CA1066141A - Method and device for monitoring vapor concentration at a phase interface - Google Patents
Method and device for monitoring vapor concentration at a phase interfaceInfo
- Publication number
- CA1066141A CA1066141A CA253,864A CA253864A CA1066141A CA 1066141 A CA1066141 A CA 1066141A CA 253864 A CA253864 A CA 253864A CA 1066141 A CA1066141 A CA 1066141A
- Authority
- CA
- Canada
- Prior art keywords
- vapor
- cover
- concentration
- soil
- base
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- A—HUMAN NECESSITIES
- A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
- A01G—HORTICULTURE; CULTIVATION OF VEGETABLES, FLOWERS, RICE, FRUIT, VINES, HOPS OR SEAWEED; FORESTRY; WATERING
- A01G27/00—Self-acting watering devices, e.g. for flower-pots
- A01G27/008—Component parts, e.g. dispensing fittings, level indicators
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N31/00—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods
- G01N31/22—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods using chemical indicators
- G01N31/222—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods using chemical indicators for investigating moisture content
Abstract
Abstract of the Disclosure Method of monitoring and indicating the concentra-tion of vapor components at a phase interface comprising sampling vapor at the vapor source phase interface, com-paring the vapor concentration in the sample with a standard, and indicating the concentration of the vapor relative to the standard. A monitoring device is disclosed which comprises a sensing means and means for responsively coupling the sensing means to the vapor source phase to be monitored so that a representative vapor sample is presented to the sensing means. The method and device disclosed herein can be advantageously used to monitor volatile components, especially moisture, available to potted plants.
Description
912,283 METHOD AND DEVICE FOR MONITORING VAPOR
CONCENTRATION AT A PHASE INTERFACE
The present invention relates to a method and device for monitoring and indicating the concentration of a selected vapor component at a phase interfaceO
The measured concentration is related to a parametric concentration of the vapor and the concentration of vapor relative to the parametric concentration is indicated.
In a preferred embodiment, the present invention relates to a method and device for continuously monitoring and indicating concentrations of volatile components, eOgO
moisture, in soilO The method comprises sampling selected vapors present at the surface of the soil, comparing the vapor concentration in the sample with a standard, and indicating the concentration of a corresponding volatile component in the soil.
Monitoring devices are disclosed which perform the described functions The monitoring devices comprise sensing and comparing means enclosed within a moisture-impermeable, vapor-permeable envelopeO The disclosed devices are adapted to be located at a phase interface from which a vapor is issuing and can effectively sample and indicate the concentration of various selected vapors at the interface~ This concentration can then be compared to a standard representative of some parametric concentra-tion of the vapor which can be related to the concentra-tion of a corresponding unvaporized volatile componentfrom which the vapor issues, a chemical reactant or agent causing formation of the vapor or the likeO The concentration of the vapor relative to the standard is indicated by the device such as by a visible color changeO
1 - ~k5 ~066141 The method and monitorlng devices dlsclosed herein can be used to particular advantage for monitor-ing the moisture available to potted plants and can visibly indicate the point at which the soils containing the plants should be wateredO Alternatively, the method and devices can be used to monitor the concentration of other volatile components, such as ammonia, in soil and visibly indicate their concentrationO The devices can also be used to indicate the presence of moisture in diapers, surgical dressings, or the like, as will be described in greater detail hereinafterO
Devices for monitoring the moisture content of the soil around potted plants are known~ These devices generally employ a wick with a color indicator associated therewith which indicates the presence of moisture in the wick when the wick is submerged in the soil near the plant. A change in color indicates the need to water the soil. U~S. Patents 3,019,638 and 3,702,755 exemplify devices of this typeO
These wick-type devices do not operate satis-factorily under certain conditions. In some cases the construction of these devices causes the wick to dry prematurely by evaporation and the device does not reflect the actual status of the soil's moisture condi-tion. Furthermore, wicks tend to concentrate water soluble materials wlthin their structure and thereby become less transmissive, particularly the portion above the soil's surface where the wicks can dry out and actually become hydrophobic and inoperative due to the build-up of these water soluble residuesQ These ~066141 phenomena can produce lnaccurate readlngs whlch may cause the plant to be watered more often than necessa~y, resultir.~ i~ plant damageO Cellulosic wlcks tend to degrade ~ithin a short time and may requlre replacement of these indicating devices rather frequentlyO
U.SO Patent 3!788,128 discloses a devlce for determining the moisture content of soil at a dlstance ~elow the surface of the soilO The device is adapted to be submerged in the soil and contains one or more lndicating members adjacent a cavity within the devi~e and separated therefrom by a membrane which is permeable to moisture but not to liquid waterO The cavity communicates with the soil through water vapor permeable passagesO The indicating members change color in response to a specific humidity range in the cavityO
By determining the temperature and the amount of humldity - in the subsoil, the device aids in determining the optimum concentration of seed to be sownO
UOSO Patent 3,680,364 dlscloses a humidity .monitoring device for-curing concreteO The devi~e comprises a chamber having a base member and a viewing cover and containing therewithin a humidity indicating element.O The base.portion of the chamber is permeable to moisture, while the remainder of the chamber is impermeable to moisture The device ls placed on the surface of, or is pressed into the surface of, curing conGrete and visibly indicates, by a color change, when the concrete requires watering for proper hydratlonO
UOSO Patent 3,oo4j895 discloses a deYice fo~
absorbing large quantities of ammoniaO The abscrb~ng ~()66~41 agent is enclosed within a liquid impermeable, ammonia permeable envelope.
An indicating material is included in the envelope which changes color when the absorbing agent is depleted.
According to the present invention a relatively simple, but effective, method and device are provided for monitoring and indicating the concentration of vapor at a phase interface such as a solid/gas, liquid/gas or even a gas/gas interface, the device itself being preferably located in the gas phase which is not the source of the vapor and which is usually air.
The method comprises (a) continuously collecting a representative vapor sample in a differentially vapor permeable, liquid impermeable, envelope directly from a vapor source phase at the phase interface, said envelope comprising a base and a cover vapor permeable, said cover having a vapor transmission rate equivalent to a water vapor transmission rate of between 20 and 60 grams/1000 cm2/24 hours; (b) comparing the concentration of a selected vapor component in said sample with a standard contained in said envelope which is representative of a selected parametric concentration of said vapor in said sample; and (c) visibly indicating the concentration of said vapor in said sample relative to said standard.
The parametric concentration which is selected can be a vapor con-centration which is deleterious or advantageous in itself or can be a con-centration which can be related to a concentration of the vapor inrthe source phase from which the vapor issues, the concentration of a corresponding volatile component in the source phase, the concentration of a chemical reactant or agent which acts to produce the vapor within the source phase or the like. Thus, the method and device can be used to monitor the moisture in soil as well as detect and indicate the presence of moisture in diapers, surgical dressings and other absorbent materials. The invention also has utility in the detection and indication of vapors other than moisture vapor, e.g. ammonia, contained in or issuing from soil, water, decomposing ~0~6~41 proteinaceous material or other sources.
According to an aspect of the present invention there is provided a device for monitoring and indicating the concentration of a vapor at a phase interface comprising (a) a sensing means for comparing the concentra-tion of a selected vapor component in a sample with a standard which is representative of a selected parametric concentration of said vapor in said sample, said sensing means including means for indicating the concentration of said vapor in said sample relative to said standard, and (b) a differ-entially vapor permeable, liquid impermeable envelope enclosing said sensing means to responsively couple said sensing means to a vapor source phase at said phase interface, said envelope comprising a base adapted to rest on said vapor source phase and a cover for said base, said base and said cover vapor permeable defining a sealed, closely conforming envelope containing said sensing means, said cover having a vapor transmission rate equivalent to a water vapor transmission rate of between 20 and 60 grams/1000 cm2/24 hours, said base having a vapor transmission rate at least 50% greater than the vapor transmission rate of said cover, said cover adapted for viewing said indicat-ing means.
Typical sensing and indicating means are materials which change color or other optical, chemical or electrical properties in response to exposure to a given concentration of a vapor component, e.g. cobalt chloride for sensing moisture vapor; alizarin or pH papers for sensing ammonia.
The monitoring device also includes, in combination with the sens-ing and indicating means, a liquid-impermeable, vapor-permeable envelope enclosing the sensing means The nevelope comprises a base and a cover wherein the base is adapted to rest on or otherwise communicate with the phase from which the vapor issues. The base transmits vapor at a rate greater than the cover. Preferably the base has a vapor transmission rate at ~066~4~
least about 50% greater than the cover and most preferably at least about 100% greater than the cover.
