WO1995014228A1

WO1995014228A1 - Moisture-sensing apparatus

Info

Publication number: WO1995014228A1
Application number: PCT/GB1994/002525
Authority: WO
Inventors: Tudor Roberts; Mark Collier
Original assignee: Perstorp Analytical Limited
Priority date: 1993-11-17
Filing date: 1994-11-17
Publication date: 1995-05-26
Also published as: EP0729578A1; GB9323693D0; CA2176497A1

Abstract

A moisture-sensing apparatus comprises a housing (10) which contains a moisture-sensing element (15). The housing has, at its upper end, an inlet (14) for flowable material and has, at its lower end, means (16) defining an outward flow path for material within the housing. The housing incorporates means to control the packing density of flowable material within the housing. Thus the upper part of the housing is provided with a cover (13) having an upper surface (12) which prevents direct pressure being applied to material within the housing, the inlet to the housing being defined by apertures (14) which lie in a substantially vertical plane.

Description

MOISTURE-SENSING APPARATUS

THE PRESENT INVENTION relates to a moisture-sensing apparatus and more particularly relates to a moisture- sensing apparatus adapted to sense the moisture of a flowable material, such as grain, pulses or manufactured material of a granular or "flowable" nature. The sensor may be used to sense the moisture content of almost any granular, flowable material.

It has been proposed previously to provide a moisture-sensing apparatus for sensing the moisture content of a material such as grain, the apparatus comprising an elongate spear having, at one end, a reading "head". The spear may be plunged into a pile of grain or the like so that the "head" is fully embedded within the grain. The moisture content of the grain is measured using variations in temperature compensated electric field strength. An embodiment of this particular type of moisture-sensor which is suitable for use with agricultural grains such as wheat, barley, oats, etc., is described in full in British Patent Specification No. 2,222,683A, the disclosure of this earlier Specification being incorporated herein by reference.

This particular sensor operates well with a pile of grain or the like, but is not practicable for use when the moisture content of a flow of grain or the like is to be determined. There are many situations when it is desirable to be able to determine the moisture content of a flow of grain or the like.

For example, when agricultural grain is being harvested using a combine harvester, it is desirable to be able to determine the moisture content of the grain as it is harvested. There are two reasons for this. Firstly, in many cases a farmer is anxious to know the moisture content of the grain, so as to be able to determine whether it is economic to harvest the grain. If grain is harvested which is very moist, it is necessary to dry the grain after harvesting before the grain can be stored or sold. This drying procedure is time consuming and expensive. A farmer may, therefore, prefer not to harvest grain when the moisture content is too high, but instead may choose to leave the grain standing in the field until the sun has dried the grain to a lower moisture content. Secondly, it is to be noted that many combine harvesters have a "yield per acre" meter which determines the quantity of grain being harvested as the combine harvester advances through the crop, providing an instantaneous read-out as to the quantity of grain measured on a "tonnes per hectare" basis. The combine harvester can, of course, only measure the weight of the grain and if the grain has a high moisture content, then the grain "weighs heavy" and may give an over-optimistic reading in terms of tonnes per hectare. Alternatively, if the grain has a very low moisture content it will "weigh light" and may give a pessimistic reading in tonnes per hectare. However, if it were possible to determine substantially instantaneously the moisture content of the grain, then the reading provided could be corrected for the moisture content, and could provide a "tonnes per hectare" reading corrected to a predetermined moisture level. It is envisaged that further situations may well exist where it is desirable to be able to measure substantially instantaneously the moisture content of a flow of grain. For example, in a re-circulating agricultural grain dryer moist grain is circulated continuously through a drying chamber. In order to determine the moisture content of grain within a dryer it is presently necessary to withdraw a sample of grain for moisture measurement. If it were possible, however, to measure the moisture of the grain which is recycling within the dryer substantially instantaneously, the dryer could be operated until a predetermined moisture level is detected, and then the dryer could be automatically stopped, or an appropriate indicator could be activated.

There are many other potential applications for a device which can measure the moisture content of a stream of material. For example, reference may be made to food products such as rice, pasta, processed cereal products, animal feed, dried vegetables and the like.

