AU627094B2 - Ultrasonic detector - Google Patents

Description

IA 0 627094 FORM COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION S F Ref: 57471D1

(ORIGINAL)

FOR OFFICE USE: Class Int Class Complete Spec ification Lodged: Accepted: Published: 0 oo 00 09 0n 0 0 '4*44 Priority: Related Art: Name and Address of Applicant: Abbott Laboratories Abbott Park Illinois 60064 UNITED STATES OF AMERICA Address for Service: Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia

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Complete Specification for the invention entitled: Ultrasonic Detector The following statement is a full description of this invention, including the best method of performing it known to me/us jO/ 12//9 L. i 5845/3 4: i W ft.

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ft ft ft ot 1 ULTRASONIC DETECTOR This is a divisional of Application No 5316/88.

The present invention relates to a detector which is adapted to detect whether a gas or a liquid is present in a fluid delivery conduit, The detector of the present invention is particularly suited for use as a low cost air-in-line detector in intravenous flow control equipment for delivering intravenous fluid to patients.

In administering intravenous fluid to patients, it is important to monitor the fluid being administered for the presence of air because if air is infused into a patient, an embolism can occur. Air can be introduced into a system through a leak in a tubing connector, through a crack in the equipment, or when the container from which the fluid is delivered is emptied. In some cases, particularly with flexible walled IV containers, the container is not completely filled at the factory, leaving an air space. This air may be infused into the patient if the fluid is delivered with a volumetric pump.

However, optical detectors can often produce false air-iti-line signals when the tube or conduit is actually filled with liquid. Some IV fluids scatter and do not focus light, particularly IV fluids which contain particulates. Some IV fluids may be semi-opaque. The result is that the detector cannot distinguish between a liquid filled and an air filled conduit.

Furthermore, optical detectors of the type described above require the use of clear plastics in the liquid conduit. However, many useful medical grade plastics are not clear, so an optical detector cannot be used with them.

According to a first embodiment of the present invention there is disclosed an ultrasonic liquid detector comprising: an ultrasonic sound generator and an ultrasonic sound receiver spacedly separated apart from one another so as to receive a liquid carrying member therebetween; each of said sound generator and sound receiver including a substrate and a layer of conductive material on said substrate, said conductive layer having at least two regions electrically isolated from each other, a piezoelectric chip placed in electrical contact over at least a portion of a first region of said conductive layer, and a conductive member extending *0#4 40 f 0 ft I I 4~ II Oftr 0 :i si :r I i I-i i

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a I t 00 0 49 00 0 0 4 0 04 S01 between said piezoelectric chip and a second region of said conductive layer; whereby when an electrical signal is applied between said first and second regions, the piezoelectric chip on said sound generator is excited, causing ultrasonic sound to be generated and whereby an amplitude of the ultrasonic sound received by said piezoelectric chip on said sound receiver is electrically detected by monitoring the electrical signal produced between the first and second regions of the conductive layer on said sound receiver, the amplitude of the ultrasonic sound received increases substantially when liquid is present in the liquid carrying member between the sound generator and the sound receiver.

According to the second embodiment of the present invention there is disclosed device for detecting air in a liquid conduit, comprising: acoustic receiver means having a resonant frequency, disposed to receive an acoustic signal transmitted across the conduit; and acoustic transmitter means for generating acoustic signals acrcss said conduit in a frequency range embracing the resonant frequency of said acoustic receiver means, said acoustic transmitter means including: oscillator means for generating electrical signals that vary across said frequency range and applying said electrical signals to a transmitter means; and a tuned load including an element responsive to said electrical signals to produce acoustical signals within said range for transmission to and reception by said receiver means; whereby if a liquid is in the conduit, said acoustical signals will pass across the conduit and be received by said receiver means indicating the presence of liquid in the conduit; but if air is in the conduit, said acoustic signals will substantially not pass across the conduit, indicating the absence of liquid.

According to a fifth embodiment of the present invention there is disclosed an ultrasonic liquid detector for use with a liquid carrying member, comprising: a housing defining an opening sized to accept the liquid carrying member; an ultrasonic sound source and an ultrasonic sound receiver disposed within the housing, on opposite sides of the opening; IAD/1083o 0444r *44 4 4t.

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1 1_ i i i I ii-i L o cc 04a 0o 0 0 6 0900 0I g I 0ti L 4 1,, said ultrasonic sound source and ultrasonic sound receiver each comprising a dielectric substrate having a generally planar surface including a conductive layer disposed thereon, divided into a plurality of discrete areas; said ultrasonic sound source including means disposed in electrical contact with one of the discrete areas on the dielectric substrate for generating an ultrasonic sound signal at a resonant frequency in response to an applied electrical signal, a fluid within the liquid carrying member adjacent the ultrasonic sound source conducting the ultrasonic sound signal to the ultrasonic sound receiver; said ultrasonic sound receiver including means disposed in electrical contact with one of the discrete areas on the dielectric substrate, for producing an output electrical signal at the resonant frequency in response to the ultrasonic sound signal; and conductor means for respectively conveying the applied electrical signal to the means for generating the ultrasonic sound signal, and the output electrical signal from the means for producing said output signal, whereby when a liquid is present within the liquid carrying member between the ultrasonic sound source and the ultrasonic sound receiver, the output signal indicates the presence of the liquid due to a relatively higher amplitude in the ultrasonic sound signal at the ultrasonic sound receiver, as compared to said signal in the absence of the liquid.

According to a fourth embodiment of the present invention there is disclosed a device for detecting the presence of fluid in a conduit, comprising: an acoustic transmitter means for generating acoustic signals across the conduit, said acoustic transmitter generating said acoustic signals in response to a drive signal at a selected frequency applied thereto; signal generating means for applying a drive signal to said acoustic transmitter, said signal generator means generating said drive signal over a sweep range of frequencies including said acoustic transmitter drive signal frequency; and acoustic receiver means responsive to said acoustic signals emitted by said acoustic transmitter, for producing a signal indicative of whether liquid or vapor is present in the conduit.

