Method and apparatus for testing humidity sensors

Abstract

Method for testing humidity sensors, comprising the steps of: providing a plurality of devices (12) comprising the humidity sensors (11); generating, by a humidity generator (21), a flow of humid air, wherein the flow of humid air has a first relative humidity, a first temperature and a first pressure; cooling, by a heat exchanger (31), the flow of humid air so that it reaches a second relative humidity, a second temperature and a second pressure, wherein the second relative humidity is substantially equal to a predetermined relative humidity, wherein the second temperature is substantially equal to a predetermined temperature less than the first temperature and greater than the dew point temperature of the flow of humid air, wherein the second pressure is substantially equal to the first pressure; and distributing, by a distribution system (41), substantially equally the flow of humid air, having the second relative humidity and the second temperature, to the humidity sensors (11) of the devices (12).

Description

[0001] "METHOD AND APPARATUS FOR TESTING HUMIDITY SENSORS"

[0002] Cross-Reference to Related Applications

[0003] This Patent Application claims priority from Italian Patent Application No . 102024000019462 filed on August 30 , 2024 , the entire disclosure of which is incorporated herein by reference .

[0004] Technical Field

[0005] The present invention relates to a method and an apparatus for testing humidity sensors .

[0006] Background Art

[0007] As is known, a humidity sensor is configured to generate and transmit an output indicative of a humidity present in the environment in which the sensor is located .

[0008] Humidity sensors are present in di f ferent types of devices , for example they can be present in the micro electro-mechanical systems ( also known as MEMS ) .

[0009] Humidity sensors need to be tested, in particular so as to be calibrated and / or so as to veri fy that the outputs generated and transmitted by the calibrated humidity sensors are acceptable , i . e . within a predetermined range .

[0010] However, the testing of the humidity sensors is long and complex . Typically, such testing occurs in climatic chambers , which are substantially cabinet-shaped structures internally comprising a plurality of shelves on which the humidity sensors are positioned .

[0011] Controlling the ambient conditions inside the cl imatic chambers is a process which requires a lot of time and is subj ect to errors .

[0012] Furthermore , the humidity sensors need to be accurately positioned inside the climatic chambers , since the positioning of the humidity sensors inside the climatic chambers af fects the testing .

[0013] A purpose of the present invention is to provide a method for testing humidity sensors , which allows the above problems to be overcome .

[0014] Disclosure of the Invention

[0015] The aforementioned purpose is achieved by a method for testing humidity sensors as claimed in claim 1 .

[0016] The present invention further relates to an apparatus for testing humidity sensors as claimed in claim 7 .

[0017] The present invention further relates to a machine for testing humidity sensors as claimed in claim 15 .

[0018] Brief Description of the Drawings

[0019] For a better understanding of the present invention, a preferred embodiment is described hereinafter, by way of non-limiting example and with reference to the accompanying drawings , wherein :

[0020] - Figure 1 is a schematic view of an apparatus according to the present invention;

[0021] - Figure 2 is a diagram of a thermodynamic trans formation obtainable with the apparatus according to the present invention;

[0022] - Figure 3 is a perspective view, with parts removed for the sake of clarity, of a detail of a machine comprising the apparatus according to the present invention;

[0023] - Figure 4 is a perspective cross-sectional view, with parts removed for the sake of clarity, of a detail of the apparatus ; - Figure 5 is a perspective view of a first component of the apparatus ;

[0024] - Figure 6 is a perspective view of the component of Figure 5 , with transparent parts ;

[0025] - Figure 7 is a perspective view of a second component of the apparatus ;

[0026] - Figure 8 is a perspective view of the component of Figure 7 , with transparent parts ; and

[0027] - Figures 9 and 10 are respectively a front cross- sectional view and a perspective cross-sectional view, with parts removed for the sake of clarity, of a detail of the apparatus .

[0028] Detailed Description of the Invention

[0029] With reference to Figure 1 , there is indicated by 1 an apparatus for testing humidity sensors 11 according to the present invention .

[0030] In particular, the humidity sensors 11 belong to devices 12 , which are the devices under test ( also known as DUTs ) .

[0031] For example , the devices 12 are micro electro-mechanical systems ( also known as MEMS ) . In the illustrated embodiment , each device 12 comprises a respective humidity sensor 11 .

[0032] The apparatus 1 comprises a humidity generator 21 ( schematically illustrated in Figure 1 ) configured to generate a flow of humid air (which in Figure 1 is schematically illustrated with a dashed line ) .

