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
  • A01G25/00—Watering gardens, fields, sports grounds or the like
  • A01G25/16—Control of watering
  • A01G25/167—Control by humidity of the soil itself or of devices simulating soil or of the atmosphere; Soil humidity sensors
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/24—Earth materials
  • G01N33/246—Earth materials for water content

Definitions

• the present invention relates to an irrigation sensor device.
• the present invention comprises a plant analogue Irrigation sensor device which Is operative in a similar manner to a living plant to give an indication of water status, e.g. the water content of the soil in the neighbourhood of the device or the dynamic water status likely to be prevalent in plants growing in the neighbourhood of the device, i.e. the flow rate of water being taken in by these plants from the surrounding soi 1.
• the device includes a water-attracting base portion and indicator means operative to indicate the amount of water entering the base portion of the device from soil in the immediate vicinity of the base portion.
• the base portion comprises a water-attractive material e.g. a sugar or like solution, housed in a water-permeable container e.g. formed of a semi-permeable membrane.
• a water-attractive material e.g. a sugar or like solution
• a water-permeable container e.g. formed of a semi-permeable membrane.
• the device includes control means for preserving the water-attracting properties of the base portion during use of the device.
• control means conveniently comprises a pump for extracting over- diluted solution from the root portion, passing the extracted solution through a supply (e.g. crystals) of the dissolved material to increase the concentration of the solution, and thereafter returning the solution to the root portion.
• the indicator means comprises a flow eter operated by the flow of liquid from the sensor device to indicate the dynamic water status likely to be prevalent in plants growing in the vicinity of the device.
• the flowmeter comprises a peristaltic motor.
• the peristaltic motor comprises a roller member engaging a small-bore soft PVC lay-flat tube, the roller member being rotated in operation of the motor as the roller-induced depression in the tube is moved along the tube by a flow of liquid therethrough.
• the flowmeter may instead comprise a passageway, an electric contact which in operation is moved from one end of the passageway to the other by a flow of liquid through the passageway, and a control system which is operated by the contact on its arrival at either end of the passageway to reverse the flow of liquid through the passageway and thereby move the contact back in the opposite direction.
• the passageway is provided by a fine bore tube and the contact comprises a mercury pellet moving along the bore of the tube.
• the flowmeter may comprise a cylinder, a piston which is moved along the cylinder by a flow of liquid through the cylinder, and a control system which is operated by the piston on completion of its displacement in either direction to reverse the flow of liquid through the cylinder and thereby move the piston back in the opposite direction.
• the piston comprises a composite piston presenting to the liquid within the cylinder, piston heads of different area to one another.
• the piston comprises a three-headed composite piston, the areas presented to the liquid in the cylinder by the two end heads being equal to one another but less than the areas presented by the central head thereby to enhance the displacement of the piston in the cylinder 1n response to a given flow of liquid therethrough.
• the passage of liquid past the piston heads is prevented by rolling seals fitted between these heads and the inner wall of the cylinder.
• the indicator means may instead comprise a pressure gauge responsive to the pressure within the sensor to indicate the water content of the soil in the neighbourhood of the device.
• Figure 1 1s a vastly simplified schematic vertical section of the base portion of a typical plant
• Figure 2 1s a diagrammatic vertical section of a plant analogue irrigation sensor device in accordance with the present invention
• Figures 3a, 3b and 3c, collectively referred to as Figure 3 are, respectively, a diagrammatic vertical section of a preferred version of the same device, a cross-section of the root analogue component used, and a schematic vertical section of a modification to this version
• Figure 4 shows an exploded perspective view of various parts of the device shown in Figure 3;
• Figure 5 is a perspective view of a practical embodiment of the device
• Figures 6a and 6b collectively referred to as Figure 6, diagrammatically illustrate, at two different stages of operation, an alternative design of flowmeter to the peristaltic pumps used in the arrangements of Figures 3, 4 and 5
• Figure 7 shows, in exploded view, a practical embodiment of the Figure 6 design
• Figures 8a and 8b collectively referred to as Figure 8, diagrammatically Illustrate a further design of flowmeter and its principle of operation; and Figure 9 is a part elevation, part vertical section of a static version of the device for use as a moisture meter.
• the sugars "s" synthesised in the leaf cells 8 are transported via the phloem vessels 9 back to the root where they are utilised to re-concentrate the fluid in the vacuoles in the root cells 1. Without this osmoregulation system, the root cells 1 would otherwise lose their osmotic potential as a result of dilution caused by the inflow of soil water. Zig-zag Hne 10 represents radiant energy from the sun received by the leaf cells 8.
