WO2012028428A2

WO2012028428A2 - Pressure measurement transducer

Info

Publication number: WO2012028428A2
Application number: PCT/EP2011/063660
Authority: WO
Inventors: Holger Fehrmann; Christoph Paulitsch; Frank Wohlfarth
Original assignee: Siemens Aktiengesellschaft
Priority date: 2010-08-31
Filing date: 2011-08-09
Publication date: 2012-03-08
Also published as: WO2012028428A3; DE102010035965A1

Abstract

The invention relates to a pressure measurement transducer having a measurement chamber (1), which is separated from a process medium (3) to be measured by a separating diaphragm (2). Means (5), with which a force acting on the separating diaphragm is generatable for deflecting the separating diaphragm, are provided in or on the measurement chamber (1). Using an evaluation device (7), a characteristic variable is calculated on the basis of the resulting force profile and compared with a corresponding characteristic variable of a predetermined reference profile. In dependence on deviations between the two characteristic variables, a signal is output to indicate a diaphragm error. The pressure measurement transducer thus advantageously allows a diagnosis of the separating diaphragm (2), without the latter having to be removed from a process-engineering system. The diagnosis is additionally performable such that it is less dependent on the respectively prevailing boundary conditions in the system.

Description

description

Pressure Transmitter

The invention relates to a pressure transducer with a measuring chamber, which is separated by a separating membrane of a medium to be measured and filled to forward the pressure to a pressure sensor with a pressure transmission fluid, according to the preamble of claim 1.

Such a pressure sensor is already out of the

DE 103 42 368 AI known. There, a pressure transducer is disclosed with a housing in which a measuring diaphragm is arranged, which divides a housing interior into a measuring chamber and a reference chamber. Each chamber is provided with a pressure channel leading to a separation membrane. The separation membranes separate the measuring chamber or the reference chamber from a process medium. The two chambers are filled with a pressure transfer fluid, such as a silicone oil. In order to generate an electrical measuring signal which changes as a function of the applied pressure difference, the measuring diaphragm can carry a pressure sensor which, for example, is made of silicon and provided with expansion resistors. By means of a device for evaluating the measurement signal, a measured value can be ^generated and output from the electrical measurement signal.

When using pressure transducers in process engineering plants, it may happen that a separation membrane is chemically attacked by the process medium or mechanically damaged. If a hole is formed in the membrane, the pro ^¬ zessmedium enters the measuring chamber or the reference chamber and reaches the pressure sensor that is sensitive to the process medium. Before a total failure occurs, erroneous readings may occur during a transitional period that the user does not notice. This can have serious consequences in a process engineering plant. Furthermore, it can through the process medium to deposits on a Separation membrane come, which hinder the pressure transmission to the sensor. This results in incorrect measurements that are difficult to detect by the user. For example, by an optical inspection, which requires a prior expansion of the pressure transducer, such errors are recognizable.

So that a monitoring of the state of a separation membrane is already made possible without removal of the pressure transducer, it is known from the aforementioned DE 103 42 368 AI to provide the measuring chamber with means by which their volume can be varied according to a substantially predetermined time course. A thereupon-adjusting curve of the measurement signal is closed with a reference profile ver ^¬ equalized and if progress on a diaphragm failure. As a means for changing the measuring chamber volume, a piezoelectric element is listed, which is located on the housing wall and which is thus exposed to the pressure prevailing in the measuring chamber static pressure. Therefore at high static pressure, the change in the measurement chamber volume can be considerably more difficult or even impossible to ^¬. The implementation of a diaphragm diagnosis is thus highly dependent on the prevailing operating conditions, in particular of the static pressure in the known pressure transmitter.

The invention has for its object to provide a pressure measuring ^¬ converter, which allows monitoring of the state of a separation membrane with improved independence from the prevailing operating state of the pressure transducer ^¬ light.

To solve this problem, the new pressure transducer of the type mentioned in the characterizing part of claim 1 features. In the dependent claims advantageous developments of the invention are described.

The invention has the advantage that the diagnosis can be carried out with greater independence from the respective prevailing process pressure. is feasible. Without a force, the separation membrane is in a pressure equilibrium between the measuring chamber and the process medium. A displacement volume generated during a deflection of the separation membrane can be additionally connected to a corresponding deflection of a central membrane, which is also referred to as a measurement membrane, and in the case of a differential pressure transmitter additionally with a corresponding deflection of a second separation membrane. A parameter of the force curve generated for the deflection of the separation membrane is compared for diagnosis with a corresponding parameter of a reference curve, which was previously determined in good case, ie in the case of a fault-free membrane, under comparable external boundary conditions and stored in the evaluation. If changes occur, such as deposits, fatigue or cracks, the separation membrane, the characteristic of the power ^¬ course will also change. To take account of the dependence of the parameter on different operating conditions, characteristic force profiles can be recorded and stored under different operating conditions, in particular at different process pressures. Different error cases each lead to different Ver ^¬ changes in the force profile. For example, the force curve in case of damage to the membrane discontinuities z. Due to widening cracks, changing media flow into the metering chamber or spalling of deposits. With strong deposits on the separation membrane, the separation membrane of a deflection opposes a higher resistance, so that an increase in the forces can be detected in the force curve. In the case of a leak on the other hand, this resistance and, accordingly, the size of the zuwendenden on ^¬ forces in the force line decrease.

