GB2043966A - An interval timer - Google Patents

Abstract

An interval timer adapted for the repetitive timing of at least two, but preferably three, pre-set time intervals - typically of 15, 30 and 60 seconds. The timer includes an electronic circuit (Figure 3) adapted to produce distinct audible and/or visual alarm signals at the completion of each pre-set time interval following initiation of a timing cycle. The timer includes an electronic circuit (Fig. 3) operating on a digital basis having a first multivibrator (gates 30 and 31) feeding pulses to a ripple counter 37. Outputs for the required time intervals are taken from the counter to enable a multivibrator (gates 53 and 54) which drives an alarm output device 59. A reset switch 20 serves to reset the counter 37 and at the completion of a timing cycle, the multivibrator (gates 30 and 31) is rendered inoperative until the reset switch is depressed again. An alarm may be sounded or an LED flashed to warn of insufficient battery voltage. <IMAGE>

Description

SPECIFICATION An interval timer This invention relates to an interval timer, and in particular to a timer adapted for the repetitive timing of at least two particular, pre-set time intervals.

In the medical profession, and particularly in nursing, it is necessary frequently to monitor the pulse and respiration rates of a patient. This is done by counting the number of pulses or breathing cycles over a fixed period -- usually one minute - and then expressing the pulse or respiration rate as a number per minute. However, often the rates are observed for a period of time shorter than one minute, in which case the count must be multiplied up to obtain the required rateper-minute. For convenience, when monitoring the rate for a period shorter than one minute, the count is usually monitored for 15 seconds or 30 seconds and then multiplied respectively by 4 or by 2.For strict accuracy, the rates should of course be monitored for a full minute, but when a patient is making good progress, the rates need not be so accurately determined.

The time periods mentioned above are normally determined by using a conventional wrist or fob watch having a sweep second-hand. The use of such a watch means that the nurse must concentrate on the watch itself as well as on the patient the pulse or respiration rates of whom are being monitored. In a relatively dark situation, this can be extremely difficult and mistakes can easily be made. Digital watches are not recommended for it is even easier to mis-read a digital watch and moreover may require the operation of a switch to obtain a visible display.

Another operation which frequently has to be monitored by a nurse is an intravenous infusion drip rate. The drip rate normally has to be set to a particular number of drips per minute, and in order to do this a nurse has to concentrate on watching the drip itself, so as to count the number of drips that occur in a fixed time interval. Again, a watch with a sweep-second hand normally is used for this operation and this means that the nurse simultaneously has to watch both the sweepsecond hand and the drips from the infusion apparatus. This clearly is most difficult and errors frequently can occur; moreover, in dimly lit conditions such as in a ward at night, setting an infusion rate correctly can be exceptionally difficult.

It is a principal aim of this invention to provide apparatus allowing pulse, respiration and infusion rates accurately to be observed, without the observer having to concentrate on the timing thereof.

According to this invention, there is provided an interval timer for the repetitive timing of at least two particular pre-set time intervals, which timer comprises a portable housing in which is contained timing means pre-set to produce outputs at the ends of first and second particular time intervals following initiation of timing, starting means connected to the timing means for initiating timing of the intervals, and sound generating means adapted to produce a first distinct audible signal on receipt of an output from the timing means at the end of the first particular time interval and a second distinct audible signal on receipt of an output from the timing means at the end of the second particular time interval.

It will be appreciated that the interval timer of this invention is pre-set for the timing of at least two particular time intervals, to allow repetitive timing of those intervals upon initiation by the switch means. For instance, the timer could be pre-set for timing of intervals of 30 and 60 seconds, though the timer is preferably pre-set for the timing of three intervals, of respectively 15 seconds, 30 seconds and 60 seconds. At the end of each timed interval, the sound generator emits a distinct audible signal, so that an operator may clearly be informed of the expiry of each pre-set interval.Thus, when for example a pulse rate or a respiration rate is to be observed, the nurse, when ready to monitor the rate, simply operates the switch means to initiate the tinning and then counts the number of pulses or respirations until the timer emits the audible signal indicative of the expiry of the required interval; then, either the number counted is the true rate (if the pre-set interval is one minutes or the nurse multiplies the observed count by the necessary factor in order to obtain the required rate-per-minute.

The interval timer of this invention moreover finds especial advantages when setting intravenous infusion drip rates, because the nurse does not have simultaneously to observe the drip rate and the sweep second-hand of a watch.

Instead, because the timer emits a distinct audible signal at the end of each pre-set time interval, the nurse only has to watch the infusion apparatus to count the number of drips from initiation of timing until the timer emits the distinct audible signal indicative of the expiry of the required time intervals.

