Protective film system for rod-shaped sensor and sensor unit

Abstract

The invention relates to a protective film system for a rod-shaped sensor and a sensor unit. A protective film system (20) for a rod-like sensor (10) comprises a film unit (24) which is resilient and has a lattice structure, an auxiliary fastening unit (25) which is adapted to fasten the film unit (24) to the rod-like sensor (10).

Description

Technical Field

[0001] The invention relates to a protective film system of a rod-shaped sensor and a sensor unit. Background Art

[0002] In analytical measurement technology, in particular in the fields of water management, environmental analysis, industry (e.g. food technology, biotechnology and pharmaceuticals), and for various laboratory applications, measured variables such as pH, conductivity or even the concentration of analytes such as ions or dissolved gases in gaseous or liquid media are of great importance. These measured variables can be acquired and / or monitored, for example, by means of electrochemical sensors (such as optical, potentiometric, amperometric, voltammetric or coulometric sensors) or conductivity sensors.

[0003] It is important that these sensors are as durable as possible and operate extremely reliably in all conceivable areas of application. In particular, in dirty environments, the sensors must also be cleaned regularly. The sensors should therefore be particularly easy to clean without affecting the measurement quality.

[0004] A specific example of a sensor for dirty environments is an ISE sensor with an ion-sensitive membrane, which is used in wastewater treatment plants to determine ammonium and nitrate, for example, in so-called aeration basins. Here, it is important that there are no deposits on the membrane in order not to produce any differences between the concentrations in the process medium P and on the membrane. In addition to mineral deposits, bacteria, for example, can also deposit on the surface of the membrane. In order to prevent deposits from irreparably damaging the membrane, the surface must be cleaned regularly. It should therefore be easily accessible and easy to clean. Summary of the invention

[0005] The object of the present invention is therefore to propose a protective film system which enables a reliable and durable use of the sensor even under extremely dirty measuring conditions and which facilitates the cleaning of the sensor.

[0006] According to the invention, this object is achieved by a protective film system.

[0007] The protective film system according to the present invention comprises:

[0008] - membrane elements, which are elastic and have a lattice structure,

[0009] - an auxiliary fastening unit, which is suitable for fastening the membrane unit to the rod-shaped sensor.

[0010] The protective membrane system according to the invention enables the rod-shaped sensor to measure reliably over the longest possible period of use and to be easy to clean. Furthermore, the protective membrane system enables an optimal balance between the inflow of the medium onto the sensor and the protection of the sensor from premature contamination. In particular, in the case of an ion-selective electrode, the protective membrane system ensures a balanced relationship between inflow and inflow protection of the membrane.

[0011] According to one embodiment of the invention, the lattice structure has meshes with a size smaller than 1 mm, preferably smaller than 500 μm.

[0012] According to a further embodiment of the invention the membrane unit comprises a textile.

[0013] According to one embodiment of the present invention, the secondary fastening unit comprises an O-ring or a hook element.

[0014] According to an embodiment of the present invention, the protective film system further comprises an intermediate layer, which is suitable for being arranged between the film unit and the rod-shaped sensor.

[0015] According to one embodiment of the invention, the membrane unit is adapted to reduce ion transport across the membrane unit.

[0016] The above object is also achieved by a sensor unit.

[0017] The sensor unit according to the present invention comprises:

[0018] a sensor having a sensor body extending along an axis and having a first end, wherein the sensitive unit is arranged at the first end and the first end is suitable for being immersed in a process medium,

[0019] - The aforementioned protective film system, wherein the protective film system is arranged at the first end and fastened to the sensor body, so that the sensitive unit is covered by the protective film system towards the process medium.

[0020] According to one embodiment of the invention, the sensor body has a primary fastening unit which is complementary to a secondary fastening unit of the protective film system.

[0021] According to one embodiment of the present invention, the primary fastening unit is a groove extending around the axis in the sensor body (11), and the secondary fastening unit is designed as an O-ring.

[0022] According to one embodiment of the present invention, the primary fastening unit includes a hook element, and the secondary fastening unit is formed integrally with the film unit.

