DE8802025U1 - Pressure sensor - Google Patents

Description

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Pressure sensor

The invention relates to a pressure sensor consisting of a sensor head and a pressure measurement signal processing unit, which are coupled to one another via a connecting line, in particular for medical applications such as in a cardiac catheter.

<U Pressure sensors of this type are known in accordance with the state of the art. Strain gauges are usually used as measuring elements, the measured values of which are transmitted via special cables with up to 14 or more wires. However, eg pezoceramic membranes can also be used to record a differential pressure: here too, the evaluation is carried out electronically.

The disadvantages of existing pressure sensors are their large size, their complicated structure and their poor measurement value transmission, which is also subject to relatively large errors, which make medical use in particular inadvisable from the outset. Another argument against medical use, especially in cardiac catheters, is the electrical signal transmission from the sensor head to the sensor evaluation, which is only possible with relatively complex shielding.

(A It is therefore an object of the present invention to provide a pressure sensor of the type mentioned at the outset which has the smallest possible size, operates as currentlessly as possible and which has good transmission properties.

This task is solved by a pressure sensor in which the connecting line between the sensor head and the pressure measurement signal processing consists of a light guide, the first end of which protrudes into the sensor head and has a wavelength-selective mirror on the front side, which lies contactlessly opposite a pressure membrane forming part of the sensor head» and the second end of which is connected to the

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optoelectronic transmitter and receiver unit consisting of pressure measurement signal processing connected 1st.

The pressure sensor according to the invention is characterized in particular by its small size and simple construction. In addition, the pressure sensor works without current.

Light guides, also called fiberscopes, have already been used for optical inspection of cavities that are not directly accessible, e.g. via a straight channel. This makes use of the fact that glass fibers with a diameter of 1m in the pm range can serve as light guides. The use of flexible glass fibers has already been proposed in medicine for so-called endoscopes, which are inserted through an opening into the area to be inspected - enabling object illumination and a view around "edges" and "curves". Such glass fiberscopes are already used in preventive examinations, diagnostics and treatment, especially in the gastrointestinal tract.

In this case, the light guide serves as a transmission medium for optical signals of a specific wavelength, whereby, for example, only one of the two wavelengths is allowed through the wavelength-selective mirror and hits the pressure membrane, while the other is reflected by the mirror. The measuring principle is based on the fact that the light passing through the light guide experiences practically the same attenuation on the way from the light source to the sensor and back, so that an evaluation electronics can evaluate the quotient of the two light signals as a measure of the position of the bridge stem.

In order to simplify the design of the pressure sensor, it is further proposed to design the sensor head essentially in a tubular manner. The sensor head tube should preferably have a diameter of 1-2 mm, further preferably 1.5 mm and/or a length of 3-5 mm, further preferably 4 mm.

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According to a further development of the invention, the pressure membrane clamped to the front side of the sensor head has a cup shape, whereby the cup bottom forming the pressure-sensitive part of the pressure membrane is 10-20 pm thick.

SiH2O is suggested as a pressure membrane material because it has good elastic properties and can also be precisely processed into micromechanical parts, preferably by etching.

In principle, lasers can also be used as transmitters, but light-emitting diodes (luminescent diodes) are simpler in terms of construction and handling as light sources and corresponding photodetectors as receivers. In particular, it is proposed that the light-emitting diodes (LEDs) emit light with a wavelength of 850 or 950 nm, preferably at a frequency of 100 kHz, and that the mirror is only selective for one of these wavelengths.

In order to be able to easily connect and disconnect the sensor head and its supply cable from the optoelectronic transmitting and receiving unit, the end of the light guide is designed as a light guide plug and the transmitting and receiving unit is equipped with a corresponding plug socket.

The two LEDs are conveniently connected to additional light guides, which are connected to the light guide leading to the sensor head via a light guide coupler.

An embodiment of the invention is explained in more detail below with reference to the drawings.
Fig. 1 is a schematic view of the pressure sensor according to the invention and

Fig. 2 is an enlarged cross-sectional view of the sensor head in cross section.

