GB2298481A

GB2298481A - Fluid detector device

Info

Publication number: GB2298481A
Application number: GB9504123A
Authority: GB
Inventors: Geoffrey Hawke Whale; Nicholas John Beck
Original assignee: Kohler Mira Ltd
Current assignee: Kohler Mira Ltd
Priority date: 1995-03-01
Filing date: 1995-03-01
Publication date: 1996-09-04
Anticipated expiration: 2015-03-01
Also published as: GB2298481B; GB9504123D0; IE960169A1

Abstract

A device for distinguishing between air and water utilises the different refractive indices of air and water to reflect and transmit respectively a source of infra-red radiation from an emitter 32 for selective detection by a sensor 34. A flowmeter incorporating the device has the emitter and sensor arranged on opposite sides of an annular channel 20 whereby the sensor detects transmitted infra-red radiation when there is water in the channel but not reflected infra-red radiation when there is air in the channel. The flowmeter has a rotor with circumferentially spaced flags 16 rotatable in the channel to interrupt the transmitted radiation so that the frequency of the pulsed ouput from sensor 34 is representative of the flow rate. Water flow detected by the sensor may be used in conjunction with a temperature sensor 42 to control operation of a heat exchanger in an instantaneous water heater.

Description

Fluid Detector Device This invention relates to a device for distinguishing between the flow of two fluids such as air and water.

instantaneous water heaters are operable to heat water as it flows through a heat exchanger containing one or more electric heating elements.

The temperature of the water leaving the heat exchanger is controlled by the power input from the heating element(s) and the flow rate of the water.

One use of this type of instantaneous water heater is to provide water having a desired temperature for ablutionary installations such as showers.

It is important safety requirement for such use that the power to the heating elements is not switched on unless a water flow is taking place.

One way of meeting this safety requirement is to use a pressure switch which allows the heating elements to switch on if there is sufficient water pressure to generate the minimum required flow rate. A disadvantage of this solution is that there could be a blockage preventing water flow taking place. Hence the pressure does not guarantee a flow of water.

Another way of meeting this safety requirement is to use a flowmeter which allows the heating elements to switch on when the minimum required flow rate is present. A disadvantage of this solution is that the flowmeter can be operated by air which could be trapped in the pipework, especially in new installations. Hence the operation of the flowmeter does not guarantee a flow of water.

The present invention has been made from a consideration of this problem.

According to the present invention a fluid detector device for distinguishing between two fluids such as air and water having different refractive indices comprises an emitter providing a source of radiation and a sensor for detecting the radiation wherein, in use, the emitter and sensor are arranged so that the sensor detects radiation from the emitter for the flow of one fluid but not the other fluid.

In a preferred application of the invention, the device is incorporated in a flowmeter so that as well as measuring water flow rate, the flowmeter can distinguish between water flow and air flow. This can then be used to control operation of the heating elements of an instantaneous water heater so that the heating elements are switched on only when there is sufficient water flow and are switched off if there is insufficient water flow and/or if the water flow is replaced by air flow for any reason.

The invention will not be described in more detail by way of example only with reference to the accompanying drawings wherein: FIGURE 1 is a side view of a flowmeter embodying the invention and a flow control valve; FIGURE 2 is a front view of the flowmeter and flow control valve shown in Figure 1; FIGURE 3 is a part-section on the line 3-3 of Figure 2; FIGURE 4 is a part-section on the line 4-4 of Figure 1; and FIGURE 5 is an enlarged part-section through the cover of the flowmeter.

Referring to the drawings, the flowmeter 2 is shown with an inlet 4 connected to a flow control valve 6 and has an outlet 8 for connection to a heat exchanger (not shown) of an instantaneous water heater for an ablutionary shower.

The flowmeter 2 has a turbine rotor 10 which is loosely located in a vortex chamber 12. The rotor 10 is made of plastics material having a density similar to that of water so that the rotor 10 is suspended and rotates freely in the vortex chamber 12 without the need for bearings to support it.

The rotor 10 has a plurality of radially extending curved blades 14 uniformly spaced apart in the circumferential direction on one side and a plurality of axially extending curved flags 16 uniformly spaced apart in the circumferential direction on the other side.

The blades 14 are aligned at the periphery of the rotor 10 with a circumferential slot 18 in the vortex chamber 12 so that the rotor 10 is centred in the vortex flow produced by the incoming water in which the rotor 10 is suspended to rotate freely.

