Precipitation detector and mechanism for stopping and restarting machinery at initiation and cessation of rai

Long, H. R.

Menges, M. J.

Mugler, S. W.

English

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Inventors 
Appl. No. 
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ee nted 
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I561 
2,904,995 9/1959 Obermaier ................... 340/235UX 
ENTS 
: A precipitation detector and mechanism used to 
shut down a load during precipitation and activate a load upon 
completion of precipitation. The detector has thermistors in a 
bridge circuit. One of the thermistors is exposed to the 
elements and cooled upon being contacted with precipitation. 
This causes an imbalance in the bridge circuit the output of 
which actuates a relay that shuts down the load. Termination 
of precipitation allows the thermistor to warm up balancing 
the bridge circuit and the relay closes activating the load. 
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. ."* INVENTORS , "*" '* 
1 
Origin of invention 
"he invention d e s c d M  Rerein was made by employees of 
the US. Government and may be manufactured and used by 
or for thc Government for governmental purposes without the 
payment of my roydties thereon or therefor. 
This invention relates to a precipitation detector, and more 
particularly to a mechanism which vrill energize or deenergize 
a load depending on precipitation. 
%P is sometimes necessary to expose various materials to the 
atmospheric elements. One such arrangement is where test 
specimens of, for example, aircraft skin structure is fatigue 
tested over a period of many months. Although it is sometimes 
desirable to test the specimens under all atmospheric 
conditions, it is also often desirable to test certain of the 
specimens only during p e r i d s  when there is no precipitation. 
En the past, the technique for energizing or deenerguing a 
machine for cyclically loading the test specimens under 
setected weather conditions was a manual switch. Since it is 
impossible to always predict when theee will b precipitation, 
it was necessary to maintain workmen around the clock to 
enable closing down the machine should it start raining, and to 
again activate the machine when it stopped raining. 
TsAeeefore, it can be seen that it would be highly desirable to 
have a detector which is operative upon the falling of precip- 
itation, to deenepgiare the loadling machine. ami &er precip- 
itation has cerased, energize the machine to continue the 
fatigue testing. The present invention provides a detector 
which will automatically accomplish energition and 
l d m g  machine Bepending on 
it is, therefore, an object of this invention to provide a 
shut down a load upon falling of 
upon the cessation of precip- 
A further object ofthe invention is to provide the utilization 
a relay 
ing on 
Another objecF of the invention is to provide a precipitation 
of heat-sensing elements in aa bridge circuit to 
system to energize and deenergize a load 
atmospheric conditions. 
detector which is extremely simple in design, has 
number of moving parts, is highly reliable, and is 
be exposed to &e atmospbric elements over ton 
time rendering trouble-free opedon. 
These and other objects and advantages of the invention 
will become more apparent upon reading the specification in 
conjunction with the accompanying drawings. 
In the drawings: 
FIG. B is a side etevational view of the precipitation 
detector; and 
FIG. 2 is a schemtlc d the precipitaFion d e b t o r  bridge 
circuit shown in coRjua&on with the relay and load. 
Referring m w  more specifidly to &e details of the 
invention, FIG. P illustrates the precipitation detector, 
designated generally by the reference numeral 88. The 
detector 1@ has a M y  12 which is made of some g o d  h a t -  
conducting m t e f i d  such as dminum. lt b? not required that 
the body 11 have any particular shape; however, the top 
surface of the W y  is of a h t w o n i c P  shape providing a 
surface which will shed precipitation, md also a flattened area 
to p i t i o n  the them0 dementi go be e x p i s i d  more &ally 
heminafter. An aperture or hob 13 is 
f o d  in tke side d &e M y  12, a d  is 
heitper elemen 
md is a b m  as eaw electrid heating 
dot 39 is formed in mother side of the 
s w  &e d e t a t m  may be 
machiwe or some other 
* * 
Of a 
~~~~~ OYa top d Ck@%&X 83 & 8WChkIll 
r. This mechru'.sm includes an 
upper outside plate 15 and upper inside plate 1 
5 seen in FIG. 1, the temperature-sensitive element is also 
centered with respect to the plates 15 and 16 and the body 92. 
The upper outside plate 89 is exposed, and will be directly 
subjected to atmospheric conditions such as rain or snow. The 
plates 15 and $45 should be made of some type of heat- 
lo  conductive material, and also of a material which will 
withstand corrosion. The particular material chosen for the 
device constructed was brass, however, it should be 
understood that other suitable materials might be utilized. 
A similar mechanism is mounted on the bottom surface of 
l5  the body I 2  directly opposite the previously described 
mechanism. outside plate 22, a 
lower inside which connect the 
