GB2112947A - Measuring water availability or humidity - Google Patents
Measuring water availability or humidity Download PDFInfo
- Publication number
- GB2112947A GB2112947A GB08200307A GB8200307A GB2112947A GB 2112947 A GB2112947 A GB 2112947A GB 08200307 A GB08200307 A GB 08200307A GB 8200307 A GB8200307 A GB 8200307A GB 2112947 A GB2112947 A GB 2112947A
- Authority
- GB
- United Kingdom
- Prior art keywords
- piece
- humidity
- relative humidity
- hygroscopic material
- location
- 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.)
- Granted
Links
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 title claims description 30
- 239000000463 material Substances 0.000 claims abstract description 72
- 238000000034 method Methods 0.000 claims abstract description 25
- 239000011324 bead Substances 0.000 claims abstract description 20
- 238000005259 measurement Methods 0.000 claims description 14
- 239000000853 adhesive Substances 0.000 claims description 8
- 230000001070 adhesive effect Effects 0.000 claims description 8
- 238000005303 weighing Methods 0.000 claims description 5
- 239000002131 composite material Substances 0.000 claims description 4
- 230000000295 complement effect Effects 0.000 claims description 2
- 239000011888 foil Substances 0.000 abstract description 10
- 239000002023 wood Substances 0.000 abstract description 7
- 230000000694 effects Effects 0.000 description 16
- 230000002745 absorbent Effects 0.000 description 4
- 239000002250 absorbent Substances 0.000 description 4
- 239000004033 plastic Substances 0.000 description 4
- 229920003023 plastic Polymers 0.000 description 4
- 239000011241 protective layer Substances 0.000 description 4
- 239000007787 solid Substances 0.000 description 3
- 239000002184 metal Substances 0.000 description 2
- 239000002985 plastic film Substances 0.000 description 2
- 229920006255 plastic film Polymers 0.000 description 2
- 239000004821 Contact adhesive Substances 0.000 description 1
- 239000004677 Nylon Substances 0.000 description 1
- 239000004698 Polyethylene Substances 0.000 description 1
- 229920001131 Pulp (paper) Polymers 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 230000002925 chemical effect Effects 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 238000012937 correction Methods 0.000 description 1
- 239000002178 crystalline material Substances 0.000 description 1
- 238000003795 desorption Methods 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 238000011067 equilibration Methods 0.000 description 1
- 238000009413 insulation Methods 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 239000010410 layer Substances 0.000 description 1
- 239000011344 liquid material Substances 0.000 description 1
- 239000013521 mastic Substances 0.000 description 1
- 229920001778 nylon Polymers 0.000 description 1
- 238000012856 packing Methods 0.000 description 1
- 239000011236 particulate material Substances 0.000 description 1
- -1 polyethylene Polymers 0.000 description 1
- 229920000573 polyethylene Polymers 0.000 description 1
- 230000000750 progressive effect Effects 0.000 description 1
- 230000000284 resting effect Effects 0.000 description 1
- 239000000565 sealant Substances 0.000 description 1
- 229920002379 silicone rubber Polymers 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 238000009736 wetting Methods 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N25/00—Investigating or analyzing materials by the use of thermal means
- G01N25/56—Investigating or analyzing materials by the use of thermal means by investigating moisture content
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N5/00—Analysing materials by weighing, e.g. weighing small particles separated from a gas or liquid
- G01N5/02—Analysing materials by weighing, e.g. weighing small particles separated from a gas or liquid by absorbing or adsorbing components of a material and determining change of weight of the adsorbent, e.g. determining moisture content
- G01N5/025—Analysing materials by weighing, e.g. weighing small particles separated from a gas or liquid by absorbing or adsorbing components of a material and determining change of weight of the adsorbent, e.g. determining moisture content for determining moisture content
Landscapes
- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Investigating Or Analyzing Non-Biological Materials By The Use Of Chemical Means (AREA)
Abstract
Hygroscopic material is placed in a location where the humidity is to be determined, and after attaining equilibrium is removed and wrapped in impermeable foil so that it can be kept for a long period at the humidity it has attained so that the humidity determination can be made at a time and place which is convenient. A device comprising a rod of impermeable material, having threaded thereon alternate cylindrical beads of wood and impermeable material, is inserted within a freshly drilled bore in the wail or the like in which the device fits closely. The device is kept sealed into the wall or like for a time to allow the wooden beads to reach humidity equilibrium with their surroundings, after which the device is removed and dismantled and the humidities at the levels of the respective beads subsequently determined. In a variant method, for determining humidity at a surface, a strip of veneer is applied to the surface and covered by a sheet of impermeable foil until it has reached humidity equilibrium with its surroundings, after which it is removed and its humidity subsequently determined.
