GB1583746A - Apparatus for and method of detecting and/or identifying a liquid - Google Patents

Description

(54) APPARATUS FOR, AND METHOD OF DETECTING AND/OR IDENTIFYING A LIQUID (71) I, THOMAS EDWARD EVANS, a British Subject, of 32, Muster Court, Haywards Heath, Sussex RM16 4AW, do hereby declare the invention for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a method of, and apparatus for detecting, detecting changes in, and/or identifying a liquid.

It has previously been proposed to detect and/or identify a liquid by transmitting sound to a body of liquid and to measure some physical characteristic of the liquid by means of the transmitted sound. Thus, it has previously been proposed to identify liquids by measuring the velocity of sound through a body of the liquid by timing how long a sound takes to travel a given distance through the liquid.

Other sound-based apparatuses have sought to measure the acoustic absorption of the liquid.

According to a first aspect of the present invention, there is provided apparatus for detect ing, detecting changes in, and/or identifying a liquid comprising a transducer arrangement, including at least one transducer, for transmitting acoustic waves to, and receiving acoustic waves from, a body of liquid; means for energising the transducer arrangement; and an electrical circuit connected to the transducer arrangement and arranged to provide an electrical signal representative of the reverberation time of the body of liquid.

A second aspect of the invention provides a method of detecting, detecting changes in, and/ or identifying a liquid comprising transmitting sound waves to a body of liquid and thereby measuring the reverberation time of the body of liquid.

The apparatus and method can be used in a wide variety of applications. Thus, for example, they can be used to detect the presence of a liquid in a vessel or in an open or closed conduit, or to identify the liquid in those situations.

A further important area of application of the method and apparatus is to the identification of liquids at the receiving end of a pipeline or other elongate conduit along which different liquids or different liquid products derived from the same basic liquid, such as various fractions derived from crude oil, are conveyed in succession.

With a pipeline of appreciable length, it is impractical to rely on calculations of the time taken for a particular liquid to pass along the pipeline and it is therefore desirable to be able to identify liquid on arrival at the downstream end of the line. By identifying the arriving liquids using the embodiments described below of the present invention the liquids can be reliably routed to their respective destinations e.g. separate storage tanks or parts of a plant.

The present invention can also be used for identifying the interface between two liquids, or the mixing zone therebetween if the two are miscible. This can be done either under static or flow conditions. Under static conditions, it is possible to locate the interface or mixing zone by simultaneously measuring the parament under consideration at various locations within the body of liquid.

It will be appreciated that the term "sound" as used in the present Specification and appended claims is not intended to be limited to sound which can be heard by humans since the frequency of sound desirable or necessary in certain applications of the invention extends up to several megahertz.

The invention will be further described with reference to the accompanying drawings, in which: Figure 1 shows the disposition of transducers used in an embodiment of the present invention; Figure 2 shows graphs illustrating the operation of the embodiment of Figure 1; Figure 3 is a block diagram of circuitry which may be used in the embodiment of Figure 1; and Figure 4 illustrates how the embodiment of Figures 1 to 3 can be used in a conveying system.

In the illustrated embodiment an electrical signal is produced which is representative of the reverberation time of a body of liquid 1 flowing through a closed conduit 2. Thus, two piezo-electric transducers 3 and 3' are mounted in or on the outer wall of the pipe 2 so as to face one another across a diameter of the pipe and sound is transmitted from the transducer 3 to the transducer 3' through the body of liquid 1. The transducer 3 is periodically energised with a signal which comprises a burst of sine-waves of constant amplitude with an appropriately long interval between successive bursts. The operation of this embodiment is based on the fact that after the cessation of each burst, the transducer 3' will continue to receive sound from the transducer 3 arriving by other than the shortest paths between the two transducers.This effect is, of course, the well known effect of "reverberation". After the cessation of each burst the amplitude of the signal received by transducer 3 dies away exponentially at a rate which is dependent on the product of the acoustic absorption of, and velocity of sound in, the liquid. Figure 3 illustrates one of the bursts 20 of sine-waves followed by an interval 21, and the envelope 22 of the sound received by the transducer 3'. By measuring the time taken for the amplitude of signals received by the transducer 3' to reduce to a predetermined value or by measuring the amount by which the amplitude of the signals has fallen after a predetermined time, it is possible to produce an electrical signal which is representative of the reverberation time of the liquid which can be used to detect and/or identify the liquid in the pipe 2.

