GB2199405A - Drop rate sensor - Google Patents

Abstract

A drop rate sensor, e.g. for medical infusion apparatus, comprises an infra-red emitter L1 and receiver L2 which normally receives radiation from the emitter but which receives no radiation as a drop passes. The receiver is in use coupled to integrated circuitry which measures the time interval between successive drops. If this is too long, indicating deletion of the liquid in the bottle A or indicating that an infusion needle has slipped out of a patients' vein, then an alarm buzzer is activated. <IMAGE>

Description

AN INSTILLATION SAFETY DEVICE This invention relates to an instillation safety device.

Instillation is done widely in modern hospitals.

Since the time of instillation varies with the physical make-up of patient, a doctor or nurse hardly knows when the liquid medicine in the drop bottle will be exhausted and when a new bottle of liquid medicine must be replaced.

So the patient or his/her attendent must pay attention to it without negligence. If the empty bottle is not replaced on time, the blood will flow into the plastic hose and condense therein. The instillation can not go on unless a new hose is used. It would be more troublesome if the condensed blood flows-back in the vein.

For this reason, the inventor studied hard and developed the instillation safety device of this invention.

With an infrared emitter and receiver and by the reflection and refraction of infrared ray as a drop of liquid medicine passes, the device can tell when the bottle of liquid medicine is exhausted or when the needle slips out of the vein.

BRIEF DESCRIPTION OF THE DRAWING 1. Fig. I is a sectional view of the instillation safety device of this invention.

2. Fig. 2 is a sectional view of the light censor of the said device.

3. Fig. 3 is a diagram of the control circuit of the said device.

4. Fig. 4 illustrares the infrared refraction of the said device.

DETAILED DESCRIPTION Referring now to the drawings, the nature of this invention is described as follows: As shown in Fig. 1, the instillation safety device of this invention comprises a drop bottle A, a connector B, a burette C, and infrared emitter L1 and an infrared receiver L2.

The connector B consists of a body 1, two passages 2, 3 and a ball valve 4. When the pressure in the passage 2 is one atmosphere, the pressure in the passage 3 should be one atmosphere, too. When the liquid medicine is fed slowly from the burette C through the conduit and needle into the vein, the pressure in the burette C reduces gradully and the liquid medicine in the drop bottle A flows through the passage 3 to the outlet 6 and drops into the burette C. With liquid medicine dropping into the burette C, the pressure in the burette C increases gradually. As the pressure in the burette C becomes equal to that in the drop bottle A, the liquid medicine stops dropping.As the pressure in the bottle A, the liquid medicine outflow of liquid medicine to lower level than one atmosphere, the air flows through the ball valve 4 and passage 2 into the bottle A to balance the pressure inside and outside the bottle A. Under this principle, the liquid medicine is put into the vein drop by drop. The speed of instillation can be regulated with the flow regulator installed on the tube G (not shown).

As shown in Fig. 3, the pins 9, 10, 11 of IC1 are connected with capactor C B and resistors R1, R2 respectively to form an oscillatory circuit N1. Where the resistor R #l0R and the frequency of oscillation fl 2 1 2.2xRlxCB ~ If the preset frequency of IC1 is f2, the ratio of the two frequencies is time T, then, T(sec)= f . Where f is a constant and T is in inverse 2 proportion to fl, i.e. the inverse proportion to the product of CB by Rl. So the desired time can be obtained by an appropriate selected resistor R1 and capacitor CB.

When the drop passes, the infrared ray in chopped and the transistor Q1 (equal to receiver L2) is off. The pole C.E is not on and the transistor Q2 is off, too. So the voltage V12 of the pin 12 of IC1 is in high level. On the contrary, when no drop passes, the infrared ray is received by infrared receiver L2. The transistor Q1 changes to "ON" and the current flows from the pole E to the pole B of the transistor Q2 and makes the transistor Q2 "ON" and voltage V12 of the pin 12 of ICl is in zero level. A fixed frequency f2 of ICl is set as said above.

