MXPA94009546A - Ultrasonic device to detect the presence of a fluid in a definite place - Google Patents

Abstract

The present invention relates to a device for detecting the presence of a fluid at a defined location, comprising: transducer means for generating vibrations as a function of an electrical impulse signal and for generating a transducer output as a function of vibrations received, the transducer means being disposed proximate to the defined location such that at least a portion of the output of the transducer responds to the presence of the fluid at the defined location, an excitation circuit that provides an electrical impulse signal to induce the vibrations simultaneously to first and second frequencies, first and second filter circuits that receive the output of the transducer and selectively pass in first and second frequency component, respectively, to generate first and second filter outputs, respectively; a control unit coupled to the first and second filter circuits, the c unit Ontrol indicating the presence of fluid in the clear as a function of the first filter output and indicating the integrity of the device as a function of the second filt output

Description

ULTRASONIC DEVICE TO DETECT THE PRESENCE OF A FLUID IN A DEFINED PLACE Inventor (e): LAWRENCE JONES, ALEXANDER 3. ESIN AND BORIS S. ROSSELSON, the first North American and the second and third without nationality (resident in the US) residing at 14N &29 Lac du Beatrice, West Dundee, Illinois 6011 &; 9251 Fern Lane, Des Plaines, Illinois 60016 and 1070 Twisted Oa Lane, Buffalo Grove, Illinois 60G &9, E.U.A » Causairee; KAY-RAY / SENSALL, INC., A North American corporation organized and existing in accordance with the laws of the State of Delaware residing at 1400 Business Center Drive, Mount Prospect, Illinois 60056-21604, E.U "A.

SUMMARY OF THE DESCRIPTION An ultrasonic level instrument detects the presence of a fluid in a defined luqar and provides a verification of autod iagnostic integrity. An excitation circuit simultaneously induces vibrations to a first and second frequencies in a transmission symmetrical crystal, and the vibrations are detected by a receiver crystal. A circuit of the first and second filters comprises first and second filter outputs, respectively, by selectively passing the output of the receiver crystal to the first and second frequencies, respectively. The first filter outlet is indicative of the presence of fluid and the second filter outlet is indicative of the integrity of the detector.

BACKGROUND OF THE INVENTION The present invention relates to ultrasonic devices that detect the presence of a material at a defined location. More particularly, the invention relates to a method and apparatus for monitoring the presence of a material at said defined station while also monitoring the integrity of the ultrasonic device itself. In the patent of E.U.A. 4,299,114, Silvermetz et al. Teach a method of testing the integrity of an ultrasonic system to detect liquid-fluid interfaces. The transmitting and receiving crystals are arranged through a gap in a housing, and the output of the receiving crystal feeds an amplifier and a bandpass filter network back towards the transmission crystal »If the gain of the amplifier is sufficiently high to overcome the attenuation of the ultrasonic signal through the clear, then a self-sustaining oscillation occurs. Means are provided for changing the bandpass filter network from a high frequency pass band to a low frequency pass band. The high frequency pass band is used to detect the presence of fluid in the housing gap, and the low frequency pass band is used to detect the integrity of the system. A real imentation system of this type requires, for reliable operation, relatively stable liquid properties, and a relatively large difference between the amount of actual inlet with and without liquid present in the clear. In the pending US patent application, No. 06 / 037,523, entitled "Time Bate Ultrasonic Sensor and Method", incorporated herein by reference, Esin and others teach a device that oversees a ultrasonic signal received during a main time gate window to detect a property of a material in a defined space of the device housing. The device also monitors the ultrasonic signal received during a self-contained time gate window to detect the integrity of the detector. Both monitoring means receive the ultrasonic signal after the signal has been filtered by a single high-pass filter. This device does not allow the use of different ultrasonic frequencies that are optimally adjusted for material property detection and integrity detection functions.

