GB2100431A - Detection of ultrasonic signals from disturbed liquid interfaces or surfaces - Google Patents

Abstract

Reflected ultrasonic signals from liquid interfaces or surfaces may vary widely in amplitude if the interface or surface is disturbed by, for example, agitation. The detection problem posed by this wide dynamic range of reflected signals is overcome by amplifying each reflected signal to such an extent that the relevant noise level is always a significant proportion of the associated detection threshold. In general, if the threshold detection level is constant then the amplifier gain must vary in a controlled manner during the period within which a specific reflected signal might be received. This procedure ensures that the greatest possible proportion of individual reflected signals are recognized whilst maintaining freedom from spurious responses. <IMAGE>

Description

SPECIFICATION Detection of ultrasonic signals from disturbed liquid interfaces or surfaces The invention relates to the detection of reflected elastic wave signals, typically pulses at ultrasonic frequency, from liquid-liquid interfaces and/or liquid-gas surfaces which are disturbed such as by mechanical vibration or agitation.

Apparatus is known for providing an indication of the level of one or more liquid interfaces and/or the surface by detecting the time taken for an elastic wave signal pulse to travel to the interface or surface and to return after reflection therefrom. In such apparatus it is known to adjust the gain of the receiver amplifier continuously with time according to the appropriate law to compensate for the expected attenuation with distance travelled of the reflected signal pulse. In order to achieve appropriate compensation, the gain of the receiver amplifier is swept from an initial low setting through a smoothly increasing level as a function of time commencing with each excitation of the transducer.

The setting of the receiver amplifier and the detection threshold level is such that the reflected signal amplitude will be several times greater than the threshold level (typically greater by a factor of four) throughout the range of time during which that signal might be received.

Such an apparatus usually works reliably if the liquid interface or surface from which reflected signals are detected is static and undisturbed. If the liquid is agitated, the reflectivity of the interfaces or surface varies widely. In general, a static flat surface is the best reflector and any superimposed irregularities will reduce the intensity of the reflected signal. Acoustic energy returns to the transducer from only that fraction of the surface or interface which has the correct orientation at the instant of reflection. In effect, a disturbed interface or surface scatters ultrasound over a wide angle and frequently only a small proportion of the acoustic energy returns to the receiving transducer. Consequently, from an agitated liquid interface or surface, there will be a very wide dynamic range encountered in a series of individual reflected signals.Typically the smallest reflected signal will be about two orders of magnitude less than that from a static surface. On the other hand the reflected signal can only be completely lost if the characteristic lateral dimension of the mechanical disturbance exceeds the diameter of the area at the surface or interface illuminated by the transducer. The geometry of the container and position of the transducer can often be selected so as to avoid such long wavelength disturbances at the surface or interface. In general, it is desirable that the diameter of the area illuminated by the transmitting transducer at the interface or surface should be appreciably greater than the lateral wavelength of any disturbance.

A disadvantage of the known apparatus is that it cannot cope with the above mentioned wide dynamic range of signals reflected from disturbed interfaces or surfaces. Useful information from low intensity reflected signals is lost, even although a high proportion of such weak signals may nonetheless exceed the relevant noise level.

This disadvantage is overcome or ameliorated in accordance with the present invention which provides apparatus for detecting a surface or interface level of a liquid, which apparatus comprises means for injecting elastic wave signal pulses into the liquid towards the surface or interface, receiver means for receiving elastic wave signal pulses reflected back from the surface or interface, an amplifier and threshold level detector, the relationship between the gain of the amplifier and the threshold level setting of the threshold level detector being so adjusted that the effective peak noise level during the period within which a reflected signal pulse is expected to arrive is amplified to a level which is a predetermined significant proportion less than unity of the said threshold level setting.

It is convenient electronically to hold the threshold level constant and adjust the gain of the amplifier. However, it will be appreciated that it is electronically equivalent to hold constant the gain of the amplifier and adjust the setting of the threshold level. For simplifying the description in the remainder of this specification reference will be made only to apparatus in which the threshold level is set and held constant whilst amplifier gain is adjusted.

With such an arrangement many of the reflected signal pulses will drive the amplifier into saturation (because of the practical limit to the maximum output voltage), but this will not inhibit threshold detection provided the amplifier recovers sufficiently rapidly from such saturation. The benefit of this procedure is that the signal may be reduced almost to the noise level without loss of detection.

