Rain gauge with clogging detection device

A rain gauge having a collecting funnel and a discharged nozzle is provided with a detector for detecting the abstraction of a filter at the input of the nozzle. The detector comprises a light source disposed on an upper portion of said funnel and illuminating the bottom of the funnel above the filter. A sensor located outside of the funnel and nozzle, detects light which is reflected and diffused by the inner surface of the funnel and which passed through the filter and along the nozzle. The sensor is offset laterally with respect to the nozzle. An electronic box is connected to the source for causing the source to emit light pulses at regular time intervals and is connected to the sensor for detecting those output signals of the sensor which exceed a predetermined threshold.

BACKGROUND OF THE INVENTION 
The invention relates to rain gauges of the type comprising a stationary 
reception funnel, having at its lower part a water discharge nozzle at the 
input of which a filter is disposed. 
The rain gauges used practically universally by meteorological services are 
of the above defined type. The nozzle of the fixed reception funnel is 
placed above a receptacle arranged to rock on a support plate and having 
two symmetrical compartments alternatively receiving water flowing through 
the nozzle. The receptacle rocks about the horizontal edge on the plate 
when the amount of water contained in a compartment reaches a given value. 
This compartment then discharges its contents outside and the other 
compartment begins to receive any water which flows from the funnel. A 
switch, generally formed by a mercury bulb with contacts which is fixed to 
the receptacle indicates, by its open or closed state, the position of the 
receptacle. From the knowledge of the cross-sectional area of the input of 
the funnel and from the amount of water which causes the receptacle to 
rock, the amount of precipitation can be determined by counting the number 
of times the switch has operated and, by detecting the times of rocking 
with respect to data delivered by a clock, the distribution thereof in 
time. 
Many rain gauges are located in isolated stations and are only inspected at 
long intervals. Between two inspections, the filter, which is intended to 
retain the impurities while letting the rain water or the water from 
molten snow pass, may be progressively clogged by debris such as leaves, 
dust and insects. Such progressive clogging is not detected until the 
first inspection which follows it. Consequently, it is impossible to know 
how long the filter has been clogged and to determine how long the 
recorded has been doubtful. 
SUMMARY OF THE INVENTION 
An object of the invention is to provide a rain gauge comprising a detector 
for detecting the obstruction of the filter, before it is complete, so as 
to locate it in time and give an alarm; it is a more specific object to 
reach this result without hindering collection of water by the funnel or 
the flow thereof and in limiting disturbances of the detection device 
during precipitations. 
To this end, there is provided a rain gauge of the above defined type, 
comprising a device for detecting clogging of the filter having a light 
source disposed at the input of the funnel, placed so as to illuminate the 
bottom of the funnel above the filter, a sensor detecting light which is 
reflected and diffused by the bottom of the funnel and which passed 
through the filter and the nozzle, said sensor being placed below the 
nozzle and offset laterally with respect thereto; and electronic means 
connected to the source for causing the latter to emit light pulses at 
regular time intervals and for detecting these output signals of said 
sensor which exceed a predetermined threshold. 
With this arrangement, the detection device does not hinder collection and 
flow of the water; the sensor is not directly sprinkled with water which 
flows through the nozzle. Contrarily to what might be feared, the amount 
of light received by the sensor through the filter and the funnel, when 
the filter is not clogged, is sufficient to permit reliable operation of 
the sensor despite the losses due to reflection and diffusion. 
The reliability of the clogging detection device may be further increased 
by comparing the ratio between the number of output signals of the sensor 
which exceeding a threshold and the total number of light pulses emitted 
during a given time, one hour for example, and assuming the absence of 
clogging when the ratio exceeds a predetermined value, less than 1 and 
which may be determined experimentally. The use of such a criterion to a 
large extent overcomes the influence of the total reflections which are 
sometimes observed when rain water streams along the wall of the funnel 
and reduces the light intensity which reaches the sensor at a value less 
than the threshold. Practice has shown that in general the total reflexion 
phenomenon does not occur in more than 70% of the cases, i.e. for more 
than 70% of the time. 