It has been found that whilst the spear of British Patent Specification No. 2,222,683A operates satisfactorily when plunged into a pile of agricultural grain, a spear of this type does not operate in a reliable manner when inserted into a stream of flowing material. The spear requires substantially stationary material adjacent the operative parts of the spear in order to provide a reliable reading. It has been found also that if such a spear is located with the operative part of the spear in the lower region of the grain-storing hopper present on a combine harvester, the reading that is provided is again erratic since, as the quantity of grain within the hopper increases, the packing density of the grain adjacent the operative part of the spear increases due to the increased pressure within the grain. Thus a fluctuating reading is provided, the fluctuations being dependent upon the quantity of grain within the grain storage hopper.

The present invention seeks to provide an improved moisture-sensing apparatus.

According to one aspect of this invention there is provided a moisture-sensing apparatus, the apparatus comprising a moisture-sensing element, a housing containing the moisture-sensing element, the housing having, at its upper end, an inlet for a flowable material, the housing having, at its lower end, means defining an outward flow path for material within the housing, the housing forming part of a means to control the packing density of said flowable material within the housing.

Preferably the said means to control packing density additionally comprise an upper element provided with means which prevent material from flowing vertically downwardly into the housing and which define one or more apertures, each aperture lying in a substantially vertical plane to permit material to flow into the housing.

Conveniently the means to control packing density additionally comprise an open topped funnel to direct a flow of said flowable material to said inlet.

According to another aspect of this invention there is provided a moisture-sensing apparatus, for sensing the moisture content of a flowable material the apparatus comprising a moisture-sensing element, a housing containing a moisture-sensing element, the housing having, at its upper end, an inlet for flowable material associated with an upper element provided with means which prevent material from flowing vertically downwardly into the housing and which define one or more apertures, each aperture lying in a substantially vertical plane to permit material to flow into the housing, the housing having, at its lower end, means defining an outward flow path for material within the housing.

Advantageously the upper element of the housing comprises means defining a horizontal upper wall and a depending side wall, there being one or more of said apertures in the side wall.

Conveniently each aperture is of elongate oval form.

Preferably each aperture extends substantially horizontally peripherally around said side wall.

In an alternative embodiment to the invention the upper element of the housing comprises a plurality of baffles, an upper baffle being provided adapted to substantially overlap a lower baffle.

Conveniently each baffle comprises a substantially planar plate inclined at a predetermined angle to the horizontal angle, the said aperture being defined between the overlapping regions of the two baffles.

Preferably sensor means are provided adapted to sense when the housing is full of the material whose moisture content is to be sensed.

Conveniently the means defining the outward flow path comprises means to adjust the size of outlet flow path from the housing. Preferably the means defining the outward flow path comprises a spider defining a plurality of apertures and a co-operating shutter disc defining a corresponding plurality of apertures, means being provided to move the shutter disc relative to the spider to adjust the degree of overlap between the apertures in the spider and the apertures in the shutter disc.

Conveniently the upper part of the housing is provided with a funnel adapted to direct grain towards the said one or more apertures formed in the upper element of the housing.

Advantageously the funnel is provided with a mesh or guard to prevent straw or the like entering the funnel.

In one embodiment of the invention the means to control packing density comprise an upper shutter operable to control the flow of material into the housing. Conveniently the housing is also provided with a lower shutter operable to control the flow of material out of the housing.

An apparatus as described above may be arranged to sense the moisture content of material flowing along a pipe or conduit.

Advantageously means are provided to mount the housing within the grain-carrying hopper of a combine harvester.

Conveniently the said mounting means comprise a shoe, adjustable means to locate the housing relative to the shoe, and a plurality of magnets carried by the shoe adapted to mount the shoe in position on the sloping part of the grain-containing hopper of a combine harvester.

The invention also relates to a combine harvester provided with an apparatus as described above to sense the moisture content of grain or the like harvested by the combine harvester.