Because of the random and unpredictable nature of the noise, an adequate safety margin between noise and threshold level must be allowed to ensure freedom from spurious responses.

Preferably the gain of the amplifier is adjusted such that the effective peak noise level during the period within which the reflected signal pulse is expected to arrive is amplified to a level which is a predetermined major proportion of the threshold level setting of the threshold detector. Preferably the peak background noise level is about half the said threshold level setting.

In general, if the threshold detection level is constant then the amplifier gain must vary in a controlled manner during the period within which the reflected signal is expected to arrive. This variation of amplifier gain with time is required to compensate for any variation in noise level with time.

It is often convenient that the same transducer should perform the combined function of converting an electrical signal pulse into an elastic wave signal pulse for transmission and the converse for reception.

Where the levels of more than a single interface or surface are to be detected, it is generally necessary for optimum performance that a separate amplifier and threshold detector should be provided for each respective reflected signal which is to be detected. Independent control of amplifier gain (together with an appropriate variation of that gain with time) is necessary when the relevant noise level associated with each signal is of different origin or magnitude (or otherwise has a different variation as a function of time). Where the noise level relevant to a particular reflected signal pulse is determined by the decaying tail of the transmitted or the preceding reflected signal pulse, then the gain of the appropriate amplifier is swept in a compensating manner to hold the noise level at the said predetermined proportion of the threshold level setting.

A specific construction of apparatus embodying the invention will now be described by way of example and with reference to the drawings filed herewith, in which: Figure 1 is a diagrammatic cross-section of part of the apparatus; Figure 2 illustrates typical waveform patterns produced in operation of the apparatus.

Figure 3 is an electrical circuit block diagram; and Figures 4, 5 and 6 show various reflected signal waveforms subject to different amplifier gains.

In this example a container 11 carries two liquids one 12 of which is aqueous and the other 13 of which is an immiscible organic solvent of lower density. A transducer 14, together with associated electrical equipment, injects signal pulses of elastic waves at ultrasonic frequency into the aqueous liquid 12 at the bottom of the container 11. Part of each signal pulse is reflected from the interface 1 5 between the aqueous liquid 12 and the organic solvent 13. A further part of each signal pulse is reflected from the surface 16 of the organic solvent 13. In this example, the same transducer 14 converts the received elastic wave signal pulses back into electrical signal pulses.

The time delays between the initial transmission of each signal pulse and reception of the two independent reflected signal pulses is used to provide an indication of the levels of the interface and the surface.

Figure 2 is a graph of signal amplitude against time which shows the envelope of the alternating waveform of a typical transmitted signal pulse 17, first reflected signal pulse 1 8 from the interface 1 5 and second reflected signal pulse 1 9 from the surface 1 6.

It should be noted that the transmitted signal pulse does not decay instantaneously to zero but has a tail produced by reverberations of the pulse within the wall of the container 11. This relatively slow decaying tail is reproduced in each of the reflected signal pulses. It should also be noted that the change in acoustic impedance across the liquid-liquid interface is less than across the liquid-gas surface. The interface reflected signal pulse 1 8 has therefore a lower amplitude than the surface reflected signal pulse 1 9 if the liquids are undisturbed. Any agitation, however, will cause the amplitudes of the two signals to fluctuate independently and their ratio will then vary widely.

Figure 3 shows the principal electrical components the apparatus. Ultrasonic transmitter unit 21 includes a clock pulse generator and provides a drive pulse on line 23 and a coincident trigger pulse on line 22 at time intervals chosen to provide a suitable frequency of measurement consistent with adequate delay between transmission to allow all acoustic echoes and reverberations within the container and elsewhere to decay between each excitation of the transducer.

The drive pulse on line 23 activates transmit/receive unit 24 which excites the transducer 14. The trigger pulse on line 22 resets swept gain controllers 25 and 26 and also initiates a delay within strobe generator 27 after which this strobe generator is enabled.

For signal detection, conventional ultrasonic measurement systems empoy amplifiers (which often incorporate appropriate filtering to improve signal-to-noise ratio) in conjunction with two special purpose modules. One module, here described as a swept-gain controller, is able to vary with time the gain of any associated amplifier to which it is coupled by means of a control interconnection.

