GB2111205A - Ultrasonic measuring system - Google Patents

Abstract

A system for measuring and controlling fluid comprises ultra-sonic signal transmission means (16), echo signal receiving means (16), and means (53) for measuring the time span between the transmission of the ultra-sonic signal and a receipt of the echo signal to obtain the distance that the signal has travelled. The system may include means responsive to said distance being outside of a certain span for varying the distance so as to bring the distance to a desired value within the span. The system may measure liquid level or flow rate when the ultra-sonic signal is reflected from a drag body (Fig. 3, not shown). <IMAGE>

Description

SPECIFICATION Sensor system This invention relates to sensor and control systems and more particularly to such sensor and control systems for use in fluid monitoring and control.

During many different processes the monitoring and control of fluids is essential. Such monitoring and control extends from industrial processes to medical processes. The extra-corporeal treatment of blood such as, for example, is accomplished in artificial kidney machines, requires the close monitoring of the conditions of the blood. Among the conditions monitored for example, is the flow rate of the blood and the dialysate. Another condition that is monitored in such treatment of blood is the blood level in bubble eliminator equipment.

It should be understood that while the system described herein is used in the extra-corporeal treatment of blood, such system could be also used in monitoring liquid flow in industrial processes.

The prior art system for monitoring different functions of fluids in the medical field, such as the flow rate or the level of a fluid such as blood, use sonic energy. In such systems, the sonic energy is transmitted on one side of a tube or cylinder and received on the other side. The transmission through air and the transmission through the fluid have different characteristics and therefore the monitor can determine when the level of the fluid has reached a height where it begins to interfere with the sonic transmission or where it stops interfering with the sonic transmission.

Flow rates on the other hand are often measured using venturi tube arrangements wherein pressure differentials are measured. The invasion of the actual liquid is obviated through the use of membrane devices separating the fluid whose flow is being measured from the measuring portions of the instrumentation. The prior art devices however leave something to be desired with regard to accuracy per cost of equipment and in general with regard to the ability to discriminate between small measurement differences.

Since the measurement of the characteristics of the fluid oftentimes is crucial and in fact may be determinative of whether or not a patient lives or dies, it is extremely important to be able to adequately measure such characteristics as blood flow rate and/or the level of the blood in a bubble eliminator tube.

Accordingly it is an object of the present invention to provide new and improved sensor systems for use in measurements of fluid characteristics especially when it is important that expensive portions of the measuring systems that are subject to corrosion be physically separated from the actual fluid and in which the disadvantages referred to hereinabove are substantially reduced or overcome.

According to the present invention a sensor system for measuring and controlling fluid is provided, such system comprises: ultra-sonic signal transmission means, echo signal receiver means, and means for measuring the time span between the transmission of the ultra-conic signal and a receipt of the echo signal to obtain the distance that the signal has travelled.

Another feature of the invention provides means responsive to said distance being outside of a certain span for varying the distance so as to bring the distance to a desired value that is within the certain span.

A further feature of the invention is to use the system for maintaining the level of blood in a bubble eliminator within certain specified limits.

Yet another feature of the invention is to use the output of the system to operate a pump to add or eliminate air from the bubble eliminating tube, thereby to raise or reduce the level of the blood therein.

Yet another feature of the present invention is to utilize the system to make known to the extracorporeal blood treatment system that the blood in the tube has dropped below a certain minimum level and to therefore provide saline solutions to the blood to once again raise the level.

Yet a further feature of the present invention is to use the ultra-sonic transmitting and receiving means for determining the position of a drag body in a vertical fluid carrying tube and to thereby determine the rate of flow of fluid in the tube.

A further feature provides means for operating a pump responsive to said flow measurements so as to maintain the flow within certain specified limits.

The operation and utilization of the present invention will be more fully apparent from the description of preferred embodiments taken in conjunction with the accompanying drawings, in which: Fig. 1 is a simplified block diagram showing the electronic sensor and control circuitry of the system; Fig. 2 is a block diagram showing of the servosystem utilized for operating the air pump to maintain the desired level span within the bubble eliminating device; and Fig. 3 is a block diagram showing the closed loop system utilized for controlling the rate of flow of the fluid by controlling a pump used in sending the fluid through the treatment system.

In Fig. 1 the basic sensor system 11 is shown. It comprises a tube 12 in which a distance is to be measured. In this exemplary situation it is shown as the distance "D" extending from the bottom 1 3 of the tube to the level of a liquid 14 in the tube.

Means are provided for transmitting a signal, preferably a sonic or ultrasonic signal into the liquid. More particularly, a transducer 1 6 such as a piezo-electric transducer is shown attached to the bottom 13 of the tube 12. The transducer 1 6 also receives any echo signal from the surface whose distance is being measured. In this exemplary case, the distance being measured is to the surface 14 that reflects the sonic vibrations.

