The present invention relates to a pressure sensor with features defined in the preamble of claim 1.
A pressure sensor of the afore-mentioned kind is, for example, known from U.S. Pat. No. 3,100,997 A.
Further pressure sensors are, for example, known from DE 79 06 132 U1, EP 0 580 458 A1, U.S. Pat. No. 4,122,337 or U.S. Pat. No. 5,005,584. DE 74 05 439 U1 also shows a pressure sensor.
All the afore-mentioned pressure sensors have the disadvantage that they are costly designed with respect to their structure so that their use in mass production is not possible due to high costs. Furthermore, the respective design is sensitive to vibrations so that this characteristic prevents their use on a large scale.
In view of the above, it is an object of the present invention to provide a pressure sensor of the afore-mentioned kind which may be produced cost effectively on the one hand, and which is small on the other hand, however, without deteriorating its sensibility.
This object is solved by a pressure sensor of the afore-mentioned kind such that a holding device is provided which may be inserted into the housing and which comprises a receiving opening for the light means and the light detection means, the holding device supporting the first and the second reflection surface, preferably the first and the second prism in the area of the respective receiving opening and being made of a transparent material, preferably a plastic material.
This kind of arrangement results in a very compact assembly of the pressure sensor and allows a very cost effective production. Particularly, off-the-shelf components may be used because of the employment of prisms for deflecting the light beams, without enlarging the design. Furthermore, the use of prisms allows to employ the normal geometry for example of standard LEDs and to use the whole beam width of the LEDs, so that the detectible path of the deflectable membrane increases. Therewith, the measuring range of the pressure sensor or its sensitivity may be increased.
At this point, it is to be noted that the expression xe2x80x9coptical axisxe2x80x9d means the axis of the light means and the light detection means, respectively, which defines the main beam direction. A further advantage may be seen in that the orientation of the light means and the light detection means, respectively, to the respective prism is already defined by the holding device so that no errors will occur during assembly. The light means and the light detection means, respectively only have to be inserted into the receiving opening of the holding device and will then have the desired orientation with respect to the respective prism. Moreover, the integration of the prisms in the holding device results in a very cost effective design. A further cost reduction is achieved in that the holding device is made of a transparent material, preferably a plastic material. That means in other words that the whole holding device with the prisms is made of one material.
In a preferred embodiment of the inventive pressure sensor the light blocker comprises a truncated portion lying in the beam path.
This measure allows a very simple and hence cost effective design of the light blocker, wherein there is a further advantage that due to the rotational symmetry of this portion no orientation or adjusting errors of the light blockers may occur during assembly.
In a preferred embodiment the holding device comprises at least two snap-in pins mounted on the exterior which engage with respective recesses in the housing.
This measure has the advantage that the assembly of the pressure sensor is simple and fast and may be carried out without tools.
In a preferred embodiment the housing comprises an interior shoulder extending along the whole circumference, a respective supporting surface of the holding device lying on the shoulder, wherein a edge region of the membrane is clamped between the supporting surface and the shoulder.
This measure has the advantage that a separate mounting element for the membrane in the interior of the housing is not necessary. Rather, fixing the membrane within the housing is achieved by putting on the holding device, which clamps the membrane to the shoulder of the housing. The advantage is that a further simplification of the production may be achieved.
In a preferred embodiment, the light means comprises a solid-state light source such as a LED and the light detection means comprises a solid-state light detector such as a phototransistor.
This measure has the advantage that off-the-shelf components may be used so that the use of expensive special components may be avoided.
Further advantages and embodiments of the invention can be taken from the following description and the enclosed drawings. It is to be understood that the features mentioned above and those yet to be explained below can be used not only in the respective combinations indicated, but also in other combinations or in isolation without leaving the scope of the present invention.