The exact functional relationship of the swept variation of gain with time is preset by appropriate adjustments and the sweep is initiated by a trigger signal input to the controller. The other module, here described as a strobe generator, incorporates a threshold level detector such that a standard strobe pulse is transmitted immediately on detection of the first signal pulse which is received during a predetermined time period (or time 'window") and whose amplitude exceeds a preset threshold level.

All subsequent signals are ignored, regardless of amplitude -- that is during any one time window, only one strobe pulse can be generated. The strobe generator in this example includes appropriate gating circuitry to provide that the time window, during which the strobe generator is enabled, commences only after a prest delay has elapsed from receipt of an initial start signal input to the strobe generator.

The gating circuitry further provides that the time window optionally may (and preferably should) be closed after it has been open for a predetermined duration. Thus the initial start signal, preset delay time and (optional) duration should define precisely the duration of the period within which a specific reflected signal is expected to be received. All signals received outside this predefined time window will be ignored.

In this example the configuration, interconnection and calibration of these standard modules is so arranged in accordance with the invention that reliable measurement of disturbed liquid interfaces and surfaces may be achieved.

Separate amplifiers are provided respectively at 28, 29 to optimize subsequent detection of the reflected signal pulse 18 from the interface and at 31, 32 to optimize subsequent detection of the reflected signal pulse 1 9 from the surface. All received signal pulses are fed in parallel to both amplifiers 28 and 31 from the transmit/receive unit 24.

The delay incorporated in interface strobe generator unit 27 is preset such that this unit 27 is enabled just prior to the earliest expected time of arrival of the interface reflected signal pulse 1 8. After this time window has been opened, a strobe output pulse is generated on line 33 immediately on receipt of the first received signal (amplified by 28 and 29) whose amplitude exceeds the preset threshold level. Conventional electrical equipment (not shown) measures the time elapsed between the trigger pulse and the strobe pulse on line 33 to give an indication of the interface level 15. Optional logic circuitry may be included to recognise when a reflected interface signal is lost because no strobe pulse has been generated by the end of the time window.

The strobe output pulse on line 33 also provides an initial start signal to surface strobe generator unit 34; after a subsequent preset delay, strobe generator 34 is enabled. The time window applied to detection of the surface reflected signal 19 is thus referred to the time of recognition of the interface reflected signal 18; this procedure is appropriate because the reflected signal from the solvent-air surface must occur after the strobe generator has detected the interface reflection. The preset delay determined by strobe generator 34 corresponds to a dead time or inactive period after detection of the interface signal 1 8 but during which the surface signal 1 9 will not be detected, even if present.Therefore it is usually desirable that this preset delay should be as short as possible because the value of this delay determines the thinnest delay of organic solvent 1 3 which can be monitored with the measurement system.

The separate amplifiers 31 and 32 amplify all received signals and as soon as the threshold level setting of the strobe generator 34 is exceeded, a strobe output pulse is transmitted on line 35. Again this is fed to conventional electrical equipment (not shown) for providing an indication of the surface level 1 6. Optional logic circuitry may be used to recognise when a surface reflected signal pulse is lost. If strobe generator 27 fails to detect the interface signal 1 8, it may instead detect the surface signal 1 9. In such a case, strobe generator 34 will generally fail to detect any signal within the duration of its (relatively short) time window and therefore no strobe pulse will be generated on line 35.

Alternatively if strobe generator 27 fails to detect any signal within its appropriate time window, then no strobe pulse will be transmitted on line 33 and consequently no initial start pulse will be provided to strobe generator 34; consequently no strobe pulse would be generated on line 35 also. Thus the most likely modes of maloperation can be recognised by the absence of one or both of the strobe pulses on lines 33 and 35 subsequent to a particular excitation of the transducer.

Control of the receiver amplifier gain is effected in this example by swept gain controller 25, which controls amplifier 28 and swept gain controller 26, which controls amplifier 31. These controllers are capable of sweeping the amplifer gain setting through a predetermined functional relationship with time, starting again with each trigger pulse on line 22. The form of this function applied by each controller has to be set up empirically and, in accordance with the invention, is such that the peak noise level is amplified to about one half the threshold level setting of the relevant strobe generator unit throughout the duration of the time window defined by that strobe generator.