BRIEF DESCRIPTION OF THE INVENTION In accordance with one aspect of the present invention, an ultrasonic level instrument includes transducer means for generating vibrations as a function of a driven electrical signal and for generating a transducer output as a function of the received vibrations.,. An excitation circuit provides the electrical impulse signal to induce the vibrations simultaneously to a first and second frequencies. First and second filter circuits receive the output from the transducer and selectively pass the first and second frequency components, respectively, from the output of the transducer, thereby generating a first and second filter outputs, respectively. A control unit is coupled to the first and second filter circuits and indicates the presence of a fluid of interest as a function of the first filter output and indicates the integrity of the detector as a second filter output.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a representation of an ultrasonic device in accordance with the invention, including a partial cross-sectional view of one end of a detector; Figure 2 is a schematic diagram of a filter circuit usable with the invention; and Figure 3 is a representation of signals obtained at selected points in the circuit shown in Figure 1 when the material to be detected is present in the housing glade.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES In Figure 1, the ultrasonic level instrument 10 comprises a detector 14 and a controller 11. The instrument 10 detects the presence of a fluid, such as a liquid or other material, in a lumen 12 at the tip of the detector 14. Typically , the detector 14 is a bar-shaped device mounted inside a tank in which the fluid is stored. The detector 14 includes a detector housing 15 which contacts the fluid and isolates the components inside the detector 14 from contact with the fluid. The housing 15 of the detector is preferably composed of metal, plastic or other non-corroding materials. In the controller 11, a cycle generator 16 periodically activates a pulse generator Iñ, which sends a signal pulse P on the line 20 in response to each activation by cycle generator 16. The amplifier 22 receives the pulse P and generates an amplifier pulse, which excites a transmission crystal 26 on the line 24. The transmission crystal 26, when excited in this manner, vibrates simultaneously at two different ultrasonic frequencies, here known as £ M -tM and ft,. ^ . The term "simultaneous" refers to at least some temporary overlap of the two vibrations. The duration of the pulse P is approximately 1 / (2 * f? T «> • Preferably, the transmission crystal 26 is selected such that it has a longitudinal frequency f.lt? Of the order of a few megahertz, example of approximately 1 MHz to 5 MHz. Vibrations at said high frequencies are advantageous for use in fluid detection because their attenuation through most of the fluids of interest is lower than through detector housings. plastic or metal However, such vibrations are not preferred as indicators of detector integrity since the attenuation through the plastic detector housings is strongly affected by the temperature, and furthermore the attenuation can be significantly different between plastic parts The diameter (or other transverse dimension) of transmission crystal 26 e preferably selects such that f ", j" has a value of 40 KHz to 40. 0 KHz, f _ »_. ** and í.,» ,,, »preferably having a relative ratio of 10 or more .. It has been found that unlike high frequency vibrations, the attenuation of low vibrations Frequency through plastic materials changes very little as a function of temperature and between similar plastic materials, such as the group of Teflon-based plastic materials. Therefore, it is particularly advantageous to use low frequency vibrations as an indicator of the integrity of detectors having plastic housings. The low and high frequency vibrations are illustrated in Figure 1 as reference numbers 2 & and 30, respectively »The low frequency vibrations 2 & they are produced from the radial glass vibrations 26, thus emanating preferentially outwards from the glass periphery 26 as shown in FIG. 1. The high frequency vibrations 30 result from the vibrations-thickness of the crystal 26, thus emanating predominantly from two opposite faces of the crystal 26 (high frequency vibrations of upward propagation are not shown). Both vibrations 2 £ > , 30 are able to propagate through the detector housing 15 (including the bridge portion 32) and also through the gap 12. Some of the vibrations reach a receiver crystal 34.arranged, through the gap 12 from the transmitting crystal 26. The receiving crystal 34 is preferably identical to the transmitting crystal 26. Both crystals 26, 34 are composed of a piezoelectric material such as lead zirconate (PZT), or for high temperature applications, lead lobate. The epoxy layers 35, 35 firmly bond crystals 26, 34 to portions 15a, 15a of the detector housing 15 near the lumen 12. The portions 15a, 15a are commonly referred