$i 1: IAD/10830 :r -1 i A number of preferred embodiments of the present invention will now be described with reference to the drawings in which: FIGURE 1 is a perspective view of a disposable pump cassette of one embodiment together with preferred ultrasonic detectors.

FIGURE 2 is a cross section of one of the ultrasonic detectors of FIGURE 1 taken along the plane of line II-II of FIGURE 1; FIGURE 3 is a cross section taken along the plane of line III-III of FIGURE 1; FIGURE 3A is a cross sectional view of the components of FIGS. 2 and 3 shown in engaged position; FIGURE 4 is a cross section taken along the plane of line IV-IV of FIGURE 3; FIGURE 5 is a perspective view of the ultrasonic sound generator and/or the ultrasonic sound receiver employed in the ultrasonic detector of FIGURE 2; FIGURE 6 is a cross section taken along the plane of lines VI-VI of FIGURE FIGURE 7 is a cross section taken along the plane of line VII-VII of S FIGURE t FIGURE 8 is a schematic of the circuitry used in an embr iment of an air-in-line detection system; and FIGURE 9 is a graph of the frequency response of a piezoelectric chip.

FIGURE 10 is a block diagram of a microprocessor used to control and monitor the air-in-line detector circuit.

FIGURE 11 is a schematic diagram of an alternative embodiment of an air-in-line detection circuit; and FIGURES 12A-G are timing diagrams illustrating the signals asserted o during the operation of the microprocessor of FIGURE 10 and the alternative air-in-line detector circuit of FIGURE 11.

The preferred embodiment is an ultrasonic air-in-line detector system 0 particularly adapted for use with a disposable intravenous fluid pumping cassette disclosed in U.S. Patent 4,818,186 entitled Disposable Fluid Infusion Pumping Chamber Cassette, filed by Giovanni Pastrone on an even J date herewith, the disclosure of which is incorporated herein by reference. The pumping cassette 10 includes a rigid face member 12 and a rigid back member 14 with elastomeric member 16 positioned therebetween SIAD/1083o L i 1 r 1 f :i rW~ 4A (FIGS. The cassette includes an inlet 18 to receive fluid from a fluid source (not shown) and an outlet (not shown) for delivering fluid at a positive pressure to the patient. Between the inlet and outlet is a fluid path 20 (FIG. 4) through air-in-line detection means 22, 24 which project outwardly from the surface of face member 12. Air-in-line detection means 22 engages an ultrascnic detector 26. Air-in-line detection means 24 engages ultrasonic detector 28. Air-in-line detection means 22 is identical to air-in-line detection means 24, so only one of them will be described in detail. Likewise, ultrasonic detector 26 is structurally the same as ultrasonic detector 28, so only the former will be described. Basically, the fluid path through the 000 0 PB 0 0 ~40 p Oea *000 4 0 e r 4 4, 0(0 84(tj itl 4$ IAD/10830

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cassette passes through both air-in-line detection means 22 and 24, and ultrasonic detectors 26 and 28 are adapted to detect the presence of air being pumped through pumping cassette 10 to prevent air from being pumped into the patient.

Air-in-line detection means 22 includes a pocket 30 formed integrally as part of elastomeric member 16. Pocket 30 extends through an opening 32 in face member 12 and projects outwardly beyond the surface of face member 12. (FIGS. 1, 3, 3A. and Pocket has a hollow recess 34 within it which is formed .within two sidewalls 35 and 35' and an arcuate endwall 38. A finger 36 projects from the inner surface of back member 14 into recess 34 and fits interferingly between sidewalls 35 and 35', but does not contact endwall 38.

Rather, a fluid passage 40 is formed between the inside surfaces of endwall 38 and the perimeter of finger 36 which forms part of the fluid path 20 through the cassette. Fluid passage 40 allows the fluid flowing through fluid path 20 in the cassette to loop outwardly from the surface of face member 12 so that any air in the fluid path can be detected by an ultra;ric detector 26 (or 28) outside of the cassette. Ultrasonic detectors 26 and 28 are to be mounted on a cassette driver, a nondisposable item, whereas the cassette is inexpensive and disposable after each use.

Ultrasonic detector 26 includes two substantially mirror image housing portions 42 and 44.

Housing member 42 is generally L-shaped and is joined to the mirror imaged L-shaped housing 44 at the bottom of the L's so as to form a U-shaped housing assembly with recess 46 between the arms of the U adapted to receive air-in-line detection means 22. On one side of recess 46, housing portion 42 has an opening 48, while on the *44 4 994 -L 9 4 91 a 1 4 4 *44 L.

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9 0 00 0 *i *0 0 0 0 004 0 00 4 0044 other side of recess 46, housing portion 44 has an opening 50. Housing members 42 and 44 are hollow, each containing a passage 52 for the necessary electrical pins described below. Positioned across opening 4V2 is an ultrasonic generator 54, facing an ultrasonic receiver 56 positioned in opening 50 across recess 46.

Ultrasonic generator 54 is structurally the same as ultrasonic receiver 56, so only ultrasonic generator 54 will be described.

Ultrasonic generator 54 (FIG. 5-7) includes a substrate 58, preferably made of glass coated on one side with a conductive layer 60, preferably a layer of gold. Conductive layer 60 includes three sections 62, 64, *and 66 which are electrically isolated from one another with a gap 68 between regions 62 and 64 and between regions 64 and 66, and a gap 70 which divides regions 60 and 62. A chip 72 made of a piezoelectric material such as lead zirconate titanate (PZT), irfrby a Murata P7 or Valpey-Fisher piezoelectric crystal, is adhered to conductive layer with a conductive epoxy adhesive, and is positioned such that one face of chip 72 overlays at least a portion of layer region 64, but the same f ace does not contact layer region 66. A conductive filament 74 extends from the opposite face of chip 72 to layer region 66, establishing an electrical connection therebet,4een, An electrically conductive pin 76 is electrically connected to layer region 64 while a pin 78 is electrically connected to layer region 66. This electrical connection is accomplished by glueing each pin to the appropriate region with an electrically conduL~tive epoxy adhesive 75 (Figs. 2, 3A and When the assembly shown in FIGS. 5-7 is used as an ultrasonic ~jenerator, an electrical signal having a frequency the 0000 0000 0000 0 0 0 00 Og 4-.