A -5a-1~)66141 As noted, the base of the device can rest directly on the vapor source phase or otherwlse be fastened in contact wlth the vapor source phaseO
Alternatively, the base can be spaced from the source phase if other means, such as a tube or other connectlng means, is used to maintain the base in communication wlth the vapor source phase so that the devlce can effectively sample the vapor issuing therefromO
The differentially transmissive envelope used in the device of the present invention is necessary to effectively obtain representative vapor samples from a vapor source phaseO Use of the differentially vapor permeable envelope provides a device which is capable of sensing and indicating low levels of vapor or slight or slow changes in the vapor concentration whereas other devices, not having a differentially vapor permeable envelope, fail to accurately indicate the levels or changes of vapor concentration~
In a preferred embodiment of the present invention, there is provided a method and device for accurately and continuously monitoring and indlcating parametric concentrations of selected volatile components in a soil phaseO For example, the selected parametris concentration may be the minimum amount of soil moisture content necessary to keep a potted plant from wiltlng, or a deleterious concentration of ammonia ln the soil or some other meaningful concentration~ The devlce disclosed in the present invention overcomes the deficiencies of prior art wick-type devices sinse the device described herein can be used for monitoring soll ~066~41 moisture without requiring the presence of liquids wi~hln the device and particularly eliminates the use of wicks and the problems associated therewithO
The present inventor has discovered that the concentration of various volatile soil components in the upper levels of soil, for example the top 30 cm of soil can be determined by analyzing the vapor released from the surface of the soil at the air-soil interfaceO The concentratlons of these vapors can be empirically correlated with a corresponding concentration of the volatile components in the soilO These correlations can be used with the method and devices of the present inven-tion to indicate selected parametric concentrations of volatile components in soil, and are particularly useful in indicating moisture available to shallow-rooted plants. The correlations for available moisture are use-ful for various types of soil ranging from heavy clay to light potting mixO Thus, although plants growing in a heavy clay may begin to wilt at lower absolute soil moisture concentrations than those growing in lighter, more loosely packed soil, the moisture in the soil wh~ch is effectively available to the plant can be correlated with the molsture available at the surface ln the form of water vapor and is substantially independent of the soil type~
Similarly, a concentratlon of other volatile components in soil, such as ammonia, can be determined by measuring the level of the desired vapor componen~ avail-able at the surface of the soil and correlating this amount with the amount in the soil~
~:)66141 By choosing an appropr3.ate standard, various desired parametrlc concentrations of volatlle soil components can be indicated by the method and devices of this inventionO Accordingly, one aspect of the present invention relates to a method for continuously monitoring the concentration of volatile soil components, particul~rly water, which comprises (1) sampling directly from the surface of the soil a representative portion of a selected vapor component released from the air-soil interface of the soil to be monitored, (2) comparing the vapor con-centration in the sample with a standard which is representative o~ a parametric concentratlon of a corres-ponding volatile component in the soil, and (3) indicating the concentration of the vapor in the sample relatlve to the standard and thereby indicating the concentration of the corresponding volatile component in the soilO The method is particularly useful in monitoring available amounts of moisture and ammonia in soil contain.ing shallow-rooted plantsO In one embodiment the moisture Yapor risirg from the surface of the soil around a potted plant i8 sampledO The relative humidity of the moisture vapor is determined and compared to the relative humidity of moisture vapor rising from soil having a selected para-metric concentration of moisture, such as the available moisture needed to sustain the life of a plantO The sampling and comparing process is continuous, and when the moisture vapor concentration in the sample is equal to or l.ess than the standard concentration, the need for additional water in the soil is indicated, such as by a visible color changeO
1066~4~
An aspect of the present invention also relates to particular devices adapted to rest on the surface of soil and continuously monitor and indicate the concentra-tlon of specific volatile components in the sollO The devices of the present invention include a sensing means and means for responsively coupllng the sensing means directly to the,surface of the soil so that a representative sample of the volatile components released at the air-soil interface are presented to the sensing meansO The sensing means is capable of continuously comparing the concentration of a selected volatile component ln the sample with a standard which is representative of a parametric concentration of a corresponding vola~ile component in the soil, and includes means for indicating the concentration of the selected volatile component in the soilO In one embodiment the device comprises in combination a sensing element overlying a flat baseO A cover sheet having a viewing means, such as a transparent cover or a cover hav-ing a transparent window in register with the sensing element, overlies the sensing elementO The edges of the cover sheet are ~oined to the base to form an envelope which closely conforms to the sensing element leaving a minimum of free space within the envelopeO
The cover sheet and base must be permeable to vaporous components, but must be impermeable to liquidsO
The vapor transmisæion rate (expressed as vapor weight/unit area/unit time~ of the base should be greater than the vapor transmission rate of the cover sheetO
The differentially vapor-pe~meable envelope formed by the cover sheet and the base, which can rest _ g _ ~0661~L
directly on the soil, serves to responsively couple the sensing element to the soil surface and is capable of sampling a representative portion of vapor released from the surface of the soil corresponding to a selected volatile soil component.
The sensing element comprises a vapor-responsive indicating component which is capable of continuously sensing a vapor sample and providing a detectable change in property, preferably a visible change in property such as a change in color, in response to changes in vapor concentration in the sample relatlve to a selected standard concentrationO For example, where soil moisture is being monitored, the standard may be 75% R~H~ ~ which has been found to correlate with a para-metric concentration representing the plant-life-sustain-ing available moisture in the soilO When the continuously monitored sample concentration changes from above to below the standard (or vise versa) indicating the change from above to below (or vice versa) a parametric concentration of moisture in the soil, a visible change in the color of the sensing element or some other detectable change in property may be effectedO Thus, a material whlch changes color or visibly responds to a change in RoH~ at the 75%
level can be used as an effective indicating meansO
Particularly useful as indicating components in the sensing elements are hydrated salts which change color in response to given changes in relative humidity or deliquescent compounds which exhibit a change in color or other optical properties in response to given changes in relative humidityO Alternatively, materials which are ~066~41 sensitive to other vapor components, such as ammonia, can be used for monltoring varlous soil volatilesO
While for most applications it is preferred to use a reversible sensing element, iOe one that can repeatedly change a property, such as color, ln response to repeated changes in vapor concentration, so that continuous monitoring can be achleved. However, for some applications the device can employ a sen~ing element which undergoes an irreversible change in response to exposure to a given vapor concentration As noted previously, the differentially vapor-permeable envelope used in the monitoring device allows particularly effective continuous monitoring of subtle changes in vapor concentration and, accordingly, the use of a reversible sensing element provides a most advantageous combination ln accordance with this invention The devices of the present invention are placed in intimate contact with the surface of the soil The device can be used to monitor the concentration of volatile components in potted soil as well as unpotted soil and can be successfully used in determining the moisture andother volatile components available to potted plants as well as outdoor vegetation, such as grass or other shallow rooted plants When the device is adapted to monitor the moisture content of soil, the device, in one embodiment, exhlbits a given col.or when there is sufficient available water in the soil to sustain the life of the plantO When the available moisture in the soil approaches a selected parametric concentratlon, such as when the available moisture is J
r lnsufficlent to malntaln the health of the plant, the indicating element changes color to warn that the soll surrounding the plant needs wateringO When sufficient water has been added, the indicatlng element resume~ lts former color until the moisture concentration in the soil again approaches the parametric concentrationc Different parametric concentrations can be indicated by employing various indicating elements which change color at characterlstic vapor concentratlonsO
The lnvention can be further illustrated by reference to the specific embodiments shown in the drawings wherein:
FIGURE 1 is a perspective view partlally in cross section of a monitoring device according to the present invention;
FIGURE 2 is a perspective view of an alternate embodiment of the disclosed monltorlng device, FIGURE 3 is a cross section along line 3-3 of the monitoring device shown in FIGURE 2;
FIGURE 4 ls a perspective view of a potted plant showing a monitoring device such as that shown in FIGURE 3 positioned on the soll in close proximity to the plantO
FIGURE 1 shows one embodiment of a vapor monitor-ing device 10 comprising a sensing element 16 enclosed in a closely conforming envelope which comprises base 12 and cover 140 Base 12 is permeable to vapor, but ls lmpermeable to soil and other solid or llquid components which may be presentO Cover 14 is shown in FIGURE 1 as being coe~tensi~e 3G with base 12 and is ~oined to base 12 at the common periphery of base 12 and cover 14~ The base 12 and cover 14 can be ~oined by conventional means such as by heat seallng or by the use of adhesivesO Cover 14 is permeable to vapor, but is impermeable to bulk liquids or solidsO
While base 12 and cover 14 are both permeable to vapor, cover 14 has a maximum vapor transmission rate which is less than the vapor transmission rate of base 12 so that the envelope formed by base 12 and cover 14 is differentially vapor permeableO The vapor transmission rate of the base would ideally be infinitely higher than the cover. The vapor transmlssion rate of the base should be at least 50% greater than that of the cover and prefer-ably at least about lO0~ greater than that of the coverO
The minimum vapor transmission rate of the cover should be sufficient to allow a reasonably quick response timeO Generally the response time for the monitoring device should be about 15 minutes or lessO For example, for monitoring moisture vapor issuing from soil, the minimum rate of water Yapor transmission (WVT) of cover 14 should be about 2 g/1000 cm2/24 hours, and the maximum WVT
can be as high as about 60 g/lO00 cm2/24 hoursO Preferably cover 14 has a WVT in the range of about 20 to 40 g/lO00 cm2/24 hoursO Base 12 must have a minimum WVT of at least about 3g/lO00 cm2/24 hours, and preferably at least about 40 g/lO00 cm2/24 hoursO Corresponding rates can be readily determined for monitoring other vaporsO
Cover 14 should be transparent or be provided with other means for observing sensing element 16 such as a window in register with senslng element 16~
1066~41 Sensing element 16 includes an indicatlng component which provides a detectable change in property in response to given changes in the vapor concentration within the envelope, such as a vislble change in color, and will be described in greater detail hereinafterO
As noted previously3 base 12 must be permeable to vapor and impermeable to bulk liquids or solidsO
Materials which meet this requirement are vapor permeable or microporous polymeric films or alternatively hydro-phobic porous pads, such as an oil-absorbent, polypropylene microfiber matO These microfiber mats are known in the art as exemplified in U~S0 Patent 3,847,821 (Column 5)0 The vapor permeable films which can be used for base 12 or cover 14 are well known in the artO Polymeric materials such as cellulose polymers and copolymers, polyesters, polyethers, polyurethanes, polyalkylenes, polyacetates and the like which have the required vapor transmission properties can be usedO Microporous polyester and poly ether urethanes can also be usedO Cellulose acetate is particularly preferred as a cover material for devices monitoring moisture vaporO As noted previously, these materials should not transmit bulk water, and therefcre excessively hydrophilic polymers such as hydrophilic polyoxyethylene polyurethane polymers should not be used in the devices of this inventionO
The aforementioned characteristiGs of base 12 are critical to the successful operation of device lOo If base 12 is permeable to liquid water or is constructed so as to wick water into contact wlth sensing eleme~t 16, the de~ice will provide erronecus indications due to ~he 1066~41 presence of the liquid water in contact with the sens.ing elementO In addition, the liqu'Ld water may ~end t~ leach indicating component from sensing element 16, shortenlng the useful life of the monltoring device lOo Thus 3 base 12 is not a wick material as used in prior art devices, and in fact must be hydrophobic or otherwise impermeable to bulk liquid for the device of the present invention to operate successfullyO The liquid impermeability of device 10 is particularly advantageous when the monit~r-ing device is to be used for potted plants, wherein thedevice may be sub~ected to periodic floodlng during watering of the plant~
As shown in FIGURE 1, cover 14 should closely conform to the sensing element 16 so as to minimize the free space in the envelope defined by cover 14 and base 120 Mi~imizing the free space helps to prevent condensation of moisture within the envelopeO
Sensing element 16 includes an indicating component which alone, or in comblnation with other portlons o~ the senslng element, exhibits a detectable change in property in response to changes in concentration of specific vapor components relative to a selected standardO It is preferred that the indicating component of sensing element 16 be capable of exhibiting-a visible change such as a change in color or optical propertiesO
Alternatively, the indicating component can exhibit non-visible changes which can be detected such as a change in conductivity, permeability, density, crystalline formg and the likeO
- 1.5 -` 106614~L
For devices used to monltor soll molsture9 chemicals~ such as hydrated salts, which visibly respond to changes in relative humldity by changlng color, are particularly suitableO A pre~erred hydrated salt is cobalt chloride ~CoCl2 6H20)0 This salt, when applled to or absorbed in a cellulosic material, gelatin, s~llca gel, or polymeric materlal, can change from a pink to a blue color depending on the level of the relatlve humidity to which the salt is exposedO These salts are well known and have been used in various humidity indicating means as descrlbed in UOS. Patents 2,4~0,071,
CONCENTRATION AT A PHASE INTERFACE
The present invention relates to a method and device for monitoring and indicating the concentration of a selected vapor component at a phase interfaceO
The measured concentration is related to a parametric concentration of the vapor and the concentration of vapor relative to the parametric concentration is indicated.
