Wrist-worm rate of ascent/descent indicator

A wrist-worn, real-time-indicating, actual rate of ascent/decent meter includes a non-corrodable, hermetic enclosure with a window. A display, visible through the window, includes numeric rate-related indicia and arrows, both clearly visible against a contrasting backdrop. The contrast may be black on silver. A hysterisis-free transducer in the enclosure produces first signals proportional to the ambient pressure. The first signals are converted to second signals representing depth in the ambient, the latter signals being periodically sampled. Each sample is compared to the previous sample and third rate-of-change-of-depth-with-time signals result from successive comparisons. The third signals are displayed numerically and direction (ascending or descending) is indicated by the arrows. Signal processing is controlled and performed by a microprocessor within the enclosure. Facilities are provided to replace a battery and to turn the meter on and off without affecting the hermeticity of the enclosure.

FIELD OF THE INVENTION 
The present invention relates to a device which indicates the rate of 
ascent/descent in an ambient, and, more particularly, to a wrist-worn, 
watch type device which presents a real time indication of the actual rate 
of ascent and descent to a person involved in underwater activities, such 
as SCUBA, snorkling or skindiving. 
BACKGROUND OF THE INVENTION 
For many years the dangers involved with ascending too rapidly following a 
dive in water have been known. These dangers derive from the action of 
gases within the body as the body experiences pressure changes. 
Air is a mixture of many gases, primarily nitrogen (78%) and oxygen (20%). 
In a normal ambient conditions, a person inhales air at a normal 
atmospheric pressure of about 14.7 p.s.i., a portion of the air passing 
through the lung tissues into the blood. The blood supplies the body cells 
with oxygen from the air and in turn receives waste carbon dioxide from 
the cells which it transports to the lung tissues for exhalation. The 
gases in air when inhaled at normal atmospheric pressure are absorbed by 
the body. 
When air for respiration is supplied to a person in an ambient having a 
pressure substantially higher than normal atmospheric pressure--such as 
occurs in an underwater ambient--the air must be supplied at an elevated 
pressure to offset the pressure of the ambient. The increased pressure 
results in higher quantities of air, and its constituent gases, being 
absorbed by the body than would be absorbed at normal atmospheric 
pressure. 
Various types of equipment for supplying air at higher pressure such as 
self-contained underwater breathing apparatus, or SCUBA) are today readily 
available and have made possible extended dives in water to great depths. 
However, the use of such equipment is accompanied by the possibility of 
hazard. 
If inert gases in air, primarily nitrogen, which are dissolved in the body 
are too quickly released from solution and cannot be safely discharged 
from the body through the lungs, decompression sickness, or "the bends," 
occurs. If the ambient pressure to which a person is subjected decreases, 
inert gases previously dissolved in the blood and body tissues tend to be 
released from the solution. Such a pressure decrease occurs during ascent 
from a lower level in a body of water. If the rate of ascent is 
sufficiently low, the body is able to efficiently discharge the inert 
gases released from solution and no harm to the body occurs. If the rate 
of ascent is too high, the body is not able to efficiently discharge these 
gases (primarily nitrogen) released from solution. As a result, nitrogen 
gas bubbles form in the body due to the now supersaturated condition of 
the blood and tissues in which they are located. 
These released nitrogen bubbles travel with the blood stream. Should a 
bubble become lodged in the heart or brain, it can cause death or 
paralysis. Less serious, but extremely unpleasant and/or painful, are the 
physiological effects on body tissue of the gasses and the bubbles thereof 
as they are released from solution. These effects include pain, numbness 
and muscle weakness. All of the foregoing are often, possibly somewhat 
imprecisely, referred to as "the bends." 
Avoiding "the bends" has been found to be a matter of giving the body 
sufficient time to discharge through the lungs gases which are released 
from solution so that bubbles do not form. The body may be afforded this 
time by appropriate control of the rate of ascent. Ascent at a controlled 
rate which enables the discharge of nitrogen from the body through the 
lungs is a part of every experienced diver's basic lore. Ascent at an 
appropriate rate assures that nitrogen will not be released into or from 
the blood as bubbles. This appropriate rate may combine controlled ascent 
with decompression or rest stops during ascent. 