• FIG. 2 of the drawings shows a plant analogue irrigation sensor device 12 which is designed in accordance with the teachings of the present invention so as to provide a rough mechanical equivalent of those parts of the plant's structure that enable it to effect, water transference from the soil, through the plant's xylem vessels, into the atmosphere.
• the water-absorbing cells 1 of the plant's root cortex are replaced by a cylinder of semi-permeable membrane 13 containing a solution 14 of sugar.
• the entire cylinder is buried in the soil 15.
• the osmotic influx of water "w” from the moist soil into the cylinder 13 flows out of the root via the tube 16 which in the device of Figure 2 replaces the xylem vessels 5 of the plant 2 in Figure 1.
• the mesophyll tissue in the leaf from which water evaporates into the atmosphere in a real plant is modelled in the sensor device 12 by the porous pot 21 which is connected by tube 22 to the xylem vessel analogue tube 16 as shown.
• the phloem analogue circuit composed of items 16,17,18,19,20 and 13 comprises a closed circuit and hence the osmotic influx of water into the root analogue cylinder 13 must pass out of this system through tube 22 to the leaf analogue porous pot 21.
• the negative suction potential generated by the evaporation of water from the leaf analogue porous pot 21 is applied directly to the root analogue cylinder 13, this enhances the available potential for the movement of water into the cylinder 13.
• the root analogue component 23 of the device 24 consists of a rigid backing tube 25 which has a pointed end 26 to facilitate installation in the soil.
• This backing tube is provided with a number of external grooves 27 which hold the sugar solution.
• a semi-permeable membrane 28 fits snugly on the backing tube 25 and is sealed thereto by an O-ring fitted at the top end of the device.
• a protective outer sleeve 29 (Figure 3£>> which can either be left in place (if suitably perforated) or can be withdrawn after positioning the root analogue component 23 in the soil at site.
• Osmotic inflow of water from the soil will take place into the grooves 27 and the solution in these is replenished by fresh sugar solution through a phloem analogue tube 30 which forms part of the closed sugar solution pumping circuit by tubes 31, a glandless recirculating pump 32, sugar crystals 33, sealed compartment 34, tube 35 and feed tube 30.
• the tube 30 communicates with grooves 27 via radially disposed drillings at the lower end of the rod 25.
• a leaf analogue porous pot 36 is connected through the xylem vessel analogue tube 37 to a water reservoir 38.
• the flowrate "r" into the root analogue is monitored by a first flowrate measuring device 39 and the corresponding transpiration rate "t" from the leaf analogue is assessed by a second flowrate measuring device 40.
• the main difference in the fluid transport arrangement in the apparatus shown in Figure 3 and that described with reference to Figure 2 is the fact that in the Figure 3 version, the suction developed by the porous pot is not applied directly to the root analogue component 23. This change is desirable because the high suction pressure developed in the porous pot 36 cannot generally be sustained reliably in the xylem vessel analogue tube 37 without serious risk of local cavltation problems.
• the actual transpiration rate of a plant is not necessarily the full potential rate indicated by flowmeter 40, because in a real plant the stomatal opening in the leaf would normally alter the connection to the free atmosphere, the degree of stomatal opening depending on the water status of the plant.
• This effect can be simulated mechanically in the device of Figure 3 by fitting a suitable adjustable sliding shield (not shown) to mask the evaporation area of the porous pot 36. This shield will then have to be adjusted to match the surface area exposed to the atmosphere by a real plant.
• the porous pot is left to sense the maximum evapo-transpiration rate and the signal obtained from the flowmeter 40 is suitably weighted to match stomatal adjustment in response to the physiological needs of the plant.
• the following discussion assumes weighting of the flowmeter 40 signal in this way.
• Flow eters 39 and 40 are preferably such as to produce a digital or analogue electric signal which is fed to a microprocessor (not shown). This latter 1s programmed to record the two signals and after comparing them with each other and/or with certain preselected reference values, to output an appropriate signal to a visual indicator (not shown).
• the information provided by the flowmeters 39 and 40 can be utilised so that the onset of moisture stress in the system is signalled by the visual indicator when the output from flowmeter 39 falls below a certain pre-set value (calibrated against the crop being monitored and the soil type in which it is grown).
• the visual indicator signals a danger of temporary wilting of the crop.
• flowrate is estimated by measuring the speed of movement of a liquid meniscus in a fine capillary tube and the advance of the meniscus is timed between opto-electronic sensors set at fixed intervals along the tube.
• a peristaltic motor (the inverse of a peristaltic pump) is used for each of flowmeters 39,40, the rotor speed of the motor being directly proportional to the rate of fluid flow through it.
• the angular position of the rotor is sensed electronically and the resulting signal sent to an appropriate microprocessor as above described.
