Strini, Alberto (Via Ajaccio 6, Milano, I-20133, IT)
| 1. | A system (10) for the generation of a reference or process gas by the evaporation of a liquid in said gas, comprising a feeding line of anhydrous gas (11), an evaporation chamber (20) in turn comprising a microdrop generator (25) and fed by said anhydrous gas line (11), the system (10) being characterized in that said micro drop generator (25) is of the type in which microdrops (27) are generated and projected, in a controlled form, through a series of generating elements (26). |
| 2. | The system (10) according to claim 1, wherein said microdrop generator (25) is of the type used in the tech nology of inkjet printing heads. |
| 3. | The system (10) according to claim 1, wherein said microdrop generator (25) is of the type which can be sub stituted and integrated with a liquid tank (25'). |
| 4. | The system (10) according to claim 1, wherein said microdrop generator (25) is provided in the form of a nonrechargeable sealed cartridge. |
| 5. | The system (10) according to any of the previous claims, wherein said microdrop generator (25) is of the piezoelectric type. |
| 6. | The system (10) according to claims 1 to 5, wherein said microdrop generator (25) is of the thermal type. |
| 7. | The system (10) according to claim 1, wherein a tar get (28) is envisaged, against which the microdrops (27) are projected to favour their evaporation. |
| 8. | The system (10) according to claim 7, wherein said target (28) is heated. |
| 9. | The system (10) according to claim 8, wherein said target (28) comprises a metallic element integrated with an electric heating element. |
| 10. | The system (10) according to any of the previous claims, wherein a control device (15) is also envisaged, connected to and interacting with the elements of the system to control the variations, preferably automati cally. |
| 11. | The system (10) according to claim 10, wherein said control device (15) is set up to control the quantity of liquid vaporized in the gas by varying the generation frequency of the microdrops (27). |
| 12. | The system (10) according to any of the previous claims, wherein the liquid to be evaporated is water and the gas is air or another anhydrous gas. |
| 13. | The system (10) according to claim 10, wherein up stream of said evaporation chamber (20) there are a flow regulator (12) and a flow measurer (13) respectively, connected to said control device (15). |
| 14. | The system (10) according to any of the previous claims, wherein said system (10) is also connected to a temperature measurer (22) situated in the point of use of the reference or process gas. |
| 15. | The system (10) according to any of the previous claims, wherein said evaporation chamber (20) consists of a hermetic container in which the microdrop generator (25) and the heated target (28) are housed. |
| 16. | The system (10) according to claim 1, wherein, for the feeding of the system, a first feeding group (40) is envisaged, which contemplates the use of atmospheric air as gas source, after acquiring this by means of a collec tor (41) which feeds a pump (42) whose outflow is sent to the calibrator through a singlestep or multistep anhy drification system (43). |
| 17. | The system (10) according to claim 1, wherein, for the feeding of the system, a second feeding group is en visaged, equipped with a compressed air line (51) as gas source, after connection with the same line by means of a fitting, the group contemplates regulation of the pres sure by means of a regulator (52), filtering of the oil and other possible contaminants with a filter (53) and anhydrification with a singlestep or multistep device (54). |
| 18. | The system (10) according to claim 1, wherein, for the feeding of the system, a third feeding group (60) is envisaged, which contemplates the use of a cylinder of compressed anhydrous gas (61), connected with the cali brator by means of a pressure regulator (62). |
| 19. | A device (100) for the calibration of humidity sen sors and measurers, comprising a system (10) for the gen eration of air or other reference gas with an arbitrary degree of humidity produced according to any of the pre vious claims. |
| 20. | The device (100) for the calibration of sensors ac cording to claim 19, wherein a calibration system (10') is present, comprising a calibration chamber (30) into which the gas humidified or containing the evaporated liquid, is sent, said calibration chamber (30) comprising the temperature measurer (22), whose signal is used by the control device (15) of the microdrop generator (25) for determining the quantity of water necessary for pro viding the preestablished level of relative humidity, with the purpose of forming a verification and/or cali bration system of sensors (24) for relative humidity measurers. |
| 21. | The device (100) for the calibration of sensors ac cording to claim 19, wherein, inside said evaporation chamber (30), there is also a heating and/or cooling ele ment (23) which allows its active temperature control. |
