US 3252623 A
Description (OCR text may contain errors)
May 24, 1966 T. H. coRBlN ETAL 3,252,623
APPARATUS FOR MONITORING DISPENSING OF LIQUID Filed July 22, 1965 3 Sheets-Sheet l NON- RESET DEACTIVATOR CONTRQL msPAmTY MANIFEST ons sHoT FLIP FLoP GATE on GATE ff Anorneys May 24, 1956 T. H. coRBlN ETAL 3,252,623
APPARATUS FOR MONITORING DISPENSING OF LIQUID F l' 2 INVENTOR.
g Thomas H. Corbin BY John E: Poulsen Attorneys May 24, 1965 T. H. CORBIN ETAL 3,252,623
APPRTUS FOR MONITORING DISPENSING 0F LIQUID Filed July 22, 1965 3 Sheets-Sheet 5 I I I I I I 56T ma r.. l l I I I l I I l I I l SOLENQID LBRIVER PUSH TO TEST L /1V402 GAK F l' 3 INVENTOR,
g Thomas H. Corbin BY John E. Poulsen Attorneys 3,252,523 APPARATUS Fon MoNIToniNG nrsPENsiNr; or LroUm vThomas H. Corbin, Palo Alto, and .lohn E. Poulsen,
Sunnyvale, Calif., assignors to C-F Liquidation Corporation, a corporation of California Filed July 22, 1965, Ser. No. 474,075
7 Claims. (Cl. 222-59) This invention is a continuation-inpart of our cepending application Serial No. 362,832, liled April 27, 1964, now Patent No. 3,197,068 of July 27, 1965, and relates to apparatus for controlled feeding and monitoring of drops of liquid or other material delivered in discrete increments. The apparatus is particularly useful in maintaining a close watch over intravenous feeding of drops of liquid material to humans.
In feeding liquids intravenously to patients it is particularly important in certain circumstances to guard against feeding the patient at a faster rate than intended. In certain instances it is believed that more harm can be done the patient by feeding too rapidly than might be done, for example, in certain emergencies where all feeding might be terminated.
Systems of the kind described must safeguard the patient from the hazards of system failure or malfunctioning. lt is a general object of the present invention to provide an improved scheme for monitoring the feeding of discrete increments of material wherein the hazards of equipment failure in the uid feeding of a patient are minimized.
lt is another object of the invention to provide a system for insuring against abnormally prolonged discrete deliveries of liquid as compared to a pre-determined safe duration thereof.
It is still another yobject of the invention to provide a drop feeding system which initiates and accurately controls the number of drops per minute of intravenous liquiddelivered to a patient, and which turns itself oftif the drop rate delivered to the patient is different from the drop rate desired or if the lluid delivery mechanism should remain activated unduly long.
It is yet another object to provide a system of the kind described whereby intravenous feeding of liquid is promptly terminated in case of various emergenciessuc-h as power failure, etc., so as to be relatively fail safe.
These and other objects of the invention will be more readily apparent from the following detailed description of a preferred embodiment when considered with the accompanying drawing in which,
FIGURE t is a schematic and block diagram of a material feeding and monitoring system according to the invention; and
FIGURES 2 and 3 considered together, provide a schematic circuit digram of an operating embodiment according to the invention, including values and specifications of circuit components thereof.
The system herein as described in detail further below pertains to apparatus for delivering a series of drops of liquid. Broadly, the system comprises means defining a selected drop rate and ow control means which provides delivery of the drops responsive to the selected drop rate. The fiow control means is arranged to be operable between active and inactive states so as to respectively deliver or arrest liquid which is being delivered. In order to provide a virtually fail safe operation of the system .and to safeguard against abnormal activation of the flow control means for unduly prolonged periods, the system herein further entails means for sensing initiation of the active state of the flow control means so that after a pre-determined period of elapsed time, the
flow control means shall be de-activated in a manner requiring manual re-setting of the circuit.
