WO1989012216A1

WO1989012216A1 - Apparatus for registering leakage or unintended consumption in a pipe system

Info

Publication number: WO1989012216A1
Application number: PCT/DK1989/000146
Authority: WO
Inventors: Jørgen Askløf HANSEN; Ole Nygaard Christensen
Original assignee: Iss Electronics A/S (Automatik Division)
Priority date: 1988-06-10
Filing date: 1989-06-09
Publication date: 1989-12-14
Also published as: DK315488A; DK315488D0

Abstract

Apparatus, especially for detecting leakage or unintended consumption in pipe systems, of a type, the mode of operation of which is based on heat transmission. The design of the apparatus is such that its use does not necessitate intrusion into the installation of the pipe system. The adjustable electronic system of the apparatus collects the measured results at predetermined periods and triggers warning or alarm signals, as required by the user.

Description

APPARATUS FOR REGISTERING LEAKAGE OR UNINTENDED CONSUMPTION IN A PIPE SYSTEM The invention relates to a system capable of indicating low flow of a flowing, heat-conducting medium in a pipe system, and its design differs considerably from the volumetric or mass flow meters com¬ mercially available at the present time.

Movement of a flowing medium in a pipe system is measured by means of well-known volumetric flowmeters. The following meters are in use:

Orifices

Venturi tubes or nozzles - Propeller-type meters Woltmann meters Magnetic-inductive meters Ultrasonic meters Pluidistor meters - Coriolis meters

All these meters have this in common that the design aims at measuring volumetric amounts per unit of time within a limited, although frequently large, dynamic range, with the maximum attainable accuracy.

Common to these meters is also the fact that they can only be mounted by intrusion into the existing pipe system.

Since volumetric flowmeters are frequently used for determining volumetric consumption or when measuring the amount of energy used, the aim is to achieve optimal accuracy of the meter when the velocity of the medium as it passes through the meter is high. On the other hand it may be stated that the lower the volumetric flow, the more difficult it is to measure the flow of medium accurately, and below a certain volumetric flow the meter stalls or it is not possible to rely on the reading of the meter owing to great uncertainty in the environment. Most volumetric flowmeters are so designed that their medium, flows through the meter in the direction which is the metering direction of the meter. In the opposite case the meter will either not work at all or will also indicate undefinable 5 results.

It follows that the volumetric flowmeters known at present are not suitable for determining reliably whether movement in the medium has ceased or whether the medium is moving very slowly to or fro.

In water lines or other lines containing a fluid unintended movements .0 can occur in the medium owing to large or small leaks in the system, if the system is otherwise locked as regards intended movements of medium.

Such unintended movements in the medium may, for instance, occur in ^• the water supply system of a one-family house owing to leaking pipe i5 joints, dripping taps, deteriorated packings, pipe fissures etc., even if all tapping points are closed.

In such situations the medium will move in the direction toward the leaks. The location and size of an unintended leak cannot be predicted, nor is it therefore possible to predict the direction in 0 which the medium will move and the amount of flow. In view of this fact the volumetric flowmeters known today are not suitable for determining whether the medium is stationary or not.

In the sphere of house construction it has, during the recent decades, been very common to hide away water pipe installations, partly by

25 embedding them within walls, and partly by laying them below floors. Currently such installations give rise to ever mere cases of damage owing to feeble but persistent leakage of water from fissures in the system. Frequently such damage is noticed only after a long time, when it is both costly to repair and a great inconvenience for the

30 residents owing to the extensive repairs involving the breaking open of floors etc. To prevent such damage, a few leakage detectors are today com¬ mercially available. These are based on a mechanical rotary- meter principle with corresponding electronics and are relatively expensive, entailing, in addition, installation costs to the 5 customer.

It is the object of the invention to provide a low-cost apparatus capable of detecting leakage in the installation of a pipe system conducting a fluid, by a technology which does not require intrusion into the installation of the pipe system.

"10 The object of the invention is achieved by the system being designed as specified in the characterising part of claim 1 as also the detailed explanation contained in the following sections.

The invention is based on the physical phenomenon that a homogeneous heat-conducting medium conducts heat uniformly in all directions .5 away from a heating element which is directly or indirectly in contact with the medium, as long as the medium is stationary.