| 22. | The device (100) for the calibration of sensors ac cording to claim 19, wherein inside said evaporation chamber (30), there is also a mixer (34) for ensuring the remixing uniformity. |
| 23. | The device (100) for the calibration of sensors ac cording to any of the claims from 19 to 22, wherein a sensor control unit (14) is also envisaged, connected to said control device (15) and controlling said humidity sensor (24) when the latter is subjected to calibration inside the calibration chamber (30). |
| 24. | A process for the generation of a reference gas by the evaporation of a liquid in said gas by means of the system (10) according to the previous claims, character ized in that it envisages the use of a microdrop genera tor (25) which can be substituted at the end of its life cycle. |
| 25. | The process according to claim 24, wherein the quan tity of liquid vaporized in the gas is controlled by varying the generation frequency of microdrops (27). |
| 26. | A process for the calibration of humidity sensors and measurers comprising a device (100) according to one of the claims from 19 to 23, characterized in that the humidified gas is sent into the calibration chamber (30), said calibration chamber (30) containing the sensor (24) to besubjected to verificationand/or calibration and the temperature measurer (22) whose signal is used by the control device (15) of the microdrop generator (25) for determining the quantity of liquid/water necessary for providing the preestablished vapour level of the liquid or relative humidity. |
The invention relates, in general, to a system wherein the gas can be any reference or process gas, in which a liquid is vaporized in a controlled quantity.
The invention relates, in particular, to a system for the generation of a reference or process gas having an arbitrary degree of relative humidity.
The present invention also relates to a system for the generation of a flow of air or other gas having con- trollable humidity, destined for the production of de- vices for testing and/or calibrating sensors and measur- ing devices of the relative and/or absolute humidity.
The generation of gas flows with an arbitrary amount of liquid, constant or variable, evaporated therein, with or without the control of the gas-flow variation, allows
a wide range of particularly important technological ap- plications.
Among these, application in the field of the con- tinuous measurement of the relative humidity of air (or other gases) is of outstanding importance.
The control of environmental conditions, for exam- ple, or process control, the setting up of plants for the treatment and conditioning of air and the measurement of the atmospheric conditions, are applications in which a reliability and repetitiveness of the parameters are nec- essary.
Solid state electronic systems are currently used, based on capacitive sensors, characterized by simple use and poor maintenance, which are also ideal for the imple- mentation of permanent measurement points, planned for functioning without operators.
Systems with solid state sensors are subjected to an initial calibration, which must be repeated regularly in order to correct possible deviations of the sensor re- sponse over a period of time.
The calibration of relative humidity sensors re- quires the generation of a controlled atmosphere, with an arbitrary humidity degree, with which the response of the sensor can be tested and measured.
The term arbitrary means that the humidity degree
can be pre-established each time, according to the cali- bration requirements.
The generation in the laboratory of reference atmos- pheres with a controlled relative humidity is typically effected in an environmental chamber fed with a humidifi- cation system controlled by an adequately precise meas- urement system.
These systems have the disadvantage of being eco- nomically onerous.
For field calibrations or when more sophisticated systems are not available, containers are normally used, with aqueous solutions saturated with salts capable of generating known relative humidity, at equilibrium.
These systems however have the disadvantage of not being able to generate an arbitrary degree of humidity.
A system for generating standards of humidity based on a syringe which introduces a constant flow of water into an evaporator situated inside the gas flow to be hu- midified, is known from US patent 6,526, 803, in the name of Fraenkel-Cooper.
This system has the disadvantage of requiring the use of mechanical precision elements to guarantee the constancy and reproducibility of the extremely reduced water flow required by the application.
A system is described in US patent application Nr.
2002/0139167 in the name of Schram-Albinus, for the pro- duction of calibration mixtures, based on the evaporation in air of microdrops, with a piezoelectric generator.
