GB1595314A

GB1595314A - Temperature monitoring devices

Info

Publication number: GB1595314A
Application number: GB133480A
Authority: GB
Original assignee: Spill-Fire Alarm Systems Ltd
Current assignee: Spill-Fire Alarm Systems Ltd
Priority date: 1978-05-08
Filing date: 1978-05-08
Publication date: 1981-08-12

Description

(54) TEMPERATURE MONITORING DEVICES (71) We, SPILL-FIRE ALARM SYSTEMS LIMITED, a British Company of 10/12 Cork Street, London W1X 2PQ, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to temperature monitoring devices.

It is desirable to be able to detect leakage of cryogenic liquids from vessels reliably and quickly in order to avoid undue wastage of the liquid and/or damage caused by same. A known method of detecting such leakage involves the use of temperature sensors, such as thermocouples and resistance bulbs, which may be arranged at different positions over the surface of the vessel or in the surrounding area. If, however, the leakage does not occur in the immediate vicinity of a sensor there may be an appreciable time lag before the sensor detects the leakage and in some cases the leakage may not affect the sensor at all due to evaporation of the liquid before reaching the sensor. This problem can be overcome by using many sensors but this is inconvenient and expensve.

An object of the present invention is to provide a temperature monitoring device which can be used for monitoring temperature changes over a relatively large extent.

According to one aspect of the invention therefore there is provided a temperature monitoring device comprising an elongate chamber containing a solution which undergoes an abrupt change in a physical property thereof due to crystallisation of a substance out of said solution saturated with said substance in response to a predetermined change in the temperature of all or a portion of said solution, and monitoring means for monitoring said property and sensitive to said abrupt change therein.

According to a second aspect of the invention there is provided a temperature monitoring device comprising a flexible elongate chamber containing a medium which undergoes an abrupt change in a physical property thereof in response to a predetermined change in the temperature of all or a portion of said medium, and monitoring means for monitoring said pro perty and sensitive to said abrupt change therein, said monitoring means comprising detection means operable to receive and respond to radiated energy transmitted through said medium and arranged to pro duce an electrical output on detection of a modification in said radiated energy trans misison due o said change in the physical property of the medium.

According to a third aspect of the inven tion there is provided a temperature monitoring device comprising an elonagte chamber containing a fluent medium which undergoes an abrupt change in a physical property thereof in response to a predeter mined change in the temperature of all or a portion of said medium, and monitoring means for monitoring said property, and sensitive to said abrupt change therein, said monitoring means comprising a pump operable to circulate said medium along the chamber and arranged to produce an electrical output in response to a change in power consumption of the pump due to a change in vscosity of the medium caused by said change in the physical property thereof.

With the arrangements of the above mentioned aspects of the invention, having regard to the form of the chamber it will be appreciated that temperature changes can be readily monitored over a relatively large extent. For example. sad chamber may be appropriately formed so that it can be applied in heat exchange relationship with the whole or a major part of a surface of large area.

The chamber may be in the form of a tube or may be of flattened form being de fined for example by two closely spaced sheets interconnected at their peripheries and possibly also inwardly of their peri pheries to define separate or interconnected compartments. The chamber preferably (and eventually in the second aspect of the invention) has flexible walls.

As to the nature of the said medium this may take any suitable form but preferably (and essentially in the case of the third aspect of the invention) it is of a liquid or fluent nature whereby it can conform more readily to the dispostion of the chamber especially where such chamber is flexible.

The use of a fluent or liquid medium in a flexible chamber is particularly advantageous for use in monitoring the temperature at the external surface of a large vessel in so far as such chamber can be wrapped around the vessel in contact with the external surface.

