Instrument Power-disconnect Alarm

Abstract

An instrument power-disconnect alarm. Apparatus is disclosed which provides an alarm in the event of inadvertent power disconnection from electronic instrumentation. For normal instrument power turnoff, the alarm is disabled. The present invention is particularly useful in conjunction with instruments used in monitoring, measuring or stimulating bodily function of hospitalized bedridden patients, where accidental power turnoff of a critical electronic instrument could be a matter of life and death.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an alarm for communicating a condition of inadvertent medical-electronics instrument power failure to nearby or remote personnel.

2. Description of Prior Art

In some areas of electrical technology "power-down" systems are employed. For example, in the area of electrical power transmission and distribution, standby power systems or emergency battery-powered illumination systems are well known. In the event of a power failure, battery-operated lanterns are automatically energized by the occurrence of inadvertent power-loss.

But, in the medical-electronics field in conjunction with critical instruments, there does not appear to be means available for automatically determining an occurrence of inadvertent instrument-power disconnect nor means available for providing communication of such a power loss to nearby personnel.

In the medical field, a typical problem can occur in a hospital room where a bedridden patient is monitored by critical electronic apparatus deriving its power from a typical 115 volt, 60 cycle, external power source. This electronic apparatus is normally mounted on wheels to facilitate mobility from patient to patient. If such apparatus is accidentally rolled or moved so that a power cord (delivering power to the instrument) is made to disconnect from the external power source the instrument becomes disabled. Thus, if a patient is unconscious or too weak to call a physician or nurse (in an adjacent room, for example) there is no way for standby personnel to know that the instrument has been accidentally disconnected. But on the other hand, if an alarm is triggered by power-disconnect, appropriate action can easily and readily be taken.

The present invention solves a problem of lack of communication to standby personnel of an inadvertent instrument power-turnoff condition. The particular problem solved is with respect to vital sign measuring, monitoring, and stimulating instruments. The invention can be utilized in any electronic apparatus which derives its power from an external source subject to unintentional disconnections. However, the invention is particularly applicable in the medical area. The problem of lack of communication is solved by providing a nearby and/or remote alarm.

SUMMARY OF THE INVENTION

The present invention, used in conjunction with an electronic instrument, utilizes a capacitor to store energy in response to proper power transfer from an external source to the electronic instrument. When power is removed the capacitor discharges.

If power is inadvertently lost the capacitor discharge takes a primary path through the series arrangement of an audio alarm system and normally closed contacts of a relay. The relay contacts are held open by current from the instrument. When power is removed (purposely or accidentally) the instrument current goes to zero and the relay contacts return to a normally closed state. The audio alarm system contains an audio oscillator and provides a loud sound for communicating a power loss situation to anyone in hearing range. The same alarm relay can optionally use another set of contacts to energize remote alarms, etc.

When the instrument has not been accidentally disconnected from its power source, but is properly disconnected therefrom, as by operating a front panel on-off switch, a secondary discharge path is established. This secondary path consists of a resistor and a manually operated switch to quietly dissipate the stored energy. The capacitor discharge through the secondary path is sufficiently rapid to not activate the alarm in the primary path.

An advantage of the present invention is that it prevents human beings from needlessly suffering and/or expiring in their hospital beds because of a lack of communication of power loss of a critical electro-medical instrument. The personnel on duty can correct the power-loss condition.

Thus, it is an object of the present invention to provide improved vital sign stimulating, monitoring, and measuring electronic apparatus.

It is a further object of the present invention to provide means for communicating accidental loss of power to an electronic instrument to nearby and remote personnel.

Other objects and advantages of the present invention will become apparent to one having reasonable skill in the art after referring to the detailed description of the appended drawing.

BRIEF DESCRIPTION OF THE DRAWING

The drawing is a partial schematic, partial block diagram of a particular embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the drawing power plug 10 is shown as a two pronged plug (but could alternatively be a typical three pronged grounded plug) which receives power from an AC source typically being 115 volts, 60 cps. Conductors 39 and 38 in conjunction with switch S1 (when closed) transfer AC power to DC power supply 14 which converts AC power to DC power.