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i r i: is o 01 o 0 #r 0 'Oti same as the resonant frequency of piezoelectric chip 72 is applied to chip 72 across leads 76 and 78 with the circuitry described below to conductive regions 60 and 64 through filament 74, to excite the chip to emit a high frequency sound. As shown in Figures 1, 2 and 3A, pins 76 and 78 extend out of housings 42 and 44.

Housings 42 and 44 are mounted on a printed circuit board (not shown) through which pins 76 and 78 extend to connect to the circuitry described below.

To assemble an ultrasonic generator or receiver, chip 72 is mounted on substrate 58 by conductive adhesive. Filament 74 is attached as described above. Substrate 58 is then positioned in the opening 48 (or 50). Pin 78 (or 76) is inserted through a narrow aperture 81 (Fig. 2) in the rear of housing 42 (or 44) until the proximal end of the pin is positioned over the appropriate conductive region on the substrate. Through a large opening 83 (Figs. 2 and 3A) in the side of housing 42 (or 44), conductive adhesive is applied to adhere the proximal end of each pin 78 (and 76) to the appropriate conductive region on the substrate. These pins 76 and 78 are "potted" within housings 42 and 44 by filling the housings with non-conductive epoxy adhesive 85 (Figs. 2 and 3A).

Thus, openings 81 and adhesive 85 hold pins 76 and 78 immoveably within housings 42 and 44 so they cannot be dislodged from electrical contact with substrates 56 and 58.

Openings 83 in housings 42 and 44 are covered by covers 87 (Fig. 1) before adhesive 85 sets.

Ultrasonic detectors 26 and 28 are then mounted on a printed circuit board (not shown) through which pins 76 z i

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*1l -8- @0 O 4* A1 @41 44t4 and 78 extend. The distal ends of pins 76 and 78 are then soldered to make electrical connection with the circuitry described below on the printed circuit board.

To function as an ultrasonic receiver 56, the assembly shown in FIGS. 5-7 receives the ultrasonic sound generated by ultrasonic generator 54. The ultrasonic vibration is picked up by chip 72' and is converted to an electrical signal which is transmitted across filament 74 and through layers 60 and 64 to pins 76 and 78 (Fig. 1) where the high frequency electrical signal can be converted and amplified by the circuitry described below into a usable signal to sound an alarm in the event that air is present is fluid passage Elastomeric pocket 30 has two resilient lobes 37, 37' (FIGS. 1 and 3) which extend outwardly from sidewalls 35. The width of pocket 30 between lobes 37, 37' is somewhat less than the width of recess 46 between ultrasonic generator 54 and ultrasonic receiver 56 so that lobes 37 and 37' are compressed inwardly toward each other when air-in-line detection means 22 is inserted into ultrasonic detector 26 as shown in FIG.

3A. This insures that there will be good acoustic contact between ultrasonic generator 54 and pocket and between ultrasonic receiver 56 and pocket This arrangement also allows the air-in-line detection means 22 to be inserted and withdrawn easily from recess 46. As shown in FIG. 3A, chips 72 and 72' align with fluid passage 40 so that an ultrasonic signal is transmitted across fluid passage 40 when air-in-line detection means 22 is inserted into recess 46. The transmission of ultrasonic sound between ultrasonic generator 54 and ultrasonic receiver 56 is greatly enhanced when a liquid is present in passage 40. But when air is present in passage 40, the transmission of 1 (4, I A t 4.

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s .i ii -9ultrasonic sound through fluid passage 40 is attenuated. This difference in ultrasonic sound transmission is detected by ultrasonic receiver 56.

When air is present, the signal from ultrasonic receiver 56 drops. When a signal drops, an alarm (not shown) is sounded to stop the pumping of fluid through the cassette if the cassette is in the fluid delivery cycle.

As disclosed in U.S. Patent 4,818,186 entitled Disposable Fluid Infusion Pumping Chamber Cassette, filed by Giovanni Pastrone, the ultrasonic detectors and air--in-line detectors disclosed herein can be used also to check the integrity of several of the cassette components when the cassette is not in the fluid delivery part of its pumping cycle.

As indicated above, ultrasonic detectors 26 and 28 are parts of a nondisposable cassette driver, and cassette 10 is a disposable item. As cassette 10 is mounted on the driver, air-in-line detection means 22 and 24 slide easily into recesses 46 in ultrasonic detectors 26 and 28, but nonetheless intimate sound transmitting contact is achieved between each air-in-line detection means and its associated detector through lobes 37 and 37'. Lobes 37, 37' deflect inwardly as an air-in-line detector is slid o into a recess 46, creating the desired contact, but the lobes do not interfere with the sliding insertion of the air-in-line detectors into the ultrasonic detectors.

s o" The circuitry for the air-in-line detection system for the cassette driver of the present invention is illustrated in FIG. 8. The transmitting I crystals 72 and 72" of ultrasonic detectors 26 and 28, respectively are controlled by a pair of amplifier circuits 302 and 0o t t IAD/1083o U- 0* dl 0 0 00 0.4 .4 0 0 00 00 o 04 00 0 44.41, 0904 0 0 0044 ~0V4 0 00 00 0 0 0 0 302' Amplifier circuits 302 and 302' are driven, in turn, by a sweep oscillator 300 which includes a voltage controlled oscillator 301 and a triangle wave oscillator 301a.

