Turbidity sensor based on ultrasound measurements

Abstract

A turbidity measurement device for measuring turbidity of a fluid flowing in a flow tube. A first transducer transmits ultrasonic signals through the fluid in the turbidity measurement section so as to provide a first ultrasonic standing wave between the first and second section ends. A receiver transducer receives the ultrasonic scattered response from particles in the fluid flowing through the turbidity measurement section. A control circuit operates the transducers and generates a signal indicative of the turbidity of the fluid in response to signals received from the receiver transducer. Preferably, the device may comprise a second transducer for generating a second ultrasonic standing wave with the same frequency, and further the two transducers may be used to generate a measure of flow rate by means of known ultrasonic techniques. This flow rate may be used in the calculation of a measure of turbidity. Both turbidity facilities and flow rate facilities may be integrated in a consumption meter, such as a heat meter or a water meter.

Claims

1. A device arranged to measure turbidity of a fluid flowing in a flow tube, the device comprising: a flow tube having a through-going opening for passage of a fluid between an inlet and an outlet and a turbidity measurement section between a first section end and a second section end, a first transducer arranged to transmit ultrasonic signals having a frequency f.sub.0 through the fluid in the turbidity measurement section so as to provide a first ultrasonic wave between the first and second section ends, a second transducer arranged to transmit ultrasonic signals through the fluid in the turbidity measurement section, so as to provide a second ultrasonic wave between the second and first section ends, a receiver transducer arranged for receiving ultrasonic signals scattered on particles in the fluid flowing through the turbidity measurement section, wherein the receiver transducer has a receiving surface which is parallel to a propagation direction of the first ultrasonic wave, and a control circuit connected to the first transducer, the second transducer, and the receiver transducer, the control circuit being arranged to operate the first transducer and the second transducer, demodulate signals received from the receiver transducer such that the receiver transducer exhibits a residual oscillation at a frequency f.sub.s, and to generate a signal indicative of the turbidity of the fluid in response to signals received from the receiver transducer based, at least in part, on the frequency f.sub.s, and a flow rate of the fluid.

2. The device according to claim 1, wherein the first transducer is arranged at said first section end, and wherein a reflecting element is arranged at the second section end for reflecting the ultrasonic signals.

3. The device according to claim 1, wherein the first and second ultrasonic waves have similar frequencies.

4. The device according to claim 1, wherein a frequency of the first ultrasonic wave is a rational number p/q times a frequency of the second ultrasonic wave, or wherein a frequency of the first ultrasonic wave and a frequency of the second ultrasonic wave differ by 0.1% to 10%.

5. The device according to claim 1, wherein the first and the second ultrasonic waves are standing waves.

6. The device according to claim 1, wherein the first and second ultrasonic waves are transient waves of similar frequency in the form of wave packets, which are shorter than the distance between the first section end and the second section end, so as to form a transient standing wave in at least part of the turbidity measurement section.

7. The device according to claim 1, wherein the first ultrasonic wave is a standing wave.

8. The device according to claim 1, comprising flow measurement means, wherein said flow measurement means comprises the first transducer.

9. The device according to claim 8, wherein the control circuit is arranged to operate the first transducer in a first and a second operation time interval, wherein the first and second operation time intervals are not overlapping, wherein the control circuit is arranged to operate the first transducer for measuring the turbidity of the fluid flowing in the flow tube during the first operation time interval, and wherein the control circuit is arranged to operate the first transducer for measuring the flow rate of the fluid flowing in the flow tube during the second operation time interval.

10. The device according to claim 8, wherein the control circuit is arranged to operate the first transducer at a first frequency for measuring the turbidity, and is further arranged to operate the first transducer at a second frequency for measuring the flow rate.

11. The device according to claim 1, comprising temperature measurement means, wherein said temperature measurement means comprises the first transducer.

12. The device according to claim 1, comprising a first ultrasonic reflector arranged to guide ultrasonic signals from the first transducer in a direction of the fluid flowing in the turbidity measurement section.

13. The device according to claim 1, wherein the receiver transducer is arranged in an opening in a wall of the flow tube.

14. The device according to claim 1, comprising an acoustic lens or an aperture arranged in relation to the receiver transducer, so as to limit a volume of the turbidity measurement section from which ultrasonic signals can reach the receiver transducer.

15. An ultrasonic consumption meter comprising a device according to claim 1.

16. A system for monitoring turbidity of fluid in a utility network, the system comprising: a plurality of devices according to claim 1, wherein each of the plurality of devices is arranged to transmit signals indicative of the turbidity of the fluid, a communication system arranged to mediate said signals indicative of the turbidity of the fluid from the plurality of devices, and a processor system arranged to analyze said signals indicative of the turbidity of the fluid.

