U.S. patent number 3,746,850 [Application Number 05/179,113] was granted by the patent office on 1973-07-17 for diver decompression apparatus.
Invention is credited to Jimmy J. Moore, Allen C. Ward.
United States Patent |
3,746,850 |
Moore , et al. |
July 17, 1973 |
**Please see images for:
( Certificate of Correction ) ** |
DIVER DECOMPRESSION APPARATUS
Abstract
A diver decompression apparatus for indicating the safe ascent
criterion for returning from the ocean depths to the surface,
comprising a body tissue simulator, means for sampling exposure to
inert gas at various body tissue depths and indication means to
determine safe ascent criteria.
Inventors: |
Moore; Jimmy J. (Elgin, TX),
Ward; Allen C. (Austin, TX) |
Family
ID: |
22655285 |
Appl.
No.: |
05/179,113 |
Filed: |
September 9, 1971 |
Current U.S.
Class: |
702/139 |
Current CPC
Class: |
G06G
7/60 (20130101) |
Current International
Class: |
G06G
7/00 (20060101); G06G 7/60 (20060101); G06g
007/60 () |
Field of
Search: |
;235/183,184,185
;128/2.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Korn & Korn: "Electronic Analog Computers" (Textbook) McGraw
Hill, 1956. page 13 of interest..
|
Primary Examiner: Gruber; Felix D.
Claims
What is claimed is:
1. An apparatus for determining a safe ascent rate for a diver to
prevent decompression sickness, comprising:
a. a pressure transducer capable of producing an output voltage
which is a linear function of water depth;
b. a body tissue simulator capable of simulating the amount of
inert gas distributed in the body tissue at various water depths,
said simulator comprising a resistance-capacitance network
connected in series with said pressure transducer whereby the
capacitor included in each section of said network is charged by
said output voltage from said pressure transducer;
c. means for sampling the voltage across each section of said
resistance-capacitance network of said simulator;
d. means for summing the sample voltages across each section of
said resistance-capacitance network, including a resistor and an
amplifier; and
e. at least one detector circuit connected in series with said
summing means which is capable of producing an output signal
proportional to the voltage across said resistor, indicating the
safe ascent rate to the diver.
2. The apparatus defined by claim 1 wherein said sampling means
comprises a monostable multivibrator and a polarity detecting
amplifier.
3. The apparatus as defined by claim 1 wherein said body tissue
simulator comprises a 14 section resistance-capacitance network
wherein each section has the identical time constant.
Description
The present invention relates to a novel diver decompression
apparatus and more particularly to a diver decompression computer
for indicating the safe ascent criterion for returning from the
ocean depths to the surface.
When making a dive below the ocean surface, divers may be subjected
to very high pressures depending upon the depth to which they
descend. As a result, the diver's body tissue will pick up inert
gas by diffusion which must be released before the diver returns to
the surface. This release of the diffused gas must be accomplished
over a period of time in order to avoid the effects of
decompression sickness. The decompression time period is dependent
upon the pressure time to which the diver has been exposed.
Therefore, it would be of greater value to a diver to be able to
monitor his own ascent to be sure his rate of ascent is not so fast
as to expose him to decompression sickness.
It is therefore the principal object of the invention to provide an
apparatus which will indicate a safe rate of ascent for a diver
from the ocean depths to avoid decompression sickness.
It is a further object of the present invention to provide a diver
decompression computer which is lightweight and portable.
The foregoing and other objects of the invention are accomplished
by a decompression computer which will implement the safe ascent
criteria for a diver, the decompression computer comprising a
pressure transducer tissue simulator which can simulate the
distribution of exposure in the body tissue of a diver; means for
sampling equivalent exposure after any pressure-time product and
comparing this exposure to a threshold voltage derived from the
pressure transducer; means for integrating any exposure above this
threshold and then comparing this integral to a safe constant
criterion; and means for indicating to the diver that he has
exceeded tbe safe ascent criteria. By the term "safe constant
criterion" is meant an emperical value derived from a methematical
formula representing tissue absorption of inert gas as a result of
increased pressure, which represents the permissible exposure
without having to undergo decompression steps during ascent.
In the development of the decompression computer of the present
invention, a number of assumptions were made. These assumptions are
generally accepted by those familiar with decompression sickness.
These assumptions are:
1. An excess of inert gas in the body tissue is the cause of the
symptoms of too little decompression time following a dive.
2. Inert gas enters and penetrates the body tissue by a diffusion
process at the surface of capillaries.