Each crystal (72 72 will resonate at a variety of frequencies, but each has several peak resonating frequencies including one havi.ag a nominal value of about 5,00 MJ-z. However, the resonant frequency of a given crystal can vary from the nominal values. Furthermore, the resonant frequency of a crystal can shift when it is mounted on a substrate 58.

To reduce tle difference between the resonant frequrcies of transmitting and receiving crystals, each pair of such crystals should be cut from the same piece of piezoelectric material. Futhermore, each pair should be mounted on substrates cut from the same larger piece of material. Such precautions sufficiently reduce the frequency differences between transmitting and receiving crystals, which with imperfectly matched crystals could otherwise lead to a false alarm that air is in the cassette.

However, a problem arises in that the resonant frequency of each pair cf transmitting and receiving crystals can vary from pair to pair. Figure 9 shows the frequency response of a given crystal having a 5 MHz peak resonating frequency as well as several lower resonating frequencies. As shown in Figure 9, for example, the pairs are selected from materials which have nominal peak frequencies of about 5 MJ-z, but the peak frequencies can vary as much as 10 percent 4.50 5.50 MHz), thus, the circuitry to resonate the crystals must be, capable of resonating any selected pair within this rango if one wishes to avoid having to calibrate each circuit to each pair of crystals. This individual calibration would be extLremely laborious.

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4, 4 g 0 Sweep oscillator 300 varies the frequency of the electrical signal applied to the the transmitting crystals (72 and 72") over this relatively broad frequency spectrum 5 MHz It has been observed that this spectrum includes the resonant frequencies of the pairs of crystals which will be installed in the cassette driver. In other words, sweep oscillator 300 will hit a frequency for each pair of crystals which produces a sufficient response to avoid false signals. However, if the frequency of the electrical signal applied to the matched_ pair. of crystals is varied across the range between 4.50 and 5.50 MHz a range is swept), there will be an intermediate frequency within the range where the transmitting chip will emit acoustic signals having an amplitude sufficient to excite the receiving crystal.

This avoids the false alarm situation where the transmitting crystal is resonated at a frequency which is sufficiently different from its natural peak resonant frequency to "fool" the system that air is in the cassette.

Voltage controlled oscillator (VCO) 301 consists of a 74HC4046 phase locked loop oscillator U1 with only the voltage controlled oscillator section being used. VCO 301 output is coupled by capacitor C 6 to the transmitting crystal drivers Q1 and Q2.

VCO 301 is driven by triangle wave oscillator (TW Oscillator) 301a formed by an amplifier U2 with capacitor C 9 and resistors R 13

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16 TW Oscillator 301a uses an exclusive OR gate inside VCO 301 as a voltage buffer which improves the symmetry of its output waveform.

TW Oscillator 301a has a frequency of about 3kHz and a peak-to-peak amplitude of about 1.0 volt with an average value of 2.5 volts. This causes VCO 301 to

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The "timing elements" of VCO 301, namely resistor R 2 and capacitor C10 are selected so that the sweep range of VCO 301 includes frequencies at which the ceramic material used for the transmitting and receiving crystals will resonate.

Line A from VCO 301 is bifurcated into lines B and C, each of which applies the signals generated by VCO 301 to an amplifier circuit 302 or 4302', each of which is identical to the other. Each amplifier circuit 302 or 302' (described. in detail below) amplifies the signal to identical 10 volt peak to peak sine wave voltage signals at lines 76 and 76', respectively. The Si, frequency of the signal at lines 77 and 77' will vary within the range of sweep oscillator 300.

Amplifier circuit 302 includes a transistor SQ'. Transistor Q 1 together with resistors R 3

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4 and R 5 capacitors C 1 and C 2 and coi L 1 j form a Class C amplifier. Thus, L 1

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1 and the crystal 72 form a tuned load, nominally resonant at MHz. However, the actual resonance of this tuned load varies for reasons explained above. Crystal 72 is a Valpey-Fisher PZT-5H or a Murata P7 piezoelectric r acrystal.

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4 etc. Amplifier circuit 302 applies I i 3 F 4 a high, variable frequency sine wave signal through line i 77 to one side of piezoelectric crystal 72 of ultrasonic generator 54 of air-in-line detector 26. The other side Sof crystal 72 of ultrasonic generator 54 is connected to a 5 volt power supply (not shown) by line 78. The 5 MHz signal applied across crystal 72 excites crystal 72 to generate a high, variable frequency ultrasonic signal Sacross the gap between ultrasonic generator 54 and the a-a 'i V f l 1 1 IT~h~ 1 ON

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As previously indicated, when there is water in the fluid path in air-in-line detector 26, the ultrasonic signal generated is received virtually unattenuated by ultrasonic receiver 56. However, the high frequency sound generated by ultrasonic generator 54 is greatly attenuated if air is present in air-in-line detector 56.

Transistor Q2 and resistors R 12 R ill R 10 R 6 1 and and capacitor C 3 form an AC coupled common emitter amplifier 304. Amplifier 304 is coupled to crystal 72' of receiver 54. Capacitor C 4 is an output coupling capacitor which is coupled to transistor Q 3 Transistor Q3 forms a threshold voltage detector 306 with resistor R7and capacitor C 8 When water is in air-in-line detector 26 crystal 72' is excited by onle or more of the acoustic frequencies generated by crystal 72. The voltage signal rrcaved from amplifier 304 at the base of Q3is a sine wave a 100 to 200 m V peak. Amplif ier Q 3 increases that voltage to a sufficient level to cross the threshold formed by the base-emitter forward voltage at Q 3 Thus, the output voltage at Q3collect or indicates the presence of water.

When air is in air-in-line detector 26, crystal 72' will not be excited by any of the frequencies generated by crystal 72. The signal received at the base of Q3falls below that necessary to cross the base-emitter threshold of Q l' The output voltage at Q3 collector indicates the presence of air. Q collector is coupled to the microprocessor which detects the difference in voltage between the water/air situations. If air is in the sensor, the microprocessor sounds an alarm.