to as "windows" by those skilled in the art. The thickness of the epoxy layer 35 and each portion 15a 3e is selected to be substantially equal to one half of an ultrasonic vibration wavelength in the respective materials at the frequency fltltl. , 34 communicate efficiently with the clear 12 * at high frequency and protect the crystals against potentially harmful materials outside the detector 14. Housing configurations different from those shown in Figure 1 can be used with the invention . For example, the detector may have a slot at one end, oriented parallel to the longitudinal axis of the detector. Preferably, the transit time of the ultrasonic vibrations from the transmission crystal to the reception glass through the clearing is i amente different from Tienoo de trán =? to Is? Ultrasonic vibrations through the detector housing, to ensure that vibrations through the clear are received by the receiver glass and vibrations that pass through the detector housing are not received by the receiving glass simultaneously. The vibrations reaching the receiver crystal 34 induce electrical signals on the crystal 34 representative of said received vibrations. Line 36 communicates the induced electrical signals from the crystal 34 to a video frequency amplifier 36. The video amplifier 36 has a bandwidth that is sufficiently wide so that the output of the amplifier on the line 40 includes frequency components of the amplifier. entry signal on line 36 to ím t? * and £ tt j M. According to the invention, the output at 40 is coupled, preferably but not necessarily, simultaneously to the filters 42 and 44. The filter 42 transmits the high frequency component (f «.i. *? >; but not the low-frequency component "j" of the signal at 40. The filter 44 transmits the low-frequency component but not the high-frequency component of the signal at 40. The filter 42 may comprise a high-frequency filter. high pass with an ignition frequency between ffc,? j? »and f * > ite. «, and the filter may comprise a pass filter with a shutoff frequency between fb« j? and f «». Alternatively, the filters 42, 4 may comprise narrow band pass filters centered respectively over the false. and ít3? i M, to reduce system noise. The filters 42, 44 may also include amplification. The filters 42, 44 and other electronic components illustrated in Figure 1 can be of the type known to those skilled in the art. The filter 42 feeds its filtered output at 46 to the comparator 47. The other input to the comparator 47 is an adjustable DC voltage V-. , established by the sliding contact position M-6 on the resistance R: t, which in turn connects to the positive supply voltage * at one end and to the earth potenti- ation 50 at the other end. Similarly, the comparator 52 matches the filtered output of the filter 44 on the line 54 and also the adjustable DC voltage V;?. , established by the position of the sliding contact 56 on the resistance R? > . The output of the filter 42, which comprises high frequency components is strongly affected by the presence of fluid in the gap 12 due to the low attenuation of the high frequency vibrations that propagate through the gap 12 when the fluid is present (condition "wet") compared to when the fluid is absent from the clear .12 ("dry" condition). In this way, the amplitude of the signal on line 46 is substantially greater in the wet condition compared to the dry condition »The voltage V: l. It is optimally set at the level by ab of the largest amplitude achieved by the outlet of the filter 42 when it is wet, but above the maximum amplitude achieved when it is dry. In this setting of Vi, the output of the comparator 47 fluctuates only for a wet condition in the clear 32. The output of the comparator 47 connects to the clock input of the flip-flop 3f 56 on the line 6 ?. The input 1 to the jogger 46 not shown connects to V "* It has been observed that, where the detector housing 15 is composed of metal and where it is composed of plastic, the relatively low frequency oscillations on the filter outlet 44 They are weakly affected by the presence of fluid in the gap 12. The majority of the frequency signal ba to the crystal 34 is due to ultrasonic vibrations traveling through the housing 15 (including the bridge 32) from the transmitter crystal 26 to the receiving glass 34. Consequently, the failure of the detector caused by detachment of the glass 26 or the rigid contact glass 34 with the housing 15, or other cracks or other defects in the bridge 32, will result in a marked decrease in the signals of the detector. frequency (as well as high frequency) of the glass 34. It has been observed that the materials such as plastic, including polyfluorocarbon Teflon resin (fabr icated by uoont Corp. and hereinafter referred to as "PFA" ', they have performance features at flat frequencies (f * »xt.» > They change substantially as a function of temperature and from one type of plastic material to another. It has also been observed that those same plastics materials have thermally stable and repeatable