[0033] Humid air is a mixture of dry air and water vapour . In particular, dry air is considered as a perfect gas comprising nitrogen and oxygen, and water vapour is considered as water in the vapour state which is in a suf ficiently raref ied state to be approximated to a perfect gas . Therefore , humid air can be considered a perfect gas and thus satisfies the equation of state of perfect gases

[0034] PtV = ntRT wherein :

[0035] - Pt: humid air pressure, i.e. (total) pressure of the mixture of dry air and water vapour

[0036] - V : humid air volume, i.e. volume of the mixture of dry air and water vapour

[0037] - nt: number of moles of humid air, i.e. (total) number of moles of the mixture of dry air and water vapour

[0038] - R: constant of the perfect gases

[0039] - T : humid air temperature, i.e. temperature of the mixture of dry air and water vapour

[0040] In particular, the number of moles of humid air is equal to the number of moles of the components of the mixture, i.e. nt= na+ nvwherein :

[0041] - na: number of moles of dry air in the mixture

[0042] - nv: number of moles of water vapour in the mixture

[0043] Furthermore, according to Dalton's law, the humid air pressure is the sum of the pressures of the components of the mixture, i.e.

[0044] Pt = Pa + PVwherein : n naRT , ‘ 4_i j_

[0045] - Pa= — pressure of the dry air m the mixture

[0046] - Pv=vy: pressure of the water vapour in the mixture

[0047] In particular, the pressure Pvof the water vapour in the mixture satisfies

[0048] 0 < Pv< PS@T wherein PS@T is the saturated water vapour pressure at a temperature T . In fact , the maximum water absorption capacity of a dry air mass depends on the temperature T of the air .

[0049] In particular, the saturated water vapour pressure PS@T at a temperature T can be approximated by the Clausius- Clapeyron equation wherein e0= 0.6113 kPa, To= 273.15 K , Rv= 461 J • K-1• kg-1and L = 2.5 • 106 / • kg-1for the liquid water .

[0050] Relative humidity RH is defined as the ratio

[0051] Therefore , the relative humidity is a dimensionless quantity comprised between zero and one , and typically expressed in percentage .

[0052] Dew point temperature TDPis defined as the temperature at which the mixture becomes saturated with vapour, i . e . the temperature such that

[0053] Pv= PS@TDP

[0054] Therefore , the dew point temperature TDPcorresponds to the relative humidity RH = 100% . I f the temperature decreases , the condensation begins .

[0055] In particular, the dew point temperature TDPcan be expressed as a function of the relative humidity RH and of the temperature T . For example , by using the Magnus-Tetens formula with the Alduchov and Eskridge coef ficients , the dew point temperature TDPcan be approximated as 9 / I Q H / I i 17.625 - T

[0056] T =243-04'ln(joo) + 243.04 + T DP17 A75 l (RH\ 4. l7-625 - r

[0057] ± / .bZSlr\iOO7+243.04 + T

[0058] Absolute humidity AH, also known as humid air titre x, is defined as the ratio mv

[0059] AH = x = — - mawherein :

[0060] - mv: mass of the water vapour in the mixture

[0061] - ma: mass of the dry air in the mixture

[0062] Therefore , the absolute humidity is a dimensionless quantity, which however is typically expressed in grams of water vapour per kilogram of dry air .

[0063] It can be demonstrated that the absolute humidity AH depends on the pressure Pvof the water vapour in the mixture , i . e . depends on RH and PS@T .

[0064] In particular, i f the pressure Pvof the water vapour in the mixture is constant during a thermodynamic trans formation, the absolute humidity AH ( and equivalently the titre x) is constant during such thermodynamic trans formation, which is thus called isotitre .

[0065] The flow of humid air generated by the humidity generator 21 has a first relative humidity RHl fa first temperature T±and a first pressure Ptl.

[0066] In particular, the first temperature 7\ is greater than the dew point temperature TDPof the flow of humid air . Therefore , the first relative humidity RH±is less than 100% . In other words , the flow of humid air does not condense .

[0067] Conveniently, the first pressure Ptl= Pal+ PV1is such that the pressure PV1of the water vapour in the mixture satis fies 0 < Pvi< PS@T\

[0068] The apparatus 1 further comprises a heat exchanger 31 ( schematically illustrated in Figure 1 ) fluidically connected to the humidity generator 21 and configured to cool the flow of humid air to a second relative humidity RH2, a second temperature T2and a second pressure Pt2. The second relative humidity RH2is substantially equal to a predetermined relative humidity, the second temperature T2is substantially equal to a predetermined temperature less than the first temperature 7\ and greater than the dew point temperature TDPof the flow of humid air, and the second pressure Pt2is substantially equal to the first pressure Ptl.

[0069] In particular, the second relative humidity RH2and the second temperature T2are those at which it is desired to test each device 12 and thus each humidity sensor 11 . Since the second temperature T2is greater than the dew point temperature TDPof the flow of humid air, the second relative humidity RH2is less than 100% . In other words , the flow of humid air does not condense .

