GB1573914A - Detection of variations in sonic velocity in liquids - Google Patents

Description

(54) DETECTION OF VARIATIONS IN SONIC VELOCITY IN LIQUIDS (71) We, IMPERIAL CHEMICAL INDUSTRIES LIMITED, Imperial Chemical House, Millbank, London SWIP 3JF, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to the detection of variations of sonic velocity in liquids.

Variations in the composition of liquids, for example variations in the concentrations of solutions or changes in their composition consequent on the progress of a chemical reaction in the liquid, commonly gives rise to variations in the velocity of sound passing through them. The determination of changes in sonic velocity in liquids is thus a potentially useful tool for monitoring changes in the liquids, for example the progress of chemical reactions.

This invention comprises a process of testing liquids in containers which comprises transmitting pulses of sonic vibration from a source through the liquid to a detector of the sonic vibration and measuring the difference between the time taken for the sound to travel from the.

source to the detector and a set standard time interval.

The sonic vibration may be reflected back to a detector situated close to or within the transmitter.

Equipment and methods of transmitting vibrations through liquids are well known.

The transmitter and detector of sonic vibration may be in the liquid or communicate with it through barriers enclosing it. Apparatus for detecting the difference between the time taken for the sound to travel from a source to a detector and subtracting the standard time interval from that difference is known in connection with the location of faults in solids, i.e. metal objects. The source and the detector of sonic vibration may be in the liquid or facing the liquid through a wall of a container bounding the liquid.

It is preferred that the process should be reputed at as fast a rate as is consistent with the avoidance of the association of the wrong signal from the detector with a trans mission pulse. It is preferred also that the results of successive determinations should be averaged in order to improve the experi mental accuracy of the method.

Where, because of multiple reflections or other interfering phenomena a single trans mission pulse produces a number of detector signals, means should be provided for taking into account only the first of such detector signals.

If desired a similar process can be applied to a series of cells containing the same liquid in order to increase the number of measure ments the results of individual deter minations being averaged. If desired a common excitation signal may be applied to sources of sonic vibration for each of the cells each of which is provided with a detector the signals from which may be processed in a common system by a switching process or in separate systems.

Apparatus for use in this invention may be made intrinsically safe for operation in hazardous conditions.

The invention also comprises apparatus for testing liquids which comprise a container for holding the liquid and means for transmitting pulses of sonic vibration from a source through the liquid to a detector of the sonic vibration and means for determining the difference between the time taken for the sound to travel from the source to the detector and the set standard time interval.

The container may be part of the structure of a chemical plant e.g. a conduit or reactor.

If desired the process may be corrected for temperature changes in the liquid by varying the standard time interval automatically by an emperically determined amount in accordance with temperature measurements taken in the liquid.

The detector system should not respond to sound of sound of amplitude corresponding to electronic noise within the system but in order to cope with timing errors due to attenuation of sound in viscous fluids it should preferably respond to signals as near as is practicable to that level.

It is preferred that the detector system should produce a square wave output in response to sonic pulses detected.

The sonic vibration may be in the range 5 Hz to 40 megaherz preferably of 0.15 to 10 megaherz and more preferably 0.5 to 5 megaherz.

One form of the invention will now be described with reference to the accompanying figure which is a diagrammatic representation of the equipment. An electronic clock equipped with a counter, store means for displaying the value in the store and means for producing signals at sub multiples of its frequency and which operates at a basic frequency of 10 megaherz, 1, feeds signals at a frequency of 100 Hz to a pulse generator 2 which has an adjustable pulse width and feeds an ultrasonic transducer 3 which acts as a source of sonic vibration and is situated in a liquid 4.

Transducer 3 also acts as a detector for ultrasonic vibration and which feeds an amplifier 6 which amplifies signals received from the detector to a value suitable for transmission. The amplifier 6 is provided with means to limit large input signals from pulse generator 7 to prevent damage. The amplifier feeds a comparator 7 which compares incoming signals from the amplifier with a threshold value and transmits signals only when they are above the threshold value to a monostable 8 which passes singals to the clock/counter/store 1 to stop the counter.

Simultaneous signals at a frequency of 100 Hz are fed from clock/counter/store I to preset delay 9 which in turn feeds voltage dependent delay 10 to produce an additive delay. Voltage dependent delay 10 is fed from a temperature sensor 11 situated in liquid 4 through temperature transmitter 12 and an adjustable amplifier 13. The temperature sensor is suitably a platinum resistance thermometer. The temperature transmitter is in this case a commercial ancilliary module for a platinum resistance thermometer.

