Ultrasonic sensor mounting device

A device for mounting an ultrasonic transducer on user equipment for operation in a contaminating, ambient environment. A housing has a forwardly extending, profiled inner surface for promoting focusing along an axis of ultrasonic waves emitted by a transducer mounted against a shoulder of the casing. A chamber adjacent to a backside of the transducer is formed by a rearwardly extending portion of the casing and a cap forming an overlap portion therewith. A bladder disposed in the chamber has a port which vents into the overlap portion such that pressure equalization across the transducer is dynamically maintained. A calibrator offset by known displacement from the transducer provides a reflected wave portion to the transducer such that errors caused by temperature dependency of the velocity of propagation of the ultrasonic waves through the ambient environment can be substantially eliminated.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a device for mounting an ultrasonic sensor 
on equipment for use in a harsh environment and particularly for mounting 
an ultrasonic transducer on asphalt paving equipment for ranging and 
control applications. 
2. Description of the Related Art 
Ultrasonic transducers and sensors have been utilized for a variety of 
applications, including ranging applications for controlling quantity of 
asphalt aggregate in an augered hopper and thickness control of asphalt 
being laid on a road bed, and other widely differing applications. 
Unfortunately, several drawbacks exist for use of ultrasonic transducers 
in the largely uncontrolled, ambient environment in which many of the 
transducers are used. 
For example, an ultrasonic transducer used for ranging in asphalt paving 
applications is subjected to repeated heating and cooling cycles, due to 
the nature of those particular applications. As a result of such repeated 
heating and cooling cycles, moisture from the ambient atmosphere tends to 
condense and collect on the back side of the transducer. Over time, 
sufficient moisture and contamination resulting therefrom have collected 
on the back side of the transducer such that the performance of the 
transducer becomes erratic, usually followed by total failure thereof. 
This problem is particularly pronounced during periods of high humidity, 
such as during rains storms. 
It would appear that this problem could be overcome by hermetically sealing 
the back side of the transducer, thus isolating it from the moisture and 
contaminants of the ambient atmosphere. Such an approach, however, 
introduces a new problem. As the temperature of the gaseous medium trapped 
within the hermetically sealed enclosure changes, the medium attempts to 
expand or contract accordingly, due to the inherent thermal expansion 
characteristics of the medium. As a result, the pressure on the back side 
of the transducer within the hermetically sealed enclosure differs from 
the pressure on the opposing side or emitting face of the transducer. 
Unfortunately, the accuracy and efficiency of the transducer is dependent 
upon the maintenance of minimal or zero differential pressures between the 
face and back side thereof. In turn, the solution to this pressure 
differential problem would appear to be solvable by venting the back side 
of the transducer to the ambient atmosphere, which goes full circle to the 
problems hereinbefore described. 
Various approaches have been utilized in an attempt to alleviate the 
aforementioned problems, such as by venting through a signal cable 
connected to the transducer or other circuitous routing, desiccants, and 
the like. Unfortunately, these prior attempts have met with only limited 
or no success. 
Another potential problem which exists during use of ultrasonic transducer 
arises from the temperature dependency of the velocity of propagation of 
the ultrasonic waves through the ambient atmosphere. This problem 
particularly exists for the elevated temperatures normally involved in 
asphalt paving applications. In addition, for asphalt paving applications, 
the temperature of the atmosphere through which the waves traverse is 
constantly changing, particularly when a breeze or gusty wind is present. 
One approach for reducing the inaccuracies generated by the elevated 
temperatures is to impose a minor obstruction of known distance from the 
transducer which reflects a calibrating signal or echo. The transit time 
of ultrasonic waves associated with the calibrating echo can be compared 
with the transit time of ultrasonic waves reflected from a target surface. 
