GB2126342A

GB2126342A - Liquid level detector

Info

Publication number: GB2126342A
Application number: GB08225318A
Authority: GB
Inventors: Robert David Bellis; Nigel James Playford
Original assignee: Innovative Technology Ltd
Current assignee: Innovative Technology Ltd
Priority date: 1982-09-06
Filing date: 1982-09-06
Publication date: 1984-03-21

Abstract

A liquid level detector device, especially for detecting the liquid level in an opaque container, comprising a casing (10) having a nose (16) closed by a diaphragm (18) bearing a coupling pad (20), as of polyester based polyurethane elastomer, which, when the nose is pressed against the surface of an object to be tested, conforms to said surface to pass ultrasonic energy to and from a transmitter/receiver in the form of a transducer housed within the casing and powered from a battery in a battery compartment (12), the casing also containing the necessary circuit means for pulsing the transducer and gating and processing any returned echo pulses for lighting an LED indicator (24). An echo indicates the presence of liquid in the container adjacent to the diaphragm. Liquid level is found by moving the device up or down the container until no echo is returned. To facilitate movement the diaphragm may be in the form of a belt or roller. Device sensitivity may be adjusted to suit various sizes of container and fluid. A further LED indicator (22) lights when sufficient pressure is exerted to ensure coupling. <IMAGE>

Description

SPECIFICATION Improvements in liquid level detection This invention relates generally to liquid level detection and more particularly to a device for detecting from the outside liquid levels in closed, opaque containers.

It is common for users of gas bottles, beer barrels and like closed, opaque containers holding a consumable liquid, to require to known the amount of gas, beer or other liquid which remains in the container after it has been in use for some time.

Since the liquid level cannot be seen because the container is both closed and opaque, practices such as tapping the wall of the container and lifting the container to test its weight or sound its contents are resorted to. However, these practices do not give either an accurate or reliable indication, and can involve considerable effort if the container is heavy.

Furthermore, when the overall mass and weight is determined primarily by the container, as in the case of a gas bottle for instance, the indication obtained is liable to be so inaccurate as to be virtually useless.

It would, therefore, be highly desirable to provide a simple, reliable, hand-holdable device, selfcontained in respect of any power source, which can be used externally of the container, e.g. a gas bottle or beer drum, to measure the level of the liquid content.

According to the invention, there is provided a liquid level detection device comprising a casing having a nose fitted with a resilient coupling element for making pressurised contact with the outside of a liquid container with good conformability and air exclusion at the contact interface, a transducer assembly adapted to emit and receive ultrasonic energy, said transducer assembly being mounted in the casing in proximate relationship to the coupling element for transmission of ultrasonic energy in both directions between the transducer and the container, means in the casing for exciting the transducer to cause a burst of ultrasonic energy to be transmitted to the container, circuit means in the casing for processing an echo pulse received through the transducer, and an indicator visible from outside the casing to indicate whether or not an echo pulse has been received.

It is a particularly important feature of the invention that the coupling element should be a dense (i.e.

non-cellular) material having a smooth contact surface which will conform very closely to the exclusion of air pockets with the liquid container when said coupling element is pressed thereagainst. Clearly, said coupling element must also be resilient so that the device can be repetitively used. One example of a suitable material for the coupling element is a polyester based polyurethane elastomer such as CIL-Monothane.

The device of the invention relies for operation on the fact that a burst of ultrasonic energy, if transmitted to the container wall at a level above the liquid level, will not be transmitted through the wall/gas interface but will be largely reflected and reverberate in the cylinder wall. However, a burst of ultrasonic energy transmitted to the container wall below the liquid level will be transmitted through the wall/ liquid interface and will travel through the liquid to be reflected at the opposite liquid/wall interface, thereby to produce an echo pulse.

Conveniently, therefore, the circuit processing means may include a gating circuit which blocks the reception of ultrasonic energy during transmission and for a short period thereafter. The gating circuit may be followed by a receiver amplifier and a logic circuit such as a comparator to distinguish an echo of significant amplitude from background noise. The indicator may be a simple LED, preferably lighting only in the presence of an echo pulse, although the reverse situation is possible.

The exciting means for the transducer may comprise an inverter for producing a voltage supply appropriate to drive the transducer from a battery which can be installed in an openable battery compartment in the casing.

Atiming circuit will be associated with the exciting means to trigger the burst of ultrasonic energy. This same timing circuit can also be used to control the gating circuit which receives the echo pulse.