The timing means could be in the form of a spring-operated mechanical timing unit (i.e. a clockwork mechanism), but it is preferred for the timing means to comprise an electronic circuit, the housing then being adapted to contain an electric power source connectible to the circuit for powering the timer.

The audible signals emitted at the ends of the timing periods may be rendered distinct either by making the signals differ in pitch at the end of each pre-set period, or by making the signals of the same pitch but of an identifiable pattern. A further possibility, especially if several periods are to be timed, is to employ a combination of these two alternatives. However, in the case of a timer arranged to time intervals of 15, 30 and 60 seconds, it is preferred to employ a sound generator which emits a tone of a single frequency but identifiable by its duration or pattern. For example, at the expiry of 15 seconds a short single note could be given: at the expiry of 30 seconds a longer note but keyed on and off rapidly; and at the expiry of 60 seconds a long single note.

The starting means, in the case of an electronic timer, is preferably arranged as a re-set switch for the electronic circuit, to cause the circuit to re-set to the start of a timing cycle each time the switch means is operated, even if the timer has not completed a previous cycle. An ON/OFF switch could be provided, but if the circuit uses only CMOS active elements (as in the preferred arrangement described below), the quiescent current drain from the power source can be so low as to make such a switch unnecessary. If however such a switch is provided, it is preferred for the electronic circuit automatically to re-set on turning on that switch.

The electronic circuit for timing the pre-set interval may operate on an analogue or a digital basis. The preferred construction comprises a digital circuit in which a stable oscillator provides a pulse train to a divider, and selected outputs are taken from the divider dependent upon the intervals which are to be timed. The accuracy may be adjusted by trimming the oscillator, and the timed intervals pre-set by appropriate selection of outputs from the divider. A second oscillator preferably is provided to drive a sound generator, the second oscillator being enabled by the outputs from the divider. By combining the divider outputs appropriately, the second oscillator can be enabled for different periods, thus making the audible signals emitted by the generator distinctive for each timed period.

When employing a digital electronic circuit, it is preferred to use CMOS integrated circuits for the oscillators and the divider, in view of their very low power consumption and tolerance to supply voltage variations. With such circuits, the power source may be a dry-cell battery, the life of which will largely be determined by the type of sound generator employed, for the current consumption of such a device tends to be considerable.

However, the sound generator may take a variety of forms, but preferably is of small size so as not unduly to increase the housing size and moreover is highly efficient so as to reduce the consumption of electricity to the smallest possible value for a relatively high noise output. A Piezo-electric transducer has been found to be particularly suitable.

Other types of circuitry - for instance analogue circuits -- may require the use of a rechargeable power source. In either case, means may be arranged to sense the voltage of the power source and to provide an indication if the voltage falls below a minimum allowable value.

For example, a potential divider including a lightemitting diode can be provided across the power source to sense the voltage thereof. A switch may be arranged in series with the potential divider, so as to allow a battery test to be performed only when required. Another possibility is for the power source voltage to be sensed automatically each time the starting means is operated, and for an audible signal to be given if the power source voltage is sufficient properly to complete a timing cycle.

In addition to the audible signal provided by the timer of this invention, the timer may be arranged to provide a visible indication at the end of the required interval following the initiation of timing.

For example, a lamp or light-emitting diode may be illuminated briefly at the expiry of each timed interval, or a separate lamp or light-emitting diode, for instance of different colours, may be illuminated at the end of each timed interval.

Conveniently, a further switch is provided selectively to disable either the sound generator or the or each lamp, so that power is not wasted driving both output devices. Such a modification of the timer of this invention is of particular value when the timer is used in a ward at night; the end of a required timed interval can be discerned by observing the lamp, but patients are not disturbed by a sound output from the timer.

By way of example only, one specific embodiment of this invention will now be described, reference being made to the accompanying drawings, in which: Figure 1 is a perspective view of the interval timer of this invention; Figure 2 is a cross-section through the interval timer, taken on line Il-li marked on Figure 1; and Figure 3 is a circuit diagram of the interval timer shown in Figures 1 and 2.

Figures 1 and 2 show a completed interval timer of this invention, arranged to give distinct audible signals at 15 seconds, 30 seconds and 60 seconds following initiation of a timing cycle. The timer is constructed within a housing 10, of generally rectangular section and which is conveniently formed from a plastics material by an injection-moulding technique. The housing is divided into two compartments 11 and 12 by an internal wall 13, compartment 11 being adapted to contain a dry-cell battery (not shown), and compartment 13 containing an electronic circuit constructed on a printed circuit board 14. A battery connector 15 is disposed in compartment 11, to allow connection of a battery to the circuit board 14.The housing has a flap 16 hinged along edge 17, which flap 1 6 allows access to the battery compartment 11, whereby the dry-cell battery may be changed, when necessary.