Figure 3 illustrates very schematically, and in block diagram form, the circuitry associated with the transducers 3 and 3'. An oscillator 30 is arranged to energise the transducer 3 via a gate 31. The oscillator 30 produces a continuous, constant amplitude sine-wave output of radio frequency and this is applied to transducer 3 in the form of periodically repeating, spaced bursts, under the control of a pulse signal applied to a control input of gate 31 from a timing circuit 35. The output of transducer 3' is amplified by an amplifier 32 and delivered to a sample and hold circuit 33. A predetermined time after the end of each control pulse supplied to gate 31 by timing circuit 35, the timing circuit 35 applies a control pulse to the sample and hold circuit 33 so that the output on line 34 is representative of the reverberation time of the liquid 1.This output 34 can then be displayed and/or compared in digital or analogue fashion with signals representative of known liquids, to identify the liquid 1.

In a modified form the circuit shown in Figure 3, is used to measure the time taken for the amplitude of the signal received by the transducer 3' to reduce by a predetermined amount. In such a variation the circuit is arranged so that at the end of each control pulse applied by timing circuit 35 to the gate 31, a counter is started and a threshold detector is used to interrupt the operation of the counter once the output of transducer 3 has fallen to a predetermined value or to a predetermined fraction of its previous value. The count then in the counter would then again be representative of the reverberation time of the liquid. This provides a straightforward way of deriving a digital signal representing the reverberation time.Of course, the circuit preferably operates so that the time measured is the time taken for the output of transducer 3' to fall to a predetermined fraction of its previous value (i.e. its value during each burst) as the amplitude of the signal received by the transducer 3 will depend on the nature of the liquid and without compensating for this, the operation of the circuit could be undesirably influenced in the case of liquids having very short or very long reverberation times.

There are, of course, numerous variations which may be made in the above embodiments.

Thus, for example, in some circumstances it would be desirable to incorporate, in the amplifier circuit associated with the receiver transducer 3', a suitably designed filter to prevent other sound waves transmitted through the liquid from influencing the operation of the circuit.

When the embodiment incorporates more than one pair of transducers 3,3', the bursts of sine- waves emitted by the transducers 3 should, of course, be timed with respect of one another so that there is no confusion between the signals received at the various transducers 3' which could give way to incorrect identification of the liquid. It is, of course, also possible to construct an embodiment measuring the reverberation time of the liquid using only a single transducer, which in that case, is used alternately as a transmitter and as a receiver.

The transducer or transducers may be protected from damage by the liquid 1 by corrosion or abrasion, for example. Thus the sound transmitting surface of the transducer may be coated with a suitable protective material, or alternatively the transducer or transducers may be coupled to the body of liquid 1 via a protective acoustically transmissive barrier.

It is also possible, in versions of both the above embodiments to have the transducers mounted on the outer wall of the pipe 2. Other methods of reducing wear on the transducers may, of course, be used; thus, the transducers may be located in a portion of the pipe which is arranged to have a low local flow velocity or be located in a separate branch pipe connected in parallel with the main pipe.

Figure 4 shows how the present invention may be applied to the transporting of liquids through a pipeline. As shown in Figure 4, various different liquids, or products derived from the same basic liquid, are delivered via respective conduits 51, 52, 53, by means of a selection and pumping arrangement 54, for transport along a pipeline 2 one after the other.