In order that the invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described, by way of example, with reference to the accompanying drawings in which

FIGURE 1 is a perspective view of one embodiment of an apparatus in accordance with the invention with parts thereof cut away for the sake of clarity of illustration,

FIGURE 2 is a perspective view with parts thereof cut away, of an alternative top part for the apparatus of Figure 1,

FIGURE 3 is a perspective view with parts thereof cut away, of an alternative embodiment of the invention,

FIGURE 4 is an enlarged view of part of the apparatus of Figure 3, again partially cut away for the sake of clarity of illustration,

FIGURE 5 is a view, partly cut away, of another embodiment of the invention, and

FIGURE 6 shows the embodiment of Figure 5 incorporated in an arrangement to sense the moisture content of material flowing along a pipe or conduit. Referring initially to Figure 1 of the accompanying drawings, a moisture-sensing apparatus is illustrated adapted to be mounted within the grain hopper of a combine harvester. The illustrated apparatus includes a support shoe 1 carrying spaced apart magnets 2,3 intended to be used to mount the support shoe on a sloping part of the grain-carrying hopper of a combine harvester. The support shoe may also be connected to a chain (not shown) which is hooked to an appropriate anchorage point above the illustrated apparatus within the harvester, to prevent the apparatus falling into the auger of the combine harvester if the magnets should become disengaged from the side of the hopper. Pivotally connected to the support shoe 1 by a tightenable bolt 4 is an upright arm 5 carrying a wing nut 6 on a stud which is receivable in a slot 7 formed in a substantially horizontal arm 8. The arm 8 has one end pivotally connected, by means of a pivot 9, to an upper part of the shoe 1. By appropriately adjusting the position of the stud carrying the wing nut 6 within the slot 7 and by subsequently tightening the wing nut the arm 5 may be retained in a vertical position.

The arm 5 supports a vertical tubular housing 10. The upper part of the tubular housing 10 is provided with an upper end cover 11. The upper end cover 11 has a substantially horizontal transverse end wall 12, and a depending tubular side wall 13 provided with a plurality of oval inlet apertures 14 formed therein. The inlet apertures extend circumferentially and have a length which is greater than their width. Each aperture may be considered to lie in a substantially vertical (but curved plane) .

Contained within the housing 10 is a spear 15 of the type described in British Patent Specification No. 2,222,683A. The spear extends vertically upwardly within the housing and is retained in position by an appropriate spider 16 shown in phantom, located adjacent the open bottom of the housing 10. The spider has radially extending arms, with open spaces between the arms.

The lower end of the spear 15 projects below the open bottom of the housing 10 and a cable 17 emerges from the lower end of the spear.

The described apparatus may be mounted in position within the grain-containing hopper of a combine harvester, preferably at a position which is not directly under the input auger, so that grain entering the hopper does not actually fall directly on to the described apparatus.

As the grain-containing hopper fills with grain, the level of grain will rise, and the level of grain will submerge the lower part of the housing 10, thus effectively closing the spaces defined between the arms of the spider 16. As the level of grain continues to rise, grain will eventually start to enter the housing through the oval apertures 14. The apertures 14 are dimensioned to permit the ready ingress of grain into the housing, but to prevent the ingress of straw or other material entrained with the grain as it enters the hopper of the combine harvester.

Grain will enter the housing 10 through the apertures 14 until the housing 10 is full. Once the housing 10 is completely full, the housing 10 and the cover 11 having the horizontal upper wall 12 and the depending sidewall 13 will serve to prevent the packing density within the housing 10 from increasing further, even if the level of grain within the hopper rises to a considerable level above the top of the housing 10. Thus, the housing and the upper end cover serve to control the packing density of grain within the housing adjacent the spear. The downward pressure generated in the grain is effectively prevented from increasing the packing density within the housing 10 by virtue of the presence of the horizontal upper wall 12. Since the oval apertures 14 lie in vertical (but curved) planes the downward pressure generated by the weight to the grain above the described apparatus is not transferred to the grain inside the housing 10.