The transmitting equipment includes a signal generator 1 8 for generating the output frequency signal to be transmitted in the form of pulses. A gate means 1 9 prevents the transmission of the signal from the signal generator until the gate is enabled. The gate 19 is connected to the signal generator through conductor 21. A driver amplifier 22 feeds the signal gated from the gate to the transducer 1 6.

A burst rate oscillator 23 provides an enabling signal for gate circuit 1 9. More particularly the burst rate oscillator is operated responsive to a start signal "SS" received as a result of operation of the start switch on the control panel of the machine. The start signal "SS" is transmitted over conductor 25 and operates the burst rate oscillator 23. The output of the burst rate oscillator is transmitted over conductor 26 to one shot synchronizing circuit 24.

The output of circuit 24 performs two functions, the first function is the initiation of the operation of the ultrasonic frequency oscillator 1 8.

Responsive to the operation of the signal generator 1 8 a signal is provided over conductor 21 to gate 19. The second function is to inhibit receiver circuitry.

At the same time the output on conductor 27 received from the synchronous one shot circuit 24 is transmitted over conductor 28 to another one shot circuit 29. This is a transmit gate one shot circuit operated responsive to the receipt of the signal on conductor 28. Transmit gate one shot circuit 29 provides a signal on conductor 31 which enables gate 1 9 and thereby provides an ultrasonic frequency signal over conductor 32 to driver 22. The amplified signal at the output of the driver on conductor 33 drives the transducer 1 6 to provide an ultrasonic signal in the fluid in tube 12.

Means are provided for measuring the height or level of the surface of the fluid as indicated at 14 in Fig. 1 responsive to the receipt of an echo from the surface of the fluid 14 where it interfaces with gaseous portion of the contents of tube 1 2. More particularly, amplifying means for amplifying the signal received by the transducer 1 6 are provided.

As shown in Fig. 1 the transducer 1 6 is coupled to first and second amplifier stages, 34 and 35 respectively, through conductor 36 coupled to transducer 16 through conductor 33.

The amplifiers are shown as inhibited by a signal from a receive gate one shot circuit 37. The receive one shot circuit 37 is operated responsive to a signal on conductor 31 which is transmitted thereto over conductor 38. The output of the one shot is coupled to the first and second receive amplifiers through conductor 39 and conductors 41 and 42, respectively. It is noted that the first stage amplifier 34 is shown with a gain control feedback variable resistor 43. The amplifiers are normally operated in the absence of the inhibit signal.

Means are provided for selecting the echo signals by determining among other things the frequency of the suspected echo by selectively receiving signals with the transmitted ultrasonic frequency. More particularly a mixer circuit 44 as shown schematically has coupled thereto a filter arrangement 46 for receiving signals of the transmitted frequency. The output of the mixer is amplified by amplifier 47. Amplifier 47 is a video amplifier or a wide band amplifier. The output of amplifier 47 is provided to a pulse ratio amplifier circuit 48 used to determine the ratio of the pulse with the total pulse length to further ascertain that the proper signal is being detected. Thus circuit 48 acts as a detector for the echo signal.

Further determinations are made to assure that the proper echo signal is being received. More particularly a threshold detector circuit 51 is provided at the output of detector 48. It provides a signal only responsive to a signal to the detector above a certain threshold level. When the signal is above a certain threshold level then the output from threshold detector circuit 51 is transmitted to a pulse width discriminator circuit 52 to assure that the echo is being received and not noise.

The output of pulse width discriminator 52 is then used to operate a time interval circuit or counter circuit 53. The counter circuit starts to count responsive to the output from the one shot circuit 24 and an output on conductor 28. The output on conductor 28 is transmitted to counter circuit 53 over conductor 54. The output of the counter is then displayed on a display device by display circuit 56. The output of the counter on conductor 57 can also be used to operate switches and circuitry as desired. Thus, responsive to an ultrasonic frequency signal being transmitted by transducer 1 6 and an echo received from a device in the liquid or from liquid surface 1 4 a determination is made based on how long it takes to receive the echo after the signal is transmitted. The display circuit translates this count to a distance.The distance is further translated to a level in the units desired. Thus constant monitoring of the liquid level is automatically provided using the ultrasonic signal.

Means are provided for stopping the count of counter 53. More particularly responsive to the detection by circuit 48 of an echo having the proper pulse width, an amplifier 49 amplifies the signal from the detector and transmits it to the first and second amplifiers 34 and 35 to reduce the gain of those amplifiers, thereby stopping any further pulses from being received. Thus responsive to the start signal and the signal being transmitted by the transducer the count stop responsive to the receipt by the detector 48 of a signal determined to be the echo. Thus the count provides the time differential for the signal to be transmitted from the transducer 1 6 and for the echo to be received back at the transducer 1 6.