This system was designed to generate calibration at- mospheres with traces of volatile organic compounds through the supply of diluted solutions of the same in a suitable solvent.
This system can also be used to generate atmospheres with calibrated humidity, but has the disadvantage of be- ing economically onerous and of being subject to possible obstruction of the outlet nozzle on the part of solid particles which can be accidentally inserted in the sys- tem at the moment of the recharging of the water tank.
The microdrop generation device, integrated in the above-mentioned system, must be periodically calibrated to verify possible volume variations in the microdrops emitted.
The main objective of the present invention is to avoid the drawbacks present in the systems of the known art, in particular linked to the complexity of these sys- tems and/or to their costly production, providing a sys- tem for generating reference or process gas by the evapo- ration of a liquid in said gas.
Another objective of the present invention is to provide a system for the generation of a reference or
process gas with an arbitrary degree of relative humid- ity, wherein the introduction of microdrops of liquid is effected through a device which is simple and economical to produce and is also easy to calibrate.
Included in the objectives of the invention, is that of providing a system for the generation of reference gas having an arbitrary humidity degree, which can be applied to a calibration device of sensors and humidity measurers which allow a reliable and precise control of the quan- tity of evaporated water as well as a homogeneous distri- bution of the same in the gas.
These and other objectives according to the present invention are achieved by the system according to what is disclosed in claim 1.
A process for the generation of a reference gas by means of the evaporation of a liquid in said gas is the object of claim 24.
Further characteristics of the invention are the ob- ject of the dependent claims.
The present invention relates to a system for the generation of a reference or process gas by the evapora- tion of a liquid in said gas, and in particular to a sys- tem for the controlled humidification of a conveyed gas flow having an arbitrary degree of relative and/or abso- lute humidity, with particular application to the genera-
tion of reference atmospheres (of air or other gases) for providing calibration systems of humidity sensors.
The system according to the invention is based on the addition of a pre-established liquid or water flow to an anhydrous gas flow, by means of a series of discrete microdrops obtained from a microdrop generator array based on a technology used for producing ink-jet printing heads, which allows a high reliability and repetitiveness of the volume of drops emitted.
The evaporation of the liquid or, in particular, the humidification of the gas flow, is obtained by projecting the microdrops dispensed by the generator, against a preferably heated target.
The characteristics and advantages of the system for the generation of a reference or process gas by the evaporation of a liquid in said gas according to a pre- ferred embodiment of the present invention will appear more evident from the following illustrative and non- limitative description, referring to the enclosed sche- matic drawings in which: figures 1 to 3 schematically show a system for the generation of a reference or process gas by the evapora- tion of a liquid in said gas according to the invention, in different embodiments; figure 4 schematically shows a system according to
the invention applied to a calibration device for humid- ity sensors; figures 5 to 7 show different feeding groups of the system according to the invention, and respectively: en- vironmental air, compressed air line and compressed anhy- drous gas cylinder.
With reference to figure 1, this indicates a system for the generation of a reference or process gas by the evaporation of a liquid in said gas.
The system 10 for the generation of a reference or process gas having a controlled degree of liquid evapo- rated therein, or humidity (in the case of water), ac- cording to the invention, substantially comprises an evaporation (or humidification) chamber 20.
The system 10 is run by a control device 15 con- nected to and interacting with the elements of the system itself.
An anhydrous gas line 11 provides for the feeding of said gas, after being stripped of vapours and/or humid- ity, to the inlet 11'of the system 10.
The gas coming from the anhydrous gas line 11 ac- cording to the arrow F1, is sent to the evaporation (hu- midification) chamber 20.
The microdrop generator 25, preferably of the inter- changeable type and integrated with a tank of liquid (or
water, in particular) 25', projects a set of microdrops 27 into the evaporation chamber 20, against a preferably heated target 28.
The microdrops 27 are evaporated and mixed with the incoming gas, near to or in contact with said heated tar- get 28.
In particular, thanks to said heated target 28, use- ful for substantially supplying the whole quantity of la- tent heat for the evaporation of the liquid, said evapo- ration occurs without obliging the microdrops to follow a long course, during which they could easily coalesce.
