Measurement device for determining dielectric constant and conductivity

Abstract

The invention relates to a measurement device (1) by means of which both the dielectric constant value and the electric conductivity of a filling product (2) can be determined: At the core of the measurement device (1) are two electrodes (11, 12), each of which can be brought into galvanic contact with the filling product (2). A high-frequency measurement unit (13) couples an electric high-frequency signal (SHF) into the first electrode (12) and after said signal has interacted with the filling product (2), receives it at the second electrode (13). The dielectric constant of the filling product (2) is determined based on the received high-frequency signal (SHF). A conductivity measurement unit (14) couples an additional measurement signal (SLF) into one of the electrodes (11, 12) in order to couple the measurement signal (SLF) out of the other electrode (11, 12) after interaction with the filling product (2). The conductivity of the filling product (2) is determined based on the coupled-out measurement signal (SLF). So that the measurement values can be determined without error using the signals (SHF, SLF), a signal decoupling unit (15) separates the high-frequency measurement unit (13) and the conductivity measurement unit (14) from one another in terms of signalling.

Description

[0001] Measuring device for determining dielectric value and conductivity

[0002] The invention relates to a high-frequency-based measuring device for determining a dielectric value and a conductivity of a filling material.

[0003] In automation technology, particularly for process automation, field devices are often used to record various measured variables. The measured variable can be, for example, a level, flow, pressure, temperature, pH value, redox potential, conductivity, or dielectric value of a medium in a process plant. To record the corresponding measured values, the field devices contain suitable sensors or are based on suitable measurement methods. A wide variety of field device types are manufactured and distributed by the Endress + Hauser Group.

[0004] Determining the dielectric value (also known as "dielectric constant" or "relative permittivity") of various media is of great interest for solids, liquids, and gaseous media, such as fuels, wastewater, gases, gas phases, or chemicals, as this value can be a reliable indicator of impurities, moisture content, substance concentration, or substance composition. Using high-frequency technology, the dielectric value of a medium can be determined, for example, by measuring the amplitude, phase shift, or signal propagation time of high-frequency signals as they pass through the medium. For this purpose, a high-frequency signal with a defined frequency or...coupled into the medium within a defined frequency band: After passing through the medium, the high-frequency signal is evaluated with respect to its amplitude, phase position, or signal propagation time in relation to the emitted high-frequency signal. In the context of this patent application, the term "high-frequency signal" refers to corresponding signals with frequencies between 10 MHz and 150 GHz. A phase-based dielectric value measuring device is described, for example, in the publication WO 2022033831 A1.

[0005] Particularly in the pharmaceutical and food industries, it is helpful for process control if, in addition to the dielectric value, the conductivity of the process materials is also determined or monitored. On the other hand, however, the more measuring devices that must be brought into contact with the respective product, the more disadvantageous this is from a hygiene perspective. This is because every additional flange connection on the process vessel that must be provided for a corresponding measuring device represents a potential source of germs from a hygiene perspective and requires a correspondingly complex design. The invention is therefore based on the object of being able to determine the dielectric value and conductivity of products using as few measuring devices as possible.

[0006] The invention solves this problem by a measuring device for determining a dielectric value and an electrical conductivity of a filling material, wherein the measuring device comprises the following components:

[0007] A first electrode that can be brought into galvanic contact with the filling material, a second electrode that can be brought into galvanic contact with the filling material, a high-frequency measuring unit that is designed to o couple an electrical high-frequency signal into the first electrode via a high-frequency output, o receive the high-frequency signal after its interaction with the filling material at the second electrode via a high-frequency input, and to o determine the dielectric value of the filling material at least based on the received high-frequency signal, a conductivity measuring unit that is designed to o couple a measuring signal into one of the electrodes via a signal output, and o decouple the measuring signal from the other electrode via a signal input after interaction with the filling material, and o determine the conductivity of the filling material based on the decoupled measuring signal, and a signal decoupling unit that is designedto separate the high-frequency measuring unit and the conductivity measuring unit from each other in terms of signal technology.

[0008] The invention is based on the idea that the conductivity is also determined using the same electrodes used to determine the dielectric value using high-frequency technology. This eliminates the need for separate electrodes or an additional measuring device to determine the conductivity of the contents in addition to the dielectric value. This reduces external interference with the contents, which in turn improves the hygienic conditions in the container.