[0070] Conveniently, the second pressure Pt2= Pa2+ Pv2is such that the pressure Pv2of the water vapour in the mixture satis fies

[0071] 0 < PV2 < PS@T2

[0072] In particular, when the temperature changes and in particular decreases passing from the first temperature T±to the second temperature T2, the amount of water does not change and the ratio between temperature T and volume V is constant . Therefore , from the above definition of the pressure of water vapour in the mixture , it follows that the pressure PV1is substantially equal to the pressure Pv2. Furthermore , since the first temperature is less than the second temperature T2, the saturated water vapour pressure at the first temperature 7\ is less than the saturated water vapour pressure at the second temperature T2, i . e . PS@T1< PS@T2.

[0073] Therefore , since the pressure PV1is substantially equal to the pressure Pv2and the saturated water vapour pressure at the first temperature 7\ is less than the saturated water vapour pressure at the second temperature 12, from the above definition of relative humidity, it follows that i . e . the second relative humidity RH2is greater than the first relative humidity RH1.

[0074] In other words , the flow of humid air, having the first relative humidity RH1and the first temperature Tl freaches the second relative humidity RH2, such that RH2> RHl rand the second temperature T2, such that TDP< T2< Tl rvia a substantially isobaric trans formation .

[0075] An example of thermodynamic trans formation obtainable with the apparatus 1 is illustrated in Figure 2 via the Mollier diagram, in which the hori zontal axis is the absolute humidity AH ( also known as humid air titre x) , the vertical axis is the temperature T ( in particular the dry bulb temperature , which is the temperature measured by a common thermometer and is independent of the relative humidity) and a plurality of curves (not parallel with respect to one another ) are present such that the points on a same curve have the same relative humidity RH .

[0076] In the illustrated example , the flow of humid air, having the first relative humidity RH±= 45% and the first temperature 7\ = 35 °C (point 1 in the diagram) , reaches the second relative humidity RH2= 80% and the second temperature T2= 25 °C (point 2 in the diagram) . Since the pressure Pvof the water vapour in the mixture is constant during the thermodynamic trans formation, the absolute humidity AH ( and equivalently the titre x) is constant during such thermodynamic transformation, which is thus called isotitre and graphically corresponds to the vertical line j oining point 1 to point 2 in the diagram . The dew point temperature TDPof the flow of humid air is graphically obtainable by prolonging such vertical line up to reaching the curve corresponding to the relative humidity RH = 100% (point DP in the diagram) , and mathematically by using for example the aforementioned Magnus-Tetens formula with the Alduchov and Eskridge coef ficients , imposing the second relative humidity RH2= 80% and the second temperature T2= 25 °C .

[0077] The apparatus 11 further comprises a distribution system 41 configured to substantially equally distribute the flow of humid air, having the second relative humidity RH2and the second temperature T2, to the humidity sensors 11 of the devices 12 .

[0078] In particular, the flow of humid air, having the second relative humidity RH2and the second temperature T2, is substantially equally divided, and each device 12 and thus each humidity sensor 11 receives a portion of the flow of humid air, having the second relative humidity RH2and the second temperature T2. Therefore , each device 12 and thus each humidity sensor 11 is tested at the second relative humidity RH2and at the second temperature T2. In view of the foregoing, the present invention further relates to a method for testing humidity sensors 11 , comprising the steps of :

[0079] - providing a plurality of devices 12 comprising the humidity sensors 11 ;

[0080] - generating, by a humidity generator 21 , a flow of humid air, wherein the flow of humid air has a first relative humidity RHl fa first temperature 7\ and a first pressure Ptl;

[0081] - cooling, by a heat exchanger 31 , the flow of humid air so that it reaches a second relative humidity RH2, a second temperature T2and a second pressure Pt2, wherein the second relative humidity RH2is substantially equal to a predetermined relative humidity, wherein the second temperature T2is substantially equal to a predetermined temperature less than the first temperature 7\ and greater than the dew point temperature TDPof the flow of humid air, wherein the second pressure Pt2is substantially equal to the first pressure Ptl; and

[0082] - distributing, by a distribution system 41 , substantially equally the flow of humid air, having the second relative humidity HR2and the second temperature T2, to the humidity sensors 11 of the devices 12 .

[0083] Preferably, the method comprises the step of controlling the first relative humidity RH1as a function of the second relative humidity RH2and the second temperature T2.

[0084] In particular, after fixing the second relative humidity RH2and the second temperature T2, which are those at which it is desired to test each device 12 and thus each humidity sensor 11 , and knowing the first temperature Tl fthe first relative humidity RH±is controlled so that when the flow of humid air, having the first relative humidity RH±and the first temperature Tl freaches the second temperature T2, its relative humidity will be substantially equal to the second relative humidity RH2. According to a graphical interpretation, with reference to the Mollier diagram ( Figure 2 ) , fixing point 2 ( i . e . the second relative humidity RH2and the second temperature T2) and knowing the first temperature Tl fpoint 1 ( i . e . the first relative humidity RH±and the first temperature Tt) is determined .