As will be apparent from the description below, the system includes -means normally operative to de-activate the flow control means well before such time. In this manner, the system will normally operate the flow control means in a manner whereby Ait alternates between active .and inactive states. Whenever it remains in its active state too long for safe operation it will be positively rendered inactive so as to safeguard against the hazards of remaining in its delivery condition too long.
Thus, in short, the iluid feeding means is operable between iluid delivering and fluid impeding conditions, under the control of an elapsed time detector which monitors the lluid delivering condition and compares the elapsed duration thereof with a pre-determined period considered safe.
The system as described generally above utilizes electromechanical valve means such as a solenoid controlled plunger arranged to be operable when energized so as to deliver a drop of liquid and when de-energized to arrest delivery. .The means for normally alternately energizing and de-energizing the solenoid so as to deliver a series of drops at a selected drop rate wherein the solenoid remain normally energized for successive periods is preferably arranged as now to be described.
Generally, there is provided means deiining a selected drop rate and means serving to sense each delivered drop so as to define the actual drop rate. Means are further provided which serve to detect disparity between the actual and selected rates and inactivate the valve means gn response thereto in order to arrest further delivery of uid.
More particularly a first pulse generator is arranged which serves to provide a series of pulses at a selected rate corresponding to the rate of delivery of drops of liquid intended to be achieved. A second pulse generator is arranged to sense each drop of liquid which is delivered. The second pulse generator serves to :generate a pulse in response to sensing each drop.
A pair of bi-stable switch means such as conventional dip-dop devices are each coupled to respond to the pulses generated by both the first and second pulse generators. Each bi-stable switch means is, therefore, alternately driven between its two stable states by alternately receiving a pulse respectively from the first and the second pulse generators thereby maintaining an in-phase relationship. However, if this alternating application of pulses to both switching means is interrupted to cause successive application of pulses from either of the pulse generators to the two switching means this change is detected. Means are provided which serve to sense a change in the predetermined phase relationship of the bi-stable devices and to condition the valve so as to terminate delivery of liquid. The existence of a change in the phase relationship ofthe operation of the two switching means is thereby registered.
Referring in detail to the schematic diagram shown in FIGURE l there is provided feed-ing means 10 servicing to feed a series of discrete drops of liquid 11 from a container 12 into the arm of a patient receiving intravenous feeding. Feeding means 10 as schematically shown includes a suitable drop forming outlet 14 disposed to deliver drops from container 12 to a splash chamber 13. An attachable drop sensor assembly includes a light source 15 which directs a beam of light through an aper ture 16, and splash chamber 13, to be sensed by a photo responsive device 17. Device 17 serves to generate a signal on line 18 whenever the beam is interrupted by the presence of a drop as at 19. Drops 19 travel along a tube 21 for delivery into the arm of a patient.
Means are provided to control delivery of drops through tube 21. Thus, a valve member 24, operable in one condition to pass a drop of the liquid and operable in another condition to arrest delivery of drops through tube 21 is provided. A solenoid 25 is arranged whereby when it is energized member 24 will be withdrawn against the urging of spring 26. De-energizing solenoid 25 serves to permit spring 26 to cause member 24 to pinch tube 21. Tube 21 is pinched between the free end of member 24 and a fixed portion 27 of solenoid assembly.
From the foregoing it will be evident that the actual drop rate of liquid being dispensed is sensed by photocell 17. Photocell 17, therefore, serves to function as an impulse generator which provides an impulse corresponding to each drop to be dispensed.
There is also provided another impulse generator which serves to define the desired or selected drop rate for liquid to be fed to a particular patient. Thus, a drop rate generator 31 is provided in the form of a suitable pulse generator which provides a series of output pulses corresponding to the selected drop rate to be established. The frequency of these pulses can vary over a wide range, for example, from to 150 drops per minute or the like and such a pulse generator can readily be provided by conventional means, such as by certain relaxation oscillators or the like.