• Figure 4 shows the essential elements of one such arrangement 1n which the two (four-lobed) peristaltic motors (41,42) are sited between the phloem pump (43) arm the root analogue component 23 as shown.
• this is designed as a centrifugal pump with backwardly curved clockwise-rotating blades in the impeller 44 to give appropriate pump characteristics.
• it features a glandless electric motor impeller drive 45 using a rotating magnet. This ensures that the phloem circuit will remain sealed at all times.
• Reference numeral 46 indicates a casing for impeller 44.
• the upper peristaltic motor 42 this comprises the usual roller member 48 which is rotated anti-clockwise as the roller-induced depression 1n the peristaltic tube 49 Is moved along the tube by a flow of fluid from the root flow inlet tube 50 through to the corresponding outlet tube 51.
• the lower peristaltic motor 41 is of similar construction to motor 42 and once again, the roller member is rotated anti ⁇ clockwise by a flow of fluid from an inlet tube 52 to an outlet tube 53 (leading to the leaf analogue porous pot 36).
• FIG. 4 illustrates a production version of the irrigation sensor 55 which, it is envisaged, could be mass-produced in plastics at fairly low unit cost.
• reference numerals 23 and 35 respectively indicate the root analogue component and the leaf analogue porous pot (as before).
• Reference numeral 57 indicates a casing containing the phloem pump 43, the root flow peristaltic motor 42 and the shoot flow peristaltic motor 41.
• the casing 57 is also provided with handles 58,59, a computer output socket 60, for the microprocessor (not shown), and a solution level sight gauge 61 for a combined water reservoir and sugar container 62.
• the arrangement is completed by a differential flow visual indicator 63.
• the osmotic movement of water from the soil is induced by a sugar solution placed inside the semi-permeable cylinder.
• Sugar 1s not the only possibility, however, for use as the osmotic solution and any other chemical that can form a suitable solution in water as the solvent will do instead e.g. common salt.
• the continuous through-flow peristaltic motor flowmeter of Figures 3 and 4 can be replaced by a reciprocating system. Two possible versions of this alternative type of flowmeter will be described.
• the basic principle of the first type and its mode of operation are diagrammatically illustrated in Figures 6a and 6b where flowmeter 70 comprises a precision microbore tube 71 containing a mercury pellet 72.
• fluid displaced by the root analogue sensor enters one side of the tube 73 ( Figure 6a) and displaces the mercury pellet to the other end of the tube (marked 74).
• FIG. 6 ⁇ An electro-hydraulic system for accomplishing the change in direction of the mercury pellet is also shown in Figure 6 ⁇ .
• the tube 71 Is shown furnished with two sets of electrical contacts 75 and 76. When the mercury pellet bridges the contacts an electrical circuit is completed.
• the solenoid system 85 (incorporating coils 77 and 83 and the two-way switch 78) is essentially a latching two-way relay.
• this "relay" changes polarity but when that contact opens as the pellet moves away after fluid reversal, the switch position of switch 78 is maintained until the contact at the other end of tube 71 is again activated.
• the operator is free to select both the length between contacts 75 and 76 and the bore of the tube 71. This provides a very flexible system for deciding the degree of resolution of the flowrate measurement required. In practice a series of calibrated tubes of differing bore volume can be produced for substitution in the measuring unit in place of tube 71.
• flowmeter 90 includes a metering tube 91 which is sealed into two manifold blocks 92 and 93, into which are plumbed two electrically actuated two-way miniature hydraulic valves 94 and 95.
• These miniature valves may conveniently be the commercially produced valves which are in regular use in the United Kingdom in applications such as ink-jet printers (manufactured by Lee Co., for example). These valves represent the units labelled V-
• fluid from the sensor enters the metering system through tube 96 and is exhausted out of tube 97 (respectively labelled 81 and 82 in Figure 6b).
• the sub-manifold 98 simply contains passages which transfer fluid from one end of the metering tube to the other and it also acts as the base to which the other components are fixed.
• the mercury pellet contacts on the metering tube 91 have been omitted for clarity.
• the trap wells 99 and 100 are designed to catch any mercury that escapes from the metering tube and vent the system to exhaust.
• the tube 91 can be readily changed after first removing the manifold 93.
• the second type of reciprocating flowmeter to be described is flowmeter 109 in Figures 8a and 8b.
• the mercury pellet 72 of the previously described version is replaced by a mechanical metering piston 110 using rolling diaphragm seals.
• This latter comprises three piston sections 111, 112 and 113 each of which 1s fitted with a rolling diaphragm seal 114.
• the three piston sections are joined together by a rod 115.