Description
SPECIFICATION
Method of, and apparatus for, measuring water availability or humidity at a predetermined location
This invention relates to a method of, and apparatus for, measuring water availability or humidity at a predetermined location.
It is frequently desirable to obtain a measure of water availability (water activity) or humidity or dampness at surfaces and at various depths within solid water-permeable materials. The activity of water at surfaces can be measured by enclosing a humidity measuring device in a chamber, one wall of which is the surface being investigated and the remaining walls of which are formed by a member of impermeable, non-absorbent material. The small volume of air enclosed in the chamber will then gradually assume a relative humidity which is a direct measure of the activity of water at the surface, provided that the temperature of the air is equal to that of the surface.
To obtain a comparable measure of water activity below the surface, or in some other inaccessible situation, it is neccessary either to have a sensor so small that it can be inserted into a small hole drilled to the point at which the water activity is to be measured, or to withdraw air from such a hole sufficiently slowly to ensure that it comes into equilibrium with the walls of the hole at the point to be measured, and then to pass this air over a humidity sensor. In this case it will be necessary to know the temperature at the point being measured, and that of the sensor, and to make any necessary correction.
In many circumstances, neither of these methods is practicable or convenient.
It is an object of the present invention to provide a method of measuring water availability or humidity at a predetermined location which is practicable and convenient and is suitable for use when neither the water activity nor the temperature of the surface or body of material under investigation is changing rapidly.
According to one aspect of the invention, there is provided a method of measuring water availability or relative humidity at a predetermined location, comprising placing a piece of hygroscopic material in said location, allowing said piece of material to remain at said location until it reaches equilibrium, as regards humidity, with its surroundings at said location, removing said piece of material from said location, and maintaining the relative humidity of said piece substantially constant and subsequently measuring the relative humidity of said piece of hygroscopic material as a measure of the relative humidity at said predetermined location.
One form of the method, which may be utilised when the water availability at a predetermined depth within a material is to be tested, includes the steps of boring a hole into the material to be tested, inserting into said hole a said piece of hygroscopic material mounted on or in a carrying member of impermeable material fitting closely within said hole and affording, at least at axially opposite ends of said piece of hygroscopic material, a respective impermeable oart fittina closely with the wall of said hole, and leaving said carrying member, with said piece of hygroscopic material thereon, in position in said hole until said piece of hygroscopic material has reached humidity equilibrium with the surrounding portion of the material in which said hole is formed before withdrawing the carrying member, with said piece of hygroscopic material, for subsequent measurement of the relative humidity of said piece.
The invention also comprises, within its scope, apparatus for use in performing the above form of the method, the apparatus including a carrying member of impermeable material adapted to fit closely within a cylindrical bore of predetermined diameter, and a body of hygroscopic material adapted to fit in a complementary space afforded by said carrying member and exposed on the radial periphery of the carrying member at a location disposed axially between respective portions adapted to fit within said bore.
Another form of the method, of use for measuring the water availability at a surface, comprises applying to said surface a said piece of hygroscopic material in the form of a thin flexible sheet, covering the surface of said sheet remote from the surface to be tested with an impermeable sheet, and allowing said flexible sheet to come into humidity equilibrium with said surface before removing said impermeable sheet and said piece of hygroscopic material for subsequent measurement of the relative humidity of said hygroscopic material.
The invention also comprises, within its scope, for carrying out the last noted form of the method, apparatus including a piece of hygroscopic material in the form of a thin flexible sheet adhesively secured to a backing sheet of flexible impermeable material which is larger than said piece of hygroscopic material so as to project beyond the edge of the latter to afford an exposed margin, said margin being coated with an adhesive whereby the assembly can be stuck to a surface to be tested.
Embodiments of the invention are described below in greater detail, by way of example.
In the embodiments to be described, small discrete pieces of solid hygroscopic material are placed at locations at which water activity is to be measured, and allowed to remain there until they are substantially in equilibrium, from the point of view of humidity, with their surroundings at said location. They are then rapidly removed and placed in individual air and water-tight containers.
When convenient, the equilibrium relative humidity of each such discrete piece is then determined. The relative humidity thus measured will, in principle, be equal to that at the point, or on the surface, at which it was equilibrated. Any deviations from such equality will be due to temperature or hysteresis effects which can easily be allowed for.