[0085] Preferably, the apparatus 11 comprises a control unit 51 configured to control the humidity generator 21 so that the first relative humidity RH±is equal to a predetermined relative humidity .

[0086] In particular, the control unit 51 receives as input the first temperature Tl fthe second relative humidity RH2and the second temperature T2( at which it is desired to test each device 12 and thus each humidity sensor 11 ) , processes the value of the aforementioned predetermined relative humidity so that a flow of humid air, having the first temperature 7\ and such predetermined relative humidity, reaches the second relative humidity RH2and the second temperature T2when cooled, and controls the humidity generator 21 so that it generates a flow of humid air having the first relative humidity RH±equal to such predetermined relative humidity .

[0087] Preferably, the step of controlling the first relative humidity RH1comprises the step of detecting, by a dedicated sensor 61 ( schematically illustrated in Figure 1 ) , a relative humidity of the flow of humid air fluidically interposed between the humidity generator 21 and the heat exchanger 31 .

[0088] In particular, the heat exchanger 31 is fluidically connected to the humidity generator 21 via at least one duct 71 thermally controlled so that the flow of humid air flowing in the at least one duct 71 has a substantially constant temperature . Therefore , the flow of humid air flowing in the at least one duct 71 has the first relative humidity RHl fthe first temperature 7\ and the first pressure Ptl. In particular, since the pressure PV1of the water vapour in the mixture is constant in the at least one duct 71 and the first temperature 7\ is constant in the at least one duct 71 ( and thus the saturated water vapour pressure at the first temperature T±is constant in the at least one duct 71 ) , from the above definition of relative humidity, it follows that the first relative humidity RH1is constant in the at least one duct 71 . Therefore , the relative humidity of the flow of humid air fluidically interposed between the humidity generator 21 and the heat exchanger 31 is the first relative humidity RH1. Such humidity is detected by the dedicated sensor 61 and used for controlling the humidity generator 21 so that the first relative humidity RH1is equal to the aforementioned predetermined relative humidity .

[0089] Conveniently, the apparatus 1 comprises the dedicated sensor 61 which is configured to generate and transmit an output indicative of the first relative humidity RHl fand the control unit 51 is configured to receive and process such output and control the humidity generator 21 on the basis of such output . In particular, the control unit 51 implements a closed- loop relative humidity control , since it uses the output indicative of the first relative humidity RHl fgenerated and transmitted by the dedicated sensor 61 , for controlling the humidity generator 21 so that it generates a flow of humid air having the first relative humidity RH1equal to the aforementioned predetermined relative humidity .

[0090] Preferably, the second pressure Pt2is substantially equal to the ambient pressure Pamb •

[0091] In particular, the second pressure Pt2, which is substantially equal to the first pressure Ptl, is substantially equal to the ambient pressure Pamb r i - e . the normal ( or standard) atmospheric pressure defined as Pamb=101325 Pa .

[0092] Preferably, the distribution system 41 is housed in a chamber 81 in fluidic communication with the environment 91 . Therefore , the pressure of the chamber 81 is substantially equal to the ambient pressure Pamb • Conveniently, the devices 12 comprising the humidity sensors 11 are housed in the chamber 81 .

[0093] Conveniently, along the path of the humid air from the humidity generator 21 to the devices 12 , a pressure drop is present , for example less than 100 mbar and preferably less than 50 mbar, which imposes a continuously new flow of humid air on the devices 12 comprising the humidity sensors 11 but whose ef fects are negligible , thus allowing to state that the second pressure Pt2is substantially equal to the first pressure Ptland to consider them exactly equal in the discussion .

[0094] Preferably, the method comprises the step of veri fying that a respective output generated and transmitted by each of the humidity sensors 11 of the devices 12 is within a predetermined range comprising the second relative humidity RH2.

[0095] In particular, the method can be used for calibrating the humidity sensors 11 of the devices 12, i.e. for verifying that the outputs generated and transmitted by the humidity sensors 11 to be calibrated (i.e. by the humidity sensors 11 of the devices 12 before the calibration) are acceptable, i.e. within a predetermined range comprising the second relative humidity RH2. Additionally or alternatively, the method can be used for verifying that the outputs generated and transmitted by the calibrated humidity sensors 11 (i.e. by the humidity sensors 11 of the devices 12 after the calibration) are acceptable, i.e. within a predetermined range comprising the second relative humidity RH2.

[0096] Conveniently, such predetermined range is centred in the second relative humidity RH2and has a magnitude which depends on the required accuracy.

[0097] Conveniently, the verification step can be repeated considering different values of the second relative humidity RH2and / or different values of the second temperature T2.

[0098] Preferably, the method comprises the step of modifying at least one parameter of the humidity sensor 11 if the respective output is outside the aforementioned range comprising the second relative humidity RH2.

