GB2205427A

GB2205427A - Pipe freeze alarm

Info

Publication number: GB2205427A
Application number: GB08813152A
Authority: GB
Inventors: Simon Peter Fisher
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-06-03
Filing date: 1988-06-03
Publication date: 1988-12-07
Also published as: GB8713034D0; GB8813152D0

Abstract

A sensor is positioned in a loft space to sense the temperature of a water pipe, a water tank or the ambient atmosphere. When the sensor detects a near-freezing temperature an alarm is energized. As shown, the sensor is in the form of a bi-metallic switch BS which, when a near-freezing temperature is reached, closes to supply current from a battery B via a timer circuit T to an oscillator circuit O with causes a signalling device (e.g. a piezoelectric buzzer PZ) to emit an audible warning. The timer circuit T causes the buzzer to operate for a limited duration at periodic intervals to conserve power and prevent undue annoyance. Battery power can be tested by closing a switch SW: if the battery is in good condition, then the buzzer PZ will operate. In alternative arrangements, Figs. 1 and 2 (not shown), the sensor is in the form of a thermistor included in circuitry including a threshold level comparator. Other temperature sensors may be used. <IMAGE>

Description

Water pipe freeze alarm This invention relates to an alarm unit that indicates when water pipes are at or near freezing temperature.

Most dwellings in the U.K. have water tanks and associated pipes situated in the loft. In severe weather conditions where the outside temperature falls below freezing, the water in the pipes may freeze even if the pipes are lagged, whereu?on the flow of the water will be restricted and the pipes themselves may burst. It is difficult to know when this problem will occur.

There are convector heaters on the market fitted with frost detectors which operate around freezing point. These are however primarily used for greenhouses and the like, where frost could damage plants.

This type of heater if used in a loft suffers from the following disadvantages, thus, they require mains power via a mains extension cable since the lighting circuit normally in the loft may overload if the heater were to be Fcwe.ec ' this; the heater would be indisposed in the loft during cold weather which may be inconvenient; there would be no indication as to whether the heater is work inc; and the heat radiated is very directional and would only warm a small area making it ineffective a-nd uneconomical.

The present invention forewarns the user when the ambient temperature of the water pipes falls below freezing.

According to the present invention there is provided a water pipe freeze alarm in the form of a temperature sensor connected to an electric circuit, said circuit being housed in an enclosure comprising a comparing arrangement with a reference, and an oscillator driving some form of signalling device, said oscillator being driven from the output of the comparing arrangement.

In one embodiment of the invention a remote sensor, for example a thermistor, is moulded in a housing with means to attach wires thereof, said sensor coupled with associated components forming one input of a comparing device, the other input of which is a variable voltage reference giving a range of temperatures at which the output of said comparing device will switch to its opposite state.

The signalling device is preferably a sounder, for example a piezo-electric transducer, driven by an oscillator such that when activated the sound emitted is distinctive, for example, an audible high pitch two tone signal.

If preferred the signalling device is a light emitting device of the type that flashes when activated, secure in a visible position.

The sensor is preferably mounted as close to a water pipe or water tank as possible by way of, for example, screwing the afore mentioned moulded housing to a wooden iofe beam adjacent to said water pipe or water tank.

If desired the alarm unit may be powered from a battery, means for testing the condition of the battery being a switch, said switch when activated causing an appreciable electric current to be drawn fom the battery, and causing the s1nalling m2arìs to activate should the battery be in good condition.

If desired the alarm unit may be powered from rechargeable battery which may be trickle charged using small solar panel.

If preferred, the condition of the battery is automatically indicated by means of a signalling device such that when the battery is low, said signalling device will be activated.

In a further embodiment of the invention, means are provided to extend the life of the battery by switching the power on for a short time every five minutes, say, means provided to force the alarm unit to remain powered should the signalling means be activated.

The enclosure in which the alarm unit is housed is preferably wall mounted and preferably includes an easy access partition for the purpose of housing a battery or alternative powering means.

If desired, once the signalling means is activated, the signal may be switched off for a period of time by operating a switch, said switch when activated causing a delay, after which the signalling means will reactivate should the ambient temperature of the sensor still be below the chosen- reference temperature.

If desired, means for selecting aforementioned comparator reference being a switch or potentiometer, thus enabling a range of temperatures to be selected at which the signalling means will be activated.