A sensor 18 may be provided on the underside of the horizontal upper wall 12 to sense when the housing 10 is full of grain. The sensor may comprise a Piezo electric transducer or may comprise some sonic or optical sensor means. When the sensor provides a signal confirming that the housing is full of grain a reading may be taken from the moisture-sensing spear 15 thus determining the moisture content of the grain in the housing 10.

The output from the spear may be supplied to a display and/or printer in the cab of the combine harvester to provide a substantially instantaneous read out of moisture content, and/or may be supplied to a yield monitor in the cab to provide a yield rate which is "corrected" for the actual moisture content. The output from the spear may also be used in other ways, and may be fed to a computer controlling various functions of the combine harvester.

If no sensor 18 is provided it is possible to monitor the output reading from the spear 15 to determine when the housing is full. The output will fluctuate as the housing fills, and will then stabilise when the housing is completely full. When the hopper of the combine harvester is emptied of grain, the level of grain within the hopper will fall until the level of grain is below the level of the bottom of the housing 10. Grain within the housing 10 will then flow out of the housing through the spaces defined between the arms of the spider 16. The cycle of operation described above may then be repeated.

It is to be noted that the output of the spear will fluctuate as the housing 10 is emptied of grain. This fluctuation can be monitored to ensure that the housing 10 empties when the grain hopper of the combine harvester is emptied.

Referring now to Figure 2 of the accompanying drawings, an alternative top part 11' for the housing 10 is illustrated. This top part is not provided with a horizontal upper wall and apertures in a depending side wall, but instead is an open topped tubular element provided with two inclined baffles. The upper baffle 19 is formed from a planar plate which is inclined at an angle greater than the repose angle of grain or other flowable material which is to be utilised in conjunction with this embodiment of the invention. The repose angle of a flowable material is the angle formed by the sides of a pile of the material generated by simply pouring the material downwards on to a horizontal surface. Because the baffle 19 is inclined at an angle which is greater than the repose angle, none of the material will tend to accumulate on the baffle when a flow is established through the housing 10. The upper baffle 19 extends more than half-way across the diameter of the upper part 11' of the housing 10. The upper baffle 19 is located above a lower baffle 20 which is also formed from an inclined planar plate. The lower baffle 20 is inclined in the opposite direction to the upper baffle 19, and is again inclined at an angle which is greater than the repose angle of the material to be utilised in conjunction with this embodiment of the invention. The lower baffle 20 extends substantially half-way across the diameter of the upper part 11' of the housing 10, so that in the region 21 there is a degree of overlap of the baffles 19.

Effectively the baffles define an inlet aperture which extends between the overlapped regions of the baffle, lying in a substantially vertical plane.

The embodiment illustrated in Figure 2 will operate in a very similar manner to that of the embodiment of Figure 1. It is to be appreciated, however, that the housing 10 will not begin to fill with grain until the level of grain within the hopper reaches the top of the upper part 11* of the housing 10. The grain will then fall over the top of the upper part 11' of the housing and flow down across the top of the upper baffle 19, then being directed to flow across the top of the lower baffle 20 entering the interior of the housing 10 through the aperture effectively defined between the two baffles.

When the housing is full of grain, the presence of the baffles prevents an increase in pressure arising within the housing 10 when the level of grain above the top of the housing 10 increases. Thus the housing and the baffles again provide means for controlling the packing density of grain within the housing 10. Figure 3 and 4 illustrate a modified embodiment of the invention for use in sampling a flow of material.

The embodiment of Figures 3 and 4 comprises a housing 10 with an upper part 11 having oval apertures 14 generally as described with reference to Figure 1. However, in this illustrated embodiment the spider 16 (as can be seen more clearly in Figure 4) , which supports the shaft of the spear 15, is provided with a plurality of openings 22. A shutter disc 23 is provided located adjacent the spider 16. The shutter disc 23 is also provided with a plurality of apertures 24 which correspond with the openings 22. Whilst, in one embodiment means may be provided for moving the shutter disc 23 manually, in this embodiment the shutter disc 23 has a toothed exterior 25 which engages a gear wheel 26 through an access window 27 formed in the side of the housing 10. The gear wheel 26 is driven by means of a shaft 28 and an appropriate motor (not shown) . The motor and the gear wheel 26 are located within a housing 29 mounted on the exterior of the housing 10. The shutter disc 23 may be positioned relative to the spider 16 so that the openings 22 and 24 are aligned, or so that openings are off-set, or may be moved to an intermediate position.

