GB2129130A

GB2129130A - Fluid temperature change detector

Info

Publication number: GB2129130A
Application number: GB08323104A
Authority: GB
Inventors: Adrian Carey Tolchard; David Christopher Isaacs
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1982-09-13
Filing date: 1983-08-26
Publication date: 1984-05-10
Also published as: GB8323104D0; GB2129130B

Abstract

A fluid temperature change detector 44 incorporates a transducer 30 coupled to the outside of a wall of a fluid container 12. The transducer 30 is adapted to operate in a pulse/echo mode, so as to generate a pulse and to receive ultrasonic echo pulses reverberating between the inside and outside surfaces of the wall. Amplified return signals from the transducer 30 are supplied to a gated peak detector (54, Fig. 2) which is gated to operate during a predetermined time interval which occurs between consecutive reverberating echoes at one temperature of the wall. A change in temperature of the wall 12 due to a change in fluid temperature causes a change in the time between consecutive reverberating echoes, so that an echo is then received during the time interval when the peak detector (54) is operating, and a large output signal is then given to a visual display (56, Fig. 2). The output signal may be used to control a valve used to control or divert fluid flow. The detector may be used in the brewing industry to determine the interface between beer at 0 DEG C and sterilizing water at 100 DEG C. <IMAGE>

Description

SPECIFICATION Temperature change detector This invention provides a temperature change detector, for detecting changes in temperature of a wall of a container.

In the brewing industry it is common practice to pass beer at about 0 C along a pipe, and then to pass water at almost 1000C along the same pipe to sterilize the pipe. It is important to know exactly when the liquid change occurs, to enable valves to be operated appropriately, so as to divert the 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 of the pipe will have a long response time because of the thermal capacity of the pipe itself, while a :thermocouple attached to the inside of the pipe may provide a surface which is difficult to clean, and so act as a source of contamination.

According to the present invention there is provided a temperature change detector comprising, a transducer adapted when energised to cause a pulse of ultrasonic waves to reverberate between opposite surfaces of a wall, a transducer adapted to receive the reverberating pulses and to produee signals representative thereof, and a pulse detector responsive to the signals and gated to operate during a predetermined time interval in which a signal is expected at a first temperature of the wall but no signal is expected at a second temperature of the wall.

The transducers may be a single transducer operating in a pulse transmitting mode and a pulse receiving mode.

The time interval preferably occurs within the period between signals representing consecutive reverberating pulses at the second temperature of the wall, and desirably occurs after the second reverberating pulse and before the twentieth reverberating pulse.

Preferably the pulse detector incorporates means for comparing the signal received during the gated time interval with a signal representative of noise.

The present invention also provides a method for detecting a change in the temperature of a -waIf, comprising the operations of causing a pulse of ultrasonic waves to reverberate between opposite surfaces of the wall, receiving said reverberating pulses, and creating signals representative thereof, and determining whether a signal occurs during predetermined time interval in which a signal is expected at a first temperature of the wall but no signal is expected at a second temperature of the wall.

The invention will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 is a longitudinal sectional view of a transducer assembly attached to a pipe; Figure 2 is a block electronic circuit diagram of a temperature change detector incorporating the transducer assembly of Figure 1; Figures 3a and 3b are diagrammatic graphs of signals in the circuit of Figure 2 at two different temperatures.

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, 100 mm bore, and of wall thickness 3 mm.

The assembly 10 incorporates a tubular transducer housing 1 8 one end of which has a flange 20 on which the clip 14 bears, and the outside face of the flange 20 is curved to fit against the outside of the pipe 12 with the longitudinal axis of the housing 1 8 extending radially from the pipe 12. The end of the housing 1 8 remote from the pipe 12 has an externally threaded 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 tubular space 34 which bears against the screw cap 24. A thin layer 36 of silicone grease couples the transducer 30 ultrasonically to the wall of the pipe 12. Electrical contact to 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 transducer 30 against the pipe 12 can be adjusted by turning the screw cap 24.

When the transducer 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 fluid 42 within the pipe 12. Thus the initial pulse will reverberate to and fro between the inner and outer surfaces of the wall pipe 12, gradually decreasing in amplitude, and a corresponding sequence of pulses will propagate through the fluid 42 across a diameter of the pipe 1 2 and will be reflected back by the wall of the pipe 12 on the side remote from the transducer 30.

Referring to Figure 2, a temperature change detector 44 comprises the transducer 30 connected by the cable 38 to a transmit/receive interface unit (TX/RX) 50, which is connected to an amplifier 52 to 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 gated 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 of the temperature change detector 44, each trigger signal from the transmitter 58 causes the interface unit 50 to provide a 500 volt spike to the transducer 30. The transducer 30 is heavily damped, and oscillates at its resonant frequency (10 MHz) for a few cycles, so sending a short pulse of ultrasonic waves radially into the wall of the pipe 12 (see Figure 1).