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The pressure sensor shown in Fig. 1 consists essentially of a sensor head 1» which is connected via a light guide 2, the free end of which

designed as a fiber optic plug 3, connected to an optoelectronic transmitting-receiving unit 4. The optoelectronic transmitting-receiving unit has a plug socket 3 designed in accordance with the fiber optic plug 3. The optoelectronic transmitting-receiving unit

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Intercoupler 5, which couples two light guides 12 and 13 leading from it to transmitting electrodes (LEDs) 6 and 7. The transmitting electrodes 6 and 7 emit at a frequency of 100 kHz, each with a wavelength of 850 nm or 950 nm. The radiation reflected by the sensor head is examined by a photodetector 8 and electronically processed in accordance with a principle known from the state of the art. The sensor head is equipped with a cup-shaped pressure membrane 10 according to Fig. 2, the base surface 10* of which, as a pressure-sensitive part, consists of etched silicon with a thickness of 10-20 mm. The cup-shaped pressure membrane is flush with the sensor head housing consisting of a tube 11 and forms the front part. The sensor head tube has a diameter of 1.5 mm and a length of 4 mm. The light guide 2 is inserted centrally in the sensor head tube 11, the front side of which has a wavelength-selective mirror 9 that is selective for one of the wavelengths (850 nm or 950 nm).

The arrangement according to the invention works as follows: The two LEDs 6 and 7 alternately send light to the sensor head 1 of the frequency and wavelength mentioned, one of the two wavelengths is reflected by the selective mirror 9, the other is transmitted, extended to the bottom 10' of the pressure membrane, is reflected there into the light guide 2 and is also evaluated with the help of the photodetector 8. The light from both LEDs passes through the same light guide 2 and thus experiences practically the same attenuation on the way to the sensor and back. The position of the pressure membrane and thus the pressure to which it is exposed can be directly determined from the quotient of the two light intensities.

As is generally the case with pressure sensors, the pressure transmitter is calibrated before measurements begin. Calibration devices are, in principle, state-of-the-art.

The pressure sensor according to the invention is particularly suitable for recording the sensor characteristic curve in a microprocessor-controlled manner and storing it in a memory area in such a way that a calibrated sensor is then available for subsequent measurements.

If the pressure sensor according to the invention is used in medical technology, the measuring range should be approximately 0-300 mbar.

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Claims (10)

1. Pressure sensor, consisting of a sensor head and a pressure measurement signal processing unit, which are coupled to one another via a connecting line, in particular for medical use such as in a candle catheter, characterized in that the connecting line consists of a light guide (2), the first end of which projects into the sensor head (1) and has a wavelength-selective mirror (9) on the front side, which lies contactlessly opposite an internally mirrored pressure membrane (10') forming part of the sensor head (1) and the second end of which is connected to the pressure measurement signal processing unit consisting of an optoelectronic transmitting and receiving unit (4). 2. Pressure sensor according to claim 1, characterized in that the sensor head (1) is essentially tubular. 3. Pressure sensor according to claim 2, characterized in that the sensor head tube (11) has a diameter of 1-2 mm, preferably 1.5 mm, and/or a length 1 of 3-5 mm, preferably 4 mm. Il It
II · 4. Pressure sensor according to one of claims 1-3, characterized in that the pressure membrane (10, 10') clamped to the front side of the sensor head has a cup shape. 5. Pressure sensor according to claim 4, characterized in that the cup bottom forming the pressure-sensitive part of the pressure membrane (10') is 10-20 μm thick. 6. Pressure sensor according to claim 4 or 5, characterized in that the pressure membrane (10, 10') consists of silicon, preferably of etched silicon. 7. Pressure sensor according to one of claims 1-6, characterized in that the transmitting and receiving unit (4) consists of two light-emitting diodes (LED 6, 7) and a photodetector (8). 8. Pressure sensor according to claim 7, characterized in that the LEDs (6, 7) emit light with a wavelength of 850 nm or 950 nm, preferably with a frequency of 100 kHz, and the mirror (9) is selective for only one of these wavelengths. 9. Pressure sensor according to one of claims 1-8, characterized in that the light guide end located outside the sensor head (1) has a light guide plug (3) and the transmitting and receiving unit (4) has a corresponding plug socket (3*). 10. Pressure sensor according to one of claims 1-9, characterized in that the LEDs (6, 7) are connected to respective further light guides (12, 13) which are connected to the light guide (2) via a light guide coupler (5). &kgr; does I II)