Sensing device

A sensing device for detecting a substance including hydrocarbons on the surface of water provides a floatation device for floating on the water surface and for supporting at least one sensing element for detecting said substance, the floatation device being composed substantially of nitrile. A sensing device for use in an apparatus for detecting a substance on the surface of a liquid, the sensing device providing a mounting surface adapted for facing downwardly toward the liquid surface, a plurality of sensing elements each of which is mounted at a different predetermined distance below the mounting surface, and a flotation portion affixed to the mounting surface for supporting the mounting surface at the liquid surface whereby the sensing elements may be maintained at different known depths below the liquid surface.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention generally relates to sensing devices employing 
floatation means for supporting a sensing element near the surface of a 
liquid and, in particular, to such devices as used for detecting 
hydrocarbon substances on the surface of ground water. 
2. Statement of the Prior Art 
Wide spread use of fossil fuels in today's world has caused many problems 
with the pollution of ground water and drinking water supplies by leakage 
of such fuels and various hydrocarbon containing substances into the 
ground water. To help detect this problem, sensors have been developed for 
detecting the presence of such substances on the surface of ground water. 
One such sensing device is described in U.S. Pat. No. 4,221,125 which 
employs a semiconductor diode positioned in proximity to the surface of a 
body of water by a float means for detecting the presence of hydrocarbon 
substances. A related device is described in U.S. Pat. No. 4,223,552. It 
has been found, however, that additional information is also desirable 
such as knowing the amount of hydrocarbons present on the surface of 
ground water and either the rate of increase or decrease of the 
hydrocarbon substances present. Problems, however, have been encountered 
in the reliability of long term sensing devices due to the corrosion of 
the floatation means caused by various chemical substances present in the 
ground water and the subsequent dislocation of the sensing element 
supported thereby in respect to the water's surface. 
SUMMARY OF THE INVENTION 
Accordingly, an improved sensing device has been developed which insures 
the reliability of the floatation means in the presence of various 
corrosive substances and further allows information to be generated with 
respect to the amount of hydrocarbon substances present on the surface of 
a liquid. The present invention generally includes a sensing device for 
detecting a substance including hydrocarbons on the surface of water, 
comprising a floatation means for floating on the water and for supporting 
at least one sensing element for detecting the substance, the floatation 
means being composed substantially of nitrile. The present invention 
further includes a sensing device for detecting a substance on the surface 
of a liquid comprising, a mounting surface adapted for facing downwardly 
toward the liquid surface, a plurality of sensing elements each of which 
is mounted at a different predetermined distance below the mounting 
surface, and floatation means affixed to the mounting surface for 
supporting the mounting surface at the liquid surface whereby the sensing 
elements may be maintained at different known depths below the liquid 
surface.

DETAILED DESCRIPTION OF THE DRAWINGS 
In respect to FIGS. 1, 2 and 3, member 10 of a sensing device is shown with 
bottom, top and side views, respectively. The member 10 generally includes 
a mounting surface 12, a floatation means 14, and a top surface 16. The 
downwardly facing mounting surface 12 includes a plurality of apertures 18 
in which sensing elements may be mounted. The apertures 18 are arranged in 
pairs to allow use of dual leaded sensing elements. The sensing elements 
20, 22, 24 and 26 are shown in FIG. 3 extending from the apertures 18 to 
various distances from the downwardly facing surface 12. The sensing 
elements 20, 22, 24 and 26 are dual leaded semiconductor junction devices 
or diodes. The upper ends of the apertures 18 are shown extending to the 
upper surface 16 in FIG. 2. 
The floatation means 14 extends downwardly from the mounting surface 12 and 
is intended to exhibit a positive bouyancy in whatever medium is chosen 
for the sensor to operate. The size of the floatation means 14 is designed 
to cause the mounting surface 12 to be located at the surface of the 
liquid in which the device is operating. By these means, the sensing 
elements, which are located at predetermined distances from mounting 
surface 12, are held at known distances below the liquid surface. This 
allows accurate measurements to be taken of the depth of the substances 
located on top of the liquid medium. 
The entire sensing device member 10 including the floatation means 14 and 
an upper section 26 forming the mounting surface 12 and the upper surface 
16 is made from a closed cell foamed neoprene rubber generically known as 
nitrile and available under the tradename NITROPHYL from Rogers 
Corporation of Willimantic, Conn. The material nitrile is useful in the 
applications of the present invention because it exhibits resistance to 
chemical decomposition when exposed to a variety of substances including 
hydrocarbons. Thus, when used to detect the presence of hydrocarbons on 
the surface of ground water, the nitrile does not decompose when exposed 
to either ground minerals or the hydrocarbon substances. 
The top surface 16 is used for connecting the sensing elements 20, 22, 24 
and 26 to an electrical cable for eventual connection to a sensing or 
measurement instrument (not shown). The top view of the sensing device 
member 10 shows a plurality of printed circuit lands deposited on the top 
surface 16, which lands 28 each has one end thereof located in proximity 
to each of the apertures 18. These ends are so located to allow connection 
of the sensing elements thereto by such means as soldering. The lands 28 
each have another end 30, all of which are proximally located to allow 
connection thereof to a multiconductor cable. The lands 29 are directly 
deposited on the surface of the nitrile to avoid the use of a separate 
printed circuit board in addition to the construction of the member 10. 
The process by which the printed circuit lands are so formed on the 
surface of nitrile is covered by one or more of U.S. Pat. Nos. 3,956,041; 
4,160,050; 4,144,118, which patents are assigned to the Kollmorgen 
Corporation. The application of the printed circuit lands 28 to the 
nitrile was performed for the present embodiment by PCK Technology of Glen 
Cove, N.Y. 