[0023] According to one embodiment of the present invention, the sensor comprises an ion selective electrode, and has an electrolyte in the sensor body, and a discharge line is arranged in the electrolyte, and the sensitive unit is an ion selective membrane in direct contact with the electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be explained in more detail based on the following description of the accompanying drawings. In the accompanying drawings:

[0025] - Figure 1 is a schematic diagram of an example of a sensor unit according to the present invention,

[0026] - Figure 2 is the voltage-time diagram of the first test,

[0027] - Figure 3 is the voltage-time graph of the second test,

[0028] - Figure 4 is a plot of measured voltage versus logarithm of concentration (the unprotected electrode has been corrected for drift between additions),

[0029] - Figure 5 Schematic diagram of the layer structure of the protected electrode. DETAILED DESCRIPTION

[0030] Figure 1 An embodiment of a sensor unit 100 according to the invention is shown, which comprises a sensor 10 and a protective film system 20 according to the invention.

[0031] The sensor 10 comprises a sensor body 11 extending along an axis Z and having a first end 14. Depending on the embodiment of the sensor 10, the sensor body 11 is made of, for example, PEEK plastic, ceramic, glass or metal. A sensitive unit 13 is arranged at the first end 14 of the sensor body 11. The sensitive unit 13 is preferably arranged on the front side of the sensor body 11. The sensitive unit 13 is suitable for contacting with the process medium P. According to a first embodiment of the invention, the sensitive unit 13 is an ion selective membrane. In the case of an ion selective membrane, for example, it is bonded or directly applied to the sensor body 11.

[0032] According to another embodiment of the present invention, the sensitive unit 13 is, for example, a pH membrane of a pH sensor.

[0033] according to Figure 1In the first embodiment of the present invention shown, the sensor 10 comprises an ion selective electrode. In this embodiment, an electrolyte 17 is arranged in the sensor body 11. The electrolyte 17 is preferably a liquid or gel-like electrolyte 17, which is arranged in a chamber of the sensor body 11. Likewise, the discharge line 12 is arranged in the electrolyte 17. The ion selective membrane is in direct contact with the electrolyte 17. The ion selective membrane seals the chamber of the sensor body 11 with a high resistance against the process medium and ensures that no process medium P is in direct contact with the electrolyte 17.

[0034] The sensor body 11 has a main fastening unit 15. The main fastening unit 15 is for example a groove in the sensor body 11 extending around the axis Z. The peripheral groove is designed to accommodate an O-ring. According to an alternative embodiment of the invention not shown, the main fastening unit 15 comprises at least one hook element.

[0035] The protective film system 20 of the sensor unit 100 includes a film unit 24 and an auxiliary fastening unit 25 .

[0036] The protective film system 20 is adapted to be arranged at the first end 14 of the sensor body 11. The protective film system 20 is adapted to be fastened to the sensor body 11 by means of the secondary fastening unit 25, such that the sensitive unit 13 is completely covered by the protective film system 20.

[0037] The membrane unit 24 is elastic and has a lattice structure. The lattice structure has a mesh with a size of less than 1 mm. Preferably, the mesh size is less than 500 µm. Depending on the field of application, i.e. the degree of contamination of the process medium P, a smaller or larger mesh size can be selected. The small mesh has the effect of better keeping dirt (especially substances that damage the membrane) away from the sensitive unit 13, but reducing the inflow to the sensitive unit 13. This leads to a longer service life, i.e. the operating time of the sensor 10, but this also leads to a longer response time. The effect of a larger mesh is that less dirt is kept away from the sensitive unit 13, but the inflow to the sensitive unit 13 is increased, and a shorter service life but a shorter response time is thus obtained.

[0038] The membrane unit 24 is preferably porous or has capillaries and pores that hinder the diffusion and flow of ions in the membrane unit 24. The membrane unit 24 preferably includes a textile or is preferably designed as a textile. For example, the membrane unit 24 is designed as a nylon stocking.

[0039] The membrane unit 24 is preferably adapted to reduce ion transport through the membrane unit 24, which is made possible by the lattice structure. The membrane unit 24 is preferably high impedance and preferably has a fluid barrier to the sensitive unit 13 when the membrane unit 24 is arranged in the process medium.

[0040] Textiles are made, for example, of natural or chemical fibers. Textiles are, for example, linear textile structures made therefrom, such as yarns, twine and ropes, flat textile structures, such as woven fabrics, knitted fabrics, braided fabrics, sewn fabrics, nonwoven fabrics and felts, and spatial textile structures (main structures), such as textile tubes, stockings or textile semi-finished products for reinforcing plastic parts. Textiles also include, for example, those finished products that are made of the above products by assembly, opening and / or other operations to make them in a saleable state for transfer to processors, retailers or final consumers.

[0041] According to an alternative embodiment of the present invention, the membrane unit 24 is manufactured using a 3D printing process or a multi-component injection molding process and comprises, for example, rubber, PVC or other plastics as material.

