GB2537373A

GB2537373A - Immersion sensor

Info

Publication number: GB2537373A
Application number: GB1506241.7A
Authority: GB
Inventors: Inman Brian
Original assignee: John Yandell
Current assignee: John Yandell
Priority date: 2015-04-13
Filing date: 2015-04-13
Publication date: 2016-10-19
Also published as: GB201506241D0

Abstract

An immersion sensor 10 is described. The sensor comprises: an enclosed housing of a non-absorbent and electrically insulating material, which has a number of external faces. A first electrode 24 is provided on an internal surface of an external face of the housing, a second electrode 26 located on an internal surface of an external face of the housing. These electrodes can thus form a first capacitor. A controller 32 is also configured to detect a change in a capacitance of the first capacitor when the sensor 10 is immersed in a fluid. The location of an electrode in a recessed area of the housing helps to prevent false alarms. A second and third capacitor may also be present with associated third and fourth electrodes (figure 3, 28,40).

Description

IMMERSION SENSOR

Field of the Invention

The present application relates to an immersion sensor.

Background to the Invention

So-called "man overboard" distress systems are commonly used in the marine industry to detect persons or equipment that have fallen overboard from a vessel into the sea, and to trigger a warning such as a siren or flashing light in such circumstances. Typically these systems use a sensor to detect immersion of the system in water, and to trigger the warning. However, often these systems trigger false alarms, as the sensors detect immersion when in fact nothing has not fallen overboard, due to wet conditions on the deck of the vessel, for example.

Efforts have been made to address this problem, by reducing the sensitivity of the immersion sensors used in man overboard distress systems. However, reducing the sensitivity of the sensors can lead to unreliability and potentially failure of the system to actuate in a genuine man overboard situation.

An alternative solution to this problem involves the use of recessed conductive pins in the housing of a man overboard distress system. The recessed pins provide an electrically conductive path only when fully immersed in water or another conductive liquid, meaning that the warning is only triggered when the pins arc fully immersed. This helps to reduce the likelihood of false alarms, but increase the cost of the system, as bespoke housings are required to accommodate the recessed pins.

Accordingly, a need exists for an improved immersion sensor.

Summary of the Invention

According to a first aspect of the present invention there is provided an immersion sensor comprising: an enclosed housing of a non-absorbent electrically insulating material, the housing having a plurality of external faces; a first electrode provided on an internal surface of an external face of the housing; a second electrode provided on an internal surface of an external face of the housing, wherein the first and second electrodes form a first capacitor; and a controller configured to detect a change in a capacitance of the first capacitor when the sensor is immersed in a fluid.

The immersion sensor of the first aspect provides a more reliable and consistent means for detecting immersion than has hitherto been possible. The use of an enclosed housing with no external electrodes makes the immersion sensor suitable for a wide variety of applications, including those involving flammable liquids.

The controller may be further configured to trigger a warning system if it detects a change in the capacitance that indicates that the sensor is immersed in a fluid.

The controller may be configured to transmit a signal to the first electrode and to detect a signal generated at the second electrode in response to receiving the signal at the first electrode.

The controller may be configured to compare the signal detected at the second electrode to a threshold and to trigger the warning if the detected signal meets the threshold.

The immersion sensor may further comprise a third electrode provided on an internal surface of an external face of the housing, wherein the first and third electrodes form a second capacitor and the second and third electrodes form a third capacitor, and the controller may be configured to detect a change in a capacitance of the second or third capacitor when the sensor is immersed in a fluid.

The controller may be configured to transmit a confirmation signal to the second electrode and to detect a signal generated at the first electrode if the signal detected at the second electrode meets the threshold.

The first electrode and the second electrode may be provided on an internal surface of the same one of the plurality of external faces of the housing.

Alternatively, the first electrode and the second electrode may be provided on internal surfaces of different ones of the plurality of external faces of the housing.

The first electrode or the second electrode may be provided on an internal surface of a recessed portion of an external face of the housing.

The controller may be housed within the housing.

The warning system may be housed within the housing.