, the insulating material being positioned about the 
ry of the mechanism. Sandwiched between the plates 
the 
20 
25 described. 
uit is designated gen 
is shown schemati 
d 32 are positioned in opposing legs of the 
circuit, and a variable resistor 
30 positioned in the other legs of the bridge circuit. These 
elements are electrically wired in the form of the conventional 
bridge circuit. The bridge circuit is powered in a conventional 
manner with an AC input connected to the points 35 and 36 in 
en from points 37 
combined power 
red to a no 
tion of a lo 
peration of 
35 
40 
OPERATION 
aving set forth the structure of the invention, the 
the device should now become apparent. The 
mounted on a load, the operation of which is 
on the absence of precipitation. The detector 
may be mounted with the aid of the mounting slot 99, and 
31 and 32 will remain the same, enabling the circuit to remain 
balanced. However, if precipitation falls and strikes the plate 
P5, the plate 15 will be cooled thereby dissipating heat from 
60 the thermistor 41 causing it to cool. This will result in an 
circuit resulting in an output at the 
is conveyed to the amplifier 39. The 
the s i p 4  which operates the relay 40 
opening a circuit YO the load shutting it off. As long as precip- 
65 itation continues, the thermistor 31 will remain cool keeping 
the bridge circuit out of balance, maintabing operation of the 
amplifier, and the relay open. Th 
itation fab, the load is shut down. 
the thermistor 31 will again warm up to the temperature of the 
70 thermistor 32 resulting in the circuit again being balanced. 
mere is then no output from the circuit, and the nonnally 
closed relay will close again %ccpivating Fhe load. 
'kRe sensitivity of the detector can be varied in any 
conventional mamner such as by increasing or decreasing the 
75 resistance to the AC input, or increasing or decreasing the 
resistance in the bridge Under certain tests 
conditions, it may be des down the load only 
when there is heavy rain or smw. On the other hand, it may be 
desirable to shut down the load when there is a heavy dew, the 
sensitivity adjustment enables this flexibility. If it is desired to 
have the detector extremely sensitive, it may be desirable to 
house the mechanism on the lower surface of the detector to 
maintain a more constant temperature of the thermistor 32 
and to protect it entirely from the atmospheric elements. The 
sensitivity of the detector may also be affected by the 
temperature to which the body 12 is heated by the heating 
element 14, and in turn the heal to which the thermistors are 
heated. If the thermistors are maintained at  a temperature 
which is little higher than ambient, the precipitation probably 
will not have as quick an effect on the detector as if the 
temperatures of the thermistors are maintained at several 
degrees a b v e  ambient. Although the invention has been 
described as one wherein the load is shut down when there is 
rain or some other form of precipitation, it should be 
understood that the device would work equally well to 
energize a load when there is precipitation and shut it down 
when there is no precipitation. This could be accomplished 
very simply by merely changing the relay to a normally open 
relay, and having it clme upon precipitation thereby activating 
the load. 
From the a b v e  description of the invention, it can be seen 
that a detector is provided which will effectively control the 
operation of a load dependent upon precipitation or the lack 
of it. Such control is automatic, eliminating the necessity of 
constant attention to equipment by a workman. The device 
has few parts requiring little maintenance, thus assuring long 
and reliable operation. 
5 I. A precipitation detector and mechanism actuator 
comprising: bridge circuit means; first thermistor means 
connected in said bridge circuit exposed to precipitation and 
being located between a first pair of heatconductive plates; a 
heat-conductive body; at least one of said first heat- 
10 conductive plates being secured to the upper surface of said 
body; a second thermistor means connected .in said bridge 
circuit means and being protected from precipitation k i n g  
located between a second pair of heat-conductive plates; at 
least one of said heat-conductive plates being secured to the 
l 5  lower surface of said heat-conductive body, means for heating 
said heat-conductive body and plates, and thereby heating 
said thermistors to a temperature above ambient temperature; 
and relay means operable by unbalance of said bridge circuit 
2o means due to precipitation cooling said first thermistor means 
whereby operation of a device is terminated during precip- 
itation. 
. A precipitation detector and mechanism actuator as in 
claim 1 wherein said pairs of first and second heat-conductive 
25 plates are substantially larger than said first and second 
thermistors; and insulation means positioned between said 
pairs of first and second heat-conductive plates and 
surrounding said thermistors. 
We claim: 
30 
35 
40 
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50 
60 
65 
70 
75 


Precipitation detector Patent

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