WO1999060349A1 - Transducer surface clearing method and apparatus - Google Patents

Abstract

A submerged transducer (12) generates a sonic pulse for detecting the presence of a sludge layer (18) within a tank (16). Gas bubbles and other matter rising through the water have a tendency to cause a buildup on the transducer face (12a). One embodiment for correcting this problem involves the use of an extension (40) having a weighted rod end (43) attached to the transducer (12). A series of flights (32) skim across the bottom of the tank (16) through the use of a chain (30) attached to a drive motor (34). The weighted end (43) of the extension (40) extends down into the movement path of flights (32) so that the flights (32) engage the weight (43) and cause the extension (40) and the transducer (12) to move in the direction of arrow (61). This movement coupled with the movement of the extension (40) and the transducer (12) back to their original location allows the gas and/or solid buildup on the transducer face (12a) to be dislodged.

Description

TRANSDUCER SURFACE CLEARING METHOD AND APPARATUS

Field of the Invention

The invention relates to sonic transducers for use measurements in fluids. More particularly, the invention relates to a mechanism for preventing gas bubbles and other matter from sticking to the surface of a transducer during its use in a water treatment plant.

Background of the Invention

Waste water treatment plants remove semi-solid material from water such as waste water from manufacturing processes, sewage and the like. A variety of techniques have been developed and used in these plants for the treatment of waste water. One popular technique incorporates a settling tank that separates semi-solid material (popularly known as sludge) from the water via gravity. Using this technique, the waste water (influent) enters a tank, wherein the sludge is encouraged to settle to the bottom. As the sludge settles, sludge layers form in the tank, with the densest layers disposed toward the bottom.

Controlling such water treatment systems often entails taking a variety of measurements of the sludge and other water quality factors. Sonic transducers have been used in a variety of water treatment tank measurement devices. In co-pending, commonly assigned U.S. Patent application serial number 08/741408 filed on October 29, 1996, method and apparatus are described for measuring sludge blankets and clarity in water treatment plants via sonic transducers. As described therein, the sonic transducer is at least partially submerged in the water where the measurements are being taken. Applicants have recognized that this submersion of the transducer exposes the surface of the transducer to elements in the water. Of particular concern in the case of sludge treatment, gas is produced in the sludge layers that rises as bubbles in the water. Rising gas bubbles that attach to the transducer surface interfere with the accuracy of the transducer. Similar bubble problems exist in water treatment facilities wherein dissolved oxygen may produce gas bubbles.

The sonic transducer generally comprises a single piezoelectric crystal (i.e., the transducer) with a relatively flat transducer face (i.e., the surface that transmits and/or receives energy). The water to transducer interface is designed to provide an extremely efficient transfer of sonic energy into the water and sonic energy returning from the measurement surface. Of particular concern in the measurement of sludge is the influence of undissolved gas generated by either mechanical or chemical means. For example, changes in the composition of the sludge can release excessive amounts of gas as does the use of intentional aeration. The undissolved gases coalesce into bubbles that rise toward the top of the tank. The mere presence of gas bubbles does not present a measurement problem; however, the relatively flat surface of the transducer face tends to accumulate material rising up in the tank. Bubbles or other materials that form a layer under the transducer seriously impair or eliminate the efficient transfer of sonic energy. This impairment occurs because of the gas/water interface provides poor sonic energy coupling and tends to reflect sonic energy. As a result, transmitted and received signals can be substantially reduced, interfering with the measurement process.

Suspended solids that attach to the gas bubbles can produce a similar denigrating effect on the measurement process. In some sludge recovery processes, solids become attached to air (i.e., gas) bubbles that are present at or slightly below the water surface. If an excess of these types of solids become attached to the transducer surface, a similar poor interface obtains. Thus by either stiction or mechanical trapping the transducer becomes fouled. Typically, measurement devices (i.e., transducers) that are currently available require frequent cleaning to clear the transducer face of buildup. A device for preventing the buildup of material on the transducer surface is described in commonly assigned and co-pending patent application no. 08/782,660, entitled TRANSDUCER SHROUD FOR IMPROVED TRANSDUCER OPERATION IN THE TREATMENT OF WASTE WATER, which is hereby incorporated by reference in its entirety. That application teaches the use of a shroud cover that passively acts to shed bubbles and other material as it rises up in the tank.

