In particular, the present invention relates to a sensor unit for measuring the temperature and/or pressure of hot water flowing out of a domestic installation gas-fired water heater (sometimes called a"boiler").

Use of water pressure sensors to measure the output of a domestic water heater is relatively new.

Water heaters currently use water pressure gauges and pressure switches for measuring small changes in air pressure and other water heaters used just temperature sensors (for example one at the inlet and one at the outlet and a safety bimetal thermostat). New models of water heaters make use of a signal output by a pressure sensor to ensure more efficient functioning of the heater. Also temperature sensors sensing the temperature of water output by water heaters are used.

It is a technical problem to install pressure sensors and/or temperature sensors in a pipeline leading to and/or from a water heater. Often this involves time-consuming drilling and fixing operations on site with an operator having to drill into pre- assembled pipework and then fix one or more sensors to the pipework.

In a first aspect of the present invention there is provided a sensor unit connectable in a water pipeline of a water system of a domestic water heater, the sensor unit comprising: a housing; and

a pressure sensor located in the housing and operable to provide an electrical signal indicative of water pressure; wherein: the housing has a communication aperture in a surface thereof which allows communication of water pressure to the pressure sensor located in the housing; and the housing comprises a pipe section connectable in the water pipeline as part of the pipeline so that water flowing in the water pipeline flows through the pipe section; and the communication aperture is formed in an inwardly facing surface of the pipe section.

In a second aspect of the present invention there is provided a sensor unit connectable in a water pipeline of a water system of domestic water heater, the sensor unit comprising: a housing; and a temperature sensor located in the housing and operable to provide an electrical signal indicative of water temperature; wherein: the housing has an arm which when the sensor unit is connected in the water pipeline extends towards a centre of a water flow and which has located therein at least a part of the temperature sensor; the housing comprises a pipe section connectable in the water pipeline as part of the pipeline so that water flowing in the pipeline flows through the pipe section; and the arm is an integral part of the pipe section which extends inwardly towards the centre of the pipe section.

The present invention provides in a third aspect a sensor unit connectable in a water pipeline of a water system of a domestic water heater, the sensor unit comprising: a housing; a pressure sensor located in the housing and operable to provide an electrical output signal indicative of water pressure; and a temperature sensor located in the housing and operable to provide an electrical output signal indicative of water temperature; wherein: the housing has a communication aperture in a surface thereof which alldws communication of water pressure to the pressure sensor located in the housing; and the housing has an arm which when the sensor unit is connected in the water pipeline extends towards the centre of a water flow and which has located therein at least a part of the temperature sensor; the housing comprises a pipe section connectable in the water pipeline as part of the pipeline so that water flowing in the pipeline flows through the pipe section; the communication aperture is formed in an inwardly facing surface of the pipe section; and the arm is an integral part of the pipe section which extends inwardly towards the centre of the pipe section.

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a schematic cross-section through a first embodiment of a combined pressure and temperature sensor unit according to the present invention;

Figure 2 is a schematic perspective exterior view of the first embodiment of sensor unit; and Figure 3 is a schematic exterior view of a second embodiment of combined pressure and temperature sensor unit according to the present invention.

Turning first to Figure 1, there can be seen a combined pressure and temperature sensor unit 10. The unit 10 is an in-line unit connected in a water pipeline of a water system comprising a domestic water heater. For instance, the unit 10 can be connected in an outlet water pipe leading from a domestic water heater, as will be described later.

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The unit 10 has a housing comprising a pipe section 11 and a cover 12. Located in the unit 10 there are a pressure sensor 13 and a temperature sensor 14. The sensors 13 and 14 are located in a cavity defined between the pipe section 11 and the cover 12. The sensors 13 and 14 are embedded in the unit 10 and are integral parts thereof.

The pipe section 11 is L-shaped. The sensors 13 and 14 are located at an elbow part of the pipe section. A boss 15 extends inwardly into the flow channel at the elbow and also an arm 16 extends inwardly into the flow channel, to a greater degree than the boss 15. The boss 15 and the arm 16 are both integral features of the moulded pipe section. An aperture 17 is provided in the boss 15 and this allows communication of the water in the pipe section 11 with the cavity housing the pressure sensor 13. The arm 16 provides a shroud for the temperature sensor 14.