17. The system for monitoring turbidity of fluid in a utility network according to claim 16, wherein at least one of the plurality of devices is arranged to be a leak indicator in the event the turbidity of the fluid associated with the at least one of the plurality of devices is higher than the turbidity of the fluid associated with a different at least one of the plurality of devices.

18. The device according to claim 1, wherein: the through-going opening of the flow tube defines a flow path for passage of the fluid; the first transducer is arranged to transmit ultrasonic signals along a path through the fluid in the turbidity measurement section; and the receiver transducer is positioned outside of the flow path of the fluid and outside of the path of the transmitted ultrasound signals.

19. A method of measuring turbidity of a fluid flowing in a turbidity measurement section of a flow tube, the method comprising: transmitting ultrasonic signals having a frequency f.sub.0 from a first transducer to generate an ultrasound wave between a first section end and a second section end, transmitting ultrasonic signals from a second transducer to generate a second ultrasound wave between the first section end and the second section, receiving, by means of a receiver transducer having a receiving surface which is parallel to a propagation direction of the first ultrasonic wave, ultrasonic signals scattered on particles in the fluid, demodulating signals received from the receiver transducer with the frequency f.sub.0 such that the receiver transducer exhibits a residual oscillation at a frequency f.sub.s, and generating a signal indicative of the turbidity of the fluid in response to signals received from the receiver transducer based, at least in part, on the frequency f.sub.s, and a flow rate of the fluid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention will be described, by way of example only, with reference to the drawings, in which

(2) FIG. 1 illustrates a sketch of an embodiment with two transducers generating an ultrasonic standing wave between them, and the receiver transducer arranged at the wall of the flow tube,

(3) FIG. 2 illustrates a sketch of an embodiment similar to that of FIG. 1 but with reflectors serving to direct ultrasonic waves from the two transducers,

(4) FIG. 3 illustrates an embodiment similar to FIG. 1 but with a plurality of receiver transducers distributed along the flow tube,

(5) FIG. 4 illustrates a sketch of an embodiment with one transducer generating an ultrasonic travelling wave, and the receiver transducer arranged at the wall of the flow tube,

(6) FIG. 5 illustrates a system embodiment with a plurality of water meters with turbidity measurement facilities connected to a utility net and communicating turbidity data to a central facility for processing,

(7) FIG. 6 shows the variation of the residual frequency f.sub.s with the flow velocity v,

(8) FIG. 7 shows the variation of the intensity of the frequency shifted signal vs. the turbidity level, and

(9) FIG. 8 illustrates steps of a method embodiment.

DESCRIPTION OF EMBODIMENTS

(10) FIG. 1 illustrates a sketch of a turbidity measurement device embodiment with a flow tube with walls W, where two transducers T1, T2 are arranged in the flow tube and serve as end sections for the turbidity measurement section TMS between which two ultrasonic standing waves are generated. The dark circles indicate particles flowing along the fluid in the flow tube with flow rate v. A receiver transducer R1 is arranged at the wall W of the flow tube at a central position between the two transducers T1, T2. For one particle an ultrasonic response to the ultrasonic standing wave is indicated with a dashed arrow towards the receiver transducer R1 which then captures the ultrasonic response from the particle. With an ultrasonic standing wave with frequency f.sub.0, the expected frequency f.sub.s of high intensity scattering of a particle in a fluid with flow rate v is: f.sub.s=(v/c)f.sub.0, where c is the speed of the ultrasonic wave in the fluid. Thus, a high intensity response from particle scattering of the ultrasonic standing wave can then be expected with a period time of P=1/f.sub.s at the receiver transducer, as indicated in the response versus time t to the upper right corner of FIG. 1.

(11) A control circuit CC comprises an electric generator that applies electric drive signals to the transducers T1, T2 at the single frequency f.sub.0, receives the response from the receiver transducer R1 and generates in response a signal indicative of turbidity TB. As indicated, the signal from the generator may be applied to a multiplier together with the response from the receiver transducer R1, thus demodulating the received signal. Further, the control circuit CC preferably applies a filtering, e.g. involving Fast Fourier Transform finite impulse response or infinite impulse response digital filters, so as to explore the actual high intensity response from particles at the expected periodicity P. The resulting signal can then be quantified so as to provide a measure of particle density in the fluid, i.e. a measure of turbidity.

(12) It is to be understood that the same two transducers T1, T2 can be used as well for ultrasonic flow rate measurement, such as known in the art, and thus preferably the flow rate v can be measured with the device as well, thus delivering the flow rate v to the control circuit, thereby allowing the above described calculation of f.sub.s.

(13) Not shown, the receiver transducer R1 may be retracted from the flow tube wall W, so as to receive only ultrasonic response from a limited portion of the flow tube, rather than all response including reflections.

