Method for detecting a membrane rupture of a pressure-measuring transducer

Abstract

A method for detecting a membrane rupture of a pressure-measuring transducer, comprising the following steps: a) recording measured pressure values, in particular following one after the other in time, by means of the pressure-measuring transducer (100); b) extracting positive and negative pressure peaks from the measured pressure values recorded; c) dividing the pressure peaks into negative and positive pressure peaks (Ppos, Pneg); d) determining a relationship of the difference in pressure between the positive and negative pressure peaks; e) deciding / establishing, on the basis of the relationship of the difference in pressure (Pver) determined between the positive and negative pressure peaks ((Ppos, Pneg), whether a membrane rupture has occurred.

Description

[0001] Method for detecting a diaphragm rupture of a pressure sensor

[0002] The invention relates to a method for detecting a diaphragm rupture of a pressure transducer, a computer program with instructions which, when the program is executed by a computer, cause the computer to carry out the method, a computer-readable medium with commands which, when executed by a computer, cause the computer to carry out the method, and a pressure transducer.

[0003] In pressure measurement technology, absolute pressure, differential pressure, and gauge pressure sensors are known. Absolute pressure sensors measure the prevailing pressure absolutely, i.e., relative to a vacuum, while differential pressure sensors measure the difference between two different pressures. With gauge pressure sensors, the pressure to be measured is determined relative to a reference pressure, with the atmospheric pressure prevailing in the vicinity of the gauge pressure sensor serving as the reference pressure. A wide variety of such absolute pressure, differential pressure, and gauge pressure sensors are manufactured and distributed by companies in the Endress + Hauser Group.

[0004] Pressure transducers are used to measure pressure and / or to control, regulate, and / or automate a process occurring within a plant. Pressure measuring devices are used in automation technology in a wide variety of industries, e.g., the chemical and food industries, to name just a few important areas of application. Differential pressure measuring devices are used, in particular, for the continuous measurement of pressure differences in measuring media, e.g., liquids, vapors, gases, and dusts. The differential pressure can be used, for example, to determine the fill level of a medium in a container or the flow rate of a measuring medium through a pipeline.

[0005] Pressure and differential pressure transducers have a pressure-sensitive element, a so-called pressure sensor, which is subjected to a first pressure and a second pressure on two opposite surfaces. The medium is generally not in direct contact with the pressure sensor, but is sensed by one (in the case of the pressure transducer) and two (in the case of the differential pressure transducer) pressure-sensitive diaphragm(s) facing the process. Each diaphragm can have an associated diaphragm bed, which can be used to shape the diaphragm and to limit its displacement in the event of an overload. A diaphragm seal fluid is often used in addition, which transmits the pressure of the medium acting on the diaphragm to one of the two surfaces of the pressure sensor via a pressure transmission path.

[0006] To achieve sufficiently high hydraulic capacity, these membranes, also known as separating membranes, are typically made of steel sheets or foils with thicknesses ranging from a few tens of microns to a few hundred microns. However, this thin material thickness carries a certain risk of leakage, especially when the separating membranes are exposed to abrasive or corrosive media.

[0007] This problem is generally known, and there are numerous approaches to diagnosing a leak. For example, DE 102 00 779 B4, EP 1 275 951 B1, and EP 0 838 672 A1 describe devices in which the properties of the transmission fluid are to be monitored. After a leak occurs, an exchange should therefore occur between the transmission fluid and the measuring medium, which should result in a change in the electrical conductivity or dielectric constant. However, it has been shown that the medium exchange that occurs in the event of a leak occurs essentially by diffusion and is therefore too slow to result in a detectable change in a property of the transmission fluid contained in the diaphragm seal chamber within a useful time frame.

[0008] DE 199 49 831 B4 discloses a double membrane system comprising two membranes positioned one above the other. A vacuum is created between the membranes, which is monitored. If a change in the vacuum is detected, particles must have entered between the membranes. This is considered an indication of a membrane rupture. The disadvantage is that such double membrane systems are relatively expensive to manufacture due to their high complexity. Furthermore, an additional sensor is required to monitor the vacuum.

[0009] The invention is therefore based on the object of proposing a simple and cost-effective method by means of which a membrane rupture can be detected.

