Dual sensor air-in-line detector

Details Dual sensor air-in-line detector Dual sensor air-in-line detector

1995-09-22

1997-10-21

Hofsass, Jeffery

Communications: electrical

Condition responsive indicating system

Specific condition

340627, 250573, 250574, 250575, 250576, G08B 1710

Patent

active

056801114

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to devices for detecting gas, e.g. air or air bubbles, in fluid conducting tubing and in particular in fluid conducting tubing forming part of a fluid flow system utilized for the intravenous supply of fluid to a medical patient.


DISCUSSION OF BACKGROUND

Typically transparent walled p.v.c. tubing is employed in systems as last-mentioned because it is hygienic and cheap it being common practice to change and discard the length of tubing in use frequently. A known arrangement for use in clinical analysis and capable of detecting air in tubing utilizes a device as illustrated in transverse section in FIG. 1 of the accompanying drawings.
Referring to FIG. 1, the known device includes a body member 1 having a passage 2 passing therethrough in which may be accommodated a length of transparent walled p.v.c. tubing 3. Passage 2 is open at the top (as viewed) in order that the tubing 3 may readily be slotted into position and of course removed after use. Extending into the body 1 from its base and right-hand side (as viewed) respectively are two circular-cylindrical passages 4 and 5 which are orthogonal to each other and exit via apertures 6, 7 respectively into tubing passage 2. Located in circular cylindrical passage 4 is an infra-red receiver 8 (a phototransistor) which receives infra-red energy transmitted by an infra-red transmitter 9 (an LED).
In operation the output level of receiver 8 depends upon the nature of the fluid passing through the tubing 3 past receiver 8 and transmitter 9. Different fluids will result in different output levels with a significant change if a gas, e.g. air, is present. For example, in a test a voltmeter 10 connected to the output of a suitable detector circuit 11 was found to indicate 0.1 volts when the fluid passing through tubing 3 was distilled water; 0.2 volts when the fluid was semi-skimmed milk; 1.4 volts when the fluid was a 20% intralipid solution and 4.2 volts when air passed through.
While not a primary function of a clinical analyzer, a device as shown in FIG. 1 will therefore operate as a detector of air passing through tubing 3. However, as is represented, p.v.c. tubing typically used in a clinical analyzer is small bore thick-walled tubing with an outside diameter of 2.5 mm and an inside diameter of 0.9 mm. In the intravenous supply of fluids to a patient however, the standard p.v.c. tubing used is of relatively large bore and thin walled having an outside diameter of 4 mm and an inside diameter of 3.1 mm.
Experiments have been carried out in connection with the detection of air-in-line with a device generally as illustrated in FIG. 1, but adapted dimensionally to accept the relatively large bore, thin wailed tubing utilized for the intravenous supply of fluid to a patient but the results achieved were not satisfactory. Particularly bearing in mind the critical importance of detecting "air-in-line" in such applications, the changes that took place in the output of the receiver corresponding to receiver 8 in FIG. 1 were insufficiently marked for the device to be regarded as useful in this connection. However, further experimentation led to the introduction of an optical spacer between the transmitter and the tubing, and the tubing and the receiver and with this, markedly improved results were achieved.
Such an optical spacer is known from EP-A-0481656, which discloses a device for detecting the presence of air in liquid conducting, translucent or transparent tubing, the device comprising a passage for accommodating of said tubing, a transmitter for transmitting radiation (in this case, light) towards said passage; a receiver for receiving radiation from said passage which has passed through the tubing, the receiver being operable to produce an output signal (i) when air is present in the tubing and/or (ii) when the dilution ratio of the liquid in the tubing is below a first predetermined threshold; and processing means. The processing means processes said output signal to provide an indication that air is present in th

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