The invention may be utilised in the context of the detection of an abrupt fall in tempearture as for example to detect leakage of cryogenic liquid from a vessel; or the temperature monitoring device of the invention may be used at an elevated temperature where for example the transducer is to be used to detect cold spots or hot spots on the surface of a boiler. Also, the temperature monitoring device may be used in a protective capacity, for example, for protecting an enclosure, such as a room against fire, for protecting an enclosure such as a cold room, horticultural enclosure or the like against failure of refrigeration or heating equipment, for protecting a strong room, safe or article from unauthorised entry theren or tampering therewith using thermic lances, blow torches or the like, in which case the device responds to a predetermined temperature change in order that appropriate warning or remedial action can be taken. In this case, the elongate chamber of the temperature monitoring device may be appropriately shaped and disposed, for example the chamber may be an elongated rigid or flexible tube extending around or along a room, around the periphery of a safe door, or the like. Where temperature monitoring of a building or large room is to be effected for example for fire warning purposes, there may be a grid of separate, crossing chambers so that the location of an incidence of elevated temperature can be determined. Further, the temperature monitoring device may also be used for temperature monitoring purposes in relation to a large area or volume, or a number of separate areas and volumes, for example in a horticultural context or in a centrally heated building. In ths case, the temperature monitoring device may be particularly suitable in so far as it can be readily arranged to give a temperature averaging effect, that is the arrangement may be such that the detection means is responsive to an average change in overall physical properties of the said medium.

Still further, the temperature monitoring device may be used for detecting the level of material to which it is exposed. That is, the said chamber may etxend within a container containjing fia material such as a liquid or fluent particulate material whereby a level indication can be given in terms of a temperature indication, the temperature indeation being a function of the proportions of the length of the chamber which are respectively exposed to the material and to the air or other medium above the material.

The monitoring means may take any suitable form appropriate to the property of the medium to which it is to respond.

Thus, in the case of the first aspect of the present invention, where the property is electrical conductivity, the monitoring means may comprise electrodes in contact with the substance at different positions in the chamber and connected to a conductivity testing device such as an a.c. or d.c. bridge circuit. In the case of the second aspect of the present invention the monitoring means comprises a detection means operable to receive and respond to radiated energy, particularly light or sound waves, transmitted through said medium, such transmission being modified by change in properties of said substance such as by change in viscosity or production of crystals bubbles or other bodies which reflect or deflect the radiation. An ASDIC principle may be used. In the case of the third aspect of the present invention the monitoring means comprises a pump, for example a peristaltic pump which continuously circulates the medium through the chamber and responds to any change in viscosity by increasing its power consumption. In each case, the monitoring means may (and must in the case of the second and third aspects of the invention) produce an output signal of electrical form which can be used for operating a visual and/or audible warning device and/or an automatic system such as a sprinkler system.

The medium in the chamber may take any suitable form. Where the monitorable property of the substance is ts conductivity, the substance may be an electrolyte in the form of a liquid, gel or paste. Such electrolyte may comprise one or more inorganic compounds in an aqueous medium.

With regard to the second and third aspects of the invention, the abrupt change in the said property of the medium may be produced as a result of a phase change in the medium. In a particular preferred embodiment the abrupt change is a function of the change between liquid and liquid / solid states as for example when a salt crystallises out from a saturated solution of such salt.

Tn one embodiment of the first aspect of the invention, in the context of the detection of leaks in a vessel containing cryogenic liquid, the temperature monitoring device has the chamber thereof arranged for appleation to the outer surface of the vessel and containing a salt solution which is saturated at a temperature just below the normal range of ambient temperature (say at --20"C, and the detection means is sensitive to the electrical conductivity of the solution. With this arrangement, in the event of a leak, the cryogenic liquid contacts or a close to a portion of the chamber reducing the temperature thereof and causing salt to crystallise out from the solution at least at that portion of the chamber. The overall conductivity of the medium within the chamber changes abruptly and warning can be given of the leakage. The salt solution may comprise a mixture of water, a substance such as ethylene glycol which prevents freezing at ambient temperature, a further substance such as a mixture of Boric Acd and ammonium hydroxide which dissolves in the water and renders same of good electrical conductivity despite the poor conductivity of the glycol, and an ionic salt such as potassium nitrate with which the solution is saturated.

The invention will now be described further by way of example only and with reference to the accompanying drawing which is a diagrammatic view of one form of a temperature monitoring device according to the invention.

The temperature monitoring device is for use n detecting leakage of cryogenic liquid, such as liquid nitrogen, liquid natural gas or the like, from a vessel containing such liquid.