At the receiving end of the pipeline 2' a selection valve 58 is to be used to direct the liquid products via conduits 55, 56, and 57 to their respective destinations, which may, for example, be separate tanks or the like. One or more transducers 3 of an embodiment of the present invention are associated with the downstream end of the pipe and serve to detect the arrival of each of the individual liquids and a control device (not shown) is used to operate the selection valve 58 to route the various liquids to their correct destinations. It will be appreciated that in the case of nonmiscible liquids, a moderately well defined interface will form between liquids conveyed successively along the pipe 2, in which case detection of the change from one liquid to another passing the transducer(s) 3 can be effected relatively simply.

Circuitry associated with the transducer or transducers can be used to time the operation of the selector valve 58 so that only the desired liquid is sent along any one conduit 55, 56, 57.

Where successively transported liquids are miscible, a mixing zone will form between the liquids and this may give rise to a more gradual change in the measurements made by the transducers 3 and associated circuitry and it may therefore be desirable in those circumstances to place several transducers at longitudinally spaced locations at the downstream end of the pipeline so that the progress of the interface can be monitored and the selector valve 58 operated accordingly.

Where only detection of an interface is of interest, the apparatus is not required actually to identify the liquids but simply to detect, preferably as soon as possible, changes in the parameter under consideration.

The apparatus could, of course, be arranged to operate on the basis of the time integral of the response of the receiver-transducer 3' for example by monitoring the time required for the integral to reach a predetermined value.

It is envisaged that the above methods of identifying liquids, or interfaces between liquids could prove sufficiently reliable as to enable liquids to be routed automatically on the basis of the identification.

WHAT I CLAIM IS: 1. Apparatus for detecting, detecting changes in, and/or identifying a liquid comprising a transducer arrangement, including at least one transducer, for transmitting acoustic waves to, and receiving acoustic waves from, a body of liquid; means for energising the transducer ararrangement; and an electrical circuit connected to the transducer arrangement and arranged to provide an electrical signal representative of the reverberation time of the body of liquid.

2. An apparatus according to claim 1, wherein the energising means is arranged so as to energise the transducer arrangement intermittently to emit bursts of sound waves and the electrical circuit is arranged to measure acoustic signals received by the transducer arrangement during the intervals between the bursts.

3. An apparatus according to claim 2, wherein the electrical circuit is arranged to measure the length of time taken for the amplitube of reverberation signals received by the transducer arrangement after the cessation of each burst to fall to a predetermined value.

4. An apparatus according to claim 2, wherein the electrical circuit is arranged to measure the amplitude of the reverberation signals at a predetermined time after the cessation of each burst.

5. An apparatus according to any one of the preceding claims, wherein the transducer arrangement includes at least one piezoelectric transducer.

6. An apparatus according to any one of the preceding claims, wherein means are provided to display the value of the reverberation time as measured by the electrical circuit.

7. An apparatus according to any one of the preceding claims, wherein a comparator is provided for determining whether the value of the electrical signal is within a range characteristic of a preselected liquid.

8. A method of detecting, detecting changes in, and/or identifying a liquid comprising transmitting sound waves to a body of liquid and thereby measuring the reverberation time of the body of liquid.

9. A method according to claim 8, wherein the reverberation time is measured by periodically transmitting bursts of sound waves through the liquid and detecting reverberation waves occurring after the cessation of each burst.

10. Apparatus for detecting, detecting changes in, and/or identifying a liquid constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in Figures 1 to 3 of the accompanying drawings.

11. A method of detecting, detecting changes in, and/or identifying a liquid, such method being substantially as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawings.

12. A method of transporting liquids in which different liquids are conveyed in succession along a common open or closed conduit, on arrival at a predetermined location, are identified or the interface therebetween detected using an apparatus according to any one of the claims 1 to 7 and 10 or a method according to any one of claims 8, 9 and 11 and are routed to individual destinations on the basis of the identification.

13. A method of transporting liquids substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.

14. Liquid transported by the method of

Claims (1)

1. claim 12 or 13.