[0010] The object is achieved according to the invention by the method for detecting a diaphragm rupture of a pressure measuring sensor according to patent claim 1, a computer program according to patent claim 9, a computer-readable medium according to patent claim 10 and a pressure measuring sensor according to patent claim 11.

[0011] The method according to the invention for detecting a diaphragm rupture of a pressure transducer comprises the following steps: a) recording, in particular, temporally successive pressure measurement values ​​using the pressure transducer; b) extracting positive and negative pressure peaks from the recorded pressure measurement values; c) classifying the pressure peaks into negative and positive pressure peaks; d) determining a pressure difference ratio between the positive and negative pressure peaks; e) deciding / determining whether a diaphragm rupture has occurred based on the determined pressure difference ratio between the positive and negative pressure peaks.

[0012] The invention is based on the idea that diaphragm rupture detection is possible by determining and evaluating successive pressure peaks resulting from both deflection directions of the diaphragm, which are extracted from the recorded pressure measurements. This means that the evaluation of the pressure measurement signal and the detection of a possible diaphragm rupture takes place in the time domain, based solely on the recorded pressure measurements. A complex transformation, e.g., into the frequency domain, for further evaluation or analysis of the pressure measurements is not necessary.

[0013] An advantageous embodiment of the method according to the invention can provide that, in order to extract the positive and negative pressure peaks, the recorded pressure measurement values ​​are first divided into sections and a median or a mean is determined for each section, wherein the pressure measurement values ​​that lie above the determined median or mean are characterized as positive pressure fluctuations and the pressure measurement values ​​that lie below the determined median or mean are characterized as negative pressure fluctuations, from which the positive and negative pressure peaks are then extracted. The advantageous embodiment of the method according to the invention can further provide that, in order to extract the positive and negative pressure peaks, an envelope curve is determined for the positive pressure fluctuations and an envelope curve for the negative pressure fluctuations and / or that a strictly monotonic, in particularA strictly x-monotonic envelope is used. In particular, the embodiment can further provide that the high points of both envelopes are treated as positive and negative pressure peaks, respectively. A strictly x-monotonic envelope has only points P_n that are temporally prior to point P_n+1.

[0014] A further advantageous embodiment of the method according to the invention can provide that, in order to determine the pressure interval ratio between the positive and the negative pressure peaks, pressure intervals of temporally successive pressure peaks are first determined for both the positive and the negative pressure peaks and the pressure intervals are included in the determination of the pressure interval ratio.In particular, the embodiment can provide that, in order to determine the pressure interval ratio, a frequency distribution is created in which the previously determined pressure intervals for the positive and negative pressure peaks are recorded numerically, and wherein the pressure interval ratio between the positive and negative pressure peaks is determined based on the frequency distribution and / or that a diaphragm rupture is detected if there are significantly more pressure intervals for the positive pressure peaks than pressure intervals for the negative pressure peaks in a pressure interval range, in particular in a pressure interval range around the zero point. Significantly more pressure intervals for the positive pressure peaks than pressure intervals for the negative pressure peaks can exist, for example, if a modal class for the positive pressure peaks is at least approx.10% greater than for the negative pressure peaks, whereby this applies to typical pressure and / or temperature ranges in which the pressure sensor is used.

[0015] The invention further relates to a computer program with instructions which, when the program is executed by a computer, cause the computer to carry out the method according to one of the previously described embodiments.

[0016] The invention further relates to a computer-readable medium having instructions which, when executed by a computer, cause the computer to carry out the method according to one of the previously described embodiments.

[0017] The invention further relates to a pressure transducer comprising at least: a) a pressure sensor for detecting pressure measurement values; b) a diaphragm rupture detection unit configured to carry out the method according to one of the previously described embodiments starting from method step b).

[0018] The invention is explained in more detail with reference to the following drawings. It shows:

[0019] Fig. 1 : an overall view of an embodiment of a pressure sensor according to the invention,

[0020] Fig. 2: a section with 512 temporally consecutive pressure readings recorded by the pressure sensor, in which the pressure readings are divided into positive and negative pressure fluctuations, each of which is enveloped by an envelope curve,

[0021] Fig. 3: the envelope of the positive pressure fluctuations, Fig. 4: a frequency distribution of positive and negative pressure peaks of an intact membrane, and

[0022] Fig. 5: a frequency distribution of positive and negative pressure peaks of a non-intact membrane.

