Note: Descriptions are shown in the official language in which they were submitted.
PHOTODOSIMETER
Background of the Invention
1. Field of the Invention
The present invention relates generally to
dosimeters and, more specifically, to an ultraviolet
dosimeter for use by sunbathers.
II. Description of the Prior Art
There are a number of previously known dosimeters
which measure the cumulative exposure of the sensor to
radiation, such as light. A number of these previously
known dosimeters also include optical filters which
limit the measured radiation to a predefined range, such
as ultraviolet light and a number of these dosimeters
are designed for use by sunbathers in order to prevent
sunburn. Examples of these previously known devices can
be found in U.S. Patent Numbers 3,710,115 to Jubb and
3,917,948 to S-trutz.
A primary disadvantage of these previously known
devices, however, is that they do not include any means
for determining whether the internal components of the
dosimeter are functioning correctly. For example, the
light sensor, typically a photocell, may accidentally be
obscured by a blanket or an article and thus detect a
very low radiation when, in fact, the sunbather is
exposed to a much higher radiation dosage. Li]cewise,
the electrical circuitry of the photodosimeter may
malfunction in other respects and subject the sunbather
to a higher than desired radiation dosage.
Summary of the Present Invention
The present invention provides a photodosimeter
which overcomes the above mentioned disadvantages of the
previously known devices.
An aspect of the invention is as followso
A photodosimeter comprising:
a housing having an opening,
electrical circuit means comprising means mounted
beneath said opening for generating an output signal
having a magnitude proportional to the intensity of
ultxaviolet radiation entering said housirlg opening,
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means for repeatedly reading said output signals
and for storing a cumulative value of said output
signals,
means for determining and storing the maximum read
value of said output signal,
an alarm,
means for activating said alarm when said
cumulative value exceeds a preset value,
means for comparing a currently read output signal
with the previouslv stored maximum value of said output
signal, and
means responsive to said comparing means for
activating said alarm when said output signal is between
ten and thirty-five percent of the previously determined
maximum read value of said output signal from said
generating means.
In brief, and by way of further explanation, the
photodosimeter of the present invention comp~ises a
housing having an opening and containing an electrical
circuit. A photocell is mounted beneath the opening
which generates an output signal having a magnitude
proportional to the intensity of ultraviolet radiation
entering the housing openingO Preferably, an optical
filter is positioned within the housing opening so that
the photocell generates an output signal only during the
presence of ultraviolet radiation.
The electrical circuit is preferably microprocessor
based and repeatedly reads the output signal from the
photocell via an A/D converter. The microprocessor
maintains a cumulative total of the ultraviolet
radiation in a memory location and, when the total
radiation exceeds a preset amount, activates the alarm
to warn the sunbather.
In addition to reading and accumulating the
ultraviolet radiation dosage, the microprocessor is also
programmed to perform a series of tests on the
electrical circuit in order to prevent an excessive
radiation dose for the sunbather. In one such test, a
microprocessor first reads the value of the output
signal from the photocell and compares this value with
the maximum output signal expected from the photocell.
In the event that the read value equals or exceeds the
maximum output value, the microprocessor activates the
5 alarm to warn the sunbather that the radiation dose
received is actually greater than that which can be
measured by the photodosimeter.
The microprocessor next compares the output from
the photocell with a zero value indicative that the
photocell and/or its associated components are
nonfunctioning. If the output from the photocell is
zero, the microprocessor immediately activates the alarm
to warn the sunbather of the malfunction.
The microprocessor then compares the output signal
from the photocell with a predetermined percentage which
would be indicative that the photocell housing opening
has been obscured, partially covered or otherwise
shaded. In such an event, the sunbather may be
receiving a greater radiation dosage than detected by
the photodosimeter and, consequently, the microprocessor
again activates the alarm.
In the event that the electrica] circuitry of the
dosimeter is functioning properly, the microprocessor
periodically and momentarily activates the alarm in
order to assure the user that the dosimeter is
functioning properly. Thus, for example, in the event
of a complete battery or power failure, the absence of
the periodic and momentary activation of the alarm would
advise the user that the dosimeter is not functioning.