The monitoring of correct operation obtained by using the invention on a 
rain gauge makes it possible to space out and often to suppress the 
periodic inspections and to replace them by on the spot checking carried 
out solely should an alarm be given. All the advantages which result 
therefrom are reached if the rain gauge may operate independently, without 
external electric supply, for a very long time, practically of the order 
of one year. To allow independent operation from a source formed by a 
commercial battery, for example an alkaline 4.5 V battery, the electric 
consumption of the electronic box must be low. This result is reached 
using a self-sufficient electronic box incorporating: a local electric 
supply; means causing the emission, by the source, of light pulses at time 
intervals determined by a time base; a receiver connected to the sensor 
comprising an amplifier and threshold detector means delivering an output 
signal when the energy received by the sensor exceeds the threshold; and 
means supplying the receiver from the source solely during predetermined 
time intervals, corresponding to the time durations of light emissions by 
the source. 
The invention will be better understood from the following description of a 
particular embodiment, given by way of example. The description refers to 
the accompanying drawings.

DETAILED DESCRIPTION OF THE EMBODIMENTS 
The rain gauge shown schematically in FIG. 1 has a generally known 
construction. It is of the type having a rocking receptacle 20 which is 
used practically universally in the present time. It comprises a fixed 
collecting funnel, with a vertical axis, having an upper receiving ring 10 
with sharp edges and a cone 12 having at its lower part a metal filter 14 
with fine meshes (1 to 2 mm in general). The funnel often has a rotational 
symmetry and its ring then has a diameter of a few tens of millimeters. 
The cone is extended by a nozzle 16 which opens above the horizontal 
oscillating edge 18 of a rocking receptacle 20. By rocking about the 
horizontal edge 18, the receptacle may take either the predetermined 
position in which it is shown in FIG. 1, or a position which is 
symmetrical with respect to a vertical plane passing through the edge. The 
receptacle rocks from one position to the other when the amount of water 
received by the compartment placed below the nozzle 16 has reached a given 
value. The filled compartment then spills its water content and the other 
compartment begins to receive any water flowing from the funnel. The 
receptacle 20 has a switch 21, actuated by rocking, generally formed by a 
bulb with mercury for closing contacts, which delivers information about 
the position of the receptacle or a pulse responsive to each rocking 
movement. Each rocking movement of the receptacle results from a given 
amount of precipitation. Counting the number of rocking occurrences and 
times, recorded by means 22 of known construction or transmitted to a 
central monitoring location by telecommunication means, make it possible 
to know the pluvometry at the station. 
The rain gauge shown in FIG. 1 is provided with a device according to a 
particular embodiment of the invention. The device comprises optical means 
designed so that clogging of the filter forms an optical barrier and an 
electronic box 24, with its own electric energy source, shown as a battery 
26. The only connection between the box and the outside is the delivered 
output information consisting binary values (0 to 1). 
The optical elements of the device comprise a light source 30 disposed at 
the input of the funnel and a sensor 32 placed below nozzle 16 and offset 
laterally with respect thereto, in a position such that it receives the 
light from the source, reflected and diffused by the bottom of the funnel, 
when the filter 14 is not clogged. 
Source 30 will generally be a high efficiency light emitting diode or LED, 
driven by shot current pulses of high intensity. For instance the LED may 
be of CQY 90D type sold by the firm RTC, delivering infrared radiation. 
Sensor 32 may then be a photodiode matched to the emission range of the 
LED, such as a photodiode BPW 50 from the firm RTC. 
The electronic box 24 embodies low consumption components so as to have a 
long independent life using a commercial 4.5 volt alkaline battery as a 
power source. It comprises a time base 34 capable, when fed from source 26 
by a manually controlled switch 36, to supply: 
rectangular pulses on an output B at relatively high rate (for example, as 
illustrated in FIG. 2, pulses of one second at the end of each minute), 
on an output D, pulses delayed with respect to the preceding pulses (for 
example one second pulses delayed by 0.5 second with respect to those 
which appear at output B), 
on an output G, rectangular pulses, at a much slower rate than the pulses 
appearing at output B (for example with a period of one hour). 
The advantage of having pulses appearing at the same rate, with a time 
offset, at outputs B and D will appear further on. 