3. The concentration of inert gas in the body tissue is called the
exposure and is due to the diffusion of the gas into the tissue as
the diver is exposed to various pressures.
4. Time constants involved with the diffusion process in the tissue
are very long compared to the time constants involved with the
transport of inert gas between the lungs and capillaries.
5. The layout of capillaries in the body tissue is very complex
since there is no uniform pattern.
A fuller understanding of this invention will be facilitated by
reference to the accompanying drawing, wherein:
FIG. 1 is a diagrammatic view of a preferred embodiment of the
diver decompression circuitry of the present invention;
FIG. 2 is a diagrammatic view of the circuitry of pressure
transducer which is an element of the present invention; and
FIG. 3 is a timing diagram which illustrates the operation of the
diver decompression computer of the present invention.
With particular reference to FIG. 1, the tissue simulator 10 is
composed of a fourteen section resistance-capacitance network, each
section having identical time constants. The 95 percent time
constant of the entire 14 sections is 900 minutes. The entire
network is charged by a voltage derived from a pressure transducer
as hereinafter explained, which voltage is a linear function of the
water depth. The charge on each capacitor 12.sub.1 -12.sub.14,
which is indicated by the voltage across the capacitor 12.sub.1
-12.sub.14, represents the exposure at a particular depth in the
body tissue at any time. The voltage appearing across the network
of the 14 capacitors 12.sub.1 -12.sub.14 represents the exposure
into the body tissue at any one time. For a 900 minute time
constant this places a stringent requirement on the allowable
leakage of the capacitors which must be less than 1 .times.
10.sup..sup.-10 amperes at the largest voltage. Preferably, these
requirements may be realized by keeping the maximum voltage for a
200 ft. depth at less than 1 volt and using solid tantalum
capacitors.
An electronic sampling switch 15 for sampling the charge voltage on
the capacitor of a given RC section must be capable of being turned
on separately and when it is turned on it must recognize the
polarity of a voltage and turn itself off for one polarity
(positive) and remain on for a fixed time for the other polarity
(negative) and then turn itself off. During the time that the
switch 15 is on it must take very little charge from the capacitor
12 it is sampling and during the time that it is off it must not
contribute appreciably to the leakage of the capacitor 12. This
requires a leakage of less than 1 .times. 10.sup..sup.-10 amperes
during the off time of the switch 15. The switch 15 must have a
very low voltage drop across it in the on condition, preferably
less than 1 millivolt. Preferably, the sampling switch 15 used is a
silicon transistor which meets these requirements used in the
inverted connection. The switch 15 is controlled by a monostable
multivibrator 16 with a fixed on time with the provision that it
can be turned off before the fixed time is up. A high gain
amplifier 18 is used as a polarity detector which when turned on
produces a pulse of sufficient amplitude to turn the monostable
multivibrator 16 off if the input is as much as 5 millivolts
positive. If the polarity is negative, the multivibrator 16 remains
on for the preset time. One electronic sampling switch 15 is
required for each capacitor 12.sub.1 -12.sub.14 in the tissue
simulator 10. The total time that the sampling switch 15 may be on
is about 30 microseconds out of every 2.5 seconds.
The electronic integration is accomplished by converting each of
the sampled capacitor 12.sub.1 -12.sub.14 voltages which is above
the threshold V.sub.1, FIG. 2 to a current and summing these
currents in a single resistor 20. The voltage developed across this
resistor 20 is then amplified by amplifier 22 and used to trigger a
detector circuit 24,26 which is composed of a tunnel diode and
transistor. The tunnel diode is used because its trigger point is
stable over the expected operating temperature range. The voltage
amplifier 22 is turned on after the polarity detecting amplifiers
18 in the sampling switches 15 with sufficient delay to allow
switching transients to subside. Two detectors 24,26 which are set
at different trigger levels are used; one 24 for a red light and
one 26 for an amber light.
The desired information must be presented to the diver on a visual
display. Three flashing lights 28,30,32 are used. One is a green
light 32 to indicate that the electronics is functioning. One is an
amber light 30 to give a warning when the diver is within
approximately 10 ft. of requiring a decompression stop. The third
is a red light 28 which indicates that a decompression stop is
necessary. The separation of the amber light 30 trigger point from
the red light 28 trigger point is non-linear with depth becoming
less than 10 ft. at the shallow depths. In order for a flashing
light to be visible the duration of the flash must last at least 40
milliseconds. A 50 millisecond duration is used in the
decompression gauge. A monostable multivibrator 34,34 a,34 b is
used to trigger each light 28,30,32. Each time a sampling period is
initiated the green light 32 is flashed. Each time an integration
is performed, which is each sampling period, the amber 30 and red
28 lights will flash only if the appropriate detector 24,26 is
energized. The detectors 24, 26 are manually settable. The trigger
levels are set to be the maximum equivalent exposure without
decompression for the red light 28. The same level plus the D+7
reference is used for the amber light 30. Warning of an impeding
decompression stop is given some ten feet prior to ascent depth at
which the diver must stop.
