Technical Field

The present invention relates generally to gas pressure measurement, and more particularly toward an apparatus for measuring gas pressure and articulating gas pressure values. The invention has particular utility to monitoring tank gas pressure in scuba diving equipment.

Background Art

The most important variable affecting a scuba diver is the instantaneous gas pressure ^' within his or her scuba tank. Most diving accidents occur due to inadequate monitoring of the remaining air supply by the diver.

Gas pressure in scuba diving equipment typically ranges from 0-4500 psi. -A diver will typically fully charge the breathing tank before diving, but during the dive will not be cognizant of the remaining gas pressure. For long dives, the tank pressure may drop to below 500 psi, which is the critical pressure at which the diver should consider surfacing. Fatalities have been caused by divers who miscalculated the amount of remaining air supply and have not had adequate time to ascend for surfacing.

Gas pressure monitoring in scuba gear has been provided in the past by a mechanical gauge pneumatically coupled to the high pressure valve of a breathing tank. In Krasberg 3,252,458, for example, tank gas pressure is

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displayed on a mechanical gauge coupled to the high pressure valve of the tank and strapped to the wrist of the diver. In practice, however, the diver may not read the pressure guage. His or her vision may be obscured, or the diver may simply forget to periodically poll the gauge. There thus exists a current need to provide a tank pressure gauge that reports tank pressure to the diver without any involvement on his or her part.

Disclosure of the Invention

A broad object of this invention is therefore to provide an apparatus for monitoring and articulating gas pressure.

Another, more particular object of the invention, is to provide an apparatus for measuring scuba tank gas pressure and providing periodic audible pressure reports to the diver.

An additional object is to provide an apparatus for measuring scuba tank gas pressure and providing periodic articulated pressure reports to a diver.

Yet a further object of the invention is to provide an apparatus for measuring scuba tank gas pressure and periodically providing articulated pressure reports to the diver, with the frequency of the reports increasing as tank gas pressure decreases.

A further object is to provide a scuba tank gas pressure monitoring apparatus having a battery operated, microprocessor controlled circuit that provides periodic articulated pressure reports to the diver, and wherein battery consumption is minimized.

The above and additional objects of the invention are satisfied by a pressure monitoring system comprising a pressure transducer exposed to gas pressure to be measured. Speech synthesizer circuitry responsive to the transducer drives a speaker to articulate gas

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pressure values.

In accordance with another aspect of the invention, the instantaneous gas pressure in the scuba tank is measured by pneumatically coupling a transducer to the high pressure regulator port of a scuba tank. A water tight housing carried by the diver contains a speech synthesizer circuitry responsive to the transducer for driving a speaker to articulate gas pressure values. The speaker, which is preferably a piezoelectric type, is bonded to the inner surface of the housing.

Pressure reports are generated by the speaker in response to manual operation of a command button on the housing. In addition, pressure reports are generated automatically in response to each predetermined incremental decrease in measured gas pressure, e.g., 100 psi. The pressure differentials at which reports are articulated are reduced as tank pressure approaches and falls below the critical pressure at which the diver should begin his ascent for surfacing, to maintain the diver alert. As an example, pressure reports may be articulated to the diver upon each 50 psi reduction when tank pressure is between 1000 psi and 500 psi, and upon each 25 psi reduction when tank pressure is under 500 psi.

The circuitry is powered by a rechargeable battery stored within the water-tight housing and accessed for recharging through a sealed plug. To conserve battery power, the battery is normally disconnected from the circuitry when the tank is empty. As tank gas pressure is increased during charging, a second, mechanical pressure transducer exposed to tank pressure controls a switch that connects the battery to the microprocessor r. ^' n

I and spee<* synthesizer circuitry. Thereafter, when the tank is substantially fully depleted of gas, the

microprocessor controls the switch to disconnect the battery.

Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein I have shown and described only the preferred embodiment of the invention, simply by way of illustration of the best mode contemplated by me of carrying out my inventon. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive._

Brief Description of the Drawings

Figure 1 is a view illustrating a scuba diver carrying a breathing tank, fitted with a pressure gauge in accordance with the invention;

Figure 2 is a perspective view of a water-tight housing containing the speaker, battery and circuitry for generating articulated pressure reports to the diver.

Figure 3 is a block diagram of microprocessor and speech synthesizer circuitry contained in the housing of Figure 2; and

Figure 4-6 are a program flow chart describing firmware for controlling the microprocessor.