~he present invention further provides a fail safe
alarm system which is deactivated only upon the receipt
of the pulse train. This pulse train is generated by
the microprocessor only when the electrical circuitry of
the dosimeter is functioning properly. Conversely, the
absence of the pulse train, which would occur during a
malfunction of the circuit, terminates the pulse train
and activates the alarm.
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Brief Description of the Drawing
A better understanding of the present invention
will be had upon reference to the following detailed
description when read in conjunction with the
accompanying drawing, wherein like reference characters
refer to like parts throughout the several views, and in
which:
FIG. 1 is a block diagrammatic view illustrating a
preferred embodiment of the present invention;
FIG. 2 is a schematic view illustrating a portion
of the preferred embodiment of the invention; and
FIG. 3 is a flow chart illustrating the operation
of the preferred embodiment of the invention.
Detailed Description of the
Preferred Embodiment of the Invention
~ ith reference first to FIG. 1, a block
diagrammatic view of the preferred embodiment of the
present invention is there shown and comprises an
electronic circuit 10 which is contained within a
housing 12 having an opening 14. A photocell 16 is
mounted in alignment with the housing opening 14 and
generates an analog signal on its output 13 to a signal
processor 20. In addition, an optical filter 22 is
preferably positioned within the housing 14 above the
photocell 16 so that the photocell 16 generates an
analog signal on its outpu-t 18 representative of the
magnitude of ultraviolet radiation.
The signal processor 20 can be of any conventional
construction, but preferably comprises an analog to
digital (A/D) converter as well as a signal conditioner.
The signal processor 20 in turn generates a signal on
its output 22 to the data input of a microprocessor 24.
A computer program is stored in a read only memory (ROM)
26 which controls -the operation of the microprocessor
24. The ~OM 26 may be either external to the
microprocessor 24, as illustrated in the drawing, or
self contained on the microprocessor 24.
The microprocessor 24 includes output lines 28 and
30 which respectively control a display 32 and an alarm
34O Preferably the display 32 is an LCD display while
the alarm 3~ is an audio beeper.
The microprocessor 24 periodically samples the
output from the photocell 16 and maintains a cumulative
total of the radiation dosage detected by the photocell
16 in random access memory. When this cumulative
radiation dosage exceeds a preset amount, the
microprocessor 24 activates the alarm 34 to warn the
sunbather to avoid the sun in order to prevent sunburn.
With reference now to FIG. 3, in between each
sampling of photocell 16, the microprocessor 24 executes
an internal self checking routine to ensure the proper
operation of electrical circuit 10. This self checking
routine begins at entry point 50 and at step 52
immediately sets two variables, TICTIM and BEPCNT to 0.
As is described more fully below, the TICTIM variable is
employed as a two minute counting register while the
BEPCNT variable is used as a flag register for an error
condition in the electronic circuit 10.
At step 54 the value of TICTIM is compared with a
value equal to two minutes. If unegual, TICTI~ is
incremented at step 56 and then proceeds to step 58.
Conversely, if TICTIM is e~ual to or greater than two
minutes, step 54 instead branches to step 60 which
activates the alarm 34 for a short period of time, for
example .6 seconds, to advise the user that the
electronic circuit is operating. Step 62 then resets
TICTIM to zero and proceeds to step 58.
At step 58, the microprocessor reads the value from
the photocell 16 indicative of the current radiation
dosage and stores this value in variable RVAL. Step 58
then proceeds to step 60 where variable RVAL is compared
to a variable UVMA~ The variable UVMAX represents the
maximum radiation dosage that the electronic circuit 10
is capable of accurately measuring. Conseguently, in
the event that RVAL is greater than UVMAX, an error
condition of electronic circuit has occurred whereupon
step 64 branches to step 66 and sets BEPCNT to 1.
In the event that RVAL is less than UVMAX, step 64
branches to step 68 and tests for a zero value of RVAL.
A zero value for ~VAL is also indicative of an error in
condition, i.e. a zero reading from the photocell 16.