If desired, the alarm unit could be adapted to switch on a mains powered device, for example a convector heater, by means of a relay, triac, thyristor or like switching device.

If preferred the electric circuit may be powered from the mains electricity supply, this supply being converted to direct current by means of, for example, a transformer and rectifier, or a resistive or capacitative dropper circuit and rectifier.

If preferred, the sensing device could be a bimetal strip, a thermocouple, a semiconductor sensor, or a thermistor type device.

If desired, the alarm unit could be combined with, for example, a smoke alarm, both alarm units sharing the same enclosure, powering means and signalling means.

If desired, the alarm unit could be adapted in such a way as to sense the temperature of two or more areas by electrical 'ORing' the output of each comparing arrangement, there being one comparing arrangement for each temperature sensor employed.

Reference will be made, by way of example only, to the accompanying drawings in which: Figure 1 is a circuit diagram of one embodiment of a pipe freeze alarm according to the present invention; Figures 2A, 2B and 2C collectively show a second embodiment of a pipe freeze alarm according to the invention; and Figure 3 is a circuit diagram of a third embodiment of a pipe freeze alarm according to the present invention.

Referring to Figure 1, thermistor Thl, remotely connected in series with current limiting resistor R1 and preset potentiometer VR1, and in parallel with interference suppression capacitor C4 forms the inverting input to op-amp IC1, the non-inverting input of which is an arrangement providing a variable reference comprising ranging resistors R2 and R3, potentiometers VR2 and VR3, and a single pole two way switch SW1. VR2 and VR3 are preset, one being set so that the alarm will activate when the ambient temperature of the sensor is just below freezing point, the other set so that the alarm will activate at a lower temperature, the required temperature being selected by switch SW1.The function of VR1 is to bring the thermistor voltage level into range, R1 being a relatively high value to limit the current used by the circuit. Feedback resistor R4 provides the op-amp IC1 with hysteresis.

Resistor R5 prevents the op-amp output from shorting to OV when the battery test switch SW2 is pressed and furthermore the value of R5 is chosen so that- when switch SW2 is pressed an appreciable current is drawn in order to adequately test the condition of the battery.

The output of the op-amp IC1 when switched low enables two oscillators, the first of low frequency comprising resistors R6 and R7, capacitor C1, and NOR gates IC2a and IC2b; the second of high frequency comprising resistors R9 and R10, capacitor C2, and NOR gates iC2c and IC2d: The high frequency oscillator drives the piezo electric sounder LS1 at a nominal frequency of approximately 3.8 KHz.

Diode D1, in series with current limiting resistor R8, when forward biased by a logic high on the output of NOR gate IC2b, will alter the time constant of the high frequency oscillator.

The low frequency oscillator runs at a nominal frequency of approxlmately 1 Hz thus altering the pitch of the piezo-electric sounder appreciably twice every second producing a distinctive two tone soun.

Referring to figure 2A, the electric circuit illustrated is essentially similar to that shown in figure 1, and acts as one input to the logic circuit shown in figure 2C.

Thermistor Thl has a greater effective range due to the decrease in the value of series resistors R1 and R3 when compared to that of figure 1. VR1 and VR2 are preset at the manufacturing stage ensuring that all alarm units operate at the same temperatures. Feedback resistor R6 provide-s op-amp IC1 with hysteresis, the active high output labelled A being one input to the logic circuit shown in figure 2C. C1 and C2 are interference suppression capacitors.

Referring to figure 2B1 the battery condition circuit illustrated comprises op-amp IC2, one in-put being a fixed voltage reference provided by zener diode Z1, the other input derived from the battery supply voltage. Feedback resistor R10 provides the active high output of the op-amp with hysteresis.

The output of the op-amp IC2, labelled B provides one input to the logic circuit shown in figure 2C, the zener diode chosen such that the output of IC2 goes high at a supply voltage of around 7 volts, assuming a 9 volt battery supply.

Referring to figure 2C, the logic circuit illustrated is clocked by a low frequency oscillator labelled L.F.O.