The output D of time base 34 drives the triggering input of a pulse 
generator 38 which, in response to the leading edge of the pulse of the 
time base, emits n brief successive identical pulses, each of which has a 
duration which is much smaller (by several orders of magnitude) than that 
of the pulse appearing at output D. In practice, n will be between 4 and 
10. As shown in FIG. 2, a generator 38 delivering six pulses of 25 micro 
seconds each may possibly be used. The pulses, appearing at output E of 
the generator, drives source 30. 
The sensor 32 is connected to a receiver circuit which, in the case 
illustrated in FIG. 1, comprises an amplifier 40, a band-pass filter 42 
and a synchronous detector 44. 
To reduce the consumption of the electronic box, the receiver circuit is 
not continuously supplied with power. Its power supply inputs are 
connected to a regulated and controlled supply circuit 45 which only 
switches the receiver circuit on during the time when it is likely to 
receive pulses caused by output B of the time base. The time which 
separates the leading edges of the pulses appearing at outputs B and D of 
the time base is selected sufficiently large so that the receiver circuit 
is able to operate when it receives the signals delivered by sensor 32 
(FIG. 2). 
The synchronous detector 44 is designed to deliver, at its output F, a 
square wave of calibrated length (150 .mu.s at mid-height for example) 
when the mean level of the signal received by the sensor, after filtering 
and detection, exceeds a predetermined threshold. 
The output F of the reception circuit drives an accumulation counting 
circuit 46, which maintains on its output H a voltage indicating the 
absence of clogging during the whole time which separates two successive 
pulses appearing at the output G, when the number of pulses appearing at 
output F during the preceding time interval has exceeded a predetermined 
fraction of the total number of pulses expected. 
As illustrated in FIG. 3 for example, where the maximum number of pulses 
likely to appear at output F is 60 per hour, the output voltage of the 
counting and accumulation circuit 46 is kept at level 1 each time 16 
pulses at least have been received during the preceding hour: this 
condition is only fulfilled for the first and third period of one hour. 
The choice of a minimum ratio appreciably less than 1/2, such as 16/60, 
takes into account the possibility (in the case of rain, hale or snow), of 
a total reflection phenomenon due to water flowing along the edges of the 
reception funnel, or to a temporary obturation. 
The components of the circuit shown schematically in FIG. 1 may be as shown 
in FIGS. 4 to 6. 
In particular, the time base 34 may be as shown in FIG. 4 and comprise an 
oscillator 48 oscillating at a frequency of 1 Hz, followed by two cascaded 
dividers 50 and 52, respectively delivering frequencies of 0.1 and 0.01 
Hz. An initialization circuit 54 is provided for resetting the counters 
each time the circuit is switched on due to closure of switch 36. Each of 
the dividers comprises a monostable (one-shot) for obtaining an output 
square wave of one second at the end of each minute or each hour, at 
outputs B and G. A retarder 56 receives the pulses at 1 mn rate and 
generates at its output D pulses of one second, delayed by 0.5 seconds 
with respect to those delivered by divider 50. 
The components of the receiver circuit may be grouped together into a 
single integrated circuit. In the case illustrated in FIG. 6, the receiver 
comprises a circuit TDA 3047 forming amplifier, filter and synchronous 
detector. The reference signal required for synchronous detection may be 
delivered by the time base (not shown) or the generator 38. The filtering 
pass band is set by an inductance-capacity circuit tuned, for example, to 
38 KHz in the case envisaged above. 
Finally, the pulse generator 38 may have the general construction shown in 
FIG. 6, where the notations "reset", "CK", "carry out" and "clock enable" 
designate conventionally on such circuits, the reset input, the clock 
input, the overflow output and the clock enable input. The generator, 
delivering pulses at a frequency of 38 KHZ, comprises a set of four 
threshold comparators 60 driven by the output D of the time base 34, a 
decade counter 62 and an amplifier with two transistors 64 and 66 mounted 
in a Darlington circuit. 
Numerous modifications of the invention are possible, particularly insofar 
as the construction of the electronic box is concerned. It should be 
understood that the range of the present invention is not limited to the 
arrangements which have been shown by way of examples.