The device has a chamber 1 defined by a 15ft length of 1" diameter flexible black plastics tubing which is sealed at both ends 2,3. The tubing contains an aqueous solution of ethylene glycol boric acid ammonium hydroxide potassium nitrate The glycol content is such as to ensure that the solution will not freeze at a temperature of --20"C. The boric acid and ammonium hydroxide ensure that the solution has good electrical conductivity irrespectve of the potassium nitrate content.

The potassium nitrate content is such that the solution is saturated with this salt at --20"C.

The tube 1 is almost completely filled with the solution, a small space being left which is filled with an inert gas (say nitrogen) to accommodate expansion of the solution such as occurs on freezing of same.

Within the tube 1, there are two electrodes 4, 5 terminating in platinum or other corrosion resistant tips which are in contact with the solution at opposite ends of the tube. The electrodes pass through one sealed end 3 of the tube 1 and the electrode 5 which terminates remote from said end 3 is insulated along the length of the tube.

The end 3 of the tube is secured to an eletcrical junction box 6 and the electrodes 4, 5 are connected to terminals' in the box.

The terminals in the box are also connected to one arm of a bridge circuit (not shown).

The bridge crcuit is such that the current flow between the electrodes 4, 5 through the solution is not normally large and/or is of an a.c. nature having a frequency greater than 1000Hz so as to prevent polarisation problems in the solution. The bridge circuit has an output which is connected to a trigger circuit or the like which is arranged to actuate a warnng system when the bridge goes appreciably out of balance.

Tn use, the device is arranged with the tube 1 wrapped around the outer surface of the vessel. The bridge circuit is set so that it is in balance.

In the event that cryogenic liquid leaks from the vessel and contacts or is close to a portion of the tube 1, the temperature of the liquid within such portion will drop rapidly whereby potassium nitrate will suddenly crystallise out from the solution.

Removal of the ionic potassium nitrate from the solution, and conversion of the solution to a liquid/solid mixture of high solid content causes the conductivity of the solution as a whole to drop abruptly whereupon the bridge circuit goes out of balance and the warning system is actuated. The warning system may be arranged to operate a warning lamp or bell and/or may operate an automatic sprinkler system in the vicinity of the vessel.

The juncton box 6 is well sealed to ensure that there is no danger of electrically igniting leaking inflammable substances.

With the embodiment so far described it will be appreciated that a single device can be used to monitor a large surface area in a simple, convenient and inexpensive manner.

It is of course to be understood that the invention is not intended to be restricted to the details of the above embodiment which are described by way of example only.

For example, a smaller bore plastics tube, say 48 or t" bore may be used. The length of the tube will be selected in accordance with the intended use. Also, the tube may be attached in convoluted form to the surface of a flexible mat which is applied to the surface the temperature of which is to be monitored. Where the tube is very long, say over 50 metres, a higher a.c.

frequency, say in the MHZ range may be desirable to give a better signal/noise ratio.

Any suitable ionic salts other than those specifically mentioned may be used dependent on ionic mobility, conductivity, and solubility properties. Preferably, one or more salts of Group 1 elements, particularly lithium, sodium, potassium are used and possibly also rubidium, cesium, francium.

Reference is made to Application No.

05035/77 (Serial No. 1 595 313) from which the present Application was divided.

WHAT WE CLAIM IS: 1. A temperature monitoring device comprising an elongate chamber containing a solution which undergoes an abrupt change in a physical property thereof due to crystallisation of a substance out of said solution saturated with said substance in response to a predetermined change in the temperature of all or a portion of said solution, and monitoring means for monitoring said property and sensitive to said abrupt change therein.

2. A device according to claim 1, wherein said chamber also contains electrodes between which the solution extends, the solution is electrically conductive, the monitoring means comprises electrical detection means responsive to the electrical conductivity of the solution between the electrodes, and said change in the physical property of the solution is such as to influence said conductivity.

3. A device according to claim 2, wherein the solution is an electrolyte in the form of a liquid, paste or gel.

4. A device according to claim 3, wherein said electrolyte comprises an aqueous electrolyte.

5. A device according to any one of claims 2 to 4, wherein the electrodes are at opposite ends of the chamber.

6. A temperature monitoring device comprising a flexible elongate chamber containing a medium which undergoes an abrupt change in a physical property thereof in response to a predetermined change in the temperature of all or a portion of said medium, and monitoring means for monitoring said property and sensitive to said abrupt change therein, said monitoring means comprising detection means operable to receive and respond to radiated energy transmitted through said medium and arranged to produce an electrical output on detection of a modification in said radiated energy transmission due to said change in the physical property of the medium.