Two convenient methods for measurement of
the equilibrium relative humidity of such discrete
pieces of solid hygroscopic material are by weighing and by direct determination.
Where measurement of the relative humidity of such pieces of hygroscopic material is to be effected by weighing, before use, each such piece, individually marked, for example by an indentification number, is allowed to come into equilibrium, successively, with air at various different relative humidities within a range of such humidities and is weighed at each equilibration. In -this way there is established, for each individually marked piece, a calibration relationship between weight and relative humidity. Because of hysteresis effects, two weights will normally need to be established for each relative humidity, depending on whether the approach to equilibrium was by adsorption or desorption.
Where measurement of the relative humidity of such pieces of hygroscopic material is to be made by direct determination, a suitably small humidity sensor of a type which makes an extremely small demand on the moisture in the air is enclosed together with the piece of material in a minimaily small volume of air, conveniently by wrapping the two together in plastic film or foil. A suitable instrument for such a measurement is the Protimeter Dew Point Meter manufactured by
Protimeter Limited.
In one embodiment of the invention, of use, for example, for measuring water activity in walls, floors and ceilings at various depths, apparatus is used which comprises a rod or spindle of impermeable material such as metal, on which are threaded cylindrical beads of wood and of impermeable, non-absorbent material such as metal, these beads each having an axial through bore to receive said spindle, the wooden beads and the non-absorbent beads being arranged alternately along said rod.
The rod also carries, at either end, end stops which retain the beads on the rod, at least one of said end stops being detachably secured to the rod, for example being screwed onto the rod, to allow removal of the beads from the rod. The end stop at one end of the rod may terminate in a blunt point, while the other end of the rod is preferably screw-threaded for engagement with a complementarily screw threaded handle. The beads and end stops are all of the same external diameter so that in the assembled conditions, the peripheries of the beads lie on a common cylindrical surface coaxial with the rod.
In use, this device is pushed, pointed end first, into a freshly drilled hole in the body to be investigated, said hole being deep enough to accommodate the entire length of the part of the device between, and including, said two end stops, and being of a diameter to receive the beads and end stops snugly. The handle is then unscrewed and the hole may be plugged with mastic. After an appropriate time, typically between 24 and 200 hours, the handle is reattached, the device is quickly withdrawn from the
hole and is immediately wrapped in plastic film or foil, or inserted into a carrying tube into which it fits closely, until it is convenient to dismantle the device and determine the humidities of the wooden beads by either of the methods referred to above.Because of the intervening non-absorbent beads the wooden beads are isolated from each other and will retain their equilibrium relative humidities unchanged for a considerable time, certainly several days.
In another embodiment of the invention, for measurement of water activity at surfaces, apparatus is used which comprises an elongated rectangular strip of wood veneer of less than 1 mm thickness and having its grain running perpendicular to the long axis of the strip in order to enable the strip to be rolled round a humidity sensor after the strip has been brought into equilibrium, as regards humidity, with the surface being investigated. The strip of veneer is stuck, by adhesive, to a backing sheet of flexible, watervapour-proof material (e.g. polyethylene or metallic foil) somewhat larger than itself, so that all around the strip a margin of the backing sheet is exposed, the exposed margin of the sheet being coated with an adhesive, for example a contact adhesive.The combination of veneer and backing sheet is attached, via the adhesive margin of the backing sheet, to any surface of which it is desired to measure the water activity, so that the veneer is adjacent to the surface and is protected from contact with the atmosphere by the backing sheet.
When it is judged that the veneer is in equilibrium, as regards humidity, with said surface, typically after a period of between 24 and 60 hours, the combination is removed from the surface and immediately placed in an envelope composed of a material impermeable to water vapour and is kept in the envelope until it is convenient to measure the humidity of the veneer. The veneer will retain its equilibrium relative humidity for long periods in such a packing.
The humidity of the wood veneer strip cannot conveniently be measured by weighing, e.g.
because of variations in the amount of adhesive remaining attached to the veneer strip when it is removed from the backing sheet. However, the veneer strip can be wrapped around a humidity sensor for measurement of the humidity directly.
The sensor of the Protimeter Dew Point Meter is especially suitable for this purpose.