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I- 7' o 04 a,, I' I 1 O I ti I (1 Ic 1 14 In practice, sweep oscillator 300 sweeps a range of electrical signal frequencies from about 4.50 MHz to about 5.50 MHz. The signal is amplified by amplifier 302, and the variable frequency signal is applied to the transmitting crystals. One or more of these frequencies will excite the transmitting crystals. If water is in the cassette, one or more of the high, variable frequency signals generated by the transmitting crystals will be received by and excite the receiving crystals. The signals generated by the receiving crystals will be amplified and indicate to the microprocessor that water is in the cassette. If air is in either of the air-in-line detection means 22 or 24, none of the acoustic frequencies emitted by transmitting crystals 72 or 72" will be sufficient to excite either of the receiving crystal 72' or 72' adjacent the empty detection means 22 or 24. Thus, the microprocessor will sound an alarm.

FIGURE 10 depicts in block diagram a microprocessor 305 used to control the air-in-line detection circuit 298 and monitor the output therefrom. As will be discussed in greater detail hereinafter, microprocessor 305 periodically asserts a VCO-on signal over an oscillator control line 306 to VCO 301. The VCO-on signal triggers the generation of an AC signal by VCO 301, which excites transmitting crystals 72 and 72" to emit bursts of ultrasonic energy. Microprocessor 305 receives the output from Q3 and Q 3 through a pair of sensor input lines 307 and 307' respectively. When the VCO 301 is triggered to oscillate, if either Q3 or Q 3 assert a signal that indicates excess air in the line, microprocessor 305 asserts a signal on an alarm line 308 to trigger the appropriate annunciators and shut-off valves.

In some embodiments of the invention, the signals from Q3 and Q3' are supplied to comparators (not illustrated). Reference voltages are applied to the comparators that are identical to the voltages that would appear across Q3 and Q3' when the maximum-amount-of-air/minimum-amountof-fluid is sensed by detectors 26 and 28. Depending on the voltages from Q3 and Q 3 the comparators assert either fluid-in-line or air-in-line signals over sensor input lines 307 and 307' to the microprocessor 305. If an air-in-line signal is asserted, microprocessor 305 asserts an appropriate signal on alarm line 308.

An alternative air-in-line detection circuit 298' is depicted in FIGURE 11. The circuit 298' includes the sweep oscillator 300 previously 411f 1 1 4. 1 4 o 1 4 4 4 IAD/1083o -C7"-lf ~r i~ .1 r r 3 1: I:i s 15 described with respect to FIGURE 8 for supplying a variable frequency signal. An alternative amplifier circuit 310 is driven by the output ,signal from the sweep oscillator 300 and generates drive signals that are input to the transmitting crystals 72 and 72". Air-in-line detection circuit 298' further includes a pair of essentially identical sensor circuits 312 and 312' for generating signals indicative of air/fluid state sensed by detectors 26 and 28, respectively.

Amplifier circuit 310 includes an enhancement-type MOSPET transistor 314 that is driven by the output signal of the sweep oscillator 300 applied through a resistor 316. Transistor 314 is biased by a resistor 318 extending between the ground and the source. A reverse-biased Schottky diode 320 is tied between the input end of resistor 316 and source terminal of transistor 314 to clamp the negative voltage excursion of the gate of transistor 314 to a maximum of -0.3 volts. This prevents damage to the phase locked loop oscillator Ul that could otherwise result from large negative transient voltages that develop in the below-discussed tank circuit.

The output of transistor 314 is applied to a tank circuit comprising an inductor 322 and a capacitor 324 connected in parallel. Inductor 322 and capacitor 324 are selected so that the signal developed across the tank

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tr *i *t j circuit has the appropriate characteristics to excite the transmitting crystals 72 and 72" into emitting ultrasonic energy sufficient to stimulate sensor circuits 312 and 312' into generating signals of appropriate 1 4 t magnitude. In one embodiment of the invention, inductor 322 and capacitor St" 0 1, 324 are selected so that a 20 Vpp signal can be developed thereacross. An appropriate DC power supply, not illustrated, is coupled to the second end of the tank circuit. One or more filter capacitors 326 (one illustrated), are connected to the output from the power supply, as may be required.

Drive signals are supplied from the tank circuit to the transmitting crystals 72 and 72" through parallel-connected variable resistors 328 and 330 respectively. The variable resistors 328 and 330 are used to control the voltages of signals applied to transmitting crystals 72 and 72".

Variable resistors 328 and 330 thus allow the circuit 298' gain to be set at a specific DC voltage level across the sensor circuits 312 and 312' for the situations when the cassette 10 is filled with fluid and there is maximum ultrasonic coupling between the transmit and receive crystals.

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IAD/10830 16 Sensor circuit 312 is controlled by the signals developed across ii1 receiver crystal 72' in response to the ultrasonic energy received thereby. Sensor circuit 312 includes a bipolar transistor 332 driven by signals developed across receiver crystal 72'. A power supply, not illustrated, supplies a collector voltage to transistor 332 through a resistor 334. Transistor 332 is biased by series-connected resistors 336 and 338 that are connected between the transistor's collector and base, and a resistor 340 which is connected between the base and emitter of the transistor. A capacitor 342 tied between the junction of resistors 336 and 338 and ground filters AC signals from the bias voltage. Transistor 332 is emitter-biased by a resistor 344 extending between the emitter and ground.

Signals produced by the transistor 332 are applied through an AC ol coupling capacitor 348 to a transistor 346 that is part of an AM detector.

Transistor 346 is biased by a resistor 350 connected between the power 0I supply and its base and a resistor 352 connected between the base and 4 ground. Resistors 350 and 352 are selected so that a minimal positive voltage biases transistor 346 into conduction. The output signal from transistor 346 is demodulated across a resistor 358 and a capacitor 360 that are both tied to ground. Resistor 358 and capacitor 360 are also selected to function as a quick charge-slow discharge peak follower 356.