When V12=0, the frequency of oscillation of the oscillatory circuit N1 enters IC1 and is accumulated by IC1. The value of accumulation fe fc is compared with f2 immediately. If f = c f the voltage V1 of the pin l of ICl will change from zero level to high level and the current flows to the pin 13 of IC2 to activate the buzzer F to buzz. In case of both, the fJf2 and the voltage V12 changes from low level to high# level, IC1 will reset f=O automatically. Then, the accumulation f will start again from zero when the C voltage V12 changes from high level to low level and the accumulation f begins with 0.So as long as the time c f2 interval between two drops is smaller than T= fl , the buzzer will not operate. On the contrary, if no drop Since the pressure in the vein is stable before the liquid medicine in the drop bottle A is exhausted, the time intervals between every two drops are virtually almost equal. The time interval can be adjusted with the flow regulator. It always fall into the range from 1 to 2 seconds depending on the age of the patient and the nature of the liquid medicine being used. So, a time interval of 2 to 4 seconds of timer will be suitable to find whether the drop bottle A is emptied.In case the needle slips out of the vein and is left beneath the skin the higher pressure under the skin than that in the vein, will result in longer time interval between two drops than the preset time period of the timer IC, and the timer IC will activate the buzzer to raise an alarm.

As shown in Fig. 1 and Fig. 2, both the infrared emitter and receiver have a small hole H. The small hole H of the infrared emitter is the only way for the infrared ray to emit straightly ahead and the small hole H of the infrared receiver is the only way to receive the straight infrared ray from the emitter. Refracted infrared rays will not be received no matter what direction of the refraction is.

While light entering from one media to another, refraction occurs if mediums are of different density. In this invention, the infrared ray is refracted when it enters the liquid from the air. So the receiver L2 receives no infrared ray and changes from "ON" to "OFF" (See Fig. 3, L1 and L2). Contrarily, after the liquid has passed the part in burette C, where the infrared emitter L1 an receiver L2 are installed, there is no liquid between L1 and L2, then, the infrared receiver L2 changes from "OFF" to "ON".

passes during the time T, the buzzer F will buzz to call for peoples attention.

The current delivering from the pin 1 of ICl must meet both requirements: the voltage V12 is in low level and fc=~2. But since the change of voltage V12 c 2 depends on the pass of drop, the buzzer F will buzz once only and will stop buzzing as the next drop passes, if there is no auxiliary device. To eliminate this disadvantage the pin 9 of IC1 is connected to the pole C of the transistor Q3 and the pole E is earthed so that the current from the pin 1 will enter the pin 13 of IC2 fo activate the buzzer and simultaneously put one the transistor Q3 to make the pin 9 in low level to keep the buzzer F operating until some on puts off the circuit.

The transistor Q4 is provided for the same purpose to prevent the current from the pin 1 from being interrupted.

Besides, when the current from the pin 1 of ICl flows through the pin 13 of 1C2 and the pin 11 to activate the transistor Q5, the buzzer F will begin to operate. Other circuits of IC2 are designed to make a variable rhythmic tone for pleasant only. So no futher description is needed to make here.

A light censor is provided in this invention.

Below is a description on how it works.

As mentioned above, refraction causes a light beam to bend as the beam passes from one medium into another and the relationship between the incidence and refraction is elucidated by the Snell's Law. As shown in Fig. 2 the media inside and outside the circle 0 are of different density. A moving point P revolves clockwise along the circumference of the circle 0. The incidence 1 meets the point P on the circumference. The interface direction of the point P is represented by the tangent F1-F2, and the normal by OP. Then the relationship between the angle of refraction #2 and the angle of incidence #1 can be formulated as follows: Sin #l = N2 N2Sin H2 (1) The incidence goes into straightly in the circle 0 and passes the second interface C.The interface direction of the point C is represented by the tangent F3 F4, and the normal by OC. Since OC=OP, the angle of incidence #3=#2 After passing the point C, the beam enters the medium where the density same as before the point P. Sc #5+#4=#1 Then the beam goes straightly to the point R', evidently the infrared can not be located by the receiver which takes place at R.