(14) FIG. 2 shows an embodiment similar to FIG. 1 except for the position of the two transducers T1, T1, since here section ends of the turbidity measurement section TMS are constituted by respective ultrasonic reflectors RF1, RF2, e.g. polymeric, composite, or metallic reflectors. Thus, the transducers T1, T2 are positioned out of the fluid flow, along the wall W of the flow tube, and their ultrasound signals are then directed in the flow direction, such that the ultrasonic standing waves between the reflectors is along the flow direction.

(15) FIG. 3 shows an embodiment similar to FIG. 1 except for the use of 6 separate receiver transducers R1-R6 arranged along the flow tube wall. The responses from these receiver transducers R1-R6 are then combined in the processing of the control circuit to result in one single measure of turbidity TB.

(16) FIG. 4 illustrates an alternative embodiment of the invention. Compared to the embodiment of the invention of FIG. 1, this embodiment comprises only one transducer T1, and the ultrasonic wave is a travelling wave, i.e. a non-standing wave, as it is only scarcely reflected at the section end E2, or not at all.

(17) The intensity response from particle scattering will not be enhanced by the cavity build up enhancement factor, but it will still exist owing to the Doppler effect. The expected frequency remains f.sub.s, as described above.

(18) FIG. 5 shows a system embodiment. Two groups G1, G2 of water meters W_M are connected to measure consumed water at respective consumers on a water utility network U_N. The water meters W_M are arranged to measure turbidity according to the present invention, preferably using one or two ultrasonic transducers which are also involved in flow rate measurement for generating a measure of consumed water. Consumed water data and turbidity data are transmitted wirelessly by the water meters W_M to a central communication module which extracts the turbidity data TB_D which are then applied to a data processing DP for further analysis. E.g. in case turbidity is generally higher in group G1 than group G2, it may be used as an indicator that a leak in the piping system between the positions of the two groups G1, G2 of water meters W_M allows soil or other contamination in the water utility network U_N, and thus helps in finding such broken pipe. Otherwise, the turbidity data TB_D may be used to generally monitor water quality delivered to the consumers.

(19) FIG. 6 shows the variation of the residual frequency f.sub.s with the flow velocity v.

(20) A device according to the invention as sketched with FIG. 1 was connected to a flow system having a constant turbidity. The transducer was driven with a constant frequency in the range 5-15 MHz and an external time-of-flight flow meter was measuring the flow rate. The signal from a receiver transducer, placed in the turbidity measurement section, was collected and its frequency shift f.sub.s analyzed. The flow velocity based on flow measurement is shown on the x-axis. The y-axis represent the frequency shift where the carrier frequency has been used as units. As can be seen from the figure, the frequency shift varies linearly with flow velocity according to the principle of the residual oscillation frequency of the invention.

(21) FIG. 7 shows the variation of the intensity of the frequency shifted signal vs. the turbidity level.

(22) The setup described in FIG. 6 was employed with a constant flow velocity, i.e. the frequency shift is constant. A series of measurement with varying turbidity (based on a 4000 NTU polystyrene standard) of the fluid flow was conducted. The intensity of the frequency shifted signal is analyzed and plotted as a function of the turbidity. A clear monotonic correspondence is seen between the turbidity and receiver response, even over the broad operational range of the sensor.

(23) FIG. 8 shows steps of a method embodiment for measurement of turbidity of a fluid flowing in a flow tube. First, an ultrasound signal is transmitted T_US_F1 at a first frequency from a first transducer trough the fluid, to generate a first ultrasonic standing wave in the flow tube. A response is received R_US_1 by means of a receiver transducer capturing ultrasonic signals scattered on particles in the fluid, and generating G_TB a signal indicative of the turbidity of the fluid in response to signals received from the receiver transducer. Further, another ultrasonic signal is transmitted T_US_F2 from the transducer at a second frequency which is lower than the first frequency. A response thereto is received R_US_2 at a second transducer, and in response a signal indicative of flow rate of fluid flowing in the flow tube is generated G_FR accordingly. Preferably, this flow rate is used in the generation of the signal indicative of the turbidity.

(24) To sum up, the invention provides a turbidity measurement device for measuring turbidity of a fluid flowing in a flow tube. A first transducer transmits ultrasonic signals through the fluid in the turbidity measurement section so as to provide a first ultrasonic wave between the first and second section ends. A receiver transducer receives the ultrasonic scattered response from particles in the fluid flowing through the turbidity measurement section. A control circuit operates the transducers and generates a signal indicative of the turbidity of the fluid in response to signals received from the receiver transducer. Preferably, the device may comprise a second transducer for generating a second ultrasonic wave with the same frequency, and further the two transducer may be used to generate a measure of flow rate by means of known ultrasonic techniques. This flow rate may be used in the calculation of a measure of turbidity. Both turbidity facilities and flow rate facilities may be integrated in a consumption meter, such as a heat meter or a water meter.

(25) Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The invention can be implemented by any suitable means; and the scope of the present invention is to be interpreted in the light of the accompanying claim set. Any reference signs in the claims should not be construed as limiting the scope.