The amount of heat conveyed depends on the heat conducting capacity of the medium and on the difference in temperature between the heat source and the medium. If the medium is in motion, more heat is 0 transported in the direction in which the medium is moving.

If temperature-sensing elements are fitted abcut and in the proximity of the heat source they make it possible to detect whether the medium is stationary or in motion.

Flowmetering based on this principle is kncwn, inter alia, from US 5 patents nc. 4-391.137 and 4.400.975- These and other patents based on the same principle have this in common that both the heat source and the sensing elements are fitted within the medium or contained within an apparatus which must be installed within the pipe system itself, e.g. US patent 4.255.968. The invention provides for a technological novelty in that the heat source, the heat-sensing elements and most of the corresponding electronics are installed in a removable structure surrounding the pipe in which medium movements or leakages are to be mesured. As a result a low-cost product is achieved, which does not necessitate intrusion into the pipe system and can, in its special embodiment, be portable, e.g. for servicing purposes.

The main feature of the design of a leakage meter according to the invention is shown in fig. 1.

In casing (K) , which is in contact with the actual pipe (R) of the water system, a heating element (Hi) is installed, together with three heat sensors (D1), (D2) and ( 3) • The heat element (Hi) is installed in casing (HiJ so that (Ξ1) is in contact with the bottom of pipe (R) . The three heat sensors are in contact with the top of the pipe, sensor (D2) being in the middle directly above the heating element, while sensors (D1) and ( 3) are at equal distances to the right and to the le t of sensor (D2) .

The measuring principle accordingly consists in the fact that heat is periodically supplied to the bottom of the pipe via heating element (H.). If there is no flow in the pipe, the heat will rise vertically and heat up (D2) by comparison with (D"l) and (D3), whereas the relationship between (Dl) and (D3) will not be affected. If, for instance, there is a slight flow towards the right, the heat will flow towards the right and heat up (D3) by comparison with (D ), and if there is an intense flow, the heat will be conducted away without heating up any of the sensors.

A possible low-cost electric circuit for measuring leakage is shown in the block diagram in fig. 2. At the bottom left is shown the flow transducer. By way of temperature sensors use is made of SMD diodes with a temperature coefficient of about 2 mV/°C, the cost of which is low. The voltages across sensors D1 and D3 are transmitted tc input amplifier 1 , which is an instrument ampli ier with a differential gain of 1000. The voltage across sensor D2 and the mean value of D. and 3 are transmitted to input amplifier 2, like¬ wise an instrument amplifier with a differential gain of 1000.

In order to compensate for differences in the base values of the sensors and possible static temperature differences along the pipe, each instrument amplifier is provided with a zeroing circuit. The zeroing circuit consists of two 6-bit digital/analog-converters and an operational amplifier.

Two comparators are connected to the outlet of each instrument amplifier. One comparator compares the output voltage of the amplifier with 0 volt and controls the zeroing circuit accordingly. The other compares the output voltage of the amplifier with a reference voltage and gives a signal when the temperature difference at the sensors causes the output voltage of the amplifier to exceed this value.

For controlling the various functions a timing circuit is provided, and, for reading data and triggering an alarm if a leak is registered, there is a control circuit with a number of light- emitting diodes as well as an acoustic alarm generator. Lastly the system comprises a heating unit, which consists of a transistor operating as a constant current generator and which, during the heating period, receives, for instance, 3 W.

A simple measuring cycle is described below with a view to explaining the leakage detector's method of operation. The sequence of the various timing signals can be sketched as shown in fig. 3_'

The sequence is introduced with the circuit at zero. When timing- signal 1 is "1", the output voltage of the D/A coarse converter increases step-by-step. This voltage is fed via an operational amplifier and a divider resistance network, to one minus input of the instrument amplifier, whereas the other minus input is supplied, via a voltage divider, with a reference voltage in the middle of the operational range of the D/A-converter. During this process the output voltage of the instrument amplifier will drop step-by-step, dropping at a certain point in time below the comparator's reference value of 0 volt. This causes the output of the comparator to go to "1"_. which locks the D/A coarse converter in its current position. Once the D/A coarse setting is completed, the timing 2 signal goes to "1", which causes the voltage, of the D/A fine converters to increase step-by-step. This voltage is divided by 50, and the D/A coarse voltage to the instrument amplifier is subtracted via the operational amplifier. The output voltage of the instrument amplifier will then increase in steps amounting to 1/50 of the steps of the D/A coarse setting. In this process the output voltage will again, at a certain point of time, exceed the comparator's reference value of 0 volt, which causes the output value of the comparator to shift to "0". This locks the D/A fine converter at the current value, and the zeroing procedure is completed.