In a preferred embodiment, the present invention relates to a method and device for continuously monitoring and indicating concentrations of volatile components, eOgO
moisture, in soilO The method comprises sampling selected vapors present at the surface of the soil, comparing the vapor concentration in the sample with a standard, and indicating the concentration of a corresponding volatile component in the soil.
Monitoring devices are disclosed which perform the described functions The monitoring devices comprise sensing and comparing means enclosed within a moisture-impermeable, vapor-permeable envelopeO The disclosed devices are adapted to be located at a phase interface from which a vapor is issuing and can effectively sample and indicate the concentration of various selected vapors at the interface~ This concentration can then be compared to a standard representative of some parametric concentra-tion of the vapor which can be related to the concentra-tion of a corresponding unvaporized volatile componentfrom which the vapor issues, a chemical reactant or agent causing formation of the vapor or the likeO The concentration of the vapor relative to the standard is indicated by the device such as by a visible color changeO
1 - ~k5 ~066141 The method and monitorlng devices dlsclosed herein can be used to particular advantage for monitor-ing the moisture available to potted plants and can visibly indicate the point at which the soils containing the plants should be wateredO Alternatively, the method and devices can be used to monitor the concentration of other volatile components, such as ammonia, in soil and visibly indicate their concentrationO The devices can also be used to indicate the presence of moisture in diapers, surgical dressings, or the like, as will be described in greater detail hereinafterO
Devices for monitoring the moisture content of the soil around potted plants are known~ These devices generally employ a wick with a color indicator associated therewith which indicates the presence of moisture in the wick when the wick is submerged in the soil near the plant. A change in color indicates the need to water the soil. U~S. Patents 3,019,638 and 3,702,755 exemplify devices of this typeO
These wick-type devices do not operate satis-factorily under certain conditions. In some cases the construction of these devices causes the wick to dry prematurely by evaporation and the device does not reflect the actual status of the soil's moisture condi-tion. Furthermore, wicks tend to concentrate water soluble materials wlthin their structure and thereby become less transmissive, particularly the portion above the soil's surface where the wicks can dry out and actually become hydrophobic and inoperative due to the build-up of these water soluble residuesQ These ~066141 phenomena can produce lnaccurate readlngs whlch may cause the plant to be watered more often than necessa~y, resultir.~ i~ plant damageO Cellulosic wlcks tend to degrade ~ithin a short time and may requlre replacement of these indicating devices rather frequentlyO
U.SO Patent 3!788,128 discloses a devlce for determining the moisture content of soil at a dlstance ~elow the surface of the soilO The device is adapted to be submerged in the soil and contains one or more lndicating members adjacent a cavity within the devi~e and separated therefrom by a membrane which is permeable to moisture but not to liquid waterO The cavity communicates with the soil through water vapor permeable passagesO The indicating members change color in response to a specific humidity range in the cavityO
By determining the temperature and the amount of humldity - in the subsoil, the device aids in determining the optimum concentration of seed to be sownO
UOSO Patent 3,680,364 dlscloses a humidity .monitoring device for-curing concreteO The devi~e comprises a chamber having a base member and a viewing cover and containing therewithin a humidity indicating element.O The base.portion of the chamber is permeable to moisture, while the remainder of the chamber is impermeable to moisture The device ls placed on the surface of, or is pressed into the surface of, curing conGrete and visibly indicates, by a color change, when the concrete requires watering for proper hydratlonO
UOSO Patent 3,oo4j895 discloses a deYice fo~
absorbing large quantities of ammoniaO The abscrb~ng ~()66~41 agent is enclosed within a liquid impermeable, ammonia permeable envelope.
An indicating material is included in the envelope which changes color when the absorbing agent is depleted.
According to the present invention a relatively simple, but effective, method and device are provided for monitoring and indicating the concentration of vapor at a phase interface such as a solid/gas, liquid/gas or even a gas/gas interface, the device itself being preferably located in the gas phase which is not the source of the vapor and which is usually air.
The method comprises (a) continuously collecting a representative vapor sample in a differentially vapor permeable, liquid impermeable, envelope directly from a vapor source phase at the phase interface, said envelope comprising a base and a cover vapor permeable, said cover having a vapor transmission rate equivalent to a water vapor transmission rate of between 20 and 60 grams/1000 cm2/24 hours; (b) comparing the concentration of a selected vapor component in said sample with a standard contained in said envelope which is representative of a selected parametric concentration of said vapor in said sample; and (c) visibly indicating the concentration of said vapor in said sample relative to said standard.
The parametric concentration which is selected can be a vapor con-centration which is deleterious or advantageous in itself or can be a con-centration which can be related to a concentration of the vapor inrthe source phase from which the vapor issues, the concentration of a corresponding volatile component in the source phase, the concentration of a chemical reactant or agent which acts to produce the vapor within the source phase or the like. Thus, the method and device can be used to monitor the moisture in soil as well as detect and indicate the presence of moisture in diapers, surgical dressings and other absorbent materials. The invention also has utility in the detection and indication of vapors other than moisture vapor, e.g. ammonia, contained in or issuing from soil, water, decomposing ~0~6~41 proteinaceous material or other sources.
According to an aspect of the present invention there is provided a device for monitoring and indicating the concentration of a vapor at a phase interface comprising (a) a sensing means for comparing the concentra-tion of a selected vapor component in a sample with a standard which is representative of a selected parametric concentration of said vapor in said sample, said sensing means including means for indicating the concentration of said vapor in said sample relative to said standard, and (b) a differ-entially vapor permeable, liquid impermeable envelope enclosing said sensing means to responsively couple said sensing means to a vapor source phase at said phase interface, said envelope comprising a base adapted to rest on said vapor source phase and a cover for said base, said base and said cover vapor permeable defining a sealed, closely conforming envelope containing said sensing means, said cover having a vapor transmission rate equivalent to a water vapor transmission rate of between 20 and 60 grams/1000 cm2/24 hours, said base having a vapor transmission rate at least 50% greater than the vapor transmission rate of said cover, said cover adapted for viewing said indicat-ing means.
Typical sensing and indicating means are materials which change color or other optical, chemical or electrical properties in response to exposure to a given concentration of a vapor component, e.g. cobalt chloride for sensing moisture vapor; alizarin or pH papers for sensing ammonia.
The monitoring device also includes, in combination with the sens-ing and indicating means, a liquid-impermeable, vapor-permeable envelope enclosing the sensing means The nevelope comprises a base and a cover wherein the base is adapted to rest on or otherwise communicate with the phase from which the vapor issues. The base transmits vapor at a rate greater than the cover. Preferably the base has a vapor transmission rate at ~066~4~
least about 50% greater than the cover and most preferably at least about 100% greater than the cover.
