GB2295013A - Heat detection - Google Patents

Abstract

A method of detecting excessive heat at a given location 6 such as the duct 4 of a grain dryer comprises providing an elongate heat responsive member 5, positioning the member such that a portion thereof is at the location, tensioning the heat responsive member by means 9 - 12, sensing tension in the heat responsive member, and actuating a detector device such as switch 14, 15 in response to variation or loss of tension. <IMAGE>

Description

TITLE: HEAT DETECTION DESCRIPTION The invention relates to heat detection, including heat detecting or sensing device and a method of detecting heat more particularly, but not exclusively, intended for use in preventing fires, e.g. in agricultural equipment such as grain driers.

It is known to provide a bimetallic strip device which changes shape to activate or deactivate an electrical circuit when a given temperature is reached. It is also known to provide eutectic metal links which melt when subjected to temperatures above a desired ceiling and which, in melting, activate devices such as sprinkler systems or electric devices.

It is also known to provide thermocouples to detect temperature to provide warning of temperatures outside a desired range.

It is an object of the invention to provide a simple and inexpensive temperature sensing means and method particularly but not exclusively in fire prevention or control e.g. for use with agricultural equipment of the nature of grain dryers. In such dryers heated air is drawn through a plurality of air ducts in a column through which the grain to be dried is passed, for example under gravity, so as to heat and thus dry the grain. It sometimes happens that a local hot spot occurs in the column caused, by an obstruction in the column to free movement of the grain.

Such an obstruction may be caused, for example, by an accumulation of straw. The hot spot can rapidly result in a fire in the column which results not only in loss of the grain but, potentially more seriously, in the destruction of the grain dryer itself. At least in theory it would be possible to place an electrical temperature sensor in each of the air ducts in the column but since it is usual to provide a large number of such ducts in a grain dryer then the cost of such an installation would be prohibitive.

From one aspect the invention is a method of detecting heat comprising providing an elongate heat responsive member, positioning the member at a location, tensioning the heat responsive member, sensing motion due to variation or loss of tension in the member and actuating a device (e.g. a safety device) in response to detected motion.

Preferably the method comprises arranging the same elongate heat responsive member to extend into a plurality of discrete locations, each of which requires heat detection.

From another aspect the invention is a heat sensing device comprising an elongate heat responsive member, means tensioning the heat responsive member and means responsive to loss of tension or elongation of the heat responsive member and arranged to activate a safety device. The safety device may comprise electrical switch means by which the heating means of a grain dryer is shut down and/or an alarm and/or a fan and/or other fire control means is activated.

The heat responsive member may be thermoplastic or combustible and may be in the form of a string or cord of thermoplastics material, e.g. polypropylene twine or nylon filament or may be a combustible string or cord e.g. of the nature of sisal bailer twine. Preferably the heat responsive member is stretched across the exhaust ends of a plurality of the hot air ducts.

The heat responsive member may be tensioned by attaching a weight to one or both ends. If desired, one end of the heat responsive member may be secured to a fixture such as the frame of the grain dryer, in which case the weight or other tensioning means will be attached to the other end. Obviously only a relatively light tensioning is required so as not to risk breaking the elongate member under ordinary operating conditions.

Alternatively the heat responsive member may be in the form of a thermoplastic or combustible tube which can be tensioned lengthwise as described above and/or tensioned laterally by pressurising the interior of the tube with a gaseous medium. Preferably the gaseous medium will be such as not to support combustion, e.g. carbon dioxide. Thus the means responsive to loss or reduction of tension may sense loss or reduction of pressure in the tube due to puncturing of the tube or due to ballooning caused by thermoplastic deformation.

Associated with the or each tensioning means may be an electrical switch arranged to cut electric power to the hot air furnace of the grain dryer and the associated hot air circulating fan and to sound an alarm.

The heat responsive member may be trained over a series of pulleys in sinuous manner to extend across the exhaust outlets of all of the hot air ducts of a grain dryer or alternatively a plurality of such devices may be arranged to cover different zones of the grain dryer.

Thus in operation an unwanted rise in temperature of the air from any one of the ducts caused by an obstruction in the column will cause the elongate member to break or at least stretch if it is thermoplastic in nature, although it may be possible to arrange the apparatus will work if the elongate member is such that it shrinks on being subjected to high temperatures so that the tension in the member tends to rise. If the elongate member is in the form of twine or the like, it will be combustible and will burn and, ultimately, break. The same can be arranged to be so in the case of a pressurised tube.

Thus overheating will release or reduce the tension in the elongate heat responsive member and operate the switch(es) to shut down the heating means, to sound an alarm and switch off the fan to prevent as far as possible damage to the dryer and its contents. After the obstruction has been cleared, the device can be reactivated by replacing the length of twine or string or tube or perhaps in the case of the string by tying together the broken ends.

Although the invention has been described mainly in relation to a grain dryer it will be appreciated that the invention might also find application in heat detection of other devices especially involving heated air or other gases.