Once zeroing has been completed, the timing 3 signal goes to "1". The signal activates he heating unit, and the pipe is heated by 3 f for 32 seconds. The heating period is followed by the measuring period, during which the timing 4 signal is "1". During the measuring period, which lasts for 32 seconds, a comparator compares the current output voltage of the instrument amplifier with the output voltage prior to application of heat, and if this difference exceeds a predetermined limit value, depending on the comparator's reference voltage, a signal goes to the control unit, which stores this information.

The last sequence of the measuring procedure consists in treatment of the signals registered and reading the results. This takes place when the timing 5 signal is "1".

Once each of the two transducer units has either registered or not registered some temperature deviations at the sensors, the following probability table can be devised, in which "1" indicates a registered temperature deviation.

Transducer 1 Transducer 2 Result (side sensors) (middle sensor)

0 0 High flow 0 1 No flow

1 0 Medium flow

1 1 Low flow

The result is read from the light-emitting diodes and continues to be indicated by them until the result from the next measurement is available. This concludes the measuring procedure, and there follows a pause of 17 minutes duration, enabling the transducer to stabilise thermally, and after those 17 minutes the above procedure starts again. The results of the various measurements are stored, and if, over a period of 24 hours, no "no flow" result is registered at any point of time, the alarm is activated, which may be a light signal, an acoustic alarm, a telephone contact etc.

The user must then acknowledge the alarm and decide whether there has been continuous consumption during the most recent period of 24 hours or whether the alarm is due to an unintended leak from the system.

However, there is nothing to prevent the electronic system of the apparatus to be designed in such a way that registration cf a "high flow" result immediately activates the alarm, during periods in which the user requires such a function.

The sensitivity of the leakage meter can be adjusted, depending entirely on the type of pipe on which the apparatus is mounted. A flow of less than 0.6 litre/hour may, for instance, be detected in a 3/4" pipe where the water temperature amounts to about 25°C. The invention is characterised in that the leakage meter is mounted on the outside of a pipe pertaining to the system in which leakage, if any, is to be detected. It may be mounted permanently but there is no reason why the apparatus should not be moved from system to system with a view to carrying out servicing tasks.

A possible design of the leakage meter according to the invention is shown in fig. 4_» hoth in section and pictorially.

The casing of the apparatus encompassing pipe 1 , consists of two half parts, an upper part 2 and a lower part > . These half parts are clamped together about pipe 1 with the aid of locking or fastening elements such as screws _° At both ends of the casing are inserted replaceable two-part elastic guide bushes 5, which, on the one hand, make it possible to mount the leakage meter on pipes of different dimensions, while, on the other hand, preventing moisture from entering the meter in this way.

In the lower part 3 is mounted pcb 6 with corresponding electronics and with a heating element J.

In upper part 2 is mounted pcb 8 with corresponding electronics and three sensor elements 9_. 10 and 11.

Both heating elements 7 and sensor elements 9. 10 and 11 may be by simple means displaceable at right angles to the longitudinal direction of pipe 1, thus ensuring that any obliquenesses and diametral faults of the pipe do not influence the contact pressure between the pipe and the sensor elements and the heating element, respectively.

The contact pressure exerted by heating element 7 and sensor elements 9. 10, 11 on pipe 1 is ensured with the aid of spring elements 2. Another possible design of sensor pcb 8 may consist in the fact that three copper electrodes are soldered directly into the pcb, as shown in fig. 5. and in that three SMD S0T89 transistors 15 are used there by way of temperature sensors, said transistors being soldered on to the pcb next to the respective electrodes in such a way that the copper tracks on the pcb provide the thermal connection between the copper electrodes and the cooling surface of the SMI transistor soldered directly to the copper track on the pcb.

Using an SMD SOT89 transistor in this way is novel, since the cooling surface serves by way of heat-receiving connection.