[0099] In particular, the possibility and the extent of the modification can depend on the specific value of the second relative humidity RH2and / or on the magnitude of the range centred in the second relative humidity RH2. For example, the magnitude of the range can be smaller when considering the humidity sensors 11 to be calibrated than when considering the calibrated humidity sensors 11 , since high accuracy is typically required during the calibration .

[0100] For example , by assuming for the sake of simplicity that the response of the humidity sensor 11 is linear, the at least one parameter of the humidity sensor 11 is the of fset and / or the gain of such humidity sensor 11 .

[0101] Figure 3 illustrates a detail of a machine 101 which comprises a fixed frame 111 and the apparatus 1 .

[0102] In particular, the machine 101 comprises a plurality of ducts , among which the at least one duct 71 operatively downstream of the humidity generator 21 (not illustrated in Figure 3 ) and in which the flow of humid air flows , having the first relative humidity RHl fthe first temperature 7\ and the first pressure Ptl, and at least one duct operatively downstream of the chamber 81 and in which the humid air flows out of the chamber 81 . Preferably, there is an exhaust mani fold 121 connected to the chamber 81 and configured to put the chamber 81 in fluidic communication with the environment , so that the pressure of the chamber 81 is substantially equal to the ambient pressure Pamb.

[0103] Conveniently, the chamber 81 is delimited by a base 122 , substantially tray-shaped and carried by the fixed frame 111 , and by a cover 123 facing the base 122 . In the illustrated embodiment , the base 122 and the cover 123 substantially extend hori zontally and the cover is above the base 122 .

[0104] Preferably ( Figure 4 ) , the heat exchanger 31 comprises a plate 131 internally provided with a plurality of cooling channels 132.

[0105] In particular, the plate 131 has a first dimension (length) and a second dimension (width) , extending respectively along a first direction (X) and a second direction (Y) orthogonal with respect to each other, greater than a third dimension (thickness) , extending along a third direction (Z) orthogonal to the first direction (X) and to the second direction (Y) .

[0106] Conveniently, the plate 131 is substantially flat, i.e. has a first face 141 and a second face 142, opposite the first face 141, which extend along the first direction (X) and the second direction (Y) .

[0107] In the illustrated embodiment, the first face 141 and the second face 142 are substantially rectangular. In particular, the first face 141 and the second face 142 are substantially square, i.e. the first dimension and the second dimension of the plate 131 are substantially equal to each other .

[0108] With reference to Figure 3, the plate 131 extends substantially horizontally, i.e. the third direction (Z) is vertical .

[0109] Preferably, the plate 131 is made of aluminium.

[0110] Preferably (Figure 6) , the cooling channels 132 extend along the first direction (X) , i.e. are parallel with respect to one another, and are equidistant along the second direction (Y) .

[0111] Preferably (Figure 4) , there are two rows of cooling channels 132 spaced apart along the third direction (Z) . In particular (Figure 6) , the cooling channels 132 are arranged in pairs aligned along the third direction (Z) . Preferably, the cooling channels 132 belonging to the same pair are j oined by a j oint portion 133 extending along the third direction ( Z ) .

[0112] Conveniently, inside the cooling channels 132 a fluid, for example water, flows at a temperature less than the second temperature T2and such that , via the plate 131 of the heat exchanger 31 , the flow of humid air, having the first temperature Tl freaches the second temperature T2less than the first temperature 7\ and greater than the dew point temperature TDPof the flow of humid air . Conveniently ( Figure 3 ) , the machine 101 comprises at least one connection 143 via which such fluid enters the cooling channels 132 , and at least one connection 144 via which such fluid exits the cooling channels 132 .

[0113] Preferably ( Figure 4 ) , the heat exchanger comprises a heater 135 configured to heat the plate 131 , i f necessary . In the illustrated embodiment , the heater 135 is substantially a plate in contact with the first face 141 of the plate 131 .

[0114] Preferably ( Figure 6 ) , the plate 131 is internally provided with a plurality of distribution channels 151 of the distribution system 41 .

[0115] In other words , via the distribution channels 151 , the plate 131 is also part of the distribution system 41 .

[0116] In particular, the distribution channels 151 are fluidically connected to the at least one duct 71 and operatively downstream of the sensor 61 . Preferably, the distribution channels comprise a pair of channels 152 extending, along the first direction (X) , from opposite sides of the plate 131 and are connected by a plurality of channels 153 extending along the second direction (Y) .

[0117] Conveniently, the channels 153 are equidistant with respect to one another. Preferably, the channels 153 are interposed, along the third direction (Z) , between the cooling channels 132 and preferably equidistant from the cooling channels 132.

[0118] Conveniently (Figure 5) , the second face 142 has a plurality of openings 154 fluidically connected to the channels 153, preferably via respective joints 155 (Figures 4 and 6) extending along the third direction (Z) .

[0119] In the illustrated embodiment, forty-nine openings 154 are present.

