Mounting structure for transducers with sonic-energy absorbing means

The transducers in a transit time clamp-on flowmeter are positioned relative to one another by abutting against pin stops located in selected openings of one or more rows of openings extending longitudinally along the pipe axis. A block or strip of sonic-energy absorbing material is fixed to the conduit surface between the spaced transducers and absorbs sound energy which tends to flow in the pipe wall between the transducers, substantially improving the signal-to-noise ratio of the flowmeter system.

BACKGROUND OF THE INVENTION 
This invention relates to a mounting structure for mounting transducers on 
the surface of a fluid-containing conduit, and more particularly relates 
to a novel mounting structure which improves the signal-to-noise ratio of 
the transducer signal output and which simplifies the location of spaced 
transducers relative to one another. 
Flowmeters which employ clamp-on transducers are well known, and are 
described, for example, in U.S. Pat. Nos. 4,425,803, 4,373,401, 3,987,674 
and 3,869,915, each in the name of Joseph Baumoel. The disclosures of 
these and all other prior art materials mentioned herein are expressly 
incorporated by reference. 
In flowmeters such as those described in the above patents, two spaced 
transducers are clamped to the outer surface of a conduit. One transducer 
transmits a train of pulses through the pipe or conduit wall, through the 
fluid and back through the pipe wall to the other transducer. The other 
transducer, in turn, transmits a signal through the fluid in the conduit 
and back to the first transducer. In the direct mode, the transducers are 
on opposite sides of the conduit. In the reflect mode, the transducers are 
on the same side, and the signal reflects off the facing inner wall of the 
conduit as it passes from one transducer to the other. In either mode, the 
difference in the time taken for sonic signals to travel first upstream 
and then downstream of the conduit relative to the direction of flow of 
fluid within the conduit is a measure of the flow velocity of the material 
within the conduit. 
A clamping structure for holding transducers on the surface of the conduit 
or pipe is described in Baumoel, U.S. Pat. No. 4,425,803, referred to 
above. When mounting such transducers, they should be located a known 
distance apart along the axis of the conduit, which distance depends upon 
the conduit material, the conduit size, and the fluid within the conduit, 
among other parameters. As disclosed in above-mentioned U.S. Pat. No. 
4,425,803, an index scale is provided on the transducer mounting track and 
the edges of the transducers are located at particular index numbers 
determined by the manufacturer and the transducers are then firmly clamped 
in place. This technique requires a skilled operator who can find the 
correct index marking for each transducer and requires that the transducer 
be held firmly in place while it is being clamped at the location in which 
it was set on the index scale. 
As will be described, the present invention provides a novel positioning 
means for accurately positioning transducers in predetermined axial 
locations along the conduit length to a high degree of accuracy by 
untrained persons. 
It is also well known that, during the operation of spaced transducers in 
the reflect mode, some of the pulse energy from the transmitting 
transducer will propagate axially along the pipe wall toward the receiving 
transducer. This direct pulse reaches the receiving transducer earlier 
than the pulse energy which traverses the fluid. Conventionally, the 
receiving transducer is gated so that it receives energy only during the 
period that the sonic energy through the fluid could be expected to be 
received. Therefore, the direct pulse through the pipe is not expected to 
interfere with the reflect-mode measurement taking place, with respect to 
the time of arrival of the sound traversing the fluid at the second 
transducer. 
However, although the peak energy of the initial pulse which passes through 
the pipe has passed long before the reflect-mode signal which traverses 
the fluid arrives at the receiving transducer, there is nevertheless a 
"ringing" or oscillation through the pipe wall, so that some of the energy 
of the direct wall pulse is received by the receiving transducer at the 
time the energy traversing the fluid reaches the second transducer. This 
residual pipe noise, while small, adversely affects the signal-to-noise 
ratio of the measurement. 
The structure of the present invention eliminates or considerably reduces 
the effect of energy which traverses between the transducers directly 
through the pipe wall when making a measurement in the reflect mode of the 
time taken for sonic energy to pass through the fluid within the conduit. 