The warning system may comprise one or more of: an optical warning device; an audible warning device; a radio beacon transmitter; and an induction loop.

The optical warning device may comprise a device which operates in a human-visible range of the electromagnetic spectrum or in a range that is not normally visible to the human eye.

For example, the optical warning device may comprise a light or light emitting diode which emits light in the infra-red or ultra-violet range.

According to a second aspect of the invention there is provided an item of equipment comprising an immersion sensor according to the first aspect.

Brief Description of the Drawings

Embodiments of the present invention will now be described, strictly by way of example only, with reference to the accompanying drawing, of which: Figure 1 is a schematic perspective view of an immersion sensor; Figure 2 is a schematic view from above, showing the interior of the immersion sensor illustrated in Figure 1; and Figure 3 is a schematic representation of a controller and electrodes used in the immersion sensor shown in Figures 1 and 2.

Detailed Description of the Invention

Figure 1 is a schematic perspective view of an immersion sensor. The immersion sensor, shown generally at 10, comprises an enclosed and sealed generally hollow housing made of an electrically insulating and non-absorbent material such as a plastics material. In the illustrated example, the container is generally cuboidal, having a base 12, a lid 14 and four sides 16, 18, 20, 22 (of which only two, first side 16 and second side 18, arc visible in Figure 1) which form external faces of the sensor 10.

Figure 2 is a schematic view from above, showing the interior of the immersion sensor 10. As can be seen from Figure 2, a first electrode 24 is provided on an internal surface of the first side 16 of the sensor 10. A second electrode 26 is provided on an internal surface of the second side 18 of the sensor 10, whilst a third electrode 28 is provided on an internal surface of a third side 20 of the sensor 10, and a fourth electrode 30 is provided on an internal surface of a fourth side 22 of the sensor 10.

Each of the electrodes 24, 26, 28, 30 acts as a first plate of a capacitor, with another of the electrodes 26, 28, 30, 24 acting as a second plate of the capacitor. For example, the first. electrode 24 and the second electrode 26 act as first and second plates of a first capacitor, which are separated by a dielectric comprising the material of the first and second sides 16, 18 of the housing and, when the sensor 10 is not immersed in water, air. When the sensor 10 is immersed in a liquid such as water, the dielectric comprises the material of the first and second sides 16, 18 of the housing and the liquid. As will be appreciated, the dielectric constant of the dielectric between the first and second electrodes 24, 26 will be different when the sensor 10 is immersed in liquid from the dielectric constant when the sensor 10 is not immersed.

Similarly, the second electrode 28 and the third electrode 28 act as first and second plates of a second capacitor, which are separated by a dielectric comprising the material of the second and third sides 18, 20 of the housing and, when the sensor 10 is not immersed in water, air. When the sensor 10 is immersed in a liquid such as water, the dielectric comprises the material of the second and third sides 18, 20 of the housing and the liquid. Again, the dielectric constant of the dielectric between the second and third electrodes 26, 28 will be different when the sensor 10 is immersed in liquid from the dielectric constant when the sensor 10 is not immersed.

Likewise, the third electrode 28 and the fourth electrode 30 act as first and second plates of a third capacitor, whose dielectric is the material of the third and fourth sides 20, 22 of the housing and either air (when the sensor 10 is not submerged) or liquid (when the sensor 10 is submerged) and the fourth electrode 30 and the first electrode 24 act as first and second plates of a fourth capacitor, whose dielectric is the material of the fourth and first sides 22, 16 and either air (when the sensor 10 is not submerged) or liquid (when the sensor 10 is submerged).

The electrodes 24, 26, 28, 30 may be provided in any convenient manner. For example, the electrodes 24, 26, 28, 30 may be strips of copper or another electrically conductive material which are glued or otherwise affixed to the inner surfaces of the sides 16, 18, 20, 22 of the housing.