It has been found, however, that an integral strip of veneer of the type referred to above can be rather stiff and thus difficult to wrap easily around a humidity sensor. In order to overcome this problem, it is preferred to use, in place of an integral strip of veneer, a rectangular web about 80 mm by 12 mm by 0.6 mm thick formed from an array of small strips each 12 mm by approximately 2.5 mm by 0.6 mm stuck side by side on a sheet of foil (or plastic/foil laminate), with adjacent said small strips being spaced about 1 mm apart. These dimensions signify only to the extent that they are convenient for the Protimeter
Dew Point Meter. Naturally these dimensions may
be varied if desired, e.g. for use with other
measuring instruments.The strips are cross-cut,
i.e. the grain runs in the direction of the minimum
dimension, i.e. the thickness dimension of the strip
(and thus, in the example described, the direction
in which the 0.6 mm is measured). This
arrangement of the grain exposes the vessels and
fibres in the wood maximally to the air and
hastens the attainment of equilibrium. It is
preferred to use a flexible adhesive (such as a
water curing silicone elastomer sealant) to secure
the individual small strips to the sheet of foil or
plastic/foil laminate, so that the web retains
maximum flexibility.
The term "thin flexible sheet" as used herein and in the claims, is intended to include a composite web of the type disclosed above.
Some surfaces or material to be tested may be contaminated with liquid, particulate, or crystalline
materials which it would be unwise to allow to come into contact with the hygroscopic material, for example because of its possible chemical effect on the hygroscopic material or on the sensor which is used to measure the humidity of the hygroscopic material, or because the contaminating material would change the weight of the piece of hygroscopic material and thus
cause errors when humidity is measured by weighing. Such contamination may be prevented
by interposing a protective layer, such as a non
hygroscopic gauze or perforated film between the
hygroscopic material and the surface or material
being tested. The interposition of said protective
layer may lengthen the time needed for equilibrium to be attained, but will not affect the level finally reached.In the case of the apparatus comprising a series of beads threaded on a rod, the protective layer would take the form, for example, of a gauze cylinder, the hole in the material under test being made larger in order to accommodate this. In the case of the apparatus comprising a strip of veneer, the protective layer may simply take the form of a sheet of bolting silk or fine wire mesh placed between the veneer strip and the wall.
Instead of the thin flexible sheet of veneer or the composite equivalent disclosed above being stuck to a backing sheet of larger area the margin of which is stuck to the surface at which it is desired to measure the water activity, it may be preferable to enclose the flexible strip, on its foil backing, in a plastic envelope of flexible sheet plastics with a rectangular hole to correspond with the sensitive wooden strip, this hole being covered with a fine nylon mesh. The envelope itself may be
made adhesive or may simply, in use be pressed physically against the desired surface. For example, the envelope may be pressed into position on a floor surface by weighting it down or may be pressed into position on a wall surface by means of a length of wood resting at one end on the floor and inclined against the wall to engage -and hold in place the envelope.
Useful applications for this invention include
measurement of water activity at the surfaces of, and at various depths below such surfaces of, walls, floors ceilings of buildings, and in cold stores, and the measurement of water activity in baulks of timber or wooden poles. The invention may also be used in assessing water availability or activity in beds of powdered, granular, or foamed material which are static for long periods and have been subject to drying or wetting, for example, layers of insulation in buildings.
The hygroscopic materials used are preferably capable of being repeatedly cycled over a range of humidities without progressive change, and with minimal hysteresis. Examples of such material include cellulosics such as paper, paper pulp, and wood (if necessary extracted with water or other solvents to; remove extractives.
Claims (16)
1. A method of measuring water availability or relative humidity at a predetermined location, comprising placing a piece of hygroscopic material in said location, allowing said piece of material to remain at said location until it reaches equilibrium, as regards humidity, with its surroundings at said location, removing said piece of material from said location, and maintaining the relative humidity of said piece substantially constant and subsequently measuring the relative humidity of said piece of hygroscopic material as a measure of the relative humidity at said predetermined location.
2, A method according to claim 1 wherein the relative humidity of said piece is maintained substantially constant after removal from said location by enclosing said piece in a substantially air and water-tight package.
3. A method according to claim 1 or claim 2 wherein said piece of hygroscopic material, prior to being placed at said predetermined location, is calibrated in terms of weight versus relative humidity, and wherein the relative humidity of said piece, after removal from said location, is determined by weighing.
4. A method according to claim 1 or claim 2, wherein the relative humidity of said piece, after removal from said location, is determined by placing said piece, with a humidity sensor, in a closed volume of air or other gas, allowing said piece and said air or other gas to reach humidity equilibrium in relation to one another, and measuring the relative humidity of said volume of air or other gas, by means of said sensor, as a measurement of the relative humidity of said piece.