These characteristics desensitie the circuit 298' to small bubbles that inevitably form in the fluid and that do not affect the safety of the IV delivery system.

0 The signal from peak follower 356 is applied to a comparator 354 that asserts a signal indicating whether circuit 298' has detected air or fluid across detector 26. The signal from peak follower 356, is compared with a reference voltage, Vr, which is the expected voltage that is developed across the peak follower when the minimum acceptable amount of fluid is in fluid passage 40 (FIGURE In the depicted embodiment, comparator 354 I asserts a low "fluid-in-line" signal whenever sufficient fluid is in the fluid passage, and a high "air-in-line" signal whenever there is too much air in the fluid passage. A resistor 362, tied between the positive input of the comparator 354 and ground, and a resistor 364, tied between the output of the comparator and the positive input, provide positive feedback i, that results in 20 mV of hysteresis at the comparator threshold so as to minimize noise in the output signal. The output signal from comparator 354 Sis applied to the microprocessor 305 over sensor input line 307.

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fJO 17 Sensor circuit 312', which is responsive to signals developed across receiving crystal is in the reference voltages applied to their comparators 354 and 354', respectively. Ultrasonic detector 26, the empty detector, is primarily used to monitor whether the IV container and associated fluid line are empty. Since detector 26 is between the IV container and a pumping chamber (not illustrated) in the cassette sensor circuit 312 does not have to assert air-in-line signals when smaller bubbles are in the fluid passage 40. Accordingly, an appropriate reference voltage is applied to comparator 354 so that it asserts an air-in-line signal only when large bubbles are detected that indicate the source container is about empty. In one embodiment of the invention, the reference voltage applied to comparator 354 is approximately 500 mV, which is approximately one-fifth of the fluid filled voltage level. Ultrasonic detector 28 is used to monitor the fluid infused into the patient and sensor circuit 314' thus is set to be more sensitive to smaller bubbles.

,o 0 Accordingly, a low reference voltage, 300 mV, which is approximately one-fifth of the fluid filled voltage level, is applied to comparator 354' so that when smaller bubbles are in the fluid passage 40, air-in-line will be asserted.

S. FIGURES 12A-G are timing diagrams of the signals asserted during operation of the air-in-line detection circuit 298'. As depicted in FIGURE 12A, TW oscillator 301a is always active and constantly generates a triangular wave. In one embodiment of the invention, TN oscillator i generates an output signal centered at 2.5 V with a 2.0 V peak-to-peak amplitude and a frequency of approximately 3K Hz.

Microprocessor 305 periodically asserts a VCO-on signal represented by the "low" signal depicted in FIGURE 12B. The frequency with which the VCO-on signal is asserted depends on the specific use of the invention.

For example, when the ultrasonic detector is used with a plunger-type IV fluid pump (not illustrated), the VCO-on signal is asserted simultaneously with the depression of the pump plunger so that an air-in-line measurement I occurs simultaneously with the pumping of fluid through the fluid passages (FIGURE The VCO-on signal is asserted for a selected time so that if there is sufficient fluid in the fluid passages 40, consequential bursts SIAD/10830 14; ,t f 'I v IAD/1083o I 18 of ultrasonic energy received by the receiving crystal-sensor circuit subassemblies induce voltages that fully charge the peak followers 356 and 356'. In practice, at least 5 to 10 burst of ultrasonic energy from transmitting crystals 72 and 72' are normally needed to fully charge the peak followers 356 and 356', respectively. In the described embodiment, the VCO-on signal is asserted for approxi'mately 1 millisecond.

When the VCO-on signal is asserted, VCO 301 generates an AC signal as represented by FIGURE 12C. The triangular wave signal driving VCO 301 causes the oscillator to generate a variable frequency output signal within the normal resonant frequency range of the transmitting crystals 72 and 72". For transmitting crystals having a nominal peak frequency of 5 MHz, VCO 301 generates an output signal having a frequency sweep between 4 and 6 MHz.

Output signals from VCO 301 centered around the resonant frequencies 0 of transmitting crystals 72 and 72" cause bursts of ultrasonic energy 0 therefrom as represented in FIGURE 12D. The bursts of ultrasonic energy Share transmitted through the fluid passages 40 to the receiving crystals 72' I and 72". The received energy causes voltages to be developed across receiving crystals 72' and 72" so that, in turn, voltages are developed across the peak followers 356 and 356' of the sensor circuits 312 and 312' as depicted by FIGURE 12E. When there are sufficient amounts of fluid in fluid passages 40, the voltages developed across peak followers 356 and 356' are greater than the corresponding reference voltages. Comparators S 354 and 354' assert fluid-in-line signals represented by the low signal of FIGURE 12F. When there is sufficient fluid in the passages, the peak followers rapidly charge and the comparators 354 and 354' assert fluid-in-line signals several microseconds after the VCO-on signal is asserted. After the VCO-on signal is negated, peak followers 356 and 356' maintain their voltages above the reference voltages until they discharge, with a 4.7 millisecond time constant. Comparators 354 and 354' thus assert 1 fluid-in-line signals for a similar amount of time after the VCO-on signal is negated.

As indicated by arrow 370 in FIGURE 12g, microprocessor 305 is programmed to monitor the signals from comparators 354 and 354' simultaneously with the negation of the VCO-on signal. If there is sufficient fluid in the passages, comparators 354 and 354' will assert fluid-in-line signals as described. If there are a significant number of IAD/10830 o S 19 bubbles in either fluid passage 40, the ultrasonic energy received by the receiving crystal 72' or 72" is noticeably attenuated. The voltage developed across the peak follower 356 or 356' is then below the appropriate reference voltage, and comparator 354 or 354' asserts an air-in-line signal. In response to the asserted air-in-line signal, microprocessor 305 (FIGURE 10) asserts an appropriate signal on alarm line 308.