[0009] The high-frequency measuring unit can determine the dielectric value either in the form of the imaginary or real part, or as a value. Depending on the design of the high-frequency measuring unit, the dielectric value can be determined based on the amplitude, the signal or signal group propagation time, the signal quality, and / or the impulse or frequency response of the received high-frequency signal. The frequency of the high-frequency signal should generally be selected depending on the dielectric value measurement range. For a dielectric value measurement range between 60 and 90, i.e., for highly moist media, the high-frequency measuring unit should be designed to generate the electrical high-frequency signal corresponding to this measurement range with a frequency between 0.1 GHz and 30 GHz, in particular between 2 GHz and 8 GHz.

[0010] With regard to conductivity determination, any measuring principle that allows conductivity to be determined using two electrodes is suitable within the scope of the invention. Accordingly, the conductivity measuring unit can implement, for example, the capacitive, conductive, or transmissive measuring principle, since all of these principles are based on the use of two electrodes. A measuring device intended for process automation based on the capacitive-conductive measuring principle is described, for example, in the publication WO 2019141464 A1.

[0011] The implementation of the signal decoupling unit is also not strictly prescribed within the scope of the invention, as long as the high-frequency measuring unit and the conductivity measuring unit are sufficiently separated from each other in terms of signal technology towards the electrodes. The design of the signal decoupling unit depends, among other things, on how the measuring units are implemented. Depending on this, the signal decoupling unit can, for example, comprise a first diode arrangement, which is / is connected upstream or downstream of the high-frequency output and / or the high-frequency input in the signal direction. Additionally or alternatively, the signal decoupling unit can comprise a second diode arrangement, which is / is connected upstream or downstream of the signal output and / or the signal input in the signal direction.The term “diode” is to be understood in such a way that it also includes correspondingly connected transistors as well as corresponding electronic components with equivalent functions.

[0012] Alternatively or in addition to diodes, the signal decoupling unit can also be equipped with a first signal splitter connected upstream of the first electrode and / or a second signal splitter connected upstream of the second electrode. A circulator, a duplexer, and / or a diplexer can function as the signal splitter, for example.

[0013] It is also conceivable for the signal decoupling unit to comprise a first frequency filter connected upstream of the high-frequency measuring unit and / or a second frequency filter connected upstream of the conductivity measuring unit for decoupling the measuring units. In this context, it is conceivable to construct the signal decoupling unit not only on the basis of frequency filters, signal filters, or diode arrangements, but also a mixture. This means that in this case, in addition to one or more frequency filters, the signal decoupling unit additionally comprises one or more signal filters or diodes. A mixed design of the signal decoupling unit based on signal filters and diode arrangements is also possible.

[0014] Regardless of which electrical components the signal decoupling unit includes for signal separation, depending on the design of the measuring units, another design variable is that either the outputs of both measuring units are connected to the first electrode via the signal decoupling unit, in which case the inputs of both measuring units are connected to the second electrode (again via the signal decoupling unit). Or the signal output of the conductivity measuring unit and the high-frequency unit are each connected to the second electrode via the signal decoupling unit, while the high-frequency output and the signal input are each connected to the first electrode via the signal decoupling unit.

[0015] The design of the signal decoupling unit, based on frequency filters, signal dividers, or diode arrays, is designed to achieve signal separation between the measuring units and the electrodes. An alternative or additional design variant for this is to operate the measuring units at different times. In this case, the signal decoupling unit is designed to control the high-frequency measuring unit and the conductivity measuring unit, for example, using a control signal, such that one of the units is active and the other is inactive.

[0016] In general, the term "unit" within the scope of the invention refers to any electronic circuit that is suitably designed for the intended purpose. Depending on the requirements, it can therefore be an analog circuit for generating or processing corresponding analog signals. However, it can also be a digital circuit such as an FPGA or a storage medium in conjunction with a program. The program is designed to carry out the corresponding method steps or apply the necessary computing operations of the respective unit. In this context, different electronic units of the measuring device within the meaning of the invention can potentially also access a common physical memory or be operated using the same physical digital circuit.