[0023] The pressure transducer 100 shown in Fig. 1 comprises a pressure sensor, here a piezoresistive pressure sensor 110 with a measuring diaphragm 112. The pressure sensor 110 has resistance elements in a bridge circuit to convert a pressure-dependent deformation or deflection of the measuring diaphragm into an electrical signal. Instead of the piezoresistive pressure sensor, a capacitive pressure sensor can also be provided, in which case the measuring diaphragm has an electrode whose capacitance relative to an electrode on a rigid counter-body is a measure of the pressure-dependent deformation or deflection of the measuring diaphragm. Details of electrical transducers are familiar to a person skilled in the field of pressure measurement technology and need not be explained in detail here.

[0024] The pressure transducer 100 can further comprise, as shown in Fig. 1, a hydraulic diaphragm seal 130 with a diaphragm seal body 132 and a separating diaphragm 134. The separating diaphragm 134 is joined, i.e. welded or soldered, to the diaphragm seal body 132 along a circumferential edge, so that the diaphragm seal chamber 136 is formed between the two joining partners. A channel 138 extends from the diaphragm seal chamber 136 into a pressure sensor chamber 140, in which the pressure sensor 110 is arranged. The pressure sensor chamber 140 is coupled to the diaphragm seal chamber via a transmission fluid, so that the measuring diaphragm 112 is hydraulically coupled to the separating diaphragm 134. This means that the pressure introduced into the diaphragm seal chamber 136 via the separating diaphragm 134 is essentially present at the measuring diaphragm 112.

[0025] Dividing the described hydraulic system into a pressure sensor chamber 140 and a diaphragm seal chamber 136, as well as a channel connecting the chambers, is advantageous but not absolutely necessary. To implement the invention, the pressure sensor can also be arranged in the diaphragm seal chamber.

[0026] The transfer fluid generally exhibits a greater thermal volume expansion than the chambers and channels enclosing it. This results in a volumetric displacement that is accommodated not by deflection of the sensor membrane 112 but by deflection of the separating membrane 134. This means that the measuring membrane 112 has a first hydraulic capacity dV1 / dp, and the separating membrane 134 has a second hydraulic capacity dV2 / dp, with the second hydraulic capacity being significantly greater than the first hydraulic capacity.

[0027] The separating diaphragm 134 is an elastic body for which an equilibrium position exists, in which the pressure in the diaphragm seal chamber 136 is equal to the pressure on an outer side of the separating diaphragm 134 facing away from the diaphragm seal chamber 136. The equilibrium position of the separating diaphragm 134 corresponds to an equilibrium volume of the diaphragm seal chamber 136.

[0028] However, it is provided that the diaphragm seal chamber 136, in an operational state—in short, the operating state—of the pressure transducer 100 has an operating volume VB that deviates from the equilibrium volume VO to such an extent that a pressure difference ApB between a pressure in the diaphragm seal chamber 136 and the pressure on the outside of the separating membrane 134 is not less than a threshold value ApS of, for example, a few tens of mbar, in particular of at least 40 mbar, very particularly of at least 60 mbar, very particularly of approximately 70 mbar. This causes transmission fluid to be forced out of the diaphragm seal chamber 136 in the event of a leak until pressure equalization between the diaphragm seal chamber 136 and the volume on the outside of the separating membrane 134 has occurred. As a result, the current position of the separating membrane 134 also changes, in particular.

[0029] To generate a pressure measurement signal comprising the pressure measurement values, the pressure sensor 100 has an operating and / or evaluation circuit 160 configured to output a pressure measurement signal corresponding to a deflection of the measuring diaphragm 112. For this purpose, the operating and / or evaluation circuit can, for example, comprise a microprocessor 162 for processing signals from the pressure sensor 110 digitized by means of an ADC 164.

[0030] Furthermore, the pressure sensor 100 in this case has a diaphragm rupture detection unit 150 configured to detect a rupture of the separating diaphragm 134. The diaphragm rupture detection unit 150 can, as shown in Fig. 1, be configured as part of the operating and evaluation circuit 160. Alternatively, the diaphragm rupture detection unit 150 can also be configured as a separate unit. For example, the diaphragm rupture detection unit 150 can also be configured separately from the pressure sensor, e.g., in a cloud or the like.

