurements to be performed by the air quality sensor9.

Advantageously, the air quality sensor9can set a new baseline measurement (or a new “zero”). Every new measurement of the air quality sensor9can then be estimated by being compared with this new baseline measurement. This ensures a good reliability and accuracy of the air quality sensor9over time.

In particular, the air quality sensor9may be adapted to measure several air compounds but can be calibrated according to only one air compound.

When calibration is implemented, other parameters, such as the ambient temperature, ambient humidity, ambient pressure or the electric intensity flowing through the air quality sensor9, may also be measured or set as reference values.

The material of the cavity5may also be advantageously chosen not to affect the measurements made by the air quality sensor9. For instance, when the air quality sensor9is adapted to measure a concentration of NO2, the cavity5may be made of polytetrafluoroethylene (PTFE).

We here below describe two embodiments of the cavity5so that it can be in the open or closed state.

First Embodiment of the Device

According to a first embodiment, the device1comprises a first grid101and a second grid102. The first grid101is fixed relative to the cavity5. In particular, the first grid101may be integral with the cavity5. The first grid101is located at the inlet of, or forms, the opening52of the cavity5.

The second grid102is adapted to move relative to the first grid101so that the cavity5can be in the open state or in the closed state. More precisely, the second grid102is adapted to slide relative to the first grid101along a longitudinal direction X1. The longitudinal direction X1 can be perpendicular to the vertical direction Z.

To move the second grid102, the device1may comprise an actuator or motor (not illustrated) adapted to allow small displacements. The motor can for instance be piezoelectric, electromagnetic or it can be a stepper motor.

Each of the first and second grids101,102comprises a plurality of through apertures103,104. The through apertures103,104of the first and second grids101,102are respectively spaced apart regularly in the longitudinal direction X1.

As illustrated onFIGS. 4, 5A and 5B, each of the first and second grids101,102comprises fourteen through apertures103,104. However, this is not limitative and the first and second grids101,102can comprise less or more through apertures103,104.

The through apertures103,104of the first and second grids101,102can be of rectangular shapes. However, other shapes are possible.

As illustrated onFIG. 4, the through apertures103of the first grid101have a width n in the longitudinal direction X1. The width n of the through apertures103of the first grid101can be less than 1 mm (millimeter), or even less than 0.5 mm. The width n can be for instance equal to 0.3 mm.

The through apertures103of the first grid101are spaced apart regularly from each other by a distance d (also called “pitch”).

Similarly, as illustrated onFIGS. 5A and 5B, the through apertures104of the second grid102have a width n′ in the longitudinal direction X1. The width n′ of the through apertures104of the second grid102can be less than 1 mm (millimeter), or even less than 0.5 mm. The width n′ can be for instance equal to 0.3 millimeters. The through apertures104of the second grid102are spaced apart regularly from each other by a distance d′.

The widths n, n′ and the distances d, d′ are interrelated so that the cavity5can be opened or closed in a satisfactory manner by moving the second grid102relative to the first grid101

Advantageously, the first and second grids101,102are such that:
n′≥n,
This way, in the open position, a through aperture104of the second grid102overlaps totally a though aperture103of the first grid101. All or some of the though apertures103,104face each other. The cavity5is thus open as illustrated onFIG. 7.

Advantageously, the first and second grids101,102are such that:
d′≥nandd≥n′

This way, in the closed position, the solid space between two consecutive through apertures104of the second grid102overlaps totally, or covers, a through aperture103of the first grid101. Similarly, the solid space between two consecutive through apertures103of the first grid101overlaps totally, or covers, a through aperture104of the second grid102. The through apertures103,104of the first and second grids101,102are offset to one another in the longitudinal direction X1. The cavity5is thus totally closed as illustrated onFIG. 6.

Second Embodiment of the Device

According to a second embodiment, the device1comprises a door105. The door105is adapted to move relative to the opening52so that the cavity5can be in the open state or in the closed state. More precisely, the door105is adapted to slide relative to the opening52along a longitudinal direction X2. The opening52may consist in a single aperture which extends in the longitudinal direction X2.

To move the door105, the device1may comprise a toothed disk or a pinion106. The door105comprises a rack107that can engage with the toothed disk106, as illustrated more particularly onFIG. 13.

The door105is a full solid surface, which does not comprise any through apertures unlike the second grid102of the first embodiment described above.

In the closed state, the door105faces the opening52. The cavity5is thus totally closed as illustrated onFIG. 11.

In the open state, the door105does not cover the opening52by being slidably moved, preferably totally, on a side of the opening52along the longitudinal direction X2. The cavity5is thus open as illustrated onFIG. 12.

Advantages of the Disclosure

Thanks to the fact that the cavity5can switch from the open state to the closed state, it is possible to recalibrate the air quality sensor9when the air compound to be measured has been totally, or almost totally, consumed in the internal volume.

This calibration is advantageously implemented when the user is unlikely to use the device1as well as the embedded air quality sensor9for a given period of time.

To this end, the device1may also comprise a biosensor of a physiological signal of the user, such as an accelerometer (not illustrated) adapted to detect a movement of the user. Calibration of the air quality sensor9can then be implemented when the biosensor does not detect any activity of the user, and in particular when the accelerometer does no detect any movement of the user.

Such calibration can for instance occur during a sleeping phase of the user or, in the embodiment wherein the device1is a wearable device, when the device1is not worn by the user.

Such calibration can also be repeated in a periodic manner. For instance, such calibration can occur at least once a month, or at least once a week, or even at least once a day. This way, it ensures that the air quality sensor9always output a reliable measurement of the concentration of the air compound.

Obviously, the disclosure is not limited to the embodiments described previously and given purely by way of example. It encompasses a wide range of modifications, alternative forms and other variants that a person skilled in the art will be able to envisage within the scope of the present disclosure and notably all combinations of the different modes of operation described previously, being able to be taken separately or together.