Switch element 11 is manually moveable, and can be made to contact terminal 13 (closed position) or can be made to contact terminal 12 (open position). Switch elements 11 and 40 move together. When element 11 is in contact with terminal 12, switch element 40 makes contact with terminal 31 as shown.

The output of DC power supply 14 is depicted as (+) and (-) and is conducted to junctions 15 and 34 respectively. DC power is conducted from these junctions to circuitry 16 of some associated instrument. Instrument circuitry 16 comprises any electronic circuitry arranged to perform a particular function or functions. In a particular case, it can perform the task of measuring, monitoring, or stimulating bodily functions of a human being. For example, a very critical stimulating instrument is a heart pacer. Lack of proper stimulation to the heart when necessary could be a matter of life and death.

Conductors 35 and 36 are depicted as conducting current from instrument circuitry 16 to current-activated switch 17. This emphasizes the fact that instrument circuitry 16 itself must receive power for current flow to be set up within conductors 35 and 36.

Current activated switch 17 includes resistor 18 and relay coil 19 with switch S3. Conductor 35 is connected to one end of resistor 18, the other end being connected to one end of coil 19. The other end of coil 19 is connected to a junction comprised of switch terminal 23 and conductor 36.

Switch S3 is comprised of moveable element 22, fixed closed terminal 23 and fixed open terminal 21. Moveable element 22 is conductively connected via conductor 24 to one terminal (not shown) of audio alarm 25, the other terminal (not shown) being conducted via conductor 26 to a junction 41. (Alarm 25 contains an audio oscillator, not shown)

Junction 41 is conductively connected to the cathode of diode 28, the positive polarity side of capacitor 27, and one end of resistor 29. The other side of capacitor 27 is conductively connected to the (-) terminal of DC power supply 14 and to terminal 32 of switch S2 via conductor 37. The anode of diode 28 is conductively connected to the (+) terminal of DC power supply 14. The other end of resistor 29 is conductively connected to terminal 31 of S2.

In operation, consider switch S1 and S2 to be in the positions shown. Power plug 10 is inserted into a source of AC power. Switches S1 and S2, ganged together, are made to simultaneously change state, and in this particular case are manually switched. Moveable element 11, in contacting terminal 13 of switch S1, in conjunction with conductor 38 allows current to flow from an external source (not shown) to DC power supply 14 thereby causing it to function normally.

Moveable element 40 makes contact with terminal 30 and is out of the circuit, electrically. Thus, capacitor 27 is made to charge to a value of voltage near that of the output of DC power supply 14. Current flows from junction 15 through diode 28 to capacitor 27. Capacitor 27 is charged in a short time because of a small charging time constant. (Diode 28 has a small inherent resistance allowing rapid charging of capacitor 27.) Instrument circuitry 16 is thus energized by application of DC power thereto, and is functioning properly under normal circumstances.

Conductor 36 represents a continuation of the (-) side of DC power supply 14. Conductor 35 may represent a (+) power supply bus line, but more appropriately is a value of voltage which represents proper operation of instrument circuitry 16. This voltage value is picked off a sampling resistor (not shown) within instrument circuitry 16. It is a value which represents overall normal operation of instrument circuitry 16.

Current flow through conductors 36 and 35 and through current operated switch 17 maintains switch 17 in a "no-alarm" state. Current flows into switch 17 at resistor 18 which is used to adjust voltage cross the coil of relay 19 to a proper value. Proper current flow through the coil causes it to maintain moveable element 22 in contact with out-of-circuit terminal 21. This magnetic effect is shown by dotted lines 20.

In this condition, capacitor 27 is charged and has no discharge path. Moveable element 40 is at terminal 30 and moveable element 22 is at terminal 21. There is no current flow through alarm 25; thus audio alarm 25 is not activated.