[0042] The membrane unit 24 preferably has a greater elasticity than hard rubber, in particular an elastic modulus of <5 GPa.

[0043] The secondary fastening unit 25 is suitable for fastening the membrane unit 24 to the rod-shaped sensor 10. The secondary fastening unit 25 is suitable for releasably fastening to the main fastening unit 15. According to one embodiment of the invention, the secondary fastening unit 25 is formed integrally with the membrane unit 24. This means that, in case the membrane unit 24 is a textile, the secondary fastening unit 25 is, for example, woven into the textile or is part of the textile. In particular, if the main fastening unit 15 comprises hook elements, these hooks can engage in the lattice structure of the textile. The hook elements are, for example, Velcro hooks made of plastic or metal hook elements.

[0044] According to one embodiment of the present invention, the auxiliary fastening unit 25 is designed as an O-ring. This embodiment is particularly useful when the main fastening unit 15 is designed as the above-mentioned groove. This allows the membrane unit 24 to be firmly attached to the sensor body 11 through the auxiliary fastening unit 25. In addition to the rubber O-ring, for example, a tension ring or a metal clip or a cable tie or an elastic band can also be used. Due to the detachable auxiliary fastening unit 25, it is possible to remove the membrane unit 24 without spending a lot of time, for example for cleaning or calibrating the sensor 10, reattach it after cleaning the sensitive unit 13, or replace it with a new fastening unit 25.

[0045] According to one embodiment of the invention, the protective film system 20 further comprises an intermediate layer 26. The intermediate layer 26 is suitable, for example, to be arranged between the film unit 24 and the rod-shaped sensor 10. According to an alternative embodiment of the invention, the intermediate layer 26 can be fastened to the film unit 24. This makes it possible to fasten the intermediate layer between the sensitive unit 13 and the film unit 24, i.e. inside the film unit 24.

[0046] The intermediate layer 26 has a lattice structure similar to the membrane unit 24, but is tighter than the mesh structure of the membrane unit 24 in order to adjust the inflow, and the elastic membrane unit 24 is particularly responsible for the correct fit of the intermediate layer 26. For example, the intermediate layer 26 is made of wool, felt or other membrane materials for filtering aqueous media or other similar textile materials.

[0047] The intermediate layer 26 makes it possible to decouple the membrane unit 24 from the sensitive unit 13. The term "decoupling" here particularly refers to both chemical decoupling and electrochemical decoupling, so that harmful substances do not directly enter the sensitive unit 13 from the membrane unit 24, and the potential formed in the membrane unit 24 is not transferred to the sensitive unit 13 by ionic conduction. This decoupling is achieved by the fact that the intermediate layer 26 is composed of a material that forms a strong phase boundary with 13 and 24, and ideally has good ionic conductivity, so that all solution potentials reach the potential of the process medium. Therefore, for example, a thin paper soaked with process water can be used as the intermediate layer 26 of the nitrate ISE.

[0048] If the sensor unit 100 has an intermediate layer 26 , the membrane unit 24 and the sensitive unit 13 are preferably made of similar or identical materials.

[0049] Next, when Figure 1 The test results of the above-described protective film system 20 when used together with the ISE electrode shown are as follows.

[0050] Figure 2 A comparison of different ISE electrodes and ISE sensors is shown. A first sensor was tested without a protective film system 20 according to the invention and its measurement curve is shown in the figure as a dot-dashed line. A second sensor was tested with a protective film system 20 according to the invention (in this particular case a piece of nylon stocking) and its measurement curve is shown in the figure as a short dashed line. A third sensor was tested with a protective film system 20 according to the invention and additionally the above-mentioned intermediate layer 26 (in this particular case a piece of cellulose cloth) and its measurement curve is shown in the figure as a dot-dashed line. Figure 2 In FIG. 1 , the abscissa axis is the time axis T, and the ordinate axis is the voltage U measured at the ISE sensor. In this embodiment, this is a nitrate-selective ISE; in this ISE, the voltage U decreases when the nitrate concentration increases.

[0051] Reference Figure 2 Initially, i.e. at time T0, the three sensors were operated in analyte-free water. Subsequently, ammonium nitrate was added at time T1, followed by the addition of a surfactant (SDS = sodium dodecyl sulfate or sodium dodecyl sulfonate, which serves as a model substance for membrane-damaging substances that may be present in wastewater) at time T2, and then ammonium nitrate was added again at time T3.