[0017] The invention is explained in more detail with reference to the following figures. Shown are: Fig. 1: A measuring device according to the invention for measuring the conductivity and dielectric values ​​of a filling material in a container,

[0018] Fig. 2: a detailed view of the measuring device with signal decoupling unit,

[0019] Fig. 3: a first embodiment of the signal decoupling unit,

[0020] Fig. 4: a second embodiment of the signal decoupling unit,

[0021] Fig. 5: a third embodiment of the signal decoupling unit, and

[0022] Fig. 6: a fourth embodiment of the signal decoupling unit.

[0023] To understand the invention, Fig. 1 shows a container 3 which is used, for example, in a pharmaceutical manufacturing process.

[0024] Accordingly, the container 3 is filled with a medium 2 whose dielectric value and conductivity are to be determined. For this purpose, a measuring device 1 according to the invention is attached via a lateral external connection of the container 3, such as a flange of size DN50, such that two electrodes 11, 12 protrude into the container interior or are immersed in the medium 2. Optionally, the measuring device 1 can be connected to a higher-level unit 4, such as a process control system. The interface can be, for example, "PROFIBUS", "HART", "Wireless HART" or

[0025] "Ethernet 1 be implemented. The measured values ​​can be transmitted via this interface. However, other information about the general operating status of measuring device 1 can also be communicated.

[0026] In the exemplary embodiment shown, the dielectric value and the conductivity of the filling material 2 are each determined by the measuring device 1 according to the invention on the basis of transmittive measurement. For this purpose, high-frequency signals SHF are emitted with regard to the dielectric value via one of the electrodes 11, which functions as the first electrode 11 in this regard. The second electrode 12 serves to receive the high-frequency signals SHF after the high-frequency signals SHF have passed through the filling material 2. The measuring distance d through which the high-frequency signal SHF passes is determined by the structural distance d between the electrodes 11, 12. As can be seen from Fig. 2, the electrodes 11, 12 protrude to a defined depth h into the interior of the container or towards the filling material 2 for transmission and reception respectively.The high-frequency signals SHF are generated in a specially designed high-frequency measuring unit 13 of the measuring device 1 and fed to the first electrode 11 via a high-frequency output 131. The high-frequency measuring unit 13 is connected to the second electrode 12 via a high-frequency input 132 in order to evaluate the high-frequency signals SHF accordingly after reception.

[0027] Within the scope of the invention, it is irrelevant whether the electrodes 11, 12 are made entirely of a conductive material, such as turned stainless steel, or whether the electrodes 11, 12 merely have an electrically conductive surface coating. Any metallization of the electrode surface can be applied, for example, using plasma coating such as PECVD ("Plasma Enhanced Vapor Deposition").

[0028] Based on the amplitude of the received high-frequency signal SHF, the high-frequency measuring unit 13 can determine the real part of the dielectric value. Based on the signal propagation time or the phase position of the received high-frequency signal SHF, the real part of the dielectric value can be determined. Analogous to radar-based distance measurement, the pulse propagation time or the FMCW method can be implemented as measurement principles for determining the signal propagation time. Accordingly, the high-frequency measuring unit 13 must be designed according to the respective measurement principle.

[0029] Particularly in the food or pharmaceutical industries, the filling material 2 can be liquids with a high water content, such as beverages or vaccines. Accordingly, the dielectric value range to be measured in these cases is between 60 and 90. According to this range, the high-frequency measuring unit 13 is preferably designed to generate the high-frequency signals SHF with a frequency f between 2 GHz and 8 GHz. It goes without saying that in the case of other dielectric value measurement ranges, different frequencies must be implemented accordingly.

[0030] In order to achieve a high resolution, particularly in the dielectric value range between 60 and 90, the near field of the high-frequency signal SHF is preferably coupled out via the first electrode 11. The advantage of this is the low attenuation in media 2 with high dielectric values ​​and the associated high measurement sensitivity. Furthermore, disturbing effects of the far field are avoided, such as unwanted reflections on the inner wall of the container 2, which can distort the measurement. For this purpose, the first electrode 11 is designed for predominantly near-field radiation with a depth h, which is is significantly smaller than a quarter of the wavelength A of the high-frequency signal SHF, for example one eighth of the wavelength A. Here, c is the propagation speed of the high-frequency signal SHF in the filling material 2 according to the speed of light; DK is the dielectric value of the filling material 2. The design of the electrode depth h also ensures that the measuring device 1 can be constructed with compact dimensions. This means that the measuring device can also be attached to small container openings. The depth h of the electrodes 11, 12 refers to a wall 16 of the measuring device 1 which is planar towards the filling material 2 or the interior of the container and which, in the exemplary embodiment shown, also functions as a signal ground for the high-frequency signal SHF. Accordingly, the wall 16 can be made of stainless steel, for example. A minimum depth h of the electrodes 12, 13 in relation to the wall 16 is not fixed.In principle, it is even conceivable for the electrodes 11, 12 not to protrude beyond the wall 16 into the container interior. However, the advantage of a depth h of the electrodes 11, 12 greater than zero is the higher sensitivity of the dielectric value measurement.

