Pressure sensor with foresighted maintenance control and monitoring for diaphragm fracture and to a method for monitoring for diaphragm fracture

• US 6,776,046 B2
• Filed: 07/11/2002
• Issued: 08/17/2004
• 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
• Primary Examiner(s): Lefkowitz, Edward
• Assistant Examiner(s): JENKINS, JERMAINE L
• Application Number:
  US10/192,817
• Publication Number:
  US 20030024319A1
• Time in Patent Office: 768 Days
• Field of Search: 737/00--56, 361/283-283
• US Class Current: 73/715
• 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 with a passage whose two openings at the end faces of the housing are closed by a first deformation body and a second deformation body. The passage is completely filled with a transmission liquid in order to transmit the process pressure from the first deformation body to the second deformation body. The device has components 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 having a passage defining a first opening and a second opening;

a metal diaphragm exposed to a measuring medium and situated to close off said first opening;

a deformation body situated to close off said second opening;

transmission liquid situated between said metal diaphragm and said deformation body for communicating pressure at said metal diaphragm to said deformation body;

a capacitive pressure sensor situated in said housing which produces a measuring signal based upon a deflection of said deformation; and

means for monitoring a material property of said transmission liquid, said means for monitoring being means for monitoring the relative dielectric constant ε

_r of said transmission liquid and being adapted to produce a signal indicating fracture of said metal diaphragm if said material property changes beyond a tolerance value.

2. The device as defined in claim 1, wherein:

said deformation body has a disk made of a brittle material.

3. The device as defined in claim 2, wherein:

said disk made as a ceramic disk having a high proportion of A1₂O₃.

4. The device as defined in claim 1, wherein:

said means or monitoring comprising an electronic control arrangement which determines the relative dielectric constant ε

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

5. The device a defined in claim 1, wherein:

said means or monitoring comprising at least two electrodes which are arranged in an essentially pressure-independent geometrical relationship to one another, with the capacitance between said electrodes serving to monitor the relative dielectric constant ε

_r.

6. The device a defined in claim 1, wherein:

said capacitive pressure sensor is an absolute-pressure sensor.

7. The device a defined in claim 1, wherein:

said capacitive pressure sensor is a differential-pressure sensor.

8. A method of monitoring for diaphragm fracture for the diaphragm of a pressure-measuring device in which the process pressure is transmitted by means of transmission liquid from a metal diaphragm to a deformation body of the device, the method comprising the steps of:

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

establishing at least one reference value fo the measured variable;

comprising said at least one recorded measured variable, or a variable derived therefrom with said established at least one reference value; and

producing an alarm signal if the comparison results in a deviation or deviations from the reference value or reference values, wherein;

the material property is the relative dielectric constant ε

_r of the transmission liquid.

9. A program for operating on an electronic data processing system for carrying out the method as defined in claim 8.