In this event, step 68 branches to step 66 and sets
BEPCNT equal to 1.
Assuming that RVAL is between zero and UVMAX, step
68 branches to step 70 and compares RVAL with PMAX. The
value of PMAX is equal to the maximum value of R~AL
during current operating session of the device. If RVAL
is greater than PMAX, indicative that the radiation
dosage has increased, step 70 branches to step 72 and
sets PMAX to the value of RVAL. Step 72 then branches
to step 74.
Assuming that RVAI, is equal to or less than PMAX,
step 70 instead branches to step 76 which compares RVAL
to a predetermined percentage of PMAX. This
predetermined percentage is in the range of 10~35
percent and is preferably 25~. A value of RVAL less
than this predetermined percentage of PMAX is indicative
that the photocell 16 has been covered or otherwise
obscured, i.e. a shade condition. In this event, the
sunbather may be receiving a greater radiation dosage
than is read by the photocell 16 and, consequently,
branches to step 66 and sets BEPCNT to l. If not, step
66 branches to step 74.
At step 74, the condition or voltage of the battery
is checked by the microprocessor. If the battery is
low, step 74 branches to step 78 and both sounds the
alarm 34 and sets the display 32 to indicate a low
battery condition. If the battery condition is within
acceptable limits, step 74 branches to step 80 where the
condition of BEP~NT is tested. If BEPCNT equals zero
indicative that the electronic circuit lO is operating
as desired, step 80 branches to step 82 wherein the
microprocessor generates a pulse on output line 30 (FI~.
1) to the alarm 34 and then returns to the calling
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program via step 84. On the other hand, if BEPC~T is
unequal to 0, indicative of an error condition, step 80
instead branches to step 86 where BEPCNT is decremented
and then returns to the calling program through step 84.
Consequently, in the event of an error condition, the
microprocessor does not execute step 82 and thus does
not generate a pulse on the output line 30 to the alarm
34.
With reference now to FIG. 2, the alarm 34 is there
shown in greater detail in which the microprocessor line
30 is coupled through a DC blocking capacitor 90 to one
side of both a ground clamp diode 92 and a rectifier 94.
The output from the rectifier 94 is connected to one
side of both a bleed resistor 96 and a capacitor 98.
The other sides of both the capacitor 98, bleed resistor
96 and ground clamp 92 are coupled to ground 100. The
output from the rectifier 94 is also connected to an
audio~beeper 102 having one side tied to a positive
voltaye.
During normal operation of -the microprocessor and
assuming that the electronic circuit 10 is operating
properly, step 82 generates a pulse train 104 on the
microprocessor output line 30. The pulse train passes
through the rectifier 94 and reiteratively charges the
capacitor 98 and, in doing so, deactivates the beeper
102. Between each pulse of the pulse train 104, the
bleed resistor 96 drains the voltage from the capacitor
98 toward ground but before the voltage from the
capacitor 98 reaches zero the next pulse on the pulse
train 104 again charges the capacitor 98 and maintains
the deactivation of the beeper 102.
On the other hand, in the event of an error
condition, step 82 is not executed so that the pulse
train 104 is not generated on the microprccessor output
line 30. In this event, the bleed resistor 96 bleeds
the voltage from the capacitor 98 and activates the
beeper 102.
Therefore, it can be seen that the alarm 34
provides a fail safe system which requires a constant
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pulse train 104 in order to deactivate the beeper 102.
Consequently, in the event of a malfunction of the
electrical circuitry, in addition to any one of the
several conditions tested by the microprocessor, the
pulse train 104 will not be genexated on line 30 so that
the beeper 102 will be activated.
The only failure of the electronic circuitry which
would also deactivate the beeper 102 would constitute a
complete power failure to the system. In this event,
however, step 60 (FIG. 3) will not be executed by the
program and the continued silence from the beeper serves
to alert the sunbather that the unit is not functioning.
Having described my invention, however, man~
modifications thereto will become apparent to those
skilled in the art to which it pertains without
deviation from the spirit of the invention as defined by
the scope of the appended claims.