[0031] The distance d between the first electrode 11 and the second electrode 12 is preferably a maximum of one-quarter and a minimum of one-eighth of the wavelength A that corresponds to the frequency f of the high-frequency signal SHF according to the above formula. This exploits the effect whereby the first electrode 11 emits the high-frequency signal SHF with the highest field density at this distance A / 8 < d A / 4. The distance "d" refers to the distance between the two points on the surfaces of the electrodes 11, 12 that are closest to each other.

[0032] This positioning of the second electrode 12 in relation to the first electrode 11 maximizes the sensitivity of the dielectric value measurement. This effect is supported if both electrodes 11, 12 have the same geometry or the same depth h and / or taper conically with increasing depth h, as is the case in Fig. 2. In the embodiment shown in Fig. 2, both electrodes 11, 12 also each have a rounded electrode end. This is particularly advantageous in hygienically sensitive applications in which deposits of the filling material must be avoided. This design of the electrodes 11, 12 is also advantageous for applications in which the filling material 2 is not stationary in the container s, but flows through a section of pipe, for example, in order to suppress the formation of vortices in the pipe section, provided the measuring device is arranged there.The cross-sectional shape of the electrodes 11, 12 is not fixed within the scope of the invention. In principle, the cross-section can, for example, have a round, elliptical or rectangular shape. The electrodes 11, 12 are each electrically insulated by an insulation 17 which separates the respective electrode 11, 12 from the wall 16. The electrical insulation 17 can, for example, be realized as an injection-molded part. PP, PTFE, PEEK or a ceramic such as aluminum oxide can be used as the material. In the embodiment shown in Fig. 2, the two insulations 17 are designed such that they are flush with the wall 16 towards the filling material 2. Furthermore, it can be seen from Fig. 2 that the insulations 17 of the electrodes 11, 12 are each in turn separated by the wall 16 which functions as the signal ground.This achieves the additional advantageous effect that the high-frequency signal SHF must completely pass through the filling material 2 without being able to couple at least partially directly from the first electrode 11 into the second electrode 12. This further increases the sensitivity of the dielectric value measurement.

[0033] According to the invention, the electrodes 11, 12 are used to determine not only the dielectric value of the filling material 2, but also its conductivity. This eliminates the need to attach a separate conductivity measuring device to the container s, thus creating better hygienic conditions. As shown in Fig. 2, the measuring device 1 comprises, in addition to the high-frequency unit 13, a conductivity measuring unit 14, which is connected to one of the electrodes 11, 12 via a signal output 141. A signal input 142 of the conductivity measuring unit 14 is connected to the other electrode 11, 12. Analogous to the high-frequency unit 13, the conductivity measuring unit 14 couples a measuring signal SLF into the corresponding electrode 11, 12 via the signal output 141 in order to decouple or receive it from the other electrode 11, 12 after interaction with the filling material 2.As a result, the conductivity measuring unit 14 can determine the electrical conductivity of the filling material 2 based on the coupled measuring signal SLF, in particular according to the capacitive-conductive measuring principle.

[0034] In order to be able to determine both the conductivity and the dielectric value via the two electrodes 1, 12, the measuring device 1 according to the invention comprises a signal decoupling unit 15, which separates the high-frequency signal SHF of the high-frequency measuring unit 13 from the measurement signal SLF of the conductivity measuring unit 14. As illustrated in Fig. 3 to Fig. 6, there are in principle several embodiments:

[0035] The embodiment of the signal decoupling unit 15 shown in Fig. 3 comprises two circulators 153, 154, each of which is connected upstream of one of the electrodes 11, 12. Instead of the circulators 153, 154, it is also conceivable to use any other form of signal separator. In the embodiment shown in Fig. 3, the signal outputs 131, 141 of both measuring units 13, 14 are connected to the first electrode 11 via the first circulator 153, while the signal inputs 131, 141 are electrically connected to the second electrode 12 via the second circulator 154.Instead of this connection, it is of course also conceivable that the signal output 131 of the high-frequency measuring unit 13 and the signal input 142 of the conductivity measuring unit 14 are connected to the first electrode 11 via the first circulator 153, while the signal input 132 of the high-frequency measuring unit 13 and the signal output 141 of the conductivity measuring unit 14 are connected to the second electrode 12 via the second circulator 154.