IC5 is a 6 input logical AND gate, which when the output labelled C is a logic high, powers the analogue circuits shown in figures 2A and 2B. The inputs to ICS are the Q2 through Q7 outputs of a 12 bit binary up counter IC3, thus powering the analogue circuits for 4 cycles every 256 of the L.F.O., ie 1/64th of the time. To allow -the analogue circuits to settle before being sampled after power up, TC9a is employed to provide the clock inputs to D-type latches IC4a and IC4b, thus latching the inputs labelled A and B a further 3 cycles of the L.F.O. after output C goes high.The L.F.O. is a very low power square wave oscillator with a frequency of approximately 1 Hz.

Resistor Rll and capacitor C3 keep the clear inputs to the two D-type latches i04a and 104b at an active high state long enough after power up to ensure that their outputs Q are low initially.

The output of 3 input logical NOR gate IC8a will be at a logic high state for the first 512 L.F.O. clock cycles, and low for the remaining full cycle period of 12 bit binary counter IC3. The output of IC8a, through invertor IC7, ensures that the SR flip-flop IC10 is normally in a reset condition, the NOT Q output of IC10 being at a logic high.

In the specific case where a low temperature condition is reached and the battery is in good condition, input A will settle in a high state after powering up of: the temperature sensing circuit and will then be latched to the output of IC4a when the output of IC9a goes to a logic high.

The transition of the output of IC4a from logic low to logic high will reset the 12 bit counter via C5 and R12, and cause the counter outputs Q9, Q10 and Q11 to remain in å logic low state, thus keeping the output of IC8a in a logic high state.

With threes of the four inputs to the logical AND gate IC9b at a logic high, the output of this gate and hence the output of IC8b, will change state at the L.F.O. frequency, thus enabling a high frequency oscillator labelled H.F.O. to drive the piezo-electric sounder LS1 in a repetitive manner.

Once the alarm is activated the sounder will continue to sound for 512 cycles of the L.F.O. whereupon the Q9 output of the counter IC3 will change to a logic high state switching the output of IC8a low, disabling logical AND gate IC9b, and consequently silencing the sounder until the Q9, Q10 and Qil outputs of counter IC3 all go to a logic low state. This arrangement reduces the power consumption of the circuit by enabling the sounder for 1/8th of the time that the temperature low condition is met.

During the active part of the alarm sounder cycle, the sounder can be silenced until the next cycle begins by pressing the push-to-make momentary contact switch 5W2. This action takes the output of the two input logical AND -- gate IC6b to a logic high, thus setting the flip-flop 1010 and disabling the logical AND gate IC9b.

For the time that the contacts of switch SW2 are made, the output of the two input logical AND gate IC6c will follow the L.F.O. enabling sounder LS1 through IC8b and the H.F.O. This allows part of the unit to be tested by the -user.

In the specific case where the battery supply voltage is low, below say 7 volts a-ssuming a 9 volt battery is used, and a temperature low condition has not been met, the input B will settle in a high state after powering- up of the battery condition circuit, and the Q output of IC4b will go to a logic high state. Once this condition is reached, a bleep lasting for a single cycle of the L.F.O. will be heard@ froni the sounder. This will re-occur every 256 cycles of the L.F.O.

by logically Aiding the output of ICtb with the output of IC9a.

If CMOS technology is utilised in the circuits of figures 2A, 2B and 2C, then it would be possible to power the alarm unit for a few years with the same 9 volt battery. It is envisaged that a customized integrated circuit could perform the function of the logic circuit detailed in figure 2C.

Thus, the circuit shown in Figure 2C performs four functions, namely it controls the outputs from the temperature sensing and battery condition circuits, it reduces the overall power consumption of the alarm unit thereby prolonging the life of the battery, it enables the audible alarm signal to be temporarily silenced once activated, and it provides a means for testing the alarm unit.

In the embodiment shown in Figure 3, the thermistor is replaced by a bi-metallic switch BS which is normally open but which closes when the temperature of the associated pipe or of the surrounding atmosphere approaches the freezing point of water. Such closure of the switch connects a battery B to a timer circuit T having two transistors TRA and TRB: this circuit supplies power to an oscillator circuit 0 in such a manner that the oscillator operates for a limited duration at periodic intervals (e.g. 5 seconds every 15 minutes). This not only conserves battery power but also prevents undue annoyance which might otherwise be caused by a continuous alarm signal. The oscillator circuit 0 itself comprises two oscillators which operate at high and low frequency, respectively. The high frequency oscillator (designated generally as HFO) powers a piezoelectric buzzer PZ and is switched on and off by the low frequency oscillator LFO at.such a rate that a warbling sound is produced. An integrated circuit is employed as part of the oscillator circuit, and comprises a CMOS quad logical NAND Schmitt trigger, each such trigger being designated IC in Figure 3.