Voltage dependent delay 10 feeds a start signal to the counter in clock/counter/store 1 at a delay after each signal of frequency 100 Hz from timer 1 which is the sum of the preset delay of 9 and a delay depending on the temperature of the liquid.

A monostable 16 is fed with a signal from clock/counter/store 1 at a frequency of 1 Hz and feeds an updating signal to the store of the clock/counter/store 1. Monostable 16 also feeds a second monostable 17 which in turn gives a reset signal to the counter of clock/counter/store 1 at a small time interval after the incoming signal from monostable 16. By this means the value in the counter is transferred to the store once per second and the counter is cleared for accumulation of fresh values.

Clock/counter/store 1 is adapted to feed binary coded digital to analogue convertors 14 and 15 which may feed a graphical display. These can be used for fine or coarse display of changes in the store values. The binary coded digital outputs may also be fed if desired to alarm systems.

The apparatus operates as follows:- Clock/counter/store I feeds a signal to pulse generator 2 which causes ultrasonic transducer 3 to transmit a pulse of sonic vibration to the opposite wall of container 5 from which it is reflected to the transducer.

Simultaneously a signal is passed to preset delay 9 which after the addition of a voltage dependent delay relating to the temperature of the liquid as recorded by temperature senser 11 serves to start the counter.

The signal from the sonic detector after amplification and filtering through the comparator 7 produces a signal from monostable 8 which serves to stop the counter in clock/counter/store 1. By this means counting proceeds only after the preset delay and voltage dependant delay and until receipt of the reflected sonic vibration by the detector. False signals passed to monostable 8 as a result of the initial transmission of sound by transducer 3 are irrelevant because they occur in the interval before the counter in clock/counter/store 1 starts.

After the results of 100 counts have been transferred to the store of the clock/counter/store 1 the value accumulated in the store is displayed in digital form and if desired after processing by the binary coded digital to analogue converters 14 and 15 in analogue form the counter then being reset to zero. The value displayed indicates the difference between the time taken for the sound to travel from the transducer 3 and back to it and a standard time interval, (the standard time interval being reset for the temperature of the fluid) multiplied by 100. The average value of 100 individual measurements is thus readily derivable in this form of the invention.

False stop signals resulting from multiple reflections of the previous pulses of sound may be eliminated by an appropriate selection of pulsing frequency.

Claims (12)

WHAT WE CLAIM IS:

1. A process of testing liquids in containers which comprises transmitting pulses of sonic vibration from a source through the liquid to a detector of the sonic vibration and measuring the difference between the time taken for the sound to travel from the source to the detector and a set standard time interval.

2. A process as claimed in Claim 1 in which the sonic vibration is reflected back to a detector situated close to or within the transmitter.

3. A process as claimed in either preceding claim which is repeated at as fast a rate as is consistent with the avoidance of the association of the wrong signal from the detector with a transmission pulse.

4. A process as claimed in any preceding claim which is carried out repeatedly and in which the results of successive determinations are averaged.

5. A process as claimed in any preceding claim in which means is employed for taking account of only the first detector signal in cases in which a single transmission pulse produces a number of detector signals.

6. A process as claimed in any preceding claim which is applied to a series of cells containing the same liquid, the results of individual determinations being averaged.

7. A process as claimed in Claim 6 in which a common excitation signal Is applied to sources of sonic vibration for each of the cells each of which is provided with a detector the signals from which may be processed in a common system by a switching process or in separate systems.

8. Apparatus for testing liquids by a process as claimed in any preceding claim which comprises a container for holding the liquid and means for transmitting pulses of sonic vibration from a source through the liquid to a detector of the sonic vibration and means for determining the difference between the time taken for the sound to travel from the source to the detector and a set standard time interval.

9. A process or apparatus as claimed in any preceding claim in which the detector system produces a square wave output in response to sonic pulses detected.

10. A process for apparatus as claimed in any. preceding claim in which the sonic vibration is in the range 0.15 to 10 megaherz.

11. A process of testing liquids substantially as described with reference to the drawing.

12. Apparatus for testing liquids substantially as described with reference to the drawing.