Best Mode For Practicing the Invention

In Figure 1, a diver is fitted with a breathing tank 10 coupled to a mouthpiece 12 through a length of flexible tubing 14. The tank 10 carries a cutoff and first stage pressure regulator valve 16, having a high

pressure port 18 (see Figure 2). Coupled to the high pressure port 18 through tubing 28 is a water-tight housing 20 which, in accordance with the invention, monitors tank gas pressure and periodically articulates tank gas pressure values to the diver. A conventional pressure gauge 22 is coupled to the first stage regulator 16 at port 24.

The housing is formed of plastic or other suitable material. A speaker 48 (Figure 3), bonded to the inner surface of the housing at 30, is driven by microprocessor and speech synthesizer circuitry 21 to periodically articulate scuba tank gas pressure values. In addition, a manual switch 32 on the housing 20 enables the diver to receive articulated gas pressure values on command.

Further within the housing 20 is a pressure transducer, preferably of a piezo-resisti ve type, pneumatically coupled to the scuba tank gas pressure through the flexible tubing 28. A rechargeable battery 52 (Figure 3) within the housing 20 supplies electrical power to the microprocessor and speech synthesizer circuitry 21. The battery 52 is recharged through a port 34 that is enclosed by a threaded 0-ring sealed plug 36.

The battery 52 is normally connected to supply electrical power to the microprocessor and speech synthesizer circuitry 21, eliminating the requirement of an on-off switch. An on-off switch (not shown) could, however, be optionally included. To conserve battery power, a mechanical pressure responsive switch 54, coupled to tank 10 through tubing 28, interconnects the battery and circuitry 21 only when tank pressure is above 5 or 10 psi; this prevents the battery from draining when the scuba tank 10 is empty. The switch 54 is conventional; it may be, for example, of a standard

normally open, pressure responsive type, including a piston carrying suitable electrical conductors and exposed to gas pressure at housing port 26. The piston is spring biased to an electrically "open" condition, and is "closed" in response to gas pressure above a predetermined value.

Referring now to Figure 3, the analog, pressure responsive signal developed by transducer 42 is applied to an analog to frequency-converter (A/f) 43, which generates a signal having a frequency that is a function of tank gas pressure. This signal is applied to a microprocessor 40 that polls the signal and in response, generates control signals to speech synthesizer 44 and speech read only memory (ROM) 46. The speech synthesizer 44 in turn receives pre-digi t ized information from speech ROM 46 to drive a piezo-electric speaker 48 with human recognizable, pressure values corresponding to the output of transducer 42.

The microprocessor 40 is programmed to drive speaker 48 to articulate pressure values upon incremental decreases, e.g., each 100 psi, of measured tank gas pressure, as described in detail below. In addition, the speaker 48 is driven, on command, by operation of the manual switch 32 outside housing 20. To maintain housing 20 water tight, switch 32 is magnetically coupled to an internal reed switch 50 connected to an interrupt port of the microprocessor 40.

All circuit components are conventional. The piezo-resistive pressure transducer may be a Sensyn LX1470 that is pressure responsive between 0 and 5,000 psi (absolute) and is relatively well matched to the typical pressures extant at the high pressure port of the first stage regulator 16. Microprocessor 40 may be an MC146805E2 CMOS type, made by Motorola Corporation, for minimum battery consumption. The A/F converter 43

may be an LM 331, manufactured by National Semiconductor Corporation, this particular device is calibrated to yield an output frequency of løKHz for a 5000 psi input, i.e., its sensitivity is 2Hz/psi. Speech ROM 46 may be an SPR 016, or equivalent, and the speech synthesizer 44 may be a SP-0256, both manufactured by Any of a number of different types of piezoelectric speakers can be bonded to the inner surface of the housing, depending upon the required frequency response and other factors required.

As mentioned above, and of particular importance to the s afety of the diver, he or she should be prompted periodically with tank gas pressure readings, especially as the pressure approaches approximately 500 psi. THis is the "critical pressure" at which for optimum safety, the diver must begin to surface. Prompting to the diver of the tank gas pressure can, if desired, be made in the time domain, e.g., every 10 minutes. Preferably, however, and in accordance with a preferred embodiment of the invention, a gas pressure report is supplied to the diver each time the pressure decreases by a predetermined increment. This increment is reduced as the measured pressure approaches and falls below the critical pressure, to maintain the diver more alert as the time for surfacing approaches. With full charge tank pressure being approximately 4500 psi, a pressure report is preferably articulated once for each 100 psi reduction in pressure, down to 1000 psi. Pressure reports are now increased in frequency to one report for each 50 psi change in pressure, down to 500 psi. Thereafter, the pressure differential or increment between reports is 25 psi. Following generation of a warning, the battery is disconnected from circuitry 21 when gas pressure drops below approximately 10 psi.