To simplify the calculation; Supposing that POA= 450, the index of refraction of air Nl=l (an approximate value of 1.0003), and the approximate value of the liquid drop=1.33, the outcome is: 81 450 02=32.10 03=32.1 04=19.2 0#=25 .80 06=45 -32.1 =12.9 Supposing OP=2.5mm, and PH=2.5 Cos 32.10=2.12 PC = 2r Cos #2 = 2x 2.5 Cos 32.10 =4.24 PD = PC Cos #6 =4.24 Cos 12.90 =4.13 6 CD = PC Sin 6 = 4.24 Sin 12.90 =0.95mm.

the outcome is: ER =CD =0.95mm.

CE = DR =HPx + PH - PD = 7 + 2.12 - 4.13 =4.99 R'E =CE tan #5 = 4.99 tan 25.80=2.4mm.

So RR' = ER + ER' = 0.95 + 2.4 = 3.35mm.

Since the drop is spherical, the locus of refraction of the infrared ray from the point 5 through the drop to the surface of the receiver is a circle with R as its center and RR' (3.35mm) as its radius. But the receiving area is within a radius of 0.75mm. Therefore, the receiver receives no infrared ray from the emitter.

For an instantaneous- time, when the point A of the falling drop passes IR, the infrared beam is fully reflected. As the drop goes on passing through, the full reflection chances clockwise to refraction. At the very moment when the point K of the falling drop passes IR, the infrared beam radiates without refraction straightly and can be received by the receiver. When Point K passing through IR, it will be the only chance for the receiver to receive a straight radiated infrared beam in the whole route of the drop passes. But as soon as point K has passed over, the infrared beam bends downward. As point P moves clockwise and near the point G, the refraction changes rapidly to full reflection again.

In other words at the moment when the drop passes, the trial of refraction printed on the receiving plain is a circle with variable radius. It varies from infinitive to zero and continuously from zero to infinitive. So the receiver had two times to receive no infrared ray.

Since the initial speed of drop begins at Q, the closer the infrared device is to the drop outlet, the longer the drop passes the infrared beam area. This is why the infrared emitter and receiver must be installed as close as possible to the drop outlet.

The diameter of the infrared emitter and rece#iver is 3mm so the maximum size of the case of the light censor is 40mm x 30mm x lOmm as shown in Fig. 2. The infrared censor is made of light plastics which caved a groove with 2.5mum in deep to accommodate the electric wires. The volume is less than 5.6cm3 and the total weight is less than lOgm.

As shown in Fig. 2, the censor has an elliptic hole 20 x 14mm in the center, and a split opening K at the end of the elliptic hole. The censor can be connected with burette between the size of 16-18mma. By pressing hose G through split opening K into the elliptic hole, then the censor can be pushed up until it firmly holds the burette. The wall of the burette is lmm thick and is elastic. With its expansibility, the censor can be fitted firmly on the burette without need of any retainer.

Claims (6)

CLAIM:

1. An instillation safety device comprising warning means, integrated circuit means, a burette, an infrared emitter and receiver arranged to detect the time interval between each two consecutive drops of liquid medicine dropping in a burette and installed so that the receiver receives infrared rays emitted by the emitter when there is no drop passing through the rays and does not receive the infrared rays when there is drop through the rays because of refraction of the rays within the drop, the receiver thereby being switched on and off as a drop passes and emits an output current pulse.

2. An instillation safety device comprising a buzzer, two ICs, a burette, an infrared emitter and receiver designed to detect the time interval of each two consecutive drops of liquid medicine dropping in a burette and installed in such way that the receiver can receive the infrared rays emitted by the emitter when there is no drop passing, and because of refraction the receiver can not receive the infrared ray when there is a drop passing in the area, so that as each one medical drop passes the receiver will be once on and off and send out pulse current.

3. An instillation safety device according to claim 2, wherein the burette is transparent to facilitate detection of the drop of liquid medicine.

4. An instillation safety device according to claim 1, 2 or 3, wherein the integrated circuit means or the two ICs comrpises a timer which will activate a buzzer when the number of accumulated frequency from the oscillator is equal to the present value in the timer.

5. An instillation safety device according to claim 4, wherein the timer will have the number of accumulated frequency reset to O each time as the infrared ray is chopped off.

6. An instillation safety device substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.