The printed circuit board 14 carries various electronic components, such as a resistor 18, an integrated circuit 19, a switch 20, and a Piezoelectric crystal sound transducer 21, these various components being soldered to tracks provided on the lower side of the printed circuit board 14. The region of the housing 10 above the sound generator 21 is formed as a grille 22, through which sound may leave the housing 10 when the generator 21 is energized. At the end of the housing remote from the battery compartment 11, there is provided a panel 23 which is connected to the major part of the housing 10 by a wall section 24 of reduced thickness, so that the panel 23 may be depressed by applying external pressure thereto, inwardly of the housing, for instance by a finger.The switch 20 is disposed centrally beneath the panel 23, the switch having an operating button 24 upstanding therefrom to lie immediately beneath the panel 23. The switch is of the push-to-make single pole variety, and thus the switch contacts are normally open but will be closed when pressure is applied to the panel 23, as the push button 24 of the switch 20 is depressed.

Figure 3 shows the schematic circuit diagram for the electronic circuit constructed on the printed board 14. The circuit is constructed around three CMOS integrated circuits, the first being a package of four 2-input NAND-gates, the second being a package of four 2-input NOR-gates and the third being a fourteen stage ripple counter serving as a divider. Suitable type numbers for these CMOS integrated circuits are respectively 4011,4001 and 4020.

The electronic circuit comprises a first oscillator, made up from two NAND-gates 30 and 31, connected as a multivibrator with capacitors 32 and 33, resistors 34 and 35 and a pre-set variable resistor 36. The precise frequency of the oscillation can be trimmed by means of the pre-set variable resistor 36. The two inputs of the NORgate 30 are connected together, whereas one of the inputs to NOR-gate 31 is connected to the ripple counter, as will be described below, to inhibit operation of the oscillator at the completion of a timing cycle.

The ripple counter 37 has its pulse input CLK connected to the output of NOR-gate 30, and the re-set input RST is normally held low (i.e. to the supply common VDD) by a resistor 38. However, this input can be connected direct to the battery supply rail (V59) through switch 20, when operated by panel 23, to re-set the counter 37.

The counter is held re-set so long as switch 20 is depressed and will start to count input pulses only when the switch 20 is released allowing the re-set input RST to go low once more. Outputs A, B and C are the outputs of three of the available stages of counter 37, these three outputs being selected having regard to the frequency of oscillation of the oscillator such that following release of the re-set, output A briefly goes high at the expiry of 15 seconds, output B goes high for a longer time at the expiry of 30 seconds, and output C goes high for a yet longer time at the expiry of 60 seconds.

Output A will of course also go high at the expiry of 30 seconds, 45 seconds and 60 seconds, whereas outputs B will also go high at the expiry of 60 seconds.

When output A goes high, this is transferred through capacitor 39 to one input of NAND-gate 40, this input normally being held low by means of resistor 41. Provided that output B is still low which 1 5 seconds after the re-set is released it will be - the output from NAND-gate 42 is high, and consequently the output from NAND-gate 40 may go low for the duration of the high pulse at output A of the counter 37. In a similar way, when output B goes high, this is transferred through capacitor 43 to one input of NAND-gate 44, resistor 45 normally holding this input low. The other input of the NAND-gate 44 is connected to output D of the counter, which is the output of a stage which goes high every 0.058 seconds-and thus there is a pulse train at this output of about 17 Hz.Consequently, a pulse train at this frequency appears at the output of the NAND-gate 44 for the duration of the high pulse present at output B from the counter 37. Output C from counter 37 is coupled through a capacitor 45 to one input of NOR-gate 46, this input normally being held low by resistor 47. Thus, as soon as a high pulse appears at output C (at the expiry of 60 seconds) the output of the NOR-gate 46 goes low.

Output C is also connected to one input of NORgate 31, to inhibit operation of the associated multivibrator at the conclusion of a timing cycle of 60 seconds, when output C goes high.

The output of NOR-gate 46 will also go low on operation of the re-set switch 20, provided that the battery voltage V99 is sufficiently high to overcome the Zener voltage of Zener diode 48, connecting the second input of NOR-gate 46 to the re-set switch 20. Typically, for a supply voltage Vss of 9 volts, the Zener diode is selected to have a Zener voltage of 3 volts. Resistor 49 serves to maintain the second input of the NORgate 46 low, other than when the re-set switch 20 is operated. Signal diodes 50, 51 and 52 respectively connect the outputs of gates 40, 44 and 46 to one input of NOR-gate 53, connected along with another NAND-gate 54, resistor 55 and capacitor 56 as a multivibrator.Resistor 57 normally holds the one input of NOR-gate 53 high, to inhibit operation of the multivibrator; however, when the output of any one of gates 40, 44 or 46 go low, operation of the multivibrator is no longer inhibited and oscillation may commence, for as long as one of the gates 40, 44 or 46 has a low output. The multivibrator is arranged to oscillate in the audio band and its output is fed to a Piezoelectric sound transducer 59, so that the circuit emits an audible tone.