[0120] Preferably (Figures 9 and 10) , the apparatus 1 comprises at least one housing 161 facing the plate 131 and comprising a plurality of seats 162 configured to house the devices 12 comprising the humidity sensors 11.

[0121] In particular, each housing 161 is carried by the base 122 of the chamber 81 and is stationary with respect to the base 122. Each seat 162 faces the plate 131 and houses a respective device 12. Preferably, each device 12 is carried by a respective movable element 163 which is housed in the seat 162 and comprises at least one appendage 164, for example two or four legs 164, which extends along the third direction (Z) and engages at least one recess 165 present in the housing 161. Each recess 165 accommodates elastic means 166, for example a respective compression coil spring 167, operatively interposed between the housing 161 and the movable element 163 and configured to push the movable element 163 towards the plate 131.

[0122] Preferably, the seats 162 (and thus the devices 12) are substantially arranged in a matrix arrangement , i . e . an arrangement comprising a plurality of rows and a plurality of columns .

[0123] Conveniently, each movable element 163 comprises a support portion 171 configured to carry the respective device 12 and extending substantially parallel to the plate 131 , and an appendage 172 , for example cylindrical , extending towards the plate 131 and in which there are a plurality of grooves 173 communicating with the support portion 171 and configured to convey the humid air , which has hit the device 12 , orthogonally with respect to the third direction ( Z ) .

[0124] Conveniently, the support portion 171 has a plurality of through holes configured to be engaged by respective electric contacts 175 extending along the third direction ( Z ) and configured to be in electrical contact with the device 12 .

[0125] In the illustrated embodiment , the apparatus 1 comprises fourteen housings 161 extending along the first direction (X ) and equidistant along the second direction (Y) . In particular, seven pairs of housings 161 are present , and the housings 161 of the same pair are aligned along the first direction (X ) . Each housing 161 comprises fourteen seats 162 aligned along the first direction (X ) , for a total of one hundred and ninety-six seats 162 , and thus one hundred and ninety-six devices 12 which can be housed .

[0126] Preferably, the distribution system 41 comprises at least one adapter 181 interposed between the plate 131 and the at least one housing 161 and comprising a plurality of tips 182 facing the seats 162 and configured to be in contact with the devices 12 . The tips 182 are internally provided with respective channels 183 fluidically connected to the distribution channels 151 of the plate 131 and configured to convey the flow of humid air, having the second relative humidity RH2and the second temperature T2, to the humidity sensors 11 of the devices 12.

[0127] In particular (Figure 4) , each adapter 181 is carried by the plate 131, for example is fixed to the plate 131 via fixing means 184, for example screws.

[0128] Preferably, each adapter 181 is substantially plateshaped having a first dimension (length) and a second dimension (width) , extending respectively along the first direction (X) and the second direction (Y) , greater than a third dimension (thickness) , extending along the third direction (Z) .

[0129] Conveniently, each adapter 181 has a first face 191 and a second face 192, opposite the first face 191, which extend along the first direction (X) and the second direction (Y) .

[0130] In particular, the first face 191 of each adapter 181 faces the second face 142 of the plate 131, and the second face 192 of each adapter 181 faces the at least one housing 161.

[0131] In the illustrated embodiment, the first face 191 and the second face 192 are substantially rectangular. In particular, the first dimension is greater than the second dimension .

[0132] With reference to Figure 3, each adapter 181 extends substantially horizontally, i.e. the third direction (Z) is vertical .

[0133] Conveniently (Figures 9 and 10) , the tips 182 extend from the second face 142 of each adapter 181. Each tip 182 is configured to be in contact with a respective device 12 via the elastic means 166 . In particular, each tip 182 is configured to push a respective device 12 against the action of the compression coil springs 167 acting on the movable element 163 which supports the respective device 12 .

[0134] Conveniently, each tip 182 comprises a contact portion

[0135] 193 configured to be in contact with a respective portion

[0136] 194 of the respective device 12 .

[0137] In the illustrated embodiment , the contact portion 193 is substantially flat and substantially square-shaped, and is configured to be in contact with a respective substantially flat and substantially square-shaped portion 194 of the respective device 12 . The contact portion 193 ( Figures 4 , 7 and 8 ) has a groove 195 extending along a diagonal of such square and configured to convey the humid air, which has j ust hit the device 12 , orthogonally with respect to the third direction ( Z ) .

[0138] Conveniently, each tip 182 has a respective opening 196 configured to face towards a respective humidity sensor 11 of a respective device 12 , which for example has a hole defining an input port for the respective humidity sensor 11 . Preferably, the channels 183 fluidically connect the openings 154 ( Figures 5 and 6 ) present on the second face 142 of the plate 131 with the openings 196 ( Figures 7 and 8 ) of the tips 182 via respective openings present on the first face 191 of the adapter 181 . Preferably ( Figures 9 and 10 ) , each channel 183 has an output portion 197 substantially cylinder-shaped and extending along the third direction ( Z ) towards the respective opening 196 .