In order to monitor and detect disparity between the actual drop rate and the desired drop rate there is provided a bistable switch means such Ias the main drive ip-op 32. Flip-flop 32 is of conventional known design. Thus, it will be understood that flip-flop 32 includes a lirst input to be applied along'line 33 to set the lijpflop and a second input to be applied on line 34 to reset the flip-Hop. As known, a flip-flop has two stable states and these are indicated by the relative voltage level appearing on the two output channels 35, 36.
A second bi-stable switch means such as the alarm flipflop 37 is arranged similarly to the main drive flip-flop 32 except that there is provided only a single input 38. Input 38 is arranged to receive the output pulses from drop rate generator 31 via line 39 and the OR gate 41 of conventional construction, which is arranged to pass a signal on either of two inputs 39, 42. Alarm flip-flop 37 having but a'single input is a complementary flipflop of conventional construction whereby each succeeding pulse received on input 38 serves to switch the state thereof from one stable condition to the other. vThe condition of flip-flop 37 is indicated by the voltage level or other suitable signal on each of two output channels 43, 44.
Means are provided whereby the drop rate generator 31, serves to dispense a drop of liquid to the patent. Thus, a's a pulse appears at the output line 33 from drop rate generator 31, flip-hop 32 sets output channel 35 in its relatively high level potential. Channel 35, when high, operates a solenoid driver circuit 45 which feeds a pulse on line 46 to energize solenoid 25 subject to control of an alarm disconnect relay circuit 37. When solenoid 25 is energized, member 24 is withdrawn per- -mitting a drop to be dispensed.
The formation of a drop as sensed by photocell 17 provides a signal which is filtered and amplilied by a conventional amplifier unit 49. This sensing signal serves to reset flip-flop 32 by developing a long pulse on input 34.
The signal from the photo-responsive device 17 is gated via a 150 millisecond monostable one-shot multivibrator 51 in order to prevent noise or extra signals from reaching flip-flop 32 and alarm flip-flop 37 for an elongated period, for example, on the order of 150v milliseconds after the drop occurs, thereby preventing false alarms. Multivibrator 51 can be of any suitable known construction whereby two operating states can be established. One state is a stable state while the other is unstable and after being established will revert, after a predetermined period to the stable state. The output of multivibrator 51 appears simultaneously on leads 34 and 42.
From the foregoing it will be readily apparent that a predetermined phase relationship is established between `the bistable state of flip-llop 32 and the bi-stable state 4of alarm flip-Hop 37, and that by alternately energizing solenoid 25, a series of drops will be dispensed.
In operation, as drop rate generator 31 provides an input pulse simultaneously to both dip-flops 32 and 37, one stable state of each will be established. At the same time adrop will be dispensed. Thereafter, formation of each drop will cause a pulse to be generated whereby flip flop 32 and flip-flop 37 change from their preceding state to their other stable state. So long as the pulse repetition frequency lof drop rate generator 31 remains matched with the actual drop formati-on rate, flip-flop 32 will remain in its predetermined phase relation with respect to flip-flop 37.
However, means are provided to sense a change in the phase relationship and to cause the valve means to terminate the feeding of liquid.
Accordingly, a rst and second AND gate have been provided, each being coupled to .both hip-flops 32, 37. Flip-flop 32 and flip-dop 37 are each arranged whereby they can operate in-phase with each other. Thus, the high output from flip-flop 32 switches Ibetween lines 35 and 36 whereby it appears yon line 315 at a time when line 43 is high and neither AND gate receives coincident application of the high states. On the other hand. when line 36 is high from the reset pulse to liip-iiop 32, line 44 will also be high. y
The rst and second AND gates are designated and shown as a low rate alarm AND gate 52 and as a high rate alarm AND gate 53. Gate 52 is fed by channels 36, 43. Gate 53 is fed by channels 35, 44. The AND gates `52, `53 'are of a known style whereby coincident application of two relatively high voltage state signals is required to produce an output signal. It is to be noted that while flip-flops 32, 37 are operatively coupled so as to alternate in-phase between one stable state and the other they are coupled out `of phase to AND gates `52, 53. Thus, normally only one high voltage state signal will be applied to each of the Itwo AND gates 52, 53.