This procedure ensures by simple means thermal contact between pipe 1 and the signal-generating unit-(15) •

Pcb 8 with the three soldered sensor elements 9_. 10 and 1 | can be displaced at right angles to the longitudinal direction of pipe 1 located in half part 2, and is pressed against pipe 1 with the aid of spring elements subject to a constant force K.

Good heat transmission between the pipe and the heating element or the pipe and the sensor elements, respectively, is achieved with the aid of known technical means such as cambered surfaces, heat- sink compound (14) or heat-conducting rubber between the pipe and the elements. The current supply to the electronics of the meter and signals from the meter to the control unit can be conducted through cable 13- However, there is nothing to prevent both the current supply and the control unit from being installed in the meter casing. This solution can be chosen if the leakage meter is a transportable apparatus.

According to the invention the leakage meter requires no intrusion into the pipe system and can be assembled by the user himself. In view of the simple, maintenance-free design of the apparatus as well as its small dimensions and modern electronics, it is a technical novelty which at reasonable costs can ensure private and collective savings.

Claims

1. Apparatus for registering flow in a liquid-filled pipe system, e.g. a water system in a house or industrial plant, registration of the flow being achieved with the aid of the physical phenomenon according to which a heat-conducting medium conducts heat in all directions away from a heating element directly or indirectly in contact with the mediums, and with which the path in which heat is conducted is detected by attachment of at least one heating element and at least one sensor directly or indirectly in contact with the medium, c h a r a c t e r i s e d in that the apparatus is used above all for registering leaks or unintended consumption in the system, and in that the apparatus consists of design units, preferably two half parts 2 and 3. which, in detachable manner, encompass pipe 1, in which the medium can move, and in that the apparatus can thereby be mounted without intrusion into the pipe system in which leakage is to be detected, and in that in one half part 3 a heating element 7 s fitted together with the corresponding electronics on pcb 6, and in that in the other half part 2 are fitted electronics on pcb 8 together with three sensor elements 9_. 10 and 11, so that sensor element 9 is located diametrally opposite heating element 7_. whereas sensor element 10 and sensor element 11 are located symmetrically about sensor element 9 at the same level, and in that both heating element 7 and the three sensor elements 9. 10, 11 can be displaced at right angles to the longitudinal direction of pipe 1 and are acted upon by means of spring elements exerting a force K in the direction of the pipe ensuring a constant contact pressure between pipe 1 and elements 7_. 9_. 10 and 11.

2. Apparatus according to claim 1, c h a r a c t e r i s e d in that the apparatus has an electronic control circuit so designed that heating element 7 is heated for a relatively short period followed by a measuring period, a pause period following at the end of the measuring period, and in that the duration of the pause period is considerably longer than that of the heating and measuring periods jointly, and that the individual periods can be adjusted entirely in accordance with the dimensions of the pipe system, and in that the various measuring results are stored in the memory of the electronic system.

3. Apparatus according to claims 1 and 2, c h a r a c t e r - i s e d in that the apparatus comprises an electronic unit processing the measuring results stored in the memory and that, if during a predetermined period, e.g. in the course of 24 hours, no "nc flow" result is registered at any point of time, an alarm signal is activated.

4- Apparatus according to claim 1, c h a r a c t e r i s e d in that the sensor elements 9, 10 and \\ can be displaced simply and irrespective of one another at right angles to the longitudinal direction of pipe 1 , and in that each of these sensor elements is acted upon by a force exerted by spring element 1 in the direction of pipe 1.

• Apparatus according to claim 1, c h a r a c t e r i s e d in that the sensor elements 9_> 10 and 11 are soldered to printed tracks of pcb 8 and in that the cooling surface of an appropriate SMI¹-type transistor 15 is soldered to the same printed track in the proximity of each sensor element, and in that the cooling surface of transistor 15 serves as a heat-receiving connection with the signal-generating element, which is itself transistor 15, and in that pcb 8 with the three soldered sensor elements 9. 10 and H is mounted so that it can be displaced at right angles to the longitudinal direction of pipe 1 , and in that the pcb is acted upon by at least one spring element exerting a force in the direction of pipe 1.

6. Apparatus according to each of the preceding claims, c h ar a c t e r i s e d in that the apparatus is transportable.