The flags 16 are received in an annular channel 20 in a cover 22 secured to a main body 24 of the flowmeter 2 by screws 26 and sealed by an O-ring 28.

The cover 22 is made of a material which is transparent to infra-red radiation and mounts a device 30 to detect rotation of the rotor 10 using an infra-red optical system to distinguish between water flow and air flow.

The device 30 comprises an infra-red emitter 32 and an infra-red sensor 34 positioned on opposite sides of the channel 20 in which the flags 16 are located.

As best shown in Figure 5, angle of incidence of the beam of infra-red radiation from the emitter 32 with the channel 20 is such that the beam is transmitted when water is in the channel 20 and is reflected if air is in the channel 20 due to the difference between the refractive indices of water and air. A shield 36 is fitted to trap stray radiation from the sides of the emitter 30.

The sensor 34 is positioned to receive the transmitted beam which is partially deflected by refraction due to the difference between the refractive indices of water and the material of the cover 22 When the rotor 10 spins due to the flow of water, the flags 16 interrupt the transmitted beam and generate a pulsed output from the sensor 34. The pulse frequency is a measure of the water flow rate. When the rotor 10 spins due to the flow of air, the beam is reflected and the sensor 34 does not generate an output.

The channel 20 is provided with a radial slot 38 which communicates with the outlet 8 through an opening 40 in the centre of the rotor 10. This slot 38 acts to suck-up drops of water and dry-out the channel 20 very quickly when air flow replaces the water flow. This stops any small drops of water remaining in the channel 20 being blown around the channel 20 and generating a pulsed output from the sensor 34 thereby improving the response of the device 30 to the absence of a flow of water.

The flowmeter 2 is also provided with a temperature sensor 42 mounted in the cover 22 and sealed by an O-ring 44. The sensor 42 is located in the opening 40 in the rotor 10 and monitors the temperature of the incoming water flow.

In an instantaneous water heater, the output from the sensors 34 and 42 can be used to adjust the flow control valve 4 to provide the flow rate required to heat the water to a selected temperature for a given power input to the heat exchanger and to switch off the heating element(s) within the heat exchanger if the water flow is insufficient for safe operation of the heat exchanger or is replaced by an air flow for any reason.

We have found that the device 30 can respond to switch-off the heating element(s) in approximately one second if air flow replaces the water flow thereby enhancing considerably the safety of the instantaneous water heater.

It will be understood that the invention is not limited to the embodiment above-described and that the principle of the flow detector device is of general application where it is desirable to distinguish between two fluids for any reason. For example, where flowmeters are used to measure the consumption of water. the flow detector device may be fitted so that the flowmeter only operates to record actual water flow and is not operated by air trapped in the pipework.

Claims

Claims:

1. A fluid detector device for distinguishing between two fluids such as air and water having different refractive indices comprises an emitter providing a source of radiation and a sensor for detecting the radiation wherein, in use, the emitter and sensor are arranged so that the sensor detects radiation from the emitter for the flow of one fluid but not the other fluid.

2. A device according to Claim 1 wherein the emitter provides a source of infra-red radiation.

3. A device according to Claim 1 or Claim 2 wherein the emitter and sensor are arranged to distinguish between air and water.

4. A device according to Claim 3 wherein the radiation from the emitter is transmitted by water and is reflected by air.

5. A device according to Claim 4 wherein the sensor is arranged to detect transmitted radiation.

6. A fluid detector device for distinguishing between two fluids such as air and water substantially as hereinbefore described with reference to the accompanying drawings.

7. A flowmeter incorporating a fluid detector device according to any one of the preceding Claims.

8. A flowmeter according to Claim 7 wherein the emitter is arranged on one side of an annular flow channel such that radiation from the emitter is transmitted when the channel contains water and is reflected when the channel contains air, and the sensor is arranged on the opposite side of the channel to detect transmitted radiation.

9. A flowmeter according to Claim 8 wherein the channel communicates with an outlet for draining the channel when air replaces water in the channel.

10. A flowmeter according to Claim 8 or Claim 9 wherein a rotor responsive to water flow has a part rotatable in the channel such that the transmitted radiation detected by the sensor is representative of flow rate.

11. An instantaneous water heater incorporating a flowmeter according to any one of Claims 7 to 10.

12. An instantaneous water heater according to Claim 11 wherein a heat exchanger is operable in response to water flow detected by the sensor.

13. An instantaneous water heater according to Claim 12 wherein the sensor produces an output representative of water flow rate and a further sensor produces an output representative of water inlet temperature for use in adjusting a flow control valve.