For the purpose of testing the alarm, a momentary contact push-to-make switch SW is closed and this connects the battery B to the oscillator circuit 0 by-passing the timer T in the process, so that the buzzer PZ will produce a continuous warble for the time the switch -5W is closed if the battery is in good condition.

In each of the above-described embodiments, the sensor (i.e.

the thermistor or the bi-metallic strip) is preferably contained in-a housing separate from the remainder of the alarm, so that it can be positioned near e.g. a pipe or water tank. The housing can be provided with screw holes to enable the sensor to be mounted on a wooden beam in the loft adjacent to the pipe or tank. The remainder of the alarm can be housed in an enclosure which is wall-mounted, the enclosure having an easy access partition for housing the battery or whatever other power source is employed. This power source can be a rechargeable battery which is trickle-charged from a small solar panel. Alternatively, the alarm can be powered from a mains electricity supply, in which case suitable circuitry will be needed to convert the mains signal into a direct current.

Although the above embodiments describe the invention with reference to a signalling device which produces an audible warning, a visual warning can be provided instead of or as well as this; for example, a light-emitting element which flashes when activated can be used.

Instead of providing for battery testing upon demand, the alarm can be arranged so that a signal is automatically given when the battery charge falls to a low level.

In addition to emitting a visible or audible warning in response to a- fall in temperature'to near-freezing, the alarm can also be arranged to activate a device (such as a convector heater) by means of a switching device such as a relay, triac or thyristor.

In the above description, reference has been made to the sensor being in the form of a thermistor or a bi-metallic strip. Other forms of sensor can however be used, such as a thermocouple platinum resistance thermometer or a semiconductor sensor.

In a modified arrangement (not shown), the alarm includes two or more sensors which can be disposed at various locations in a loft space, and the sensors are connected to the remainder of the alarm by suitable OR logic circuitry so that the alarm will operate when any one of the sensors detects a near-freezing temperature.

The alarm unit can be combined e.g. with a smoke alarm, with both alarms sharing a common enclosure, power source and signalling device.

In an alternative embodiment of the invention (not shown), the sensor is set so as to operate at a rather higher temperature and is contained in the same casing as the remainder of the alarm, so that the whole unit can then be employed e.g. as an alarm to indicate to elderly persons that the temperature of a room or a building has fallen below a level where there may be a danger of hypothermia. In this case, the alarm can be provided with a switch (e.g. in the form of a button) which can be operated to terminate the emission of an alarm signal.

Claims

1. A pipe freeze alarm comprisng a sensing circuit which includes a sensor adapted to sense the temperature of a pipe or the like or to sense ambient temperature, the sensing circuit being arranged to produce an output signal substantially when the temperature thus sensed falls 'below a predetermined level, and a signal generator which in response to said output signal operates a signalling device to produce an audible and/or visible warning.

2. A pipe freeze alarm as claimed in claim 1 wherein the sensor comprises a switch which operates when the sensed temperature reaches said predetermined level.

3. A pipe freeze alarm as claimed in claim 1, wherein the sensor produces a first signal in dependence upon the temperature sensed, the sensing circuit includes a comparator which compares the first signal with a second reference signal corresponding to said predetermined level and the sensing circuit produces its output signal when the first signal reaches the level of the second signal.

4. A pipe freeze alarm as claimed in claim 3, further comprising means producing a third reference signal corresponding to a predetermined temperature below the freezing point of water, and switch means enabling the second and third signals to be supplied selectively to the comparator.

5. A pipe freeze alarm as claimed in any preceding claim, wherein the signalling device emits an audible signal, and the signal generator comprises first and second generators which produce signals of relatively high and relatively low frequency, respectively, the first generator powering the signalling device and the second generator causing the signal produced by the first generator to alternate between two different frequencies.

6. A pipe freeze alarm as claimed in any preceding claim wherein the alarm is battery powered and includes means for testing the battery.