In the embodiment of the invention used with a plunger pump, ultrasonic detectors 26 and 28 are monitored in 5 millisecond cycles, the rate at which the plunger makes downward strokes. During each cycle, the VCO-on signal is asserted for one millisecond, the signals from the comparators 354 and 354' are briefly monitored, and there is a four millisecond pause before the start of a new cycle. When an air bubble starts to transit between one of the detectors 26 or 28, the peak follower 0, 356 or 356' may not discharge to a level below the reference voltage during the four millisecond pause. Accordingly, during the subsequent monitoring period, comparator 354 or 354' may assert a fluid-in-line signal even o' s though a bubble is present. However, the minimum transit time for bubbles a: xo, across an ultrasonic detector 26 or 28 is about 100 milliseconds. Thus, when a bubble is present, it attenuates the ultrasonic energy detected by the sensor circuit 312 or 312' during several consecutive monitoring periods. During at least the latter monitoring periods, the peak follower 356 or 356' is discharged below the reference voltage and the comparator 354 or 354' asserts an air-in-line signal. Thus, bubbles do not escape detection even though the fluid passages are not continuously monitored.

Microprocessor 305 also determines whether or not the air-in-line o2oj detection circuit 298' is operating properly. The test is performed by 0o00 monitoring the signals asserted by the comparators after the VCO-on signal has been negated. As depicted by arrow 372 in FIGURE 12G, the monitoring o*0 is done at least 10 milliseconds after the VCO-on signal is negated, so that the peak followers 356 and 356' have had time to fully discharge. If the detector circuit 298' is operating properly, the signals across peak followers 356 and 356' should be below the reference voltage levels, and comparators 354 and 354' should assert air-in-line signals. If fluid-in-line signals are asserted, there is a malfunction in the detection circuit 298', and microprocessor 305 asserts an appropriate signal on alarm 1i line 308. The test is normally performed when an IV container is first IAD/1083o K T -i ii: i Zne atsi1uLy a.Y n wtia. s. i generator, an electrical signal having a frequency the

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L" ~ii'l -i lii- i ;l 20 o 48 00 4 *0 o 0e 4 4 0 «t 0 o 4 05 8 04 0 wlD o 0 4 4 004 4 804 0 0044 6 0 Sa t llmoo 8r4 8 84 0 o Q 00440 4 0 0 0 9 o 0 attached to the pump-detector assembly or other times when it is known there is fluid in the passages 40. Tests are performed at these times because it is desirable to verify that the circuit 298' does indeed switch from asserting fluid-in-line signals to asserting air-in-line signals after the VCO-on signal is negated.

The above-discussed polarities, voltages, time constants and frequencies describe the signals asserted during operation of the second air-in-line detection circuit 298'. It is understood that the signals asserted during the operation of the first-described air-in-line detection circuit 298 have similar characteristics to those described, since the two circuits 298 and 298' have the same basic principles of operation.

Differences in asserted signals during the operation of the different air-in-line detection circuits 298 and 298' merely reflect the different construction of the circuits.

The VCO 301 of the sweep oscillator 300 of this invention generates a variable frequency output signal, a portion of which excites the transmitting crystals 72 and 72" into releasing bursts of ultrasonic energy. This technique eliminates the need to provide the detector circuit with a finely tuned oscillator to excite the transmitting crystals precisely at their resonant frequency. Moreover, the sweep oscillator excites both transmitted crystals 72 and 72" into releasing ultrasonic energy even though the crystals may have different resonant frequencies.

This eliminates having to provide individual drive circuits for the separate ultrasonic detectors 26 and 28.

Still other advantages are associated with the second detection circuit 298' of this invention. Transistor 314 in amplifier circuit 310 switches off current flow in the amplifier circuit 310 when VCO 301 is not triggered to oscillate. Thus, the amplifier circuit 310 uses a minimal amount of current, which makes it well suited for use with portable, battery-powered IV pumping and bubble detection systems. The single amplifier circuit 310 supplies signals for driving the multiple transmitting crystals so as to minimize both the cost and size of the detection circuit. Variable resistors 328 and 330 provide a convenient means for limiting the energy applied to receive crystals 72' and which is useful for preventing sensor circuits 312 and 312' from being overdriven.

IAD/1083o i p -If Sii

I

-21 Air-in-line detection circuit 298' is also well suited for use in high electrical and sonic noise environments such as hospitals. Feedback resistors 336 and 338 stabilize the operating point of sensor circuit transistor 332 so that collector voltage swings thereacross can approximate the supply voltage. This makes it possible to adjust the detection circuit 298' so that the presence of fluid in fluid passage 40 results in high, readily distinguishable voltages being developed across transistor 332 and in turn across peak detector 356. The reference voltage can thus be set to a relatively high level so that low voltage noise signals that develop across transistor 332 do not cause comparator 354 to assert a false fluid-in-line signal. Moreover, AM detector transistor 346 provides the sensor circuit 312 output signal with a near-linear received ultrasonic energy-output voltage profile. This approach facilitates applying a reference voltage to the comparator 354 that accurately reflects the sensor S circuit voltage when a minimum acceptable amount of fluid is detected.

0, It should be understood that this description of the preferred o embodiments of the invention is for the purpose of illustration only. It should be apparent that this invention can be practiced using diverse circuitry or in systems that use different circuitry than is disclosed in this specification, with the attainment of some or all of the advantages of this invention. For example, the transmitting circuit 302 and receiving amplifier circuit 304 of the first air-in-line detection circuit 298 may be interchanged with the amplifier circuit 310 and sensor circuits 312 and 4. 4 312' of the second air-in-line detection circuit 298' as desired. A sweep oscillator substantially different from the one described may be used to provide the variable frequency signals that drive the transmitting crystals 72 and 72".