Furthermore, the invention has the advantage that the means for generating force are arranged in or on the measuring chamber and thus protected ge against a possibly aggressive process medium ge ^{¬ are} stored. Compared to the known optical inspection of the separation membrane, the invention has the advantage that a reliable statement about the state of the separation membrane can be obtained without the pressure transmitter must be removed previously, for example, from a pipeline. Thus, the diagnosis can be made virtually during operation of the pressure transmitter. In addition, an aging process of the separation membrane is recognizable and it can be responded to in time before a failure of the pressure transmitter threatens and it may come to a halt in the process plant in which the pressure transducer is operated. A further advantage is the fact that the measured value delivered by a pressure transducer according to the invention becomes more reliable since changes in the separating membrane, for example deposits or material erosion due to corrosion or abrasion, which could falsify the measured value, can be automatically detected and reported to the new pressure transducer by diagnosis , In addition, the new pressure transmitter has the advantage that a possible optical inspection, which was previously required for certain measuring media, is eliminated, and thus the monitoring of the state of a separation membrane is connected with much less effort.

Advantageously, no special force sensors is then required, for example ^¬ Lich for detecting the force curve, when an electro-mechanical linear drive is used as means for power generation, which is driven by the evaluation device ^¬. The evaluation device can then advantageously determine the generated force curve and thus its characteristic used for comparison with a reference based on the drive current.

In the case of an electromechanical linear drive, a further parameter can advantageously be determined and evaluated on the basis of the drive ^clamping voltage. From the induced electrical voltage can namely be concluded that the movement speed of the separation membrane, in particular when using an electrodynamic linear drive, so that From the current and voltage, the generated force or the Geschwin ^¬ speed can be estimated directly. The evaluation of the additional parameter allows an improvement of Reliable ^¬ ness of diagnostic statements. In the case of heavy deposits, for example, the speed of movement of the separating membrane falls below a reference value of the speed previously recorded in good case. In the case of a leak, on the other hand, it is exceeded because the separating membrane opposes a movement of a lower resistance.

A limitation of the deflection of the separation membrane by a predetermined end position has the advantage that the force curves generated can be recorded for a predetermined range of the deflection and compared with corresponding reference curves. The reliability of the diagnosis statement can thereby be further improved.

In a particularly advantageous embodiment of the invention, the predetermined end position is determined by a mechanical An ^¬ impact. In a known travel until it stops a distance measurement is unnecessary. The stop may be realized, for example, by a membrane bed on which the membrane bears at maximum deflection, or as the travel limit of the linear drive.

Advantageously, a preventive maintenance of a pressure transmitter before an impending failure is possible if a trend statement is determined and output by the evaluation based on temporal changes in a characteristic of the self-adjusting course of the force generated at time spaced, for example cyclically performed diagnostic operations, based on which War can estimate ^¬ maintenance personnel when to expect an imminent failure.

The functions of an evaluation device required for monitoring a separation membrane can be carried out without great effort by suitable design of an operating program Arithmetic unit are realized when an evaluation unit is used on the basis of a microprocessor. The Her ^¬ position free of the pressure transmitter are thus beneficial ^¬ way hardly affected by the new method of diagnosis. In this case, the evaluation device can be realized by the same arithmetic unit which, in the case of a pressure transmitter, carries out anyway required functions of the measured value processing and communication.

With reference to the figures, in which embodiments of the invention are illustrated, the invention and refinements and advantages are explained below.

Show it:

Figure 1 is a sectional view of a process connection with integ ^¬ oriented linear drive and

Figure 2 is a sectional view of a process connection with in the

Housing wall built-in linear drive.

In the figures, like parts are given the same reference numerals.

The drawings show only the parts of a pressure measurement transducer ^¬ which are modified to implement the invention compared to a conventional pressure transducer. Other parts of the pressure transducer, such as pressure sensor, measuring diaphragm, reference chamber and a separation membrane on the reference side of the measuring cell, can be constructed as in known Abso ^¬ lutdruck- or differential pressure transducers.