The timing is selected with several considerations in mind.
Preferably, and with particular reference to FIG. 3, the capacitors
12.sub.1 -12.sub.14 should not be sampled any oftener than required
by the information rate in order to preserve their information on
the exposure distribution.
Additionally, the lights 28,30,32 must not be flashed any oftener
than necessary in order to preserve battery life and reduce battery
size. With these factors in mind, a sampling rate was chosen at
approximately once every 2.5 seconds. This is also the rate of
flashing the lights 28,30,32 which simplifies the electronic
circuitry.
A single unijunction transistor oscillator circuit 36 is used to
generate a pulse every 2.5 seconds. This pulse triggers all 14
sampling switches 15 simultaneously turning them on. After a 1
microsecond delay to allow switching transients to subside the
polarity detecting amplifiers 18 in the sampling switches 15 are
turned on for approximately 2 microseconds. Those amplifiers 18
that have a positive input turn their switches off. Again after a
15 microsecond delay to allow switching transients to subside the
integrator voltage amplifier 22 is turned on for 2 microseconds and
the output pulse applied to the amber red detectors 26, 24. The
lights 28,30,32 that were turned on in the process remain on for
approximately 50 milliseconds. Approximately 30 microseconds after
the initiation of the sampling cycle all remaining sampling
switches 15 are turned off by their own monostable multivibrator
circuits 16. After approximately 2.5 seconds the process is
repeated.
The pressure transducer 40 is required to produce two voltages
which are a function of water depth. One voltage is proportional to
0.79D and the other voltage required is proportional to D + 7 feet,
where D is the water depth in feet. The voltage proportional to
0.79D is used to charge the tissue simulator 10 and the voltage
proportional to D + 7 is used as the reference in the sampling
circuits. Preferably, the pressure transducer 40 used is a sea
water potentiometer whose resistance will vary linearly with depth.
This transducer 40 is used in the circuit shown in FIG. 2 to derive
the two voltages. Since the pressure transducer 40 measures
absolute pressure a voltage representing 33 feet of water is
produced at the surface. In order to obtain D + 7, 26 feet of this
must be balanced out and to obtain D all 33 feet must be balanced
out.
In order to produce voltages proportional to D and D + 7, the
elements of the pressure transducer circuit, as shown in FIG. 2,
should have the following values: R.sub.1 = 10.5K; R.sub.2 = 39.2K;
R.sub.3 = 2430.OMEGA. ; R.sub.4 = 56.2.OMEGA. ; R.sub.5 =
210.OMEGA. ; R.sub.6 = 987.OMEGA.; and B.sub.1 = 1.35 V. This will
give 0.79D at V.sub.1 and D + 7 at V.sub.2.
There are four different battery supplies used in the decompression
gauge. A 1.35 volt supply is used to supply voltage to the pressure
transducer 40. A 2.7 volt supply is used to bias off the transistor
sampling switches 15. One 4.05 volt supply is used to supply all of
the sampling switch amplifiers 18, the integrated voltage amplifier
22, and the timing circuitry 36. Another 4.05 volt supply is used
to furnish power for the detectors 24, 26 and three lights
28,30,32. Three batteries in parallel are used for each of the 4.05
volt supplies. Two batteries are used in parallel for the 1.35 volt
supply and one battery is used for the 2.7 volt supply. The drain
on the batteries is such that the gauge will operate continuously
for one week on one set of batteries over the expected operating
temperature range.
EXAMPLE I
A gauge was packaged in the form of a brass cylindrical housing
approximately 5.5 inches long by 2.4 inches in diameter. There were
two separate water tight housings. The top portion which occupies
about 2.5 inches of length houses all of the electronics except the
lighting circuits. The bottom portion houses the pressure
transducer, the lighting circuits and the batteries. The three
lights which were potted in epoxy were supplied as a separate
package to be mounted on tbe wrist of the diver and connected to
the decompression gauge by a waterproof cable and waterproof
stuffing gland. Another waterproof stuffing gland was used to house
a socket which was used for zeroing the gauge. An external shorting
plug was used with this socket to set the gauge to zero before
starting a dive.
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