A -5a-1~)66141 As noted, the base of the device can rest directly on the vapor source phase or otherwlse be fastened in contact wlth the vapor source phaseO
Alternatively, the base can be spaced from the source phase if other means, such as a tube or other connectlng means, is used to maintain the base in communication wlth the vapor source phase so that the devlce can effectively sample the vapor issuing therefromO
The differentially transmissive envelope used in the device of the present invention is necessary to effectively obtain representative vapor samples from a vapor source phaseO Use of the differentially vapor permeable envelope provides a device which is capable of sensing and indicating low levels of vapor or slight or slow changes in the vapor concentration whereas other devices, not having a differentially vapor permeable envelope, fail to accurately indicate the levels or changes of vapor concentration~
In a preferred embodiment of the present invention, there is provided a method and device for accurately and continuously monitoring and indlcating parametric concentrations of selected volatile components in a soil phaseO For example, the selected parametris concentration may be the minimum amount of soil moisture content necessary to keep a potted plant from wiltlng, or a deleterious concentration of ammonia ln the soil or some other meaningful concentration~ The devlce disclosed in the present invention overcomes the deficiencies of prior art wick-type devices sinse the device described herein can be used for monitoring soll ~066~41 moisture without requiring the presence of liquids wi~hln the device and particularly eliminates the use of wicks and the problems associated therewithO
The present inventor has discovered that the concentration of various volatile soil components in the upper levels of soil, for example the top 30 cm of soil can be determined by analyzing the vapor released from the surface of the soil at the air-soil interfaceO The concentratlons of these vapors can be empirically correlated with a corresponding concentration of the volatile components in the soilO These correlations can be used with the method and devices of the present inven-tion to indicate selected parametric concentrations of volatile components in soil, and are particularly useful in indicating moisture available to shallow-rooted plants. The correlations for available moisture are use-ful for various types of soil ranging from heavy clay to light potting mixO Thus, although plants growing in a heavy clay may begin to wilt at lower absolute soil moisture concentrations than those growing in lighter, more loosely packed soil, the moisture in the soil wh~ch is effectively available to the plant can be correlated with the molsture available at the surface ln the form of water vapor and is substantially independent of the soil type~
Similarly, a concentratlon of other volatile components in soil, such as ammonia, can be determined by measuring the level of the desired vapor componen~ avail-able at the surface of the soil and correlating this amount with the amount in the soil~
~:)66141 By choosing an appropr3.ate standard, various desired parametrlc concentrations of volatlle soil components can be indicated by the method and devices of this inventionO Accordingly, one aspect of the present invention relates to a method for continuously monitoring the concentration of volatile soil components, particul~rly water, which comprises (1) sampling directly from the surface of the soil a representative portion of a selected vapor component released from the air-soil interface of the soil to be monitored, (2) comparing the vapor con-centration in the sample with a standard which is representative o~ a parametric concentratlon of a corres-ponding volatile component in the soil, and (3) indicating the concentration of the vapor in the sample relatlve to the standard and thereby indicating the concentration of the corresponding volatile component in the soilO The method is particularly useful in monitoring available amounts of moisture and ammonia in soil contain.ing shallow-rooted plantsO In one embodiment the moisture Yapor risirg from the surface of the soil around a potted plant i8 sampledO The relative humidity of the moisture vapor is determined and compared to the relative humidity of moisture vapor rising from soil having a selected para-metric concentration of moisture, such as the available moisture needed to sustain the life of a plantO The sampling and comparing process is continuous, and when the moisture vapor concentration in the sample is equal to or l.ess than the standard concentration, the need for additional water in the soil is indicated, such as by a visible color changeO
1066~4~
An aspect of the present invention also relates to particular devices adapted to rest on the surface of soil and continuously monitor and indicate the concentra-tlon of specific volatile components in the sollO The devices of the present invention include a sensing means and means for responsively coupllng the sensing means directly to the,surface of the soil so that a representative sample of the volatile components released at the air-soil interface are presented to the sensing meansO The sensing means is capable of continuously comparing the concentration of a selected volatile component ln the sample with a standard which is representative of a parametric concentration of a corresponding vola~ile component in the soil, and includes means for indicating the concentration of the selected volatile component in the soilO In one embodiment the device comprises in combination a sensing element overlying a flat baseO A cover sheet having a viewing means, such as a transparent cover or a cover hav-ing a transparent window in register with the sensing element, overlies the sensing elementO The edges of the cover sheet are ~oined to the base to form an envelope which closely conforms to the sensing element leaving a minimum of free space within the envelopeO
The cover sheet and base must be permeable to vaporous components, but must be impermeable to liquidsO
The vapor transmisæion rate (expressed as vapor weight/unit area/unit time~ of the base should be greater than the vapor transmission rate of the cover sheetO
The differentially vapor-pe~meable envelope formed by the cover sheet and the base, which can rest _ g _ ~0661~L
directly on the soil, serves to responsively couple the sensing element to the soil surface and is capable of sampling a representative portion of vapor released from the surface of the soil corresponding to a selected volatile soil component.
The sensing element comprises a vapor-responsive indicating component which is capable of continuously sensing a vapor sample and providing a detectable change in property, preferably a visible change in property such as a change in color, in response to changes in vapor concentration in the sample relatlve to a selected standard concentrationO For example, where soil moisture is being monitored, the standard may be 75% R~H~ ~ which has been found to correlate with a para-metric concentration representing the plant-life-sustain-ing available moisture in the soilO When the continuously monitored sample concentration changes from above to below the standard (or vise versa) indicating the change from above to below (or vice versa) a parametric concentration of moisture in the soil, a visible change in the color of the sensing element or some other detectable change in property may be effectedO Thus, a material whlch changes color or visibly responds to a change in RoH~ at the 75%
level can be used as an effective indicating meansO
Particularly useful as indicating components in the sensing elements are hydrated salts which change color in response to given changes in relative humidity or deliquescent compounds which exhibit a change in color or other optical properties in response to given changes in relative humidityO Alternatively, materials which are ~066~41 sensitive to other vapor components, such as ammonia, can be used for monltoring varlous soil volatilesO
While for most applications it is preferred to use a reversible sensing element, iOe one that can repeatedly change a property, such as color, ln response to repeated changes in vapor concentration, so that continuous monitoring can be achleved. However, for some applications the device can employ a sen~ing element which undergoes an irreversible change in response to exposure to a given vapor concentration As noted previously, the differentially vapor-permeable envelope used in the monitoring device allows particularly effective continuous monitoring of subtle changes in vapor concentration and, accordingly, the use of a reversible sensing element provides a most advantageous combination ln accordance with this invention The devices of the present invention are placed in intimate contact with the surface of the soil The device can be used to monitor the concentration of volatile components in potted soil as well as unpotted soil and can be successfully used in determining the moisture andother volatile components available to potted plants as well as outdoor vegetation, such as grass or other shallow rooted plants When the device is adapted to monitor the moisture content of soil, the device, in one embodiment, exhlbits a given col.or when there is sufficient available water in the soil to sustain the life of the plantO When the available moisture in the soil approaches a selected parametric concentratlon, such as when the available moisture is J
r lnsufficlent to malntaln the health of the plant, the indicating element changes color to warn that the soll surrounding the plant needs wateringO When sufficient water has been added, the indicatlng element resume~ lts former color until the moisture concentration in the soil again approaches the parametric concentrationc Different parametric concentrations can be indicated by employing various indicating elements which change color at characterlstic vapor concentratlonsO
The lnvention can be further illustrated by reference to the specific embodiments shown in the drawings wherein:
FIGURE 1 is a perspective view partlally in cross section of a monitoring device according to the present invention;
FIGURE 2 is a perspective view of an alternate embodiment of the disclosed monltorlng device, FIGURE 3 is a cross section along line 3-3 of the monitoring device shown in FIGURE 2;
FIGURE 4 ls a perspective view of a potted plant showing a monitoring device such as that shown in FIGURE 3 positioned on the soll in close proximity to the plantO
FIGURE 1 shows one embodiment of a vapor monitor-ing device 10 comprising a sensing element 16 enclosed in a closely conforming envelope which comprises base 12 and cover 140 Base 12 is permeable to vapor, but ls lmpermeable to soil and other solid or llquid components which may be presentO Cover 14 is shown in FIGURE 1 as being coe~tensi~e 3G with base 12 and is ~oined to base 12 at the common periphery of base 12 and cover 14~ The base 12 and cover 14 can be ~oined by conventional means such as by heat seallng or by the use of adhesivesO Cover 14 is permeable to vapor, but is impermeable to bulk liquids or solidsO
While base 12 and cover 14 are both permeable to vapor, cover 14 has a maximum vapor transmission rate which is less than the vapor transmission rate of base 12 so that the envelope formed by base 12 and cover 14 is differentially vapor permeableO The vapor transmission rate of the base would ideally be infinitely higher than the cover. The vapor transmlssion rate of the base should be at least 50% greater than that of the cover and prefer-ably at least about lO0~ greater than that of the coverO
The minimum vapor transmission rate of the cover should be sufficient to allow a reasonably quick response timeO Generally the response time for the monitoring device should be about 15 minutes or lessO For example, for monitoring moisture vapor issuing from soil, the minimum rate of water Yapor transmission (WVT) of cover 14 should be about 2 g/1000 cm2/24 hours, and the maximum WVT
can be as high as about 60 g/lO00 cm2/24 hoursO Preferably cover 14 has a WVT in the range of about 20 to 40 g/lO00 cm2/24 hoursO Base 12 must have a minimum WVT of at least about 3g/lO00 cm2/24 hours, and preferably at least about 40 g/lO00 cm2/24 hoursO Corresponding rates can be readily determined for monitoring other vaporsO
Cover 14 should be transparent or be provided with other means for observing sensing element 16 such as a window in register with senslng element 16~
1066~41 Sensing element 16 includes an indicatlng component which provides a detectable change in property in response to given changes in the vapor concentration within the envelope, such as a vislble change in color, and will be described in greater detail hereinafterO
As noted previously3 base 12 must be permeable to vapor and impermeable to bulk liquids or solidsO
Materials which meet this requirement are vapor permeable or microporous polymeric films or alternatively hydro-phobic porous pads, such as an oil-absorbent, polypropylene microfiber matO These microfiber mats are known in the art as exemplified in U~S0 Patent 3,847,821 (Column 5)0 The vapor permeable films which can be used for base 12 or cover 14 are well known in the artO Polymeric materials such as cellulose polymers and copolymers, polyesters, polyethers, polyurethanes, polyalkylenes, polyacetates and the like which have the required vapor transmission properties can be usedO Microporous polyester and poly ether urethanes can also be usedO Cellulose acetate is particularly preferred as a cover material for devices monitoring moisture vaporO As noted previously, these materials should not transmit bulk water, and therefcre excessively hydrophilic polymers such as hydrophilic polyoxyethylene polyurethane polymers should not be used in the devices of this inventionO
The aforementioned characteristiGs of base 12 are critical to the successful operation of device lOo If base 12 is permeable to liquid water or is constructed so as to wick water into contact wlth sensing eleme~t 16, the de~ice will provide erronecus indications due to ~he 1066~41 presence of the liquid water in contact with the sens.ing elementO In addition, the liqu'Ld water may ~end t~ leach indicating component from sensing element 16, shortenlng the useful life of the monltoring device lOo Thus 3 base 12 is not a wick material as used in prior art devices, and in fact must be hydrophobic or otherwise impermeable to bulk liquid for the device of the present invention to operate successfullyO The liquid impermeability of device 10 is particularly advantageous when the monit~r-ing device is to be used for potted plants, wherein thedevice may be sub~ected to periodic floodlng during watering of the plant~