[0036] In the embodiment shown in Fig. 4, the signal decoupling unit 15 is based on two frequency filters 155, 156, each of which is connected upstream of one of the signal inputs 132, 142. The first frequency filter 155 is connected upstream of the signal input 132 of the high-frequency measuring unit 13 and is designed as a bandpass filter to allow only the frequency of the high-frequency signal SHF to pass through. The second bandpass filter 156 is connected upstream of the signal input 142 of the conductivity measuring unit 14 and is permeable to the frequency of its measurement signal SLF. Instead of designing the frequency filters 155, 156 as bandpass filters, it is alternatively also conceivable to design the first frequency filter 155 as a high-pass filter for the high-frequency signal SHF, while the second frequency filter 156 forms a low-pass filter for the measurement signal SLF.

[0037] Also in the embodiment shown in Fig. 4, the signal outputs 131, 141 of the measuring units 13, 14 are connected to the first electrode 11, while the signal inputs 132, 142 are connected via the respective frequency filter 155, 156 to the second electrode

[0038] 12. Analogous to Fig. 3, it is also conceivable with regard to the embodiment shown in Fig. 4 that the signal output 131 of the high-frequency measuring unit

[0039] 13 and the signal input 142 of the conductivity measuring unit 14 with the first electrode

[0040] 11, while the signal input 132 of the high-frequency measuring unit 13 and the signal output 141 of the conductivity measuring unit 14 are connected to the second electrode

[0041] 12. In this case, too, the corresponding frequency filter 155, 156 must be connected upstream of the signal input 132, 142.

[0042] Instead of connecting the frequency filters 155, 156 upstream of the signal input 132, 142 of the measuring unit 13, 14, it is also conceivable to connect the frequency filters 155, 156 downstream of the signal outputs 131, 141: Due to the resulting bandwidth limitation, this leads to a reduction in noise.

[0043] The embodiment of the signal decoupling unit 15 shown in Fig. 5 is based on two diode arrangements 151, 152 arranged between the measuring units 13, 14 and the electrodes 11, 12. The first diode arrangement 151 is assigned to the high-frequency measuring unit 13 and comprises two diodes, the first of which is connected downstream of the high-frequency output 131 in the signal direction or upstream of the first electrode 11. The second diode of the first diode arrangement 151 is connected upstream of the high-frequency input 132 in the signal direction or downstream of the second electrode 12. The second diode arrangement 152 relates to the conductivity measuring unit 14. Corresponding to the first diode arrangement 151, a third diode of the second diode arrangement 152 is connected downstream of the signal output 141 of the conductivity measuring unit 14. A fourth diode of the second diode arrangement 152 is connected upstream of the signal input 142 of the conductivity measuring unit 14.

[0044] It goes without saying that the embodiment variants of the signal decoupling unit 15 shown in Fig. 3 to Fig. 5 cannot be implemented solely separately within the scope of the invention. For example, an embodiment shown can additionally include elements of other embodiments for better signal separation: For example, the variant of the signal decoupling unit 15 shown in Fig. 3 can be expanded to include frequency filters 155, 156 between the circulators 153, 154 and the measuring units 13, 14.

