Pressure or Temperature Transducer

Technical Field.

This invention relates to transducers for measuring pressure or temperature.

Background Art.

Pressure transducers are well known instruments with a wide variety of applications. They usually comprise a chamber, often cylindrical, with one side occupied by an elastic diaphragm. The deformation of the diaphragm caused by the pressure under measurement is sensed in various ways depending on the principle of the transducer. However transducers whose function is based on the deformation of a diaphragm present several problems. This is because the diaphragm material and thickness are . important factors determining the transducer performance and require meticulus care and also the secure mounting of the diaphragm at the appropriate site is an elaborate task given the small dimensions of these instruments.

Temperature transducers are usually based on the thermoelectric phenomenon (thermocouples), or the phenomenon of thermally affected resistance, or the thermal expansion phenomenon whereby the change in dimension of a medium is monitored. This medium can be either liquid or solid. In the case of solid mediums they are sometimes of the form of a diaphragm whose shape depends on the temperature. In this later case identical problems to the ones mentioned above are encountered especially for miniaturised diaphragm-type temperature

transducers.

Disclosure of Invention.

According to the present invention there are provided transducers of simple construction capable of measuring pressure or temperature. They comprize according to one embodiment of the present invention of a quantity of compressible deformable material, a quantity of gas for example, or combination of materials forming a compressible deformable structure; and a quantity of essentially incompressible deformable material such as liquid or gel for example. Said compressible deformable material or said combination of materials forming a compressible deformable structure will be referred to throughout the rest of the present Description, up to and including the part "Industrial Applicability", as "gas" and said essentially incompressible deformable material will be referred to throughout the rest of the present description, up to and including the part "Industrial Applicability", as "liquid".

Said gas is either concentrated in one volume or dispersed in a number of volumes so as to form one or more ^* interfaee(s) with said liquid. Pressure and/or temperature variations of said liquid alter the volume and/or the geometry of said ςas. Near said gas and said liquid are proper means for detection to sense the changes in said gas volume and/or the geometry of said gas interface(s) with said liquid. These changes are induced by the physical quantity under measurement (pressure or temperature). When pressure is measured said liquid communicates with the pressure source and its temperature should

be kept constant or be continuously monitored. When temperature is measured said liquid communicates with a source of constant or continuously monitored pressure. The only deformable element of the transducer is said gas, every other part of it being substantially rigid.

Electrolytic, chemical or physical methods can be used to introduce or generate said gas. By way of example reference is made to some appropriate methods. As an example of an electrolytic method, two electrodes are placed at appropriate positions in said liquid and an electric current passes through said liquid, which in this case is electrically conductive. By proper selection of the chemical composition of said electrodes and said electrically conductive liquid, gaseous substance is formed on the surface of said electrodes said gaseous substance being in this case said compressible deformable material or combination of materials forming a compressible deformable structure.

As an example of a chemical method, a properly selected chemical substance is placed at appropriate place(s) either on the surface of said appropriate means for detection referred to above or on the surface of body or bodies introduced at appropriate place(s) in the proximity of said appropriate means for detection. Said liquid is subsequently put into place so that it comes into contact with said chemical substance which can be concentrated in one place or divided in o a number of quantities deposited in more than one place. If said liquid has in this case a properly selected chemical composition, chemical reaction(s)

can occur between said liquid and said chemical substance. Having properly selected the exact chemical composition of said liquid and said chemical substance, product(s) of said chemical reaction(s) are of gaseous nature and remain, especially if produced in small quantities, close to the place(s) of their production. Said chemical reaction(s) can occur either spontaneously or upon action of appropriate factors such as heat or other radiation of any type for example. Said gaseous substance is in this case said compressible deformable material or combination of materials forming a compressible deformable structure.