[0052] exist Figure 2 In the graph, it can be easily seen that immediately after the addition of SDS, i.e. at time T2, the unprotected electrode, i.e. the first sensor without the protective membrane system 20, starts to drift (dotted curve), which is indicated by the black arrow. This means that the voltage measured at the second sensor changes even if the analyte concentration does not change; in this case, it decreases. Likewise, in the case of the second sensor, i.e. the sensor with the protective membrane system 20, and in the case of the third sensor, i.e. the sensor with the protective membrane system 20 and the intermediate layer 26, no significant distortion or drift of the measured voltage can be detected. It can be seen that after the addition of SDS (at time T2), the voltage of the two electrodes with the protective membrane system 20 stabilizes very quickly and then no longer changes compared to the sensor without protection. The response of all sensors to the addition of the analyte (at time T3) is at the same level, but the sensor with the protective system 20 reacts slightly slower. This proves that the protective membrane system 20 effectively prevents harmful chemical influences and significantly reduces the drift of the sensor 10, while at the same time only slightly attenuating the time response of the measurement signal.

[0053] Figure 3 Another test using the above three sensors is shown. The electrodes are placed in a solution containing SDS for several days and then immersed in an analyte-free solution at the same time (at time T0'). This means that before time T0', the unprotected electrode has been saturated with SDS and therefore drifts. Between time T0' and time T1', the electrode reacts to a decrease in analyte concentration. At time T1' and subsequently at T2', T3', T4' and T5', an analyte (nitrate in this case) is added at a defined concentration. It can be seen that the electrode reacts very quickly to changes in analyte concentration. The voltage jump caused by the addition is also the same for all electrodes. This means that the slope of the electrode is comparable. However, the electrode without the protection system 20 also shows a significant change in the measured voltage between additions (dotted curve). In contrast, the electrode with the protection system 20 remains stable and only changes its voltage as needed when added. The drift of the unprotected electrode in SDS-free water is caused by the reverse process of leaching (in this case, the SDS accumulated in the electrode is washed away again) and the distribution of SDS in the membrane. In this case, this results in a rise in voltage. At time T6', the electrode is immersed in a fresh SDS-free and analyte-free solution again. It can be seen that the unprotected electrode has recovered by washing off the SDS. It shows a larger voltage in the analyte-free medium (just before T7'), and the drift between the new additions (T7', T8', T9', T10') is significantly lower. It turns out that the drift of the electrode using 20 protection is significantly lower, and they react equally well to changes in analyte concentration.

[0054] In this test, the responses of the unprotected and protected electrodes to the analyte additions are nearly equal. If the drift between additions is calculated from the measurements, all electrodes obtain an ideal slope close to the Nernst slope. It should be noted that in practice it is impossible to calculate the drift and therefore the drift inevitably leads to large measurement errors.

[0055] To illustrate, Figure 4 The slope graphs for three electrodes of three sensors tested in the above test are shown. To plot the slopes for electrodes without protective membrane system 20, only the jumps are used and added.

[0056] The chemical process or charging process which occurs between the process medium P, the protective membrane system 20 , the sensor element 13 and the electrolyte 17 by the migration of ions is explained in detail below.

[0057] Figure 5 Shown is the schematic structure of the ISE electrode layer.

[0058] like Figure 5 As shown, the ion migration from the process medium P through the protective membrane system 20 to the sensitive element 13 is depicted by The ion migration from the sensitive element 13 through the protective membrane system 20 to the process medium P is represented by The migration from the sensitive element 13 to the electrolyte 17 is represented by express.

[0059] The sensitive element 13 is designed to contain cations which, due to their extremely low water solubility, cannot migrate out of the sensitive element 13. To compensate for this excess charge, anions migrate into the sensitive element 13. In the case of the nitrate ISE sensor, these are nitrate anions.

[0060] The voltage measured at the ISE consists of two so-called phase boundary voltages and , i.e., the voltage or potential components present at the so-called phase boundaries. The phase boundaries are the inner and outer surfaces of the sensitive element 13, i.e., Figure 5 As shown, the outer phase boundary between the protective film system 24 (wherein the protective film system 24 is immersed in the process medium during use) and the sensitive element 13 , and the internal phase boundary between the sensitive element 13 and the internal electrolyte 17 The two voltages across these interfaces and The concentration ratios of the two adjacent phases are , This can be formulated as follows:

[0061]

[0062] in, is the concentration of the analyte in the process medium P, where is the concentration of the analyte in the inner electrolyte 17, and wherein, is the concentration of the analyte in the sensitive element 13. Since the actual correlation voltage is the sum of the two voltages, the following Nernst equation is obtained:

[0063]

[0064] It can be seen that the general Nernst equation is valid only if the inner and outer (close to and ) is the same in concentration of the analyte ion (nitrate ion) in the sensing element 13, or at least the ratio remains constant over a longer period of time. Only in this case, the two logarithmic terms They cancel each other out, and the Also disappears (if a=-b) or becomes a constant (zero point or reference voltage).