Typically the swept gain function of the controller 25 will be the inverse of the form of the acoustic background noise due to the decaying transmitted signal pulse 17, increasing the gain of amplifier 28 as the noise from the tail of the transmitted signal pulse dies away and then holding the gain substantially constant as the noise level settles to a constant value determined largely by random (thermal) electronic noise. Alternatively, where it is known that the interface reflected signal pulse will always be well clear of the decaying tail of the transmitted signal pulse it may be possible to dispense with sweeping of the gain of amplifier 28 and simply set this gain at a fixed level which will amplify the peak electronic background noise to about one half the threshold level of the strobe generator unit 27.The time window defined by strobe generator 27 would then not be opened until the acoustic background noise had decayed b'elow the electronic noise level.

In general, the noise level at the input to strobe generator 27 (and consequently the ratio of threshold to noise) is required to be essentially independent of time within the duration of the time window applicable to that strobe generator. As a result, the immunity to disturbance (represented by the ratio of signal to threshold for a signal reflected from a static surface) is not necessarily invariant with time; however, at all times, that immunity is as great as the corresponding noise level will permit.

Since the amplifier gain is set as high as the noise level permits, many reflected signals will drive the amplifier to saturation. It is therefore necessary that the amplifier recovers sufficiently rapidly from saturation and in practice this means that the amplifier should recover at least as rapidly as the exponential decay of the tail of the signal pulses; this requirement is readily met with available amplifiers.

It is desirable in many applications that the acoustic background noise 1 7 resulting from the initial transducer excitation should decay with time as fast as possible. Any reduction in acoustic background noise results in an improvement in the signal-to-noise ratio of echo pulses received from reflectors (such as the interface 1 5) located near the transducer. Where background noise is reduced, then, in accordance with this invention, the amplifier gain is correspondingly increased during the period immediately after transducer excitation in order to increase the reliability of signal detection. In situations where an intermediate medium is necessary between the transducer and the liquid (the soiid base of the container 11, for example), acoustic background noise results predominantly from reverberations within that intermediate medium.The nature of these reverberations, together with a technique for the reduction of such acoustic background noise, are described in our Patent Specification No.8118333 Agents ref: 12866 LgH filed on the same day as the present application. Forthe purposes of this invention, it is sufficient to appreciate that any reduction in acoustic noise (or indeed any reduction in electronic or other significant noise level) can result in improved reliability of detection of a specific received signal where that signal is subject to instantaneous and unpredictable reductions in amplitude. However this additional immunity to disturbance can only be realised if the amplifier gain is adjusted to the maximum possible as determined by the actual noise level, as described above.

In this example, the optimum gain control function of controller 26 is not identical to that of controller 25 because the noise level applicable to detection of the surface signal 1 9 does not have the same magnitude or variation with time as the noise level applicable to detection of the interface signal 1 8. If the thickness of solvent layer 13 is relatively small, then the noise level applicable to detection of the surface signal 19 is determined by the decaying tail of the interface signal pulse 1 8.

It was stated above that the preset delay applicable to strobe generator 34 should be as short as possible in order that thin layers of solvent 13 may be detected. This delay is initiated only on detection of the interface signal 18 because the surface signal 19 must necessarily be received at a later time. The delay is necessary because of the finite duration of interface signal 18. There is an inherent compromise, however, between the duration of the delay applicable to strobe generator 34 and the maximum permissible combined gain of the amplifiers 31 and 32. In other words, there is an inherent compromise between the mimimum detectable solvent thickness and the immunity of the detection system to the effect of disturbances upon the surface signal 1 9.

The nature of this compromise is illustrated in Figures 4 to 6 which represent interface and surface signals subject to different amplifier gains. The amplitudes (before amplification) of the interface signal and of the surface signal are the same for all three Figures and have the maximum values corresponding to undisturbed liquids. Furthermore the threshold voltage V0 for detection of the surface signal (1 9a, 1 9b or 19c) at strobe generator 34 is the same for all three Figures. It is clear that in Figure 5 (corresponding to an intermediate amplifier gain) the preset delay for strobe generator 34 must be of minimum duration tb in order to avoid possible spurious responses resulting from detection of the tail of the earlier interface signal 18b.However, if the combined gain of amplifiers 31 and 32 is increased (as in Figure 6) in order to improve the immunity to disturbance of the surface, then the preset delay must be increased to at least tc in order to avoid spurious responses due to the interface signal 1 8c. In practice, an adequate margin of safety (typically a factor of two) must be allowed between the threshold voltage V0 and the maximum possible amplitude of the amplified tail of the interface signal immediately after the preset delay (corresponding to opening of the time window applicable to strobe generator 34).