Surrounding the upper part of the housing 10 is a conical funnel 30 having an open top 31. The open top is provided with a substantially conical mesh or grid 32.

It is envisaged that the apparatus of Figure 3 will be located directly under a falling stream of grain or the like. The conical mesh 32 has apertures therein dimensioned to permit grain to pass through the apertures and fall into the funnel 30, but provides the function of minimising the amount of straw or other material present within the grain from entering the funnel 30.

As grain enters the funnel 30, the funnel will fill, and if the funnel is completely full grain will spill over the upper lip defining the open upper mouth of the funnel 30.

The grain within the funnel 30 will pass through the apertures 14 into the housing 10. The shutter disc 23 may be moved to such a position relative to the spider 16 that the apertures 24 are in a predetermined hit-and-miss relationship with regard to the apertures 22 in the spider 16 so that the effective flow path through the combination of the spider 16 and the shutter disc 23 is adjusted to provide a predetermined flow rate for grain. Grain will thus leave the bottom part of the housing 10 at a predetermined rate and if grain is present in the funnel 30 grain will enter the top part of the housing 10, through the apertures 14, at a corresponding predetermined rate. The amount of grain within the housing 10 will be substantially constant over a period of time, and the flow rate of grain will be so slow through the housing that the grain adjacent the operative parts of the spear 15 will be substantially stationary thus enabling the spear to provide an accurate output. However, it will be appreciated that since the housing 10 is continually being emptied, and continually being re-filled from material from the funnel 31, the spear provides an almost "instantaneous" output relating to the moisture content of grain present within the stream of grain being directed towards the open mouth 31 of the funnel 30.

It is to be appreciated that the combination of the housing and the funnel will control the packing density of grain within the housing, since only a certain predetermined maximum amount of grain can be present in the combination of the funnel and the housing. It is preferred, however, for the housing to be of the design of Figure 1 and Figure 2 with the top element or with the baffles.

It is envisaged that instead of the described "hit- and-miss" shutter arrangement of Figure 4 an adjustable iris could be utilised. The iris may be manually adjusted or may be motor-driven.

Means may be provided automatically to pre-select the size for the flow passage through the lower part of the housing 10 in dependence upon the nature of the grain to be utilised in conjunction with the apparatus. For example, for grain of a small size, such as oil seed rape, the flow passage would be small, whereas for a more bulky grain, such as wheat, the flow passage would be larger. If the described apparatus is mounted in a combine harvester, an appropriate pre-selector may be provided in the cab of the combine harvester to enable the operator to select the size of the flow passage in accordance with the crop being harvested.

It is envisaged that since moist grain is more likely to "clog" than dry grain, means may be provided to control the size of the flow passage through the housing 10 in response to the measured moisture content of grain within the housing 10. Thus, if moist grain, having a moisture content in excess of a predetermined limit, is present within the housing, the size of the flow passage through the housing may be increased, in order to minimise the risk clogging or blocking of the flow path, whereas if "dry" grain having a moisture content less than a predetermined moisture content is present within the housing, the size of the flow path through the lower part of the housing may be reduced in order to prevent grain flowing through the housing too quickly.

The apparatus of Figures 3 and 4 may be associated with a grain dryer, and if the grain has been "cleaned" before it is dried the mesh 32 may be omitted. The signal from the spear may be supplied to a central arrangement which automatically stops the dryer when a predetermined moisture level has been reached, or which activates an indicator, such as a flashing light or a buzzer, to indicate that the grain is "dry".

It is thus to be appreciated that the apparatus described may be inserted directly within a pipe or conduit through which a material is flowing, when the moisture content of that material is to be measured. The apparatus may incorporate the entire cross-section of the pipe or conduit or may preferably incorporate less than the entire cross-section of pipe or conduit. Thus if the housing of the apparatus described above becomes full of material, and further material is flowing the through the pipe or conduit, then that further material may flow past the housing.

