GB2130368A - Liquid change detector - Google Patents

Abstract

A liquid change detector 44 (70) incorporates an ultrasonic transducer 30 coupled to the outside of a wall of a container 12. The transducer 30 is adapted to operate in a pulse/echo mode, so as to generate an ultrasonic pulse and to receive ultrasonic echo pulses after propagation through the liquid 42 in the container 12. Amplified return signals from the transducer are supplied to a gated signal analyser 54, (72) which is gated to operate during a predetermined time interval in which an echo pulse is expected to be received if the velocity of sound in the liquid has a first value, but in which no echo pulse is expected if the liquid changes so that the velocity of sound has a second value. The output of the gated signal analyser 54,72 may be used to give a visual indication that the liquid 42 has changed, or may be used to operate valves so as to control flow of the liquid 42 appropriately. The detector may be used in a brewery to distinguish between cold beer and hot water with which pipelines are cleaned. <IMAGE>

Description

SPECIFICATION Liquid change detector This invention provides an instrumentto detect ultrasonically a change in a liquid in a pipe, for example from cold beer to hot water.

In the brewing industry it is common practice to pass beer at about along a pipe, and then to pass water at almost 1 OO"C along the same pipe to sterilize the pipe. It is importantto know exactly when the liquid change occurs,to enable valves to be operated appropriately, so asto divertthe cold beer and hot water to different outlets. For this purpose it is known to use thermocouples attached to the pipe to detect the temperature change which occurs when one liquid replaces the other at the positions of the thermocouples.However a thermocouple attached to the outside ofthe pipe will have a long response time because of thethermal capacity of the pipe itself, while a thermocouple attached to the inside of the pipe may provide a surface which is difficu It to clean, and so act as a source of contamination.

According to the present invention there is provided a liquid change detector for a container having a front wall and a rearwall, and a space between the front wall and the rear wall to accommodate a liquid, the detector comprising, a transducer adapted to cause a pulse of ultrasonicwaves to propagate through the liquid, a transducer adapted to receive the pulse after propagation ofthe pulsethrough a predetermined distance in the liquid, and to emit an electrical signal representative of the received pulse, and a gated signal analyser responsive to the electrical signal, gated to operate during a presettime interval during which the ultrasonic pulse is expected to be received if the speed ofsound in the liquid has a first value, but in which no ultrasonic pulse is expected to be received if the liquid has undergone a change such that the speed of sound in the liquid has a second value. Desirably thetransducers are acoustically coupled to the outside surfaceofthe container. The transducers may be a single transducer operating in a pulse-transmitting mode and a pulse-receiving mode, the pulse being received after reflection offthe rearwall of the container.

Thefrontwall and the rearwall of the container may be opposite walls of a pipe.

The change undergone bythe liquid may be a change in temperature or a change in composition, or a change of both temperature and composition.

The gated signal analyser may comprise a gated peak detector or a gated sampling integrator. Preferably the gated signal analyser incorporates means to distinguish between the signal and noise.

The present invention also provides a method for detecting a change in a liquid within a container having a front wall and a rearwall, and a space between thefrontwall and the rear wall to accommodate the liquid, comprising the operations of causing a pulse of ultrasonicwaves to propagate through the liquid, receiving the pulse after propagation ofthe pulse th rough a predetermined distance in the liquid and creating an electrical signal representative of the received pulse, and detecting whether a signal occurs during a preset time interval during which the pulse is expected to be received ifthe speed of sound in the liquid has a firstvalue, but in which no pulse is expected to be received if the liquid has undergone a change such that the speed of sound in the liquid has a second value.

The invention will now be described by way of example only and with reference to the accompanying drawings, in which: Figure lisa longitudinal sectiona I view of a transducer assembly attached to a pipe; Figure 2 is a block electronic circuit diagram of a liquid change detector incorporating the transducer assembly of Figure 1; Figures 3a and 3b are diagrammatic graphs of signals in the circuit of Figure 2, for cold beer and hot water respectively; and Figure 4 is a block electronic circuit diagram of an alternative liquid change detector incorporating the transducer assembly of Figure 1.

Referring to Figure 1 a transducer assembly 10 is shown attached to the outside of a pipe 12 by a worm-drive clip 14. The pipe 12 is of stainless steel, 1 00mm bore, andofwall thickness 3mm. The assembly 10 incorporates a tubulartransducer housing 18 one end ofwhich has a flange 20 on which the clip 14 bears, and the outside face oftheflange 20 is curved to fit against the outside ofthe pipe 12 with the longitudinal axis of the housing 18 extending radially from the pipe 12. The end ofthe housing 18 remote from the pipe 12 has an externallythreaded portion 22 with which a screw cap 24 engages.A 10 MHz ultrasonic transducer 30 is located within the housing 18, and is resiliently urged towards the pipe 12 by a helical spring 32 and a tubuiar spacer 34 which bears againstthe screw cap 24. Athin layer 36 of silicone grease couples the transducer 30 ultrasonically to the wall of the pipe 12. Electrical contactto the transducer 30 is made by a cable 38 passing through a central hole 40 in the screw cap 24. The resilient force urging the transducer30 against the pipe 12 can thus be adjusted by turning the screw cap 24.