Early diving experience with large numbers of divers led the U.S. Navy to 
produce and circulate its Decompression Tables. These Tables have set the 
"standard" for ascents at 60 feet per minute. Although dives to great 
depths may require the earlier noted combination of controlled ascent and 
rest stops, the U.S. Navy Decompression Tables instruct that ascents from 
typical depths at rates of 60 feet per minute or less will permit the body 
to safely discharge gases released from solution to avoid bubble formation 
and "the bends." 
Unfortunately, these Decompression Tables and the 60 feet per minute ascent 
rate were originally set for male divers aged 19-25 years and in peak 
physical condition. Recent research indicates that age, sex, physical 
fitness and individual physiological differences among people all have a 
bearing on a safe ascent rate, as do depth and duration of dive. The 
weight of evidence is that a "typical safe" rate of ascent generally 
applicable is less than 60 feet per minute. Further, there is strong 
evidence that each person's "safe" rate of ascent is unique and can be 
arrived at by experience gained from numerous dives and experimentation. 
One method of determining one's rate of ascent and for ensuring that a 
"standard" such as 60 feet per minute is not exceeded, is to carry during 
the dive a depth guage and a watch. These two measuring devices can be 
used to periodically calculate rate of ascent. The foregoing technique is 
inconvenient and subject to error. Two measuring instruments must be 
carried and nearly simultaneously read and then a calculation must be 
made. The stress of the dive itself and of events or emergencies--such as 
low air supply, injury, loss of sense of vertical direction or poor 
visibility--occurring during the dive create the possibility that the 
calculations will be erroneously performed, if they are performed at all. 
Devices which can accompany a diver and which can alert or inform the diver 
that a "standard" rate of ascent is being exceeded are known. See, for 
example the following U.S. Pat. Nos.: 4,820,953; 4,109,140; 4, 107,995; 
and 3,992,948. Typically, the "standard" is the 60 feet per minute from 
the U.S. Navy's Dive Tables. In some cases the "standard" may be 
adjustable to some other ascent rate. The output from the devices of the 
foregoing patents is of the "go/no-go" variety. Specifically, these prior 
art devices give the diver no indication of the rate of ascent but merely 
alert or inform when a pre-set "standard" rate of ascent is being 
exceeded. By the time the diver receives this information, conditions 
conducive to "the bends" may have been present for an appreciable time. 
The diver receives no quantitative data regarding rates of ascent below or 
above the "standard," and, thus, the diver cannot determine how much or 
for how long to slow or stop ascent to counteract those effects which may 
cause "the bends." 
U.S. Pat. No. 4,658,358 discloses an underwater computer. This device 
includes a microprocessor which computes water pressure, depth, minimum 
depth to which the diver can safely ascent, the minimum time for safe 
ascent to the water surface, and the elapsed time since the beginning at 
the dive. The minimum depth and minimum time values are based on an 
algorithm controlling the operation of the microprocessor. The results of 
the computation are displayed to the diver. The device does not calculate 
or display the real time rate of ascent of the diver. Accordingly, if the 
diver does not "match" the algorithm, the minimum depth and time 
calculations may be misleading. 
Safe diving would seem to require a device which provides a real time 
indication of the actual rate of ascent and descent of a diver, as opposed 
to a go/no-go indication that a possibly inapplicable "standard" has been 
exceeded. Such a device should be easy to use, reliable, easy to read and, 
preferably, wearable on the diver's body or mounted in a divers console. 
All of the foregoing are objects of the present invention. 
There is some evidence that a diver's rate of descent may play a role in 
physiological condition during and after a dive. Although the precise role 
played by descent rate is presently not well defined, a convenient means 
for ascertaining this value during a dive would be desirable, and the 
provision of such a means is a further object of the present invention. 