As can be seen from the schematic representation of Figure 3, the electrodes 24, 26, 28, 30 are each electrically connected to a controller 32, which may be, for example, a battery powered microcontroller. The controller 32 is in turn connected to a warning system 34 which may include, for example, an optical warning device 36 such as a flashing light or LED (light emitting diodes) operating in the human-visible range of the electromagnetic spectrum or alternatively a light or LED operating in a range of the electromagnetic spectrum that is not normally visible to the human eye (e.2. a light or LED which emits light in the infra-red range or the ultra-violet range), an audible warning device 38 such as a loudspeaker, a radio beacon transmitter 40 and an induction link 42. It will be appreciated that the warning system need not include all of these warning devices, but that a subset of these warning devices may be employed depending upon the application of the sensor 10. Equally, additional warning devices may be used if appropriate for the application. Additionally, in some applications of the sensor 10 the warning system 34 may include a wired connection to an external device.

In operation of the sensor 10, the controller 32 periodically transmits an electrical signal such as a pulse to one of the electrodes, for example the first electrode 24. This signal is detected by each of the other electrodes 26, 28, 30, and the detected signal is transmitted by each of those other electrodes 26, 28, 30 to the controller 32. The amplitude of the detected signal will depend on whether the sensor 10 is immersed in liquid or not, as the dielectric constant of liquids such as water is much greater than the dielectric constant of air. Thus, the capacitance of the capacitor formed by the first and second electrodes 24, 26 will be different when the sensor 10 is immersed in a liquid than when the sensor 10 is not immersed, and this change in the capacitance affects the amplitude of the detected signal. For a transmitted signal of a constant frequency, the amplitude of the detected signal will be lower when the dielectric is air than when the dielectric is a liquid.

The controller 32 indirectly detects the change in capacitance that occurs when the sensor 10 is immersed. The controller 32 compares the amplitude of the detected signal received from each of the electrodes 26, 28, 30 to a predetermined threshold value, and if one or more of the detected signals meets or exceeds the threshold (indicating that the sensor 10 is immersed in liquid), the controller 32 transmits a signal to the warning system 34 to trigger one or more of the warning devices 36, 38, 40, 42.

To reduce the risk of false alarms, the controller 32 may be configured to transmit a signal to the warning system 34 only if the amplitude of all of the signals detected by the electrodes 26, 28, 30 meet the predetermined threshold.

To further reduce the risk of false alarms, the controller 32 may be configured to perform a verification step prior to transmitting a signal to the warning system 34. Thus, if the amplitude of a signal detected by one or more of the electrodes 26, 28, 30 meets the predetermined threshold, the controller 32 may transmit a further signal such as a pulse to a different one of the electrodes, for example the second electrode 26. This signal is detected by each of the other electrodes 24, 28, 30, and the detected signal is transmitted by each of those electrodes 24, 28, 30 to the controller 32, which compares the amplitude of the received signal to the predetermined threshold. If one or more of the detected signals meets the threshold, indicating that the sensor 10 is immersed, and confirming the previous determination that the sensor 10 is immersed, the controller 32 may transmit a signal to the warning system 34 to trigger one or more of the warning devices 36, 38, 40, 42.

In the example discussed above, only one "confirmation" signal is transmitted by the controller 32 to a different one of the electrodes 24, 26, 28, 30 than the one to which the original signal was transmitted. It will be appreciated, however, that additional confirmation pulses may be transmitted by the controller 32 to any of the other electrodes as described above to confirm that the sensor is immersed before the controller 32 transmits a signal to the warning system 34 to trigger one or more of the warning devices 36, 38, 40, 42.

The exemplary sensor 10 described above with reference to the drawings has four electrodes, but it will be appreciated that the number of electrodes employed by the sensor may vary depending upon the application of the sensor. Thus, in some applications only two electrodes will be required. Additionally, in some applications one or more of the electrodes may be recessed, to further reduce the risk that the warning system 34 will be triggered when the sensor 10 is not immersed. Moreover, although in the example illustrated in Figure 2 each of the electrodes 24, 26, 28, 30 is provided on the internal surface of a different side 16, 18, 20, 22 or face of the housing, two or more electrodes 24, 26, 28, 30 may be provided on the internal surface of a single side 16, 18, 20.22 or face of the housing if required or appropriate for a particular application of the sensor 10.