Others have recognized that exposure of a transducer transmission and reception mechanism to the elements in waste water could effect the operation of transducers. U.S. Patent No. 4,940,902 issued to Mechalas et al. discloses a wiping mechanism that reciprocates over a light sensing probe and clears the surface of buildup. Mechalas purports to have recognized that constant exposure to waste water would cause a film to buildup on the surface of a light source and light sensor. By providing a periodic wiping of the respective transducer surfaces the accuracy of the measurement is said to improve. Unfortunately, the Mechalas mechanism requires a complex mechanical mechanism to clear the transducer surface. As such, system costs are increased and system failure is more likely.

Accordingly, there is a need for a simple mechanism to ensure that the transducer surface is kept free of gas and or solids that could effect its efficient operation.

Summary of the Invention

The present invention employs an apparatus for transducer displacement so that gas and/or solids are discouraged from attaching or are removed from the transducer face. A number of mechanisms can be used to perform the displacement, for example, mechanical, electrical, hydraulic, or like means could be used to perform the displacement. Moreover, the movement can be vibratory, or periodic. The displacement motion could follow any number of paths, for example, up and down, side-to-side, circular, and so on.

According to an aspect of the invention, a rotating cam impinges on a portion of the transducer. The rotational motion of the cam causes the transducer to pivot back and forth and thereby deter the buildup of gas and/or solids on the transducer face. According to another aspect of the invention, a rod extends downwardly from the transducer. The rod is engaged by a rake or other moving element within the tank. As the rod is engaged by the moving element, the rod is displaced, thereby displacing the transducer. Brief Description of the Drawings

The foregoing summary, as well as the following detailed description of the preferred embodiment, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings an embodiment that is presently preferred, it being understood, however, that the invention is not limited to the specific methods and instrumentalities disclosed.

In the drawings:

Figure 1 illustrates an arrangement of a transducer in a waste water treatment tank;

Figure 2, illustrates a typical sonic transducer;

Figure 3 shows the buildup of gas on the transducer surface; Figure 4 shows the buildup of gas and attached solids on the transducer surface;

Figure 5 is a block diagram of the apparatus of the present invention; Figure 6 is an embodiment of the apparatus of the present invention;

Figure 7 is a preferred embodiment of a system employing the present invention;

Figures 8 A and 8B illustrate a theory of the forces that effect the operation of the present invention; Figures 9A-9C illustrate alternative displacement motions for the operation of the present invention;

Figure 10 illustrates a second arrangement of a transducer in a waste water treatment tank; and

Figure 11 is a second embodiment of the apparatus of the- present invention particularly for use in a tank as described in Figure 10.

Detailed Description of the Preferred Embodiments

According to a presently preferred embodiment, a sonic transducer displacement mechanism for use in a water treatment system will now be described with reference to the Figures. It will be appreciated by those of ordinary skill in the art that the description given herein with respect to those Figures is for exemplary purposes only and is not intended in any way to limit the scope of the invention. For example, the transducer displacement mechanism will be described herein with reference to a waste water treatment plant. However, such exemplary use of the transducer mechanism is merely for the purpose of clearly describing the present invention and in not intended as a limitation, except as expressly specified in the appended claims.

Referring now to FIGURE 1, a water tank 10 having sludge layers 18 is depicted. Such a tank may be used in a variety of water treatment processes. For example, the water tank 16 may be a clarifier for use in the treatment of waste water. In such a case, sludge layers 18 settle to the bottom of the clarifier. Transducer 12 generates a sonic pulse that is directed at sludge layers 18. The sonic pulse then travels through the waste water of tank 16 in a direction substantially perpendicular to water level 22. During its travel through the water, the sonic pulse encounters a variety of impedances, depending upon the varying sludge concentrations in the water. As the sonic pulse 15 experiences changes in the sludge concentration at various points, a corresponding change in impedance is experienced by the sonic pulse. Consequently, a portion of the sonic pulse reflects back in the general direction of transducer 12. The reflected pulse results in an echo (not shown), which is received by transducer 12. The energy in the echo excites transducer 12, which in turn, converts the echo into an electrical signal. The electrical signal is then provided to a controller via conductor 20 for processing.