SUMMARY OF THE DISCLOSURE 
With the above and other objects in view, the present invention 
contemplates a wrist-worn or console mounted device for use during diving. 
The device calculates and displays to the diver the real time, actual rate 
of ascent and descent of the diver. 
The device includes an enclosure surrounding a hermetically sealed volume. 
The enclosure is preferably constructed of plastic or other non-corrodable 
material. The enclosure includes a window. Within the enclosure and 
visible through the window is a display. The display comprises indicia, 
which constitute both numbers and arrow-like characters, which are visible 
against a contrasting backdrop. Preferably, the display is a liquid 
crystal array which displays black indicia and the backdrop is reflective 
silver. Tests have shown that black against reflective silver is highly 
visible and discernible in low-light, underwater environments. 
Located within the volume is a non-temperature sensitive, hysterisis-free, 
solid state pressure transducer. The transducer produces a first output 
signal which is proportional to the pressure of the surrounding ambient. 
In preferred embodiments, the transducer includes a diaphragm and four 
piezoresistive strain gauge resistors which are implanted or diffused in 
the diaphragm. The resistors are connected together in a Wheatstone bridge 
configuration. When the diaphragm deflects in response to the pressure of 
the ambient, the output of the bridge, which is the first output signal, 
is proportional to the actual real-time value of such pressure. 
A first facility within the volume converts the first output signal to a 
second output signal representative of the actual real-time depth of the 
device within the ambient. The first facility comprise may comprise a 
conditioner for the first output signal and an analog-to-digital converter 
for converting the conditioned, analog, first output signal to a digital 
second output signal. 
A second facility within the volume periodically samples the second output 
signal following successive equal time intervals. This second facility 
compares successive second output signals and produces successive third 
output signals indicative of the actual, real-time rate of change of depth 
with time. 
A third facility within the volume activates the display in response to the 
third output signals. As so activated, the display presents visually 
detectable numeric indicia indicative of the real-time rate of ascent or 
descent in the ambient. These indicia preferably indicate the actual, 
real-time rate of ascent or descent in units such as feet per minute or 
meters per minute. The indicia also include arrow-like characters which 
indicate which, ascent or descent, is presently occurring. 
The first, second and third facilities may include or may constitute a 
portion of a microprocessor within the volume. The microprocessor, which 
may include a crystal-stabilized clock, executes a non-volatile program 
which is stored in a read-only memory accompanying the microprocessor. 
A power source energizes the display, the transducer and the first, second 
and third facilities. The power source, preferably a small battery, is 
located in a compartment formed in the enclosure separately from the 
volume. When the compartment is closed, the power source is provided with 
an ambient-proof environment. When the compartment is opened to test or 
replace the power source, the hermetic character of the volume is not 
invaded or affected. 
A fourth facility selectively connects and disconnects the power source to 
the display, the transducer and the first, second and third facilities. 
Connection and disconnection are achieved without invading or in any way 
affecting the hermetic character of the volume. Preferably, the fourth 
facility includes a normally open magnetically operated switch, such as a 
reed switch, within the volume. When the switch is open, the power source 
is disconnected from the display, the transducer and the facilities within 
the volume. When the switch is closed, the power source energizes all of 
these items, rendering them operative. The switch is rotatably mounted to 
the exterior of the enclosure, preferably about the window, in a bezel. 
The bezel includes a magnet or magnetized segment. Rotation of the bezel 
selectively positions the magnet close to or remote from the switch. When 
the magnet is close to the switch, the switch is held closed. When the 
magnet is remote from the switch, the switch assumes its normal open 
state. Indicia may be included on the bezel and the enclosure which 
mutually indicate whether the reed switch is open or closed indicating 
"on" or "off" depending on the rotational position of the bezel.