As shown in FIGS. 1 and 2, a central aperture 32 is located through the 
middle of the member 10 for allowing slidable mounting of the member 10 on 
a vertical member facilitating the ability of the member 10 to follow the 
level of the liquid or water being monitored. 
FIG. 4 shows the sensing device 10 having an electrical conductor in the 
form of a ribbon cable 33 connected to the lands 28. The cable 33 used for 
the present embodiment is available from Amp Incorporated under part No. 
5107-1202-2. The cable includes eight separate conductors 34 located along 
the edges of the cable 33 in pairs of four. Each of the conductors 34 has 
a terminal 35 connected to the end thereof which terminals 35 are soldered 
to the separate lands 28 at their ends 30. The cable 33 is modified by the 
inclusion of a series of holes 36 located approximately midway between the 
folds of the cable. In the present embodiment, a guide cable (not shown) 
passes through the holes 36. During construction, the cable is initially 
held to the top surface of the device 10 by means of a strain relief bar 
37 which is secured by a pair of screws 38 to the top surface 16 of the 
device 10. FIG. 4 further shows a guide pipe means 39 which is secured 
within the aperture 32 of FIG. 2. In operation, a guide cable is located 
through the holes 36 and the guide pipe 39 to stabilize the sensing device 
from lateral movement but to allow vertical movement in accordance with 
changes in water level. 
FIG. 5 shows the sensing device 10 as assembled in FIG. 4 and further 
including an expoxy resin sealant 40 located over the top of surface 16. 
During construction of the device 10, a peripheral ridge 41 located around 
the surface 16 helps to confine the liquid epoxy mixture prior to its 
setting. Any suitable epoxy mixture may be used for the sealant covering 
40. One such mixture is described below in reference to FIG. 7. 
FIGS. 6 and 7 show partially sectional views of the sensing device member 
10 having a plurality of sensing elements 22, 24 and 26 mounted thereon. 
The sections are taken along view lines 6--6 of FIG. 2 and show two 
different means for mounting the sensing element 26, either of which means 
may be used for the other elements 20, 22 and 24. In FIG. 6, the apertures 
18 are shown as being plated through from the upper surface 16 to the 
lower mounting surface 12. By this means, the sensing element 26 is 
mounted to the member 10 and electrically connected by the soldering of 
its leads 42 at the points 43 which points are the lower extremities of 
the plated through apertures 18. The plating on the inside of apertures 18 
is made as a part of the lands 28 located on the upper surface 16 and thus 
no further coupling is needed thereto. In FIG. 7, the apertures 18 are not 
plated through and thus the leads 42 must extend all the way therethrough 
in order to be connected to the lands 28. This connection may be made by 
any means such as soldering. In the case of sensing elements such as 26 
which extend to some distance below the mounting surface 12, the leads 42 
thereof must be extended. In this case, the extension is formed by a pair 
of electrical leads 44 which are butt-welded at their ends to the ends of 
leads 42. The leads 44 are made of nickel for their low thermal 
conductivity characteristics. 
The sensing elements 22, 24 and 26 are shown encased in electrical 
insulation 46. The insulation shown is commonly known as shrink tubing and 
is available from Amp Incorporated under part No. 603342-1. The tubing 
used is clear in color and has a minimized thickness to reduce 
desensitizing effects on the sensing elements. In the present embodiment, 
tubing having a thickness of 0.015 inches (0.38 millimeters) or less is 
used. the ends of the tubing extend into a pair of recesses 48 located in 
the bottom mounting surface 12 and are sealed thereto by an epoxy sealant 
contained within said recesses 48. Any suitable epoxy resin will suffice 
and the material used for the present embodiment is Isochem 401 NV clear 
with an aliphatic amine curing agent, Isochem 9/22 hardner, with a 
Thermoset 50Z black coloring in the ratio of 75%-22%-3%, respectively. 
These are available from Isochem Resins, Inc., of Lincoln, R.I. Thus 
mounted, the sensing element or diode is very well insulated from the 
environment in which it is located. Because the sensing device depends 
upon measurement of the current flowing through the various elements or 
diodes, it is important that leakage current between the leads 42 and 44 
not be allowed to flow. Such leakage current would usually be caused by 
substances located in the liquid being monitored such as ground water 
minerals and the like. The combination of the shrink tubing surrounding 
the diode and the sealing of the ends thereof to the float or member 10 
electrically isolate the diode from the liquid being monitored and thus 
block any such leakage current. 
Thus, the present invention provides a means for increasing the amount and 
reliability of information derived from the sensing device. The mounting 
surface located at the liquid or water surface allows for easy 
construction of a sensing device having sensing elements which will be 
located at various depths below the liquid surface and thus be capable of 
measuring both the thickness of the hydrocarbons substances present and 
their rate of increase or decrease. The use of nitrile for the floatation 
means of the sensing device provides a stable substance which will not be 
corroded by various substances present in ground water supplies including 
hydrocarbon containing substances. This enables the sensing device to 
operate over extended periods of time which may include a constant 
monitoring of hydrocarbon substances present for that entire period. The 
resistivity of the nitrile material to various corrosive substances 
insures the location of the sensing elements at the proper liquid depth 
over the extended periods of time. 
The present invention relates in subject matter to two copending patent 
applications for "SENSING DEVICE" by Ralph A. Perry and Raymond J. 
Andrejasich Ser. No. 197,555, and "SENSING DEVICE" By Ralph A. Perry and 
James M. Booe, Ser. No. 198,005 both filed Oct. 17, 1980. The disclosures 
of these copending applications are hereby incorporated by reference 
herein. 
The description of the embodiments of the present invention contained 
herein are intended to be taken in an illustratively and not in a limiting 
sense. Various modifications and changes may be made to the embodiments 
described herewith without departing from the scope of the present 
invention as defined by the appended claims.