attenuation characteristics at low frequencies. J *) • Therefore, the ultrasonic instrument 10 independently monitors low frequency signals of receiver crystal 34, through the filter 44, as an indicator of system integrity and high frequency signals from the glass 34, through the filter 42, as an indicator of the presence of fluid. The monitoring of low frequency vibrations results in a more reliable indication of the integrity of the detector. The voltage V.B is set at a level slightly below the low frequency amplitude output expected by the filter 42, so that the detachment of crystals 26 or 34, or similar malfunctions, will cause the low frequency amplitude to fall below Va ». The output of the comparator 52 therefore oscillates only when the detector is intact. Said oscillations are received at the bistable circuit clock input 3K 62 on line 64. The pulse P is coupled via line 20 to the wet / dry time gate generator 66 and to the self-test time gate generator. 66. The combination of capacitor C: L, resistor R3 or inverter I., as shown, generates a normally "LO" signal on line 1 70, but generates an "HI" output for a period that begins in the downward transition of pulse P and continues during a first period dictated by C.x and Ra,. The transition of comparator I: l. of HT. to LO initiates on line 72 a transition at the output of the inverter I? a, and of the wet / dry time gate generator 66, from a normally LO state to a HI state for a second period dictated by C-a and R l +. In this mode, the wet / dry time gate generator 66 generates a "time gate" on the line 72, defined as the time interval when the generator outputs is HI. The self-test time gate generator 66 operates in a similar manner, and includes capacitors C; 3 and Ct +, resistors Rs and R,., And inverters I:;, and I. +, connected as shown »The output of the inverter I: i, on line 74 is fed into inverter In. through the capacitor C +, and the output of the inverter IL + gives a gate output of the self-test time on the line 76. The time gate output 72, 76 is provided to the input 3 of the flip-flops JK 56, 62, respectmente amente. The outputs of the bistable circuits JK 56, 66 at 0 are reset to LO by operation of the pulse P along the line 20 to the reset inputs ("RST") of the bistable circuits 56, 62. If desired, the logic function exerted by the bistable circuits JK 56, 62 can be performed by the NAND gates or other digital components. However, the use of bistable circuits 3 reduces the number of components needed for the controller 11, thus simplifying the controller and increasing the confidence of the instrument. The outputs of the bistable circuits JK 56, 62 are provided to the control unit 62 along the lines 76, 60, respectively. The control unit 62 may include cutters or another circuit for monitoring the outputs 76, G for evaluating the presence or absence of fluid in the gap 12 and also for evaluating the integrity of the detector 14. For example, the control unit 62 may include a counting circuit coupled to line 76 indicating a dry condition on indicator 64 unless it has 3 or more pulses on line 76 for each timing pulse P, in which case said continuation circuit indicates a wet condition on indicator 64. A similar continuation circuit can monitor the signal on line 60 to indicate the integrity of the detector at indicator 66, whereby indicator 66 indicates malfunction at detector 14 unless a number is detected. programmed pulse on the line 60 between the successive pulses P. Preferably, the control unit 62 activates the indicators 64, 66 regardless of the signals on the lines 60, 7 & ^ respectively. The control unit 62 may also include current sources and relay impellers that respond to the presence of fluid in the gap 12 and to the integrity of the detector 14. Figure 2 shows a pure axis of a band pass filter 102 useful with the invention either as the filter ^ 2 or the filter 44 depending on the values of the passive circuit components used. In the bandpass filter 1G2, the line 104 carries an input signal and the line 106 carries a filtered output signal. Numerous other known filters can be used. Preferably, the filters 42 and 44 and the rest of the controller circuit 11 satisfy the intrinsic safety requirements, whereby the controller 11 can be operated in a hazardous environment. Figure 3 illustrates signals at various points in the circuit shown in Figure 1. The vertical e represents an electric potential (voltage) or electric current, and the horizontal e represents time. The signals of figure 3 are vertically displaced from each other for clarity and ease of comparison, and the reference number used for each signal is the same as the number used on the corresponding conductor in figure i, except that a bonus symbol (') is added to the number to distinguish the signal from the driver »In practical systems, the pulse P in signal 2? It can cause instantaneous cssi noise noise in the signals 46 '/ 54', shown in the signal 46 'as a band 110 train. The noise is due to electromagnetic