The microdrop generator 25 is a device of the type in which the microdrops are generated and projected in a controlled form by means of a series of generating ele- ments 26.
The microdrop generator 25 is of the type used in the technology for ink-jet printing heads, both thermal and piezoelectric.
The drops generated by said microdrop generator 25 are characterized by a high volume constancy and repeat- ability.
The control device 15 of the microdrop generator 25 regulates the flow of liquid to be evaporated (or humidi- fication water) by varying the emission frequency of the microdrops themselves.
In the case of humidification, the use of a micro- drop generator produced in the form of a thermal head possibly connected to a tank 25'so as to produce a re- placeable cartridge, is particularly advantageous.
The purified feeding water of the microdrop genera- tor can, in fact, come from a separate tank or from a tank integrated with the generator itself.
Even more advantageously, the cartridge of the mi- crodrop generator 25 is of the sealed non-rechargeable type, i. e. mono-charged, so that a pre-established quan- tity of liquid is introduced to be used in the operating life of the cartridge itself.
The use of specific cartridges with the integrated water tank allows the gravimetric precalibration of the single pieces, during production, for example by emitting a pre-established quantity of microdrops and measuring the difference in weight of the system.
In an embodiment, the heated target 28 comprises a metallic element integrated with an electric heating ele- ment, possibly using the electric resistance variation of the latter for measuring the temperature of the element itself.
The heating of the--target ensures a rapid and com- plete evaporation of the liquid without the formation of macroscopic drops.
The system 10 in the configuration described above, allows the generation of a gas flow with an absolute quantity of predefined and possibly variable evaporated liquid, operating by means of a control line c which con- nects the control device 15 to the microdrop generator 25.
The system also advantageously comprises a line d for the regulation of the heated target 28 so as to adapt its temperature to the different operating conditions.
The evaporation chamber is also equipped with an outgoing duct 16 for conveying the humidified gas (or more generally the gas in which the liquid has been evaporated) to the user system, through an outlet 17 in the direction of the arrow F2.
According to a different embodiment illustrated in figure 2, the generation system 10 is implemented with a flow measurer 13, situated along the line 11 upstream of the evaporation chamber to measure the entering gas flow, communicating it to the control device 15 by means of a line b, for example for the production of variable gas flows containing humidity or vapours in a constant volu- metric ratio.
Another embodiment also envisages a flow regulator 12 controlled by the control device 15 by means of a line a, for the control and also the measurement of the flow.
This latter application allows, for example in the case of water, the generation of gas flows with a con- trolled absolute humidity.
An embodiment illustrated in figure 3 envisages, downstream of the evaporation chamber 20, a temperature measurer or sensor 22 placed in the point of use of the reference or process gas and connected to the control de- vice 15 by means of a line e, and allowing the control of the relative humidity of the flow.
With reference to figure 4, this illustrates a de- vice for the calibration 100 of humidity sensors and measurers comprising the system 10 for the generation of a reference gas by the evaporation of a liquid in said gas and a system 10'for effecting the calibration of a humidity sensor 24 using said reference gas.
According to the illustration selected, the device 100, which is used for verifying and/or calibrating sen- sors and measuring devices 24 of the relative and/or ab- solute humidity, integrates the generation system 10 con- nected to the calibration system 10'by means of the duct 16.
Said calibration system 10'substantially comprises a calibration chamber 30 in which it is possible to in- sert the sensor 24, to be subjected to calibration, in turn connected to a sensor control unit 14.
The outgoing gas from the anhydrous gas line 11 ac- cording to the arrow Fl, is sent to the humidification (evaporation) chamber 20 situated downstream of the pos- sible flow regulator 12 and flow measurer 13.
The humidification chamber 20 is of the type already described above and integrates its advantages.
The control device 15 receives information from the flow measurer 13 and controls the flow regulator 12 by means of lines b and a, respectively.
The microdrop generator 25 and heated target 28 are situated inside the evaporation chamber 20, which con- sists of a hermetic container.