Assuming the temperature characteristics for each of the paths for the 
waves generating the calibrating signal and target signal are identical, 
then the temperature dependency of the velocity of propagation of the 
ultrasonic waves along their respective paths can conceivably be 
eliminated. Many such applications using this approach, however, space the 
minor obstruction within a somewhat protected enclosure, such as within a 
sleeve extending forwardly from the emitting face of the transducer. Such 
an arrangement generally prevents the temperature characteristics of the 
path of the ultrasonic waves generating the calibrating signal from 
matching those of the path of the ultrasonic waves generating the target 
signal, particularly during breezy or gusty conditions. 
What is needed is a mounting device which protects an ultrasonic sensor or 
transducer from moisture and contaminants without causing a pressure 
differential thereacross and which substantially or entirely eliminates 
temperature dependency of the velocity of propagation of the ultrasonic 
waves, including uses in breezy or gusty conditions. 
SUMMARY OF THE INVENTION 
An improved mounting device is provided for mounting an ultrasonic sensor 
or transducer on user equipment for operation in an ambient environment 
containing moisture or other contaminants. The mounting device includes a 
transducer having a face for emitting and receiving ultrasonic waves and a 
housing for mounting the transducer therein. The housing includes a casing 
having a front end and a rear end disposed about a longitudinal axis. A 
shoulder, disposed intermediately between the front and rear ends and 
generally transversely to the longitudinal axis, is adapted to bear 
against a rim of the transducer as the transducer is mounted in the 
casing. The casing has an inner surface extending from near the shoulder 
to the front end, with the inner surface having a shaped profile about the 
axis in order to promote focusing of the ultrasonic waves along the 
longitudinal axis. 
The housing also includes a cap which is adapted to provide an overlap 
portion between the cap and the casing, such that a chamber is provided 
adjacent to the backside of the transducer. The cap is dimensioned such 
that air can pass through the overlap portion between the cap and the 
casing, but such that dust and other contaminants cannot pass 
therebetween. The cap is constructed of a material having a thermal 
coefficient of expansion substantially similar to that of the casing. The 
casing also has an orifice which is adapted to communicate between the 
overlap portion and the chamber. 
A spacer is provided which simultaneously bears against the transducer and 
the cap as the transducer bears against the shoulder of the casing. A 
first or device gasket is spaced between the transducer and the shoulder 
such that an environmentally-tight, impervious seal is provided between 
the transducer and the shoulder. Similarly, a second or cap gasket is 
spaced between the cap and the casing such that an environmentally-tight, 
impervious seal is provided between the cap and the casing. 
The ultrasonic sensor mounting device includes a bladder disposed within 
the chamber. The bladder has an input port spaced within the orifice with 
the input port opening into the overlap portion. A plug disposed in the 
input port is adapted to provide an impervious seal between the bladder 
and the orifice. The plug is porous such that air can freely pass between 
the bladder and the overlap portion, thereby minimizing or eliminating a 
tendency for differential pressure to be formed across the transducer. 
A calibrator is spaced a desired distance from the face of the transducer 
and exteriorly to the casing such that a reflected portion of the 
ultrasonic waves emitted by the transducer are echoed back to the 
transducer in addition to those reflected by a target surface. 
OBJECTS AND ADVANTAGES OF THE INVENTION 
Therefore, the principal objects and advantages of the present invention 
include: providing a mounting device for an ultrasonic sensor o transducer 
that prevents moisture from condensing on the transducer; providing such a 
mounting device that minimizes or eliminates differential pressures across 
the transducer; providing such a mounting device with a bladder adapted to 
minimize or eliminate pressure differential across the transducer; 
providing such a mounting device wherein such a bladder is protected from 
damage due to handling; providing such a mounting device with a calibrator 
for dynamically eliminating errors caused by temperature dependency of the 
velocity of propagation of the ultrasonic waves through the ambient 
atmosphere; providing such a mounting device which is particularly 
applicable to asphalt paving applications, including those conducted in 
breezy or gusty conditions; and generally providing such a mounting device 
which is efficient and reliable, economical to manufacture, simple to 
maintain, and which generally performs the requirements of its intended 
purposes. 
Other objects and advantages of this invention will become apparent from 
the following description taken in conjunction with the accompanying 
drawings wherein are set forth, by way of illustration and example, 
certain embodiments of this invention. 
