Pressure sensor and method of operating it

• US 20030024319A1
• Filed: 07/11/2002
• Published: 02/06/2003
• Est. Priority Date: 07/11/2001
• Status: Active Grant

• Current Assignee: Endress + Hauser GmbH + Company KG (Endress+Hauser AG)
• Original Assignee: Endress + Hauser GmbH + Company KG (Endress+Hauser AG)
• Inventors: Pistorius, Stefan
• Granted Patent: US 6,776,046 B2
• Time in Patent Office: Days
• US Class Current: 73/718
• CPC Class Codes: G01L 19/0618 Overload protection
• CPC Class Codes: G01L 19/0645 using isolation membranes, specially adapted for protection
• CPC Class Codes: G01L 19/0672 Leakage or rupture protection or detection
• CPC Class Codes: G01L 9/0072 using variations in capacitance
• CPC Class Codes: G01M 3/16 using electric detection means G01M3/045, G01M3/06, G01M3/12, G01M3/20, G01M3/24, G01M3/26 take precedence

Abstract

A pressure-measuring device with monitoring for diaphragm fracture comprises a housing (10) with a passage whose two openings at the end faces of the housing (10) are closed by a first deformation body (21) and a second deformation body (22). The passage is completely filled with a transmission liquid in order to transmit the process pressure from the first deformation body (21) to the second deformation body (22). The device comprises means (31, 32) for monitoring a material property of the transmission liquid. A change in the material property indicates contamination by the process medium and thus a fracture of the first deformation body. The material property monitored is preferably the relative dielectric constant.

Claims

1. A pressure-measuring device, comprising

a housing which has a passage having a first opening and a first deformation body, which is exposed to the measuring medium and closes off the first opening, a second opening and a second deformation body, which closes off the second opening, and a transmission liquid for introducing pressure from the first deformation body to the second deformation body;

a pressure sensor which, based on the deflection of the second deformation body, produces a measuring signal;

wherein

the device also has a means for monitoring a material property of the transmission liquid.

2. The device as claimed in claim 1, the means for monitoring a material property being made in such a way that it produces a signal if the material property changes beyond a tolerance value.

3. The device as claimed in claim 1 or 2, the pressure sensor being a capacitive sensor, the means for monitoring a material property of the transmission liquid being a means for monitoring the relative dielectric constant ε

_r.

4. The device as claimed in one of claims 1 to 3, the first deformation body being a metal diaphragm.

5. The device as claimed in one of claims 1 to 4, the second deformation body having a disk made of a brittle material, in particular a ceramic disk having a high proportion of Al₂O₃.

6. The device as claimed in one of claims 3 to 5, the means for monitoring the relative dielectric constant ε

_r comprising an electronic control arrangement which determines the relative dielectric constant ε

_r with reference to the pressure-dependent capacitance of the pressure sensor.

7. The device as claimed in either of claims 1 and 2, the means for monitoring a material property of the transmission liquid being a means for monitoring the relative dielectric constant ε

_r of the transmission liquid, and the device having at least two electrodes which are arranged in an essentially pressure-independent geometrical relationship to one another, the means having an electronic control arrangement which monitors the relative dielectric constant ε

_r of the transmission liquid with reference to the capacitance between these electrodes.

8. The device as claimed in one of the preceding claims, the pressure sensor being an absolute-pressure sensor or a relative-pressure sensor or a differential-pressure sensor.

9. A method of monitoring for diaphragm fracture for a pressure-measuring device in which the process pressure is transmitted by means of a transmission liquid from a first deformation body designed as a diaphragm to a second deformation body, the method having the following steps:

i. recording at least one measured variable which gives an indication of the current value of a material property of the transmission liquid;

ii. comparing the at least one recorded measured variable or a variable derived therefrom with at least one reference value; and

iii. producing an alarm signal if the comparison results in a deviation or deviations from the reference value or reference values.

10. The method as claimed in claim 9, the material property being the relative dielectric constant ε

_r of the transmission liquid.

11. A program for operating on an electronic data processing system for carrying out the method as claimed in claim 9 or 10.