Switching means will initiate a timed test cycle, and this switching means may conveniently be actuated to initiate said test cycle by the depression of the coupling element which occurs when the nose of the device is pressed against the container. More likely, however, the switching means will be a manual switch which, when "on", switches on the power supply to enable the timer to initiate a succession of test cycles, each cycle comprising a transmission burst period and an echo detection period.

Use of the device of the invention will generally require testing of the container at a succession of levels, if the liquid level in the container is to be precisely determined. A coupling element in the form of a simple pressure pad, of a material having the previously defined characteristics, is suitable for this purpose. It may be possible, however, to employ a coupling element in the form of a resilient roller or belt, thereby to enable the device to be rolled up or down the container. In this case it would be essential for the surface conforming and air excluding characteristics of the coupling element to be maintained during rolling.

It will be appreciated that the mean amplitude of the echo will tend to vary with the nature of the container (material, wall thickness etc.) and with the nature of the liquid. For this reason, the receiver amplifier may possibly incorporate an automatic gain circuit, and/or the reference level of the comparator may be adjustable, for example against an indicator marked with different types of container, e.g. gas bottles or beer drums, with which the device is likely to be used.

Ideally, the casing will be dimensioned and shaped suitably to facilitate hand holding in a manner which readily enables the nose to be pressed towards a container to be tested. In addition to the level indicating LED, a second LED can indicate when sufficient pressure is being employed to ensure proper operation.

A practical example of liquid level testing device in accordance with the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a view of one possible embodiment of device, as seen in perspective; Figures 2 and 2A illustrate the mode of use of the device; and Figure 3 is a schematic block diagram of the internal circuitry.

The embodiment shown in Figure 1 has a two part thermoplastics casing 10, ultrasonically welded, the internal functional components being mounted in one part and the other part acting as a cover. The casing 10 has a clip-in cover 12 to a battery compartment. A wrist strap 14 is provided to facilitate carrying.

The casing 10 has a nose 16 closed by a flexible diaphragm 18. Integrally formed with this diaphragm 18 is a coupling pad 20, conveniently a polyester based polyurethane elastomer such as ClL-Monothane. Such a pad will conform readily and tightly, with the minimum of air pockets, to a surface against which it is pressed. The coupling pad 20 is a particularly important feature of the invention. A material which is dense (i.e. non-cellular) and which has a smooth contact surface which will conform accurately to the container surface against which it is pressed, with the exclusion of air pockets at the interface, is necessary to ensure transmission of ultrasonic energy through said interface in both directions. Applied to the back of the pad 20 is a transducer assembly (not shown in Figure 1).

When the coupling pad 20 at the nose of the device is pressed against a liquid container such as a gas bottle, the pad is compressed to conform tightly to the container wall. The diaphragm 18 is flexed inwardly and may automatically operate a control switch which turns the device on. Alternatively and possibly more desirably, a manual switch may be operated to switch the device "on". A burst of ultrasonic energy, consisting of say 20 diminishing amplitude pulses at a frequency of 1 MHz, is emitted by the transducer assembly and transmitted through the coupling pad 20 to the container wall. A sufficient coupling efficiency is effected through the compressed coupling pad 20 of the above defined characteristics, and especially through the pad/wall interface, to ensure that a satisfactory proportion of the ultrasonic energy burst enters the container wall.

An LED indicator 22 on the casing 10 indicates that the control switch has been operated. If the switch is operated automatically, the LED indicator 22 may also assist in ensuring that the device is being applied to the container wall with a sufficient pressure to achieve reliable operation.

Figures 2 and 2A indicate the principle of operation. Above the liquid level 32 in the container 30, the ultrasonic energy burst 34 emitted by the device 36 produces no reflected or echo burst, since the energy simply reverberates in the container wall, but below the liquid level 32 a reflection or echo burst is received from the opposite side of the container 30 to be picked up by the transducer assembly. An indicator 38 lights up to show that an echo signal is received. In Figure 1, this light 38 is shown as an LED indicator 24.

In the schematic block circuit diagram of Figure 3, the transducer assembly mounted to the back of coupling pad 20 at the centre of diaphragm 18 is referenced 40. The control switch, shown to be operable by the diaphragm, is referenced 42, and a battery housed in the above-mentioned battery compartment is referenced 44.

When the switch 42 is closed, an inverter 46 controlled by a timer 48 produces exciting pulses to excite the transducer. With a typical piezo-electric transducer and mounting therefor, the inverter 46 will be required to produce, from a low voltage d.c.

battery, exciting pulses of about 300 Vat a repetition frequency of between say 10 and 100 Hz, which constitutes the frequency at which testing cycles are repeated while the control switch is "on". An exciting pulse energises the transducer 40 through a driver circuit 50. The transducer and its mounting has a natural resonant frequency of 1 MHz, and natural damping which reduces the vibrations of the transducer substantially to zero after about twenty or so pulses at said resonant frequency.