The drawings constitute a part of this specification and include exemplary 
embodiments of the present invention and illustrate various objects and 
features thereof.

DETAILED DESCRIPTION OF THE INVENTION 
As required, detailed embodiments of the present invention are disclosed 
herein; however, it is to be understood that the disclosed embodiments are 
merely exemplary of the invention, which may be embodied in various forms. 
Therefore, specific structural and functional details disclosed herein are 
not to be interpreted as limiting, but merely as a basis for the claims 
and as a representative basis for teaching one skilled in the art to 
variously employ the present invention in virtually any appropriately 
detailed structure. 
The reference numeral 1 generally refers to an ultrasonic sensor mounting 
device in accordance with the present invention, as shown in FIGS. 1 
through 4. The device 1 includes mounting means 2 including a housing 3 
for mounting an ultrasonic sensor or transducer 5, focusing means 7, 
protecting means 9 for protecting the transducer 5, pressure equalizing 
mean 11 for dynamically equalizing differential pressures across the 
transducer 5, and calibrating means 13 for dynamically eliminating errors 
caused by temperature dependency of the velocity of propagation of 
ultrasonic waves 15 emitted and received by the transducer 5. 
The housing 3 generally includes a casing 21, having a front end 23 and a 
rear end 25. Generally, the casing 21 has a cross-sectional profile which 
is shaped similarly to that of the transducer 5. Thus, for a circularly 
shaped transducer 5, the casing 21 is generally cylindrically shaped about 
an axis A--A, as shown in FIG. 3. The casing 21 generally has a shoulder 
27, which is disposed intermediately between the front end 23 and the rear 
end 25 and which is oriented transversely to the axis A--A. The shoulder 
27 is adapted to bear against a rim 29 of the transducer 5 as the 
transducer 5 is mounted in the casing 21 as described herein. 
The focusing means 7 generally comprise extending the casing 21 forwardly 
from the shoulder 27, as shown in cross-section in FIG. 3, such that an 
inner surface 35 is generally provided from near the shoulder 27 to the 
front end 23. The inner surface 35 is generally profiled with a 
configuration which promotes focussing of the ultrasonic waves 15 emitted 
by the transducer 5 along the axis A--A, such as a parabolic, exponential, 
or other suitable configuration. 
In addition to the extension of the casing 21 forwardly from the transducer 
5 and in order to distance the transducer 5 from possible physical damage 
to the transducer 5, the protecting means 9 also generally includes 
extending the casing 21 rearwardly from the shoulder 27, as shown in 
cross-section in FIG. 3. Further, the protecting means 9 generally 
includes a cap 37 as hereinafter described for protecting a backside 39 of 
the transducer 5 from adverse elements of the environment. 
The cap 37 is adapted to be telescoped over the rear end 25 of the casing 
21 such that an overlap portion 41 is provided between the cap 37 and the 
casing 21. Thus, a chamber 47 is provided adjacent to the backside 39 of 
the transducer 5. The spacing between the casing 21 and the cap 37 at the 
overlap portion 41 is dimensioned such that air can pass between the 
casing 21 and the cap 37, but such that dust cannot pass therebetween. The 
cap 37 is generally constructed of a material having a thermal coefficient 
of expansion substantially similar to that of the material of the casing 
21. For example, both the cap 37 and the casing 21 may be constructed of 
aluminum or other suitable material. The casing 21 also incudes an orifice 
49 which is adapted to provide communication between the overlap portion 
41 and the chamber 47. 
A spacer 51 is adapted to simultaneously bear against both the backside 39 
of the transducer 5 and the cap 37 as the transducer 5 bears against the 
shoulder 27. A device gasket 57 is generally disposed between the 
transducer 5 and the shoulder 27 to provide a continuous seal 
therebetween. Similarly, a cap gasket 59 is generally disposed between the 
cap 37 and the casing 21 to provide a continuous seal therebetween. 