However, whenever lboth inputs to one or the other of the AND gates 52, 53 are high, then a disparity manifest circuit v54 receives a signal via OR gate 55 from lone or the other of gates 52, 53 to provide a signal on line `55. This signal conditions (de-energizes) circuit 47 to prevent solenoid 25 from being energized and thereby precludes further delivery of `liquid through tube 21. Circuit =54 comprises a flip-flop whereby manu-al open-circuiting of a control electrode thereof serves to reset the circuit as described below.
Thus, the high outputs from gates '52,A 53 are fed to circuit 54 via a conventional OR gate 56 of the type adapted to pass either of two input signals. Assuming Ithat the actual drop rate is low it will tbe evident that the drop rate generator 31 will provide two successive pulses on outputs 39 and 33 before an actual drop impulse is received .by either flip-flop 32 or 37. The output of drop rate generator 31 on line 33 will =be ineffective to switch flip-flop 32 inasmuch as the latter switches from one state to the other dependent upon the application of pulses alternately to the inputs 33, 34 respectively. On the other hand, flip-Hop 37 has ibut a single input 38 and in response to two successive pulses will change its stable state whereby the high state signal on output channels 43, 44 will switch from one to the other. Thus, the high state signal of one lliip-flop is switched whereas on the other, it is not. In this condition coincident existence of two high voltage signals will occur at AND gate 53.
lf the actual drop rate is higher than the desired rate two successive impulses -will appear on lines 34, 42 prior to generation of `an impulse on lines 39, 33. Successive pulses applied to line 34, however, willk not cause a transfer of the high state from `line 35 to line 36 for flip-flop 32, whereas successive pulses on line 42 will cause such a transfer from line 43 to 44. Thus, coincident existence of the high state signals will occur at AND gate 52. Accordingly, in either event circuit 54 is conditioned so as to deactivate the vaive means and terminate delivery of liquid.
After arresting the feeding of liquid through tube 2:1, as caused- .by any rate disparity, the system is reset to reestablish a proper in-phase relation between flip-flops 32, 37 and to reset circuit 54.
Thus, the reset switch 59, when turned off operates a reset circuit 62 via lines 51, `63. Circuit 62 includes a pair of output leads 64, 65 coupled to respectively reset the alarm ilipdlop 37 and the main drive dip-dop' 32.
Having in mind the foregoing system operation which serves to alternately energize and de energize the electromechanical uid feeding means, the safety release portion of the system can be initially described briefly .by reference to FIGURE 1 1before proceeding with a more d etailed description further below.
The safety release means which has been provided serves to sense unduly prolonged activation of the fluid delivery means whereby in response to such sensing the fluid delivery means is electrically de-coupled from the system. The de-coupling occurs at the solenoid 25 so as to insure against malfunctioning of the system which conceivably could retain solenoid 25 iu its energized state. Thus, a safety release relay circuit Sti is coupled by a line 82 to a junction point S4 in line 46 so as to sense activation of driver circut 45. So long as the driver circuit remains activated, an elapsed time detector or timer 86 continues to run. After a predetermined period of continuous energizaton of solenoid coil 25, timer y85 serves to operate a de-activator ycontrol circuit 88 which 4fires and energizes relay 89.
As now to be described, this action serves to de-eneri gize the valve control solenoid 25. Thus, relay 89 controls contact points 91 and 92. As will be recalled, disparity manifest circuit S4 is arranged whereby relay 74 will ordinarily be energized so as to maintain the switch 71 closed until such time as any out-of-phase relationship appears. At such time -as the selected drop rate and the actual drop rate show a disparity in their phase relation, relay 74 becomes de-energized to permit spring 93 to open line 46.