Figure 5 illustrates a modified embodiment of the invention intended primarily for use in measuring the moisture content of a material flowing along a pipe or conduit. Such material may comprise grain, such as agricultural grain, but may also include any other particular material such as manufactured food stuffs including rice, pasta, dried vegetables and the like, or other granular-type materials. Referring to Figure 5, a vertical pipe or conduit 40 is provided through which material is intended to flow in a downward direction. An upper shutter arrangement 41 is provided, which is associated with the pipe 40, the shutter arrangement 41 including a shutter blade 42 defining a through aperture 43 and a driving mechanism 44. The driving mechanism is adapted to move the shutter between open and closed positions. The upper shutter 41 is shown in the "closed" position. The shutter 41, when in the open position permits material within the pipe or conduit 40 to flow into a housing 45 defined beneath the shutter 41. The housing 45 contains a spear 46 of the type described above which is supported by a spider 47 located in the lower part of the housing 45.

A sensor 48 is provided adapted to sense the level of material within the housing 45. The sensor 48 may be of any appropriate design and may thus, for example, comprise an optical sensor.

At the lower end of the housing 45 a second or lower shutter arrangement 48 is provided which is of the same design as the upper shutter arrangement 41. The lower shutter arrangement 48 is provided with a shutter blade 49 which defines a through aperture, that through aperture not being visible in Figure 5, but instead being aligned with the axis of the housing 45. The shutter 48 is provided with a drive mechanism 50. A pipe portion 51 extends from beneath the second shutter 48 so that material within the housing may flow downwardly out of the housing 45 when the second shutter 48 is in the open position.

A electric lead 52 is directed out from the housing 45 carrying signals from the spear 46. It is to be appreciated that in use of the arrangement illustrated in Figure 5, initially the upper shutter 41 will be in the open position and the lower shutter 48 will be in the closed position. Material flowing through the pipe 40 will thus accumulate within the interior of the housing 45. When the sensor 48 senses that the housing 45 is substantially full the upper shutter 41 is moved to the closed position. Thus the packing density of the material present within the housing 45 is limited.

Readings may then be taken from the moisture sensing spear 46 to determine the moisture content of material present within the housing 45. Subsequently, the shutter 48 may be opened, permitting material within the housing 45 to flow downwardly and outwardly away from the housing through the pipe 51. The entire cycle of operation may then be repeated.

It is to be appreciated that the cycle of operation may be modified, with the lower shutter 48 always being partly open, so that there is a continuous, but relatively slow, flow of material out of the housing 45. The upper shutter 41 may then be actuated simply to maintain an appropriate quantity of material within the housing at all times.

Referring now to Figure 6, the arrangement of Figure 5 is illustrated in conjunction with a principal, substantially vertical pipe or conduit 60. It is to be seen that the pipe 40 terminates within the main pipe or conduit 60 with an open upwardly directly mouth 61 adapted to catch material moving vertically down the main conduit 60. The conduit 51 returns material discharged from the housing 45 into the main conduit 60. It is to be appreciated that in use of an arrangement as shown in Figure 6, there is no risk of the main conduit 60 becoming blocked.

In many situations, the flow of material along a conduit, such as the conduit 60, will be erratic. From time-to-time there will be very substantial flows, but during the intervening period the flow may be very spasmodic. The described apparatus can be used to measure, substantially instantaneously, the moisture content of material flowing through the conduit 60. The measured moisture content may be used to control a manufacturing process, or may be displayed. For example, if the moisture content is too high, then the time material being manufactured spends in a dryer may be increased. Alternatively, if the moisture content it too low, a procedure may be activated to add moisture to the material at a subsequent point in the manufacturing plant.

Whilst the invention has been described with reference to embodiments in which a spear as described in British Patent Specification No. 2,222,683A is used as the operative moisture-sensing means, alternative moisture sensing means may be used within the housing 10.