Figs. 2 and 3 show how the output signal on conductor 57 is used for controlling either the level of the fluid in the bubble eliminator or the rate of flow of the fluid in artificial kidney machine such as that described in the patent application filed on even date herewith and entitled "Blood Treatment System".

In Fig. 2 the tube 12 is a bubble detector or eliminator and is shown with the transducer 1 6 attached thereto. The transducer 1 6 transduces the echo signal and transmits it to the electronic equipment shown in Fig. 1. The electronic equipment herein is indicated as circuitry 61 .The output of circuitry 61 on conductor 57 activates circuit 58 to provide a signal proportional to the distance D. The output of circuit 58 is transmitted to an input of a comparator circuit 62 over conductor 63. The other input to the comparator is the analog of the "set" signal. The output of the comparator is the difference between the signal on inputs. This difference output is fed into a servoamplifier 66 over conductor 64.The output of the servo-amplifier is used to drive a pump motor 67 which in turn drives the rotor in the rotary peristaltic air pump indicated as pump 68. The pump 68 operates in a direction to remove air from the tube 12, thereby removing some of the back pressure of the air and enabling the level of the fluid 1 4 (blood, for example) to rise indicates that the level is too high, appropriate steps are taken such as, for example, rotating the pump in the opposite direction to force air into the tube 12, thus lowering the level.

Fig. 3 is representative of the system being used to determine the rate of flow of fluid, for example dialysate in an artificial kidney machine.

The echo surface 71 is a surface on a dragbody or weighted float 72. The weighted float 72 is driven by the flow of the fluid through inlet tube 73, the conical passage 74 and outlet tube 76 which leads to the rotary or peristaltic blood pump 77. In the peristaltic pump, rollers such as rollers 78 forces liquid through the tube 76 when driven by pump motor 81.

In Fig. 3 the output of the transducer 1 6 is coupled into electrical circuit 79 which includes a comparator and servo-amplifier. The output of the servo-amplifier on conductor 70 is used to adjust the rate of the pump motor to attain the set flow rate of the fluid. Thus the system maintains the rate without a given span.

In operation the fluid operating characteristics such as flow and/or level are measured with accuracy, repeatability and reliability by determining the time required for an echo of a transmitted signal to be received. The distance is equal to the time span multiplied by the velocity of the sound in the liquid being monitored divided by two.

While the principles of the invention have been described above in connection with specific apparatus and applications, it is to be understood that this description is made by way of example only and not as a limitation on the scope of the invention.

Claims (11)

1. A sensor system for measuring and controlling fluid, said system comprising ultrasonic signal transmission means, echo signal receiver means, and means for measuring the time span between the transmission of the ultrasonic signal and a receipt of the echo signal to obtain the distance that the signal has travelled.

2. The sensor system of Claim 1 including means responsive to said difference being outside of a certain span for varying the distance so as to bring the distance to a desired value that is within said certain span.

3. The sensor system of Claim 1 wherein said signal is transmitted to a surface of a drag body and the echo is received from said surface, said drag body being moved in the liquid as a function of the flow of said liquid.

4. The sensor system of Claim 1 wherein said means for measuring the time span between the transmission of the ultrasonic signal and the receipt of the echo signal includes counter means, means responsive to the transmission of the ultrasonic signal for initiating the count of the counter and means responsive to the receipt of the echo signal for terminating the count of the counter whereby the count of the counter is indicative of the distance that the signal has travelled.

5. The sensor system of Claim 4 wherein said means for terminating the count of said counter includes pulse ratio amplifier means for determining the characteristics of the transmitted signal to determine that an actual echo signal has been received and means reponsive to the receipt of an actual echo signal for inhibiting receiver circuitry from receiving further echoes thereby terminating said count.

6. The sensor system of Claim 1 wherein said ultrasonic signal transmission means and said echo receiver means includes a single transducer capable of transmitting an ultrasonic signal responsive to the input thereto of electrical signals at an ultrasonic rate and means responsive to the receipt of ultrasonic signals for converting said ultrasonic pressure signals to electrical signals.

7. The sensor system of Claim 1 wherein said ultrasonic signal transmission means transmits signals to the liquid surface in a tube at the interface between the liquid surface and a gaseous surface, and said echo being received back at said transducer from said interface surface, thereby to determine the distance that the signals have travelled.

8. The sensor system of Claim 7 wherein means are provided for comparing the determined distance to a set distance and means responsive to differences between said determined distance and said set distance for activating equipment to bring said determined distance to said set distance.

9. The sensor system of Claim 8 wherein said equipment activated to bring said determined distance to be equal to said set distance comprises pump means for pumping air to or from said tube.

10. The sensor system of Claim 9 wherein said pump means is used for varying the flow rate of said liquid.

11. A sensor system for measuring and controlling fluid substantially as hereinbefore described with reference to the accompanying drawings.