5. A method according to any preceding claim, of measuring the water availability or relative humidity at a predetermined depth within a material to be tested, including boring a hole into the material to be tested, inserting into said hole a said piece of hygroscopic material mounted on or in a carrying member of impermeable material fitting closely within said hole and affording, at least at axially opposite ends of said piece of hygroscopic material, a respective impermeable part fitting closely with the wall of said hole, and leaving said carrying member, with said bead thereon, in position in said hole until said piece of hygroscopic material has reached humidity equilibrium with the surrounding portion of the material in which said hole is formed before withdrawing the carrying member, with said piece of hygroscopic material, for subsequent measurement of the relative humidity of said piece.
6. A method according to any preceding claim, of measuring the water availability or relative humidity at a water permeable surface, comprising applying to said surface a said piece of hygroscopic material in the form of a thin flexible sheet, covering the surface of said sheet remote from the surface to be tested with an impermeable sheet, and allowing said flexible sheet to come into humidity equilibrium with said surface before removing said impermeable sheet and said piece of hygroscopic material for subsequent measurement of the relative humidity of said hygroscopic material.
7. A method according to claim 6 wherein the subsequent measurement of the relative humidity of said hygroscopic material is effected by wrapping said flexible sheet around a humidity sensor.
8. Apparatus for use in performing the method
of claim 5 including a carrying member of
impermeable material adapted to fit closely within
a cylindrical bore of predetermined diameter, and
a body of hygroscopic material adapted to fit in a
complementary space afforded by said carrying
member and exposed on the radial periphery of the carrying member at a location disposed axially
between respective portions adapted to fit within said bore.
9. Apparatus according to claim 8 wherein said hygroscopic body is in the form of a bead with a central aperture. and said carrying member includes a central spindle adapted to pass through said central aperture.
1 0. Apparatus according to claim 9 comprising a series of such beads arranged on said spindle alternately with beads of impermeable material.
11. Apparatus for carrying out the method of claim 6 including a piece of hygroscopic material in the form of a thin flexible sheet adhesively secured to a backing sheet of flexible impermeable material which is larger than said piece of hygroscopic material so as to project beyond the edge of the latter to afford an exposed margin, said margin being coated with an adhesive whereby the assembly can be stuck to a surface to be tested.
12. Apparatus for carrying out the method of claim 6 including a composite hygroscopic member in the form of a thin web comprising a plurality of thin narrow strips of hygroscopic material secured side by side in spaced-apart relationship on a flexible impermeable sheet, whereby the composite web can readily be rolled about a sensor.
13. A method of measuring water availability or relative humidity at a predetermined location, substantially as hereinbefore described.
14. Apparatus for use in the method of claim 5 and substantially as hereinbefore described.
15. Apparatus for use in the method of claim 6 and substantially as hereinbefore described.
16. Any novel feature or combination of features described herein.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08200307A GB2112947B (en) | 1982-01-06 | 1982-01-06 | Measuring water availability or humidity |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08200307A GB2112947B (en) | 1982-01-06 | 1982-01-06 | Measuring water availability or humidity |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2112947A true GB2112947A (en) | 1983-07-27 |
| GB2112947B GB2112947B (en) | 1985-09-11 |
Family
ID=10527489
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB08200307A Expired GB2112947B (en) | 1982-01-06 | 1982-01-06 | Measuring water availability or humidity |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2112947B (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2213596A (en) * | 1988-01-07 | 1989-08-16 | Protimeter Plc | Disposable humidity sensor |
| CN102109447B (en) * | 2009-12-24 | 2014-05-07 | 上海张江中药现代制剂技术工程研究中心 | Method for quickly judging hygroscopicity of traditional Chinese medicine extract powders |
| CN109443976A (en) * | 2018-11-05 | 2019-03-08 | 敦煌研究院 | A kind of Rock And Soil moisture content easily-testing tool and method |
-
1982
- 1982-01-06 GB GB08200307A patent/GB2112947B/en not_active Expired
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2213596A (en) * | 1988-01-07 | 1989-08-16 | Protimeter Plc | Disposable humidity sensor |
| CN102109447B (en) * | 2009-12-24 | 2014-05-07 | 上海张江中药现代制剂技术工程研究中心 | Method for quickly judging hygroscopicity of traditional Chinese medicine extract powders |
| CN109443976A (en) * | 2018-11-05 | 2019-03-08 | 敦煌研究院 | A kind of Rock And Soil moisture content easily-testing tool and method |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2112947B (en) | 1985-09-11 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| 732 | Registration of transactions, instruments or events in the register (sect. 32/1977) | ||
| 732 | Registration of transactions, instruments or events in the register (sect. 32/1977) | ||
| PCNP | Patent ceased through non-payment of renewal fee |