7. A device according to claim 6, wherein said radiated energy comprises sound energy.

8. A temperature monitoring device comprisng an elongate chamber containing a fluent medium which undergoes an abrupt change in a physical property thereof in response to a predetermined change in the temperature of all or a portion of said medium, and monitoring means for monitoring said property and sensitive to said abrupt change therein, said monitoring means comprising a pump operable to circulate said medium along the chamber and arranged to produce an electrical output in response to a change in power consumption of the pump due to a change in viscosity of the medium caused by said change in the physical property thereof.

9. A device according to claim 8, wherein said circulation means comprises a peristaltic pump.

10. A device according to any one of claims 6 to 9, wherein said abrupt change is due to crystallisation of a substance out of solution.

11. A device according to any one of claims 1 to 7, wherein the medium is a liquid or fluent medium.

12. A device according to any one of claims 1 to 11, wherein said chamber is a flexible-walled tube.

13. A device according to any one of claims 1 to 12, when used to detect leakage of cryogenic liquid.

14. A device according to any one of claims 1 to 12, when used for protecting an enclosure, such as a room against fire.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

desirable to give a better signal/noise ratio.

Any suitable ionic salts other than those specifically mentioned may be used dependent on ionic mobility, conductivity, and solubility properties. Preferably, one or more salts of Group 1 elements, particularly lithium, sodium, potassium are used and possibly also rubidium, cesium, francium.

Reference is made to Application No.

05035/77 (Serial No. 1 595 313) from which the present Application was divided.

WHAT WE CLAIM IS: 1. A temperature monitoring device comprising an elongate chamber containing a solution which undergoes an abrupt change in a physical property thereof due to crystallisation of a substance out of said solution saturated with said substance in response to a predetermined change in the temperature of all or a portion of said solution, and monitoring means for monitoring said property and sensitive to said abrupt change therein.
2. A device according to claim 1, wherein said chamber also contains electrodes between which the solution extends, the solution is electrically conductive, the monitoring means comprises electrical detection means responsive to the electrical conductivity of the solution between the electrodes, and said change in the physical property of the solution is such as to influence said conductivity.
3. A device according to claim 2, wherein the solution is an electrolyte in the form of a liquid, paste or gel.
4. A device according to claim 3, wherein said electrolyte comprises an aqueous electrolyte.
5. A device according to any one of claims 2 to 4, wherein the electrodes are at opposite ends of the chamber.
6. A temperature monitoring device comprising a flexible elongate chamber containing a medium which undergoes an abrupt change in a physical property thereof in response to a predetermined change in the temperature of all or a portion of said medium, and monitoring means for monitoring said property and sensitive to said abrupt change therein, said monitoring means comprising detection means operable to receive and respond to radiated energy transmitted through said medium and arranged to produce an electrical output on detection of a modification in said radiated energy transmission due to said change in the physical property of the medium.
7. A device according to claim 6, wherein said radiated energy comprises sound energy.
8. A temperature monitoring device comprisng an elongate chamber containing a fluent medium which undergoes an abrupt change in a physical property thereof in response to a predetermined change in the temperature of all or a portion of said medium, and monitoring means for monitoring said property and sensitive to said abrupt change therein, said monitoring means comprising a pump operable to circulate said medium along the chamber and arranged to produce an electrical output in response to a change in power consumption of the pump due to a change in viscosity of the medium caused by said change in the physical property thereof.
9. A device according to claim 8, wherein said circulation means comprises a peristaltic pump.
10. A device according to any one of claims 6 to 9, wherein said abrupt change is due to crystallisation of a substance out of solution.
11. A device according to any one of claims 1 to 7, wherein the medium is a liquid or fluent medium.
12. A device according to any one of claims 1 to 11, wherein said chamber is a flexible-walled tube.
13. A device according to any one of claims 1 to 12, when used to detect leakage of cryogenic liquid.
14. A device according to any one of claims 1 to 12, when used for protecting an enclosure, such as a room against fire.