FIGS. 1 and 2 each show a part of a measuring chamber 1 which is separated by a separation membrane 2 from a process medium 3 located in a pipe 13, whose pressure is detected by the pressure transmitter and measured as a measured value to a display or to a higher-level control ^¬ station is issued in a process engineering plant. The measuring chamber 1 is located in a housing 4, which in addition for the storage of the separation membrane 2 and a linear drive 5 is used. By the linear drive 5, acting on the separation membrane 2 force F can be generated, through which the separation membrane 2 can be deflected over a path length S to an end position 6. The position of the end position 6 is determined by a limitation of the travel of the linear drive 5. Alternatively, it is possible to limit the travel S through a membrane bed, against which the separation membrane 2 rests in the end position 6. To carry out a separation membrane diagnosis, the electrodynamic linear drive 5 is preferably controlled by an evaluation device 7 such that the separation membrane 2 experiences a defined deflection and reaches the end position 6. By evaluating the ^¬ as to be fed in with the linear drive 5 current I ermit ^¬ telt the evaluation device 7 the timing of the force F which must be generated to carry out the movement of the diaphragm by means of the linear drive. 5 On the basis of the course, the evaluation device 7 calculates a parameter which is compared with a corresponding parameter of a reference profile, which was previously determined in good case and stored in a memory 8 of the evaluation 7, to make a statement about the state of the separation membrane 2. From the induced electrical voltage U is also closed to the travel speed of the linear drive 5. If changes, z. As a result of deposits on the separation membrane 2, a material fatigue or a crack of the separation membrane 2, so both the course of the generated force F and the time course of the travel speed changed. Since the changes of external boundary conditions such. B. may be dependent on the process pressure, the diagnosis should be performed only at defined boundary conditions, for which reference curves for the case of a fault-free separation membrane 2 are present. As parameters of the curves, for example, maximum values, minimum values ^¬, gradients, step heights can be calculated at points of discontinuity or durations of transitions and compared with corresponding parameters of the reference patterns. In the case of heavy deposits, for example, the force exceeds a threshold value determined on the basis of a reference curve and the Movement speed ^falls below the movement ^¬ speed associated, another threshold. In order to detect widening cracks, changing media flow into the cell, or spalling of deposits on the separation membrane, characteristics that are characteristic of discontinuities of the processes can be used. In one hole or a crack in the separation membrane, however, the force is below a predetermined threshold value and the moving speed exceeds a further prior ^¬ certain threshold. These are just examples of characteristic ^¬ sizes. In practice, it is possible to check the condition of the separation membrane 2 a variety of other parameters that are determined based on the determined force curve or the movement ^¬ speed, to be compared with corresponding characteristic ^¬ sizes of reference waveforms to a diagnostic statement about the condition of the separation membrane 2 hold true.

When using the new pressure transducer in a process ^¬ technical system, the obtained diagnosis ^statement is transmitted via, for example, a field bus 12 to a control station, not shown in the figures for further processing. If a membrane fault occurs, suitable measures for error handling can thus be initiated by the operating or maintenance personnel.

FIG. 1 shows an arrangement of an electrodynamic drive 5 in the center of the measuring chamber 1. Here be ^¬ there is the drive 5 is completely protected within the measuring cell and is fixedly mounted in an unspecified dargestell ^¬ th in Figure 1, in the housing. 4

FIG. 2 shows an alternative mounting of the linear drive 5 in a side wall of the housing 4. In order for the linear movement of a push rod 9 of the linear drive 5 to be deflected to the center of the separating membrane 2, a lever 10 is provided, which is pivotably mounted about a hinge 11. Figures 1 and 2 are merely schematic representations to illustrate the principle of action. Of course, any other mounting types of linear drives and transfer gears are possible. For example, linear drives can be used, which have a diameter of 3 to 4 mm, a length of 10 to 15 mm and a force of 3 to 6 N at a travel of 5 to 10 mm. At a speed of about 120 mm / min is sufficient to drive a power of less than 10 mW. This allows a separating diaphragm of a differential pressure transmitter with a stiffness of approx. 20 kN / m to be deflected in the desired manner. Preferably, during the deflection, a limit value of the movement speed is not exceeded so that a pressure sensor located in the measuring cell is not exposed to any unacceptable loads.

Claims

claims

1. Pressure transmitter with a measuring chamber (1), which is separated by a separating membrane (2) from a process medium to be measured (3) and filled to forward the pressure to a pressure sensor with a pressure transmitting fluid, characterized

that the measuring chamber (1) is provided with means (5), by means of which a force (F) acting on the separating membrane (2) can be generated for the deflection of the separating membrane, and

that an evaluation device (7) is designed such that at least one parameter of the generated to the deflection of the separating ^membrane-¬ (2) force curve with a corresponding characteristic of a reference curve is comparable and

that, depending on deviations between the two parameters a signal for displaying an error from membrane is ^¬ gebbar.

2. Pressure transmitter according to claim 1, characterized in that

in that the means (5) for generating force comprise an electromechanical linear drive (5) which can be activated by the evaluation device (7), and

in that the evaluation device (7) is designed to determine the parameter on the basis of the drive current (I).

3. pressure transmitter according to claim 2, characterized in that the evaluation device (7) is adapted to determine a further characteristic on the basis of the drive voltage (U) and evaluate.

4. Pressure transmitter according to one of the preceding claims, characterized in that the deflection of the separation membrane (2) by a predetermined end position (6) is limited.

5. Pressure transmitter according to one of the preceding claims, characterized in that the predetermined end ^¬ position (6) is fixed by a mechanical stop.