[0065] If anions from the process enter the sensor 13, these anions have a higher affinity for the sensor 13 than the nitrate ions (such as lipids or surfactants, for example SDS), they replace the nitrate ions and change the surface of the sensor 13 on the process side. Where (Assuming neutral charge). This causes the electrode to drift. If too many ions are removed from the surface, becomes very small, then changes during potential adjustment, and the electrode becomes dull and loses its slope.

[0066] Therefore, it is necessary to maintain the interface The concentration of these interfering anions in the vicinity is as small as possible. The concentration increases upon entry and from Leaving (almost impossible) and moving further towards The concentration decreases as the interfering ions migrate (most likely). The protection system 20 prevents all ions from entering the sensitive element 13 by slowing down the diffusion. This initially only hinders the entry and exit of interfering ions and reduces drift. However, as interfering ions further away from the interface Orientation interface Migration is unimpeded, so even after a long period of time, The concentration of interfering ions in the vicinity is still small. Significant interference only occurs when the entire sensitive element 13 is rich in interfering anions. Since the protective membrane system 20 also reduces the ingress, the saturation of the sensitive element 13 is also greatly delayed, and the drift during application is greatly reduced.

[0067] Reference numerals list

[0068] 10 Sensors

[0069] 11Sensor body

[0070] 12 discharge circuit

[0071] 13 Sensitive Units

[0072] 14 First End

[0073] 15 Main fastening unit

[0074] 17 Electrolytes

[0075] 20 Protective film system

[0076] 24 membrane units

[0077] 25 auxiliary sensor units

[0078] 26 Middle Layer

[0079] 100 sensor units

[0080] Process Medium

[0081] Analyte concentration in process media

[0082] Analyte concentration in the sensing element

[0083] Analyte concentration in the inner electrolyte

[0084] Outer Phase Boundary

[0085] Inner Phase Boundary

[0086] Z-axis

Claims

1. A protective film system (20) for a rod-shaped sensor (10), comprising: - a membrane unit (24), which is elastic and has a lattice structure, - an auxiliary fastening unit (25) suitable for fastening the membrane unit (24) to the rod-shaped sensor (10).

2. The protective film system (20) according to claim 1, wherein: The lattice structure has meshes with dimensions less than 1 mm, preferably less than 500 μm.

3. The protective film system (20) according to claim 1 or 2, wherein: The membrane unit (24) comprises textile fabric.

4. The protective film system (20) according to any one of the preceding claims, wherein: The auxiliary fastening unit (25) comprises an O-ring or a hook element.

5. The protective film system (20) according to any one of the preceding claims, wherein: The protective film system (20) further comprises an intermediate layer (26), which is suitable for being arranged between the film unit (24) and the rod-shaped sensor (10).

6. The protective film system (20) according to any one of the preceding claims, wherein: The membrane unit (24) is adapted to reduce ion transport through the membrane unit (24).

7. A sensor unit (100), comprising: - a sensor (10) having a sensor body (11) extending along an axis (Z) and having a first end (14), wherein the sensitive unit (13) is arranged at the first end (14), and the first end (14) is suitable for being immersed in a process medium, - The protective film system (20) according to any of the preceding claims, wherein the protective film system (20) is arranged at the first end (14) and fastened to the sensor body (11) such that the sensitive unit (13) is covered by the protective film system (20) towards the process medium.

8. The sensor unit (100) according to claim 7, wherein: The sensor body (11) has a main fastening unit (15) which is complementary to the auxiliary fastening unit (25) of the protective film system (20).

9. The sensor unit (100) according to claim 8, wherein: The primary fastening unit (15) is a groove in the sensor body (11) extending around the axis (Z), and the secondary fastening unit (25) is designed as an O-ring.

10. The sensor unit (100) according to claim 8, wherein: The main fastening unit (15) includes a hook element, and the auxiliary fastening unit (25) is formed integrally with the membrane unit (24).

11. The sensor unit (100) according to any one of claims 7 to 10, wherein: The sensor (10) comprises an ion selective electrode and has an electrolyte (17) in the sensor body (11), and a discharge line (12) is arranged in the electrolyte (17), wherein the sensitive unit (13) is an ion selective membrane in direct contact with the electrolyte (17).

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