Switch 71 is also opened whenever relay 89 is energized since such action serves to open the contact points 92 through which relay 74 must `be energized. Relay 89, when energized, also opens contact points 91 so as to deenergize solenoid 25 at a point immediately electrically adjacent same. While this action would normally be expected to de-activate solenoid 25, in the event that contact points 91 should happen somehow to .become welded in closed position, the opening of contact points 92 would serve to disable relay 74 so as to insure deactivation of solenoid 25.
The elapsed time detector or timer 86, in general, includes a condenser 95 for graduaily forming a predetermined control signal during energization of the solenoid 25. Condenser 95 is gradually charged via line 82 through a rst circuit including resistances 95, `97, the other side of condenser 95 being connecte-d to supply voltage via line 98, junction point 99, lead 1M, contact points 91, and le-ads 162, 163, 104. Thus, the foregoing circuit serves to gradually charge condenser 95 immediately upon operation of solenoid driver 45, as will be described further ibelow, so as to cause a comparison to be made between the elapsed period of solenoid` energization and a predetermined period defined by the changing time of condenser 95.
A second circuit is provided which serves to remove the accumulated charge on condenser 95 at a time rate substantially greater than the time rate of forming the accumulated charge therein. Thus, resistance 105 and diode 107 are arranged in parallel with the circuit which included resistances 96, 97 whereby upon discharge of condenser the parallel -circuit so formed will quickly dissipate the accumulated charge and thereby reset the elapsed time generator circuit 86. Diode 107 is poled whereby during charging of condenser 95 the branch of the parallel circuit including resistance is bypassed.
FIGURES 2 and 3 when taken together provide a preferred operable embodiment of the system when taken with the component values and designa-tions shown on the drawing.
For ease in correlating the system taught in FIGURE l to the schematic circuit diagram of FIGURES 2 and 3 phantom lines have been used which somewhat generally enclose the elements thereof in the latter and have been given corresponding reference numerals.
Thus, the ampliiier and filter circuit 49 is comprised of an RC coupled transistor fed from the photoresponsive device 17.V The one-shot mono-stable multivibrator 51 includes a pair of transistors of opposite conductivity type wherein the emitter of one Iincludes a pair of `diodes poled in a common direction.
-Main drive dip-flop 32 includes two transistors wherein the collector of one is fed back to the base electrode of the other. Separate input signals are received 4to set and reset the device as in the well known Eccles-Jordan trigger. Thus, flip-flop 32 is diode coupled to receive, and be reset by, pulses or step functions via line 34 dening the actual drop rate. Flip-flop 62 is set by pulses or step functions on line 33 which indicate the desired drop rate developed by pulse generator 31.
Pulse generator 31 includes a unij-unction transistor wherein the control electrode is coupled to a junction between a series of three resistors and a relatively large capacitance formed by a pair of parallel condensers which serve to establish the pulse rate when the resistors are varied.
OR gate 41 includes a conventional arrangement ofthe two diodes shown wherein a signal on either line 39 or 42 will 4be fed out on -line 3S from the junction between the diodes. The alarm flip-flop 37 is a conventional complementary flip-dop wherein a single input receives a succession of signals. Each signal received serves to switch 'the device from one stable state to the other. Thus, since signals .are passed to flip-flop 37 via OR gate 41 from either the desired or actual pulse rate generator circuits without ability to distinguish one from the other, its state can be compared with the state of flipdiop 32 by means of AND gates 52, 53.
A-ND gates 52, 53 each include a pair of diodes arranged as is well Iknown.
Relay driver circuit 54 includes a tiip-op circuit employing a pair of transistors. The output from circuit 54, when disparity in the phase relation between Bipdilops 32 and 37 has been sensed, serves to de-energize a normally energized relay coil 74 in circuit '47. When the coil ='74 is tie-energized an armature 71 is sprin-g-transferred by spring 93 to open-circuit the solenoid coil 25 of the valve operating solenoid.