It will be appreciated that on operation of the re-set switch 20, the output of NOR-gate 46 goes low and the second multivibrator will oscillate for as long as the switch is held down. A sound emitted from the generator 59 serves as a battery check, for should the battery voltage Vss fall below two-times the Zener voltage of diode 48, no longer will a sound be emitted on the operation of the re-set switch 20. Upon release of the re-set switch 20, the counter 37 starts operating and a single short tone is emitted at the expiry of 15 seconds, when the output of the NAND-gate 40 goes low. At the expiry of 30 seconds, the output of NAND-gate 44 is keyed low at about 17 Hz, so that the sound transducer produces a distinct note keyed rapidly. Finally, at the expiry of 60 seconds, the output of NOR-gate 46 goes low, but for a longer period, and the sound transducer produces a relatively long continuous note. In addition, the high signal at output C of the counter 37 inhibits further operation of the first multivibrator, so that the counting of pulses ceases. However, even though output C remains high, resistor 47 gradually pulls the associated input of gate 46 low, by draining charge from the capacitor 45, until the output of gate 46 goes high again, turning off the audible tone. The timer remains in this state, drawing a very small quiescent current from the battery, until once more the circuit is reset by closing switch 20.

Claims (21)

1. An interval timer for the repetitive timing of at least two particular pre-set time intervals, which timer comprises a portable housing in which is contained timing means pre-set to produce outputs at the ends of first and second particular time intervals following initiation of timing, starting means connected to the timing means for initiating timing of the intervals, and sound generating means adapted to produce a first distinct audible signal on receipt of an output from the timing means at the end of the first particular time interval and a second distinct audible signal on receipt of an output from the timing means at the end of the second particular time interval.

2. An interval timer as claimed in claim 1, wherein the two particular pre-set time intervals are 30 and 60 seconds.

3. An interval timer as claimed in claim 1 or claim 2, wherein the timer is pre-set to time a third particular pre-set time interval.

4. An interval timer as claimed in claim 3, wherein the third particular pre-set time interval is 15 seconds.

5. An interval timer as claimed in any of the preceding claims, wherein the audible signals emitted at the ends of the particular timing periods are rendered distinct by being of different pitch.

6. An interval timer as claimed in any of claims 1 to 4, wherein the audible signals emitted at the ends of the particular timing periods are of the same pitch but rendered distinct by being of different durations.

7. An interval timer as claimed in claim 6, wherein at least one of the audible signals is keyed on and off at a pre-set rate.

8. An interval timer as claimed in any of claims 1 to 7, wherein the timing means comprises a spring-operated mechanical timing unit.

9. An interval timer as claimed in any of claims 1 to 7, wherein the timing means comprises an electronic circuit, the housing being adapted to contain an electric power source connectible to the circuit.

10. An interval timer as claimed in claim 9, wherein the starting means comprises an electrical switch connected to the electronic circuit.

11. A timer as claimed in claim 10, wherein the electrical switch is arranged as a re-set switch for the electronic timing circuit.

12. An interval timer as claimed in claim 11, wherein the re-set switch causes complete resetting of the electronic circuit to initiate a timing cycle each time the switch is operated, irrespective of the completion of a previous timing cycle.

13. A timer as claimed in any of claims 9 to 12, wherein the electronic circuit operates on a digital basis, there being an oscillator which provides a pulse train to a divider, and selected outputs are taken from the divider dependent upon the intervals which are to be timed.

14. A timer as claimed in claim 13, wherein the sound generating means comprises a second oscillator provided to drive an electrical sound generator, the second oscillator being enabled by the outputs from the divider.

15. A timer as claimed in claim 13 or claim 14, wherein the electronic circuit employs CMOS integrated circuits for the oscillators and the divider.

16. A timer as claimed in any of claims 9 to 15, wherein the sound generating means is in the form of a Piezo-electric transducer.

1 7. A timer as claimed in any of claims 9 to 16, wherein means are arranged to sense the voltage of a power source connected to the circuit and to provide an indication if the voltage falls below a minimum allowable value.

18. A timer as claimed in claim 17, wherein the sensing means is arranged to sense the voltage of the power source each time the electrical switch is operated, and to give an audible signal if the power source voltage is sufficient properly to complete a timing cycle.

19. A timer as claimed in any of claims 9 to 18, in combination with a power source in the form of a dry-cell battery connected to the electronic circuit.

20. A timer as claimed in any of the preceding claims wherein a visible indication is given at the end of the pre-set intervals following the initiation of timing.

21. A timer as claimed in claim 9 and substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.