Transducer 12 is positioned in the water tank at least one to two inches, and preferably about three inches, below the water level to couple the sonic energy with the liquid medium under consideration. The air/water interface 22 represents a sharp change in impedance. As a result, a transducer positioned above air/water interface 22 would receive a large echo from interface 22, greatly increasing the difficulty of measuring activity within the water. By contrast, a transducer positioned below interface 22 will avoid the major impedance change that occurs at interface 22, increasing the measurement accuracy. However, positioning transducer 12 below air/water interface 22 has the unfortunate side- effect of exposing transducer 12 to elements in the water. As described above, one significant transducer exposure problem is created by gas bubbles and other matter that rise up through the water in tank 16. As these bubbles and such, represented by bubbles 14 in the Figure, rise through the water, some of them may strike the transducer measurement surface and stick, creating a gas buildup 14a as indicated in the Figure. Thereafter, the gas buildup 14a will remain on the transducer surface until it dissolves or is otherwise dislodged from the transducer surface. Furthermore, after a sufficient amount of buildup, gas buildup (e.g., 14a) will become a high impedance interface similar to interface 22, reducing the transmission of sonic pulses and the reception of desired echo signals. As a result, the accuracy of any subsequent measurements will be compromised and the effectiveness of the entire water treatment system may suffer.

Transducer 12 comprises a commercially available device, such as a piezoelectric transducer. As shown in Figure 2, in the embodiment disclosed herein, transducer 12 has a measurement surface 12a (the transmit receive surface) that is substantially round in cross section and has a substantially flat surface (the measurement surface). During transmission, measurement surface 12a oscillates at a predetermined frequency (e.g., 200 kHz). During reception, echoes strike surface 12a, causing it to generate an electrical signal in proportion to the frequency of the echo signal. Further details and operation of piezoelectric transducers are well-known to those of ordinary skill in the art. As such, further operational characteristics are omitted from the present description for clarity and brevity.

The invention provides method and apparatus for the improvement of transducer measurement capabilities. According to an aspect of the invention displacement of a transducer 12 immersed in a liquid provides a means to remove, the build-up of gas or solids from the transducer face 12a. The transducer displacement prevents the interruption of the measurement process and in essence eliminates the need for frequentυleaning/attention. As a result, the system operates unattended and is more reliable.

As best shown in Figures 3 and 4 build-up of gas 30 and/or gas mixed with solid material 32 build-up causes a barrier 22b between transducer 12 and the water. It is an object of the present invention to prevent such build-up or to dislodge it when it occurs. As shown in Figure 5, an apparatus in accordance with the present invention comprises a transducer 12, transducer electronics 28 that process the signal output from transducer 12, and displacement mechanism 36. In general, displacement mechanism 36 couples mechanical energy to transducer 12 to impart a displacement sufficient to discourage or dislodge foreign products (e.g., gas/solids) from transducer face 12a. Displacement mechanism 36 can be powered by either electrical, mechanical, hydraulic, or similar means. The motion itself may be horizontal, radial, vertical, horizontal, vibratory, or the like.

In a preferred embodiment shown in Figure 6, transducer 12 is mounted to a hinge 40 which allows arm 12c of transducer 12 to pivot. Alternatively, transducer 12 could be mounted on a wire or other flexible material that would allow freedom of movement of transducer 12. Cam 38 is in mechanical communication with the arm 12c of transducer 12. As cam 38 rotates, transducer 12 is displaced as shown in phantom and returned. Preferably, cam 38 bears against hinge plate 42, which causes motion of transducer 12. The shape of the cam can be designed to impart a variety of responses. For example, a saw tooth relaxation motion (left and drop return) is shown in Figure 6. A variety of other devices and configurations could be used to impart the same end effect. For example, similar devices using a solenoid and magnetic vibrator could also be used.

A block diagram of the motorized cam unit is shown in Figure 7. The control unit consists of the following basic function: 1. Interval Timer 44 establishes how often the apparatus will operate (e.g., every 5 minutes, 10 minutes, etc. This could be a programmable function so that the apparatus can be adapted for specific tank environments.

2. Event Timer 45 establishes how many cam cycles (i.e., displacement events) are applied to transducer 12. 3. Drive 46 applies power via relay 47 for a period established by event timer

45.