Assuming an echo is received, due to the device being placed against the container below the liquid level, an echo burst will commence to be received, in atypical case, some 0.25 to 0.75 millisec. after the termination of transmission. The transducer assembly 40 senses this echo and supplies it to a receiveramplifier 52. The timer 48 is therefore also employed to control a gate circuit 54 through which the echo burst is fed to the amplifier 52. Typically, the timer 48 may open the gate 54 for a duration of about 1 millisec. starting about 0.1 millisec. after the end of a transmission burst of say about 0.02 to 0.05 millisec.

duration.

The output of the amplifier 52 is fed to a comparator 56 (or logic gate providing an equivalent function) which distinguishes between a true echo burst and background signals. In Figure 3, a reference voltage generator for the comparator 56 is referenced 58. The detection threshold of the comparator 56 may, if desired, be adjustable, for example to enable the device to be more readily adapted to the sensing of liquid containers of differing types, sizes and materials, containing differing liquids. Optionally, the amplifier may be associated with an automatic gain control circuit 62. The output of the comparator 56 switches the onloff LED indicator 24.

The device shown in Figure 1 is adapted for repetitive location on the container wall at different levels in order to ascertain the liquid level. A possible modification will enable the device to be rolled up and down the container wall, assuming the use of a coupling element, retaining the abovedescribed characteristics, in the form of a resilient, highly conformable, air excluding roller or belt.

It will be appreciated that the above described embodiments are by way of example only and may be modified in various ways within the scope of the invention as hereinbefore defined.

Claims

CLAIMS (Filed on 6/9/83)

1. A liquid level detection device comprising a casing having a nose fitted with a resilient coupling element for making pressurised contact with the outside of a liquid container with good conformabil ity and air exclusion at the contact interface, a transducer assembly adapted to emit and receive ultrasonic energy, said transducer assembly being mounted in the casing in proximate relationship to the coupling element for transmission of ultrasonic energy in both directions between the transducer and the container, means in the casing for exciting the transducer to cause a burst of ultrasonic energy to be transmitted to the container, circuit means in the casing for processing an echo pulse received through the transducer, and an indicator visible from outside the casing to indicate whether or not an echo pulse has been received.

2. A device according to claim 1, wherein the coupling element is a dense, non-cellular, resilient material affording a smooth contact surface with conformability to the exclusion of air pockets.

3. A device according to claim 2, wherein said coupling element is a polyester based polyurethane elastomer.

4. A device according to claim 3, wherein said elastomer is ClL-Monothane.

5. A device according to any of claims 1 to 4, wherein the circuit processing means includes a gating circuit which blocks the reception of ultraso nic energy during transmission and for a short period thereafter.

6. A device according to claim 5, wherein the processing means also includes a receiver amplifier and a logic circuit adapted to distinguish an echo of amplitude above a predetermined level from back ground noise.

7. A device according to claim 6, wherein the logic circuit comprises or includes a comparator.

8. A device according to any of claims 1 to 7, wherein the indicator is an LED lighting in the presence of an echo pulse.

9. A device according to any of claims 1 to 8, wherein the exciting means for the transducer includes an inverter for deriving a transducer drive voltage from a battery installed in an openable battery compartment in the casing.

10. A device according to any of claims 1 to 9, including a timing circuit connected to the exciting means.

11. A device according to claim 10 when appen dant to claim 5, wherein the said timer also controls the gating circuit.

12. A device according to any of claims 1 to 11, including a switching means automatically actuable to initiate a test cycle by depression of the coupling element when the nose of the device is pressed against an object to be tested.

13. A device according to any of claims 1 to 11, including a manual switch for connecting the power supply to the exciting means and processing circuit.

14. A device according to any of claims 1 to 13, wherein the coupling element is a pressure pad.

15. A device according to any of claims 1 to 13, wherein the coupling element is a roller or belt.

16. A device according to any of claims 1 to 15, wherein the processing circuit includes an amplifier with an automatic gain circuit.

17. A device according to any of claims 1 to 16, wherein the processing circuit includes a comparator having an adjustable reference level.

18. A device according to any of claims 1 to 17, having a casing shaped and dimensioned to be held by hand.

19. A device according to any of claims 1 to 18, including an indicator for indicating when the nose is pressed against an object to be tested with a pressure above a predetermined minimum.

20. A liquid level detection device substantially as hereinbefore described with reference to the accompanying drawings.