[0139] In the illustrated embodiment , a plurality of adapters 181 are present , for a total of one hundred and ninety-six tips 182 , i . e . as many as the seats 162 ( and thus the devices 12 ) . At least some adapters 181 are internally provided with sets of four channels 183 ( Figure 8 ) which fluidically connect four respective openings 196 with a single opening 154 ( Figures 5 and 6 ) present on the second face 142 of the plate 131 via a respective opening present on the first face 191 of the adapter 181 . In particular, the four channels 183 of each set of four j ointly define a substantially X-shaped structure , in which the intersection is fluidically connected to the opening 154 and the four ends are fluidically connected to the four respective openings 196 . Each opening 196 is substantially arranged in the centre of the square defining the contact portion 193 , i . e . is substantially arranged midway along the respective groove 195 . Furthermore , at least some adapters 181 comprise fourteen tips 182 ( Figures 7 and 8 ) , in particular seven pairs of tips 182 , and the tips 182 of the same pair are aligned along the second direction (Y) .

[0140] In use , the apparatus 1 allows the above method to be implemented .

[0141] In particular, the devices 12 are housed in the seats 162 of the housings 161 , in particular each device 12 is arranged on the support portion 171 of the respective movable element 163 housed in the respective seat 162 . Subsequently, the adapters 181 and the plate 131 are arranged such that the adapters 181 are interposed between the plate 131 and the housings 161 , in particular such that the tips 182 are in contact with the devices 12 , i . e . the contact portions 193 are in contact with the respective portions 194 of the devices 12 , and the openings 196 of the tips 182 face the respective humidity sensors 11 of the devices 12 . During the testing of the humidity sensors 11 , the flow of humid air, having the second relative humidity RH2and the second temperature T2, is substantially equally distributed to the humidity sensors 11 , and preferably hits them with a speed approximately equal to 1 m / s, and subsequently the humid air flows out of the chamber 81 via the grooves 195 of the contact portions 193 of the tips 192 and the grooves 173 of the movable element 163 . After the testing of the humidity sensors 11 , the adapters 181 and the plate 131 are spaced apart from the housings 161 and the devices 12 are removed from the seats 162 . Preferably, during the spacing apart of the adapters 181 from the housings 161 , in the channels 183 dry air is caused to flow, which i s conveyed to the devices 12 , in particular via the output portions 197 and the openings 196 , for facilitating the detachment between the devices 12 and the adapters 181 , i . e . for preventing the contact portions 193 from remaining adhered to the respective portions 194 of the devices 12 .

[0142] Upon examination of the characteristics of the method and of the apparatus 1 , the advantages of the present invention are evident .

[0143] In particular, the method allows to test the humidity sensors 11 in a quicker and easier manner with respect , for example , to the testing in the climatic chambers .

[0144] Cooling the flow of humid air, having the first relative humidity RH±and the first temperature Tl fto the second temperature T2, which is substantially equal to a predetermined temperature less than the first temperature 7\ and greater than the dew point temperature TDPof the flow of humid air, allows to maintain the absolute humidity AH ( and equivalently the titre x) constant during the thermodynamic transformation, and to maintain the dew point temperature TDPof the flow of humid air constant .

[0145] Furthermore , the fact that the second pressure Pt2is substantially equal to the first pressure Ptlallows to avoid the di f fusion phenomenon, which occurs when the flow of a substance passes from a high-concentration region to a low- concentration region of such substance , and is a stochastic process which is to be avoided during the testing of the humidity sensors 11 , in which predictabil ity and repeatability are required .

[0146] Therefore , each humidity sensor 11 receives a portion of the flow of humid air having the same properties , in particular the second relative humidity RH2and the second temperature T2, and the positioning of the humidity sensors

[0147] 11 inside the chamber 81 does not af fect the testing . In other words , the position of a device 12 is equivalent to the position of any other device 12 inside the chamber 81 . Therefore , the devices 12 can be arranged arbitrarily inside the chamber 81 , which can thus house a high number of devices

[0148] 12 .

[0149] I f present , the closed-loop control , in particular of the first relative humidity RHl fallows to increase the accuracy of the test .

[0150] The humidity generator 21 , the heat exchanger 31 and the distribution system 41 allow to implement the method .

[0151] The plate 131 allows to manufacture part of the heat exchanger 31 and part of the distribution system 41 in a single component , being internally provided with both the cooling channels 132 and the distribution channels 151.

[0152] The at least one housing 161 and the at least one adapter 181 allow to increase the customisation of the apparatus 1, also based on the humidity sensors 11 and / or on the devices 12 to be tested.

[0153] Furthermore, the possibility to have a plurality of housings 161 and / or a plurality of adapters 181 allows for a modular structure.

[0154] Finally, it is clear that modifications can be made to the method and the apparatus 1 without departing from the scope of protection defined by the claims.