• the middle piston section 111 divides the metering tube into two chambers A and B, and ports.116 and 117 respectively connect with these two chambers. It will be seen that piston sections 112 and 113 are of equal size (sectional area A 2 ) but are smaller than piston section 111, which has a greater sectional area of A-
• the differential area arrangement is also necessitated at present by practical considerations which limit the minimum size of commercially available rolling diaphragm seals.
• the mercury bead version it is currently not possible to make the bore of the tube smaller than about 7 mm and the configuration of the diaphragm limits the stroke L to about 5mm.
• the differential area arrangement described above thus gives a very much wider latitude than would otherwise be possible, in the selection of piston stroke and the volume of fluid metered per stroke.
• Reference numeral 118 indicates a microswitch to which the composite piston rod is mechanically connected, e.g. to operate an identical electro-hydraulic system (not shown) to that illustrated in Figure 6a.
• the metering mechanism provides an electrical signal when a carefully measured quantity of fluid passes through the system.
• each pulse is proportional to a known volume of fluid passing through the mechanism.
• To estimate the flowrate it is only necessary to count the number of pulses in a given period.
• the flowrate is simply proportional to the number of pulses per unit time.
• glandless re-circulating pump 32 Another important component of the sensor is the glandless re-circulating pump 32. This centrifugal unit with backwardly-curved blades works well and no great change is envisaged. It is therefore a simple matter to develop this unit in a miniaturised form.
• the proposed sensor is capable of sensing the dynamic movement of water in the root zone of a growing crop. If the sensor is unable to abstract water from the soil in a given field, then plants in its neighbourhood too will be unable to do so; (2) the sensor has the additional property of being able to sense the onset of temporary wilt conditions and any other pre-determined moisture regimes which are damaging to the plants; (3) the sensor is readily adapted to supply electrical signals which can be readily handled by a microprocessor or computer; (4) the proportions of the soil probe, acting as the root analogue, can be adjusted to simulate the rooting pattern of a given crop; (5) the sensor can be calibrated to simulate a large number of crop types and their special needs; (6) the sensor automatically takes account of the presence of dissolved salts in the soil matrix.
• the outlet from the root analogue sensor of the present invention can be closed off so that the entry of water from the soil under the osmotic gradient will increase the pressure inside the sensor. When this pressure reaches the point where it just balances the osmotic potential, flow will cease.
• the pressure in the system is an indirect Indication of the moisture content of the soil at the sensor. If, say the moisture content were to drop, then the sensor will have a higher osmotic potential and water will flow out into the soil and the pressure in the sensor will drop. Thus the pressure 1n the sensor can be directly calibrated to represent the water content in the soil. This is essentially a static mode of operation of the sensor.
• the pressure in the sugar solution is kept at near atmospheric.
• no special precautions are necessary to support the semi-permeable membrane against the pressure within the root sensor chamber.
• the semi-permeable membrane will be subject to very high internal pressure and as currently commercially available semi-permeable membranes cannot withstand such pressures, they have to be provided with some form of mechanical support.
• the device (120) Includes a semi-permeable membrane 121 which is supported on a coarse porous plate or disc 122.
• the porous disc can be a ceramic filter type or made of sintered metal. As its pores are several magnitudes larger then the pores in the semi-permeable membrane it does not act as a barrier to the flow of water from the soil to the semi-permeable membrane and will not itself act as a semi-permeable barrier.
• the semi-permeable membrane encloses a chamber 123, which is full of a solution of either sugar or any other salt dissolved in water or any other fluid having an osmotic potential below that of pure water.
• the chamber is connected by pressure tubing 124 to a pressure gauge 125.
• a pressure gauge 125 When the chamber 123 1s placed in a moist soil, water will enter the porous support 122 and move osmotically into the solution in the chamber 123 through the semi-permeable membrane 121.
• items 123, 124 and 125 together constitute a closed system, the pressure in the system will rise as a result of this Influx of water and this pressure 1s measured by the gauge 125.
• this pressure gauge can be calibrated directly in terms of the moisture content of the soil with which 122 and 123 are in contact.
• the high pressure inside chamber 123 cannot damage the pliable membrane 121 because it is supported on the rigid porous plate 122.

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• 1990
  • 1990-09-05 GB GB909019377A patent/GB9019377D0/en active Pending
• 1991
  • 1991-09-04 WO PCT/GB1991/001497 patent/WO1992003916A1/en not_active Application Discontinuation
  • 1991-09-04 EP EP19910916286 patent/EP0547122A1/de not_active Withdrawn
  • 1991-09-04 GB GB9118990A patent/GB2249182B/en not_active Expired - Fee Related

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