The control device 15 is also connected to the evaporation chamber 20 to control the microdrop generator 25 and heated target 28 by means of lines c and d, re- spectively.
The evaporation chamber is equipped with an ingoing duct which is identified with the anhydrous gas line 11 for feeding with anhydrous air or other anhydrous gases, and an outgoing duct 16 for conveying the humidified gas (or more generally gas in which the liquid has been evaporated) to the user system, which, in the case illus- trated, consists of the system 10'for the calibration of sensors.
In particular applications, it is also possible to
position the generator-target system directly inside a duct or chamber washed with the gas to be humidified.
The evaporation chamber can be optionally entirely heated, for example to avoid possible recondensation phe- nomena in the generation of atmospheres close to satura- tion point, by exploiting the same heating element of the target or with an independent element.
The flow of humidified gas is then sent to the cali- bration chamber 30 where a mixer 34 ensures its remixing uniformity.
In this way, the gas does not have humidity gradi- ents, as it is homogenously humidified (or in general the gas does not have vapour concentration gradients).
Inside the calibration chamber 30, there is a tem- perature measurer 22 for detecting the temperature of the gas inside the chamber and communicating it to the con- trol device 15 by means of line e.
Inside the calibration chamber, there is optionally a heating and/or cooling element 23 which allows the ac- tive control of its temperature, controlled by the con- trol device through line f.
The control device 15 runs the microdrop generator and possible heating elements 7 and 13 and flow regula- tion elements 12.
In particular, the control system ensures the neces-
sary piloting frequency for the microdrop generator to supply the water flow required by the system in relation to the calibration parameters of the generator itself, the desired humidity value, the temperature of the cali- bration chamber and the ingoing gas flow.
The humidity sensor 24, subjected to calibration, is situated inside the calibration chamber 30 and is con- trolled by the sensor control unit 14 by means of line g.
The sensor control unit 14 is preferably directly interfaced with the control device of the calibration system 15 so as to automate the whole calibration proce- dure by means of line h.
With reference to figure 5, a first feeding group 40 envisages the use of atmospheric air as gas source, after acquiring it by means of an optionally filtered collector 41 which feeds a pump 42 whose outflow is sent to the calibrator through a single-step or multi-step anhydrifi- cation system 43.
With reference to figure 6, in a different embodi- ment, a second feeding group 50 envisages a'compressed air line 51 as gas source, after connection with the same line by means of a fitting, the group contemplates pres- sure regulation by means of a regulator 52, filtering of oil and other possible contaminants with a filter 53 and anhydrification with a single-step or multi-step device
54.
With reference to figure 7, in a different embodi- ment, a third feeding group 60 contemplates the use of a compressed anhydrous gas cylinder 61, which is connected to the calibrator by means of a pressure regulator 62.
In each of the above embodiments, the feeding group 40,50, 60 sends the anhydrous gas according to the di- rection indicated by the arrow F1 to the inlet 11'of the system 10.
The system for the generation of a reference gas by the evaporation of a liquid in said gas according to the present invention not only achieves the objectives estab- lished by also has a significant series of advantages.
The system allows a flow of air or other gases to be generated with a controlled degree of absolute and/or relative humidity (or in general evaporated liquid).
The control, electronically effected, of the liq- uid/water flow introduced into the gas creates a system which is accurate, can be easily implemented and easily calibrated gravimetrically.
The use of single-use replaceable systems greatly reduces the problem of blockage of the nozzles.
The implementation of the generation system with a single-use non-rechargeable cartridge, provides a system with guaranteed performances within the life range of the
cartridge itself, with particular reference to the con- trol of the degradation of the microdrop generation sys- tem.
The use of specific cartridges with the integrated water tank allows the gravimetric pre-calibration of the single pieces, during production, for example by emitting a pre-established quantity of microdrops and measuring the difference in weight of the system.
The presence of a series of generators allows a pro- portionally shorter operating cycle for each single gen- erator and minimizes the possible malfunctioning of a single nozzle as each deviation is mediated among all the existing nozzles.
The reduced dimensions and weight of the system al- low the development of compact and portable test and con- trol equipment.