Whilst the apparatus has been described with specific reference to the measurement of moisture present in grain, it is to be clearly understood that the apparatus may be used for measuring the moisture content of other flowable materials such as pulses, rape or even manufactured items.

Claims

CLAIMS :

1. A moisture-sensing apparatus, for sensing the moisture content of a flowable material, the apparatus comprising a moisture-sensing element, a housing containing a moisture-sensing element, the housing having, at its upper end, an inlet for flowable material associated with an inlet for a flowable material, the housing having, at its lower end, means defining an outward flow path for material within the housing, the housing forming part of a means to control the packing density of said flowable material within the housing.

2. An apparatus according to Claim 1 wherein the said means to control packing density additionally comprise an upper element provided with means which prevent material from flowing vertically downwardly into the housing and which define one or more apertures, each aperture lying in a substantially vertical plane to permit material to flow into the housing.

3. An apparatus according to Claim 1 or 2 wherein the means to control packing density additionally comprise an open topped funnel to direct a flow of said flowable material to said inlet.

4. A moisture-sensing apparatus, the apparatus comprising a moisture-sensing element, a housing containing the moisture-sensing element, the housing having, at its upper end, an upper element provided with means which prevent material from flowing vertically downwardly into the housing and which define one or more apertures, each aperture lying in a substantially vertical plane to permit material to flow into the housing, the housing having, at its lower end, means defining an outward flow path for material within the housing.

5. An apparatus according to Claim 2 or Claim 3 as dependent on Claim 2, or Claim 4 wherein the upper element of the housing comprises means defining a horizontal upper wall and a depending side wall, there being one or more of said apertures in the side wall.

6. An apparatus according to Claim 5 wherein each aperture is of elongate oval form.

7. An apparatus according to Claim 6 wherein each aperture extends substantially horizontally peripherally around said side wall.

8. An apparatus according to Claim 2, or Claim 3 as dependent on Claim 2, or Claim 4 wherein the upper element of the housing comprises a plurality of baffles, an upper baffle being provided adapted to substantially overlap a lower baffle.

9. An apparatus according to Claim 8 wherein each baffle comprises a substantially planar plate inclined at a predetermined angle to the horizontal angle, the said aperture being defined between the overlapping regions of the two baffles.

10. An apparatus according to any one of the preceding Claims wherein sensor means are provided adapted to sense when the housing is full of the material whose moisture content is to be sensed.

11. An apparatus according to any one of the preceding Claims wherein the means defining the outward flow path comprises means to adjust the size of outlet flow path from the housing.

12. An apparatus according to Claim 11 wherein the means defining the outward flow path comprises a spider defining a plurality of apertures and a co-operating shutter disc defining a corresponding plurality of apertures, means being provided to move the shutter disc relative to the spider to adjust the degree of overlap between the apertures in the spider and the apertures in the shutter disc.

13. An apparatus according to Claim 4 or any Claim dependent thereon wherein the upper part of the housing is provided with a funnel adapted to direct grain towards the said one or more apertures formed in the upper element of the housing.

14. An apparatus according to Claim 3 and any Claim dependent thereon, or Claim 15 wherein the funnel is provided with a mesh or guard to prevent straw or the like entering the funnel.

15. An apparatus according to Claim 1 wherein the means to central packing density comprise an upper shutter operable to control the flow of material into the housing.

16. An apparatus according to Claim 1 or 15 wherein the housing is provided with a lower shutter operable to control the flow of material out of the housing.

17. An apparatus according to any one of the preceding Claims arranged to sense the moisture content of material flowing along a pipe or conduit.

18. An apparatus according to any one of Claims 1 to 14 wherein means are provided to mount the housing within the grain-carrying hopper of a combine harvester.

19. An apparatus according to Claim 18 wherein the said mounting means comprise a shoe, adjustable means to locate the housing relative to the shoe, and a plurality of magnets carried by the shoe adapted to mount the shoe in position on the sloping part of the grain-containing hopper of a combine harvester.

20. A combine harvester provided with an apparatus according to any one of the preceding Claims 1 to 14 or 18 or 19, to sense the moisture content of grain or the like harvested by the combine harvester.