[0155] For example, the second pressure Pt2, which is substantially equal to the first pressure Ptl, could be different from the ambient pressure Pamb •

[0156] The heat exchanger 31 and / or the distribution system 41 could be manufactured differently.

[0157] The shape and / or the inner structure of the plate 131 could be different.

[0158] The apparatus 1 could comprise a single housing 161, comprising all of the seats 162 of the apparatus 1, and / or a single adapter 181, comprising all of the tips 182 of the apparatus 1.

[0159] Number, arrangement, shape and dimensions of the seats 162 and of the tips 182 could be different, also based on the devices 12 to be tested.

[0160] The channels 183 with which the tips are internally provided could be shaped differently, also based on the arrangement of the humidity sensors 11 of the devices 12 to be tested.

Claims

CLAIMS1. Method for testing humidity sensors, comprising the steps of:- providing a plurality of devices (12) comprising the humidity sensors (11) ;- generating, by a humidity generator (21) , a flow of humid air, wherein the flow of humid air has a first relative humidity, a first temperature and a first pressure ;- cooling, by a heat exchanger (31) , the flow of humid air so that it reaches a second relative humidity, a second temperature and a second pressure, wherein the second relative humidity is substantially equal to a predetermined relative humidity, wherein the second temperature is substantially equal to a predetermined temperature less than the first temperature and greater than the dew point temperature of the flow of humid air, wherein the second pressure is substantially equal to the first pressure; and- distributing, by a distribution system (41) , substantially equally the flow of humid air, having the second relative humidity and the second temperature, to the humidity sensors (11) of the devices ( 12 ) .

2. Method as claimed in claim 1, comprising the step of controlling the first relative humidity as a function of the second relative humidity and the second temperature.

3. Method as claimed in claim 2, wherein the step of controlling the first relative humidity comprises the step of detecting, by a dedicated sensor (61) , a relative humidityof the flow of humid air fluidically interposed between the humidity generator (21) and the heat exchanger (31) .

4. Method as claimed in any of the preceding claims, wherein the second pressure is substantially equal to the ambient pressure.

5. Method as claimed in any of the preceding claims, comprising the step of verifying that a respective output generated and transmitted by each of the humidity sensors (11) of the devices (12) is within a predetermined range comprising the second relative humidity.

6. Method as claimed in claim 5, comprising the step of modifying at least one parameter of the humidity sensor (11) if the respective output is outside said range.

7. Apparatus for testing humidity sensors, comprising :- a humidity generator (21) configured to generate a flow of humid air, wherein the flow of humid air has a first relative humidity, a first temperature and a first pressure;- a heat exchanger (31) fluidically connected to the humidity generator (21) and configured to cool the flow of humid air to a second relative humidity, a second temperature and a second pressure, wherein the second relative humidity is substantially equal to a predetermined relative humidity, wherein the second temperature is substantially equal to a predetermined temperature less than the first temperature and greater than the dew point temperature of the flow of humid air, wherein the second pressure is substantially equal to the first pressure; and- a distribution system (41) configured to substantially equally distribute the flow of humid air, having the second relative humidity and the second temperature, to the humidity sensors (11) of devices (12) .

8. Apparatus as claimed in claim 7, comprising a control unit (51) configured to control the humidity generator (21) so that the first relative humidity is equal to a predetermined relative humidity.

9. Apparatus as claimed in claim 8, comprising a dedicated sensor (61) configured to generate and transmit an output indicative of the first relative humidity, wherein the control unit (51) is configured to receive and process said output and control the humidity generator (21) on the basis of said output.

10. Apparatus as claimed in any of claims 7 to 9, wherein the distribution system (41) is housed in a chamber (81) in fluidic communication with the environment (91) .

11. Apparatus as claimed in any of claims 7 to 10, wherein the heat exchanger (31) comprises a plate (131) internally provided with a plurality of cooling channels (132) .

12. Apparatus as claimed in claim 11, wherein the plate (131) is internally provided with a plurality of distribution channels (151) of the distribution system (41) .

13. Apparatus as claimed in claim 12, comprising at least one housing (161) facing the plate (131) and comprising a plurality of seats (162) configured to house said devices (12) comprising said humidity sensors (11) .

14. Apparatus as claimed in claim 13, wherein the distribution system (41) comprises at least one adapter (181)interposed between the plate (131) and the at least one housing (161) and comprising a plurality of tips (182) facing said seats (162) and configured to be in contact with said devices (12) , wherein the tips (182) are internally provided with respective channels (183) fluidically connected to the distribution channels (151) of the plate (131) and configured to convey the flow of humid air, having the second relative humidity and the second temperature, to said humidity sensors (11) of said devices (12) .

15. Machine for testing humidity sensors, comprising a fixed frame (111) and an apparatus (1) as claimed in any of claims 7 to 14.

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