The temperature sensor 14 is shrouded by an

integral feature of the pipe section 11 so that it senses conditions of the fluid flow without contacting the fluid flow. This is advantageous since the fluid tends to contain corrosive elements.

An O-ring seal 18 is located in an external groove on the exterior of the pressure sensor 13 and acts between the pressure sensor 13 and the interior surface of the boss 15 to provide a seal preventing escape of water past the pressure sensor 13. The operation of the pressure sensor 13 is described in another patent application of the applicant. The pressure sensor 13 has a void 19. A pressure sensing element 20 is located in fhe void and is abutted by a flexible element 21 which is exposed to the water pressure.

The pressure sensor is located so as not to be directly placed in the fluid flow because then it would not give an accurate reading. The water heaters common today often operate in a vacuum. Traditional pressure sensors could not sense pressure below 1 bar.

By sensing pressure using fluid removed from the fluid flow, the sensor is capable of accurately sensing pressure below 1 bar.

The unit 10 is manufactured by fitting the pressure sensor 13 and the temperature sensor 14 in sockets defined in the moulded pipe section and then the cover 12 is mechanically fixed in place.

The location of the temperature sensor at the elbow provides the temperature sensor 14 with a fast response rate to changes in water temperature since the flow is turbulent in the elbow region. In tests

the temperature sensor 14 took less than 5 seconds to change 63% of the total resistance change arising between a first and second temperature. The pressure sensor 13 also took less than 10 msec to respond to a change between two pressure states. Tests also showed that the pressure sensor 13 could read pressure to below 1 bar and had an accuracy of better than 4%, typically 2%. The sensor will be calibrated to read pressure of a typical domestic boiler in a range of 0.3 bar to 3 bar. The normal operating temperature range of the sensor unit will be 5-110°C.

The sensor unit 10 supplies two signals to a boiler management system, one for pressure and one for temperature. The pressure output signal is an analogue voltage signal typically in the range 0.5V to 4.5VDC over the measured pressure range. The extremes of the possible voltage output range e. g. 0-0.5V and 4. 5-5DV, give an indication of an error. The temperature sensor provides a resistance variable with temperature and the input supply voltage is typically 5VDC and the amount typically varies to a maximum of 250mA.

The pipe section 11 is of a size and cross- section which matches the pipework of the pipeline in which it is inserted. The pipe section 11 is designed to be easily fitted to the pipes of the surrounding pipeline. In the illustrated embodiment this is achieved by the provision of four pairs of aligned apertures, two pairs of which are shown at 22,23 and 24,25. In Figure 2 it can be seen that the sensor unit is connected to two adjacent pipes in a water pipeline of a water system. A collar 26 is shown on a pipe 27 and abutting against this is a resilient seal 28.

The L-shaped pipe section 11 is push fitted over the end of the pipe 27. Then a U-shaped clip is used to secure the connection. A U-shaped clip 29 is shown in Figure 2 in position securing the pipe section 11 to a pipe 30. Each arm of the U-shaped clip 29 is inserted through a pair of aligned apertures (e. g. 24, 25) in the pipe section 11.

The embodiment described above comprises an L- shaped pipe section 11. However, a straight pipe section could be used as shown at 31 in a second embodiment of unit 34 shown in Figure 3. Again, a U- shaped clip 32 is used to secure the pipe section 31 to a pipe 33.

Whilst clips are used above to secure units 10 and 34 in an in-line construction in a pipeline, other means of attachment could be used, e. g. screwthreads could be provided on the interior surface of a pipe section or of a sensor unit and matching screw threads on exterior surfaces of pipes to which the sensor unit is connected.

Whilst above the sensor units 10 and 34 are described at connected in an outlet pipeline of a domestic water heater to measure outlet pressure and temperature, they may be used for other functions within the water heater.

The pipe section 11 is designed to be a section of duct work. The pressure sensor and the temperature sensor are an integral part of a modular unit connectable in and disconnectable from a duct in the same way as a conventional duct or pipe section.

The sensor units 10 and 34 will be manufactured as completed modular units in an assembly plant and then transported to where they are required. Each sensor unit, with pre-installed sensors, will be installed in a pipeline by connecting the pipe section at each end to sections of pipes in the pipeline.

Whilst above the sensor units 10 and 34 described are combined pressure and temperature sensor units, the present invention also is applicable to units comprising just a temperature sensor or just a pressure sensor, since some water heaters would need only a temperature signal or only a pressure signal.