The functioning procedure of the system, object of the present invention, is synthetically described to il- lustrate the further advantages.
Said procedure mainly envisages the generation of a reference gas by the evaporation of a liquid in said gas by means of the system described above and comprising the control-of the quantity of liquid vaporized in the gas by varying the microdrop generation frequency, the volume of the microdrops generated being substantially constant and
reproducible.
The procedure also envisages conveying the humidi- fied gas into the calibration chamber 30, the sensor 24 subjected to verification and/or calibration and the tem- perature measurer 22 being situated in said calibration chamber 30.
The signal coming from the temperature measurer 22 is used by the control device 15 of the microdrop genera- tor 25 to determine the quantity of liquid/water neces- sary for providing the pre-established level of liquid vapour or relative humidity, with the purpose of forming a verification and/or calibration system for measurers of liquids evaporated in a gaseous stream or of relative hu- midity, respectively.
The use of a microdrop generator 25 which can be substituted at the end of its life cycle, is also envis- aged.
The microdrop generator can be calibrated by gra- vimetrically measuring the water used up by the genera- tion of a high number of microdrops.
In particular, the individual pre-calibration of in- tegrated generator-tank systems produced as single-use cartridge, can be effected during production, which makes it possible to offer calibration systems guaranteed for the lifetime of the cartridge itself.
The calibration can in any case be verified by the user by weighing the whole cartridge or separate tank be- fore and after the emission of a certain number of micro- drops.
The device described can be applied to systems in which a controlled and reliable humidification of flows of gas conveyed, is necessary.
The flow of air (or other gas) entering the evapora- tion chamber must be controlled by a regulation system and measured so as to guarantee the necessary precision.
The calibration chamber, which is sealed, allows the sensor subjected to calibration to be immersed in the at- mosphere with a controlled humidity and contemporaneously isolated from external disturbances.
The calibration chamber is preferably equipped with a remixing system; by ensuring the pre-remixing of the humidified gas, however, it is possible to obtain a sys- tem with a laminar flow or at least characterized by a rapid and exhaustive replacement, where the sensor being calibrated is immersed in the flow itself.
A temperature measurer, situated extremely close to the sensor undergoing calibration, detects the tempera- ture of the air in the calibration chamber.
The calibration chamber itself can be optionally thermostat-regulated within wide temperature ranges with
a heating and possibly cooling element (for example an element with a Peltier effect) so that the calibration of the sensor can be obtained at different operating tem- peratures.
The desired humidity value is reached and maintained by the control system, using the calibration data of the generator (which define the mass of the single microdrop on the basis of the piloting parameters and characteris- tics of the single generator) and the data supplied by the measurers of the system.
In particular, signals of the measurer of the ingo- ing flow and temperature in the calibration chamber are used for calculating the level of absolute and/or rela- tive humidity present in the calibration chamber and con- sequently correcting the piloting of the microdrop gen- erator and possibly the temperature and gas flow control systems.
The presence of an electronic control system allows an interface to be produced with the sensor reading sys- tem, for the production of entirely automatic calibration systems.
When available, the calibration system described can exploit the anhydrous gas coming from a line of pure air or other gas.
It is possible to use a common compressed air line,
after treatment for removing the traces of oil and other pollutants possibly present in the air of the line, fol- lowed by anhydrification with a single-step or multiple- step system based on anhydrifying substances (for exam- ple, silica gel, molecular sieves or activated carbon), on semi-permeable membranes, for example of the type based on perfluorosulfonate ionomers (for example Nafion@, a trade-name registered by Du Pont) or a combi- nation thereof.
It is possible to produce portable systems for on site use which exploit atmospheric air removed with a pump and anhydrified with a single-or multi-step an- hyrdification system as described above.
It is possible to produce portable systems fed by a small cylinder of compressed anhydrous gas.
The use of the thermal technology for the generation of microdrops, allows the low-cost implementation of sin- gle-use generator-tank integrated systems, adopting the technology of ink-jet printing cartridges and the rela- tive wealth of technological development.