As shown in FIGURE 1, cover 14 should closely conform to the sensing element 16 so as to minimize the free space in the envelope defined by cover 14 and base 120 Mi~imizing the free space helps to prevent condensation of moisture within the envelopeO
Sensing element 16 includes an indicating component which alone, or in comblnation with other portlons o~ the senslng element, exhibits a detectable change in property in response to changes in concentration of specific vapor components relative to a selected standardO It is preferred that the indicating component of sensing element 16 be capable of exhibiting-a visible change such as a change in color or optical propertiesO
Alternatively, the indicating component can exhibit non-visible changes which can be detected such as a change in conductivity, permeability, density, crystalline formg and the likeO
- 1.5 -` 106614~L
For devices used to monltor soll molsture9 chemicals~ such as hydrated salts, which visibly respond to changes in relative humldity by changlng color, are particularly suitableO A pre~erred hydrated salt is cobalt chloride ~CoCl2 6H20)0 This salt, when applled to or absorbed in a cellulosic material, gelatin, s~llca gel, or polymeric materlal, can change from a pink to a blue color depending on the level of the relatlve humidity to which the salt is exposedO These salts are well known and have been used in various humidity indicating means as descrlbed in UOS. Patents 2,4~0,071,
2,580,737, 3,702,755 and 3,788,1280 Salt mixtures comprising cobalt chloride with other materials can also be used as indlcating components 15 of senslng element 160 Mixtures of cobalt chloride with cobalt thiocyanate (eOgo equal parts by weight) have been - used to provide a visible color change in the relative humidity range of about 50 to 75 percent R~Ho U SO Pa~ents 2,460,074 and 3,788,128 describe the use Or these salt mixtures as humidity indicating materialsO This combina-tion of chemicals can be used to provide a pink color at relative humidities above about 75% When the relative humidity goes below 75% the indicating material gradually changes to a lavendar color, becoming blue at a relative humidity of about 50% ~nd belowO The humidity at whi~h ~he color change occurs can be ad~usted by varying the ratio of cobalt chloride to cobalt thiocyanateO For example, a sensing element can be prepared by sat~lrating a piece of porous filter paper~ such as Whatman NoO 1 rilter paper, with a 20% aqueous composition of equal ¢
~06614~
parts by weight cobalt chloride and cobalt thiocyanate and drylng the saturated filter paperO The response range of the senslng element can be varled to some degree by controlling the concentration of salt in the sensing element, A use~ul indicating component which exhiblts a detectable color change over a relatlvely narrow relative humidity range comprises a mixture of cobalt chloride with a copolymer of polyvinyl pyrrolldone/vinyl acetate ("I 535,"
General Analine and Fllm). Copolymer to cobalt chloride ratios of about 6:1 to about 1:1 are preferredO m e mixture is dissolved in water and absorbed in or applied to an absorbent pad or other carrier, and when dried provldes a sensing element which exhiblts a readily observable color change in the 70% to 80~ relative humidlty rangeO
In one embodiment o~ the device 10 shown in FIGURE 1 the sensing element 16 is prepared by applying an lndicating component directly to the underside of cover 140 For example, the cobalt chloride/copolymer solution described-above can be coated on the underside of cover 1 in the form of a dot or other shape havlng a diameter of about 0.5 to lo 5 centimetersO After the solution dries~
the coating which forms sensing element 16 ls ready for useO
In yet another embodiment-sensing element 16 can include as the indicating component a deliquescent compound which exhibits a reversible change in optical properties at a glven level of relative humidity~ Fo~
example, the sensing element 16 can comprise a coherent, continuous layer of deliquescent compound which is 3paque at humidlty levels below the point at which the compound 1066~4~
deliquesces and which becomes optically transparent on dellquescing~ together with a layer underlying the deliquescent compound which i5 at least partlally colored ln contrast to the opaque compound so as to be observable, and preferably conspicuous, when the compound deliquesces and becomes transparentO
When the surrounding humldity is below a glven level, the deliquescent compound remains opaque and the underlying layer is not visibleO When the humidity rises above the point at whlch the compound dellquesces, the compound becomes transparent and the underlayer is visible preferably conspicuous, to the observer, thereby indicat-ing exposure to a selected level of relative humidity within the envelope~ When the humidity level within the envelope is again lowered below the deliquescent point of the compound, the compound effloresces and again becomes opaque and the underlayer is no longer visible to the observerO In one embodiment the underlayer can be a contrasting color or can have intelligence printed on the surface thereof so that when the deliquescent compound becomes transparent a conspicuous color or an appropriate message such as "wet" or the like is observedO
A preferred means of providing a continuous layer o~ deliquescent compound is to absorb a solution of the deliquescent compound in a thin layer of tissue paper and dry the paperO Sodium bromide is a preferred deliquescent salt, although other deliquescent compounds known in the art are suitableO The sensing element 15 ~hich includes sodium bromide as the deliquescent compound proYldes a change in optical properties when the relati~e ~066~
hum~dity within the envelope is about 57%O
When the device 10 is used to monitor the concentration of vapor components other than moisture, eOgO ammonia, the sensing element 16 comprises indicating components capable of responding to changes in the concentration of these specific volatile componentsO
For example, a device for monitoring the ammonia concen-tration of soil can be provided by employing alizarin or pH papers sensitive to the 3 - 5O5 pH range such as are available commercially under the trade name "pHydrion"
papers from Micro Essential LaboratoryO Indicators employing the "pHydrion" papers visibly respond by changing color from yellow/orange to blue/green, which color change is correlative to the ammonia concentration (in parts per million) in the soilO
In addition, by selecting a sensing which responds to other specific vapors, the monitoring device may be used to detect and monitor the concentration and change in concentratlon of various vapors such as the oxides o~ nitrogen, sulfur and carbon, and the halogens~
FIGURE 2 is an alternate embodiment of a vapor monitoring device according to the present inventionO
Monitoring device 20 is similar to that shown in FIGURE 1 comprising vapor permeable base 22, sensing element 2~, 25 and vapor permeable cover 260 Device 20 also contains a protective layer 28 underlylng base 22 and containlng pores 30O Layer 28 and cover 26 are shown extending beyond base 22 and are ~oined at their periphery to enclo~e base ~2 and sensing element 24 in a closely ccn-forming envelopeO Protective layer 28 is shown as a ~066~4~
porous layer which is permeable to vapor and whlch may be permeable to llquid water since base 22 and cover 26 are impermeable to liquids and protect sensing element 240 Protective layer 28 serves to protect base 22 during handling and helps prevent base 22~ particularly when base 22 is a porous mat of blown microfibers, from becoming clogged with dirt and the li~eO Representative of materials which can be used for protective layer 28 are porous polyethylene films such as 3M Brand "TRANSPORE"
tape and a microporous tape having a non-woven backing such as 3M Brand t'MICROPORE" tape, both available commercially from the 3M Company.
FIGURE 3 is a cross section along line 3-3 of the monitorlng device shown in FIGURE 20 As can be seen, cover 26 together with base 22 and protective layer 28 envelop and closely conform to sensing element 24, minimizing the free space within the envelope surrounding sensing element 240 In order to operate successfully as a monitoring device 10, 20, the sensing element 16, 24 shown in FIGURES
1-3 must be responsively coupled to the vapor source phase at the interface so that the monitoring device can accurately sample and compare a representative surface vapor concentrationO This is achieved in the present invention by enclosing the sensing element 16, 24 in a sampling envelope defined by base 12 and cover 14 as in FIGURE 1, or by base 22 and cover 26 as in FIGURE 20 The sampling envelope shown in FIGURE 3 is adapted to rest on9 and intimately ~ontact 3 the surface of the vapor source phase, such as the soil surrounding a potted plant, collect 106614~.
a representative sample of Yapors released from the surface of the phase, and present the sample to sensing element 16, 240 Due to the difference in vapor transmisslon rates between the cover 14, 26 and the base 12, 22 a sudden change in vapor input through base 12, 22 will not cause the interior of the envelope to become immediately overwhelmed with or starved of vapor; that is, the vapor concentration within the envelope may be slightly different than the actual vapor concentration at the base-vapor source phase interface until steady state is achieved This lagging response tends to reduce any effect of transient peaks and valleys of vapor concentra-tion released from the vapor source phase~
Further, the relatively slow vapor transmission rate of the cover 14 prevents the vapors entering the envelope through the base 12, 22 from being overwhelmed by vapors entering through the cover 14, 26 from the surrounding atmosphereO Temporary changes ln relative humidity in the surrounding envlronment will have little or no effect on a sensing element sensitive to changes in relative humidityO However, constant operation at humidity levels above the selected standard relative humidity, eOgO above 75% R~Ha~ which has been found to be a useful R~Ho Standard, may ultimately overcome the monitoring device and impair the ability of the device to accurately indicate the selected parametric moisture concentrationO
Although cover 14, 26 is relatively less 30 permeable than base 12, 22 3 the cover must have the ~066~41 aforementloned minimum vapor transmission rateO If cover 14, 26 does not have the necessary vapor transmiss~on rate3 moisture or other vapors can accumulate within the envelope and allow undesirable condensation in the envelopea causlng the sensing element 16, 24 to be contacted by bulk liquid which can leach chemicals from the sensing element or cause a false reading by a humidity sensitive sensing elementO
The monitoring device of the pre~ent invention should be large enough to sample vapor released from a representative area of the vapor source phaseO Discs about lo 25 to 5 cm in diameter have been found sufficient to provide accurate resultsO Shapes other than discs can be used with equivalent resultsO
A disc of about 205 cm in diameter is an effec-tive compromise size to achieve convenlent handling and accurate samplingO This allows the device to accumulate vapors released from about 5 cm of the surface of the vapor source phaseO
Because the vapors reside in the monitoring device for a short period of tlme before passing through the cover, some mixing of the vapors takes place and the monitoring device, in effect, averages the concentration of vapor with time and over the area covered by the device and can provide a more accurate reading than a wick or other point sampling device can provideO
Generally monitoring devices having a base area of less than about 1025 cm2 are not preferred since the device becomes difficult to observe and handle and does not s~mple a l.arge enough area of the vapor source phase 1~6~4~
surfaceO Monltoring de~ices which have a base area of greater than about 20 cm2 can function effectively but may be too large for some applications, for example, they may be difficult to fit into small quarters such as a small flower pot or may be unsightly in a small flower potO
When used for monitoring the available moisture content of soil around potted plants, the monitoring device is located on the surface of the soil in close proximlty to the potted plant as shown in FIGURE 40 When the plant is watered and the soil has sufficient moisture, the sensing element which is visible through the cover has a detectable characteristic property such as a characterlstic colorO As the moisture is taken from the soil by the plant and by evaporation and reaches a parametric concentration, eOgO the moisture concentration determined to be ~ust above that at which the plant will wilt, the relative humidlty within the device will fall to a level below the selected standard, e.gO 75% R~Ho ~ and the sensing element changes a detectable property, eOgO colorO This change indicates the need for additional water in the soilO The addition of water to the soil so that the moisture concentratlon in the soil rises above the parametric amount causes the initlal detectable property, eOgO the initial color, of the sensing element to return after a short equilibration ~5 periodO
Because the monitoring device protects the sensing element from bulk liquid, plants can be watered with the monitoring device in position next to the plant, although it is preferred to ha~e the monltoring devLce remo~ed dur.ing wateringO In tests using the monitoring ~6614~
device of the present lnvention to regulate the waterlng schedule of a wide variety of plants in both heavy and light soils, the plants thrived and did not suffer from overwatering, as did plants which had their watering schedules fixed by prior art, wick-type devicesO
The monitoring devices are useful to detect and indicate the presence of moisture in other environ-mentsO Particularly the monitoring devices have proven useful in detecting the presence of certain levels of liquids in body dresslngs such as dlapers and surglcal dressings, thereby eliminating the need to touch or remove the articles for examinatlonO This is particularly useful where the body dressings have a liquid-impermeable outer covering, eOgO polyethylene film, and the presence of moisture is not detectable by touching the outer surface of the dressingO A monitoring dev~ce, simllar to that shown in FIGURES 1-3 or having other shapes, can be attached to the dressing with the base resting on the dressing and the cover disposed outwardly of the dressing and the body to whlch it is applied~ When the body dressing becomes moist, the monitoring device can indicate, eagO change color, when the moist condition existsO
Where the body dressing has a vapor permeable covering, eOgO polyethylene, the monitorlng device can be incorporated into the dresslng using a portion of the outer covering of the dressing as the cover of the monitoring device.