Fastening means, such as a plurality of machine screws 61, are adapted to 
connect the cap 37 to the casing 21 such that environmentally-tight or 
impervious seals are provided between the transducer 5 and the shoulder 27 
by the device gasket 57 and between the cap 37 and the casing 21 by the 
cap gasket 59 as the machine screws 61 are tightened, urging the cap 37 
against the spacer 51. 
The pressure equalization means 11 generally include a bladder 69 disposed 
within the chamber 47. The bladder 69, which is constructed of suitable 
flexible material, has an input port 71 spaced within the orifice 49. The 
input port 71 opens into the overlap portion 41 between the cap 37 and the 
casing 21. A plug 73 is disposed within the input port 71 such that an 
environmentally tight and impervious seal is provided between the bladder 
69 and the orifice 49. The plug 73 is porous, such that a cavity 75 of the 
bladder 69 communicates with the overlap portion 41. With the arrangement 
as described, the bladder 69 provides a means whereby the volume of air 
inside the chamber 47 can expand or contract as the temperature changes 
without causing a pressure differential across the transducer. 
A slot 77 is generally provided in the spacer 51 to facilitate placement of 
the input port 71 in the orifice 49. Also, the slot 77 may open toward the 
cap 37, as show in FIG. 3, or, alternatively, may open toward the 
transducer 5 to facilitate removal of the spacer 51. 
The calibrating means 13, such as a rod 81 oriented generally transversely 
relative to the axis A--A, is spaced such that the ultrasonic waves 15 
emitted by the transducer 5 impinge thereon and a reflected portion 83 of 
the longitudinal waves 15 emitted by the transducer 5 is echoed back to 
the transducer 5. For example, the rod 81 may have a 1/4 inch diameter and 
be spaced approximately 6-8 inches from the transducer 5. Note that the 
rod 81 can be spaced off-center from axis A--A if desired, as shown in 
FIG. 3. By spacing the calibrator 81 a known distance from the transducer 
5, any change in transit time due to change in the velocity of propagation 
of the ultrasonic waves 15 through the ambient environment, such as that 
resulting from temperature dependency, can be minimized or eliminated from 
the waves 84 reflected from a surface 85 which is the object of one of the 
applications of the invention 1. 
Conductors 86 interconnect the transducer 5 with a connector 87 for 
connecting the transducer 5 to sensor equipment 89, such as control and 
monitor equipment commonly available in the industry. It is to be 
understood that, alternatively, the connector 87 can be disposed on a side 
of the casing 21 to facilitate unhindered removal of the cap 37, or other 
suitable location, if desired. 
The mounting means 2 also include clamping means 91, which are provided to 
affix the device 1 to associated equipment 93, such as a paving machine or 
other application. 
In an application of the present invention, the sensor equipment 89 is 
activated such that the transducer 5 emits ultrasonic waves 15. The rod 81 
is offset from the transducer 5 such that the spacing between the rod 81 
and the front end 23 represents a substantial fraction of the spacing 
between the front end 23 and the target surface 85, such as a road bed 
beneath the paving machine 93 for controlling thickness of asphalt paving 
95 being laid therebeneath, or a surface 96 of asphalt aggregate 97 in a 
hopper 98 for volume control, or other application as desired. 
As a result of the spacing between the rod 81 and the front end 23, 
temperature variations along the paths from emission to reception of the 
reflected portion 83 are substantially similar to those experienced by a 
target portion 84 of the ultrasonic waves 15 which are reflected by the 
target surface 85 even under breezy or gusty conditions. Thus, by causing 
the transducer 5 to emit a square-type transmission and comparing the 
transit time from emission to reception of the reflected portion 83 with 
the transit time from emission to reception of the target portion 84, the 
temperature dependency of the velocity of propagation of the ultrasonic 
waves 15 through the ambient environment can be substantially minimized or 
entirely eliminated, thus providing enhanced accuracy by use of the device 
1 for ranging purposes. 
It is to be understood that while certain forms of the present invention 
have been illustrated and described herein, it is not to be limited to the 
specific forms or arrangement of parts described and shown.