Circuit 62 includes the two diodes poled in a normally non-conducting direction and passes a transient reset pulse from the condenser 60 upon initially plugging in the system to apply a reset function to the base (control) elcc A trodes of one side of each hip-ilop 32, 37.
Circuit 45 4is Zener diode coupled by diode 72 to iipop 32 and includes a conventional two stage transistor amplifier circuit with the collector of the second stage directly coupled to solenoid coil 25 via leads 46, 48 and armature 71.
A manually operated switch 73, when positioned to the off position serves to de-energize the holding coil 74. Another position of switch 73 serves tovpermit pulse generator 31 to start dispensing drops while the system becomes adjusted, before implementing the drop arresting control portion of the circuit.
System opera-tion of the safety rele-ase is as follows.
As noted above, condenser 95 is connected :to supply voltage (V) via line v98 land leads 101, contact points 91, and leads 102, 103, 104. When solenoid driver transist-or 108 is driven into conduction i-ts collector 109 will go virtually to ground on line 110. The lead 46 from its collector will accordingly be virtually at ground as will be junction point 84. The -ground potential at junction point 84 serves to commence application of a charge to condenser 95 since the other side of condenser 95 is connected to ground. The ground potential of point 84 is further applied via the closed switch'larmature 71 of relay 74 which is then being Iheld closed whereby supply voltage (-V) is applied across the coil of solenoid 25. The other side of coil 25 is connected to supply voltage V) via line 111 to junction point 99 and thence via leads 101, contactpoints 91, and leads 4102, 103, 104.
As was 'mentioned switch relay armature 71 is held closed by the energized coil 74 operated by a circuit traced as follows. Lead 104 carries supply voltage (-V) to one side of coil 74. The other side of coil 74 is connected by a lead 55 -through a resistance 112 and lead 113 to contact points 92 and thence by line 114 to its relay driver Itransistor 116. (It can be noted ,at this point that any disparity signal via line 117 is -fed to .the disparity mani- !fest circuit 54 via manual switch armature 713 when positioned to its run position. Accordingly, the disparity signal on line 117 is connected so as to switch the disparity manifest circuit 54 oi whereupon coil 74 would become de-energized.)
During the .time that junction point 84 is held virtually at ground potential, condenser 95 will be charging. In the event that solenoid driver 45 is not turned off before condenser 9'5 acquires a predetermined charge then, in such event, as the charge on condenser 95 approaches the voltage on the emitter of transistor 11'5, transistor 115 will be switched on thereby switching on transistor 1118-.
When transistor 118 is driven into conduction, emitter 119 thereof will be carried substantially at ground potential via line 110. Accordingly, ground potential will be seen at one side of relay `89 Whereas the other side of relay y89 will be carried at a potential between ground and supply (-V) via resistance 121 and lead 122. Therefore, when the control circuit y88 lires, relay 89 is energized and opens contact points `91, 92 thereby opening the circuit at a point electrically immediately adjacent rthe solenoid (contact points 91) fand also disabling the disparity manifest output capability via line (Contact points 92).
It is to be appreciated that in the normal circumstance in the foregoing system, solenoid 25 will be de-energized prior to such .time as condenser 95 acquires suflicient charge to ire circuit 88. In such event, condenser 95 is discharged quickly through the parallel circuit formed in one branch by resistances 96, 97 and inthe other branch by resistance 105 and diode 107.
A circuit with the component values and voltages shown was constructed and operated.
Thus, there is provided an improved system for the controlled feeding and monitoring of drops of liquid. Drops are fed at a rate established by an impulse generator whereby an intended selected rate can be established. yIf the rate sought varies from .the actual rate, the system manifests this disparity by a visual signal and shuts itself off. The system is relatively fail safe, since if power fails, the intravenous feeding tube will be im'- mediately pinched closed. Furthermore, the voltage level sensing means provided by elapsed time generator circuit 86 is not responsive to electrical noise and other interference but serves to shut down feeding in the event that the fluid feeding line 21 remains open abnormally long.