BRIEF DESCRIPTION OF THE INVENTION 
In accordance with a first aspect of the present invention, a novel 
mounting structure is provided in which the two transducers are mounted 
between spaced rails which define a mounting track and are clamped to the 
rails in any desired manner. In one embodiment, the transducers are on the 
same mounting track and, in another, similar mounting tracks for each 
respective transducer are on opposite sides of the conduit. The rails 
contain a series of spaced, pinreceiving openings which extend parallel to 
the conduit axis, and are positioned and spaced in a predetermined 
accurate manner. The pin openings are located at a height on the track 
that ensures that, if a pin is inserted perpendicular to the conduit axis 
and through a selected opening and into a corresponding opening on the 
other rail, the pin will intersect the side edge of a transducer housing 
to accurately locate the transducer housing at an exact location 
determined by the pin location. The second transducer is similarly located 
by abutting a pin which is inserted through an opening in a second line of 
openings which are parallel to the first and are axially spaced relative 
to the first. Therefore, an exact predetermined spacing can be easily set 
by untrained personnel who simply place pins in numbered and lettered sets 
of openings defined by a program in a flow measurement computer on the 
basis of, e.g., the measured properties of the liquid, or identified from 
a chart provided by the manufacturer which designates pairs of pin 
openings on the basis of, e.g., conduit size and liquid properties. The 
installer simply places the transducer on the mounting track and moves it 
so that the transducers engage the pins and then tightens the clamps which 
fix the transducers on the mounting track or tracks and on the conduit to 
which the transducer must be coupled. The pins can then be removed if 
desired. 
The function of the pins described above can be carried out by any type of 
insertable blocking member which need only project sufficiently into the 
slot receiving the transducers as to engage the transducer side and thus 
position it within the track. 
As a second aspect of the present invention, and in order to increase the 
signal-to-noise ratio of the received signal when making reflect-mode 
measurements, a novel sonic absorbent body is fixed to the conduit wall 
and is disposed between the two spaced transducers. This sound-absorbent 
body is preferably made of a material with the same or similar sonic 
impedance as the pipe and the transducers, so that sound passing through 
the pipe wall will more easily enter the sound-absorbing body. The 
sound-absorbing body can contain structure similar to that disclosed in 
Baumoel, U.S. Pat. No. 4,556,813, in order to appropriately capture and 
then dissipate the energy which enters the sound-absorbing body so that 
this energy is not reflected back into the pipe wall. It has been found 
that the use of such a novel sound-absorbing body disposed on the pipe 
wall and located between the two spaced reflect-mode transducers can 
increase the signal-to-noise ratio by a factor between two and four. 
The novel sound-absorbing block disposed between the two spaced 
reflect-mode transducers can be used in any transducer arrangement where 
it is desired to reduce the noise level of sound energy traversing 
directly through the pipe wall and between two spaced transducers. The 
sound-absorbing block is primarily useful in applications using the 
reflective mode of operation using a short path between transducers. 
The novel mounting structure of the invention employing location pins, as 
described above, can be used by itself or in combination with the novel 
sound-absorbing block. 
In a third embodiment of the invention, particularly useful for transducers 
operated in a direct mode, a non-rigid absorbent material such as a mastic 
or duct tape is fixed around any or all portions of the periphery of the 
conduit, including between the transducers. Any suitable viscous, highly 
sonically damping material can be used. It has been found that such 
viscous materials can increase signal-to-noise ratio up to fivefold.

DETAILED DESCRIPTION OF THE DRAWINGS 
Referring first to FIG. 1, there is shown a hollow conduit or pipe 20 
having a flow axis within which any desired fluid may translate or be 
contained. Pipe 20 may be of steel or any other material suitable for use 
with clamp-on transducers and may typically have an inner diameter from 
1/2 inch to 240 inches, although there is no limit on diameter. The pipe 
wall can have any thickness. The purpose of one aspect of the present 
invention is to secure flow-monitoring transducers to the surface of the 
conduit and to permit the accurate location of the transducers relative to 
one another along the axis of the conduit 20. 
Before the installation procedure, the pipe 20 if desired may be abraded to 
have a flat about 1/8 inch wide extending parallel to the axis of the 
pipe. All grit, corrosion, coatings or loose paint is removed from the 
pipe surface and it is cleaned and degreased. The location chosen for the 
mounting of the transducers is one which remains full at zero flow and 
which is located preferably away from pipe bends and on a straight run of 
the pipe. 
Each of a pair of mounting chains or straps 21 and 22 receives a respective 
track-mounting nut such as the track-mounting nut 24 of FIG. 4. Chains or 
straps 21 and 22 are then wrapped around and are fastened by respective 
chain hooks 25 of FIG. 6. An adjustment screw of conventional variety 
(shown in FIG. 12) permits tightening of the chain, as desired. The chains 
21 and 22 and the track-mounting nuts which they carry permit the fixing 
of a mounting track 30 of FIGS. 2 and 3 to pipe 20. 