4. Relay 47 supplies power to motor 48.

5. Motor 48 in conjunction with cam 38 imparts mechanical displacement to transducer 12 via the hinge motion. In the displacement of transducer 12 as shown in Figure 6, two forces interact to remove bubbles and the like from the transducer face 12a. Referring also to Figure 8 A, transducer 12 is shown in a displacement position such that it has moved from an angle normal to the air/ water interface 22. In this position, the buoyancy of bubble 14 provides a force to move bubble 14 in a direction indicated by arrow 50. Moreover, as shown in Figure 8B, as transducer 12 moves back toward its position substantially normal to air/water interface 22. The motion of transducer 12 back toward normal, as indicated by arrow 52, causes relative motion of tank water in a direction indicated by arrow 51. This relative water motion acts as an additional force to push the bubbles away from transducer face 12a. Figures 9A-9C, present alternate displacement motions for transducer 12 to encourage the bubble removal from transducer 12. In Figure 9 A, transducer 12 undergoes a reciprocating motion. In its first position, position A, a gaseous interface 22a has formed on transducer face 12a. In position B, transducer 12, undergoes a downward motion as indicated by arrow 53. This motion causes the gas to breakdown as bubbles 14 buoyantly move toward the water surface. In position C, transducer 12 moves in a direction indicated by arrow 55 back to its original position.

Figure 9B illustrates another transducer motion. Here, transducer 12 moves laterally, to use the force of the relative water motion alone to remove the gaseous buildup 22a. In position A, a gaseous interface 22a has formed over transducer face 12a. In position B, transducer 12 moves slowly in the direction indicated by arrow 57. Thereafter, transducer 12 moves relatively quickly in the direction indicated by arrow 58a back to its original position. This movement back to it original position causes the relative motion of the water to encourage bubbles 14, which tend to stay in position B as transducer 12 moves to position C, to move off of transducer face 12a. Figure 9C further illustrated the preferred method, which incorporates aspect of the methods of Figures 9 A and 9B. Here, transducer 12 begins in the position A. Again, a gaseous interface 22a has accumulated on the transducer face 12a. Transducer 12 is moved slowly to position B, as indicated by arrow 59. Thereafter, transducer 12, as indicated by position C, is dropped back in the direction of arrow 60 toward its original position. Bubbles 14 move up and away from transducer face 12a. In each case the object is to provide relative motion between the water in the tank and transducer 12. To the extent that other mechanism can be used to accomplish the same objective of relative motion between the tank water and the transducer, they to would be within the intended scope of the present invention.

Figure 10 shows a second tank and transducer embodiment in accordance with the present invention. The tank 16' of Figure IB is generally of rectangular shape and has a series of flights 32 that skim across the bottom of tank 16' as is well understood in the art. Preferably, flights 32 return in close proximity to the bottom of tank 16'. In the exemplary embodiment of Figure IB, for example, the return of flights 32 is about three feet above the bottom of tank 16'. Flights 32 are coupled to a chain 30, which rides in a track (not shown). Chain 30 is powered by a drive motor 34 that drives chain 30 around gears, e.g., 36,38, that, along with the track, control the path of chain 30. Chain 30 moves flights 32 to rake the bottom of tank 16'. As described in more detail below, according to a second embodiment of the present invention, transducer 12 also comprises an extension 40 that projects downwardly past the face of transducer 12 and engages flights 32 to improve the performance of transducer 12.

The second embodiment of the arrangement of the present invention is illustrated in Figure 11. As shown, an extension 40 is coupled to transducer 12, extending downwardly into tank 16' toward the bottom of tank 16'. The extension preferably comprises a cable 40 with a weighted rod end 43, but could also be formed of a rod like material. Extension 40 extends past transducer face 12 a and extends to a region above the bottom of tank 16' proximate the level of the return path of flights 32. Extension 40 has a weight 43 coupled to one end. A counter weight 42 extends outwardly from the opposite side of transducer 12 to counter balance the weight 43.