As an example of a physical method, the whole assembly is placed in a gaseous atmosphere and pressurised. One or more small containe (s) containing gaseous substance and bearing one or more small opening(s) are placed at some place(s) in the proximity of said appropriate means for detection. Then said liquid is put into place. Said liquid, due to the small dimensions of said container(s) and their said opening(s), cannot completely displace said gaseous substance from within said containers. After introduction of said liquid, depressurising the whole assembly part of said gaseous substance, which in this case is said compressible deformable material, comes out of said container(s) and remains in the proximity. thus forming one or more interface(s) .

Brief Description of Drawings.

In the present part, by way of example only, radiation is used to detect changes of volume of said gas and/or changes of

geometry of said interface(s) between said gas and said liquid. Throughout the present document the term radiation refers to any type of electromagnetic radiation or any other type of wave and the term waveguide includes any type of optical fibre or any other system through which said electromagnetic radiation or any other type of wave is capable of travelling.

For the purpose of promoting a better understanding of the principles of the invention particular arrangements will now be described by way of example with reference to the accompanying drawings in which:

Figs 1,2, 3,1, present longitudinal section views of transducer embodiments differing in the way said gas quantity is irradiated and the way the radiation is detected.

Fig.5 shows an arrangement similar to that of Fig. 1 but including- n accessory tube.

Figs 6 and 7 represent longitudinal section views of additional embodiments of the transducer with changes in the details of the chamber containing said gas and liquid quantities.

Figs S.9 ,10 and 11 represent longitudinal section views of further embodiments of the transducer.

It will nevertheless be understood that no limitation of the scope of the invention is thereby intended and that the figures presented are merely examples of the many more embodiments that the invention can assume.

Ref rring to Fig.1 the transducer comprises a cylindrical chamber 13, with one end open. Two waveguides, namely the launching waveguide 10 and the detecting waveguide 11, transverse the closed end of said chamber. There is a gas-liquid interface

lϋ at some distance from said chamber's closed end, The shape of said interface depends on the material of said chamber. Radiation generated by a proper source 16, and transmitted through said launching waveguide is reflected and/or refracted at said gas- liquid interface and a fraction of said radiation is transmitted back by said detecting waveguide to a proper detector of said radiation 17. Pressure or temperature variation alters the volume of said gas quantity and deforms said gas-liquid interface and consequently said detected radiation changes. Due to this change of radiation said detector produces an electrical signal which is subsequently amplified and/or displayed and/or otherwise processed.

Referring to the embodiment of Fig. the arrangement is similar to that of Fig.1 but the two waveguides of Fig. 1 have been replaced by a bundle of waveguides 20. At some distance from said chamber said bundle splits into the launching bundle 21 and the detecting bundle 22.

Referring to Fig.3 the arrangement differs from that of Fig.1 in that the two waveguides of Fig. 1 have been replaced by a single waveguide 30. Said single waveguide serves both to irradiate the chamber with radiation of a proper source lό and to transmit back changes of radiation to a proper detector 17. A semi-transparent mirror 31 or any other device having a similar action (a beam splitter) separates the two waves of opposite directions namely the radiation from said source and the radiation to said detector.

Referring to Fig. & the arrangement is similar to that of

Fig.l, however said launching and detecting waveguides are absent and said radiation source and said radiation detector are placed within said chamber 13. Electrical cables H O and Hi are connected to said source and detector.

Referring to Fig.5 the arrangement is similar to that of Fig.l but an accessory tube 50 is added, which crosses the closed end of said chamber and terminates at some distance from said end. This accessory tube is particularly useful when pressure measurement is required and serves initially to form said gas- liquid interface and subsequently to maintain a flow of liquid in order to keep the transducer clear of debris at the open end. The flushing liquid may be required for example when intravascular blood pressure is measured, to prevent formation of blood clots. Said accessory tube can be used for the in-situ calibration of the transducer (mean pressure determination) by connecting it to a reference manometer. The initial formation of the gas-liquid interface should be carried out before any pressure measurements and the transducer placed in position subsequently.

In the same way as the embodiment of Fig.5 was derived from the embodiment of Fig.l, three further embodiments can derive from Figs 2.3 and -l having the additional element of said accessory tube 50 as described above in the embodiment of Fig.5.