The mounting track 30, as shown in FIG. 2, may consist of a pair of 
parallel-spaced steel or aluminum angles or rails 31 and 32. Rails 31 and 
32 are fixed relative to one another by a pair of cross pieces 33 and 34 
which are riveted or welded to the opposite respective ends of the rails 
31 and 32. Cross pieces 33 and 34 have respective central openings 35 and 
36 which are best seen in FIG. 2. 
As best shown in FIG. 5, rail 32 is provided with an upper row of four 
spaced openings labeled A, B, C and D, respectively, and a lower row of up 
to 16 spaced openings labeled for example 0 through 15, or a selected 
subset such as 0 through 8 as shown, for shorter tracks. Each of the rows 
of openings is parallel to the axis of conduit 20. 
A plurality of corresponding rows of openings (not shown) is in line with 
and disposed on rail 32. Therefore, a pin can be inserted perpendicularly 
to rail 32 through any one of the openings into a corresponding opening in 
the other rail. Openings A through D and 1 through 9 in the two rails 32 
and 31 are located at predetermined positions relative to one another to 
correspond to a menu or predetermined list of transducer locations for 
various pipe sizes and material. Thus, when the transducer assembly is 
provided to the user, the flow measurement and display computer determines 
which openings are to be selected for the specific application. The exact 
spacings used will depend in part on the nature of the transducers used 
and can be easily defined by the manufacturer for different conduits and 
liquids monitored. 
The rail assembly 30 is fixed to the conduit 20 by the chains 21 and 22 and 
by track mounting screws 40 and 41 which pass through openings 35 and 36, 
respectively, in cross bars 33 and 34, respectively. Screws 40 and 41 are 
threaded into the threaded interior openings of track mounting nuts 24 
which are fixed to the pipe wall 20 by the chains 21 and 22. Consequently, 
by tightening screws 40 and 41, the rail 30 is fixed to pipe wall 20. 
The transducers are next clamped to the track 30 so that the operative face 
of the transducers is physically pressed into contact with the outer 
surface of the pipe wall 20 when screws 40 and 41 are tightened. More 
specifically, and as is shown best in FIG. 5, transducers 50 and 51 are 
fitted between the spaced rails 31 and 32 of track 30. Each transducer may 
have the shape shown in FIG. 7 and will have an active bottom surface 
which can receive a suitable sonic coupling compound 53, before it is 
inserted in the track 30 and applied against the pipe wall 20. Transducers 
50 and 51 have appropriate electrical cables 55 and 56, respectively, 
extending therefrom and which carry the electrical signals which may be 
processed in accordance with the description of U.S. Pat. No. 3,987,674, 
referred to above, or by any other desired known processing technique. 
Transducers 50 and 51 are secured to rail assembly 30 by respective clamps 
60 and 61 which may be of sheet steel bent to shape, as shown in FIG. 6. 
Thus, each of clamps 60 and 61 has inwardly projecting flanges 64 and 65, 
respectively, of FIG. 6, which hook beneath rails 31 and 32, respectively. 
Each of the clamps contains pressure screws 66 and 67, respectively (FIG. 
5). By tightening screws 66 and 67 against the upper surface of 
transducers 50 and 51, it is possible to forcibly press the bottom 
surfaces of transducers 50 and 51 into good coupling relationship with the 
wall of the pipe 20. The bottom and body of rails 31 and 32 may be lifted 
from conduit 20 when the transducers 50 and 51 are pressed against conduit 
20. 
In accordance with the invention, two index pins 70 and 71, shown in FIG. 
5, extend into opening D in the top row of openings and pin 71 extends 
into opening 9 in the bottom row. 
The index pin 71 is shown in detail in FIG. 8 and has an extending shank 73 
and a finger loop 74 for inserting the pin and for removing it in a 
convenient fashion. Each index pin 70 and 71 can be connected to its 
respective transducer clamp 60 and 61 by chains 75 and 76, respectively, 
to prevent accidental loss of the pins. 