interference diffused from the generating portion of the circuit pulse to other portions. of the circuit. The wave train 112 in the signal 46 'represents high frequency vibrations 30 propagated through the detector housing 15 and through the bridge 32, and detected by the receiving crystal 34'. It has been found that the wave train 112 is undesirable to be used as an indicator of detector integrity where the detector housing 15 is composed of PFA because the amplitude of the wave train 112 shrinks dramatically at detector temperatures. low (0 ° C to -20 ° C) compared to moderate to high temperatures (25 ° C to + 100 ° C). Where the alloy of the detector 15 is composed of a metal such as 316 stainless steel, however, few or no amplitude variations of the wave train .1.12 will be observed with the temperature of the detector. The wave train 114 and the signal 46 'represent high frequency vibrations 30 propagated through the fluid of interest in the gap .1.2 and detected by the crystal 34. Where the fluid is absent from the gap 12, the amplitude of the train of waves 114 is much smaller than the one shown in figure 3, well below the level 46 'represents io of electric potential V; l .. The wave trains 112 and 114 are deliberately separated in shape. temporary, by the detector shape 14 and the building materials used for housing the detector 15. In the case of a slot-type detector mentioned above, the wave train 112 may occur after the wave train 114 due to the trajectory longer through the detector housing. The wave train 116 represents high frequency vibrations propagated multiple times through the fluid of interest in the gap 12 as a result of one or more reflections. As with the wave train 114, the amplitude of the wave train 116 decreases significantly when the fluid of interest no longer occupies the gap 12. The signal 60 'shows the signal output by the comparator 47. The signal 60' makes a transition whenever a signal 46 'rises above the signal 46', and whenever the signal 46 'passes below the signal 46'. The wave train 116 of the signal 54 'represents low frequency vibrations 26 propagated through the detector housing 15 and detected by the receiving crystal 34 »It has been found that the low frequency wave train 116 is advantageous to be used as a detector integrity indicator because the amplitude of the wave train 116 remains relatively constant in the temperature scale of the entire detector, and for different detector housing materials. The signal level 56 '(i.e. voltage v') is selected such that the amplitude of the wave train 116 is greater than -B only when the detector 14 is intact, i.e., when the crystals 26 and 34 are firmly attached to the detector housing 15 and when the detector housing 15 is not damaged. Theoretically, a second low frequency wave train, which results from the low frequency vibrations propagated through the clear 12 and which are at the start time of the corresponding high frequency wave train 114, can overlap with and distort the wave train 116. However, said second low frequency wave train has not been observed in practical systems due, it is believed, to the orientation of the transmitting glass 26 in relation to the clear 12 and to the method of fixing glass 26 to the detector housing .15. Therefore, it is believed that the overlap? of the wave train 116 and the wave train 114 is unacceptable. The low frequency signal 54 'and the high frequency signal 46', simultaneously present on the line 36 of the receiving crystal 34, are effectively isolated from one another by filters 42, M4. If desired, the video amplifier 36 can be eliminated and, if required, individual amplifiers can be added at the output of each filter 42, 44. Other means known to those skilled in the art can also be used, as long as they are provided means for isolating detected high frequency vibrations from the detected low frequency vibrations. The high frequency signal 46 ', after the transformation by the comparator 47 in the signal 60', is put into gate with the time gate signal 72 'to give a gate output signal 76'. The pulse P initially sets the signal 76 'to LO. Subsequently, signal 76 'goes through a transition from HI to LO or from LO to HI as long as signal 60' makes a downward transition (from HI to LO) within the time gate window of signal 72 '. Similarly, the low frequency signal 54 ', after the transformation by the comparator 52 in the signal 64', is put into gate with the time gate signal 76 'to produce a gate output signal 60'. The time gate windows of the signals 72 ', 76' are selected to overlap with the characteristics of interest, ie wave trains 114 and 116, respectively, and are preferably slightly wider to allow room for regulatory variations of light time in relation to the P pulse due to variations in the detector construction or other variables. However, the time gate windows are preferably "off" (in a LO state) at all other times, so that alterations of the electromagnetic ringer, echoes and other noise sources do not affect the 7 & amp; ', 60'.