4 i. e: Still other embodiments of the invention may be provided wherein the peak detectors 356 and 356' are eliminated from sensor circuits 312 and t. 3312' so that the comparators 354 and 354' assert signals that are h: near-instantaneous representations of the detected air/fluid state. In these embodiments of the invention, VCO 301 would most likely be triggered to continually provide a drive signal to the transmitting crystals 72 and 72" and the output signals from the comparators 354 and 354' would most likely be monitored continually. Other alternative circuit constructions are, of course, possible. For example, if a higher drive level voltage is IAD/1083o y sol eaprn htti nenincnb rcie sn ies ./wsi r£

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lPer L- i I' I 1- 22 applied to the receiving crystals 72' and 72 1 the sensor circuit may comprise an RF-type autotransformer followed by a Schottky diode detector.

Furthermore, while the disclosed air-in-line detector circuits 298 and 298' can be used in conjunction with two complementary ultrasonic detectors 26 and 28, it is readily understood that the circuits of this invention can be used with one, three or more ultrasonic detectors as may be required in any particular embodiment of the invention. Therefore, it is the object of the appended claims to cover all such modifications and variations as come within the true spirit and scope of the invention.

Whilst only a number of embodiments of the present invention have been disclosed, other embodiments will be apparent to those of ordinary skill in the art. These embodiments are to be included in the scope of the present invention unless the claims which follow expressly state otherwise.

9.

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Claims (11)

1. An ultrasonic liquid detector comprising: an ultrasonic sound generator and an ultrasonic sound receiver spacedly separated apart from one another so as to receive a liquid carrying member therebetween; each of said sound generator and sound receiver including a substrate and a layer of conductive material on said substrate, said conductive layer having at least two regions electrically isolated from each other, a piezoelectric chip placed in electrical contact over at least a portion of a first region of said conductive layer, and a conductive member extending between said piezoelectric chip and a second region of said conductive layer; whereby when an electrical signal is applied between said first and second regions, the piezoelectric chip on said sound generator is excited, causing ultrasonic sound to be generated and whereby an amplitude of the ultrasonic sound received by said piezoelectric chip on said sound receiver is electrically detected by monitoring the electrical signal produced between the first and second regions of the conductive layer on said sound receiver, the amplitude of the ultrasonic sound .ceived increases substantially when liquid is present in the liquid carrying member between the sound generator and the sound receiver.

2. The ultrasonic detector of claim 1 further including a housing member for each of said sound generator and sound receiver, the substrate of said generator and the substrate of the receiver being positioned across an opening on the corresponding housing.

3. The ultrasonic detector of claim 2 wherein said two housings are secured together and configured so as to form a U-shaped configuration, with said openings of the respective housings facing each other in opposite arms of said U-shaped configuration.

4. The ultrasonic detector as claimed in any one of claims 1 to 3 which includes a push connector pin mounted on each of said regions to which electrical leads can be connected.

An ultrasonic liquid detector for use with a liquid carrying member, comprising: 'AD/1518o 4 44 ar I .4 a 44' 4 I L 413 a 55 a housing defining an opening sized to accept the liquid carrying member; an ultrasonic sound source and an ultrasonic sound receiver disposed within the housing, on opposite sides of the opening; said ultrasonic sound source and ultrasonic sound receiver each comprising a dielectric substrate having a generally planar surface including a conductive layer disposed thereon, divided into a plurality of discrete areas; said ultrasonic sound source including means disposed in electrical contact with one of the discrete areas on the dielectric substrate for generating an ultrasonic sound signal at a resonant frequency in response to an applied electrical signal, a fluid within the liquid carrying member adjacent the ultrasonic sound source conducting the ultrasonic sound signal to the ultrasonic sound receiver; said ultrasonic sound receiver including means disposed in electrical contact with one of the discrete areas on the dielectric substrate, for producing an output electrical signal at the resonant frequency in response to the ultrasonic sound signal; And conductor means for respectively conveying the applied electrical signal to the means for generating the ultrasonic sound signal, and the output electrical signal from the means for producing said output signal, whereby when a liquid is present within the liquid carrying member between the ultrasonic sound source and the ultrasonic sound receiver, the output signal indicates the presence of the liquid due to a relatively higher amplitude in the ultrasonic sound signal at the ultrasonic sound receiver, as compared to said signal in the absence of the liquid.

6. The ultrasonic liquid detector of 'claim 5, wherein the S dielectric substrates of the ultrasonic sound source and ultrasonic sound receiver are mounted within the housing so as to directly contact the liquid carrying member, thereby providing good acoustic contact between the liquid carrying member and the dielectric substrates.

7. The ultrasonic liquid detector of claim 5, wherein the means for generating the ultrasonic sound signal and the means for producing AD/l .5 8 I:i L: 1 i ~i ttl: ii j'j i 25 i :ji :'i ir the output electrical signal each comprise piezoelectric crystals having substantially the same resonant frequency characteristics.

8. The ultrasonic liquid detector of claim 5, wherein the conductor means comprise a plurality of terminals fixed in place within the housing and connected to the discrete areas on the dielectric substrates.

9. The ultrasonic liquid detector of claim 8, wherein the conductor means further comprise a lead extending between the means for generating the ultrasonic sound signal and one of the discrete areas to which one of the terminals is connected, and a lead extending between the means for producing the output signal and another of the discrete areas to which another of the terminals is connected.

The ultrasonic liquid detector of claim 5, wherein a primary path for the ultrasonic sound signal is provided between the dielectric substrate of the ultrasonic sound source and the dielectric substrate of the ultrasonic sound receiver, directly through the liquid carrying member, the absence of liquid within the liquid carrying member greatly reducing transmission of the ultrasonic sound signal therebetween, causing a substantial change in the output electrical signal.

11. An ultrasonic liquid detector substantially as described herein with reference to Figs. 1 to 9, or Figs. 1 to 7 and 9 to 12 of the drawings. DATED this NINETEENTH day of MAY 1992 r Abbott Laboratories a a :Patent Attorneys for the Applicant SPRUSON FERGUSON 0 *0 I O o* if 111 o *e 6o 0* ""t i I'Ab 1518o