In order to install the transducers 50 and 51 with a predetermined spacing 
between them for a given application, the installer will know as 
previously described which openings in the rows of openings must be 
selected for pins 70 and 71 for his particular installation. Such pin 
settings may be provided by the manufacturer or can be calculated by the 
built-in computer supplied with such equipment. The particular spacing 
used will vary for equipment of different manufacturers and using 
different operation modes. After identifying the openings, pins 70 and 71 
are placed in their appropriate identified opening. Transducer 50 and 
transducer 51 are then simply laterally moved toward one another along the 
track 30 until the sides of the transducers engage their respective pin as 
is best shown in FIG. 5a and as shown for the transducer 51 engaging pin 
71 in FIG. 8. The installer then tightens the screws 66 and 67 to fix the 
transducer positions. Pins 70 and 71 may then be removed, if desired. 
Although pins 70 and 71 are shown extending between both rails 31 and 32, 
the pin need only extend through a single location opening in one rail and 
only at least partly into the slot defined between rails 31 and 32. 
FIGS. 9 through 13 show a second embodiment of the invention wherein the 
transducers are mounted on opposite sides of the conduit for a direct 
operation mode instead of on the same side for a reflective operation mode 
as is shown in FIG. 5. In FIGS. 9 through 13, components which are the 
same as or similar to those of FIGS. 1 through 8 have been given similar 
identifying numerals. It will be noted that in FIG. 12 a pair of track 
assemblies 30 is secured to the opposite lateral sides of the pipe 20. It 
is preferred that the transducers be mounted in a horizontal plane 
relative to the ground in both the embodiment of FIGS. 1 through 8 and in 
the embodiment of FIGS. 9 through 13 so that sediment on the bottom of the 
pipe does not interfere with the transmission of sonic energy through the 
interior of the conduit. 
The index openings in tracks 30 in FIG. 12, however, differ from those of 
FIG. 5 since only a single row of index openings need be contained in each 
of the two track assemblies. Thus, in FIG. 12, only index openings A, B, C 
and D are formed in the upper rail whereas a row of index openings 0 
through 15 appear in the lower track assembly. When upper and lower tracks 
30 in FIG. 5 (which are, in fact, in a common horizontal plane) are 
laterally aligned, the spacing between selected openings in rows A to D 
and 0 to 15 is well defined. 
In mounting transducers as in FIG. 12, a pair of chains is first assembled 
as shown in FIGS. 9, 10 and 11. Thus, chains 21 and 22 in FIG. 10 will 
have pairs of track-mounting nuts 24 fitted thereon and located exactly 
180.degree. apart from one another. FIG. 9 shows chain 21 before it is 
secured in place. The upper rail 30 of FIG. 12 is mounted on the upper set 
of spaced nuts 24 on chains 21 and 22. Similarly, the lower rail 30 is 
fixed to the lower set of spaced nuts 24, as shown in FIG. 12. FIG. 12 
also shows the strap-tension adjustment screws 21a and 22a for the straps 
21 and 22, respectively. 
A single transducer 80 is then disposed between the spaced rails of upper 
track 30 and is mounted to the track 30 by the strap or clamp 81 as shown 
in FIG. 12. The transducer 80 is also shown in perspective view in FIG. 
13. Note that a transducer wiring housing 83 is fixed atop the transducer 
80 and that an appropriate wiring cable extends therefrom which is to be 
connected to the control circuitry for driving the transducer assembly. 
A similar arrangement is provided at the bottom of FIG. 12 for the track 
containing second transducer 85. Transducer 85 has a wiring assembly 86 
connected thereto, and is fixed to the track 30 by the clamp 87. Clamps 81 
and 87 and their mounting screws 88 and 89, respectively, may be identical 
in construction to those of FIGS. 5, 6 and 8. 
In accordance with the invention, pins 90 and 91, each of which may be 
identical to the index pin 72 of FIG. 8, are then appropriately located by 
the installer in openings D for the upper track 30 and 7 for the lower 
track 30, or any of the other pin openings which have been identified to 
the user for his particular assembly. The transducers 80 and 85 are 
abutted or "banked" against their respective pins 90 and 91 and screws 88 
and 89 are then tightened. In this way, the transducers 80 and 85 have the 
preferred spacing between them for a particular installation. 