Claims (7)

Although the present invention has been described with reference to preferred embodiments, those skilled in the art will recognize that changes in form and detail can be made without departing from the spirit and scope of the invention. For example, one of the two transducer crystals can be removed and the remaining crystal can be used to generate ultrasonic vibrations and to generate electric transducer signal co or a function of received vibrations, with the addition of an ultrasonic vibration reflection member . Also, digital signal processing techniques can replace the functions performed by the individual circuit components in Figures 1 and 2. NOVELTY OF THE INVENTION CLAIMS

1. - A device for detecting the presence of a fluid in a defined place, comprising: transducer means for generating vibrations as a function of an electrical impulse signal and for generating a transducer output as a function of the received vibrations, the nedio? transducers being arranged next to one luqar defined in such a way that at least a portion of the output of the transducer responds to the presence of the fluid at the defined location; an excitation circuit that provides an electrical impulse signal to induce the vibrations simultaneously to a first and second frequencies; first and second filter circuits that receive the output of the transducer and selectively pass in first and second frequency component, respectively, to thereby generate first and second filter outputs, respectively; and a control unit coupled to the first and second filter circuits, the control unit indicating the presence of the fluid in the clear as a function of the first filter output and indicating the integrity of the device as a function of the second output of the filter. filter.

2. A device for detecting the presence of a fluid in a defined place according to claim 1, further characterized in that it comprises: a detector housing that carries the transducer means, the defined place comprising a clear in the detector housing.

3. A device for detecting the presence of a fluid in a defined place according to claim 2, further characterized in that the detector housing comprises plastic material.

4. A device for detecting the presence of a fluid in a defined place according to claim 1, further characterized in that the first frequency has a value in the range of 40 KHz to 400 KHz.

5. A device for detecting the presence of a fluid in a defined place according to claim 1, further characterized in that the excitation circuit comprises a pulse generator.

6. A device for detecting the presence of a fluid in a defined place according to claim 1, further characterized in that the first and second filter circuits comprise bandpass filters.

7. A device for detecting the presence of a fluid at a defined place according to claim 1, further characterized in that the first filter comprises a high-pass filter and the second filter comprises a low-pass filter. 6. An ultrasonic detector for detecting the presence of a fluid in a defined place, comprising: transducer means for generating vibrations as a function of an electrical impulse signal and for generating one. Transducer output as a function > n of vibrations received, the transducer output having a first and second frequency components, the transducer means being arranged close to the defined place in such a way that at least the first frequency component responds to the presence of the fluid in the defined place, a pulse generator coupled to transducer means for generating the electrical impulse signal; and first and second filter circuits that receive the output of the transducer and selectively pass the first and second frequency components, respectively, to thereby generate first and second filter outputs, respectively, the first filter output responding to the presence of the fluid at the defined place and the second filter output responding to the integrity of the detector. 9. An ultrasonic detector for detecting the presence of a fluid at a defined location according to claim 6, further characterized in that it comprises: a first and second time gate generators for generating first and second time gate signals, respectively; a first logic circuit that receives the first time gate signal and the first filter output to provide a first output of the detector that? indicates the presence of the fluid in the defined place; and a second logic circuit that receives the second time gate signal and the second filter output to provide a second detector output indicating the integrity of the detector. 10. A method for detecting the presence of a fluid in a defined place, comprising the steps of: providing a body having a body portion adjacent to the defined place; initiate vibrations in the body portion simultaneously to a first and second frequencies, detect the vibrations in the body portion, filter the vibrations detected through a first and second filters selectively passing the first and second frequencies, respectively, to produce a first and second filtered signals, respectively; providing a first detector output indicating the presence of fluid in the defined place as a function of the first filter signal; and providing a second detector output that indicates the reliability of the first detector output as a function of the second filtered signal. 11. A method for detecting the presence of a fluid in a defined place according to claim 10, further characterized in that it comprises the steps of: putting in gate the first filtered signal through a first time gate window for produce a first filtered signal in gate; and putting the second filtered signal in gate with a second time gate window to produce a second gate filtered signal; wherein the provision of a first output step of the detector is a function of the first gate filtered signal; and wherein the provision of a second output step of the detector is a function of the second gate filtered signal. In testimony of which I sign the above in this City of Mexico, D.F », on the 6th day of the month of December of 1994. By KAY-RAY / SENSALL, INC. 3J / mep * / crm #