The weighted end 43 coupled to extension 40 extends down into the path of the return of flights 32 so that the flights engage weight 43 as the flights 32-are moved across tank 16' by chain 30. As a flight 32 engages weight 43, the extension 40 is caused to move in the direction indicated by arrow 61. As that flight 32 continues to move along its path, weight 43 and flight 32 eventually disengage and weight 43 moves back in the direction indicated by arrow 62. Because extension 40 is coupled to transducer 21, the movement of extension 40 causes a corresponding movement in transducer 12. Hence, transducer 12 is caused to have a motion similar to the motion induced by the cam type apparatus as described with reference to Figure 6. However, this second embodiment does not require an additional motor to cause the motion of the transducer but rather relies on the apparatus already present in the tank, i.e., flights 32 and chain 30. Preferably, the portion of extension 40 that engages flights 32 (e.g., weighted end 43) has a surface designed to enhance engagement between extension 40 and flights 32. For example, the surface could have irregularities formed therein.

The above description of preferred embodiments is not intended to impliedly limit the scope of protection of the following claims. Thus, for example, except where they are expressly so limited, the following claims are not limited to applications waste water treatment systems.

Claims

What is claimed is:

1) An apparatus for making sonic measurements in a fluid filled tank, comprising: a sonic transducer having a measurement surface; a means for displacing said sonic transducer for encouraging bubbles and other matter away from said measurement surface during use.

2) The apparatus as recited in claim 1 wherein said means for displacing comprises a rotating cam in mechanical communication with said transducer.

3) The apparatus as recited in claim 2 wherein said means for displacing further comprises a motor coupled to said cam for providing rotational movement to said cam.

4) The apparatus as recited in claim 1 wherein said means for displacing said transducer comprises a cable mechanically coupled to said transducer and extending toward a bottom surface of said tank so that movement of said cable causes a corresponding movement of said transducer.

5) The apparatus as recited in claim 1 wherein said means for displacing said transducer comprises a rod mechanically coupled to said transducer and extending toward a bottom surface of said tank so that movement of said rod causes a corresponding movement of said transducer.

6) The apparatus as recited in claim 4 wherein said tank comprises a waste water treatment tank having a rake periodically moving across the bottom of said tank and wherein said cable has a length sufficient to engage said rake when said rake moves across the tank in the vicinity of the shaft.

7) A method for conducting sonic measurements in a fluid filled tank, comprising: positioning a transducer below a fluid surface; displacing said transducer face from a first position to a second position; and moving said transducer back to said first position after the transducer is displaced.

8) The method as recited in claim 7 wherein the transducer is displaced by way of a periodic function.

9) The method as recited in claim 8 wherein the periodic function is supplied by a rotating cam in mechanical communication with the transducer.

10) The method as recited in claim 8 wherein the periodic function is suppled by an extension coupled to said transducer and extending toward a bottom of said tank such that movement of said extension causes a corresponding movement of said transducer.

11) The method as recited in claim 10 wherein said movement of said extension is caused by said extension periodically engaging a portion of a tank flight.

12) A system for measuring at least one density level in a fluid, wherein said fluid experiences gas bubbles, the system comprising: a tank capable of containing a fluid; a sonic transducer extending into said tank; and an extension extending from said transducer toward a bottom of said tank, said extension having a length extending past a measuring surface of said sonic transducer.

13) The system as recited in claim 12 wherein said sonic transducer is movably coupled to the tank.

14) The system as recited in claim 12 wherein said extension extends from one side of said transducer and a counter weight is coupled to another side of said transducer. 15) The system as recited in claim 12 wherein said tank comprises a waste water treatment tank.

16) The system as recited in claim 15 further comprising a rake movably coupled within said tank proximate the bottom of said tank, said rake periodically contacting a portion of said shaft.

17) The system as recited in claim 12 wherein said sonic transducer is pi votally coupled to said tank.

18) A method of removing bubbles from the measuring surface of a transducer submerged in a waste water treatment tank, the method comprising: pivotally coupling a transducer to the tank; positioning said transducer at a first position so that the measuring surface is directed toward a bottom of the waste water treatment tank; and providing a mechanical force to the transducer to move the measuring surface at an angle with respect to the first position.

19) The method as recited in claim 18 wherein the mechanical force is provided to the transducer by way of a rotating cam.

20) The method as recited in claim 18 wherein the mechanical force is provided to the transducer by providing an extension that extends from the transducer toward a bottom of the tank so that the extension is periodically moved by a moving rake in the bottom of the tank.