Pressure-measuring cell with a temperature sensor

#The present invention relates to a pressure-measuring cell with a temperature sensor. Temperature sensors are frequently integrated into pressure-measuring cells in order to compensate for the static temperature errors that arise in pressure measurement. In the case of ceramic pressure-measuring cells this temperature sensor is usually applied to the back of the ceramic piece, although it can also be contained in an adjoining electronic evaluating unit. A disadvantage of such pressure-measuring cells is that temperature changes in the medium whose pressure is to be measured—a medium which often acts with direct contact on the pressure-measuring cell—only have an effect on the temperature of the temperature sensor after a considerable delay, and at times in dampened fashion. Any resulting temperature deviation between the medium to be measured and the temperature sensor will lead to errors in the correction of the measured pressure value provided by the measuring cell.

#In order to solve this problem the present invention proposes—in a pressure-measuring cell that exhibits a base as well as a diaphragm that is positioned on the base and that is deformed by the pressure to be measured—that a temperature sensor be positioned between the diaphragm and the base. This positioning guarantees that there is a slight distance between the temperature sensor and the medium that exerts a pressure on the diaphragm, so that the measured value of the temperature sensor is able to quickly follow temperature changes in the medium. As a result, the disruptive influence exerted by abrupt temperature changes in the medium on the pressure measurement is reduced considerably.

#A typical separating distance between the temperature sensor and an outer diaphragm area that is exposed to the pressure being measured lies between 0.1 and 3 mm, depending on the thickness of the diaphragm, i.e., depending on the dimensions of the pressure-measuring cell or the pressures to be measured by the cell.

#Other features and advantages of the invention will emerge from the following description of an exemplary embodiment, which makes reference to the attached drawings. Shown in the figures are:

#FIG. 1 a pressure-measuring cell in an axial section;

#FIGS. 2 to 4 sections through the pressure-measuring cell of FIG. 1, along plane A—A.

#FIG. 1 shows the pressure-measuring cell according to the invention, in an initial section. The pressure-measuring cell comprises a essentially cylindrical base 1 and a diaphragm 2, each made of a ceramic material, which are held apart by a material layer 4 that runs in circular fashion along the rims of the facing sides of the base 1 and the diaphragm 2. The material layer 4 consists of a glass material. Jointly with the base 1 and the diaphragm 2 it tightly encloses a flat, cylindrical compartment 3. In the area of the compartment 3 the face of the base 1 bears a centrally positioned electrode 6 and a circular electrode 7 concentric to it. Feed-through contacts 9 connect the two electrodes with the connecting areas 10 on the back of the base 1. On the opposite side of the compartment 3 the diaphragm 2 bears an opposing electrode 8, which is not provided with a contact. The diaphragm 2 is deformed by the pressure of a medium acting on its outer surface 11. Deformation of the diaphragm modifies the capacity of the capacitor formed by the electrodes 6, 7, 8, so that conclusions concerning the pressure acting on the outer surface 11 can be reached by measuring this capacity—for example, through the installation of a pressure-measuring cell as the capacitor in an oscillating circuit and through the measurement of the latter's resonant frequency.

#Embedded in the material layer 4 that functions as a seal for the compartment 3 is a resistor element 5 with a temperature-dependent resistance value. The two opposite ends of the extended resistor element 5 are connected to the connection areas 10 on the back of the base 1 by means of feed-through contacts 9.

#In the embodiment shown in FIG. 1 the resistor element 5 is in direct contact with the surface of the base 1 and is separated from the diaphragm 2 by a portion of the material layer 4. The direct application of the resistor element 5 to the base 1 facilitates the production of an electrical connection between the resistor element and the surrounding area by means of the feed-through contacts 9. The surface of the resistor element 5 that faces away from the base 1 forms a large heat exchange area with the material layer 4 and, through it, with the diaphragm 2 and the medium (not shown) that exerts the pressure that is being measured on the diaphragm.