7. A pipe freeze alarm as claimed in claim 6, wherein the testing means when operated causes the signalling means to operate if a current drawn from the battery is above a predetermined level.

8. A pipe freeze alarm as claimed in any preceding claim, wherein a connection circuit connects a power source to the alarm for a limited duration at periodic intervals.

9. A pipe freeze alarm as claimed in any preceding claim, wherein the sensor is a bi-metallic strip, a thermocouple, a semiconductor sensor, platinum resistance thermometer or a thermistor.

10. A pipe freeze alarm as claimed in any preceding claim, wherein the signalling device comprises a piezoelectric transducer.

11. A pipe freeze alarm as claimed in any preceding claim, wherein the signalling device comprises a flashing lamp.

12. A pipe freeze alarm as claimed in any preceding claim, wherein the sensor is mounted in a housing remote from the remainder of the alarm.

13. A pipe freeze alarm as claimed in any preceding claim, further comprising a switching device which operates in response to the output signal from the sensing circuit to operate an external appliance, such as a heater.

14. A pipe freeze alarm substantially as hereinbefore described with reference to Fig. 1 or Figs. 2A, 2B and 2C or Fig. 3 of the accompanying drawings.

Amendments to the claims have been filed as follows CLAIMS 1. A pipe freeze alarm comprising a sensing circuit which includes a sensor adapted to sense the temperature of a pipe or the like or to sense ambient temperature, the sensing circuit being arranged to produce an output signal substantially when the temperature thus sensed falls below a predetermined level, and a signal generator which in response to said outputKsignal operates a signalling device to produce an audible and/or visible warning, the signalling device being thus operated for a limited duration at periodic intervals.

2. A pipe freeze alarm as claimed in claim 1, wherein a connection circuit connects a power source to the alarm for a limited duration at periodic intervals.

3. A pipe freeze alarm as claimed in claim 1, wherein operation of the signalling device by the signal generator is controlled by an enabling timer circuit.

4. A pipe freeze alarm as claimed in claim 1, 2 or 3, further comprising means which is manually operable to de-activate the signalling device once actuated.

5. A pipe freeze alarm as claimed in any preceding claim, wherein the alarm is battery powered and includes means operative to indicate automatically when the battery charge is low.

6. A pipe freeze alarm as claimed in any one of claims 1 to 4, wherein the alarm is battery powered and includes means for testing the battery.

8. A pipe freeze alarm as claimed in any preceding claim, wherein the sensor comprises a switch which operates when the sensed temperature reaches said predetermined level.

9. A pipe freeze alarm as claimed in any one of claims 1 to 7, wherein the sensor produces a first signal in dependance upon the temperature sensed, the sensing circuit includes a comparator which compares the first signal with a second reference signal corresponding to said predetermined level and the sensing circuit produces its ouput signal when the first signal reaches the level of the second signal.

10. A pipe freeze alarm as claimed in claim 9, further comprising means producing a third reference signal corresponding to a predetermined temperature below the freezing point of water, and switch means enabling the second and third signals to be supplied selectively to the comparator.

11. A pipe freeze alarm as claimed in any preceding claim, wherein the signalling device emits an audible signal, and the signal generator comprises first and second generators which produce signals of relatively high and relatively low frequency, respectively, the first generator powering the signalling device and the second generator causing the signal produced by the first generator to alternate between two different frequencies.

12. A pipe freeze alarm as claimed in any preceding claim, wherein the sensor is a bi-metallic strip, a thermocouple, a semiconductor sensor, platinum resistance thermometer or a thermistor.

13. A pipe freeze alarm as claimed in any preceding claim, wherein the signalling device comprises a piezoelectric transducer.

14. A pipe freeze alarm as claimed in any preceding claim, wherein the signalling, device comprises a flashing lamp.

15. A pipe freeze alarm as claimed in any preceding claim, wherein the sensor is mounted in a housing remote from the remainder of the alarm.

16. A pipe freeze alarm as claimed in any preceding claim, further comprising a switching device which operates in response to the output signal from the sensing circuit to operate an external appliance, such as a heater.

17. A pipe freeze alarm substantially as hereinbefore described with reference to Fig. 1 or Figs. 2A, 2B and 2C or Fig. 3 of the accompanying drawings.