[0031] The diaphragm rupture detection unit is designed to detect a diaphragm rupture by determining successive pressure peaks for both deflection directions of the diaphragm in the time domain. To do this, the pressure measurement signal is first recorded or acquired over any desired period of time. This can occur in particular during the actual measuring operation of the pressure sensor. The pressure measurement values ​​are preferably recorded by the pressure sensor at a recording or sampling rate of more than 100 Hz, preferably more than 150 Hz, particularly preferably more than 200 Hz. The pressure measurement signal is then divided by the diaphragm rupture detection unit into successive non-overlapping sections. For example, the pressure measurement signal can be divided into sections having 512 successive pressure measurement values. Fig. 2 shows such a section with 512 successive pressure measurement values. The length of each section, i.e.The length of the sample, i.e., the number of consecutive pressure measurements, can be varied to adapt the diaphragm rupture detection to individual circumstances, e.g., the memory size of the diaphragm rupture detection unit or the platform on which the process is running. Regarding a minimum length, it has been found that each section advantageously has at least 10 pressure measurements, preferably at least several tens of pressure measurements, particularly preferably at least 20 pressure measurements.

[0032] The diaphragm rupture detection unit then determines, or in particular calculates, a median or mean value for each section, as shown by way of example in Fig. 2. Based on the determined median or mean value, the diaphragm rupture detection unit then determines both negative and positive pressure fluctuations. For this purpose, the diaphragm rupture detection unit is configured to treat all measured values ​​below the median or mean value as negative pressure fluctuations, and all measured values ​​above the median or mean value as positive pressure fluctuations. In a subsequent step, all sufficiently high peaks are determined by the diaphragm rupture detection unit for each pressure fluctuation direction (positive, negative) and each section. Which peaks are considered sufficiently high is variably adjustable and depends essentially on the specified pressure measuring range of the pressure sensor.For example, in a pressure sensor with a specified pressure measuring range of ± 400 mbar, a distance between two peaks of less than 1 / 10 mbar, preferably less than 1 / 15 mbar, particularly preferably approximately 1 / 20 mbar, can be considered sufficiently high, so that at least the higher of the two peaks is considered a sufficiently high peak. Accordingly, the diaphragm rupture detection unit can be configured to specify which peaks it should consider sufficiently high.

[0033] In order to determine sufficiently high peaks for each pressure fluctuation direction (positive, negative), the diaphragm rupture detection unit can be set up to create or determine a strictly x-monotonic envelope curve for the positive and negative pressure fluctuations (cf. Fig. 2, dashed line). The term “strictly x-monotonic” is to be understood in such a way that for each point of the envelope curve (P_1, P_2, ...) P_n, this point lies chronologically before the point P_n+1. The high points of both envelope curves, more precisely the high points of the envelope curve for the positive pressure fluctuations and the low points of the envelope curve for the negative pressure fluctuations, are the pressure peaks. In the next step, the pressure intervals between the successive pressure peaks are calculated and stored. Fig. 3 shows the envelope curve of the positive pressure fluctuations. As an example, Fig.3 For the first three pressure peaks, the calculated pressure intervals are marked by an arrow.

[0034] If we now look at a frequency distribution, e.g. in a histogram, of the previously calculated and saved distances for the positive pressure peaks in comparison to the previously calculated distances for the negative pressure peaks, a membrane rupture can be determined if significantly more positive distances from the positive pressure peaks are close to one another than is the case with the negative distances from the negative pressure peaks. Significantly more pressure distances for the positive pressure peaks than pressure distances for the negative pressure peaks occur when a modal class for the positive pressure peaks is at least approx. 10% larger than for the negative pressure peaks. In other words and in relation to the frequency distributions shown in Fig. 4 and 5, this means that in the case that the highest bar for the positive pressure peaks, which in Fig. 4 and 5 is at a difference of approx. 0 mbar, is approx.10% higher than the bar for negative pressure peaks, a diaphragm rupture can be detected. This primarily applies to the typical pressure and / or temperature ranges in which the pressure sensor is used. However, the value of approximately 10% may be lower, especially if the pressure sensor is operated in a non-typical pressure and / or temperature range, for example, if the pressure sensor is operated at very low temperatures (T < 0°C, especially T < -15°C).