The embodiment of the transducer represented in Fig.6 resembles that of Fig.l the difference being in the gas-liquid interface configuration. In the present embodiment there is a recess 60, communicating with the lumen of said chamber at some point via the internal surface of said chamber and accommodating part of said gas quantity. The rest of the gas quantity protrudes

outside said recess and occupies part of said chamber lumen forming the gas-liquid interface δl. Three additional embodiments can be derived by combining the gas-liquid interface represented in Fig.6 with the different ways of irradiating the chamber represented in Figs 2,3 and H , namely waveguide bundle, single waveguide and irradiating and detecting devices contained within said chamber. When pressure measurement is required, an accessory tube, as in the embodiment of Fig.5, may be combined with all four arrangements described in the present paragraph. The purpose of said accessory tube is to calibrate the instrument and/or flush the chamber and/or help in the meniscus forming process.

Referring to Fig.7 the one additional characteristic with respect to the arrangement of Fig.6 is the reflecting or diffusing surface 70, placed at some distance beyond said recess towards said chamber open end in such a manner that it does not occlude the lumen of said chamber. Said gas-liquid interface lies ^' between said waveguide tips and said surface. Radiation transmitted through said launching waveguide is reflected or diffused back by said surface 70. The quantity of radiation detected changes with the change of volume of said gas quantity which depends on pressure or temperature. Further embodiments can be derived by either using the different ways of irradiating the chamber as in Figs 2,3 and H and/or including in all the newly derived embodiments the accessory tube described in detail in the arrangement of Fig.5. The accessory tube is more likely to be useful in the case of pressure transducers.

Referring to Fig.8 the transducer comprises a cylindrical

chamber 80 with both ends closed, one end being transversed by a launching waveguide 81, coupled to a proper radiation source 16 and the other end being transversed by a detecting waveguide 33, coupled to a proper detector 17. Said chamber wall has a number of openings and a small recess to accommodate part of gas quantity the rest of which protrudes into the lumen of said chamber between the two said waveguide tips. The rest of the space of said chamber is occupied by liquid.

The only difference between the arrangement of Fig.9 and that of Fig.8 is that in the former the two said waveguides have been replaced by two bundles of waveguides of radiation namely the launching bundle 90 and the detecting bundle 91.

Referring to Fig.10 the waveguides of radiation are absent and both the source and detector of radiation are placed within said chamber 80. .Electrical cables 100 and 101 are connected to said source and detector.

Three futher embodiments of the invention can be derived by connecting an accessory tube to said chamber 80 in the arrangements of Figs 8,9 and 10. The utility of said accessory tube refers mainly to pressure measurements and has been analysed in the arrangement of Fig. .

According to the embodiment of Fig.11 a number of gas volumes is deposited on the surface of radiation detector 17,. placed near the radiation source 16. Liquid surrounds said gas and said radiation source and detector. Electrical cables 100 and 101 are connected to said source and detector.

An alternative embodiment to Fig.11 would involve the gas volumes being on the surface of said radiation source.

Alternative embodiments to all those considered involve either the source or the detector but not both being close to the gas volume(s) and the other being communicated with via waveguide(s) .

Modes of Carrying out the Invention.

The embodiments referring to Fig. 1 and 11.

Industrial Applicability.

The rationale for the development of these transducers is the need for simple, efficient, low cost and possibly disposable transducers for the measurement of pressure or temperature. Another desirable characteristic is small size especially for physiological pressure measurements either centrally or peripherally (microcirculation) . Disposability is a particularly desirable characteristic especially in the medical field as it reduces the patients risk of catheter-induced infections and eliminates cumbersome sterilizing procedures. An additional advantage of the disclosed transducers in the biomedical field is its freedom, in many embodiments, from electrical potential that under certain circumstances could harm the patient especially in cases of intracardiac pressure measurements.

The disclosed transducers could also find applications in industrial situations where small dimensions and robust construction is required in order to measure pressure or temperature or provide indication of pressure or temperature variation.