The monitoring devlces can also be uæed to detect and lndicate vapQrs from decomposlng matter in 1o66l~l solld and llquid phasesO For example, a monitorlng device having a sensing element which is responsive to ammonia can be placed on proteinaceous matter such as fish, and the concentration of ammonia produced by decompositlon detected and indlcatedO Alternatively, the indicators can be floated on a pool of liquid such as sewage or other effluent streams and detect and indicate vapors dissolved therein or produced by decompositlon within the liquidO
The following examples will serve to illus-trate the practice of the method and the use of the vapor monitoring devices of the present inventionO
Example 1 To demonstrate the utility of the monitoring devlce in indicating the need for watering a potted plant at proper intervals, a monitoring device was prepared as in FIGURES 2 and 3 wherein protective layer 28 was a 205 cm diameter disc of a microporous polyethylene film (3M brand "TRANSPORE" tape, 3M Company)g pad 22 was an oil sorbent pad of blown polypropylene microfibers, sensing element 24 comprised a mixture of equal parts hydrated cobalt chloride and cobalt thiocyanate absorbed in a disc of NoO 1 Whatman filter paperO CoYer 26 was a piece of cellulose acetate film (3M brand "Magic Mendlng"
tape, NoO 810, 3M Company) adhesively bonded to protectlve layer 280 Several zebra plants (Aphelandra) were potted in 15 cm diameter foamed plastic azalea pots 13 sm deepO
A light potting soil of equal parts peat and vermiculite (Terra-Lite "Redi-Earth'l~ WO Ro Grace CoO~ was used for ~06614~
some plants, while a heavler clay loam was used fsr othersO Zebra plants were used because they are partic-ularly sensltive to moisture and prone to wilting lf given insufflcient waterO
The plants were kept indoors at room temperature (22 C) at a fairly constant relative humidity of about 20% RoH~ with fluorescent lightlngO
The plants were properly watered so the surface of the soil was moist and the monitoring devices were placed next to some of the plants on the leveled soil surfaceO The plants were watered during the remainder of the testO
The color of the monitoring devices changed from the original pink color to a visibly detectable lavender color after about 11 days for the plants in the light 50il and after 7 days for the plants in the heavy soil (corres-ponding to a humidity level within the monitoring device of about 70-75% RoHo ) ~ The weight % moisture in the top 205 cm of soil and the bottom 10 cm of soil in each pot was then separately determined~
Other plants were monitored by employing the common method of touching the soil surfaceO When the surface was dry to the touch (6 days heavy soil, 10 days light soil) the weight % moisture in the top 205 cm and bottom 10 cm of soil was determined~
Plants containing wick-type indicators were also tested and the soil moisture measured as above when the need for water was indic~ted (1 day heavy soil, 7 days light soil)O
_ 26 -~066141 In addition, some soil samples were allowed to dry to the polnt where the plants wilted (12 days heavy soil, 17 days light soil) and the moisture in the top 205 cm of soil then determinedO
The results of the molsture tests were as follows:
W~
Monitoring _ _ D~ S9~l_ ____ Devloe Uaed Top Bottom Top Bottom - 205 cm 10 cm Time ~ 10 cm Time lo Wick-Type21% 22%1 day 74% 75% 7 days Device 2. Touch 12% 16%6 days 62% 67% 10 days Monitor-9% 14%7 days 57% 65% 11 days ing Device of the Present Invention 4. Wilting6% -- 12 days 46% -- 17 days The above data indicate that the monitoring device of the present invention can be used to accura~ely indicate a parametric concentration of moisture in soll, io eO in this case the point at which the plant needs water before wilting, and can closelg approximate the point at whlch an experienced horticulturalist would indlcate the need for waterO
The wick-type devices indicated the plant required water before the moisture level was sufficiently : low to require water, Example 2 A False Aralla (Dizygotheca elegantissima) plant about 1 meter high was potted in a pot 25 cm in diameter 106614~
and 20 cm deep contalnlng a sandy loam soil and exposed to the conditlon of llght, temperature, and relative humldity as in Example lo Touch tests indicate this plant should be watered about every 9 days under these condl-tlons in order to thrlve A monltoring devlce was prepared as in Example 1 and placed on-level soil in the pot near the plant~ The initlal pink color changed to lavender in a perlod of between 9 and 10 daysO Upon watering the soil to satura-tlon the color changed back to plnk after about 15 - 30 mlnutes and remalned plnk for another perlod of 9 - 10 days, and then agaln changed to lavender, and the waterlng repeated.
After 3 months of this repeated watering cycle, the plant was thriving.
E~
Monitoring devices were prepared as in Example 1 except that the sensing elements comprised 3 - 5O5 pH
"pHydrion" papers (Micro Essential Laboratory)O
Soils having various ammonla content were placed in polyethylene bags, the monitoring devices placed on the leveled surface of the soil within the bags, and the bags sealedO After 90 minutes the indicators were observed on each soil sampleO The ammonia content of the soils were confirmed by analysisO The results were as follows:
1~6619L1 Soil Soll Ammonla Sample NoO Indicator Color Con~ent, ppm 1 Dark green/blue 7,8 2 Green 4O8
~06614~
parts by weight cobalt chloride and cobalt thiocyanate and drylng the saturated filter paperO The response range of the senslng element can be varled to some degree by controlling the concentration of salt in the sensing element, A use~ul indicating component which exhiblts a detectable color change over a relatlvely narrow relative humidity range comprises a mixture of cobalt chloride with a copolymer of polyvinyl pyrrolldone/vinyl acetate ("I 535,"
General Analine and Fllm). Copolymer to cobalt chloride ratios of about 6:1 to about 1:1 are preferredO m e mixture is dissolved in water and absorbed in or applied to an absorbent pad or other carrier, and when dried provldes a sensing element which exhiblts a readily observable color change in the 70% to 80~ relative humidlty rangeO
In one embodiment o~ the device 10 shown in FIGURE 1 the sensing element 16 is prepared by applying an lndicating component directly to the underside of cover 140 For example, the cobalt chloride/copolymer solution described-above can be coated on the underside of cover 1 in the form of a dot or other shape havlng a diameter of about 0.5 to lo 5 centimetersO After the solution dries~
the coating which forms sensing element 16 ls ready for useO
In yet another embodiment-sensing element 16 can include as the indicating component a deliquescent compound which exhibits a reversible change in optical properties at a glven level of relative humidity~ Fo~
example, the sensing element 16 can comprise a coherent, continuous layer of deliquescent compound which is 3paque at humidlty levels below the point at which the compound 1066~4~
deliquesces and which becomes optically transparent on dellquescing~ together with a layer underlying the deliquescent compound which i5 at least partlally colored ln contrast to the opaque compound so as to be observable, and preferably conspicuous, when the compound deliquesces and becomes transparentO
When the surrounding humldity is below a glven level, the deliquescent compound remains opaque and the underlying layer is not visibleO When the humidity rises above the point at whlch the compound dellquesces, the compound becomes transparent and the underlayer is visible preferably conspicuous, to the observer, thereby indicat-ing exposure to a selected level of relative humidity within the envelope~ When the humidity level within the envelope is again lowered below the deliquescent point of the compound, the compound effloresces and again becomes opaque and the underlayer is no longer visible to the observerO In one embodiment the underlayer can be a contrasting color or can have intelligence printed on the surface thereof so that when the deliquescent compound becomes transparent a conspicuous color or an appropriate message such as "wet" or the like is observedO
A preferred means of providing a continuous layer o~ deliquescent compound is to absorb a solution of the deliquescent compound in a thin layer of tissue paper and dry the paperO Sodium bromide is a preferred deliquescent salt, although other deliquescent compounds known in the art are suitableO The sensing element 15 ~hich includes sodium bromide as the deliquescent compound proYldes a change in optical properties when the relati~e ~066~
hum~dity within the envelope is about 57%O
When the device 10 is used to monitor the concentration of vapor components other than moisture, eOgO ammonia, the sensing element 16 comprises indicating components capable of responding to changes in the concentration of these specific volatile componentsO
For example, a device for monitoring the ammonia concen-tration of soil can be provided by employing alizarin or pH papers sensitive to the 3 - 5O5 pH range such as are available commercially under the trade name "pHydrion"
papers from Micro Essential LaboratoryO Indicators employing the "pHydrion" papers visibly respond by changing color from yellow/orange to blue/green, which color change is correlative to the ammonia concentration (in parts per million) in the soilO
In addition, by selecting a sensing which responds to other specific vapors, the monitoring device may be used to detect and monitor the concentration and change in concentratlon of various vapors such as the oxides o~ nitrogen, sulfur and carbon, and the halogens~
FIGURE 2 is an alternate embodiment of a vapor monitoring device according to the present inventionO
Monitoring device 20 is similar to that shown in FIGURE 1 comprising vapor permeable base 22, sensing element 2~, 25 and vapor permeable cover 260 Device 20 also contains a protective layer 28 underlylng base 22 and containlng pores 30O Layer 28 and cover 26 are shown extending beyond base 22 and are ~oined at their periphery to enclo~e base ~2 and sensing element 24 in a closely ccn-forming envelopeO Protective layer 28 is shown as a ~066~4~
porous layer which is permeable to vapor and whlch may be permeable to llquid water since base 22 and cover 26 are impermeable to liquids and protect sensing element 240 Protective layer 28 serves to protect base 22 during handling and helps prevent base 22~ particularly when base 22 is a porous mat of blown microfibers, from becoming clogged with dirt and the li~eO Representative of materials which can be used for protective layer 28 are porous polyethylene films such as 3M Brand "TRANSPORE"
tape and a microporous tape having a non-woven backing such as 3M Brand t'MICROPORE" tape, both available commercially from the 3M Company.