As a special case (shown in Figure 4), this delay may indeed be reduced towards zero (enabling detection of very thin layers of solvent 1 3) but only if the combined gain of amplifiers 31 and 32 is sufficiently reduced that the maximum possible peak amplitude of the interface signal 1 8a always remains safely below the threshold level of strobe generator 34. Typically the amplitude of the surface signal is only about five times greater than the amplitude of the interface signal when both liquids are undisturbed. Therefore, with this low amplifier gain, the threshold level V0 will usually be only marginally below the maximum possible amplitude of the surface signal 1 9a and the measurement will have virtually no immunity to liquid disturbances which reduce the amplitude of that signal.

The following table summarises the characteristics of the conditions represented in Figures 4, 5 and 6:

Fig 4 Fig 5 Fig'6 Amplifier Gain Low Intermediate High xl x4 x8 Immunity to Poor Moderate Good Disturbance 2:1 8:1 16:1 Minimum Detectable Zero Low High Thickness v.tb v.tc where "v" is the velocity of sound in the liquid 1 3 "tb" and "tc" are periods of duration indicated in Figures 5 and 6 respectively.

In the arrangement described with reference to Figures 1 and 2, detection of the second reflected signal 19 from the surface 16 is limited by the finite duration of the first reflected signal 18 from the interface 1 5. In order to ensure optimum operation regardless of the position of the interface 1 5, swept gain controller 26 must vary the gain of amplifier 31 with time in such a manner that the amplified tail of the interface signal immediately after the preset delay determined by strobe generator 34 does not vary with interface position. This is equivalent to a requirement that the effective peak amplitude of the interface signal 1 8 should be maintained constant, regardless of time elapsed since transducer excitation (note that the actual peak amplitude may be limited in practice by amplifier saturation).

Whilst the pattern of swept gain applied by controller 26 does compensate for expected attenuation with distance, there are two significant differences from conventional measurement systems. Firstly, it is the interface signal 1 8 whose variation of amplitude with distance is compensated, not the surface signal 19 which is to be detected by that channel of the measurement system. Secondly, the absolute value of the combined gain of amplifiers 31 and 32 is such as to maintain constant (relative to the threshold level of strobe generator 34) not the peak amplitude of the interface signal but the effective acoustic background noise contribution after a preset delay.

The extent of the compromise between minimum detectable thickness and immunity to disturbance depends on the duration and rate of decay of the tail on the interface signal 18. Any technique which can reduce the effective duration of the tail can either reduce the minimum detectable thickness and/or increase the reliability of measurements from disturbed surfaces. In general, any intermediate medium between the transducer and the liquid (such as the solid base of the container 11) should be of the minimum possible thickness. However, further improvement can result from application of the pulse compression techniques described in our Patent Specification No. 8118333 Agents ref: 12866 LgH filed on the same day as the present application.

During operation of a measurement system (such as that shown in Figure 3) which is configured, interconnected and calibrated according to this invention, amplifiers will often be saturated by signal sx pulses, but surface or interface disturbance can be tolerated up to the point that the signal pulse amplitude decreases almost down to the background noise level. As indicated above, an important appreciation in accordance with this invention is that, when interfaces and surfaces are disturbed, reliable detection of specific reflected signals requires the application of the maximum possible amplifier gain (varied, if necessary, with time) in order to operate with the minimum possible ratio (greater than unity) of threshold voltage to noise level consistent with freedom from spurious responses.In contrast, conventional measurement systems operate with an arbitrary ratio (greater than unity) of reflected signal amplitude (from a static surface) to threshold voltage. According to the present invention, the function of the swept gain controller is to compensate for variation in noise level as a function of time, not for the variation as a function of time in amplitude of the reflected signal which is to be detected.

Furthermore the noise level (and any associated variation with time) is generally different for each specific reflected signal which is to be detected; consequently each such signal requires independent control of the variation of amplifier gain with time. Amplifier gain need only be controlled within the time window defined by the associated strobe generator since this time window limits the period (relative to some reference input signal) during which a specific reflected signal can be detected.