When thetransducer 30 is energised, it causes a pulse of ultrasonic waves to propagate radially through the wall of the pipe 12. At the inner surface of the wall part of the energy is reflected, and part transmitted into a liquid 42 withinthe pipe 12. Thus the initial pulse will reverberate to andfro between the inner and outer surfaces ofthe wall of the pipe 12, gradually decreasing in amplitude, and a correspond ing sequence of pulses will propagate through the liquid 42 across a diameter of the pipe 12 and will be reflected back by the wall of the pipe 12 on the side remotefrom the transducer 30.

Referring to Figure 2, a liquid change detector 44 comprises the transducer 30 connected by the cable 38to atransmit/receive interface unit (TXIRX) 50, which is connected to an amplifier 52to amplify signals from the transducer 30. Amplified signals from the amplifier 52 are supplied to an input of a gated peak detector 54, the output from which operates a visual display unit 56. The operations, of the g ated peak detector 54 and the interface unit 50 are controlled by trigger signals supplied by a transmitter 58 simultaneously to both the gated peak detector 54 and the interface unit 50 at a repetition frequency of 2.5 kHz.

In operation ofthe liquid change detector44, each triggersignal from the transmitter 58 causes the interface unit 50 to excite the transducer 30 with a 500 volt spike. The transducer 30 is heavily damped, and oscillates at its natural frequency (10 MHz) for a few cycles, so sending a pulse of ultrasonic waves radially into the wall of the pipe 12 (see Figure 1). As described above, the ultrasonic pulse reverberates to and fro between the inner and outer surfaces of the wall of the pipe 12, and a corresponding sequence of pulses propagatesthroughthe liquid 42acrossthe diameter ofthe pipe 12 and is reflected back by the inner surface ofthe wall of the pipe 12 on the side remote from the transducer 30.The transducer 30 thus receives the reverberating pulses and then the reflected sequence of pulses. The amplitude of the reflected sequence of pulses is small when received because of attenuation of the pulses in the liquid 42, and because at each surface the pulses are partly reflected and partly trnnsmitted.The transducer 30 sends a series of corresponding electrical signals to the interface unit 50 and so to the amplifier 52.

The time delay between the trigger signal and the transducer 30 receiving the reflected series of pulses depends upon the velocity of sound in the liquid 42. In the case of water, the velocity of sound depends upon the temperature as shown in Table 1 (from "Speed of Sound in Pure Water" by del Grosso and Mader, Journal of the Acoustical Society of America, Vol.52, No.5 (part 2), 1972.), and for hot water at about 90"C, the time delay is about 130 microseconds.

TABLE 1 Temperature / "C Velocity / ms-t 0 1402.3 1 1407.4 2 1412.2 10 1447.3 12 1455.0 70 1554.8 80 1554.5 90 1550.5 In the case of cold beer at O"C, the velocity of sound has been measured for various samples, the results being shown in Table 2, and is about 7% less than the velocity of sound in hotwater.

TABLE 2 Sample Velocity/ ms-t Stout 1454.7 Bitter 1453.4 Lager 1 1453.2 Lager2 1469.7 Pale Ale 1455.3 As shown in Figures3a, when the liquid 42 is cold beer, the amplified signalsfrom the amplifier 52 consists of a first sequence of signals 60 correspond ing to the reverberating pulses, a second sequence of signals 62 corresponding to the reflected sequence of pulses, and at other times, noise 64. As shown in Figure 3b, when the liquid is hot water, the second sequence of signals 62 occurs 7% earlier, and is larger than with cold beer because the pulses are less attenuated bythe liquid 42. The duration of the first sequence of signals 60 and otthe second sequence of signals 62 is about 20 microseconds.

The amplified signals are supplied to an input of the gated peakdetector54which incorporates a gate which opens at a presettime A after receiving a trigger signal from the transmitter 58, remaining open for a time interval of 10 microseconds and then closing attime B. While the gate remains open the gated peak detector 54 measuresthe largest signal received, and from this measurement is subtracted a presetsignalto rep resent the noise 64.The output from the gated peak detector 54 to the visual display unit 56 is the difference between the largest signal received and the preset signal.

Thetime B is setto occur 2.5 microseconds before the start of the second sequence of signals 62when the liquid 42 is cold beer (so as to allowforvariations in the composition and temperature of the cold beer).

The outputfrom the gated peak detector 54 is consequently very small, being the difference between the noise 64 and the preset signal representing the noise 64.

If the liquid 42 in the pipe 12 changes to hot water, the second sequence of signals 62 occurs about 10 microseconds earlierthan with cold beer, and therefore starts during the time interval between A and B when the gate of the gated peak detector 54 is open.

Consequentlythe outputfrom the gated peakdetector is large, and a large signal is supplied tothevisual display unit 56, indicating that the liquid 42 has changed from cold beerto hot water.

If the liquid 42 changes back to cold beer, the output from the gated peak detector 54 will return to the very small value.