To compare discharge paths, first consider properly and purposely turning off power to the circuitry. Operation of ganged switches S1 and S2 causes moveable element 11 to make contact with out-of-circuit element 12 thereby cutting power to DC power supply 14, and simultaneously causes moveable element 40 to make contact with terminal 31. Thus, a secondary discharge path for capacitor 27 is established. Capacitor 27 can discharge via the series arrangement of resistor 29, moveable element 40, and conductor 37. This discharge is rapid so that alarm 25 will not be set off.

When power is removed (even properly so) from DC power supply 14, current flow in relay coil 19 ceases. Upon termination of current flow in relay coil 19, moveable element 22 is arranged to spring back to its normally closed position in contact with terminal 23. Thus, a primary discharge path for capacitor 27 is established through alarm 25 via conductors 26 and 24, contact 23, and conductor 36, to the negatively charged plate of capacitor 27. Therefore, in order to prevent a false alarm, a "secondary discharge" via resistor 29 must be rapid enough to prevent a "primary discharge" through the audio alarm. One way to insure a proper secondary discharge is to use a relay which has a built-in slight hysteresis (on the order of milliseconds) to maintain contact in an established position long enough for capacitor 27 to noiselessly discharge.

Now, consider the alternative power-loss situation in which a disconnect from power is inadvertent or accidental. In this case, moveable element 11 will remain in position with contact 13 and moveable element 40 will remain in contact with terminal 30. Thus, when power plug 10 is yanked from its wall socket or other source of power, there is no secondary discharge path available to capacitor 27 through resistor 29. The only discharge path available to capacitor 27 (reverse resistance of diode 28 prevents current flow therethrough), is the primary discharge path through audio alarm 25 and normally closed contact 22 of switch S3. The alarm is activated (an audio oscillator within alarm 25 is activated but is not shown) for a period of time required for capacitor 27 to discharge through resistance of the audio alarm. Typically this takes 10 to 20 seconds.

It may be apparent to one skilled in the art that other storage means besides capacitors can be used for this function. For example, an inductor stores energy in its magnetic field which can be discharged through an alarm system. Also, a battery can be arranged to be used in place of capacitor 27, but the battery would continually discharge until it was turned off via an additional manual switch.

It should be noted that alarms other than audio alarms can be used. The alarms can be nearby, or they can be remote. There can be one alarm or there can be many strategically placed alarms. (An alarm can be placed in a nurse's lounge.) The alarm can be of any variety which stimulates human senses, i.e., visual, aural, etc. A flashing light connected to the apparatus by conductive wire, for example, could be used, or alternatively a transmitter could be activated to communicate via electromagnetic wave media to various receivers, located in the hospital, (or external to the hospital).

The invention may be embodied in yet another specific forms without departing from the spirit or essential characteristics thereof. For example, the current activated switch need not necessarily be a relay but could be a transistorized switch. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

What is claimed is:

1. An electronic instrument capable of being used in an environment having standby personnel and capable of functioning with both electrical inputs from, and electrical outputs to, a human being, said instrument having a connection to an external electrical power source, wherein the improvement comprises:

detecting means for detecting occurrence of inadvertent loss of said connection to said power source, said detecting means comprising a current activated switch arranged to open in response to power transfer to said instrument, and arranged to close in response to said loss;

alarm means responsive to the operation of said detecting means for communicating the resultant power loss to said standby personnel said alarm means comprising (1 ) a storage capacitor arranged to be charged near a predetermined voltage in response to normal operation of said instrument, and (2) primary discharge means including an alarm triggered by discharge of said voltage of said capacitor through said current operated switch for communicating said power loss; and,

secondary discharge means for unnoticably discharging said voltage of said capacitor in response to normal power turnoff of said instrument.

2. Alarm means as recited in claim 1 wherein said alarm is an audio alarm.

3. Alarm means as recited in claim 1 wherein said alarm is a visual alarm.

4. Alarm means as recited in claim 1 wherein said alarm is radio frequency transmitted and received.

5. Alarm means as recited in claim 1 wherein said alarm is a plurality of individual alarms, each being separately located.

6. Alarm means as recited in claim 5 wherein at least part of said plurality of individual alarms are remotely located.