DETAILED DESCRIPTION 
Referring first to FIG. 1, there is shown a device 10 according to the 
present invention for displaying the real-time, actual rate of ascent and 
descent of a diver. The device includes an enclosure 12, which is 
preferably made of non-corrodable plastic or other material and which will 
permit the interior volume 14 of the enclosure 12 to be hermetically 
sealed. The enclosure 12 may include attaching pins (not shown) or similar 
facilities within end portions 16 thereof for mounting the ends of wrist 
straps 18 thereto. The enclosure 12 may be removably includable in a dive 
console (not shown), in which case the straps 18 may or may not be 
present. 
The face 20 of the device 10 shown in FIG. 1 includes a display 22 which is 
visible through a transparent window 24. The display 22, which may 
comprise a liquid crystal display of any well known type, comprises two 
numeric characters 26 and two arrow-like characters 28 and 30. Preferably 
the characters 26, 68, 30 show as black through the window 24. The display 
22 also includes a backdrop 32 which is colored to drastically contrast 
the color of the characters 26, 28, 30. Preferably, the backdrop 32 is a 
reflective silver color. It has been found that the black characters 26, 
28, 30 against the reflective silver backdrop 32 are easily and clearly 
readable under water in low light conditions. 
Rotatably mounted to the face 20 of the device 10 is a bezel 34 surrounding 
the window 24. The rotation of the bezel 34 may be achieved in any 
convenient manner. The bezel 34 may be black (FIG. 1) or a lighter color 
(FIG. 4). Referring to FIGS. 1 and 4, behind the backdrop 32 of the 
display 22 and within the hermetic volume 14 of the enclosure 12 is a 
small, magnetically operated switch 36, which may be a magnetic reed 
switch or any other equivalent element. The switch 36, which is normally 
open, applies power from a power source to the elements of the device 10 
within the hermetic volume 14 when it is closed. The power source and the 
elements within the volume 14 are discussed below. 
The rotatable bezel 34 includes a magnet or a magnetized segment 38 (FIG. 
4). The magnet 38 may be adhered to the bezel 34, which may be made of 
plastic or another non-magnetic material. The magnet 38 may also be molded 
into, or otherwise incorporated into the bezel 34 in any known way, as 
shown in FIG. 4, where a portion of the bezel 34 has been broken away. 
When the bezel 34 is rotated so that the magnet 38 is remote from the 
switch 36 (as in FIG. 4), the switch 36 assumes its normally open state. 
When the bezel 34 is rotated to bring the magnet 38 proximate to the 
switch 36, as shown by the phantom segment 38 in FIG. 4, the magnetic 
force thereof closes the switch 36. Closure of the switch 36 applies power 
to the elements of the device 10 within the hermetic volume 14. 
Referring to FIGS. 2 and 3 the back 40 of the device 10 may be seen to 
include an opening 42 providing access to a compartment 44 which holds a 
battery 46. The battery 46 serves as the power source for the elements of 
the device 10 within the hermetic volume 14. The compartment 44 is formed 
so as to be separated from the hermetic volume 14. Accordingly, gaining 
access to the battery 46 for purposes of replacement or testing does not 
invade the hermetic character of the volume 14. The formation of the 
compartment 44 and its separation from the hermetic volume 14 may be 
achieved by any known plastic or other technique. Electrical connection 
between the battery 46, the switch 36 and the other elements of the device 
10 within the hermetic volume 14 may be achieved by known feed-through 
techniques by which one or more electrical conductors 48 are fed through a 
web or plenum 50 separating the compartment 44 and the volume 14. 
The battery 46, which may be a 3Vdc disk-like cell, is held in the 
compartment 44 and shielded from the ambient by a plug 52 which is 
selectively insertable into and removable from the opening 42. Preferably, 
the plug 52 and the opening 42 are threaded, as at 54 and 56, to achieve 
this end. The plug 52 may include a flexible O-ring or gasket 58 which 
seals the compartment against entry of the ambient when the plug 52 is 
inserted. 