Referring to Figure 4-6, the programming,

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preferably implemented by firmware, of microprocessor 40 is initiated at step 100. In step 102, all input/output ports are initialized, all variables are initialized and battery voltage as well as the memory is checked. In step 104, the variable A takes on a value of "1" that selects the first message from synthesizer 44 and speech ROM 46 to be articulated by speaker 48. The first articulated message indicates that the apparatus is ready, e.g., "AQUA VOICE READY". This message is applied to the speaker (step 106), controlled by subroutine OUTSTR, which is conventional.

Subroutine GTPRES reads the output of the pressure to frequency converter 43, driven by transducer 42 (step 108), to determine instantaneous gas pressure at a sample time. The gas pressure value is returned as a 16 bit, 2 byte value in memory locations PSIHI, PSILO (step 110). The first pressure reading in LVALO, LVAL1 (last value) is saved. Subroutine GTPRES also converts the pressure into a four digit BCD value. The hundreds digits and the tens digits are then converted into two discrete binary values, MSHUN and MSTEN. MSHUN contains the number of hundreds of pounds per square inch and MSTEN contains the number of tens of pounds per square inch.

Subroutine OUTPRS (step 112) articulates the pressure as two discrete number words within the range 1 to 99. For example, the pressure value 2250 psi is articulated as "twenty-two fifty psi".

Advancing to the main loop of the program at step 114, the subroutine TSTKEY (step 116) tests to determine if manual pressure key 32 is depressed. If the zero flag is reset, then the manual key is depressed, and the pressure reading at the time of key depression should be articulated. Thus, if the key is depressed (step 118), subroutine GTPRES (step 120) articulates the pressure.

During the subroutine, a test must be made to determine whether the hundreds term is greater than the tens term, i.e., whether the pressure is greater than 10 times 100 (or 1000 psi), bearing in mind that the pressure report is articulated automatically for each 100 psi decrease in pressure down to 1000 psi. Pressure below 1000 psi are enunciated for each 50 psi drop in pressure, and pressures below 500 psi are enunciated upon each 25 psi drop.

Thus, assuming that the key 118 is not depressed, indicating that pressure reports will be automatic, subroutine GETPRES (step 122) monitors the output of pressure transducer 42 to obtain current gas pressure measurements. If the measured instantaneous pressure is greater than 1000 psi (step 124), the pressure drop that has occurred since pressure was last reported is computed (step 125). If the computed pressure drop is at least 1000 psi (step 130), the variables LVALO and LVALI are updated (step 131) and then the pressure is reported (step 132) through speaker 48.

If, on the other hand, the pressure measured during step 124 is not at least 1000 psi, a test is made to determine whether measured pressure is greater than 500 psi (step 126). If measured pressure is less than 500 psi, the program ^advances to LSTST in Figure 6, which generates pressure reports upon each 50 psi incremental reduction in gas pressure; otherwise the program advances to GSTST in Figure 5, which generates pressure reports upon each 25 psi incremental reduction in gas pressure.

In Figure 5, the pressure drop that has occurred since the previous pressure report was generated is measured (step 134). If the drop is at least 50 psi (step 136), the variables LVALO and LVALI are updated (step 138) and the current pressure is reported through

the speaker 48 (step 140).

In Figure 6, the pressure drop that has occurred since the previous pressure report was generated is measured (step 142). If the drop is at least 25 psi (step 144), the variables LVALO and LVALI are updated (step 146), and the current pressure is reported to the diver through speaker 48 (step 148).

When tank pressure is less than 100 psi, the microprocessor 40 is programmed (not shown) to generate an alarm signal through speaker 48 and thereafter, to open switch 55, disconnecting battery 52 from circuitry 21.

Thus, the diver has an option to obtain a gas pressure reading by manually depressing switch 32 on the housing 20, or to receive pressure values automatically, with the frequency of the pressure reports increasing as pressure decreases. This maintains the diver alert to the amount of remaining gas in the scuba tank, as the gas pressure approaches and falls below the critical value of around 500 psi when a decision should be made to begin surfacing. Since the pressure reports are audible, and generated automatically, the safety of the diver is substantially improved since the diver will be made continuously congnizant of the amount of gas remaining in the tank.

In this disclosure there is shown and described only the preferred embodiment of the invention, but as aforementioned, it is to be understood that the invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein.

For example, other values of pressure differentials

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at which reports are generated and other absolute pressures at which the frequency of reports are generated can obviously be selected. Headphones driven by circuitry 21 can be provided in lieu of or in addition to speaker 48. Further, the principles of the invention can be applied in other environments, such as in medical breathing apparatus.