[0045] In contrast to the embodiments shown in Fig. 3 to Fig. 5, the signal decoupling unit 15 in the embodiment according to Fig. 6 is not arranged between the measuring units 13, 14 and the electrodes 11, 12 in terms of signal transmission. Rather, the signal decoupling unit 15 in this embodiment controls the measuring units 13, 14 in such a way that they measure at different times: This means that one of the measuring units 13, 14 is active for a defined period and measures the respective measured value, while the other unit 13, 14 is inactive and does not measure within this period. After the end of this period, the other measuring unit 13, 14 is activated or deactivated for a subsequent period. Accordingly, the measuring units 13, 14 are

[0046] Signal decoupling unit 15. For example, they can be controlled via a control signal s cor a periodically switchable switch on and off, as shown in Fig. 6. This embodiment of the signal decoupling unit 15 can also be combined with one of the embodiments described in Figs. 3 to 5 for further improved signal separation. List of reference symbols

[0047] 1 measuring device

[0048] 2 Filling material

[0049] 3 containers

[0050] 4 Superior unit

[0051] 11 First electrode

[0052] 12 Second electrode

[0053] 13 High-frequency measuring unit

[0054] 14 Conductivity measuring unit

[0055] 15 Signal decoupling unit

[0056] 16 wall

[0057] 17 Electrical insulation

[0058] 131 High frequency output

[0059] 132 High frequency input

[0060] 141 Signal output

[0061] 142 Signal input

[0062] 151 First diode arrangement

[0063] 152 Second diode arrangement

[0064] 153 First signal switch

[0065] 154 Second signal switch

[0066] 155 First frequency filter

[0067] 156 Second frequency filter d Distance between the electrodes f Frequency of the high-frequency signal h Depth of the electrode

[0068] SHF high frequency signal

[0069] SLF measurement signal s c control signal

[0070] A Wavelength of the high-frequency signal

Claims

Patent claims 1 . Measuring device for determining a dielectric value and an electrical conductivity of a filling material (2), comprising: A first electrode (11) which can be brought into galvanic contact with the filling material (2), a second electrode (12) which can be brought into galvanic contact with the filling material (2), a high-frequency measuring unit (13) which is designed to o couple an electrical high-frequency signal (SHF) into the first electrode (12) via a high-frequency output (131), o receive it at the second electrode (13) via a high-frequency input (132) after its interaction with the filling material (2), and to o determine the dielectric value of the filling material (2) at least on the basis of the received high-frequency signal (SHF), a conductivity measuring unit (14) which is designed to o couple a measuring signal (SLF) into one of the electrodes (11, 12) via a signal output (141), and o measure the measuring signal (SLF) after interaction with the to decouple the filling material (2) from the other electrode (11, 12) via a signal input (142),and o to determine the conductivity of the filling material (2) based on the decoupled measuring signal (SLF), and a signal decoupling unit (15) which is designed to separate the high-frequency measuring unit (13) and the conductivity measuring unit (14) from each other in terms of signals., 2. Measuring device according to claim 1, wherein the high-frequency measuring unit (13) (14) is designed to determine an imaginary part, a real part or an amount of the dielectric value based on an amplitude, a signal or signal group propagation time, a signal quality and / or an impulse or frequency response of the received high-frequency signal (SHF).

3. Measuring device according to at least one of the preceding claims, wherein the high-frequency measuring unit (13) is designed to generate the electrical high-frequency signal (SHF) with a frequency between 0.1 GHz and 30 GHz, in particular between 2 GHz and 8 GHz.

4. Measuring device according to claim 1, 2 or 3, wherein the conductivity measuring unit (14) is designed to determine the conductivity of the filling material (2) by means of a capacitive, conductive and / or transmissive measuring principle.

5. Measuring device according to one of claims 1 to 4, wherein the signal decoupling unit (15) comprises a first diode arrangement (151), which is / is connected upstream or downstream of the high-frequency output (131) and / or the high-frequency input (132) in the signal direction, and / or a second diode arrangement (152), which is / is connected upstream or downstream of the signal output (141) and / or the signal input (142) in the signal direction.

6. Measuring device according to one of claims 1 to 5, wherein the signal decoupling unit (15) comprises a first signal switch (153) which is connected upstream of the first electrode (11) and / or a second signal switch (154) which is connected upstream of the second electrode (12).

7. Measuring device according to one of claims 1 to 6, wherein the signal decoupling unit (15) comprises a first frequency filter (155) which is connected upstream of the high-frequency measuring unit (13) and / or a second frequency filter (156) which is connected upstream of the conductivity measuring unit (14).

8. Measuring device according to one of claims 1 to 7, wherein the signal decoupling unit (15) is designed to connect the high-frequency measuring unit (13) and the conductivity measuring unit (14) in particular by means of a control signal (s c ) in such a way that one of the measuring units (13, 14) is active and the other measuring unit (13, 14) is inactive.

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