In most practical applications where interfaces or surfaces are disturbed, occasional individual reflections will inevitably have insufficient signal-to-noise ratio to be recognised even with the apparatus of the foregoing example. Various conventional techniques may be used to circumvent this problem including the provision of logic circuitry to recognise the absence of a strobe pulse within a specific predefined time window. However, operation with the increased amplifier gain necessary for optimum detection of the interface or surface signal may also result in an increased probability of recognising instead spurious acoustic echoes (from bubbles of gas or drops of one liquid phase in another, for example).Discrimination against such spurious signals may be achieved, for example, by application of the coincidence techniques described in our Patent Specification No. 8118334 Agents ref: 12916 LgH filed on the same day as the present application.

With application of the technique described in this specification, it has been found that if the signal to noise ratio of a reflected signal pulse from a static surface or interface is at least 40:1 (corresponding to a ratio of signal to threshold voltage of 20:1), then more than 95% of all reflections can usually be recognised however much disturbance is applied to the surface. In any particular application, the immunity to disturbance will depend directly on the extent to which signals in the undisturbed situation are in excess of the noise level.

The invention is not restricted to the details of the foregoing example and can readily be applied, for example, to detection of only a single surface or to detection of multiple interfaces.

Claims (8)

1. Apparatus for detecting a surface or interface level of a liquid, which apparatus comprises means for injecting elastic wave signal pulses into the liquid towards the surface or interface, receiver means for receiving elastic wave signal pulses reflected back from the surface or interface, an amplifier and threshold level detector, the relationship between the gain of the amplifier and the threshold level setting of the threshold level detector being so adjusted that the effective peak noise level during the period within which a reflected signal pulse is expected to arrive is amplified to a level which is a predetermined significant proportion less than unity of the said threshold level setting.

2. Apparatus as claimed in Claim 1, wherein the said relationship between the gain of the amplifier and the threshold level setting is adjusted such that the effective peak noise level during the period within which the reflected signal pulse is expected to arrive is amplified to a level which is a predetermined major proportion of the threshold level setting of the threshold detector.

3. Apparatus as claimed in Claim 1 or Claim 2, wherein the said relationship between the gain of the amplifier and the threshold level setting is adjusted such that the effective peak noise level during the period within which the reflected signal pulse is expected to arrive is amplified to about one half of the threshold level setting.

4. Apparatus as claimed in any one of the preceding claims, wherein the said relationship between the gain of the amplifier and the threshold level setting is varied in a controlled manner during the period within which the reflected signal is expected to arrive, the control being such as to compensate for variation in noise level with time during the said period.

5. Apparatus as claimed in Claim 4, wherein, for detection of a reflected signal pulse during a period in which the noise level is determined by the decaying tail of the transmitted or the preceding reflected signal pulse, the said relationship between the gain of the amplifier and the threshold level setting is swept in a compensating manner to hold the noise level at the said predetermined proportion of the threshold level setting.

6. Apparatus as claimed in any one of the preceding claims, wherein for each elastic wave signal pulse injected into the liquid a plurality of reflected signal pulses is detected, a separate amplifier and associated components being provided respectively for each reflected signal pulse expected to be received.

7. Apparatus for detecting a surface and one or more interface levels of two or more liquid layers, or a plurality of interface levels of a plurality of liquid layers, which apparatus comprises means for injecting elastic wave signal pulses into the liquid layers, receiver means for receiving elastic wave signal pulses reflected back from the surface or the interface or interfaces, at least one amplifier and threshold level detector, the relationship between the gain of the amplifier and the associated threshold level setting being adjusted during the period within which a reflected signal pulse is expected to arrive in accordance with a predetermined compromise between on the one hand minimum detectable thickness of liquid between interfaces or between an interface and the surface of the uppermost liquid layer and on the other hand maximum immunity of the system to the effects of mechanical disturbance of the liquid interfaces or surface, the said maximum immunity to the effects of mechanical disturbance being achieved by so adjusting the relationship between the gain of the amplifier and the threshold level setting that the effective peak noise level during the period within which a reflected signal pulse is expected to arrive is amplified to a level which is as close to the threshold level setting as is practicable without risk of the peak noise level exceeding the threshold level setting.

8. Apparatus substantially as hereinbefore described with reference to, and illustrated in, the drawings filed herewith.