As described above the ultrasonic pulse will reverberate to and fro between the inner and outer surfaces of the wall of the pipe 12, and the transducer 30 will therefore receive a series of ultrasonic pulses, of decreasing amplitude, and will send a series of corresponding electrical signals to the interface unit 50, and so to the amplifier 52. The interval between successive reverberating ultrasonic pulses is determined by the thickness of the wall of the pipe 14 and by the speed of sound in stainless steel, and at a temperature of OOC is about 1 microsecond.

The corresponding amplified signal, shown in Figure 3a, consists of a series of electrical pulses 60 in between which there is noise 62. The gated peak detector 54 incorporates a gate which opens at a preset time A after receiving a trigger signal from the transmitter 58, remaining open for a time of 350 nanoseconds and then closing at time B.

While the gate remains open the peak detector 54 measures the largest signal received, and from this measurement is subtracted a preset signal representing a typical noise signal 62. The output from the gated peak detector 54 is the difference between the largest signal received and the preset signal.

The time A is set to occur 5 ns after the fourth reverberating ultrasonic pulse is received, when the pipe 1 2 is at a temperature of OOC. The output from the gated peak detector 54 is consequently very small, being the difference between a noise signal and the preset signal representing a typical noise signal. If the temperature of the fluid 42 in the pipe 1 2 of Figure 1 increases to 900C, the pipe 12 will also rise in temperature. In raising the temperature of stainless steel from OOC to 900C the velocity of sound decreases by 1.5%, so the time interval between successive reverberating ultrasonic pulses increases by 1.5%, that is by 15 ns.As shown in Figure 3b the fourth reverberating ultrasonic pulse will then occur 60 ns later than when the pipe 12 was at OOC, and so an electrical pulse 60 will be received by the gated peak detector 54 during the time interval between A and B when the gate is open.

Consequently the output from the gated peak detector 54 is large, and a large signal is supplied to the visual display unit 56, indicating that the pipe 12 is hot. If the temperature of the pipe 12 returns to OOC, the output from the gated peak detector 54 will return to the very small value.

Although the output of the gated peak detector 54 has been described as being connected to the visual display unit 56 to indicate whether the pipe 12 is hot or cold, it will be understood that the output may be arranged to operate a valve (not shown) to control or divert the flow of the fluid 42 in the pipe 12. It will be appreciated that the time interval during which the gate is open must be sufficiently long to allow the peak 60 to enter (at least 20 ns) but not so long as to allow any secondary peaks or excessive noise to enter. For the wall thickness of 3 mm (and hence an interval of 1 microsecond between reverberating ultrasonic pulses) the gate is desirably arranged to be open for a time between 200 and 500 ns.It will also be appreciated that the time A at which the gate is arranged to open must not be too soon after the trigger signal, as the first few reverberating ultrasonic pulses may be swamped by noise and initial transient signals; equally the time A must not be too long after the trigger signal, as the amplitude of the reverberating ultrasonic pulses decreases exponentially with time due to attenuation and to loss of energy at each reflection. On the other hand the longer the time A is, the more sensitive will be the detector 44 to changes in temperature of the pipe 12. The attenuation of ultrasonic waves in the wall of the pipe 12 is an increasing function of their frequency. For the 10 MHz transducer 30 used in conjunction with the 3 mm thick stainless steel pipe 1 2, the time A is desirably set to occur shortly after the fourth, fifth or sixth reverberating ultrasonic pulse is received.

Claims

1. A temperature change detector comprising, a transducer adapted when energised to cause a pulse of ultrasonic waves to reverberate between opposite surfaces of a wall, a transducer adapted to receive the reverberating pulses and to produce signals representative thereof, and a pulse detector responsive to the signals and gated to operate during a predetermined time interval in which a signal is expected at a first temperature of the wall but no signal is expected at a second temperature of the wall.

2. A temperature change detector as claimed in Claim 1 wherein the time interval occurs within the period between signals representing consecutive reverberating pulses at the second temperature of the wall.

3. A temperature change detector as claimed in Claim 2 wherein the time interval occurs after the signal representing the second reverberating pulse.

4. A temperature change detector as claimed in Claim 3 wherein the time interval occurs before the signal representing the twentieth reverberating pulse.

5. A temperature change detector as claimed in any one of the preceding Claims further comprising means for comparing the said signal received from the transducer with a signal representing ultrasonic noise.

6. A temperature change detector as claimed in any one of the preceding Claims wherein the transducers are a single transducer adapted to operate in a pulse/echo mode.

7. A method for detecting a change in the temperature of a wall comprising the operations of causing a pulse of ultrasonic waves to reverberate between opposite surfaces of the wall, receiving said reverberating pulses, and creating signals representative thereof, and determining whether a signal occurs during a predetermined time interval in which a signal is expected at a first temperature of the wall but no signal is expected at a second temperature of the wall.

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

9. A method for detecting a change in temperature of a wall substantially as hereinbefore described and with reference to Figures 1, 2, 3a and 3b of the accompanying drawings.