Referring now to FIG. 5, there is shown a schematic block diagram of the 
various elements within the enclosure, schematically depicted at 12, of 
the device 10. These elements are individually known and commercially 
available and may assume any convenient configuration. 
Within the enclosure 12 is a pressure transducer 60. The pressure 
transducer 60 is non-temperature sensitive, that is, its output function 
is unaffected by changes in ambient temperature. Further, the pressure 
transducer is also hysterisis-free. The pressure transducer 60 produces an 
output signal at 61 which is proportional to its location in the 
surrounding ambient. A preferred transducer 60 is a solid-state element 
available from IC Sensors of Milpitas, Calif. as a type-model 10 and sold 
under the designation OEM Pressure Guage. This type of transducer 60 
includes a diaphragm having four piezoresistive strain gauges implanted or 
diffused therein and connected together in a Wheatstone bridge 
configuration. Changes in pressure deflect the diaphragm so that the 
analog output 61 from the bridge is proportional to such pressure. 
The pressure-dependent analog output 61 from the transducer 60 is applied 
to the input 61 of a facility 62 which converts this output 61 to a 
digital output 63 representative of the depth of the device 10 within the 
ambient. The facility 62 may include a signal conditioner 64 and 
analog-to-digital converter 66, both of standard manufacture. In a fluid 
ambient, the pressure at a given depth is proportional to the depth of the 
device 10 in the ambient, here water. An appropriate signal conditioner 64 
is available from Linear Technology of Milpitas, Calif. as a type/model 
LT1013A and sold under the designation OPAMP. A suitable digital-to-analog 
converter 66 is also available from Linear Technology of Milpitas, Calif. 
as a type/model LTC1091 and sold under the designation 10 BIT A/D. 
The output 63 of the facility 62 is applied to an input 63 of a 
microprocessor 68. A suitable microprocessor 68 is available from OKI 
Semiconductor of Sunnyvale, Calif. as a type/model MSM5052 and sold under 
the designation Microcontroller. 
Read only memory (ROM) of the microprocessor 68 stores a non-volatile 
program which causes the microprocessor 68 to operate as described below. 
The microprocessor 68 includes an internal clock which is crystal 
stabilized, as depicted at 70. 
The microprocessor 68 periodically samples the output 63 of the facility 
62. Each sampled output 63 is compared to the last output 63 of the 
facility 62 to produce an output 71 representative of the "delta" or 
change, positive or negative, between the previous and the present 
depth-representative output 63 from the facility 62. Sampling is effected 
at successive, equal time intervals. The sampling and the time intervals 
thereof are controlled by the crystal-stabilized clock of the 
microprocessor 68. 
Thus, the microprocessor 68 periodically calculates the rate of change to 
depth with respect of time and produces successive outputs 71 
representative thereof. These outputs 71 from the microprocessor 68 are 
applied to display drivers 72 for the display 22, which in turn cause the 
numeric characters 26 of the display 22 to exhibit the real-time, actual 
rate of ascent or descent. This presentation may be in any convenient 
units such as feet per minute or meters per minute. The window 24 of the 
device 10 may bear a legend 74 which informs the user of the units 
represented by the numeric characters 26. The sign or polarity, positive 
or negative, of the change between adjacent digital depth-representative 
outputs 63 from the facility 62 is utilized by the microprocessor 68 to 
activate one of the arrows 28 or 30 depending on whether the device 10 is 
ascending or descending. Each time the microprocessor 68 samples the 
output 63 of the facility 62, a new "delta" is calculated. Each successive 
new "delta" effects energization of the display 22, so that the display 22 
presents the real-time, actual rate of ascent or descent, and not merely a 
go/no-go indication that a "standard" ascent or descent rate is being 
exceeded. 
In order to conserve the battery 46, the bezel 34 may be turned to close 
the switch 36 only when a dive is being undertaken. 
Those skilled in the art will appreciate that the foregoing description is 
merely representative of selected embodiments of the present invention, as 
defined in the appended claims, which cover the foregoing and equivalent 
structure and function.