The invention is diagrammatically illustrated by way of example in the accompanying drawings, in which: Figure 1 shows schematically a heat detecting or sensing device applied to an agricultural grain drier; Figure 2 is a general perspective arrangement of an agricultural grain drier including the heat detecting or sensing device of Figure 1, and Figures 3) and 3b are respective end and side views of a detail of the heat detection device of Figure 1.

In the drawings there is shown a generally conventional agricultural grain drier 1 incorporating a heat detecting or sensing device 2 intended to detect fires such as sometimes occur when such driers are in use. The grain drier comprises a frame or housing 3 supporting a passageway (not shown) through which grain is conveyed eg mechanically and/or under gravity and having a plurality of air ducts 4, known as laterals through which heated air is passed to contact and dry the grain. If for any reason an air duct becomes blocked, eg due to a build-up of straw, the heat in the duct rises rapidly with the risk of a fire which can destroy the grain drier and its contents.

The heat detecting or sensing means 2 takes the form of a lightly tensioned cable 5, which may for example, be of string or baler twine or the like, stretched across the exhaust ends 6 of the air ducts 4 to sense the heat exhausted from the ducts. Obviously the cable will need to withstand the ordinary exhaust air temperature and we have found that ordinary thermoplastic polypropylene baler twine is adequate in this respect.

As can be seen in the drawings, we prefer to stretch a single length of cable 5 over the exhaust ends 6 of a plurality of the hot air ducts 4 so that a single detecting device can serve the grain drier if desired. The cable is trained over, or through, guides eg in the form of pulley wheels 7 or in the form of eyelets and at least one of its ends is connected to a detector generally shown at 8. The other end 18 of the cable 5 can either be connected to a separate similar detector 8 (not shown) or can be fixed against movement to any suitable part of the grain drier.

As shown in Figure 1, one end of the cable 5 is fixed to the free end 10 of a pivoted arm 9 so that the arm is suspended generally horizontally. Means 11 in the form of a pivoted arm and jockey wheel is provided to remove slack from the cable 5 when the heat detecting device is initially set-up. The arm 9 may be weighted as necessary with a weight 12 and/or may be urged downwardly by a tension spring 13. The arm carries on its upper surface one part 14 of an electrical switch, the other part 15 of which is fixed to a housing 16 enclosing the detector 8 such that if the arm falls due to loss of tension in the cable, eg the cable breakage 17 due to overheating of a duct 4, the switch is broken to cause the drier to shut down and to cause an alarm to be triggered so that the appropriate action can be taken to remove the obstruction before the occurrence of a serious fire.

Claims (18)

1. A method of detecting excessive heat at a given location comprising providing an elongate heat responsive member, positioning the member such that a portion thereof is at the location, tensioning the heat responsive member, sensing tension in the heat responsive member and actuating a detector device in response to variation or loss of tension.

2. A method according to claim 1, comprising positioning a portion of the elongate heat responsive member to be remote from the location.

3. A method according to claim 2, wherein the tension sensing is carried out remotely from the location.

4. A method according to any one of claims 1 to 3, wherein tension sensing is responsible to movement of the elongate heat responsive member.

5. A method according to any preceding claim, comprising tensioning the elongate heat responsive member by suspending a weight to one end of the member and fixing the other end of the member against movement.

6. A method according to any preceding claim, wherein the elongate heat responsive member is in the form of a tube, comprising tensioning the elongate heat responsive member by pressurising the interior of the tube with a gaseous medium.

7. A method according to any preceding claim, comprising arranging the elongate heat responsive member to extend into plurality of discrete locations in each of which heat detection is required.

8. A method of detecting heat substantially as hereinbefore described.

9. A heat sensing device for detecting excessive heat comprising an elongate heat responsive member, means arranging a portion of the heat responsive member at a location to be heat monitored, means tensioning the heat responsive member, means sensing loss of tension in the heat responsive member and a safety device operatively coupled to the sensing means for activation on loss of tension of the heat responsive member.

10. A heat sensing device according to claim 9, wherein the safety device comprises electrical switch means.

11. A heat sensing device according to claim 9 or claim 10, wherein the heat responsive member is thermoplastic or combustible.

12. A heat sensing device according to any one of claims 9 to 11, comprising weight means for tensioning the heat responsive member.

13. A heat sensing device according to any one of claims 8 to 12, wherein the heat responsive member is trained over a series of pulleys or guides in sinuous manner.

14. A heat sensing device according to any one of claims 9 to 13 wherein the heat responsive member comprises twine, yarn, string or cord.

15. A heat sensing device according to any one of claims 9 to 13, wherein the heat responsive member comprises an inflatable tube.

16. A heat sensing device according to any one of claims 9 to 15, wherein the tensioning means, the tension sensing means, and the safety device are disposed remotely of the location to be heat monitored.

17. A heat sensing device substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

18. An agricultural grain dryer comprising a heat sensing device as claimed in any one of claims 9 to 17.