FIGURE 3 is a cross section along line 3-3 of the monitorlng device shown in FIGURE 20 As can be seen, cover 26 together with base 22 and protective layer 28 envelop and closely conform to sensing element 24, minimizing the free space within the envelope surrounding sensing element 240 In order to operate successfully as a monitoring device 10, 20, the sensing element 16, 24 shown in FIGURES
1-3 must be responsively coupled to the vapor source phase at the interface so that the monitoring device can accurately sample and compare a representative surface vapor concentrationO This is achieved in the present invention by enclosing the sensing element 16, 24 in a sampling envelope defined by base 12 and cover 14 as in FIGURE 1, or by base 22 and cover 26 as in FIGURE 20 The sampling envelope shown in FIGURE 3 is adapted to rest on9 and intimately ~ontact 3 the surface of the vapor source phase, such as the soil surrounding a potted plant, collect 106614~.
a representative sample of Yapors released from the surface of the phase, and present the sample to sensing element 16, 240 Due to the difference in vapor transmisslon rates between the cover 14, 26 and the base 12, 22 a sudden change in vapor input through base 12, 22 will not cause the interior of the envelope to become immediately overwhelmed with or starved of vapor; that is, the vapor concentration within the envelope may be slightly different than the actual vapor concentration at the base-vapor source phase interface until steady state is achieved This lagging response tends to reduce any effect of transient peaks and valleys of vapor concentra-tion released from the vapor source phase~
Further, the relatively slow vapor transmission rate of the cover 14 prevents the vapors entering the envelope through the base 12, 22 from being overwhelmed by vapors entering through the cover 14, 26 from the surrounding atmosphereO Temporary changes ln relative humidity in the surrounding envlronment will have little or no effect on a sensing element sensitive to changes in relative humidityO However, constant operation at humidity levels above the selected standard relative humidity, eOgO above 75% R~Ha~ which has been found to be a useful R~Ho Standard, may ultimately overcome the monitoring device and impair the ability of the device to accurately indicate the selected parametric moisture concentrationO
Although cover 14, 26 is relatively less 30 permeable than base 12, 22 3 the cover must have the ~066~41 aforementloned minimum vapor transmission rateO If cover 14, 26 does not have the necessary vapor transmiss~on rate3 moisture or other vapors can accumulate within the envelope and allow undesirable condensation in the envelopea causlng the sensing element 16, 24 to be contacted by bulk liquid which can leach chemicals from the sensing element or cause a false reading by a humidity sensitive sensing elementO
The monitoring device of the pre~ent invention should be large enough to sample vapor released from a representative area of the vapor source phaseO Discs about lo 25 to 5 cm in diameter have been found sufficient to provide accurate resultsO Shapes other than discs can be used with equivalent resultsO
A disc of about 205 cm in diameter is an effec-tive compromise size to achieve convenlent handling and accurate samplingO This allows the device to accumulate vapors released from about 5 cm of the surface of the vapor source phaseO
Because the vapors reside in the monitoring device for a short period of tlme before passing through the cover, some mixing of the vapors takes place and the monitoring device, in effect, averages the concentration of vapor with time and over the area covered by the device and can provide a more accurate reading than a wick or other point sampling device can provideO
Generally monitoring devices having a base area of less than about 1025 cm2 are not preferred since the device becomes difficult to observe and handle and does not s~mple a l.arge enough area of the vapor source phase 1~6~4~
surfaceO Monltoring de~ices which have a base area of greater than about 20 cm2 can function effectively but may be too large for some applications, for example, they may be difficult to fit into small quarters such as a small flower pot or may be unsightly in a small flower potO
When used for monitoring the available moisture content of soil around potted plants, the monitoring device is located on the surface of the soil in close proximlty to the potted plant as shown in FIGURE 40 When the plant is watered and the soil has sufficient moisture, the sensing element which is visible through the cover has a detectable characteristic property such as a characterlstic colorO As the moisture is taken from the soil by the plant and by evaporation and reaches a parametric concentration, eOgO the moisture concentration determined to be ~ust above that at which the plant will wilt, the relative humidlty within the device will fall to a level below the selected standard, e.gO 75% R~Ho ~ and the sensing element changes a detectable property, eOgO colorO This change indicates the need for additional water in the soilO The addition of water to the soil so that the moisture concentratlon in the soil rises above the parametric amount causes the initlal detectable property, eOgO the initial color, of the sensing element to return after a short equilibration ~5 periodO
Because the monitoring device protects the sensing element from bulk liquid, plants can be watered with the monitoring device in position next to the plant, although it is preferred to ha~e the monltoring devLce remo~ed dur.ing wateringO In tests using the monitoring ~6614~
device of the present lnvention to regulate the waterlng schedule of a wide variety of plants in both heavy and light soils, the plants thrived and did not suffer from overwatering, as did plants which had their watering schedules fixed by prior art, wick-type devicesO
The monitoring devices are useful to detect and indicate the presence of moisture in other environ-mentsO Particularly the monitoring devices have proven useful in detecting the presence of certain levels of liquids in body dresslngs such as dlapers and surglcal dressings, thereby eliminating the need to touch or remove the articles for examinatlonO This is particularly useful where the body dressings have a liquid-impermeable outer covering, eOgO polyethylene film, and the presence of moisture is not detectable by touching the outer surface of the dressingO A monitoring dev~ce, simllar to that shown in FIGURES 1-3 or having other shapes, can be attached to the dressing with the base resting on the dressing and the cover disposed outwardly of the dressing and the body to whlch it is applied~ When the body dressing becomes moist, the monitoring device can indicate, eagO change color, when the moist condition existsO
Where the body dressing has a vapor permeable covering, eOgO polyethylene, the monitorlng device can be incorporated into the dresslng using a portion of the outer covering of the dressing as the cover of the monitoring device.
The monitoring devlces can also be uæed to detect and lndicate vapQrs from decomposlng matter in 1o66l~l solld and llquid phasesO For example, a monitorlng device having a sensing element which is responsive to ammonia can be placed on proteinaceous matter such as fish, and the concentration of ammonia produced by decompositlon detected and indlcatedO Alternatively, the indicators can be floated on a pool of liquid such as sewage or other effluent streams and detect and indicate vapors dissolved therein or produced by decompositlon within the liquidO
The following examples will serve to illus-trate the practice of the method and the use of the vapor monitoring devices of the present inventionO
Example 1 To demonstrate the utility of the monitoring devlce in indicating the need for watering a potted plant at proper intervals, a monitoring device was prepared as in FIGURES 2 and 3 wherein protective layer 28 was a 205 cm diameter disc of a microporous polyethylene film (3M brand "TRANSPORE" tape, 3M Company)g pad 22 was an oil sorbent pad of blown polypropylene microfibers, sensing element 24 comprised a mixture of equal parts hydrated cobalt chloride and cobalt thiocyanate absorbed in a disc of NoO 1 Whatman filter paperO CoYer 26 was a piece of cellulose acetate film (3M brand "Magic Mendlng"
tape, NoO 810, 3M Company) adhesively bonded to protectlve layer 280 Several zebra plants (Aphelandra) were potted in 15 cm diameter foamed plastic azalea pots 13 sm deepO
A light potting soil of equal parts peat and vermiculite (Terra-Lite "Redi-Earth'l~ WO Ro Grace CoO~ was used for ~06614~
some plants, while a heavler clay loam was used fsr othersO Zebra plants were used because they are partic-ularly sensltive to moisture and prone to wilting lf given insufflcient waterO
The plants were kept indoors at room temperature (22 C) at a fairly constant relative humidity of about 20% RoH~ with fluorescent lightlngO
The plants were properly watered so the surface of the soil was moist and the monitoring devices were placed next to some of the plants on the leveled soil surfaceO The plants were watered during the remainder of the testO
The color of the monitoring devices changed from the original pink color to a visibly detectable lavender color after about 11 days for the plants in the light 50il and after 7 days for the plants in the heavy soil (corres-ponding to a humidity level within the monitoring device of about 70-75% RoHo ) ~ The weight % moisture in the top 205 cm of soil and the bottom 10 cm of soil in each pot was then separately determined~
Other plants were monitored by employing the common method of touching the soil surfaceO When the surface was dry to the touch (6 days heavy soil, 10 days light soil) the weight % moisture in the top 205 cm and bottom 10 cm of soil was determined~
Plants containing wick-type indicators were also tested and the soil moisture measured as above when the need for water was indic~ted (1 day heavy soil, 7 days light soil)O
_ 26 -~066141 In addition, some soil samples were allowed to dry to the polnt where the plants wilted (12 days heavy soil, 17 days light soil) and the moisture in the top 205 cm of soil then determinedO
The results of the molsture tests were as follows:
W~
Monitoring _ _ D~ S9~l_ ____ Devloe Uaed Top Bottom Top Bottom - 205 cm 10 cm Time ~ 10 cm Time lo Wick-Type21% 22%1 day 74% 75% 7 days Device 2. Touch 12% 16%6 days 62% 67% 10 days Monitor-9% 14%7 days 57% 65% 11 days ing Device of the Present Invention 4. Wilting6% -- 12 days 46% -- 17 days The above data indicate that the monitoring device of the present invention can be used to accura~ely indicate a parametric concentration of moisture in soll, io eO in this case the point at which the plant needs water before wilting, and can closelg approximate the point at whlch an experienced horticulturalist would indlcate the need for waterO
The wick-type devices indicated the plant required water before the moisture level was sufficiently : low to require water, Example 2 A False Aralla (Dizygotheca elegantissima) plant about 1 meter high was potted in a pot 25 cm in diameter 106614~
and 20 cm deep contalnlng a sandy loam soil and exposed to the conditlon of llght, temperature, and relative humldity as in Example lo Touch tests indicate this plant should be watered about every 9 days under these condl-tlons in order to thrlve A monltoring devlce was prepared as in Example 1 and placed on-level soil in the pot near the plant~ The initlal pink color changed to lavender in a perlod of between 9 and 10 daysO Upon watering the soil to satura-tlon the color changed back to plnk after about 15 - 30 mlnutes and remalned plnk for another perlod of 9 - 10 days, and then agaln changed to lavender, and the waterlng repeated.