[0035] To clarify the above, Figs. 4 and 5 each show a histogram with the frequency distribution of the calculated distances for the positive and negative pressure peaks. Fig. 4 shows the frequency distribution for an intact membrane, and Fig. 5 shows the frequency distribution for a membrane with a rupture. From the figures, it can be deduced that a pressure-distance ratio can be determined at which a rupture can be detected if significantly more positive distances are close to one another than for the negative pressure peaks. The class frequency of the positive histogram is thus significantly higher near the zero point than that of the negative histogram.

[0036] 100 Pressure transducer 110 Pressure sensor

[0037] 112 measuring membrane

[0038] 130 Diaphragm seal 132 Diaphragm seal body

[0039] 134 Separation membrane

[0040] 136 Diaphragm seal chamber 138 Channel

[0041] 140 pressure sensor chamber

[0042] 150 Diaphragm rupture detection unit 160 Operating and evaluation circuit

[0043] 162 Microprocessor 164 ADC

[0044] 200 Process medium Ppos Positive pressure peaks Pneg Negative pressure peaks Pver Pressure gap ratio M Median or mean value H Envelope

Claims

Patent claims 1 . A method for detecting a diaphragm rupture of a pressure transducer, comprising the following steps: a) detecting, in particular, temporally successive pressure measurement values ​​by means of the pressure transducer (100); b) extracting positive and negative pressure peaks from the detected pressure measurement values; c) classifying the pressure peaks into negative and positive pressure peaks (Ppos, Pneg); d) determining a pressure difference ratio between the positive and negative pressure peaks; e) deciding / determining whether a diaphragm rupture has occurred based on the determined pressure difference ratio (Pver) between the positive and negative pressure peaks (Ppos, Pneg).

2. Method according to claim 1, wherein, in order to extract the positive and negative pressure peaks (Ppos, Pneg), the recorded pressure measurement values ​​are first divided into sections and a median or a mean value (M) is determined for each section and wherein the pressure measurement values ​​which are above the determined median or mean value (M) are characterized as positive pressure fluctuations and the pressure measurement values ​​which are below the determined median or mean value are characterized as negative pressure fluctuations, from which the positive and negative pressure peaks (Ppos, Pneg) are subsequently extracted.

3. Method according to the preceding claim, wherein, in order to extract the positive and negative pressure peaks (Ppos, Pneg), an envelope curve (H) for the positive pressure fluctuations and an envelope curve for the negative pressure fluctuations are determined.

4. Method according to the preceding claim, wherein a strictly monotonic, in particular a strictly x-monotonic envelope is used as the envelope (H).

5. Method according to one of claims 3 or 4, wherein the high points of both envelopes (H) are treated as positive or negative pressure peaks (Ppos, Pneg).

6. Method according to one or more of the preceding claims, wherein, in order to determine the pressure interval ratio (Pver) between the positive and the negative pressure peaks (Ppos, Pneg), pressure intervals of temporally successive pressure peaks for both the positive and the negative pressure peaks (Ppos, Pneg) are first determined and the pressure intervals are included in the determination of the pressure interval ratio (Pver).

7. Method according to the preceding claim, wherein, in order to determine the pressure interval ratio (Pver), a frequency distribution is further created in which the previously determined pressure intervals for the positive and negative pressure peaks (Ppos, Pneg) are recorded numerically, and wherein the pressure interval ratio (Pver) between the positive and the negative pressure peaks (Ppos, Pneg) is determined on the basis of the frequency distribution.

8. Method according to one of claims 6 or 7, wherein a diaphragm rupture is detected when there are significantly more pressure intervals for the positive pressure peaks (Ppos) than pressure intervals for the negative pressure peaks (Pneg) in a pressure interval range, in particular in a pressure interval range around the zero point.

9. A computer program comprising instructions which, when executed by a computer, cause the computer to carry out the method according to at least one of claims 1 to 8.

10. A computer-readable medium containing instructions which, when executed by a computer, cause the computer to perform the method of any one of claims 1 to 8.

11. Pressure transducer comprising at least: a) a pressure sensor (110) for detecting pressure measurement values; b) a diaphragm rupture detection unit (150) configured to carry out the method according to at least one of claims 1 to 8 starting from method step b).

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