FIGS. 14-15 show further embodiments of the invention wherein a 
sound-absorption block 100 is installed on the conduit 20 of FIG. 5 and is 
disposed between transducers 50 and 51. During the reflect-mode operation 
of transducers 50 and 51, a sonic energy pulse is initiated, for example, 
by transducer 51. It is intended that the energy of this pulse will enter 
and be refracted through the fluid flowing in the conduit 20. The energy 
is then reflected off the rear interior pipe wall and then into the 
receiving transducer 51. In a similar manner, a pulse transmitted by 
transducer 51 through the fluid within the conduit 20 will be received by 
transducer 50. The circuitry connected to these transducers will measure 
the transit time of pulses going upstream and downstream between the 
transducers 50 and 51. The time difference between the upstream time and 
downstream time will be a measure of flow velocity of fluid within conduit 
20. 
It is desirable that the measurements be as free as possible from 
extraneous sonic and electronic noise. However, it is well known that the 
output pulse of transducers 50 and 51 travels not only through the fluid 
in the conduit 20, but also travels longitudinally along the pipe wall. 
The transit time for a pulse from transducer 50 to transducer 51, for 
example, is short compared to the time taken for energy to traverse 
through the fluid and, therefore, should not interfere with the 
measurement of the sonic energy which arrives later through the fluid. 
Nevertheless, as a practical matter, the energy transmitted through the 
pipe wall has a relatively long "ring-down" or oscillation time, so some 
directly transmitted sonic energy will be received by the receiving 
transducer at the same time the energy through the fluid is received by 
that same transducer. This has an adverse effect on the signal-to-noise 
ratio of the system. 
In accordance with the present invention, block 100 is fixed to the pipe 20 
and is arranged to accept sonic energy directly transmitted down the wall 
of pipe 20. Block 100 extends longitudinally along the pipe wall and is 
between transducers 50 and 51. Preferably, the block 100 has a similar 
height and width as transducers 50 and 51, for compatability with the 
track 30. It is mounted to and within the track 30 by an appropriate clamp 
101 and mounting screw 102 so that the block 100 is firmly connected to 
the exterior surface of pipe 20. The block 100 is preferably made of the 
same material as the transducers. A suitable coupling compound may be 
placed between the bottom surface of block 100 and the pipe wall 20. 
Block 100 is provided with appropriate means to attenuate and scatter sonic 
energy once it enters the block 100 from the pipe wall 20 and to prevent 
its reflection back into the pipe 20. By way of example, as shown in 
detail in FIG. 15, the block 100 may have holes or cavities 103 filled 
with suitable metal (e.g., tungsten) or plastic powder particles, 
suspended in any suitable highly viscous liquid compound, which serve as 
scattering centers for sound energy received into the block 100. Metal 
content, for example, will assist in matching the sonic impedance of the 
block 100 to that of the viscous compound and the pipe. The particles in 
the cavity raise the sonic impedance and increase the sonic path length 
within the cavity so that the viscous bonds of the liquid material in the 
cavity can convert the sonic energy to heat. 
As illustrated, the cavities 103 advantageously have different sizes and 
are rounded in shape. They may be formed by drilling or otherwise forming 
holes into the block 100 from one side. They may be formed in other ways 
as well. They preferably are not close to the top side 101a, but rather 
are spaced therefrom by at least approximately one-half to one-third of 
their diameters. 
In its longitudinal dimension, the block 100 should not contact either of 
transducer bodies 50 or 51 and a gap should exist between the side edges 
of block 100 and the transducers. The gap dimension is not critical. 
It has been found that the block 100 can improve the signal-to-noise ratio 
by two to four times. It will be understood that the novel sound-absorbing 
block 100 of FIGS. 14 and 15 can be employed in any desired arrangement in 
which spaced transducers communicate with one another within or on or 
along the surface of a pipe in either a longitudinal or peripheral 
direction and wherein it is desired to remove or reduce the effect of 
direct communication of the transducers through the pipe wall. 
FIG. 10 discloses a further embodiment of the invention wherein a viscous 
body 110 is shown as enclosing and contacting the outer surface of conduit 
20 in the region between transducers 80 and 85 of FIG. 12. It has been 
found that body 110 will cause substantial damping of the sonic energy 
which may pass through the pipe wall and between transducers 80 and 85 in 
the direct mode of operation. Body 110 can, for example, consist of a 
layer of duct tape applied on any or all exposed portions of the conduit 
20 which may include the entire length of the tracks. Signal-to-noise 
improvements of 5 to 1 have been obtained with such viscous body damping. 
Although the present invention has been described in relation to particular 
embodiments thereof, many other variations and modifications and other 
uses will become apparent to those skilled in the art. It is preferred, 
therefore, that the present invention be limited not by the specific 
disclosure herein, but only by the appended claims.