After 3 months of this repeated watering cycle, the plant was thriving.
E~
Monitoring devices were prepared as in Example 1 except that the sensing elements comprised 3 - 5O5 pH
"pHydrion" papers (Micro Essential Laboratory)O
Soils having various ammonla content were placed in polyethylene bags, the monitoring devices placed on the leveled surface of the soil within the bags, and the bags sealedO After 90 minutes the indicators were observed on each soil sampleO The ammonia content of the soils were confirmed by analysisO The results were as follows:
1~6619L1 Soil Soll Ammonla Sample NoO Indicator Color Con~ent, ppm 1 Dark green/blue 7,8 2 Green 4O8
3 Faint green/yellow lo 8
4 Yellow/orange Not detected The monitoring devices were successful ln differentiating between soil samples having differing ammonia contentO
E ~
A disposable diaper having a polyethylene llquid impermeable covering was modified by cutting a hole in the outer covering and attaching a monitoring device similar to that described in Example 1 over the hole wlth the base of the device adjacent the diaper fabricO The diaper was then applied to a baby in the conventional mannerO When the diaper became wet with urine, the sensing element changed from blue to pink indicating the need for changlng the diaper, ExamPle 5 A monitoring devlce like that described in Example 3 was used to indicate the state of decomposition ' of crabmeatO Three samples of crabmeat were obtainedO
The first sample was fresh; the second evidenced some decomposition but was still edible, while the third was decomposed to a polnt where the meat was not edible, Twenty to fifty gram samples were placed in glass beakers~
the base of the monitoring devices placed on the crabmeat samples, and the beakers coveredO
~66~4~
After one hour the monitoring device on the flrst sample showed no color change, while the devlce on the second sample had turned slightly green at the edges of the sensing element, After 10 minutes the senslng element of the device on the third sample had turned completely green. Thus, the monitoring device can be used to accurately detect and indicate unwanted or dangerous decomposition in food products by detectlng the vapors issuing therefrom.
E ~
A disposable diaper having a polyethylene llquid impermeable covering was modified by cutting a hole in the outer covering and attaching a monitoring device similar to that described in Example 1 over the hole wlth the base of the device adjacent the diaper fabricO The diaper was then applied to a baby in the conventional mannerO When the diaper became wet with urine, the sensing element changed from blue to pink indicating the need for changlng the diaper, ExamPle 5 A monitoring devlce like that described in Example 3 was used to indicate the state of decomposition ' of crabmeatO Three samples of crabmeat were obtainedO
The first sample was fresh; the second evidenced some decomposition but was still edible, while the third was decomposed to a polnt where the meat was not edible, Twenty to fifty gram samples were placed in glass beakers~
the base of the monitoring devices placed on the crabmeat samples, and the beakers coveredO
~66~4~
After one hour the monitoring device on the flrst sample showed no color change, while the devlce on the second sample had turned slightly green at the edges of the sensing element, After 10 minutes the senslng element of the device on the third sample had turned completely green. Thus, the monitoring device can be used to accurately detect and indicate unwanted or dangerous decomposition in food products by detectlng the vapors issuing therefrom.
Claims (17)
1. A device for monitoring and indicating the con-centration of a vapor at a phase interface comprising a. a sensing means for comparing the concentration of a selected vapor component in a sample with a standard which is representative of a selected parametric concentra-tion of said vapor in said sample, said sensing means in-cluding means for indicating the concentration of said vapor in said sample relative to said standard, and b. a differentially vapor permeable, liquid impermeable envelope enclosing said sensing means to respon-sively couple said sensing means to a vapor source phase at said phase interface, said envelope comprising a base adapted to rest on said vapor source phase and a cover for said base, said base and said cover vapor permeable defining a sealed, closely conforming envelope containing said sensing means, said cover having a vapor transmission rate equivalent to a water vapor transmission rate of between 20 and 60 grams/
1000 cm2/24 hours, said base having a vapor transmission rate at least 50% greater than the vapor transmission rate of said cover, said cover adapted for viewing said indicating means.
1000 cm2/24 hours, said base having a vapor transmission rate at least 50% greater than the vapor transmission rate of said cover, said cover adapted for viewing said indicating means.
2. A device according to claim 1 wherein said sensing means comprises an indicating component capable of visibly responding to changes in the concentration of a selected vapor component.
3. A device according to claim 2 wherein said selected vapor component is ammonia.
4. A device according to claim 2 wherein said selected vapor component is water vapor.
5. A device according to claim 4 wherein said indicating component comprises cobalt chloride.
6. A device according to claim 5 wherein said sensing means is adapted to change color at a relative humidity between 50 and 75%.
7. A device according to claim 4 wherein said indicating component is a deliquescent salt capable of reversibly changing from an opaque to a transparent state in response to a change in relative humidity.
8. A soil monitoring device according to claim 4 wherein said base is a vapor permeable hydrophobic pad.
9. A soil monitoring device according to claim 8 wherein said device also includes a porous protective sheet underlying said base.
10. A soil monitoring device according to claim 9 wherein said indicating component comprises a mixture of cobalt chloride and polyvinyl pyrrolidone/vinyl acetate copolymer.
11. A soil monitoring device according to claim 9 wherein said sensing element is a film of indicating compon-ent comprising a mixture of cobalt chloride and polyvinyl pyrrolidone/vinyl acetate copolymer, and film adhered directly to said cover sheet.
12. A device according to claim 4 wherein said cover of said envelope has a water vapor transmission rate in the range of about 20 g/1000 cm2/24 hours to about 40 g/
1000 cm2/24 hours.
1000 cm2/24 hours.
13. A body dressing comprising an aqueous liquid absorbent layer and a liquid impervious layer, said body dressing including a monitoring device according to claim 1 located adjacent said absorbent layer, at least a portion of said liquid impervious layer being transparent so that said monitoring device can be viewed therethrough.
14. A method of continuously monitoring the con-centration of vapor at a phase interface which comprises a. continuously collecting a representative vapor sample in a differentially vapor permeable, liquid imperme-able, envelope directly from a vapor source phase at the phase interface, said envelope comprising a base and a cover vapor permeable, said cover having a vapor transmission rate equivalent to a water vapor transmission rate of between 20 and 60 grams/1000 cm2/24 hours;
b. comparing the concentration of a selected vapor component in said sample with a standard contained in said envelope which is representative of a selected parametric concentration of said vapor in said sample; and c. visibly indicating the concentration of said vapor in said sample relative to said standard.
b. comparing the concentration of a selected vapor component in said sample with a standard contained in said envelope which is representative of a selected parametric concentration of said vapor in said sample; and c. visibly indicating the concentration of said vapor in said sample relative to said standard.
15. A method according to claim 14 wherein said vapor component is water vapor.
16. A method according to claim 15 wherein said vapor source phase is soil containing a potted plank and said parametric vapor concentration is indicative of the minimum life-sustaining soil moisture concentration necessary for said potted plant.
17. A method according to claim 15 wherein said envelope comprises a cover having a water vapor transmission rate of from about 20 g/1000 cm2/24 hours to about 40 g/1000 cm2/24 hours and a base having a water vapor transmission rate at least 50% greater than said cover.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US59132975A | 1975-06-30 | 1975-06-30 | |
| US05/658,114 US4063452A (en) | 1975-06-30 | 1976-02-13 | Method and device for monitoring vapor concentration at a phase interface |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1066141A true CA1066141A (en) | 1979-11-13 |
Family
ID=27081118
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA253,864A Expired CA1066141A (en) | 1975-06-30 | 1976-06-01 | Method and device for monitoring vapor concentration at a phase interface |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS527792A (en) |
| AU (1) | AU506957B2 (en) |
| CA (1) | CA1066141A (en) |
| DE (1) | DE2629690A1 (en) |
| FR (1) | FR2316593A1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE102018002315A1 (en) * | 2018-03-19 | 2019-09-19 | Hydac Technology Gmbh | Pressure accumulator with a monitoring device |
| JP6897643B2 (en) * | 2018-09-05 | 2021-07-07 | 横河電機株式会社 | Sensor element and packaging |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3019638A (en) * | 1959-11-02 | 1962-02-06 | William F Klein | Moisture indicating device |
| US3198163A (en) * | 1963-02-13 | 1965-08-03 | Cadillac Products | Indicator device |
| US3680364A (en) * | 1970-06-22 | 1972-08-01 | Roger E Carrier | Monitoring humidity |
| US3702755A (en) * | 1971-07-21 | 1972-11-14 | Walter E Palmer | Moisture indicator for plants |
| US3898172A (en) * | 1973-05-03 | 1975-08-05 | Us Energy | Irreversible humidity indicator |
| US3951098A (en) * | 1975-02-12 | 1976-04-20 | Enviro-Gro, Inc. | House plant water content indicator |
-
1976
- 1976-06-01 CA CA253,864A patent/CA1066141A/en not_active Expired
- 1976-06-29 FR FR7619736A patent/FR2316593A1/en active Granted
- 1976-06-29 AU AU15399/76A patent/AU506957B2/en not_active Expired
- 1976-06-29 DE DE19762629690 patent/DE2629690A1/en not_active Withdrawn
- 1976-06-29 JP JP7698376A patent/JPS527792A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| FR2316593B1 (en) | 1982-07-02 |
| DE2629690A1 (en) | 1977-03-17 |
| FR2316593A1 (en) | 1977-01-28 |
| AU506957B2 (en) | 1980-01-31 |
| JPS527792A (en) | 1977-01-21 |
| AU1539976A (en) | 1978-01-05 |
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