It will be understood that alternative circuits may be used in liquid change detectors embodying the invention, and in Figure 4, to which reference is now made, is shown a liquid change detector 70 differing from the detector 44of Figure 2 in that the gated peak detector 54 is replaced by a dual gated sample integrator 72.

Operation of the liquid change detector70 is similar to that of liquid change detector 44 of Figure 2, differing in that amplified signals from the amplifier 52 aresuppliedto an input ofthe dual gated sample integrator 72, which incorporates a first gate set to open at a presettimeC(see Figures 3a and b} after receiving a trigger signal from the transmitter 58,to remain open foratime interval of 20 microseconds and thento close attime B (which is set 2.5 microseconds before the start of the secondsequence of signals 62 when the liquid 42 is cold beer). The integrator 72 also incorporates a second:gatewhich is setto open 190 microseconds after receivingatrigger signal from thetransmitter 58 andto remain open for a time interval of 20 microseconds before closing again; during this time interval no signals 62 should be receivedwhetherthe liquid 42 is cold beer or hot water, and so the integrator 72 will receive only the noise 64.

The integrator 72 rectifies and integrates the electrical signals received during the time interval whenthefirstgate is open, and during the time interval when the second gate is open, producing in each case a voltage signal. The outputfrom the integrator 72 is proportional to the difference between the voltage signals corresponding to thetwo time intervals, and this output is supplied to the visual display unit 56.

When the pipe 12 contains cold beerthen asshown in Figure 3a no signals 62 are received during the time interval Cto Bwhilethefirstgate is open. The corresponding voltage signal will therefore represent the result of rectifying and integrating noise 64. So too will the voltage signal corresponding to the time interval when the second gate is open, and so the output of the dual gated sample integrator 72 will be very low. If the liquid 42 in the pipe 12 then changes to hotwater, then as shown in Figure 3bthe second sequence of signals 62 will start during the time interval Cto B while the first gate is open, and so the corresponding voltage signal will represent the result of rectifying and integrating the first few signals 62.

The voltage signal corresponding to the time interval when the second gate is open will again represent the result of rectifying and integrating noise 64, and hence there will be a large difference between the voltage signals, and a large output to the visual display unit 56. If the liquid 42 changes back to cold beerthen the output to the visual display unit 56 will return to the very lowvalue.

Although the outputofthe liquid change detectors 44 and 70 has been described as being a visual display unit 56to indicate whetherthe liquid 42 in the pipe 12 is hot water or cold beer, it will be understood that the output may be arranged to operate a valve (not shown) to control or divert the flow of liquid 42 in the pipe 12.

Claims (10)

1. Aliquidchange detectorfora container having afrontwall and the rearwallto accommodate a liquid, the detector comprising, a transducer adapted to cause a pulse of ultrasonic waves to propagate through the liquid, a transducer adapted to receive the pulse after propagation of the pulse through a predetermined distance in the liquid, and to emit an electrical signal representative of the received pulse, and a gatedsignal analyser responsive to the electrical signal, gated to operate during a preset time interval during which the ultrasonic pulse is expected to be received ifthe speed of sound in the liquid has a first value, but in which no ultrasonic pulse is expected to be received if the liquid has undergone a change such thatthe speed of sound in the liquid has second value.

2. A liquid change detector as claimed in Claim 1 wherein the transducers are acoustically coupled to the outside surface of the container.

3. A liquid change detector as claimed in Claim 1 or Claim 2 wherein the gated signal analyser comprisesa peak detector.

4. A liquid change detector as claimed in Claim 1 or Claim 2 wherein the gated signal analyser comprises a sampling integrator.

5. A liquid change detector as claimed in any one of the preceding Claims wherein the gated signal analyser incorporates means to distinguish between the signal and noise.

6. A liquid change detector as claimed in any one of the preceding Claims wherein the transducers are a singletransduceradaptedto operate in a pulse/ echo mode,thedpulse being received after reflection off the rearwall ofthecontainer.

7. A method for detecting a change in a liquid within a container having afrontwall and a rear wall, and a space between the frontwall and the rear wall to accommodate the liquid, comprising the operatios of causing a pulse of ultrasonic waves to propagate through the liquid, receiving the pulse after propagation ofthe pulse through a predetermined distance in the liquid and creating an electrical signal representative of the received pulse, and detecting whether a signal occurs during a presettime interval during which the pulse is expected to be received ifthe speed of sound in the liquid has a first value, but in which no pulse is expected to be received if the liquid has undergone a change such thatthe speed of sound in the liquid has a second value.

8. A liquid change detector substantially as hereinbefore described and with reference to Figures 1, 2, 3a and 3b ofthe accompanying drawings.

9. A liquid change detector as claimed ih Claim 8 modified substantially as hereinbefore described with referenceto Figure 4 of the accompanying drawings.

10. A method for detecting a change in a liquid within a container substantially as hereinbefore described with reference to Figures 1,2, 3a and 3b, or modified substantially as described with reference to Figure 4 of the accompanying drawings.