FI101426B - pressure sensor - Google Patents

Description

101426

Pressure transmitter

The invention relates to a pressure transducer comprising a sensor housing, a first diaphragm, a second diaphragm, the diaphragms being spaced apart from each other and the transducer housing, and electrodes for measuring the movement of the diaphragms.

Such double or multi-membrane sensors are known from the past. The purpose of the multi-membrane structure is to elicit the influence of a number of physical quantities that can produce incorrect measurement results when measuring the pressure of a medium. Physical quantities that can affect a pressure-sensing membrane, directly or indirectly via the sensor housing, are, for example, temperature, ambient pressure, acceleration caused by, for example, impact, shock or gravity, and the membrane's resonant frequency of resonance.

Examples of known pressure sensors are given in the patents US 3,962,921, US 4,689,999 and US 4,974,117.

However, these known pressure transducers are very complicated in their construction and thus easily exposed to damage and defects.

The object of the present invention is to provide a pressure transducer which avoids the above-mentioned disadvantages and which, in addition to simpler manufacturing, enables measurement of low or extremely low pressure with high accuracy within a very low pressure range. This is achieved by a pressure transducer according to the invention, characterized in that the first membrane and the second membrane are connected to each other by means of an intermediate glass joint, the glass joint comprises a first layer and a second layer and the first layer consists of high temperature glass and the second layer. the layer of low temperature glass.

The invention is based on the idea of achieving as small a distance between the membranes as possible, which is necessary with respect to pour strength data and because the resolution of the sensor is proportional to the movement through the basic distance between the electrodes. This is achieved by connecting the membranes to each other at least a glass joint consisting of two layers formed in two steps. First, the high-temperature glass is applied to one membrane and then the low-temperature glass to the high-temperature glass. Preferably, each glass and the sensor housing material, ceramics, exhibit the same temperature coefficient. The difference in melting point between the glasses is preferably so large that the high temperature glass remains intact when applying the low temperature glass.

The pressure sensor preferably comprises three chambers, wherein the sensor housing and the first membrane define a first chamber, the first membrane and the second membrane define a second chamber and the second membrane and the sensor housing define a third chamber, the third chamber having an opening for receiving the medium whose pressure is to be measured and the first chamber and the second chamber exhibit a reference vacuum. Preferably, the first chamber and the second chamber communicate with one another through an opening in the first membrane, which in a simple manner maintains reference vacuum in said chambers. The chambers can of course also be provided with reference vacuum.

The invention also relates to a method of connecting pressure sensor membranes to one another at a very small distance, which is mainly characterized in that on one membrane is applied a joint of high temperature glass by furnace firing and to the high temperature glass a joint of lower tempered glass is applied to a lower tempered glass , after which the second membrane is applied to the joint of low-temperature glass.

In the following, the invention is described in more detail by way of example and with reference to the accompanying schematic drawing, in which figure 1 shows an embodiment of the pressure transducer according to the invention, and figure 2 shows the connection of the membranes to each other in detail.

In Fig. 1, the pressure transducer housing is indicated with reference numeral 1. The transducer housing encloses a first diaphragm 2 and a second diaphragm 6. The diaphragms 2, 6 are arranged at a distance from the transducer housing 1 and at a very small distance from each other by means of a glass joint 5. Between the sensor housing 1 and the first membrane 2, a first chamber 31 is formed and between the first membrane 2 and the second membrane 6 a second chamber 32 is formed, which chambers are preferably connected to each other through an opening 4 in the first membrane 2. The chambers can be Of course, they are also poured separately. The first chamber 31 and the second chamber 32 preferably exhibit a reference vacuum. Between the second diaphragm 6 and the sensor housing 1, a third chamber 33 is formed which has an opening 9 or measuring port in the sensor housing 1 to receive the medium whose pressure is to be measured. Measurement of the pressure is differentially between the two membranes 2.6 by means of electrodes (not shown) placed on the same. The second membrane 6 is affected partly by the pressure of the actual medium and partly by parasitic physical quantities, for example temperature, ambient pressure, acceleration caused by, for example, impact, shock or gravity, and the membrane's resonant frequency. The first membrane 2 is affected only by these parasitic quantities, the actual and true pressure being obtained by said differential measurement.

Figure 2 shows how the first membrane 2 and the second membrane 6 are connected to each other by means of a glass joint 5 comprising a first layer 7 of high temperature glass and a second layer 8 of low temperature glass. The connection is made by applying the high temperature glass layer 7 to the first membrane 2 in a first furnace firing step, after which the low temperature glass layer 8 is applied to the high temperature glass joint 7 during a second furnace firing moment. The diaphragm as well as the high temperature glass and the low temperature glass should exhibit the same temperature coefficient, the melting point of the high temperature glass being so much higher than the melting point of the low temperature glass that the high temperature glass remains intact when burning the low temperature glass.

With such a glass joint consisting of two layers and made in two steps the distance between the membranes can be minimized.

The pressure sensor including the diaphragm is preferably made of ceramic material, for example alumina.

The pressure sensor described above is suitable, for example, for measuring pressure from 1 dry FS (Full Scale) to 0.1 dry FS (Full Scale), the distance between the membrane being between 5-20 µm. The membrane thickness can be, for example, of the order of 50-150 µm.

The drawing and the accompanying description are intended to illustrate the basic idea of the invention. For their details, the pressure transducer may vary within the scope of the patent claims.

Claims (10)

A pressure sensor comprising a sensor housing (1), a first membrane (2), a second membrane (6), the membranes being spaced apart by a glass seam (5, 7, 8) therebetween and from the sensor housing, and electrodes for measuring the movement of the membranes , characterized in that the glass seam (5) comprises a first layer (7) and a second layer (8), and that the first layer (7) 10 consists of high-temperature glass and the second layer (8) of low-temperature glass. Pressure sensor according to Claim 1, characterized in that the first layer (7) and the second layer (8) of the glass seal (5) have the same temperature coefficient. Pressure sensor according to Claim 1 or 2, characterized in that the first layer (7) and the second layer (8) of the glass seal (5) have different melting points. Pressure sensor according to one of the preceding claims, characterized in that the pressure sensor is made of a ceramic material, the first layer (7) and the second layer (8) of the glass joint (5) having the same temperature coefficient as the ceramic material. Pressure sensor according to claim 1, characterized in that the sensor housing (1) and the first membrane (2) delimit the first chamber (31), the first membrane (2) and the second membrane (6) delimit the second chamber (32) and the second membrane ( 6) and the sensor housing (1) delimit a third chamber (33), the third chamber (33) having an opening (9) for receiving a medium whose medium pressure is to be dimensioned. Pressure sensor according to Claim 5, characterized in that the first chamber (31) and the second chamber 35 (32) communicate with one another via an opening (4) in the first membrane (31). Pressure sensor according to Claim 5 or 6, characterized in that the first chamber (31) and the second chamber (32) have a reference vacuum. 8. A method of joining pressure sensor films together at a very short distance, characterized in that a layer (7) of high temperature glass is applied to the second film (2) by furnace firing and a layer (8) of low temperature glass is applied to a high temperature glass in a separate furnace firing. (6) is applied to the low temperature glass layer (8). Method according to Claim 8, characterized in that the films (2, 6) and the glass layers (7, 8) have the same temperature coefficient. Method according to Claim 8 or 9, characterized in that the glass layers (7, 8) have different melting points.