1. In apparatus for delivering a series of drops of liquid, means defining a selected drop rate, ow control means controlling delivery of the drops responsive to the first named means, the latter named means being operable between active and inactive states to respectively deliver or arrest liquid being delivered, means responsively coupled to sensed initiation of said active state for deactivating said ow control means after a predetermined period of elapsed time from said initiation, and means normally operative to de-activate said flow control means within said period, whereby the penultimate named means serves to safeguard against unduly prolonged activation of the flow control means in the event of malfunctioning by the last named means.
2. In apparatus for delivering a series of drops of liquid, electromechanical means operable when energized to deliver a drop of the liquid and operable when deenergized to arrest delivery of a drop of the liquid, means for normally alternately energizing and de-energizing said electromechanical means to deliver a series of drops at a selected rate wherein the electromechanical means remain normally energized for successive periods, and means responsive to energization of said electromechanical means for de-energizing said electromechanical means after a predetermined period of continuous energization thereofsubstantially exceeding the duration of the rst named periods to safeguard against abnormally prolonged energization of said electromechanical means.
3. In apparatus for delivering a series of drops of liquid', electromechanical means operable when energized to deliver a drop of the liquid and operable when deenergized to arrest delivery of a drop of the liquid, means for normally alternately energizing and de-energizing said electromechanical means to deliver a series of drops at a selected rate wherein the electromechanical means remains normally energized for successive periods, and timer means for sensing initiation of energization of said electromechanical means and for gradually forming a control signal of predetermined duration, rst electrically controlled switch means controlling said electromechanical means and normally energized to energize said electromechanical means, second electrically controlled switch means normally de-energized to both energize said electromechanical means and said first switch means, and
. de-activator means responsive to said timer means to receive said signal and energize said second switch means thereby de-energizing said electromechanical means.
4. Apparatus according to claim 3` wherein one of said switch means is disposed immediately electrically adjacent said electromechanical means.
5. `In apparatus for delivering a series of drops of liquid, electromechanical means operable when energized to deliver a drop of the liquid and operable when deenergized to arrest -delivery of a drop of the liquid, means for normally alternately energizing and de-energizing said electromechanical means to deliver a series of drops at a selected rate wherein the electromechanical means is normally energized for successive periods, and safety release means comprising first circuit means for gradually forming a predetermined control signal responsive to energization of said electromechanical means and second circuit means responsive to normal de-energization of said electromechanical means for removing said signal to await re-initiation thereof via said rst circuit means, said second circuit means serving to remove said signal at a time rate substantially greater than the time rate forming said signal via said first circuit means, and means responsive to said signal to de-energize said electromechanical means thereby de-activating same.
6. In apparatus for delivering a series of drops of liquid, fluid feeding means operable between uid delivering and uid impeding conditions, elapsed time detector means operatively coupled to said feeding means to re- .spend to establishment of said delivering condition and initiate a predetermined period of time representing a maximum limit for the continuous establishment of said delivery condition, means operatively coupled to said uid feeding means and said elapsed time detector means for comparing the elapsed duration of said iiuid delivering condition With said predetermined period, and deactivating means operatively responsive to said comparing means to switch said feeding means to said iuid impeding condition whenever said elapsed duration equals said predetermined period.
7,'Apparatus as dened in claim 6 further including itl) means operatively responsive to said comparing means for resetting said elapsed time detector means upon establishment or" said Huid impeding condition prior to eX- piration of said predetermined period.
References Cited by the Examiner UNITED STATES PATENTS 2,672,581 3/1954 Gorham 222-55 X- 2,882,937 4/ 1959 Kay 222-55 X 10 2,936,096 5/ 1960 Shawhan 222-76 X RAPHAEL M. LUPO, Primary Examiner.