Although the sensor 10 described above and illustrated in the accompanying drawings is generally cuboidal, it is to be appreciated that other shapes are possible and may be desirable for particular applications of the sensor 10.

The controller 32, warning system 34 and a battery which powers the controller 32 and warning system 34 can be housed within the housing, and the lid 14 can be sealed in place, making the sensor 10 completely waterproof. As there are no external electrodes the sensor is suitable for use in applications where detecting immersion in flammable liquids is important. The controller 32 is a low-power device, which permits the use of a small, low voltage battery such as a coin or button cell battery or the like. The extremely low power consumption of the sensor 10 and its constituent components (e.g. the controller 32 and warning system 34) permits long battery life.

The sensor 10 described herein provides a more reliable and consistent means for detecting immersion than has hitherto been possible. The sensor 10 is suitable for a wide variety of immersion sensing applications, and can be provided in housings of different shapes and sizes according to the requirements of the sensing application. The sensor 10 may be provided as a standalone unit or may be incorporated in or retrofitted to other items of equipment such as, for example, life jackets and the like.

Claims

CLAIMS1. An immersion sensor comprising: an enclosed housing of a non-absorbent and electrically insulating material, the housing having a plurality of external faces; a first electrode provided on an internal surface of an external face of the housing; a second electrode provided on an internal surface of an external face of the housing, wherein the first and second electrodes form a first capacitor; and a controller configured to detect a change in a capacitance of the first capacitor when the sensor is immersed in a fluid.
2. An immersion sensor according to claim I wherein the controller is further configured to trigger a warning system if it detects a change in the capacitance that indicates that the sensor is immersed in a fluid.
3. An immersion sensor according to claim 1 or claim 2 wherein the controller is configured to transmit a signal to the first electrode and to detect a signal generated at the second electrode in response to receiving the signal at the first electrode.
4. An immersion sensor according to claims 2 and 3 wherein the controller is configured to compare the signal detected at the second electrode to a threshold and to trigger the warning if the detected signal meets the threshold.
5. An immersion sensor according to any one of the preceding claims further comprising a third electrode provided on an internal surface of an external face of the housing, wherein the first and third electrodes form a second capacitor and the second and third electrodes form a third capacitor, and wherein the controller is configured to detect a change in a capacitance of the second or third capacitor when the sensor is immersed in a fluid.
6. An immersion sensor according to claims 4 or claim 5 wherein the controller is configured to transmit a confirmation signal to the second electrode and to detect a signal generated at the first electrode if the signal detected at the second electrode meets the threshold.
7. An immersion sensor according to any one of the preceding claims wherein the first electrode and the second electrode are provided on an internal surface of the same one of the plurality of external faces of the housing.
8. An immersion sensor according to any one of claims 1 to 6 wherein the first electrode and the second electrode are provided on internal surfaces of different ones of the plurality of external faces of the housing.
9. An immersion sensor according to any one of the preceding claims wherein the first.electrode or the second electrode is provided on an internal surface of a recessed portion of an external face of the housing.
10. An immersion sensor according to any one of the preceding claims wherein the controller is housed within the housing.
11. An immersion sensor according to any one of claims 2 to 10 wherein the warning system is housed within the housing.
12. An immersion sensor according to any one of claims 2 to 11 wherein the warning system comprises one or more of: an optical warning device; an audible warning device; a radio beacon transmitter; and an induction loop.
13. An immersion sensor according to claim 12 wherein the optical warning device comprises a device which operates in a human-visible range of the electromagnetic spectrum or in a range that is not normally visible to the human eye.
14. An immersion sensor according to claim 13 wherein the optical warning device comprises a light or light emitting diode which emits light in the infra-red or ultra-violet. range.
15. An immersion sensor substantially as hereinbefore described with reference to the accompanying drawings.
16. An item of equipment comprising an immersion sensor according to any one of the preceding claims.